Vacuum heat-treatment of MgO-densified silicon nitride ceramics and their compatibility with molten aluminium and copper

Silicon nitride with 3% MgO powder mix was compacted with cold isostatic pressing followed by uniaxial pressing. Pressureless sintering of the compacted silicon nitride (Si3N4) crucibles was at 1600 °C for 30 min in the carbon furnace. The densities achieved after this process are 3140 kg/m3. One of these crucibles was vacuum heat treated at 1575 °C for 5 h to remove grain boundary glass. Both this crucible and the as-sintered crucibles were used for melting aluminium and copper by heating in, air atmospheres to 700 °C and 1100 °C, respectively. Vacuum heat-treated glass free ceramic crucible was successfully used for the molten aluminium and copper handling. On the other hand, the chemical bond occurred for as sintered Si3N4 crucible. No adherence was observed after examining of interface between Al and the heat-treated ceramic crucible with SEM and EDX analysis.