Crack healing behavior of SiC ceramics with large crack width has been studied as a function of coating and heat treatment. The SiO2 colloid coating was carried out on two types: hydrostatic pressure coating and roll coating. The crack healing was one hour at 1173？K in air. The crack part formed SiO2 oxides until the critical times by a hydrostatic pressure method. The crack does not anymore heal if it exceeds the critical times. The crack part and the base part have many O components and Si components regardless of the times of coating and heat treatment. The combined hydrostatic and rolling coating method did not have nearly an effect on crack-healing for large crack width over 1.4？ m. The study for more effective healing of a large crack width must be carried out in the future. 1. Introduction Due to a combination of unique properties, silicon carbide (SiC) ceramics find extensive application in several fields of engineering as materials for advanced energy systems, such as high-performance combustion systems, fuel-flexible gasification systems, fuel cell/turbine hybrid systems, nuclear fusion reactors, and high temperature gas-cooled fission reactors [1–4]. The SiC/SiC composite material is especially under study as the first wall material of the blanket because of its excellent heat resistance and low activation property [5–9]. Many studies are being conducted in order to solve the brittle nature of ceramics [10–14]. (a) Non-destructive inspection with very high ability, (b) Increase fracture toughness by fiber-reinforcement and decrease the sensitivity to crack, (c) Introduce self-crack-healing ability. It has also been reported that the cracks formed by machining were healed completely [15, 16]. In particular, some results suggest that the cracks in silicon carbide, once healed, surprisingly become even stronger than the original silicon carbide. They conclude from the crack length that it was an important factor of crack healing by oxidation in silicon carbide [17]. Furthermore, there has been no clear explanation about the effect of SiO2 colloid coating for crack. In this paper, the SiC ceramic with sintering additive and was prepared. We observed the effect of coating method and coating times in relation to crack healing in SiC ceramic and examined the effect of the crack width for crack healing. 2. Materials and Test Methods Commercially available SiC (Ultrafine grade, Ibiden Co., Japan), (AKP-700, Sumitomo Chemical Co. Ltd., Japan), and (CI Chemical Co., Japan) were used as the starting materials. The mean particle sizes of the SiC, , and
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