Calcium Silicate

OVERVIEW

The term calcium silicate (KAL-see-um SILL-i-kate) applies to a number of related compounds consisting of calcium, silicon, and oxygen, all of which tend to occur in a hydrated form. The most common of these forms is calcium metasilicate, for which data are given above. Calcium silicates with the formulas Ca₂SiO₄ and Ca₃SiO₅ are also well known.

Calcium silicate is a component of many minerals, including afwillite, akermanite, andradite, calcite, centrallasite, crestmoreite, diopside, eaklite, grammite, gyrolite, hillebrandite, larnite, and wollastonite. In its pure form, calcium metasilicate is a white to off-white color capable of absorbing up to two and a half times its weight of water. In this form, the hydrated powder retains its ability to flow freely. Addition of a mineral acid, such as hydrochloric acid (HCl) results in the formation of a gel.

KEY FACTS

OTHER NAMES:

Calcium metasilicate

FORMULA:

CaSiO₃

ELEMENTS:

Calcium, silicon, oxygen

COMPOUND TYPE:

Inorganic salt

STATE:

Solid

MOLECULAR WEIGHT:

116.16 g/mol

MELTING POINT:

1540°C (2800°F)

BOILING POINT:

Not applicable

SOLUBILITY:

Insoluble in water and most other common solvents

HOW IT IS MADE

Given its abundance in rocks and minerals, calcium metasilicate and its cousins can be extracted from a variety of natural sources. Nonetheless, the compound is usually prepared synthetically in order to ensure that is has the purity required for most commercial applications. The usual method of preparation involves the addition of lime (calcium oxide; CaO) to diatomaceous earth, a material consisting of the fossil remains of single-celled algae known as diatoms. The lime provides the calcium and the diatomaceous earth provides the silicon dioxide (SiO₂) required to make calcium silicate.

COMMON USES AND POTENTIAL HAZARDS

The calcium silicates have a number of uses in industry. Among the most important applications are their uses in building materials, such as some types of glass and cement (especially Portland cement), bricks and tiles for roofs, fireproof ceilings, and building boards. The compound is also used as a filler in the manufacture of paper and some types of plastics, where it gives body to the final product.

Other applications of the calcium silicates include the following:

• As an absorbent for liquids and gases in industrial processes;
• As a food additive, where it absorbs moisture and prevents a product from "caking" (becoming compacted);
• In road construction;
• As a refractory material in industrial furnaces;
• For the insulation of pipes and conduits;
• In the manufacture of paints and other types of coating materials;
• In the preparation of certain types of cosmetics;
• In some fertilizers and insecticides; and
• In some pharmaceutical products, such as antacids.

Interesting Facts

• One of the most common building materials in use today is Portland cement, made from a mixture of oxides, including lime (calcium oxide), sand (silicon dioxide), and aluminum, iron, and magnesium oxides. When these components are mixed and water is added, a complex set of chemical reactions occur in which calcium silicates are among the major products formed. These calcium silicates are responsible for the great strength for which Portland cement products are known.

There have been no reports of calcium silicate's being hazardous or harmful to humans or experimental animals. As with all chemicals, overexposure to large amounts of the compound could result in irritation of the skin, eyes, and respiratory system.

Words to Know

HYDRATE

Chemical compound formed when one or more molecules of water is added physically to the molecule of some other substance.

REFRACTORY

Having a high melting point, resistant to melting. Refractory materials are often used to line the interior of industrial furnaces.

SYNTHESIS

A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.

FOR FURTHER INFORMATION

"Occupational Safety and Health Guideline for Calcium Silicate, Synthetic." Occupational Health and Safety Administration. http://www.osha.gov/SLTC/healthguidelines/calciumsilicate/recognition.html#healthhazard (accessed on September 29, 2005).

"Scientific Principles." Materials Science and Technology Teacher's Workshop. http://matse1.mse.uiuc.edu/∼tw/concrete/prin.html (accessed on September 29, 2005).

"Wollastonite." CeramicMaterials.Info. http://ceramic-materials.com/cermat/material/1705.html (accessed on September 29, 2005).