Iron(III) Oxide

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Iron(III) Oxide

OVERVIEW

Iron(III) oxide (EYE-urn three OK-side) is a dense, reddish-brown, crystalline compound that usually occurs as lumps or a powder. It occurs in nature as the mineral hematite and is a component of the rust that forms on objects made out of iron that are exposed to the air. Rust itself is actually a complex mixture of iron oxides and hydroxides, including Fe₂O₃, FeO, Fe₃O₄ and FeO(OH). Hematite may range in color from black and silver gray to reddish brown and red depending on the type and amount of impurities present with iron(III) oxide. Iron(III) is also ferromagnetic. Ferromagnetism refers to the ability of a substance to become highly magnetic and then retain its magnetism.

KEY FACTS

OTHER NAMES:

Ferric oxide; red iron oxide; red iron trioxide

FORMULA:

Fe₂O₃

ELEMENTS:

Iron; oxygen

COMPOUND TYPE:

Metallic oxide

STATE:

Solid

MOLECULAR WEIGHT:

159.69 g/mol

MELTING POINT:

1,565°C (2,849°F)

BOILING POINT:

Not applicable

SOLUBILITY:

Insoluble in water and all conventional organic solvents; soluble in acids

HOW IT IS MADE

Hematitite forms naturally when iron-containing rocks and minerals react with oxygen in the air to form iron(III) oxide. The oxide can be made synthetically by a variety of procedures. In the most popular method, iron(II) sulfate is reacted with sodium hydroxide (NaOH) to produce iron(II) hydroxide [Fe(OH)₂]. The iron(II) hydroxide is then allowed to react with oxygen in the air, forming iron(III) oxide. The compound can also be produced by heating iron(II) sulfate, hydrated iron(II) oxide (FeO(OH)), or iron(III) oxalate [Fe₂(C₂O₃)₃].

COMMON USES AND POTENTIAL HAZARDS

Iron(III) oxides has been associated with the manufacture of iron and steel for much of human history. The Iron Age, which began in Egypt around 4000 bce was the period in human history when iron was used for tools and weapons. The general approach to refining iron metal from iron ores, such as hematite, was to heat the ore in the presence of carbon. Carbon removes oxygen from the ore, leaving the free metal behind. By the first century bce in China, the first known blast furnaces were in use. In a blast furnace, iron(III) oxide is reduced with carbon by using a blast of air and heat. The oxygen from the air reacts with carbon to give carbon monoxide, which then reacts with iron(III) oxide to produce liquid iron metal and carbon dioxide.

In the eighteenth century, the blast furnace process was further developed so that iron could be made commercially. This process can be traced to the region around Coalbrookdale in Shropshire, England, around the year 1773 and is said to have been a factor in initiating the Industrial Revolution. The blast furnace method is still one of the primary methods by which iron metal is refined from iron ores.

Iron(III) oxide is also one of the oldest known pigments and has been used for that purpose in every major civilization. Some of the best known pigments made from iron(III) oxide have been Indian red, terra Pozzuoli, and Venetian red and have been used to color ceramic glazes and paints. Depending on the exact formulation used, iron(III) oxide produces colors ranging from yellow to orange to red. For example, the hydrated oxide produces a pigment ranging from yellow to brown. Iron(III) oxide pigments have been used as pigment for rubber, paper, linoleum, glass, and many types of paints, including specialty paints used on metalwork and ship hulls.

Interesting Facts

The name hematite is derived from the Greek word for blood.
When hematite is made into an ornament, it is sometimes called black diamond.
NASA's Mars rover Opportunity found small particles thought to be mostly hematite on the planet's surface. Scientists think they formed billions of years ago when Mars had water on its surface.
Paleolithic humans in Swaziland, who lived more than 40,000 years ago, mined hematite in the oldest known mine in the archaeological record called the Lion Cave. It is thought that they mined the hematite to produce the red pigment known as ochre.

Some of the other commercial and industrial applications of iron(III) oxide include:

As a catalyst for many industrial and chemical operations;
As a component of thermite, a mixture of iron(III) oxide and aluminum powder which, when ignited, produces very hot temperatures. Thermite bombs are used in welding;
In computer hard disks, audio cassette tapes, video cassette tapes, and computer floppy disks for magnetic storage of data;
As an abrasive and polish for use with brass, steel, gems, and other hard objects;
As a mordant in the dyeing of cloth;
As a feed additive for domestic animals to ensure proper levels of iron in their systems; and
In the manufacture of magnets and magnetic materials.

Exposure to iron(III) oxide dust can cause irritation of the eyes and throat. Long-term exposure to dust particles can cause chronic inflammation of the lungs.

Words to Know

CATALYST: A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure.
MORDANT: A substance used in dyeing and printing that reacts chemically with both a dye and the material being dyed to help hold the dye permanently to the material.

FOR FURTHER INFORMATION

Crutchfield, Charlie. "Re: What Do the Different Colors of Rust Mean, Chemically." MadSci Network. http://www.madsci.org/posts/archives/2002–03/1015309769.Ch.r.html (accessed on October 12, 2005).

"Ferric Oxide." International Labour Organization. http://www.ilo.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc15/icsc1577.htm (accessed on October 12, 2005).

Ricketts, John A. "How a Blast Furnace Works." American Iron and Steel Institute. http://www.steel.org/AM/Template.cfm?Section=Home&template=/CM/HTMLDisplay.cfm&ContentID=5433 (accessed on October 12, 2005).

Chemical Compounds