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Iron

IRON

IRON. Iron is the second most abundant mineral on earth and is an essential nutrient for nearly all organisms. Iron is necessary for many varied functions in mammals, including the synthesis of DNA, the generation of energy from macronutrients by aerobic respiration, and the transport and metabolism of oxygen. Iron is highly reactive and is potentially toxic at high levels of intake; therefore, its utilization and storage present a major challenge for biological systems. Cellular iron exists primarily in its reduced ferrous (Fe+2) and oxidized ferric (Fe+3) states, and conversion of the mineral between these states serves to catalyze many reactions. One example is Fenton's reaction, whereby hydrogen peroxide is converted to highly reactive hydroxyl radicals (.OH).

Both ferric iron and the hydroxyl radicals generated by free iron in this reaction directly damage tissues by randomly inducing DNA strand breaks and by oxidizing and thereby damaging cellular proteins, lipids, metabolic cofactors, and nucleic acids. Therefore, it is not surprising that most iron in the cell is bound or sequestered by proteins, so that the concentration of free iron is very low (usually less than 1 × 1018 moles per liter). Many ironbinding proteins are enzymes that harness and bring specificity to the reactive properties of iron, whereas other proteins store or transport iron (Table 1). Protein-bound iron can accept electrons during enzyme-catalyzed reactions, enable proteins to recognize and bind substrates, and assist in the formation of defined protein structures.

Dietary Forms and Factors Affecting Iron Requirements

The Recommended Daily Allowance (RDA) for iron is 8 milligrams per day for men and postmenopausal women and 18 milligrams per day for premenopausal women. Adult males contain about 4 grams of total body iron (50 milligrams per kilogram of body weight), whereas menstruating women contain 40 milligrams per kilogram of body weight. Full-term infants are born with sufficient

Representative proteins that bind iron
Protein Function
Transport and Storage Proteins
DMT1 Intestinal iron uptake
FP1 Intestinal iron export
Ferritin Iron storage
Enzymes
Ribonucleotide reductase Synthesis of DNA precursors
Cysteine dioxygenase Amino acid metabolism
Oxygen carriers
Hemoglobin  
Myoglobin  

iron stores to meet metabolic demands for the first 4 months of life. Breast milk contains 0.2 mg iron/liter; breast-feeding infants receive about 0.27 milligrams per day.

There are two natural dietary forms of iron: (1) inorganic salts of ferric iron, and (2) iron bound to a cyclic carbon ring called heme in the form of hemoglobin and myoglobin in meat products. Inorganic iron is readily liberated from food in the acidic lumen of the stomach but is not absorbed well in the small intestine because of its poor solubility at physiological pH and because it is sequestered by many dietary components that hinder absorption, including phytates, polyphenols, calcium, and fiber. Therefore, only a small percentage of injected iron salts are actually absorbed into the body, thereby indicating that iron salts have a low bioavailability, or ability to be effectively absorbed. However, other low-molecular-weight dietary components bind inorganic iron and facilitate its absorption. These compounds, which include vitamin C and lactic acids, are commonly found in citrus and deciduous fruits and are known as metal chelators. In addition, an unidentified "meat factor" present in animal tissue also enhances the absorption of iron salts. Finally, heme iron has a much greater bioavailability than iron salts because fewer factors interfere with its absorption and it displays greater solubility in water. Hence, heme iron can account for up to 35 percent of absorbed iron in diets when accounting for only 10 percent of total dietary iron intake. In the United States, artificially fortified foods in the form of fortified grain products are a major source of dietary iron and account for nearly 50 percent of all iron consumed.

Iron absorption and transport from the intestinal lumen to the circulatory system is tightly regulated and complex. Enterocyte cells, which are responsible for the uptake and transport of nutrients from the intestinal mucosa, mediate the uptake and transport of iron to the plasma. These cells, once mature, function for only 48 to 72 hours before they are shed and excreted. The capacity of the mature enterocyte to transport inorganic iron is determined very early in its development and is inversely proportional to plasma iron status. The enterocyte iron transport protein, DMT1 (divalent metal transporter), facilitates iron uptake from the intestinal lumen into the enterocyte. DMT1 concentrations at the cell surface are increased when whole-body iron stores are depleted, which increases the rate of cellular iron accumulation into the enterocyte once it is matured. The induction of DMT1 protein synthesis results from increased DMT1 messenger RNA levels. During iron deficiency, the iron regulatory protein (IRP) binds to the 3' untranslated region of the DMT1 messenger RNA and increases its stability. Heme iron is transported into the enterocyte from the intestinal lumen by an unidentified heme iron receptor, and cellular enzymes in the enterocyte release iron from the heme ring. Iron is exported from the basolateral surface of the enterocyte to plasma by the iron transport protein ferroportin1 (Fp1). Fp1 is believed to assist in the direct transfer of iron to a soluble plasma iron transport protein called transferrin. Transferrin facilitates the delivery of two molecules of iron among the sites of absorption and storage and to all tissues and organs. The transferrin-iron complex enters the cell by binding to a specific protein, the transferrin receptor, which is present on the plasma membrane of all cells. Once transferrin binds to its receptor, the receptor-transferrin complex is engulfed by the cell, forming an internal vesicle called an endosome. Once in the cell, iron is released from transferrin by the acidification of the endosome, and the transferrin receptor is recycled to the cell surface where it can bind additional transferrin molecules.

Iron Physiology

Intestinal absorption is the primary mechanism that regulates whole body iron concentrations. There are no specific mechanisms to remove excess iron from mammals. Inorganic iron excretion is limited because of its low solubility in aqueous environments and therefore daily iron loss is minimal in the absence of blood loss. Fecal (from shed enterocytes and biliary heme products), urogenital, and integumental losses account for 4 mg/day of iron loss. Menstruation, blood donation, and pregnancy also can cause significant iron loss. Variations in iron status and requirements are influenced by individual genetic makeup as well as by differences in menstrual losses. The latter averages 0.6 mg/day but can greatly exceed that value in the individual, resulting in a need to absorb an additional 3 to 4 mg/day to maintain adequate iron status. An additional 4 to 5 mg/day of iron must be absorbed during pregnancy. States of rapid growth during childhood through adolescence also increase iron requirements.

Most absorbed iron is used by the bone marrow to make hemoglobin, an abundant protein that binds and distributes oxygen throughout the body. The remaining iron is distributed to other tissues where it is incorporated into iron-requiring proteins or stored. Nearly 70 percent of total body iron is present in red blood cells bound to hemoglobin. Another 15 percent is bound to metabolic enzymes and numerous other proteins, including muscle myoglobin, which transports oxygen to the mitochondria, and cytochromes, which act as electron carriers during respiration. The remaining iron is stored in the liver, spleen, and macrophages and can be distributed to other cells during states of dietary iron deficiency. The primary iron storage protein is ferritin, which is a hollow sphere comprised of 24 protein subunits. One ferritin molecule can store about 3,000 ferric iron molecules that can be mobilized readily when required. There are two types of ferritin subunits, heavy-chain and light-chain ferritin. Heavy-chain ferritin sequesters Fe+2 and oxidizes it to Fe+3; light-chain ferritin aids in the formation of the mineral iron core within the protein. Tissue, gender, hormones, and iron status can influence the ratio of heavy-chain and light-chain subunits that comprise a ferritin molecule, but the physiological significance of this ratio is not well understood.

Consequences of Altered Iron Status

Iron deficiency is the most common of all micronutrient deficiencies in the world, and the anemia that results affects an estimated 2 billion people. Dietary iron deficiency results in reduced iron stores in the liver, bone marrow, and spleen, followed by diminished erythropoiesis, which is the production of red blood cells, and anemia, and ultimately results in decreased activity of iron-dependent enzymes. Iron uptake in the intestine is responsive to total body stores such that iron-deficient individuals display increased iron absorption as described above. Clinical manifestations of iron deficiency include impaired endurance exercise due to an inability to deliver oxygen to tissues, microcytic anemia, glossitis, and blue scerra. Maternal iron deficiency during pregnancy is associated with several adverse outcomes for the newborn infant, including premature delivery, low birth weight, permanent cognitive deficits, developmental delay, and a wide range of behavioral disturbances. The onset of anemia and depletion of tissue iron concentrations occur concurrently, whereas the other negative consequences of iron deficiency occur after hemoglobin concentrations fall.

The tolerable upper level intake for iron for adults is 45 mg/day; intakes that exceed this level result in gastrointestinal distress. Dietary overload can occur, although it is uncommon, except in individuals with primary hereditary hemochromatosis, an iron-storage disease, which can result in up to fifty-fold increases in storage iron deposits. Hemochromatosis most commonly results from a common genetic mutation or genetic polymorphism in the HFE gene that is prevalent in populations of European descent but can also result from mutations in other iron-related proteins including a transferrin receptor. The HFE protein is involved in intestinal regulation of iron accumulation, but its precise biochemical function is unknown. This genetic disorder, if untreated by regular phlebotomy, results in liver cirrhosis, cadiomyopathy, arthritis, and cancer.

See also Gene Expression, Nutrient Regulation of; Nutrients; Nutrient Bioavailability .

BIBLIOGRAPHY

Standing Committee on the Scientific Evaluation of Dietary

Reference Intakes, Food and Nutrition Board, Institute of Medicine. Washington, D.C.: National Academy Press, 2001. Dietary Reference Intakes for vitamin A, vitamin K, arsenic, boron, chromium, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc.

Griffiths, William, and Timothy Cox. "Haemochromatosis:

Novel Gene Discovery and the Molecular Pathophysiology of Iron Metabolism." Human Molecular Genetics 9 (2000): 23772382.

Patrick J. Stover

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Iron

Iron

Background

Iron is one of the most common elements on earth. Nearly every construction of man contains at least a little iron. It is also one of the oldest metals and was first fashioned into useful and ornamental objects at least 3,500 years ago.

Pure iron is a soft, grayish-white metal. Although iron is a common element, pure iron is almost never found in nature. The only pure iron known to exist naturally comes from fallen meteorites. Most iron is found in minerals formed by the combination of iron with other elements. Iron oxides are the most common. Those minerals near the surface of the earth that have the highest iron content are known as iron ores and are mined commercially.

Iron ore is converted into various types of iron through several processes. The most common process is the use of a blast furnace to produce pig iron which is about 92-94% iron and 3-5% carbon with smaller amounts of other elements. Pig iron has only limited uses, and most of this iron goes on to a steel mill where it is converted into various steel alloys by further reducing the carbon content and adding other elements such as manganese and nickel to give the steel specific properties.

History

Historians believe that the Egyptians were the first people to work with small amounts of iron, some five or six thousand years ago. The metal they used was apparently extracted from meteorites. Evidence of what is believed to be the first example of iron mining and smelting points to the ancient Hittite culture in what is now Turkey. Because iron was a far superior material for the manufacture of weapons and tools than any other known metal, its production was a closely guarded secret. However, the basic technique was simple, and the use of iron gradually spread. As useful as it was compared to other materials, iron had disadvantages. The quality of the tools made from it was highly variable, depending on the region from which the iron ore was taken and the method used to extract the iron. The chemical nature of the changes taking place during the extraction were not understood; in particular, the importance of carbon to the metal's hardness. Practices varied widely in different parts of the world. There is evidence, for example, that the Chinese were able to melt and cast iron implements very early, and that the Japanese produced amazing results with steel in small amounts, as evidenced by heirloom swords dating back centuries. Similar breakthroughs were made in the Middle East and India, but the processes never emerged into the rest of the world. For centuries the Europeans lacked methods for heating iron to the melting point at all. To produce iron, they slowly burned iron ore with wood in a clay-lined oven. The iron separated from the surrounding rock but never quite melted. Instead, it formed a crusty slag which was removed by hammering. This repeated heating and hammering process mixed oxygen with the iron oxide to produce iron, and removed the carbon from the metal. The result was nearly pure iron, easily shaped with hammers and tongs but too soft to take and keep a good edge. Because the metal was shaped, or wrought, by hammering, it came to be called wrought iron.

Tools and weapons brought back to Europe from the East were made of an iron that had been melted and cast into shape. Retaining more carbon, cast iron is harder than wrought iron and will hold a cutting edge. However, it is also more brittle than wrought iron. The European iron workers knew the Easterners had better iron, but not the processes involved in fashioning stronger iron products. Entire nations launched efforts to discover the process.

The first known European breakthrough in the production of cast iron, which led quickly to the first practical steel, did not come until 1740. In that year, Benjamin Huntsman took out a patent for the melting of material for the production of steel springs to be used in clockmaking. Over the next 20 years or so, the procedure became more widely adopted. Huntsman used a blast furnace to melt wrought iron in a clay crucible. He then added carefully measured amounts of pure charcoal to the melted metal. The resulting alloy was both strong and flexible when cast into springs. Since Huntsman was originally interested only in making better clocks, his crucible steel led directly to the development of nautical chronometers, which, in turn, made global navigation possible by allowing mariners to precisely determine their east/west position. The fact that he had also invented modern metallurgy was a side-effect which he apparently failed to notice.

Raw Materials

The raw materials used to produce pig iron in a blast furnace are iron ore, coke, sinter, and limestone. Iron ores are mainly iron oxides and include magnetite, hematite, limonite, and many other rocks. The iron content of these ores ranges from 70% down to 20% or less. Coke is a substance made by heating coal until it becomes almost pure carbon. Sinter is made of lesser grade, finely divided iron ore which, is roasted with coke and lime to remove a large amount of the impurities in the ore. Limestone occurs naturally and is a source of calcium carbonate.

Other metals are sometimes mixed with iron in the production of various forms of steel, such as chromium, nickel, manganese, molybdenum, and tungsten.

The Ore Extraction and Refining Process

Before iron ore can be used in a blast furnace, it must be extracted from the ground and partially refined to remove most of the impurities.

Historically, iron was produced by the hot-blast method, or later, the anthracite furnace. Either way, the fundamental activity in iron making involved a worker stirring small batches of pig iron and cinder until the iron separated from the slag. Called "puddling," this was highly skilled work, but was also hot, strenuous, and dangerous. It required a lot of experience as well as a hearty constitution. Puddlers were proud, independent, and highly paid.

Puddlers founded the first trade union in the iron and steel industry, the Sons of Vulcan, in Pittsburgh in 1858. In 1876, this union merged with three other labor organizations to form the Amalgamated Association of Iron and Steel Workers. This was the union that Andrew Carnegie defeated in the Homestead Strike of 1892, leaving the union in shambles and the industry essentially unorganized until the 1930s.

William S. Pretzer

Extraction

  • 1 Much of the world's iron ore is extracted through open pit mining in which the surface of the ground is removed by heavy machines, often over a very large area, to expose the ore beneath. In cases where it is not economical to remove the surface, shafts are dug into the earth, with side tunnels to follow the layer of ore.

Refining

  • 2 The mined ore is crushed and sorted. The best grades of ore contain over 60% iron. Lesser grades are treated, or refined, to remove various contaminants before the ore is shipped to the blast furnace. Collectively, these refining methods are called beneficiation and include further crushing, washing with water to float sand and clay away, magnetic separation, pelletizing, and sintering. As more of the world's known supply of high iron content ore is depleted, these refining techniques have become increasingly important.
  • 3 The refined ore is then loaded on trains or ships and transported to the blast furnace site.

