Fabrication of Porous Silicon Carbide for Environmental Use based on Free Energy Theory

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We developed silicon carbide porous materials in order to apply to environmental use. We noticed that grain growth of fine powder made possible to fabricate porous materials.First, we reorganized that sintering and grain growth theory in the fabrication of ceramics was important as basic science. Therefore, we proposed free energy theory for material transport. In the theory, a rate of diffusion was proportional to excess free energy, a diffusion constant and a geometry factor. The theory was totally different from traditional sintering and grain growth established so far. We could analyze from this theory the role of surface energy and other free energies on the material transport.Second, we investigate new compounds that accelerated diffusion constant and found Al-B-C compounds. The compounds decreased sintering and grain growth temperatures, and also enabled us to use a sophisticated hot isostatic pressing (HIP) resulting in fabricating completely dense silicon carbide.Third, we studied silicon carbide and metal boride composites, and characterized grain growth and densification behavior. Some of metal borides elongated SiC particles.Finally, from these results, we tried to make porous material utilizing transformation induced material transport and diffusion accelerated grain growth. We used two types of silicon carbides different in crystal structure and used the Al-B-C additives that we already found. The raw powders behaved initial grain growth accelerated by surface energy and then final large grain growth due to crystal transformation. We succeeded in fabrication of strong porous silicon carbide materials having about 50% porosity and 100 MP strength that are suitable environmental use.