Some ceramics have the ability to form solid solutions.
One such group are the sialons, which contain silicon, aluminium, oxygen and nitrogen in specific proportions. The basic difference between these two is in the two different crystal structures of the silicon nitride. This type of ceramic is usually produced by the sintering of powder mixtures at temperatures up to 1850 C, during which complicated chemical reactions take place through a liquid phase. During sintering, the material is densified to a pore free body, characterized by high hardness, chemical inertness, high oxidation resistance and high strength at elevated temperature. This allowed in situ studies of the densification process to be made during sintering.