The Manufacturing
Process

Charging the blast furnace

  • 1 After processing, the ore is blended with other ore and goes to the blast furnace. A blast furnace is a tower-shaped structure, made of steel, and lined with refractory, or heat-resistant bricks. The mixture of raw material, or charge, enters at the top of the blast furnace. At the bottom of the furnace, very hot air is blown, or blasted, in through nozzles called tuye'res. The coke burns in the presence of the hot air. The oxygen in the air reacts with the carbon in the coke to form carbon monoxide. The carbon monoxide then reacts with the iron ore to form carbon dioxide and pure iron.

Separating the iron from the slag

  • 2 The melted iron sinks to the bottom of the furnace. The limestone combines with the rock and other impurities in the ore to form a slag which is lighter than the iron and floats on top. As the volume of the charge is reduced, more is continually added at the top of the furnace. The iron and slag are drawn off separately from the bottom of the furnace. The melted iron might go to a further alloying process, or might be cast into ingots called pigs. The slag is carried away for disposal.

Treating the gases

  • 3 The hot gases produced in the chemical reactions are drawn off at the top and routed to a gas cleaning plant where they are cleaned, or scrubbed, and sent back into the furnace; the remaining carbon monoxide, in particular, is useful to the chemical reactions going on within the furnace.

    A blast furnace normally runs day and night for several years. Eventually the brick lining begins to crumble, and the furnace is then shut down for maintenance.

Quality Control

The blast furnace operation is highly instrumented and is monitored continuously. Times and temperatures are checked and recorded. The chemical content of the iron ores received from the various mines are checked, and the ore is blended with other iron ore to achieve the desired charge. Samples are taken from each pour and checked for chemical content and mechanical properties such as strength and hardness.

Byproducts/Waste

There are a great many possible environmental effects from the iron industry. The first and most obvious is the process of open pit mining. Huge tracts of land are stripped to bare rock. Today, depleted mining sites are commonly used as landfills, then covered over and landscaped. Some of these landfills themselves become environmental problems, since in the recent past, some were used for the disposal of highly toxic substances which leached into soil and water.

The process of extracting iron from ore produces great quantities of poisonous and corrosive gases. In practice, these gases are scrubbed and recycled. Inevitably, however, some small amounts of toxic gases escape to the atmosphere.

A byproduct of iron purification is slag, which is produced in huge amounts. This material is largely inert, but must still be disposed of in landfills.

Ironmaking uses up huge amounts of coal. The coal is not used directly, but is first reduced to coke which consists of almost pure carbon. The many chemical byproducts of coking are almost all toxic, but they are also commercially useful. These products include ammonia, which is used in a vast number of products; phenol, which is used to make plastics, cutting oils, and antiseptics; cresols, which go into herbicides, pesticides, pharmaceuticals, and photographic chemicals; and toluene, which is an ingredient in many complex chemical products such as solvents and explosives.

Scrap iron and steelin the form of old cars, appliances and even entire steel-girdered buildingsare also an environmental concern. Most of this material is recycled, however, since steel scrap is an essential resource in steelmaking. Scrap which isn't recycled eventually turns into iron oxide, or rust, and returns to the ground.

The Future

On the surface, the future of iron productionespecially in the United Statesappears troubled. Reserves of high-quality ore have become considerably depleted in areas where it can be economically extracted. Many long-time steel mills have closed.

However, these appearances are deceiving. New ore-enrichment techniques have made the use of lower-grade ore much more attractive, and there is a vast supply of that ore. Many steel plants have closed in recent decades, but this is largely because fewer are needed. The efficiency of blast furnaces alone has improved remarkably. At the beginning of this century, the largest blast furnace in the United States produced 644 tons of pig iron a day. It is believed that soon the possible production of a single furnace will reach 4,000 tons per day. Since many of these more modern plants have been built overseas, it has actually become more economical in some cases to ship steel across the ocean than to produce it in older U.S. plants.

Where To Learn More

Books

Lambert, Mark. Spotlight on Iron and Steel. Rourke Enterprises, 1988.

Hartley, Edward N. Iron and Steel Works of the World. International Publication, 1987.

Lewis, W. David. Iron and Steel in America. Hagley Museum, 1986.

Walker, R. D. Modern Ironmaking Methods. Gower Publication, 1986.

Joel Simon

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Iron (revised)

IRON (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

The period in human history beginning in about 1200 B.C. is called the Iron Age. It was at about this time that humans first learned how to use iron metal. But in some ways, one could refer to the current era as the New Iron Age. Iron is probably the most widely used and most important metal today. No other metal is available to replace iron in all its many applications.

Iron is a transition metal. The transition metals are the elements that make up Groups 3 through 12 in the periodic table. The periodic table is a chart that shows how elements are related to one another. The transition metals are typical metals in that they tend to be bright, shiny, silvery solids. They all tend to conduct heat and electricity well. And they usually have high melting points.

SYMBOL
Fe

ATOMIC NUMBER
26

ATOMIC MASS
55.847

FAMILY
Group 8 (VIIIB)
Transition metal

PRONUNCIATION
EYE-um

Iron normally does not occur as a free element in the earth. In fact, iron was not of much value to humans until they learned how to free iron from its compounds. Once they could do that, humans were able to make tools, weapons, household implements, and other objects out of iron. This step marked the beginning of the Iron Age.

Iron is most valuable not as a pure metal, but in alloys. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals. The best known and most widely used alloy of iron is steel. Steel contains iron and at least one other element. Today, specialized steels of all kinds are available for many different applications.

Discovery and naming

Ancient Egyptians had learned how to use iron before the First Dynasty, which began in about 3400 B.C. The Egyptians probably found the iron in meteorites. Meteorites are chunks of rock and metal that fall from the sky. Some meteorites are very rich in iron. The Egyptians made tools and jewelry out of iron.

Iron is probably the most widely used and most important metal today.

Iron was also known to early Asian civilizations. In Delhi, India, for example, a pillar made out of iron built in A.D. 415 still stands. It weighs 6.5 metric tons and remains in good condition after nearly 1,600 years.

Early Chinese civilizations also knew about iron. Workers learned to produce iron as early as 200 B.C. A number of iron objects, including cannons, remain from the Han period (202 B.C. to A.D. 221).

The Bible also includes many mentions of iron. For example, a long passage in the book of Job describes the mining of iron. Other passages tell about the processing of iron ore to obtain iron metal.

By the time of the Roman civilization, iron had become an essential metal. The historian Pliny (A.D. 23-79) described the role of iron in Rome:

It is by the aid of iron that we construct houses, cleave rocks, and perform so many other useful offices of life. But it is with iron also that wars, murders, and robberies are effected, and this, not only hand to hand, but from a distance even, by the aid of weapons and winged weapons, now launched from engines, now hurled by the human arm, and now furnished with feathery wings.

Even from the earliest days, humans probably seldom used iron in a pure form. It was difficult to make iron that was free of impurities, such as carbon (charcoal) and other metals. More important, however, it became obvious that iron with impurities was a stronger metal that iron without impurities.

It was not until 1786, however, that scientists learned what it was in steel that made it a more useful metal than iron. Three researchers, Gaspard Monge (1746-1818), C. A. Vandermonde, and Claude Louis Berthollet (1748-1822) solved the puzzLe. They found that a small amount of carbon mixed with iron produced a strong alloy. That alloy was steel. Today, the vast amount of iron used in so many applications is used in the form of steel, not pure iron.

Ancient Egyptians had learned how to use iron before the First Dynasty, which began in about 3400 B.C.

The chemical symbol for iron is Fe. That symbol comes from the Latin name for iron, ferrum.

Physical properties

Iron is a silvery-white or grayish metal. It is ductile and malleable. Ductile means capable of being drawn into thin wires. Malleable means capable of being hammered into thin sheets. It is one of only three naturally occurring magnetic elements. The other two are nickel and cobalt

Iron has a very high tensile strength. Tensile means it can be stretched without breaking. Iron is also very workable. Workability is the ability to bend, roll, hammer, cut, shape, form, and otherwise work with a metal to get it into a desired shape or thickness.

The melting point of pure iron is 1,536°C (2,797°F) and its boiling point is about 3,000°C (5,400°F). Its density is 7.87 grams per cubic centimeter. The melting point, boiling point, and other physical properties of steel alloys may be quite different from those of pure iron.

Chemical properties

Iron is a very active metal. It readily combines with oxygen in moist air. The product of this reaction, iron oxide (Fe2O3), is known as rust. Iron also reacts with very hot water and steam to produce hydrogen gas. It also dissolves in most acids and reacts with many other elements.

Occurrence in nature

Iron is the fourth most abundant element in the Earth's crust. Its abundance is estimated to be about 5 percent. Most scientists believe that the Earth's core consists largely of iron. Iron is also found in the Sun, asteroids, and stars outside the solar system.

The most common ores of iron are hematite, or ferric oxide (Fe2O3); limonite, or ferric oxide (Fe2O3); magnetite, or iron oxide (Fe3O4); and siderite, or iron carbonate (FeCO3). An increasingly important source of iron is taconite. Taconite is a mixture of hematite and silica (sand). It contains about 25 percent iron.

The largest iron resources in the world are in China, Russia, Brazil, Canada, Australia, and India. The largest producers of iron from ore in the world are China, Japan, the United States, Russia, Germany, and Brazil.

Isotopes

There are four naturally occurring isotopes of iron, iron-54, iron-56, iron-57, and iron-58. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

Six radioactive isotopes of iron are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

Two radioactive isotopes of iron are used in medical and scientific research. They are iron-55 and iron-59. These isotopes are used primarily as tracers in studies on blood. A tracer is a radioactive isotope whose presence in a system can easily be detected. The isotope is injected into the system. Inside the system, the isotope gives off radiation. That radiation can be followed by detectors placed around the system. Iron-55 and iron-59 are used to study the way in which red blood cells develop in the body. These studies can be used to tell if a person's blood is healthy.

Extraction

Iron goes through a number of stages between ore and final steel product. In the first stage, iron ore is heated with limestone and coke (pure carbon) in a blast furnace. A blast furnace is a very large oven in which the temperature may reach 1,500°C (2,700°F). In the blast furnace, coke removes oxygen from iron ore:

The limestone removes impurities in the iron ore.

Iron produced by this method is about 91 to 92 percent pure. The main impurity left is carbon from the coke used in the furnace. This form of iron is known as pig iron. Pig iron is generally too brittle (it breaks too easily) to be used in most products.

Most scientists believe that the Earth's core consists largely of iron.

A number of methods have been developed for purifying pig iron. A common method used today is called the basic oxygen process. In this process, pig iron is melted in a large oven. Then pure oxygen gas is blown through the molten pig iron. The oxygen burns off much of the carbon in the pig iron:

A small amount of carbon remains in the iron. The iron produced in this reaction is known as steel.

The term "steel" actually refers to a wide variety of products. The various forms of steel all contain iron and carbon. They also contain one or more other elements, such as silicon, titanium, vanadium, chromium, manganese, cobalt, nickel, zirconium, molybdenum, and tungsten. Two other steel-like products are cast iron and wrought iron. Cast iron is an alloy of iron, carbon, and silicon. Wrought iron contains iron and any one or more of many other elements. In general, however, wrought iron tends to contain very little carbon.

Uses

It would be impossible to list all uses of iron and steel products. In general, those products can be classified into categories: (1) automotive; (2) construction; (3) containers, packaging, and shipping; (4) machinery and industrial equipment; (5) rail transportation; (6) oil and gas industries; (7) electrical equipment; and (8) appliances and utensils. (For more information on specific kinds of steel alloys, see individual elements, such as titanium, vanadium, chromium, manganese, molybdenum, and tungsten.)

Compounds

Some iron is made into compounds. The amount is very small compared to the amount used in steel and other iron alloys. Probably the fastest growing use of iron compounds is in water treatment systems. The terms ferric and ferrous refer to two different forms in which iron occurs in compounds. Some of the important iron compounds are:

The U.S. Recommended Daily Allowance (USRDA) for iron is 18 milligrams.

ferric acetate (Fe(C2H3O2)3): used in the dyeing of cloth

ferric ammonium oxalate(Fe(NH4)3(C2O4)4): blueprints

ferric arsenate (FeAsO4): insecticide

ferric chloride (FeCl3): water purification and sewage treatment systems; dyeing of cloth; coloring agent in paints; additive for animal feed; etching material for engraving, photography, and printed circuits

ferric chromate (Fe2(CrO4)3): yellow pigment (coloring) for paints and ceramics

ferric hydroxide (Fe(OH)3): brown pigment for coloring rubber; water purification systems

ferric phosphate (FePO4): fertilizer; additive for animal and human foods

ferrous acetate (Fe(C2H3O2)2): dyeing of fabrics and leather; wood preservative

ferrous gluconate (Fe(C6H11O7)2): dietary supplement in "iron pills"

ferrous oxalate (FeC2O4): yellow pigment for paints, plastics, glass, and ceramics; photographic developer

ferrous sulfate (FeSO4): water purification and sewage treatment systems; catalyst in production of ammonia; fertilizer; herbicide; additive for animal feed; wood preservative; additive to flour to increase iron levels

Health effects

Iron is of critical importance to plants, humans, and animals. It occurs in hemoglobin, a molecule that carries oxygen in the blood. Hemoglobin picks up oxygen in the lungs, and carries it to the cells. In the cells, oxygen is used to produce energy the body needs to survive, grow, and stay healthy.

The U.S. Recommended Daily Allowance (USRDA) for iron is 18 milligrams. The USRDA is the amount of an element that a person needs to stay healthy. Iron is available in a number of foods, including meat, eggs, and raisins.

An iron deficiency (lack of iron) can cause serious health problems in humans. For instance, hemoglobin molecules may not form in sufficient numbers. Or they may lose the ability to carry oxygen. If this occurs, a person develops a condition known as anemia. Anemia results in fatigue. Severe anemia can result in a lowered resistance to disease and an increase in heart and respiratory (breathing) problems. Some forms of anemia can even cause death.

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Iron

Iron

Description

Iron is a mineral that the human body uses to produce the red blood cells (hemoglobin) that carry oxygen throughout the body. It is also stored in myoglobin, an oxygen-carrying protein in the muscles that fuels cell growth.

General use

Iron is abundant in red meats, vegetables, and other foods, and a well-balanced diet can usually provide an adequate supply of the mineral. But when there is insufficient iron from dietary sources, or as a result of blood loss in the body, the amount of hemoglobin in the bloodstream is reduced and oxygen cannot be efficiently transported to tissues and organs throughout the body. The resulting condition is known as iron-deficiency anemia , and is characterized by fatigue , shortness of breath, pale skin, concentration problems, dizziness , a weakened immune system, and energy loss.

Iron-deficiency anemia can be caused by a number of factors, including poor diet, heavy menstrual cycles, pregnancy , kidney disease, burns , and gastrointestinal disorders. Individuals with iron-deficiency anemia should always undergo a thorough evaluation by a physician to determine the cause.

Children two years old and under also need adequate iron in their diets to promote proper mental and physical development. Children under two who are not breastfed should eat iron-fortified formulas and cereals. Women who breastfeed need at least 15 mg of dietary or supplementary iron a day in order to pass along adequate amounts of the mineral to their child in breast milk. Parents should consult a pediatrician or other healthcare professional for guidance on iron supplementation in children.

