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Refractories must be chemically and physically stable at high temperatures
2023-01-03
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 (magnesium oxide) are the most important materials used in the manufacture of refractories. Another oxide commonly found in refractories is the oxide of calcium (lime). Fireclay is also widely used in the manufacture of refractories.
Refractories must be selected according to the conditions they face. Some applications require special refractories. Zirconia is used when the material must withstand extremely high temperatures. Silicon carbide and carbon (graphite) are two other refractories used in some very harsh temperature conditions, but they cannot come into contact with oxygen because they oxidize and burn.
Binary compounds, such as tungsten carbide or boron nitride, can be very refractory. Carbonization is the most difficult binary compound known to melt, with a melting point of 3890°C. The ternary compound tantalum and hafnium carbide has one of the highest melting points of all known compounds (4215 ° C).
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