Magnesium Oxide

OVERVIEW

Magnesium oxide (mag-NEE-see-um OK-side) is available commercially in several forms, depending on the way it is prepared and the use for which it is intended. Most forms can be classified as either "light" or "heavy" depending on particle size, purity, and method of production. It occurs in nature in the form of the mineral periclase. In its purest form, magnesium oxide is a colorless or white crystalline material or very fine powder, with no odor and a bitter taste.

KEY FACTS

OTHER NAMES:

Magnesia; calcined magnesia; magnesia ulba

FORMULA:

MgO

ELEMENTS:

Magnesium, oxygen

COMPOUND TYPE:

Metallic oxide (inorganic)

STATE:

Solid

MOLECULAR WEIGHT:

40.30 g/mol

MELTING POINT:

2,825°C (5,117°F)

BOILING POINT:

3,600°C (6,500°F)

SOLUBILITY:

Slightly soluble in water; soluble in most acids; insoluble in alcohol

HOW IT IS MADE

A number of methods are available for the preparation of magnesium oxide. Most methods begin with either magnesium hydroxide [Mg(OH)₂] or magnesium carbonate (MgCO₃), either of which is heated under controlled conditions to produce the desired product. The primary methods of preparation are:

• Dead-burning, in which the hydroxide or carbonate is heated to temperatures ranging from 1,500°C to 2,000°C (3,000° to 4,000°F), so-called because the final product is largely chemically unreactive;
• Hard-burning (also known as caustic-burned), in which the hydroxide or carbonate is heated to somewhat lower temperatures, between 1,000°C and 1,500°C (2,000°F and 3,000°F), allowing the compound to retain some of its chemical reactivity;
• Light-burning, in which the temperature is kept between 700°C and 1,000°C (1,500°F and 2,000°F), resulting in a product with even more reactivity; and
• Fusion, in which the hydroxide or carbonate is heated to temperatures in excess of 2,650°C (4,800°F), producing a very dense, inert product.

An especially pure form of magnesium oxide can be made by taking the product from any of the above reactions and making a slurry with water. A slurry is a mud-like mixture of a solid and liquid that normally do not form a solution. Various chemicals can then be added to the magnesium oxide slurry to remove any contaminants, and the purified slurry is allowed to dry.

COMMON USES AND POTENTIAL HAZARDS

Each form of magnesium oxide has its specialized uses:

• Dead-burned: As refractory brick for cement kilns, furnaces, crucibles, and equipment used in the manufacture of steel;
• Hard-burned: In the production of fertilizers and animal feed, in the extraction of uranium oxide from uranium ore, as a catalyst, in the manufacture of ceramics, for the tanning of leather, in the synthesis of magnesium compounds, and (its most important single use) in pollution control devices that remove sulfur dioxide from plant exhaust gases;
• Light-burned: In the processing of paper and pulp; as a filler in products made of rubber; and as an ingredient in a host of household and personal care products such as dusting powders, cosmetics, and pharmaceuticals. Some of the best-known pharmaceuticals containing magnesium oxide are antacids used to treat heartburn, upset stomach, or acid indigestion and laxatives for the treatment of constipation or in preparation for surgery.
• Fusion: As refractory linings for electric arc furnaces and in insulating materials used in many household electrical products.

Interesting Facts

• Magnesium oxide is sometimes used as a gemstone called periclase. It is found in a wide range of colors from colorless or white to yellow to brown. Its use as a gemstone is somewhat limited, however, because it is not very hard.

Words to Know

CATALYST

A material that increases the rate of a chemical reaction without undergoing any change in its own chemical structure.

REFRACTORY MATERIAL

A material with a high melting point, resistant to melting, 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.

Contact with magnesium oxide dust or fumes may irritate the skin, eyes, or respiratory system. Symptoms of exposure may include fatigue and lethargy. The greatest concern for such health hazards rests with people who come into contact with the pure product in their line of work.

FOR FURTHER INFORMATION

"Everything You Wanted to Know about Magnesium Oxide." Martin Marietta Magnesia Specialties. http://www.magspecialties.com/students.htm (accessed on October 14, 2005).

"Magnesia-Magnesium Oxide (MgO)." Azom.com. http://www.azom.com/details.asp?ArticleID=54 (accessed on October 14, 2005).

See AlsoMagnesium Hydroxide