It has been theorized that excess stored iron can lead to atherosclerosis and ischemic heart disease . Phlebotomy, or blood removal, has been used to reduce stored iron in patients with iron overload with some success. Iron chelation with drugs such as desferrioxamine (Desferal) that help patients excrete excess stores of iron can be helpful in treating iron overload caused by multiple blood transfusions.

Iron levels in the body are measured by both hemoglobin and serum ferritin blood tests.

Normal total hemoglobin levels are:

  • neonates: 17-22 g/dl
  • one week: 15-20 g/dl
  • one month: 11-15 g/dl
  • children: 11-13 g/dl
  • adult males: 14-18 g/dl (12.4-14.9 g/dl after age 50)
  • adult females: 12-16 g/dl (11.7-13.8 g/dl after menopause)

Normal serum ferritin levels are:

  • neonates: 25-200 ng/ml
  • one month: 200-600 ng/ml
  • two to five months: 50-200 ng/ml
  • six months to 15 years: 7-140 ng/ml
  • adult males: 20-300 ng/ml
  • adult females: 20-120 ng/ml

Preparations

Iron can be found in a number of dietary sources, including:

  • pumpkin seeds
  • dried fruits (apricots)
  • lean meats (beef and liver)
  • fortified cereals
  • turkey (dark meat)
  • green vegetables (spinach, kale, and broccoli)
  • beans, peas, and lentils
  • enriched and whole grain breads
  • molasses
  • sea vegetables (blue-green algae and kelp)

Eating iron-rich foods in conjunction with foods rich in vitamin C (such as citrus fruits) and lactic acid (sauerkraut and yogurt) can increase absorption of dietary iron. Cooking food in cast-iron pots can also add to their iron content.

The recommended dietary allowances (RDA) of iron as outlined by the United States Department of Agriculture (USDA) are as follows:

  • Children 03: 6-10 mg/day
  • children 410: 10 mg/day
  • adolescentadult males: 10 mg/day
  • adolescentadult females: 10-15 mg/day
  • pregnant females: 30 mg/day
  • breastfeeding females: 15 mg/day

A number of herbal remedies contain iron, and can be useful as a natural supplement. The juice of the herb stinging nettle (Urtica dioica ) is rich in both iron and vitamin C (which is thought to promote the absorption of iron). It can be taken daily as a dietary supplement. Dandelion (Taraxacum officinale ), curled dock (Rumex crispus ), and parsley (Petroselinum crispum ) also have high iron content, and can be prepared in tea or syrup form.

In Chinese medicine, dang gui (dong quai ), or Angelica sinensis, the root of the angelica plant, is said to both stimulate the circulatory system and aid the digestive system. It can be administered as a decoction or tincture, and should be taken in conjunction with an iron-rich diet. Other Chinese remedies include foxglove root (Rehmannia glutinosa ), Korean ginseng (Panax ginseng ), and astragalus (Astragalus membranaceus ).

Ferrum phosphoricum (iron phosphate), is used in homeopathic medicine to treat anemia. The remedy is produced by mixing iron sulfate, phosphate, and sodium acetate, which is administered in a highly diluted form to the patient. Other homeopathic remedies for anemia include Natrum muriaticum, Chinchona officinalis, Cyclamen europaeum, Ferrum metallicum, and Manganum aceticum. As with all homeopathic remedies, the type of remedy prescribed for iron deficiency depends on the individual's overall symptom picture, mood, and temperament. Patients should speak with their homeopathic professional or physician, or healthcare professional before taking any of these remedies.

Iron is also available in a number of over-the-counter supplements (i.e., ferrous fumerate, ferrous sulfate, ferrous gluconate, iron dextran). Both heme iron and nonheme iron supplements are available. Heme iron is more efficiently absorbed by the body, but non-heme iron can also be effective if used in conjunction with vitamin C and other dietary sources of heme iron. Some multivitamins also contain supplementary iron. Ingesting excessive iron can be toxic, and may have long-term negative effects. For this reason, iron supplements should be taken only under the recommendation and supervision of a doctor.

Precautions

Iron deficiency can be a sign of a more serious problem, such as internal bleeding. Anyone suffering from iron-deficiency anemia should always undergo a thorough evaluation by a healthcare professional to determine the cause.

Iron overdose in children can be fatal, and is a leading cause of poisoning in children. Children should never take supplements intended for adults, and should receive iron supplementation only under the guidance of a physician.

Individuals with chronic or acute health conditions, including kidney infection, alcoholism , liver disease, rheumatoid arthritis, asthma , heart disease, colitis, and stomach ulcer should consult a physician before taking herbal or pharmaceutical iron supplements.

If individuals taking homeopathic dilutions of ferrum phosphoricum experience worsening of their symptoms (known as a homeopathic aggravation), they should stop taking the remedy and contact their healthcare professional. A homeopathic aggravation can be an early indication that a remedy is working properly, but it can also be a sign that a different remedy is needed.

Patients diagnosed with hemochromatosis, a genetic condition in which the body absorbs too much iron and stores the excess in organs and tissues, should never take iron supplements.

Side effects

Taking herbal or pharmaceutical iron supplements on an empty stomach may cause nausea . Iron supplementation may cause hard, dark stools, and individuals who take iron frequently experience constipation . Patients who experience dark bowel movements accompanied by stomach pains should check with their doctor, as this can also indicate bleeding in the digestive tract.

Other reported side effects include stomach cramps and chest pain . These symptoms should be evaluated by a physician if they occur.

Some iron supplements, particularly those taken in liquid form, may stain the teeth. Taking these through a straw, or with a dropper placed towards the back of the throat, may be helpful in preventing staining. Toothpaste containing baking soda and/or hydrogen peroxide can be useful in removing iron stains from teeth.

Signs of iron overdose include severe vomiting , racing heart, bloody diarrhea , stomach cramps, bluish lips and fingernails, pale skin, and weakness. If overdose is suspected, the patient should contact poison control and/or seek emergency medical attention immediately.

Interactions

Iron supplements may react with certain medications, including antacids, acetohydroxamic acid (Lithostat), dimercaprol, etidronate, fluoroquinolones. In addition, they can decrease the effectiveness of certain tetracyclines (antibiotics). Individuals taking these or any other medications should consult their healthcare professional before starting iron supplements.

Certain foods decrease the absorption of iron, including some soy-based foods, foods with large concentrations of calcium , and beverages containing caffeine and tannin (a substance found in black tea). These should not be taken within two hours of using an iron supplement. Some herbs also contain tannic acid, and should be avoided during treatment with iron supplements. These include allspice (Pimenta dioica ) and bayberry (Myrica cerifera, also called wax myrtle).

Individuals considering treatment with homeopathic remedies should also consult their healthcare professional about possible interactions with certain foods, beverages, prescription medications, aromatic compounds, and other environmental elementsfactors known in homeopathy as remedy antidotes that could counteract the efficacy of treatment for iron deficiency.

Resources

BOOKS

Medical Economics Company. PDR 2000 Physicians' Desk Reference. Montvale, NJ: Medical Economics Company, 1998.

Medical Economics Company. PDR for Herbal Medicines. Montvale, NJ: Medical Economics Company, 1998.

Ody, Penelope. The Complete Medicinal Herbal. New York: DK Publishing, 1993.

PERIODICALS

de Valk, B., and J.J.M. Marx. "Iron, Atherosclerosis, and Is-chemic Heart Disease." Archives of Internal Medicine 159(i14): 1542.

Paula Ford-Martin

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iron

iron, metallic chemical element; symbol Fe [Lat. ferrum]; at. no. 26; at. wt. 55.845; m.p. about 1,535°C; b.p. about 2,750°C; sp. gr. 7.87 at 20°C; valence +2, +3, +4, or +6. Iron is biologically significant. Because iron is a component of hemoglobin, a red oxygen-carrying pigment of the red blood cells of vertebrates, iron compounds are important in nutrition; one cause of anemia is iron deficiency. For the history of the use of iron, see Iron Age.

Properties

Iron is a lustrous, ductile, malleable, silver-gray metal found in Group 8 of the periodic table. It is known to exist in four distinct crystalline forms (see allotropy). The most common is the α-form, which is stable below about 770°C, and has a body-centered cubic crystalline structure; it is often called ferrite. Iron is attracted by a magnet and is itself easily magnetized (see magnetism). It is a good conductor of heat and electricity. It displaces hydrogen from hydrochloric or dilute sulfuric acid, but becomes passive (loses its normal chemical activity) when treated with cold nitric acid.

Compounds

Iron forms such compounds as oxides, hydroxides, halides, acetates, carbonates, sulfides, nitrates, sulfates, and a number of complex ions. It is chemically active and forms two major series of chemical compounds, the bivalent iron (II), or ferrous, compounds and the trivalent iron (III), or ferric, compounds. Ferrous sulfate heptahydrate, FeSO4·7H2O, sometimes called green vitriol, is a compound formed by the reaction of dilute sulfuric acid (formerly called oil of vitriol) with metallic iron; it is used in the manufacture of ink, in dyeing, and as a disinfectant. Ferric chloride hexahydrate, FeCl3·6H2O, is a yellow-brown crystalline compound used as a mordant in dyeing and as an etching compound. Ferric oxide, Fe2O3, is a reddish-brown powder used as a paint pigment and in abrasive rouges. Prussian blue, KFe2(CN)6, is a pigment containing the ferrocyanide complex ion. Iron rusts readily in moist air, forming a complex mixture of compounds that is mostly a ferrous-ferric oxide with the composition Fe3O4.

Natural Occurrence

Iron is an abundant element in the universe; it is found in many stars, including the sun. Iron is the fourth most abundant element in the earth's crust, of which it constitutes about 5% by weight, and is believed to be the major component of the earth's core. Iron is found distributed in the soil in low concentrations and is found dissolved in groundwaters and the ocean to a limited extent. It is rarely found uncombined in nature except in meteorites, but iron ores and minerals are abundant and widely distributed.

The principal ores of iron are hematite (ferric oxide, Fe2O3) and limonite (ferric oxide trihydrate, Fe2O3·3H2O). Other ores include siderite (ferrous carbonate, FeCO3), taconite (an iron silicate), and magnetite (ferrous-ferric oxide, Fe3O4), which often occurs as a white sand. Iron pyrite (iron disulfide, FeS2) is a crystalline gold-colored mineral known as fool's gold. Chromite is a chromium ore that contains iron. Lodestone is a form of magnetite that exhibits natural magnetic properties.

Production and Refining

Iron is produced in the United States chiefly from oxide ores. For many years rich hematite ores were produced by open-pit mining in the Mesabi Range near Lake Superior. However, these ores have been largely depleted, and iron is now produced from low-grade ores that are treated to improve their quality; this process is called beneficiation. Iron ores are refined in the blast furnace. The product of the blast furnace is called pig iron and contains about 4% carbon and small amounts of manganese, silicon, phosphorus, and sulfur. About 95% of this iron is processed further to make steel, often by the open-hearth process or the Bessemer process, but more recently in the United States and other countries by the basic oxygen process or by an electric arc furnace. The balance is cast in sand molds into blocks called pigs. It is further processed in iron foundries (see casting).

Cast Iron

Cast iron is made when pig iron is remelted in small cupola furnaces (similar to the blast furnace in design and operation) and poured into molds to make castings. It usually contains 2% to 6% carbon. Scrap iron or steel is often added to vary the composition. Cast iron is used extensively to make machine parts, engine cylinder blocks, stoves, pipes, steam radiators, and many other products. Gray cast iron, or gray iron, is produced when the iron in the mold is cooled slowly. Part of the carbon separates out in plates in the form of graphite but remains physically mixed in the iron. Gray iron is brittle but soft and easily machined. White cast iron, or white iron, which is harder and more brittle, is made by cooling the molten iron rapidly. The carbon remains distributed throughout the iron as cementite (iron carbide, Fe3C). A malleable cast iron can be made by annealing white iron castings in a special furnace. Some of the carbon separates from the cementite; it is much more finely divided than in gray iron. A ductile iron may be prepared by adding magnesium to the molten pig iron; when the iron is cast the carbon forms tiny spherical nodules around the magnesium. Ductile iron is strong, shock resistant, and easily machined.

Wrought Iron

Wrought iron is commercially purified iron. In the Aston process, pig iron is refined in a Bessemer converter and then poured into molten iron silicate slag. The resulting semisolid mass is passed between rollers that squeeze out most of the slag. The wrought iron has a fibrous structure with threads of slag running through it; it is tough, malleable, ductile, corrosion resistant, and melts only at high temperatures. It is used to make rivets, bolts, pipes, chains, and anchors, and is also used for ornamental ironwork.

Bibliography

See W. H. Dennis, Metallurgy of the Ferrous Metals (1963) and Foundations of Iron and Steel Metallurgy (1967).

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Iron

Iron

Iron is the fourth-most common element in Earth's crust , and the second-most common metal after aluminum . Its abundance is estimated to be about 5%. Sampling studies indicate that portions of Earth's core consist largely of iron, and the element is found commonly in the Sun , asteroids , and stars.

The chemical symbol for iron, Fe, comes from the Latin name for the element, ferrum. The most common ores of iron are hematite and limonite (both primarily ferric oxide; Fe2O3) and siderite iron carbonate (FeCO3). An increasingly important source of iron for commercial uses is taconite, a mixture of hematite and silica. Taconite contains about 25% iron. The largest iron resources in the world are found in China, Russia, Brazil, Canada, Australia , and India.

The traditional method for extracting pure iron from its ore is to heat the ore in a blast furnace with limestone and coke. The coke reacts with iron oxide to produce pure iron, while the limestone combines with impurities in the ore to form a slag that can then be removed from the furnace: 3C + 2Fe2O3 + heat 3CO2 + 4Fe.

Iron produced by this method is about 90% pure and is known as pig iron. Pig iron is generally too brittle to be used for most products and is further treated to convert it to wrought iron, cast iron, or steel. Wrought iron is an alloy of iron and any one of many different elements, while cast iron is an alloy of iron, carbon , and silicon . Steel is a generic term that applies to a very wide variety of alloys.

Iron is one of a handful of elements that have been known and used since the earliest periods of human history. In the period beginning about 1200 b.c. iron was so widely used for tools, ornaments, weapons, and other objects that historians and archaeologists have now named the period the Iron Age.

Iron is a silvery white or grayish metal that is ductile and malleable. It is one of only three naturally occurring magnetic elements, the other two being its neighbors in the periodic table : cobalt and nickel. Iron has a very high tensile strength and is very workable, capable of being bent, rolled, hammered, cut, shaped, formed, and otherwise worked into some desirable shape or thickness. Iron's melting point is 2,797°F (1,536°C) and its boiling point is about 5,400°F (3,000°C). Its density is 7.87 grams per cubic centimeter.

Iron is an active metal that combines readily with oxygen in moist air to form iron oxide (Fe2O3), commonly known as rust. Iron also reacts with very hot water and steam to produce hydrogen gas and with most acids and a number of other elements.

The number of commercial products made of iron and steel is very large indeed. The uses of these two materials can generally be classified into about eight large groups, including (1) automotive; (2) construction; (3) containers, packaging, and shipping; (4) machinery and industrial equipment; (5) rail transportation; (6) oil and gas industries; (7) electrical equipment; and (8) appliances and utensils.

