Views: 7 Author: Site Editor Publish Time: 2023-05-08 Origin: Site
A refractory (or refractory) is a material that resists decomposition by heat, pressure, or chemical attack and retains its strength and shape at high temperatures.Refractory materials are polycrystalline, heterogeneous, inorganic, non-metallic, porous and heterogeneous. They usually consist of oxides or carbides, nitrides, etc.of the following materials: silicon, aluminum, magnesium, calcium, boron, chromium and zirconium.ASTM C71 defines refractories as "nonmetallic materials having chemical and physical properties making them suitable for use in components of structures or systems exposed to environments above 1,000 °F (811 K; 538 °C)".Refractories are used in furnaces, kilns, incinerators and reactors.Refractories are also used to make crucibles and molds for casting glass and metals, and surface flame deflection systems for rocket launch structures.Today, the steel industry and the metal foundry industry use about 70% of all refractories.
Refractories must be chemically and physically stable at high temperatures.Depending on the operating environment, they must be resistant to thermal shock, chemically inert, and/or have a specific range of thermal conductivity and coefficient of thermal expansion.Oxides of aluminum (alumina), silicon (silica) and magnesium (magnesia) are the most important materials used in the manufacture of refractories.Another oxide commonly found in refractories is that of calcium (lime).Refractory clay is also widely used in the manufacture of refractory materials.Refractory materials must be selected according to the conditions they face.Some applications require special refractory materials used when the material must withstand extremely high temperatures.Silicon carbide and carbon (graphite) are two other refractory materials used in some very severe temperature conditions, but they cannot be used in contact with oxygen because they will oxidize and burn.Binary compounds such as tungsten carbide or boron nitride can be very refractory,carbide is the most refractory binary compound known, with a melting point of 3890 °C.The ternary compound Tahafnium carbide has one of the highest melting points of all known compounds (4215 °C).Molybdenum disilicide has a melting point as high as 2030°C and is often used as a heating element.