常圧焼結Si_3N_4セラミックスのち密化と透光性に及ぼす焼結時の詰め粉の影響

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To clarify the effect of packing powder on densification and translucency of Si_3N_4 ceramics, a Si_3N_4 ceramic doped with Al_2O_3 and Y_2O_3 was fabricated by pressureless-sintering at 1650-1850℃ under N_2 atmosphere using a carbon heating-element furnace and a graphite crucible. Three different packing powders were used: BN+Al_2O_3, Si_3N_4+ Al_2O_3 and (a raw powder for sintering) +BN. Density measurement, color of sintered body evaluation, optical absorption measurement from 200 to 2500 nm of wavelength, X-ray diffraction analysis, oxygen content analysis, scanning electron misroscopy, and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy were conducted. The specimen sintered with BN+Al_2O_3 packing powder at 1750℃ kept its original oxygen content after sintering, and reaches almost full density. This specimen was more translucent than the others at its wavelength longer than 800 nm. In the case of sintering with (a raw powder for sintering) + BN or without packing powder at 1750℃, the oxygen content in the sintered bodies decreased with the starting mixture and the color of sintered bodies changes to a more black one. The low translucency and black coloring could be attributed to pores and to a change in the microstructure or to Si, respectively. The reaction/decomposition of both Si_3N_4 and SiO_2 was effectively suppressed by sintering using the BN+Al_2O_3 packing powder, without changing composition.
2001-02-01

常圧焼結Si_3N_4セラミックスのち密化と透光性に及ぼす焼結時の詰め粉の影響

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