Keracast 6 is a totally cement free, CaO free material. It is consequently highly refractory. The chemical analysis is approximately as follows;
The mineral composition is about 87% alpha alumina, which is synthetic corundum, with a melting point of 2013ºC and 13% mullite,Al2 O3 .SiO2 , with a melting point of 1850ºC. The material therefore contains very little liquid phase below 1850ºC. Both mullite and corundum are chemically inert and immune to attack by sulphurous or acid gases. To develop good strength we pre-fire the castings to 1200ºC, so that the silica is all present in the mineral mullite. Mullite grows in needle-like crystals, which enhance the strength of the composite. Corundum is the second hardest natural mineral, with a hardness of 9 on the Moh scale. (Diamond is the hardest, at 10 on the scale.) The only refractory materials with higher melting points are lime, magnesia and zirconia. All three are prone to thermal shock.
Formulation no. 11484