Magnesia is widely used in the steel industry as a refractory brick often impregnated with carbon (tar, pitch, graphite) to give optimum 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.
Magnesia crucibles have found application in the superalloy industry, nuclear industry and chemicals industry where corrosion resistance is required. Manufacture is by firing isostatically pressed or slip cast shapes made from fused magnesia. Various purity grades are commercially available. Additives are employed to promote sintering or restrict crystal growth. These range from clay to yttria and alumina depending on application. Crucibles with stability of 2400oC in air, 1700oC in reducing atmospheres, 1600oC in vacuum and 1400oC in hydrogen have been reported in the literature.
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.
Magnesia powder is widely used as a filling for electrical heating elements for applications in contact with air or liquids such as electric cooker rings, storage heaters, washing machines, and diesel engine glow plugs. 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.
Extruded magnesia protective sheaths have been used to house thermocouples in aggressive environments.
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.
Plasma Display Screens
Magnesia has been used as a protective film for plasma display screens where its electro-optical properties are used to advantage.
Substrate for Thin Film Formation
High purity grades of magnesia have been used to grow thin film semiconductors. Other similar electronic applications have been investigated.