Abstract
The sintering behaviour of commercial and high purity RBSN with and without MgO and Y2O3 additions has been studied by high temperature dilatometry with nitrogen overpressure. Activation energies for densification are in the region 500 to 600 kJ mol−1. Commercial RBSN shows some shrinkage and α-β Si3N4 conversion without addition. High purity RBSN retains 74%αSi3N4 after 1 h at 1750° C and shows only 0.2% linear shrinkage. The effect of calcium, aluminium and iron impurities was examined. The densification curves obtained with MgO as additive show a transient expansion in the early stages of sintering which is associated with the gas overpressure. In the absence of a powder bed, decomposition was impracticably high. Both a powder bed and nitrogen overpressure were needed to suppress decomposition.
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