The term refractory refers to the quality of a material to retain its strength at high temperatures. Refractory materials are used to make crucibles and linings for furnaces, kilns and incinerators. There is no clearly established boundary between refractory and non-refractory materials, though a practical requirement often cited is the ability of the material to withstand temperatures above 1100 °C without softening.
Refractory materials must be strong at high temperatures, resistant to thermal shock, chemically inert, and have low thermal conductivities and coefficients of expansion.
The oxides of magnesium (magnesia) and calcium (lime) are the most important refractory materials, though fireclay is widely used as well. Zirconia is used when the material must withstand extremely high temperatures. Silicon carbide is another refractory material. It is very strong at high temperatures, but will burn in the presence of oxygen, if the protective silica coating comes off. Refractories must be chosen according to the conditions they will face. For example, carbon cannot be used when it will be in contact with oxygen, as it will burn.
Types of Refractories
Acidic refractories cannot be used in a basic environment and basic refractories cannot be used in acidic environment because they will be corroded. Zircon, fireclay and silica are acidic, dolomite and magnesite are basic and alumina, chromite, silicon carbide, carbon and mullite are neutral. Refractory metals are also frequently used.
Anti-abrasion refractory attached to pipes, chambers, etc, will require anchorage systems such as wire formed anchors or hexmetal to support the refractory linings.