A relatively small amount of iron is used to make compounds that have a large variety of applications, including dyeing of cloth, blueprinting, insecticides, water purification and sewage treatment, photography, additive for animal feed, fertilizer, manufacture of glass and ceramics, and wood preservative.

Iron is of critical important to plants, humans, and other animals. It occurs in hemoglobin, the molecule that carries oxygen in the blood. The U.S. Recommended Daily Allowance (USRDA) for iron is 18 mg (with some differences depending on age and sex) and it can be obtained from meats, eggs, raisins, and many other foods. Iron deficiency disorders, known as anemias, are not uncommon and can result in fatigue, reduced resistance to disease, an increase in respiratory and circulatory problems, and even death.

See also Chemical bonds and physical properties; Chemical elements; Earth, interior structure; Minerals

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iron

iron often in figurative use to mean stern and unyielding.
iron age originally the Greek and Roman poets' name for the last and worst period of human history, succeeding the gold, silver, and brazen ages; in allusive reference, an age of wickedness, cruelty, or oppression.

In archaeology, the Iron Age denotes a prehistoric period that followed the Bronze Age, when weapons and tools came to be made of iron. It is conventionally taken as beginning in the early 1st millennium bc, but iron-working began with the Hittites in Anatolia in c.1400 bc. Its arrival in Britain was associated with the first Celtic immigrants in about the 6th century bc. In much of Europe it ended at the Roman period, but outside the Roman Empire it continued to the 4th–6th centuries ad.
Iron Chancellor the nickname of the German statesman Otto von Bismarck (1815–98), Chancellor of the German Empire (1871–90). In recent times it has been applied to the British Chancellor of the Exchequer, Gordon Brown.
Iron Cross the highest German military decoration for bravery, originally awarded in Prussia (instituted 1813) and revived by Hitler in 1939.
Iron Crown of Lombardy the hereditary crown of the ancient kings of Lombardy, so called from having a circlet of iron inserted, reputed to have been made from one of the nails of the Cross.
Iron Curtain a notional barrier separating the former Soviet bloc and the West prior to the decline of communism that followed the political events in eastern Europe in 1989. The phrase is particularly associated with a speech by Winston Churchill in 1946, ‘From Stettin in the Baltic to Trieste in the Adriatic an iron curtain has descended across the Continent,’ although the term in relation to the Soviet Union and her sphere of influence is recorded intermittently from 1920.
Iron Duke a nickname of the Duke of Wellington (1769–1852), recorded from the mid 19th century.
the iron entered into someone's soul someone has become deeply and permanently affected by imprisonment or ill-treatment. It comes from the Latin ferrum pertransit animam ejus, a mistranslation in the Vulgate of the Hebrew, literally ‘his person entered into the iron’, i.e., he was placed in chains or fetters.
iron hand in a velvet glove ruthlessness disguised by courtesy; recorded in Carlyle's Latter-day Pamphlets (1850) as defined by Napoleon.
Iron Lady the nickname of Margaret Thatcher (1925– ), given her in January 1976 by the Soviet defence ministry newspaper Red Star, which accused her of trying to revive the Cold War.
iron mask that worn by the Man in the Iron Mask, a political prisoner in France at the time of Louis XIV, said by some to be a brother of the king, who was made to wear a mask supposedly of iron; he died in the Bastille in 1703, and his identity is still disputed.
iron triangle a grouping of three power bases for mutual defence and support, as for example the Pentagon, the defence industry, and Congress.

See also blood and iron, rule with a rod of iron, strike while the iron is hot.

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Iron

Iron


melting point: 1,535°C
boiling point: 2,750°C
density: 7.874 g/cm 3(at 20°C)
most common ions: Fe2+ , Fe 3+

Iron, believed to have been introduced on Earth by meteors, was found in Egyptian tombs dating from 3500 b.c.e. The Hittites (in the area known today as Turkey) smelted iron from ore around 1500 b.c.e. From ancient times to the present, the major use of iron has been in the production of steel.

Elemental iron, the major element in Earth's core, is the fourth most abundant element in Earth's crust (about 5.0% by mass overall, 0.5%5% in soils, and approximately 2.5 parts per billion in seawater.) In the crust, iron is found mainly as the oxide minerals hematite, Fe2O3, and magnetite, Fe3O4. Other common mineral forms are siderite, FeCO3, and various forms of FeO(OH). Iron is an essential element in almost all living organisms. In the human body, its concentration ranges between 3 and 380 parts per million (ppm) in bone, 380450 ppm in blood, and 201,400 ppm in tissue.

Iron has a very stable nucleus and has fourteen known isotopes . Four isotopes, 54Fe (5.9%), 56Fe (91.72%), 57Fe (2.1%), and 58Fe (0.28%) make up essentially 100 percent of naturally occurring iron. Pure iron is a soft, white, lustrous metal . Elemental iron oxidizes in moist air but is stable in dry air. Finely divided elemental iron is pyrophoric. Iron dissolves in dilute mineral acid and in hot sodium hydroxide solution. Iron has seven oxidation states (2, 0, +1, +2, +3, +4, and +6) with the +2, ferrous or Fe(II), and +3, ferric or Fe(III), states being the most common. With mild heating, iron reacts with the halogens and with sulfur, phosphorus, boron, carbon, and silicon to form a variety of compounds.

see also Hemoglobin; Industrial chemistry, Inorganic.

Douglas Cameron

Bibliography

Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; and Bochmann, Manfred (1999). Advanced Inorganic Chemistry: A Comprehensive Text, 6th edition. New York: Wiley.

Emsley, John (2001). Nature's Building Blocks: An AZ Guide to the Elements. New York: Oxford University Press.

Lide, David R., ed. (1991). The CRC Handbook of Chemistry and Physics, 71st edition. Boca Raton, FL: CRC Press.

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Iron

Iron

An ancient observation on the occult virtues of iron was made by Pliny the Elder (ca. 23-79 C.E.) in his Natural History (as translated in 1601 by Philemon Holland).

"As touching the use of Yron and steele in Physicke, it serveth otherwise than for to launce, cut and dismember withal; for take the knife or dagger, an make an ymaginerie circle two or three times round with the point thereof upon a young child or an elder bodie, and then goe round withall about the partie as often, it is a singular preservative against all poysons, sorceries, or enchantments. Also to take any yron naile out of the coffin or sepulchre wherein man or woman lieth buried, and to sticke the same fast to the lintle or side post of a dore, leading either to the house or bed-chamber where any dooth lie who is haunted with Spirits in the night, he or she shall be delivered and secured from such phanasticall illusions. Moreover, it is said, that if one be lightly pricked with the point of sword or dagger, which hath been the death of a man, it is an excellent remedy against the pains of sides or breast, which come with sudden prickes or stitches."

In certain parts of Scotland and Ireland, there was a belief in the potency of iron for warding off the attacks of fairies. An iron poker, laid across a cradle, would, it was believed, keep fairies away until the child was baptized. The Reverend John G. Campbell in his Superstitions of the Highlands and Islands of Scotland (1900) relates how, when children, he and another boy were believed to be protected from a fairy that had been seen at a certain spot because one boy possessed a knife and the other a nail.

Many other countries had folklore about iron as a religious taboo or a charm against witchcraft and the supernatural. Iron tools were prohibited in Greek and Hebrew temples in ancient times. In Korea the body of the king was never to be touched by iron. Roman priests were forbidden to shave with iron blades. In India and China evil spirits were warded off by iron.

Sources:

French, Roger. Science in the Early Roman Empire: Pliny the Elder, His Sources and His Influence. New York: Barnes & Nobel, 1986.

Pliny the Elder. Natural History. New York: Penguin, 1991.

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iron

i·ron / ˈīərn/ • n. 1. a strong, hard magnetic silvery-gray metal, the chemical element of atomic number 26, much used as a material for construction and manufacturing, esp. in the form of steel. (Symbol: Fe) ∎  compounds of this metal, esp. as a component of the diet: serve liver as it's a good source of iron | [as adj.] how are your iron levels? ∎  used figuratively as a symbol or type of firmness, strength, or resistance: her father had a will of iron | [as adj.] the iron grip of religion on minority cultures. 2. a tool or implement now or originally made of iron: a caulking iron. ∎  (irons) fetters or handcuffs. ∎ inf. a handgun. 3. a hand-held implement with a flat steel base that is heated (typically with electricity) to smooth clothes, sheets, etc. 4. a golf club with a metal head (typically with a numeral indicating the degree to which the head is angled in order to loft the ball). 5. Astron. (also iron meteorite) a meteorite containing a high proportion of iron. • v. [tr.] smooth (clothes, sheets, etc.) with an iron. PHRASES: have many (or other) irons in the fire have many (or a range of) options or courses of action available or be involved in many activities or commitments at the same time. in irons 1. having the feet or hands fettered. 2. (of a sailing vessel) stalled head to wind and unable to come about or tack either way. iron hand (or fist) used to refer to firmness or ruthlessness of attitude or behavior: Fascism's iron hand. an iron hand (or fist) in a velvet glove firmness or ruthlessness cloaked in outward gentleness.PHRASAL VERBS: iron something out remove creases from clothes, sheets, etc., by ironing. ∎ fig. solve or settle difficulties or problems: they had ironed out their differences. DERIVATIVES: i·ron·er n. i·ron·like / -ˌlīk/ adj.

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iron

iron An essential mineral. The average adult contains 4–5 g of iron, of which 60–70% is present in the blood as haem in the circulating haemoglobin, and the remainder present in myoglobin in muscles, a variety of enzymes, and tissue stores. Iron is stored in the liver as ferritin, in other tissues as haemosiderin, and as the blood transport protein transferrin.

Iron balance: losses in faeces 0.3–0.5 mg per day, in sweat and skin cells 0.5 mg, traces in hair and urine, total loss 0.5–1.5 mg per day. Blood loss leads to a considerable loss of iron. The average diet contains 10–15 mg, of which 0.5–1.5 mg is absorbed. The haem iron of meat and fish is considerably better absorbed than the inorganic iron of vegetable foods. Reference intakes are 8.7 mg for adult men and 14.8 mg for women; women who have heavy menstrual blood losses may not be able to obtain enough from food, and supplements are necessary.

Absorption of iron is aided by vitamin C taken at the same time as iron‐containing foods, and reduced by calcium, phosphate and phytic acid. Iron content of foods per 100 g: liver 6–14 mg, cereals up to 9 mg, nuts 1–5 mg, eggs 2–3 mg, meat 2–4 mg. Iron is added to flour so that it contains not less than 1.65 mg per 100 g. Fortified cereals provide 35% of the iron of British diets. Prolonged deficiency gives rise to anaemia.

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Iron

IRON

Iron is a vital component of heme, the component of hemoglobin that transports oxygen in the blood. Iron deficiency is the world's most common cause of anemia (blood with low hemoglobin and red blood cell components). While some plants have modest amounts of iron (e.g., spinach), meat (red or white) has many times more iron than plants. Meat iron is also absorbed much more efficiently than plant iron. In addition to oxygen transport, iron and heme are key to normal brain development. Iron deficiency during the first six months of life can irreversibly impair cognitive development.

Kenneth R. Bridges

(see also: Hematocrit; Hemoglobin )

Bibliography

Bridges, K. R. (2000). "Iron Deficiency." In Coun's Current Therapy, ed. R. E. Rakel. Philadelphia, PA: W. B. Saunders Company.

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iron

iron (symbol Fe) Common metallic element of the first transition series, known from the earliest times. Its chief ores are hematite (Fe2O3), magnetite (Fe3O4), and iron pyrites (FeS2). Pig iron is made in a blast furnace by smelting iron oxide with carbon monoxide from coke, using limestone to form a slag. Cast iron is made from pig iron by remelting and cooling. Wrought iron is made from pig iron by heating with ferric oxide. Iron corrodes to form rust. Most iron is alloyed with carbon and other elements in the various forms of steel used in cutlery, car parts, bridges, ships, and buildings. Properties: at.no. 26; r.a.m. 55.847; r.d. 7.86; m.p. 1535°C (2795°F); b.p. 2750°C (4982°F); most common isotope Fe56 (91.66%).

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iron

iron Symbol Fe. A silvery malleable and ductile metallic element that is the fourth most abundant element in the earth's crust. It is required as a trace element (see essential element) by living organisms. Iron is an important constituent of haemoglobin and the cytochromes, being stored in the liver in the form of ferritin. In animals deficiency of iron results in a form of anaemia.

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iron

iron (I-ŏn) n. an element essential to life. The body of an adult contains on average 4 g of iron, over half of which is contained in haemoglobin in the red blood cells. Iron is an essential component in the transfer of oxygen in the body; a deficiency of iron may lead to anaemia. Many preparations of iron are used to treat iron-deficiency anaemia. Symbol: Fe.

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iron

iron (Fe) An element required by plants. It is used in reactions in which rapid oxidation reductions occur by the transfer of electrons, as in photophosphorylation and oxidative phosphorylation. Other roles are not understood. Iron-deficient plants have chlorotic (see CHLOROSIS) young leaves; at first the veins remain green but later they too become chlorotic.

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iron

iron(Fe) An element required by plants. It is used in reactions in which rapid oxidation reductions occur by the transfer of electrons, as in photophosphorylation and oxidative phosphorylation. Other roles are not understood. Iron-deficient plants have chlorotic (see chlorosis) young leaves; at first the veins remain green but later they too become chlorotic.

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iron

iron sb. OE. īren, perh. for *īrern, alt. of īsern (by assoc. with the var. īsen) = OS., OHG. īsarn (Du. ijzer, G. eisen), ON. īsarn, Goth. eisarn :- Gmc. *īsarnam, prob. — Celt. *īsarno- (W. haearn, Ir. iarann).
Hence ironclad cased with iron or steel plates, spec. of ships, XIX. ironmonger XIV.

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iron

ironBrian, cyan, Gaian, Geminian, Hawaiian, ion, iron, Ixion, lion, Lyon, Mayan, Narayan, O'Brien, Orion, Paraguayan, prion, Ryan, scion, Uruguayan, Zion •andiron •gridiron, midiron •dandelion • anion • Bruneian •cation, flatiron •gowan, Palawan, rowen •anthozoan, bryozoan, Goan, hydrozoan, Minoan, protozoan, protozoon, rowan, Samoan, spermatozoon •Ohioan • Chicagoan • Virgoan •Idahoan •doyen, Illinoisan, IroquoianEwan, Labuan, McEwan, McLuhan, Siouan •Saskatchewan • Papuan • Paduan •Nicaraguan • gargantuan •carbon, chlorofluorocarbon, graben, hydrocarbon, Laban, radiocarbon •ebon • Melbourne • Theban •gibbon, ribbon •Brisbane, Lisbon •Tyburn •auburn, Bourbon •Alban • Manitoban • Cuban •stubborn •Durban, exurban, suburban, turban, urban

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Iron

IRON

IRON (Heb. יִרְאוֹן), city in the territory of Naphtali mentioned in the Bible only in Joshua 19:38. It may possibly occur in the inscriptions of Tiglath-Pileser iii, among the cities conquered in his campaign of 733 b.c.e., in the fragmentary form Ir-ru-[na], but the reading is uncertain. The Arab village of Yarun on the Israel-Lebanon border is situated near an ancient mound containing Iron Age and later pottery. Iron was apparently one of the cities founded by the Israelites in the mountainous and wooded area of Galilee.

bibliography:

Maisler (Mazar), in: bjpes, 1 (1933/34), 3; J. Garstang, Joshua-Judges (1931), 102, n. 1; Y. Aharoni, Hitnaḥalut Shivtei Yisrael ba-Galil ha-Elyon (1957), 130–2; Tadmor, in: H. Hirshberg (ed.), Kol Ereẓ Naftali (1967), 63ff.

