It is made from 96.5% calcined alumina and 3.5% Veegum (to provide plasticity for forming). At cone 6, with no prior firing to a higher temperature, a 5mm thick slice can support a piece like this. The larger the span the higher it should be prefired to get needed hot strength. This is just typical sintered alumina, it does not have nearly the thermal shock resistance that fully crystallized tabular alumina has.
In the ceramic industry, refractory materials are those that can withstand a high temperature without deforming or melting. Refractories are used to build and furnish kilns.