B. Matovic, G. Rixecker, S. Boskovic, F. Aldinger
May 31, 2013
This paper deals with the densification and phase transformation of Si 3 N 4 with additives of Li-exchanged zeolite during pressureless sintering at significantly reduced temperatures. Dilatometric shrinkage data show that the first liquid forms as low as 1080°C. Upon sintering at 1500°C the bulk density increases to more than 95% of the theoretical density without phase transformation from -S 3 N 4 to -Si 3 N 4 , i.e. the phase transformation lags behind the densification process. Above 1500°C the secondary phase is completely converted into a glass and the -to- transformation takes place. Under these conditions the grain growth is anisotropic, leading to a microstructure which has potential for enhanced fracture toughness. The results show that a very effective low-temperature sintering additive for silicon nitride can be obtained from Li-exchanged zeolite.