[Michael Avi-Yonah]

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iron

iron. Widely used in architecture. There are two basic types: cast iron, which is strong in compression, but weak in tension, so is used for columns, bollards, railings, and decorative features; and wrought iron, which is employed for gates, ornamental scrolls, filigree-work, and the like. Some fine medieval ironwork survives, notably associated with English tombs and chantry-chapels in cathedrals and churches. Later, iron was widely used for balcony-fronts, railings, etc., in C18. Exposed cast iron was used for components in whole façades in C19, notably by John Baird in Glasgow, and wrought iron was used to construct large trusses spanning wide spaces. There are many C19 catalogues of cast-iron components, notably by Badger in the USA and the Saracen Factory, Glasgow. Fairbairn's On the Application of Cast and Wrought Iron to Building Purposes (1854) was an important publication. Iron-and-glass structures were developed for conservatories, railway-stations, exhibition-buildings, and the like, notably by Paxton, Loudon, and others. Iron was used structurally, starting with late-C18 bridges such as at Coalbrookdale, Salop. (1777–9), Sunderland (1793–6), and Buildwas, Salop. (1795–6), and then for factories and warehouses, notably at William Strutt's Mill, Derby (1792), and the Marshall, Benyon, & Bage Mill, Shrewsbury, Salop. (1796), both of which had cast-iron columns carrying systems of beams from which sprang brick vaults. Developments in iron structures occurred when composite girders and columns were made, using rivets, and gradually framed buildings were evolved, permitting speed of erection, great heights, and light claddings. Ultimately, the steel frame permitted the building of skyscrapers. See also metal structures.

Bibliography

Fairbairn (1849, 1869, 1870);
Fairbairn & and Pole (1970);
Gayle & and Gillon (1974);
G. Hartung (1983);
Lemoine (1986);
Loudon (1834);
Mainstone (1975);
Sturgis et al. (1901–2)

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Iron

Iron

General properties

Sources of iron

How iron is obtained

How iron is used

Biochemical applications

Chemistry and compounds

Resources

Iron is a metallic chemical element of atomic number 26. Its symbol is Fe, atomic weight is 55.847, specific gravity is 7.874, melting point is 2,795°F (1,535°C), and boiling point is 4,982°F (2,750°C).

Iron is one of the transition metals, occurring in group 8 of the periodic table. Four naturally occurring isotopes exist with atomic weights of 54 (5.8%), 56 (91.7%), 57 (2.2%), and 58 (0.3%). In addition, six radioactive isotopes have been prepared, with atomic weights of 52, 53, 55, 59, 60, and 61. The element was originally known by its Latin name ferrum, from which its chemical symbol is derived.

General properties

Iron is a silver-white or gray metal that is malleable and ductile. In a pure form, it is relatively soft and slightly magnetic. When hardened, it becomes much more magnetic. Iron is the most widely used of all metals. Prior to its use, however, it must be treated in some way to improve its properties or it must be combined with one or more other elements to form an alloy. By far the most common alloy of iron is steel.

One of the most common forms of iron is pig iron, produced by smelting iron ore with coke and limestone in a blast furnace. Pig iron is approximately 90% pure iron and is used primarily in the production of cast iron and steel.

Cast iron is a term used to describe various forms of iron that also contain carbon and silicon ranging in concentrations from 0.5 to 4.2% of the former and 0.2 to 3.5% of the latter. Cast iron has a vast array of uses ranging from thin rings to massive turbine bodies. Wrought iron contains small amounts of a number of other elements including carbon, silicon, phosphorus, sulfur, chromium, nickel, cobalt, copper, and molybdenum. Wrought iron can be fabricated into a number of forms and is widely used because of its resistance to corrosion.

Sources of iron

Iron is the fourth most abundant element in Earths crust and the second most abundant metal, after aluminum. It makes up about 6.2% of the crust by weight. In addition, iron is thought to be the primary constituent of Earths core as well as of siderite meteorites. Soil samples taken from the moon indicate that about 0.5% of lunar soil consists of iron.

The primary ores of iron are hematite (Fe2O3), magnetite (Fe3O4), limonite (FeO[OH] nH2O), and siderite (FeCO3). The element also occurs as the sulfide, iron pyrite (FeS), but this compound is not used commercially as a source of iron because of the difficulty in reducing the sulfide to the pure element. Iron pyrite has a beautiful golden appearance and it is sometimes mistaken for elemental gold. This appearance explains its common name of fools gold. Taconite is a low-grade ore of iron that contains no more than about 30% of the metal.

In nature, oxides, sulfides, and silicates of iron are often converted to other forms by the action of water. Iron(II) sulfate (FeSO4) and iron(II) bicarbonate (Fe(HCO3)2) are the most commonly found of these.

How iron is obtained

Iron is one of the handful of elements that was known to ancient civilizations. Originally, it was prepared by heating a naturally occurring ore of iron with charcoal in a very hot flame. The charcoal was obtained by heating wood in the absence of air. There is some evidence that this method of preparation was known as early as 3,000 BC, but the secret of ore smelting was carefully guarded within the Hittite civilization of the Near East for almost two more millennia.

When the Hittite civilization fell in about 1200 BC, the process of iron ore smelting spread throughout eastern and southern Europe. Ironsmiths were soon making ornamental objects, simple tools, and weapons from iron. So dramatic was the impact of this new technology on human societies that the period following 1200 BC is generally known as the Iron Age.

A major change in the technique for producing iron from its ores occurred in about 1773. As trees (and therefore the charcoal made from them) grew increasingly scarce in Great Britain, English inventor Abraham Darby (c. 1678-1717) discovered a method for making coke from soft coal. Since coal was abundant in the British Isles, Darbys technique insured a constant supply of coal for the conversion of iron ores to the pure metal. The modern production of iron involves heating iron ore with coke and limestone in a blast furnace, where temperatures range from 392° F (200° C) at the top of the furnace to 3,632°F (2,000°C) at the bottom. Some blast furnaces are as tall as 15-story buildings and can produce 2,400 tons of iron per day.

Inside a blast furnace, a number of chemical reactions occur. One of these involves the reaction between coke (nearly pure carbon) with oxygen to form carbon monoxide. This carbon monoxide then reacts with iron ore to form pure iron and carbon dioxide. Limestone is added to the reaction mixture to remove impurities in the iron ore. The product of this reaction, known as slag, consists primarily of calcium silicate. The iron formed in a blast furnace exists in a molten form known as pig iron that can be drawn off at the bottom of the furnace. The slag is also molten but less dense than the iron. It is drawn off from taps just above the outlet from which the molten iron is removed.

Efforts to use pig iron for commercial and industrial applications were not successful. The material was quite brittle and objects of which it was made tended to break easily. Cannons made of pig iron, for example, were likely to blow apart when they fired a shell. By 1760, inventors had begun to find ways of toughening pig iron. These methods involved re-melting the pig iron and then burning off the carbon that remained mixed with the product. The most successful early device for accomplishing this step was the Bessemer converter, named after its English inventor Henry Bessemer (18131898). In the Bessemer converter, a blast of hot air is blown through molten pig iron. The process results in the formation of stronger forms of iron, cast and wrought iron. More importantly, when additional elements, such as manganese and chromium, are added to the converter, a new productsteelis formed.

Later inventions improved on the production of steel by the Bessemer converter. In the open hearth process, for example, a charge of molten pig iron, hematite, scrap iron, and limestone is placed into a large brick container. A blast of hot air or oxygen is, then, blown across the surface of the molten mixture. Chemical reactions within the molten mixture result in the formation of either pure iron or, with the addition of alloying metals such as manganese or chromium, a high grade of steel.

An even more recent variation on the Bessemer converter concept is the basic oxygen process (BOP). In the BOP, a mixture of pig iron, scrap iron, and scrap steel is melted in a large steel container and a blast of pure oxygen is blown through the container. The introduction of alloying metals makes possible the production of various types of steel with many different properties.

How iron is used

Alloyed with other metals, iron is the most widely used of all metallic elements. The way in which it is alloyed determines the uses to which the final product is put. Steel, for example, is a general term used to describe iron alloyed with carbon and, in some cases, with other elements. The American Iron and Steel Institute recognizes 27 standard types of steel. Three of these are designated as carbon steels that may contain, in addition to carbon, small amounts of phosphorus and/or sulfur. Another 20 types of steel are made of iron alloyed with one or more of the following elements: chromium, manganese, molybdenum, nickel, silicon, and vanadium. Finally, four types of stainless and heat-resisting steels contain some combination of chromium, nickel, and manganese alloyed with iron.

The number of commercial products made of iron and steel is very large indeed. The uses of these two materials can generally be classified into about eight large groups, including (1) automotive; (2) construction; (3) containers, packaging, and shipping; (4) machinery and industrial equipment; (5) rail transportation; (6) oil and gas industries; (7) electrical equipment; and (8) appliances and utensils. For example, steel is widely used in many types of construction. It has at least six times the strength of concrete, another traditional building material, and about three times the strength of special forms of high-strength concrete. A combination of these two materials, reinforced concrete, is one of the strongest of all building materials available to architects. The strength of steel has made possible some remarkable feats of construction, including very tall buildings (skyscrapers) and bridges with very wide spans. It has also been used in the manufacture of automobile bodies, ship hulls, and heavy machinery and machine parts.

Metallurgists have also invented special iron alloys to meet very specific needs. Alloys of cobalt and iron (both magnetic materials themselves) can be used in the manufacture of very powerful permanent magnets. Steels that contain the element niobium (originally called columbium) have unusually great strength and have been used, among other places, in the construction of nuclear reactors. Tungsten steels are also very strong and have been used in the production of high-speed metal cutting tools and drills. The alloying of aluminum with iron produces a material that can be used in AC (alternating current) magnetic circuits since it can gain and lose magnetism very quickly.

Metallic iron also has other applications. Its natural magnetic properties make it suitable for both permanent magnets and electromagnets. It is also used in the production of various types of dyes, including blueprint paper and a variety of inks, and in the manufacture of abrasives.

Biochemical applications

Iron is essential to the survival of all vertebrates. Hemoglobin, the molecule in blood that transports oxygen from the lungs to an organisms cells, contains a single iron atom buried deep within its complex structure. When humans do not take in sufficient amounts of iron in their daily diets, they may develop a disorder known as anemia. Anemia is characterized by a loss of skin color, a weakness and tendency to faint, palpitation of the heart, and a general sense of exhaustion.

Iron is also important to the good health of plants. It is found in a group of compounds known as porphyrins that play an important role in the growth and development of plant cells. Plants that lack iron have a tendency to lose their color, become weak, and die.

Chemistry and compounds

Iron typically displays one of two valences in forming compounds, 2+ and 3+. According to the older system of chemical nomenclature, these classes of compounds are known as the ferrous and ferric salts, of iron respectively. Because of the abundance of oxygen in the atmosphere, most naturally occurring iron compounds tend to be in the higher (3+) oxidation state.

One of the most widely used of iron compounds is iron(III) (or ferric) chloride, FeCl3. When added to water, it reacts with water molecules forming a thick, gelatinous precipitate of iron(III) hydroxide. The compound is used in the early steps of water purification since, as the precipitate settles out of solution, it traps and carries with it organic and inorganic particles suspended in the water. Iron(III) chloride is also used as a mordant, a substance used in dyeing that binds a dye to a textile. In gaseous form, the compound has still another use. It attacks and dissolves metal and can be used, therefore, for etching. Printed circuits, for example, are often first etched with iron(III) chloride.

Iron(II) (ferrous) compounds tend to oxidize rather easily and are, therefore, less widely used than their 3+ cousins. Iron(II) (ferrous) sulfate is an important exception. In solid form, the compound tends not to oxidize as readily as other Fe2+ compounds and is used as an additive for animal feeds, in water purification, in the manufacture of inks and pigments, and in water and sewage treatment operations.

From a commercial standpoint, probably the most important chemical reaction of iron is its tendency to oxidize. When alloys of iron (such as the steels) are used in construction, a major concern is that they tend to react with oxygen in the air, forming a coating or iron oxide, or rust. The rusting process is actually a somewhat complex process in which both

KEY TERMS

Blast furnace A structure in which a metallic ore (often, iron ore) is reduced to the elemental state.

Ductile Capable of being drawn or stretched into a thin wire.

Isotopes Two molecules in which the number of atoms and the types of atoms are identical, but their arrangement in space is different, resulting in different chemical and physical properties.

Malleable Capable of being rolled or hammered into thin sheets.

Transition metal An element found between groups IIA and IIIA in the periodic table.

oxygen and water are involved. If one or the other of these materials can be prevented from coming into contact with iron, oxidation will not occur. But if both are present, an electrochemical reaction is initiated, and iron is converted to iron oxide.

Each year, billions of dollars are lost when iron-containing structural elements degrade or disintegrate as a result of oxidation (rusting). It is hardly surprising, therefore, that a number of techniques have been developed for reducing or preventing rusting. These techniques include painting, varnishing, galvanizing, tinning, and enameling.

Resources

BOOKS

Byars, Mel. Design in Steel. London, UK: Laurence King, 2003.

Emsley, John. Natures Building Blocks: An A-Z Guide to the Elements. Oxford, UK: Oxford University Press, 2003.

Ghosh, Ahindra. Secondary Steelmaking: Principles and Applications. Boca Raton, FL: CRC Press, 2001.

Siekierski, Slawomir. Concise Chemistry of the Elements. Chichester, UK: Horwood Publishing, 2002.

David E. Newton

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Iron

Iron

Description

Iron is a mineral that the human body uses to produce the red blood cells (hemoglobin) that carry oxygen throughout the body. It is also stored in myoglobin, an oxygen-carrying protein in the muscles that fuels cell growth.

General use

Iron is abundant in red meats, vegetables, and other foods, and a well-balanced diet can usually provide an adequate supply of the mineral. But when there is insufficient iron from dietary sources, or as a result of blood loss in the body, the amount of hemoglobin in the bloodstream is reduced and oxygen cannot be efficiently transported to tissues and organs throughout the body. The resulting condition is known as iron-deficiency anemia, and is characterized by fatigue, shortness of breath, pale skin, concentration problems, dizziness, a weakened immune system, and energy loss.

Iron-deficiency anemia can be caused by a number of factors, including poor diet, heavy menstrual cycles, pregnancy, kidney disease, burns, and gastrointestinal disorders. Individuals with iron-deficiency anemia should always undergo a thorough evaluation by a physician to determine the cause.

Children two years old and under also need adequate iron in their diets to promote proper mental and physical development. Children under two who are not breastfeeding should eat iron-fortified formulas and cereals. Women who breastfeed need at least 15 mg of dietary or supplementary iron a day in order to pass along adequate amounts of the mineral to their child in breast milk. Parents should consult a pediatrician or other healthcare professional for guidance on iron supplementation in children.

It has been theorized that excess stored iron can lead to atherosclerosis and ischemic heart disease. Phlebotomy, or blood removal, has been used to reduce stored iron in patients with iron overload with some success. Iron chelation with drugs such as desferrioxamine (Desferal) that help patients excrete excess stores of iron can be helpful in treating iron overload caused by multiple blood transfusions.

