Nitrides of boron & silicon are  used to make crucibles because they are stable when this is high
[DOC] [TLE] Niobium | Plansee [PAR] Niobium is special because this high level of resistance is achieved at a ... and 
excellent formability make niobium the perfect material for the crucibles used to ... 
Our niobium crucibles are used for the high-pressure, high-temperature synthesis
.