Abstract
Amorphous Si3N4/TiO2 compacted bodies were heated at 1490°C, for 1 to 10 hr under N2 pressures of 0.92 and 1000 atm, and the effect of N2 pressure on the resulting grain refining was investigated, to clarify the role of TiO2 in the grain-refined mechanism. Thermodynamic calculation performed prior to experiments indicated that high N2 pressure inhibited the formation of SiO gas and new formation of Si3N4 by its re-nitridation. Crystallized phases after heating were α-Si3N4, Si2N2O and TiN. Although both N2 pressures formed the fine grains having a diameter of about 30 nm, high pressure accelerated the grain refining and crystallization of amorphous Si3N4 to a-Si3N4. From these results, the fine grains were considered to be formed not through re-nitridation of SiO gas but through crystallization of amorphous Si3N4.