Iron levels in the body are measured by both hemoglobin and serum ferritin blood tests.

Normal total hemoglobin levels are:

  • neonates: 17-22 g/dl
  • one week: 15-20 g/dl
  • one month: 11-15 g/dl
  • children: 11-13 g/dl
  • adult males: 14-18 g/dl (12.4-14.9 g/dl after age 50)
  • adult females: 12-16 g/dl (11.7-13.8 g/dl after menopause)

Normal serum ferritin levels are:

  • neonates: 25-200 ng/ml
  • one month: 200-600 ng/ml
  • two to five months: 50-200 ng/ml
  • six months to 15 years: 7-140 ng/ml
  • adult males: 20-300 ng/ml
  • adult females: 20-120 ng/ml

Preparations

Iron can be found in a number of dietary sources, including:

  • pumpkin seeds
  • dried fruits (apricots)
  • lean meats (beef and liver)
  • fortified cereals
  • turkey (dark meat)
  • green vegetables (spinach, kale, and broccoli)
  • beans, peas, and lentils
  • enriched and whole grain breads
  • molasses
  • sea vegetables (blue-green algae and kelp)

Eating iron-rich foods in conjunction with foods rich in vitamin C (such as citrus fruits) and lactic acid (sauerkraut and yogurt) can increase absorption of dietary iron. Cooking food in cast-iron pots can also add to their iron content.

The recommended dietary allowances (RDA) of iron as outlined by the United States Department of Agriculture (USDA) are as follows:

  • children 0-3: 6-10 mg/day
  • children 4-10: 10 mg/day
  • adolescent and adult males: 10 mg/day
  • adolescent and adult females: 10-15 mg/day
  • pregnant females: 30 mg/day
  • breastfeeding females: 15 mg/day

A number of herbal remedies contain iron, and can be useful as a natural supplement. The juice of the herb stinging nettle (Urtica dioica) is rich in both iron and vitamin C (which is thought to promote the absorption of iron). It can be taken daily as a dietary supplement. Dandelion (Taraxacum officinale), curled dock (Rumex crispus), and parsley (Petroselinum crispum) also have high iron content, and can be prepared in tea or syrup form.

In Chinese medicine, dang gui (dong quai), or Angelica sinensis, the root of the angelica plant, is said to both stimulate the circulatory system and aid the digestive system. It can be administered as a decoction or tincture, and should be taken in conjunction with an iron-rich diet. Other Chinese remedies include foxglove root (Rehmannia glutinosa), Korean ginseng (Panax ginseng), and astragalus (Astragalus membranaceus).

Ferrum phosphoricum (iron phosphate), is used in homeopathic medicine to treat anemia. The remedy is produced by mixing iron sulfate, phosphate, and sodium acetate, which is administered in a highly diluted form to the patient. Other homeopathic remedies for anemia include Natrum muriaticum, Chinchona officinalis, Cyclamen europaeum, Ferrum metallicum, and Manganum aceticum. As with all homeopathic remedies, the type of remedy prescribed for iron deficiency depends on the individual's overall symptom picture, mood, and temperament. Patients should speak with their homeopathic professional or physician, or healthcare professional before taking any of these remedies.

Iron is also available in a number of over-the-counter supplements (i.e., ferrous fumerate, ferrous sulfate, ferrous gluconate, iron dextran). Both heme iron and non-heme iron supplements are available. Heme iron is more efficiently absorbed by the body, but non-heme iron can also be effective if used in conjunction with vitamin C and other dietary sources of heme iron. Some multivitamins also contain supplementary iron. Ingesting excessive iron can be toxic, and may have long-term negative effects. For this reason, iron supplements should only be taken under the recommendation and supervision of a doctor.

Precautions

Iron deficiency can be a sign of a more serious problem, such as internal bleeding. Anyone suffering from iron-deficiency anemia should always undergo a thorough evaluation by a healthcare professional to determine the cause.

Iron overdose in children can be fatal, and is a leading cause of poisoning in children. Children should never take supplements intended for adults, and should only receive iron supplementation under the guidance of a physician.

Individuals with chronic or acute health conditions, including kidney infection, alcoholism, liver disease, rheumatoid arthritis, asthma, heart disease, colitis, and stomach ulcer should consult a physician before taking herbal or pharmaceutical iron supplements.

If individuals taking homeopathic dilutions of Ferrum phosphoricum experience worsening of their symptoms (known as a homeopathic aggravation), they should stop taking the remedy and contact their healthcare professional. A homeopathic aggravation can be an early indication that a remedy is working properly, but it can also be a sign that a different remedy is needed.

Patients diagnosed with hemochromatosis, a genetic condition in which the body absorbs too much iron and stores the excess in organs and tissues, should never take iron supplements.

Side effects

Taking herbal or pharmaceutical iron supplements on an empty stomach may cause nausea. Iron supplementation may cause hard, dark stools, and individuals who take iron frequently experience constipation. Patients who experience dark bowel movements accompanied by stomach pains should check with their doctor, as this can also indicate bleeding in the digestive tract.

Other reported side effects include stomach cramps and chest pain. These symptoms should be evaluated by a physician if they occur.

Some iron supplements, particularly those taken in liquid form, may stain the teeth. Taking these through a straw, or with a dropper placed towards the back of the throat, may be helpful in preventing staining. Toothpaste containing baking soda and/or hydrogen peroxide can be useful in removing iron stains from teeth.

Signs of iron overdose include severe vomiting, racing heart, bloody diarrhea, stomach cramps, bluish lips and fingernails, pale skin, and weakness. If over-dose is suspected, the patient should contact poison control and/or seek emergency medical attention immediately.

Interactions

Iron supplements may react with certain medications, including antacids, acetohydroxamic (Lithostat), Dimercaprol, Etidronate, Fluoroquinolones. In addition, they can decrease the effectiveness of certain tetra-cyclines (antibiotics ). Individuals taking these or any other medications should consult their healthcare professional before starting iron supplements.

Certain foods decrease the absorption of iron, including some soy-based foods, foods with large concentrations of calcium, and beverages containing caffeine and tannin (a substance found in black tea). These should not be taken within two hours of using an iron supplement. Some herbs also contain tannic acid, and should be avoided during treatment with iron supplements. These include allspice (Pimenta dioica) and bayberry (Myrica cerifera, also called wax myrtle).

Individuals considering treatment with homeopathic remedies should also consult their healthcare professional about possible interactions with certain foods, beverages, prescription medications, aromatic compounds, and other environmental elements—factors known in homeopathy as remedy antidotes—that could counteract the efficacy of treatment for iron deficiency.

KEY TERMS

Chelation— The use of a medication or herbal substances to inactivate toxic substances in the body. Chelation is used to treat iron overload in some patients.

Decoction— An herbal extract produced by mixing an herb in cold water, bringing the mixture to a boil, and letting it simmer to evaporate the excess water. The decoction is then strained and consumed hot or cold. Decoctions are usually chosen over infusion when the botanical in question is a root or berry.

Ferritin— An iron storage protein found in the blood. High levels of serum ferritin may indicate iron overload.

Hemochromatosis— Also known as iron overload; a genetic condition in which excess iron is stored in the tissues and organs by the body where it can build up to toxic amounts.

Homeopathic remedy— Used to treat illnesses that manifest symptoms similar to those that the remedy itself causes, but administered in extremely diluted doses to prevent any toxic effects.

Infusion— An herbal preparation made by mixing boiling water with an herb, letting the brew steep for 10 minutes, and then straining the herb out of the mixture. Tea is made through infusion.

Thalassemia— A group of several genetic blood diseases characterized by absent or decreased production of normal hemoglobin. Individuals who have thalassemia have to undergo frequent blood transfusions, and are at risk for iron overload.

Tincture— A liquid extract of an herb prepared by steeping the herb in an alcohol and water mixture.

Resources

BOOKS

Medical Economics Company. PDR for Herbal Medicines. Montvale, NJ: Medical Economics Company, 1998.

Medical Economics Company. PDR 2000 Physicians' Desk Reference. Montvale, NJ: Medical Economics Company, 1998.

Ody, Penelope. The Complete Medicinal Herbal. New York: DK Publishing, 1993.

PERIODICALS

de Valk, B., and J.J.M. Marx. "Iron, Atherosclerosis, and Ischemic Heart Disease." Archives of Internal Medicine 159, no. 14:1542.

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Iron

Iron

Definition

Purpose

Description

Precautions

Interactions

Complications

Parental concerns

Resources

Definition

Iron (Fe) is a metal essential to almost all bacteria, plants, and animals. In humans, iron is a compnent of the red pigment hemoglobin that gives red blood cells their color and affects the transport of oxygen throughout the body, conversion of nutrients into energy, production of new deoxyribonucleic acid (DNA, genetic material), and regulation of cell growth and cell differentiation. Without iron, life on Earth would not exist. Humans must acquire all the iron they need from diet.

Iron

Age Recommended dietary allowance (mg) Tolerable upper intake level (mg)
Children 0–6 mos0.27Not established
Children 7–12 mos.#11Not established
Children 1–3 yrs740
Children 4–8 yrs1040
Children 9–13 yrs940
Boys 14–18 yrs1145
Girls 14–18 yrs1545
Men 19–50 yrs845
Women 19–50 yrs1845
Adults 51 ≥ yrs845
Pregnant women2745
Breastfeeding women 18 ≤ yrs1045
Breastfeeding women 19≥yrs945
Food  Heme Iron (mg)
Chicken liver, cooked, 3 oz 12.8
Oysters, 6 med 5.04
Beef, cooked, 3 oz 3.2
Turkey, light meat, cooked, 3 oz 2.3
Shrimp, cooked, 8 large 1.36
Tuna, light, canned, 3 oz 1.3
Chicken, dark meat, cooked, 3 oz 1.13
Halibut, cooked, 3 oz 0.9
Crab, cooked, 3 oz 0.8
Pork loin, cooked, 3 oz 0.8
Food  Nonheme Iron (mg)
Cereal, 100% iron fortified, 1 cup 18
Soybeans, boiled, 1 cup 8.8
Tofu, firm, ½ cup 6.22
Beans, kidney, cooked, 1 cup 5.2
Beans, lima, cooked, 1 cup 4.5
Beans, pinto, cooked, 1 cup 3.6
Blackstrap molasses, 1 tbsp 3.5
Potato, med. with skin 2.75
Cashew nuts, 1 oz 1.70
Bread, whole wheat, 1 slice 0.9
Raisins, small box, 1.5 oz 0.89
mg = milligram  

(Illustration by GGS Information Services/Thomson Gale.)

Purpose

Most iron in the body is used to transport oxygen. Oxygen is carried in red blood cells through the circulatory system to all cells in the body. Hemoglobin is the protein within red blood cells that makes this possible, and iron is at the center of the hemoglobin molecule. An average-size adult man has about 4 grams of iron in his body, and an adult woman has about 3.5 grams. Approximately two-thirds of this iron is in hemoglobin. Myoglobin, a protein in muscle, also contains iron. Myoglobin provides short-term storage for oxygen. When muscles do work, this oxygen is released to meet the increased metabolic needs of muscle cells.

Iron is found in every cell in the body, including brain cells. It is needed to synthesize adenosine tri-phosphate (ATP), the compound that supplies most of the energy to drive cellular metabolism . Iron is also used in enzyme reactions that create new DNA, and in this way it affects cell division and differentiation. Iron is also essential to other enzyme reactions that break down potentially harmful molecules formed when immune system cells attack bacteria.

Description

Plants absorb iron from the earth, and humans acquire iron through eating both plants and animals. In the stomach, acid in gastric juice acts on iron and changes it into a form that the body can absorb. Absorption takes place mainly in the first part of the small intestine (the duodenum). Once iron is absorbed into the bloodstream, it binds to a protein called trans-ferrin and is carried to all parts of the body, including the bone marrow where new red blood cells are made. Once in the cells, some iron is transferred to ferritin, a protein that holds the iron in reserve. When too much iron is absorbed, there is not enough transferrin to bind all of it. Free iron can build up in cells and trigger activities that cause damage and create health problems. Too little iron interferes with the body’s ability to get enough oxygen.

Sources of iron

The body has complex mechanisms to achieve iron balance by regulating iron absorption, reuse, and storage processes. Red blood cells live about 120 days. When they die, most of the iron in hemoglobin is recycled in the liver and sent to the bone marrow where it reused in new red blood cells. As a result, humans lose only a small amount of iron daily.

Only about 10–20% of the iron in food, or 1–2 mg for every 10 mg eaten, is absorbed into the bloodstream. Under normal conditions, when iron stores in the body are low, more iron is automatically absorbed. When they are high, less is absorbed. Iron that is not absorbed enters cells that line the intestine. As these cells fill up with iron, they fall into the intestine and leave the body in waste.

Both plant and animal foods provide humans with iron, but that iron comes in two forms, heme and nonheme, that are not equally available to the body. Heme iron comes from hemoglobin. It is found mainly in animal tissue. Red meat is an especially rich source of heme iron. Only trace amounts of heme iron are found in plants. Heme iron is in a form that is easier for humans to use. It is absorbed at a higher rate than

KEY TERMS

Cell differentiation —The process by which stem cells develop into different types of specialized cells such as skin, heart, muscle, and blood cells.

Dietary supplement —A product, such as a vitamin, mineral, herb, amino acid, or enzyme, that is intended to be consumed in addition to an individual’s diet with the expectation that it will improve health.

Enzyme —A protein that change the rate of a chemical reaction within the body without themselves being used up in the reaction.

Mineral —An inorganic substance found in the earth that is necessary in small quantities for the body to maintain a health. Examples: zinc, copper, iron.

nonheme iron, and its rate of absorption is less influenced by other foods that simultaneously are present in the digestive system.

The following list gives the approximate iron content for some common sources of heme iron:

  • chicken liver, cooked, 3 ounces: 12.8 mg
  • beef, cooked, 3 ounces: 3.2 mg
  • turkey light meat, cooked, 3 ounces: 2.3 mg
  • chicken dark meat, cooked, 3 ounces: 1.13 mg
  • pork loin, cooked, 3 ounces: 0.8 mg
  • oysters, 6 medium: 5.04 mg
  • shrimp, cooked, 8 large: 1.36 mg
  • tuna, light, canned, 3 ounces: 1.3 mg
  • halibut, cooked, 3 ounces: 0.9 mg
  • crab, cooked, 3 ounces: 0.8 mg

About 40–45% of iron in animal tissue and functionally all the iron in plants is nonheme iron. Nonheme iron is also the type of iron found in dietary supplements and added to iron-fortified foods. Nonheme iron is less easily used by humans; it must be changed in the digestive system before it can be absorbed. Only about 2-10% of nonheme iron in food is absorbed compared to 20-25% of heme iron. In addition, the absorption of nonheme iron is strongly influenced by other substances present in the digestive system. The ability of the body to absorb nonheme iron is decreased by the simultaneous presence of tea, coffee, dairy products, phytic acid (a substance found in grains, dried beans and rice), eggs, soy protein, and some chocolates. Absorption of nonheme iron is increased by the simultaneous presence of vitamin C, certain organic acids, and a small amount of meat, fish, or poultry, which boosts the absorption of nonheme iron as well as providing heme iron. Vegetarians and vegans should take into consideration the influence of other foods on iron absorption when planning meals.

