Development of precursor ceramics using organic silicon polymer

Abstract This paper relates to the Bridge Building Award, which was presented to the author (Toshihiro Ishikawa) by the American Ceramic Society on 27 January 2020. We have developed many types of functional ceramics using polycarbosilane as a raw material. Since 1983, several grades of SiC‐based fibers have been produced from polycarbosilane by Ube Industries, Ltd. Of these grades, we developed the highest heat‐resistant SiC‐polycrystalline fiber (Tyranno SA), which can withstand up to 2000°C, using an organic silicon polymer (poly‐aluminocarbosilane) containing a small amount of aluminum as a precursor material. By employing curing (in air) and firing (in nitrogen atmosphere at 1300°C) processes using the precursor fiber, an amorphous fiber (Si‐Al‐C‐O fiber) containing a small amount of aluminum was obtained; subsequent heat treatment at higher temperatures (~2000°C) in argon atmosphere led to carbothermal reduction (SiO ₂ + 3C SiC + 2CO(g)) and a sintering process, producing the abovementioned SiC‐polycrystalline fiber (Tyranno SA). In the same year, using the same raw precursor fiber (Si‐Al‐C‐O fiber), we also developed a new type of tough, thermally conductive SiC composite (SA‐Tyrannohex) with high strength up to 1600°C in air. This ceramic consists of a highly ordered, close‐packed structure of very fine hexagonal columnar SiC‐polycrystalline fibers with a thin interfacial carbon layer between them. Further, by using the polycarbosilane as a starting material, we successfully developed a strong photocatalytic fiber (TiO ₂ /SiO ₂ fiber) with a gradient surface layer composed of TiO ₂ ‐nanocrystals, making the best use of controlled phase separation (bleed‐out) of additives (titanium (IV) tert‐butoxide) contained in polycarbosilane. In this paper, the story of the development of these materials and the subsequent progress will be described along with the historical background.