西暦2000年特別企画“20世紀のセラミックスを先導した論文”窒化珪素-アルミナ系焼結体

Few literature had been published on the solid solubility of oxides in nitrides before 1971. Oyama and Kamigaito originally reported that Al₂O₃ dissolves in Si₃N₄ in 1971. Jack and Wilson (1972) reported on the solid solution of Si₃N₄ with Al₂O₃ (β′-Si₃N₄) as well as a new material having the α-Si₃N₄ structure formed by the reaction of LiSi₂N₃ with Al₂O₃. The term SiAlON (Si-Al-O-N) well known these days was given by Jack and Wilson and the former material is called β-SiAlON and the latter α-SiAlON.<br>This paper reports in detail on the solid solubility of Al₂O₃ in Si₃N₄ that was reported firstly in 1971. This paper was submitted in January and published in August 1972. Jack and Wilson's paper was submitted in April and published in October 1972.<br>In both papers, almost the same figure, which relates the lattice constants of the solid solution and Al₂O₃ concentration in Si₃N₄, was given. The following facts are reported in this paper.<br>(1) Based from the specific gravity of Si₃N₄ss, the solid solution is thought to be a substitution type.<br>(2) The solubility limit of Al₂O₃ in Si₃N₄ss is estimated to be about 67mole% at 1750°C and 78mole% at 1850°C.<br>(3) The high-temperature oxidation resistance of Si₃N₄ss is excellent compared to that of Si₃N₄.<br>In our opinion, this paper should be honored from the standpoint that it has contributed much to the research on SiAlON globally. Credit is due to Oyama and Kamigaito for performing pioneering work in this field.<br>The phenomenon that nitrides dissolve oxides could not be understood at the time this paper was submitted. Incidentally, there is a story that this paper was nearly rejected by the editorial committee of Yogyo-Kyokai-Shi (Journal of the Ceramic Society of Japan).<br>Prior to 1980, at the dawn of the research on Si₃N₄ ceramics, several worldwide innovative research studies were reported in the following papers; the report on the excellent mechanical properties of reaction sintered silicon nitride, densification of Si₃N₄ ceramics with additives by hot-pressing, discovery of solid solubility of Al₂O₃ in Si₃N₄, the report on the conventional sintering of Si₃N₄, gas pressure sintering of Si₃N₄ and the patent on effectiveness of Y₂O₃ as a sintering additive of Si₃N₄ ceramics. Finally, it is worth mentioning that Japanese researchers performed three of these six globally famous and original works.