The following list gives the approximate iron content for some common foods that contain nonheme iron:

  • cereal, 100% iron fortified, 1 cup: 18 mg
  • soybeans, boiled, 1 cup: 8.8 mg
  • tofu, firm, 1/2 cup: 6.22 mg
  • kidney beans, cooked, 1 cup: 5.2 mg
  • lima beans, cooked, 1 cup: 4.5
  • pinto beans, cooked, 1 cup: 3.6 mg
  • blackstrap molasses, 1 tablespoon: 3.5 mg
  • raisins, small box, 1.5 ounces: .89 mg
  • potato, medium with skin: 2.75 mg
  • cashew nuts, 1 ounce: 1.70 mg
  • whole wheat bread, 1 slice: 0.9 mg

Normal iron requirements

The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals . The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97-98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.

Iron requirements vary substantially at different ages. Periods of rapid growth in children increase the need for iron. Women who menstruate need more iron because of blood loss during menstruation. Pregnancy puts high demands on the iron supply in the body because of increased production of red blood cells to supply the developing fetus. In 2001, the IOM set RDAs for iron based on preventing iron deficiency at each age. Iron passes into breast milk, and infants can meet their iron needs through breast milk or iron-fortified formula. RDAs and ULs for iron are measured in milligrams (mg).

The following list gives the daily RDAs and IAs and ULs for vitamin C for healthy individuals as established by the IOM.

  • children birth-6 months: RDA 0.27 mg; UL not established
  • children 7-12 months: RDA 11 mg; UL not established
  • children 1-3 years: RDA 7 mg; UL 40 mg
  • children 4-8 years: RDA 10 mg; UL 40 mg
  • children 9-13 years: RDA 9 mg; UL 40 mg
  • boys 14-18 years: RDA 11 mg; UL 45 mg
  • girls 14-18 years: RDA 55 mg; UL 45 mg
  • men age 19-50: RDA 8 mg; UL 45 mg
  • women age 19-50: RDA 18 mg; UL 45 mg
  • men who smoke: RDA 125 mg; UL 45 mg
  • pregnant women: RDA 27 mg; UL 45 mg
  • breastfeeding women 18 years and younger: RDA 10 mg; UL 45 mg
  • breastfeeding women 19 years and older: RDA 9 mg; 45 mg

Precautions

Pregnant women should consult their healthcare provider before the fifteenth week of pregnancy about the need for iron supplementation. They should not start taking an iron supplement on their own.

Men and women over age 55 are not at risk for iron deficiency and should take a multivitamin containing iron only on instructions from their healthcare provider.

People with kidney disease, liver damage, alcoholism, or ulcers should consult a healthcare professional before taking a supplement containing iron.

Interactions

Iron interacts with many drugs and nutritional supplements. General categories of substances that may increase or decrease the amount of iron that is absorbed include medications that decrease stomach acidity (e.g. antacids, Tagamet, Zantac), pancreatic enzyme supplements, calcium supplements and dairy products, vitamin C, citric, malic, tartaric, and lactic acids, and copper.

The presence of iron also increases or decreases the effectiveness of many prescription drugs. Individuals should review their medications with a doctor or pharmacist when they begin taking an iron supplement to see if their other medications need adjustment.

Complications

Iron deficiency

The World Health Organization (WHO) considers iron deficiency to be the most widespread dietary disorder in the world. WHO estimates that up to 80% of the world’s population is iron deficient and up to 30% have iron deficiency anemia. The two main causes of iron deficiency are low dietary intake and excessive blood loss. In the United States, women of childbearing age, young children, people with diseases that interfere with the absorption of iron (e.g. Crohn’s disease, celiac disease ), and people receiving kidney dialysis are most likely to seriously be iron deficient. American men rarely have low levels of iron because the tend to eat more meat than women and do not lose blood through menstruation.

At first, the body is able to use stored iron to make up for an iron deficit, but over time, the amount of hemoglobin decreases and a condition called iron deficiency anemia develops. (This is only one type of anemia; other anemias have other causes.) Iron deficiency anemia decreases the amount of oxygen reaching cells in the body. Symptoms of iron deficiency anemia include:

  • lack of energy
  • feelings of weakness
  • frequently feeling cold
  • increased infections
  • irritability
  • decreased work or school performance
  • sore swollen tongue
  • drive to eat dirt, clay or other non-food substances (pica)

The preferred way to treat mild iron deficiency is through changes in diet. If these changes are ineffective, iron supplements may be used. Dietary supplements contain different formulations such as ferrous fumarate, ferrous sulfate, and ferrous gluconate. Iron in these different formulations is absorbed at differing rates. Because too much iron can cause serious health problems, iron supplements should be taken under the supervision of a healthcare professional.

Iron excess

Iron overload caused by an inherited disorder is called hereditary hemochromatosis. This disorder affects as many as one of every 200 people of northern European descent. These people have a genetic mutation that causes them to absorb iron from the intestine at a rate far higher than normal. Hereditary hemochromatosis is treated by avoiding iron-rich foods and removing blood (usually through blood donation) from the individual on a regular basis.

People who have many blood transfusions can also develop iron overload, but by far the most common cause of excess iron is accidental poisoning. Over 20,000 American children accidentally ingest iron— usually in the form of dietary supplements—each year. Iron poisoning is the leading cause of poisoning deaths in children under age 6 in the United States. Iron overdose is a medical emergency. Symptoms occurring within the first 12 hours include nausea, vomiting, abdominal pain, black stool, weakness, rapid pulse, low blood pressure, fever, difficulty breathing, and coma. If death does not occur within the first 12 hours, damage to the kidney liver damage, cardiovascular system and nervous system may appear within two days. Long-term damage to survivors of iron poisoning include cirrhosis (liver damage), permanent central nervous system damage, and stomach problems.

Parental concerns

Parents should be aware that the RDA and UL for vitamins and minerals are much lower for children than for adults. Accidental overdose may occur if children are give adult vitamins or dietary supplements. Accidental iron overdose is a leading cause of poisoning deaths in young children. Parents should keep all dietary supplements away from children, just as they would other medicines.

Resources

BOOKS

DiSilvestro, Robert. Handbook of Minerals as Nutritional Supplements. Boca Raton, FL: CRC Press, 2005. .

Fragakis, Allison. The Health Professional’s Guide to Popular Dietary Supplement Chicago: American Dietetic Association, 2003 .

Garrison, Cheryl D., ed. The Iron Disorders Institute Guide to Anemia. Nashville, TN: Cumberland House, 2003. .

Garrison, Cheryl D., ed. The Iron Disorders Institute Guide to Hemochromatosis. Nashville, TN: Cumberland House, 2001. .

Lieberman, Shari and Nancy Bruning. The Real Vitamin and Mineral Book: The Definitive Guide to Designing Your Personal Supplement Program, 4th ed. New York: Avery, 2007. .

Pressman, Alan H. and Sheila Buff. The Complete Idiot’s Guide to Vitamins and Minerals, 3rd ed. Indianapolis, IN: Alpha Books, 2007.

PERIODICALS

Iannotti, Lora L, James M. Tielsch, Maureen M. Black, et al. “Iron Supplementation in Early Childhood: Health Benefits and Risks.” American Journal of Clinical Nutrition, 84 (2006):1261-76.

ORGANIZATIONS

American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, Illinois 60606-6995. Telephone: (800) 877-1600. Website: <http://www.eatright.org>.

International Food Information Council. 1100 Connecticut Avenue, NW Suite 430, Washington, DC 20036. Telephone: 202-296-6540. Fax: 202-296-6547. Website: <http://ific.org>.

Iron Disorders Institute. 2722 Wade Hampton Blvd., Suite A, Greenville, SC 29615. Telephone: (864) 292-1175. Fax: (864) 292-1878. Website: <http://www.irondisorders.org>.

Linus Pauling Institute. Oregon State University, 571.

Weniger Hall, Corvallis, OR 97331-6512. Telephone: (541) 717-5075. Fax: (541) 737-5077. Website: <http://lpi.oregonstate.edu>.

Office of Dietary Supplements, National Institutes of Health. 6100 Executive Blvd., Room 3B01, MSC 7517, Bethesda, MD 20892-7517 Telephone: (301)435-2920. Fax: (301) 480-1845. Website: <http://dietary-supplements.info.nih.gov>.

OTHER

Harvard School of Public Health. “Vitamins.” Harvard University, November 10, 2006. <http://www.hsph .harvard.edu/nutritionsource/vitamins.html> .

Higdon, Jane. “Iron.” Linus Pauling Institute-Oregon State University, January 6, 2006. <http://lpi.oregonstate.edu/infocenter/minerals/iron> .

Iron Disorders Institute. “About Iron.” November 3, 2006. <http://www.irondisorders.org/Disofders/about.asp> .

Mangels, Reed. “Iron in the Vegan Diet.” Vegetarian Resource Group, April 26, 2006. <http://www.vrg.org/ nutrition/iron.htm> .

Medline Plus. “Iron.” U. S. National Library of Medicine, August 1, 2006. <http://www.nlm.nih/gov/medlineplus /druginfo/natural/patient-iron.html> .

Office of Dietary Supplements. “Dietary Supplement Fact Sheet: Iron.” National Institutes of Health, July 26, 2004. <http://ods.od.nih.gov/factsheets/iron.asp>.

Tish Davidson, A.M.

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Iron

Iron

Description

Iron is a mineral that the human body uses to produce the red blood cells (hemoglobin) that carry oxygen throughout the body. It is also stored in myoglobin, an oxygen-carrying protein in the muscles that fuels cell growth.

General use

Iron is abundant in red meats, vegetables, and other foods, and a well-balanced diet can usually provide an adequate supply of the mineral. But when there is insufficient iron from dietary sources, or as a result of blood loss in the body, the amount of hemoglobin in the bloodstream is reduced and oxygen cannot be efficiently transported to tissues and organs throughout the body. The resulting condition is known as iron-deficiency anemia, and is characterized by fatigue, shortness of breath, pale skin, concentration problems, dizziness, a weakened immune system , and energy loss.

Iron-deficiency anemia can be caused by a number of factors, including poor diet, heavy menstrual cycles, pregnancy , kidney disease, burns , and gastrointestinal disorders. Individuals with iron-deficiency anemia should always undergo a thorough evaluation by a physician to determine the cause.

Children two years old and under also need adequate iron in their diets to promote proper mental and physical development. Children under two who are not breast-feeding should eat iron-fortified formulas and cereals. Women who breastfeed need at least 15 mg of dietary or supplementary iron a day in order to pass along adequate amounts of the mineral to their child in breast milk. Parents should consult a pediatrician or other healthcare


KEY TERMS


Chelation —The use of a medication or herbal substances to inactivate toxic substances in the body. Chelation is used to treat iron overload in some patients.

Decoction —An herbal extract produced by mixing an herb in cold water, bringing the mixture to a boil, and letting it simmer to evaporate the excess water. The decoction is then strained and consumed hot or cold. Decoctions are usually chosen over infusion when the botanical in question is a root or berry.

Ferritin —An iron storage protein found in the blood. High levels of serum ferritin may indicate iron overload.

Hemochromatosis —Also known as iron overload; a genetic condition in which excess iron is stored in the tissues and organs by the body where it can build up to toxic amounts.

Homeopathic remedy —Used to treat illnesses that manifest symptoms similar to those that the remedy itself causes, but administered in extremely diluted doses to prevent any toxic effects.

Infusion —An herbal preparation made by mixing boiling water with an herb, letting the brew steep for 10 minutes, and then straining the herb out of the mixture. Tea is made through infusion.

Thalassemia —A group of several genetic blood diseases characterized by absent or decreased production of normal hemoglobin. Individuals who have thalassemia have to undergo frequent blood transfusions, and are at risk for iron over-load.

Tincture —A liquid extract of an herb prepared by steeping the herb in an alcohol and water mixture.


professional for guidance on iron supplementation in children.

It has been theorized that excess stored iron can lead to atherosclerosis and ischemic heart disease. Phlebotomy, or blood removal, has been used to reduce stored iron in patients with iron overload with some success. Iron chelation with drugs such as desferrioxamine (Desferal) that help patients excrete excess stores of iron can be helpful in treating iron overload caused by multiple blood transfusions.

Iron levels in the body are measured by both hemoglobin and serum ferritin blood tests.

Normal total hemoglobin levels are:

  • neonates: 17-22 g/dl
  • one week: 15-20 g/dl
  • one month: 11-15 g/dl
  • children: 11-13 g/dl
  • adult males: 14-18 g/dl (12.4-14.9 g/dl after age 50)
  • adult females: 12-16 g/dl (11.7-13.8 g/dl after menopause)

Normal serum ferritin levels are:

  • neonates: 25-200 ng/ml
  • one month: 200-600 ng/ml
  • two to five months: 50-200 ng/ml
  • six months to 15 years: 7-140 ng/ml
  • adult males: 20-300 ng/ml
  • adult females: 20-120 ng/ml

Preparations

Iron can be found in a number of dietary sources, including:

  • pumpkin seeds
  • dried fruits (apricots)
  • lean meats (beef and liver)
  • fortified cereals
  • turkey (dark meat)
  • green vegetables (spinach, kale, and broccoli)
  • beans, peas, and lentils
  • enriched and whole grain breads
  • molasses
  • sea vegetables (blue-green algae and kelp)

Eating iron-rich foods in conjunction with foods rich in vitamin C (such as citrus fruits) and lactic acid (sauer-kraut and yogurt) can increase absorption of dietary iron. Cooking food in cast-iron pots can also add to their iron content.

The recommended dietary allowances (RDA) of iron as outlined by the United States Department of Agriculture (USDA) are as follows:

  • children 0–3: 6-10 mg/day
  • children 4–10: 10 mg/day
  • adolescent and adult males: 10 mg/day
  • adolescent and adult females: 10-15 mg/day
  • pregnant females: 30 mg/day
  • breastfeeding females: 15 mg/day

A number of herbal remedies contain iron, and can be useful as a natural supplement. The juice of the herb stinging nettle (Urtica dioica) is rich in both iron and vitamin C (which is thought to promote the absorption of iron). It can be taken daily as a dietary supplement. Dandelion (Taraxacum officinale), curled dock (Rumex crispus), and parsley (Petroselinum crispum) also have high iron content, and can be prepared in tea or syrup form.

In Chinese medicine, dang gui (dong quai), or Angelica sinensis, the root of the angelica plant, is said to both stimulate the circulatory system and aid the digestive system . It can be administered as a decoction or tincture, and should be taken in conjunction with an ironrich diet. Other Chinese remedies include foxglove root (Rehmannia glutinosa), Korean ginseng (Panax ginseng), and astragalus (Astragalus membranaceus).

Ferrum phosphoricum (iron phosphate), is used in homeopathic medicine to treat anemia. The remedy is produced by mixing iron sulfate, phosphate, and sodium acetate, which is administered in a highly diluted form to the patient. Other homeopathic remedies for anemia include Natrum muriaticum, Chinchona officinalis, Cyclamen europaeum, Ferrum metallicum, and Manganum aceticum. As with all homeopathic remedies, the type of remedy prescribed for iron deficiency depends on the individual's overall symptom picture, mood, and temperament. Patients should speak with their homeopathic professional or physician, or healthcare professional before taking any of these remedies.

