Magnesium oxide

Magnesium oxide

Magnesium oxide, or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium.
Formula: MgO
Molar mass: 40.3044 g/mol
IUPAC ID: Magnesium oxide
Melting point: 2,852 °C
Density: 3.58 g/cm³
Boiling point: 3,600 °C

Magnesia or magnesium oxide is an alkaline earth metal oxide. The majority of magnesium oxide produced today is obtained from the calcination of naturally occurring minerals. Magnesite, MgCO3, being the most common.
Both MgCO3 and Mg(OH)2 are converted to MgO by calcination. The thermal treatment of the calcination process affects the surface area and pore size and hence the reactivity of magnesium oxide formed. The source largely determines the level and nature of impurities present in the calcined material.
Caustic calcined magnesia is formed by calcining in the range 700 – 1000°C. By calcining in the range 1000 – 1500°C the magnesium oxide is used where lower chemical activity is required e.g. fertiliser and animal feed.
Dead-burned magnesia, which is produced in shaft and rotary kilns at temperatures over 1500°C, has reduced chemical reactivity therefore is more suited to refractory applications. Fused magnesia is used for a variety of refractory and electrical applications. This type of magnesia is produced in an electric arc furnace from caustic calcined magnesia at temperatures in excess of 2650°C
Key Properties
There are few dense engineering ceramics of the structural type made from pure magnesia. However there is a wide range of refractory and electrical applications where magnesia is firmly established. The properties of major interest are as follows:
Good Refractoriness
Good Corrosion Resistance e.g. Basic Steelmaking Slags, Sodium Hydroxide, Fe, Co, Ni
High Thermal Conductivity
Low Electrical Conductivity
Transparency to Infrared

Applications
Magnesium Oxide in Animal Food Supplements
Magnesium is an essential nutrient for all animals, serving a variety of vital functions within the body PPM magnesium oxide, a granular, high purity feed grade magnesium oxide processed from natural magnesite, is an excellent source of magnesium for cattle consuming low-magnesium forages.
Inadequate magnesium in the diets of grazing animals can cause a serious metabolic disorder known as “Grass Tetany.” The rapid growth rate of grass in Spring means that pastures are often lacking in magnesium. Young grass is higher in simple carbohydrates and protein, but lower in most minerals. Grass tetany occurs when the level of magnesium in blood falls below a critical threshold. Providing a palatable magnesium supplement with high biological availability is an effective strategy for maintaining magnesium requirements of grazing animals.
In dairy cattle, magnesium also helps raise the butter fat content of the milk and neutralizes acidosis caused by high amounts of grain in their diet.
The balance of magnesium performs an important role in utilization of calcium, which is released from bone into the bloodstream. As with calcium, magnesium is classified as a macro mineral, which means that it is required by the body in reasonably large quantities. Magnesium is also important in converting sugars into energy.

Refractories
Magnesia is widely used in the steel industry as a refractory brick. It is often impregnated with carbon (tar, pitch, graphite) to provide the best properties for corrosion resistance in environments of basic slags, particularly in BOF furnaces or slag lines of treatment ladles.

Magnesia bricks often in combination with spinel or chrome are also used in ferroalloy, non-ferrous, glass and cement industries. Castables and sprayables based on magnesia are widely used for basic refractory linings for steel transfer applications. The lime to silica ratio present in the magnesia has a major influence on its properties.

Cements
Magnesia (or Sorel) cement is a refractory binder based on a magnesium oxychloride formulation. It is fast-hardening and has a number of refractory and general repair applications. Magnesia is also used as a room temperature curing agent for phosphate cements.

Heating Elements
Magnesia powder is widely used as a filling for electrical heating elements for applications in contact with air or liquids.

Fused magnesia has the ideal combination of electrical resistance and thermal conductivity. The MgO forms a layer between the element and the outer sheath. It is also used as mineral insulation in cables.

Brake Linings
Magnesia has been included in brake linings due to its thermomechanical properties. Its intermediate hardness gives sufficiently low wear on metal while conducting heat from the friction contact surfaces.