Specimens of milled α-Si3N4 with 0 to 5.07 equivalent per cent of CeO2, MgO or Y2O3 additions were pressureless sintered at 1650 to 1820° C for 4 h in static nitrogen at 34.5 kPa (5 psi) gauge pressure and while covered with a mixture of Si3N4+SiO2 powders. The density — per cent addition — temperature plots showed maxima which, for all three additives, occurred between ∼ 1.2 and 2.5 equivalent per cent. Maximum densities resulted on sintering in the 1765 to 1820° C range and were 99.6 per cent of theoretical with 2.5 equivalent per cent CeO2, 98.5 per cent of theoretical with ∼ 1.24 to 1.87 equivalent per cent MgO, and 99.2 per cent of theoretical with 2.5 equivalent per cent Y2O3. Also, densities ≥ 94 per cent of theoretical were obtained with as little as 0.62 equivalent per cent additive (1.0 MgO, 2.11 CeO2 or 1.85 Y2O3, in wt%). X-ray diffraction showed that the materials were predominantly β-Si3N4 with some or no Si2N2O. Scanning electron photomicrographs showed microstructures of elongated grains with aspect ratios of about 5, with all additives.
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Arias, A. Effect of CeO2, MgO and Y2O3 additions on the sinterability of a milled Si3N3 with 14.5 wt% SiO2 . J Mater Sci 16, 787–799 (1981). https://doi.org/10.1007/BF00552218
- Aspect Ratio