Iron is also available in a number of over-the-counter supplements (i.e., ferrous fumerate, ferrous sulfate, ferrous gluconate, iron dextran). Both heme iron and non-heme iron supplements are available. Heme iron is more efficiently absorbed by the body, but non-heme iron can also be effective if used in conjunction with vitamin C and other dietary sources of heme iron. Some multivitamins also contain supplementary iron. Ingesting excessive iron can be toxic, and may have long-term negative effects. For this reason, iron supplements should only be taken under the recommendation and supervision of a doctor.

Precautions

Iron deficiency can be a sign of a more serious problem, such as internal bleeding. Anyone suffering from iron-deficiency anemia should always undergo a thorough evaluation by a healthcare professional to determine the cause.

Iron overdose in children can be fatal, and is a leading cause of poisoning in children. Children should never take supplements intended for adults, and should only receive iron supplementation under the guidance of a physician.

Individuals with chronic or acute health conditions, including kidney infection , alcoholism , liver disease, rheumatoid arthritis, asthma , heart disease, colitis, and stomach ulcer should consult a physician before taking herbal or pharmaceutical iron supplements.

If individuals taking homeopathic dilutions of Ferrum phosphoricum experience worsening of their symptoms (known as a homeopathic aggravation), they should stop taking the remedy and contact their health-care professional. A homeopathic aggravation can be an early indication that a remedy is working properly, but it can also be a sign that a different remedy is needed.

Patients diagnosed with hemochromatosis, a genetic condition in which the body absorbs too much iron and stores the excess in organs and tissues, should never take iron supplements.

Side effects

Taking herbal or pharmaceutical iron supplements on an empty stomach may cause nausea. Iron supple-mentation may cause hard, dark stools, and individuals who take iron frequently experience constipation. Patients who experience dark bowel movements accompanied by stomach pains should check with their doctor, as this can also indicate bleeding in the digestive tract.

Other reported side effects include stomach cramps and chest pain . These symptoms should be evaluated by a physician if they occur.

Some iron supplements, particularly those taken in liquid form, may stain the teeth. Taking these through a straw, or with a dropper placed towards the back of the throat, may be helpful in preventing staining. Toothpaste containing baking soda and/or hydrogen peroxide can be useful in removing iron stains from teeth.

Signs of iron overdose include severe vomiting, racing heart, bloody diarrhea , stomach cramps, bluish lips and fingernails, pale skin, and weakness. If overdose is suspected, the patient should contact poison control and/or seek emergency medical attention immediately.

Interactions

Iron supplements may react with certain medications, including antacids , acetohydroxamic (Lithostat), Dimercaprol, Etidronate, Fluoroquinolones. In addition, they can decrease the effectiveness of certain tetracyclines (antibiotics ). Individuals taking these or any other medications should consult their healthcare professional before starting iron supplements.

Certain foods decrease the absorption of iron, including some soy-based foods, foods with large concentrations of calcium , and beverages containing caffeine and tannin (a substance found in black tea). These should not be taken within two hours of using an iron supplement. Some herbs also contain tannic acid, and should be avoided during treatment with iron supplements. These include allspice (Pimenta dioica) and bayberry (Myrica cerifera, also called wax myrtle).

Individuals considering treatment with homeopathic remedies should also consult their healthcare professional about possible interactions with certain foods, beverages, prescription medications, aromatic compounds, and other environmental elements—factors known in homeopathy as remedy antidotes—that could counteract the efficacy of treatment for iron deficiency.

Resources

BOOKS

Medical Economics Company. PDR for Herbal Medicines. Montvale, NJ: Medical Economics Company, 1998.

Medical Economics Company. PDR 2000 Physicians' DeskReference. Montvale, NJ: Medical Economics Company,1998.

Ody, Penelope. The Complete Medicinal Herbal. New York: DK Publishing, 1993.

PERIODICALS

de Valk, B. and J.J.M. Marx. "Iron, Atherosclerosis, and Ischemic Heart Disease." Archives of Internal Medicine 159, no. 14: 1542.

Paula Ford-Martin

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Iron

Iron

Iron is a metallic chemical element of atomic number 26. Its symbol is Fe, atomic weight is 55.847, specific gravity is 7.874, melting point is 2,795°F (1,535°C), and boiling point is 4,982°F (2,750°C).

Iron is one of the transition metals, occurring in group 8 of the periodic table . Four naturally occurring isotopes exist with atomic weights of 54 (5.8%), 56 (91.7%), 57 (2.2%), and 58 (0.3%). In addition, six radioactive isotopes have been prepared, with atomic weights of 52, 53, 55, 59, 60, and 61. The element was originally known by its Latin name ferrum, from which its chemical symbol is derived.


General properties

Iron is a silver-white or gray metal that is malleable and ductile. In a pure form, it is relatively soft and slightly magnetic. When hardened, it becomes much more magnetic. Iron is the most widely used of all metals. Prior to its use, however, it must be treated in some way to improve its properties or it must be combined with one or more other elements to form an alloy . By far the most common alloy of iron is steel .

One of the most common forms of iron is pig iron, produced by smelting iron ore with coke and limestone in a blast furnace. Pig iron is approximately 90% pure iron and is used primarily in the production of cast iron and steel.

Cast iron is a term used to describe various forms of iron that also contain carbon and silicon ranging in concentrations from 0.5-4.2% of the former and 0.2-3.5% of the latter. Cast iron has a vast array of uses ranging from thin rings to massive turbine bodies. Wrought iron contains small amounts of a number of other elements including carbon, silicon, phosphorus , sulfur , chromium, nickel, cobalt, copper , and molybdenum. Wrought iron can be fabricated into a number of forms and is widely used because of its resistance to corrosion .


Sources of iron

Iron is the fourth most abundant element in the earth's crust and the second most abundant metal, after aluminum . It makes up about 6.2% of the crust by weight. In addition, iron is thought to be the primary constituent of the earth's core as well as of siderite meteorites. Soil samples taken from the Moon indicate that about 0.5% of lunar soil consists of iron.

The primary ores of iron are hematite (Fe2O3), magnetite (Fe3O4), limonite (FeO(OH) • nH2O), and siderite (FeCO3). The element also occurs as the sulfide, iron pyrite (FeS), but this compound is not used commercially as a source of iron because of the difficulty in reducing the sulfide to the pure element. Iron pyrite has a beautiful golden appearance and is sometimes mistaken for elemental gold. This appearance explains its common name of fool's gold. Taconite is a low-grade ore of iron that contains no more than about 30% of the metal.

In nature, oxides, sulfides, and silicates of iron are often converted to other forms by the action of water . Iron(II) sulfate (FeSO4) and iron(II) bicarbonate (Fe(HCO3)2) are the most commonly found of these.


How iron is obtained

Iron is one of the handful of elements that was known to ancient civilizations. Originally it was prepared by heating a naturally occurring ore of iron with charcoal in a very hot flame. The charcoal was obtained by heating wood in the absence of air. There is some evidence that this method of preparation was known as early as 3,000 b.c., but the secret of ore smelting was carefully guarded within the Hittite civilization of the Near East for almost two more millennia.

When the Hittite civilization fell in about 1200 b.c., the process of iron ore smelting spread throughout eastern and southern Europe . Ironsmiths were soon making ornamental objects, simple tools, and weapons from iron. So dramatic was the impact of this new technology on human societies that the period following 1200 b.c. is generally known as the Iron Age.

A major change in the technique for producing iron from its ores occurred in about 1773. As trees (and therefore the charcoal made from them) grew increasingly scarce in Great Britain, the English inventor Abraham Darby (1678?-1717) discovered a method for making coke from soft coal . Since coal was abundant in the British Isles, Darby's technique insured a constant supply of coal for the conversion of iron ores to the pure metal. The modern production of iron involves heating iron ore with coke and limestone in a blast furnace, where temperatures range from 392°F (200°C) at the top of the furnace to 3,632°F (2,000°C) at the bottom. Some blast furnaces are as tall as 15-story buildings and can produce 2,400 tons of iron per day.

Inside a blast furnace, a number of chemical reactions occur. One of these involves the reaction between coke (nearly pure carbon) with oxygen to form carbon monoxide . This carbon monoxide then reacts with iron ore to form pure iron and carbon dioxide . Limestone is added to the reaction mixture to remove impurities in the iron ore. The product of this reaction, known as slag, consists primarily of calcium silicate. The iron formed in a blast furnace exists in a molten form known as pig iron that can be drawn off at the bottom of the furnace. The slag is also molten but less dense than the iron. It is drawn off from taps just above the outlet from which the molten iron is removed.

Efforts to use pig iron for commercial and industrial applications were not very successful. The material was quite brittle and objects of which it was made tended to break easily. Cannons made of pig iron, for example, were likely to blow apart when they fired a shell. By 1760, inventors had begun to find ways of toughening pig iron. These methods involved remelting the pig iron and then burning off the carbon that remained mixed with the product. The most successful early device for accomplishing this step was the Bessemer converter, named after its English inventor Henry Bessemer (1813-1898). In the Bessemer converter, a blast of hot air is blown through molten pig iron. The process results in the formation of stronger forms of iron, cast and wrought iron. More importantly, when additional elements, such as manganese and chromium, are added to the converter, a new product—steel—is formed.

Later inventions improved on the production of steel by the Bessemer converter. In the open hearth process, for example, a charge of molten pig iron, hematite, scrap iron, and limestone is placed into a large brick container. A blast of hot air or oxygen is then blown across the surface of the molten mixture. Chemical reactions within the molten mixture result in the formation of either pure iron or, with the addition of alloying metals such as manganese or chromium, a high grade of steel.

An even more recent variation on the Bessemer converter concept is the basic oxygen process (BOP). In the BOP, a mixture of pig iron, scrap iron, and scrap steel is melted in a large steel container and a blast of pure oxygen is blown through the container. The introduction of alloying metals makes possible the production of various types of steel with many different properties.


How we use iron

Alloyed with other metals, iron is the most widely used of all metallic elements. The way in which it is alloyed determines the uses to which the final product is put. Steel, for example, is a general term used to describe iron alloyed with carbon and, in some cases, with other elements. The American Iron and Steel Institute recognizes 27 standard types of steel. Three of these are designated as carbon steels that may contain, in addition to carbon, small amounts of phosphorus and/or sulfur. Another 20 types of steel are made of iron alloyed with one or more of the following elements: chromium, manganese, molybdenum, nickel, silicon, and vanadium. Finally, four types of stainless and heat-resisting steels contain some combination of chromium, nickel, and manganese alloyed with iron.

Steel is widely used in many types of construction. It has at least six times the strength of concrete , another traditional building material, and about three times the strength of special forms of high-strength concrete. A combination of these two materials, reinforced concrete, is one of the strongest of all building materials available to architects. The strength of steel has made possible some remarkable feats of construction, including very tall buildings (skyscrapers) and bridges with very wide spans. It has also been used in the manufacture of automobile bodies, ship hulls, and heavy machinery and machine parts.

Metallurgists have also invented special iron alloys to meet very specific needs. Alloys of cobalt and iron (both magnetic materials themselves) can be used in the manufacture of very powerful permanent magnets. Steels that contain the element niobium (originally called columbium) have unusually great strength and have been used, among other places, in the construction of nuclear reactors. Tungsten steels are also very strong and have been used in the production of high-speed metal cutting tools and drills. The alloying of aluminum with iron produces a material that can be used in AC magnetic circuits since it can gain and lose magnetism very quickly.

Metallic iron also has other applications. Its natural magnetic properties make it suitable for both permanent magnets and electromagnets. It is also used in the production of various types of dyes, including blueprint paper and a variety of inks, and in the manufacture of abrasives .


Biochemical applications

Iron is essential to the survival of all vertebrates . Hemoglobin, the molecule in blood that transports oxygen from the lungs to an organism's cells, contains a single iron atom buried deep within its complex structure. When humans do not take in sufficient amounts of iron in their daily diets, they may develop a disorder known as anemia . Anemia is characterized by a loss of skin color , a weakness and tendency to faint, palpitation of the heart , and a general sense of exhaustion.

Iron is also important to the good health of plants. It is found in a group of compounds known as porphyrins that play an important role in the growth and development of plant cells. Plants that lack iron have a tendency to loose their color, become weak, and die.


Chemistry and compounds

Iron typically displays one of two valences in forming compounds, 2+ and 3+. According to the older system of chemical nomenclature, these classes of compounds are known as the ferrous and ferric salts, of iron respectively. Because of the abundance of oxygen in the atmosphere, most naturally occurring iron compounds tend to be in the higher (3+) oxidation state .

One of the most widely used of iron compounds is iron(III) (or ferric) chloride, FeCl3. When added to water, it reacts with water molecules forming a thick, gelatinous precipitate of iron(III) hydroxide. The compound is used in the early steps of water purification since, as the precipitate settles out of solution , it traps and carries with it organic and inorganic particles suspended in the water. Iron(III) chloride is also used as a mordant, a substance used in dyeing that binds a dye to a textile. In gaseous form the compound has still another use. It attacks and dissolves metal and can be used, therefore, for etching. Printed circuits, for example, are often first etched with iron(III) chloride.

Iron(II) (ferrous) compounds tend to oxidize rather easily and are, therefore, less widely used than their 3+ cousins. Iron(II) (ferrous) sulfate is an important exception. In solid form, the compound tends not to oxidize as readily as other Fe2+ compounds and is used as an additive for animal feeds, in water purification, in the manufacture of inks and pigments, and in water and sewage treatment operations.

From a commercial standpoint, probably the most important chemical reaction of iron is its tendency to oxidize. When alloys of iron (such as the steels) are used in construction, a major concern is that they tend to react with oxygen in the air, forming a coating or iron oxide, or rust. The rusting process is actually a somewhat complex process in which both oxygen and water are involved. If one or the other of these materials can be prevented from coming into contact with iron, oxidation will not occur. But if both are present, an electrochemical reaction is initiated, and iron is converted to iron oxide.

Each year, billions of dollars are lost when iron-containing structural elements degrade or disintegrate as a result of oxidation (rusting). It is hardly surprising, therefore, that a number of techniques have been developed for reducing or preventing rusting. These techniques include painting, varnishing, galvanizing, tinning, and enameling.


Resources

books

Greenwood, N. N., and A. Earnshaw. Chemistry of the Elements. 2nd ed. Oxford: Butterworth-Heinneman Press, 1997.

Hawley, Gessner G., ed. The Condensed Chemical Dictionary. 9th ed. New York: Van Nostrand Reinhold, 1977.

Joesten, Melvin D., et al. World of Chemistry. Philadelphia: Saunders, 1991.

Knepper, W. A. "Iron." Kirk-Othmer Encyclopedia of ChemicalTechnology. 4th ed. Suppl. New York: John Wiley & Sons, 1998.

Seely, Bruce Edsall, ed. Iron and Steel in the Twentieth Century. New York: Facts on File, 1994.


David E. Newton

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Blast furnace

—A structure in which a metallic ore (often, iron ore) is reduced to the elemental state.

Ductile

—Capable of being drawn or stretched into a thin wire.

Isotopes

—Two molecules in which the number of atoms and the types of atoms are identical, but their arrangement in space is different, resulting in different chemical and physical properties.

Malleable

—Capable of being rolled or hammered into thin sheets.

Transition metal

—An element found between groups IIA and IIIA in the periodic table.

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