Our refractory materials are
chemically and physically stable at high temperatures. Depending on
the operating environment, they can resistant to thermal shock, be
chemically inert, and/or have specific ranges of thermal
conductivity and of the coefficient of thermal
expansion.
The oxides of aluminium (alumina),
silicon (silica) and magnesium (magnesia) are the most important
materials used in the manufacturing of refractories. Another oxide
usually found in refractories is the oxide of calcium (lime). Fire
clays are also widely used in the manufacture of
refractories.
Refractories must be chosen
according to the conditions they will face. Some applications
require special refractory materials. Zirconia is 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, as they will oxidize and
burn.
Binary compounds such as tungsten
carbide or boron nitride can be very refractory. Hafnium carbide is
the most refractory binary compound known, with a melting point of
***0 C. The ternary compound tantalum hafnium carbide has one of
the highest melting points of all known compounds (***5
C).
