SIALON:

This class of refractory is prepared by using alumina and silicon nitride. Powdered mixture of alumina and silicon nitride is hot pressed at 18 – 30 MPa and 1700 – 1760^oC in graphite moulds  in order to produce a low porosity dense product. SIALON refractory shows

• good resistance to oxidation, and action of molten metals like Al, Zn, Cd, Fe and steel and
• resistance to H₂SO₄, HCl, borax and alkalis.

Manufacture of a refractory

Note that refractory used in high temperature furnaces does not occur as natural reserves. But refractory is produced by using naturally occurring materials like quartz, magnesite, dolomite, chromite, bauxite etc.

A general flow sheet is given in the following to illustrate the various steps and their functions.