Magnesite-zirconia refractories

They are normally cast in the form of brick and are sometimes bonded to assure stability. The outstanding property of these materials is their ability to act as insulators. The most important are fireclay (aluminum silicates), silica, high alumina (70-80% ALjOj), mullite (clay-sand), magnesite (chiefly MgO), dolomite (CaO-MgO), forsterite (MgO-sand), carbon, chrome ore-magnesite, zirconia, and silicon carbide. (2) Characterizing the ability to withstand extremely high temperature, e.g., tungsten and tantalum are refractory metals, clay is a refractory earth, ceramics are refractory mixtures. 

Refractories. Aluminosilicates, silica and aluminous material, basic materials such as magnesite, chrome-bearing materials such as magnesia-chrome bricks, zirconia-bearing materials, and silicon carbide. There are also raw materials such as fireclay, ferrosilicon, and graphite. 

Chrome-bearing refractories are particularly difficult to fuse, and, although not entirely satisfactory, a flux mixture of 10 parts of lithium metaborate and 12.5 parts of lithium tetraborate to one part of sample is generally used for chrome-magnesite, chrome-magnesia—zirconia and chrome ore samples, but not metallvugical chrome ore, which requires further dilution in MgO. 

Many refractories are derived directly from natural minerals, but synthetic materials are also widely use. Clays, espeeially those having inherent temperature resistance, are the oldest and most eommon of the naturally occurring refractory minerals. Major natural refi actoiy materials are kaolin, chromite, bauxite, zirconia, and magnesite. These are often marketed under specific trade names. Refractory materials may be acid, such as silica, or basic, such as magnesite or bauxite, for use in aeid- or basic-process steel furnaces. Graphite and chromite are generally considered neutral refractories. 

---