Millennial Special Leading Papers on Ceramic in the 20<sup>th</sup> Century: the Best of JCerSJ Hot-Pressing of Si<sub>3</sub>N<sub>4</sub>-Al<sub>2</sub>O<sub>3</sub>

Abstract

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.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.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.(1) Based from the specific gravity of Si3N4ss, the solid solution is thought to be a substitution type.(2) The solubility limit of Al2O3 in Si3N4ss is estimated to be about 67mole% at 1750°C and 78mole% at 1850°C.(3) The high-temperature oxidation resistance of Si3N4ss is excellent compared to that of Si3N4.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.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).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.