Refractory materials are chemical compounds that are used as structural materials forming insulation linings and/or as containment vessel in high temperature and corrosive environments in many industrial processes. The use of chromium in refractories is second in importance to its metallurgical applications. The mineral chromite is the only ore of chromium1. About 15% of the total world chromite consumption is from the refractories industry2. A typical analysis of a chromite suitable for refractory purpose is 38 to 48 percent Cr2O3, 12 to 24 percent Al2O3, 14 to 24 percent Fe2O3, 14 to 18 percent MgO, and less than 10 percent SiO2.
The usefulness of chromite as a refractory is based on its high melting point of 2,180 °C (3,960 °F), moderate thermal expansion, neutral chemical behavior, and relatively high corrosion resistance. Chromite enhances thermal shock and slag resistance, volume stability and mechanical strengh. In contact with iron oxide, it forms a solid solution (a homogeneous crystalline phase composed of different minerals dissolved in one another) with iron oxide and expands considerably, causing the refractory to crumble (bursting). Adding magnesia can prevent this phenomenon 3.
Chrome-based refractories4,5 are typically used in cement kilns, secondary steel refinig furnaces, foundry sands, glass melting furnaces, and incinerators. In some cases alternative materials -- such as magnesium-aluminium spinels, spinel-bonded magnesite and high alumina refractories -- have replaced chrome-containing refractories. However, these materials do not always meet performance or cost requirements.