Dr. Katsutoshi Komeya joined Toshiba Corporation after graduating from the Faculty of Engineering, Yokohama National University, in March 1962 and in the following year, 1963, he started research on synthesizing and sintering aluminum nitride (AlN) and silicon nitride (Si3N4), an area in which there were very few examples of research. After several years of basic research, he and his colleagues discoverd those sintering auxiliaries that represent a creative sintering principle applicable to both nitrides, and became the first person in the world to establish a starting point for creating new functional materials. Thereafter, materials were developed on a worldwide scale based on this principle. AlN is now used for semiconductor substrates, packing materials, and parts for semiconductor manufacturing processes as a high-thermal conductive material. Furthermore, Si3N4 is now employed for engine parts and bearings as a high-temperature, high-strength and excellent wear resistant material.
This paper dealing with sintering of AlN was the first paper to discuss the influences of various additives on the sintering of AlN. Examination of the roles of 30 types of additives clarified that rare-earth oxides, such as Y2O3, La2O3, and Sm2O3, and alkaline earth compounds, such as CaCO3 and BaCO3, form aluminates under high-temperature sintering and that densification is promoted by liquid phase sintering. It has also been shown that, when SiO2 is added to AlN, a sintered body of plate-like texture can be obtained by generating AlN polytypoid but densification is prevented by the generation of this phase. In addition to the above, this paper clarified the following two points, which are now deemed as important findings for the implementation of AlN. First, it was found that a black-gray color was created when compounds that contain transition elements, such as Ti, Zr, and Hf, áre added. Currently, these compounds are used as important additives to give a black color to AlN packages. Second, measurement of the bending strength of various sintered bodies consisting of AlN and additives revealed that, among those materials where densification is achieved, Y2O3 and CaCO3, which are now employed in practical applications, exhibit only low strength, but La2O3 and Sm2O3 are effective for providing high strength. As the achievement of high strength is now considered the most important subject in the field of AlN ceramics, this paper provides important findings for the solution of this problem as well.
As described above, this pioneering paper was the first to clarify those sintering auxiliaries that are now basic components of ceramics and their effects in the initial stage of the development of AlN ceramics. Furthermore, this paper also suggests those additives that are effective for achieving high strength as well as for coloring and is very frequently referred even though it is written in Japanese. I therefore recommend it as “a paper that leads the studies of ceramics in the 20th century”, as I judge that it is really worthy of that honor.