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

我们开发了碳化硅多孔材料，以应用于环保用途。我们注意到细粉的晶粒长大使多孔材料的制备成为可能。首先，我们重新整理了烧结和晶粒长大理论在陶瓷制备中作为基础科学的重要性。因此，我们提出了物质输运的自由能理论。在理论中，扩散速率与过量自由能、扩散常数和几何因子成正比。这一理论与迄今为止建立的传统烧结和晶粒长大理论完全不同。从理论上分析了表面能等自由能对材料输运的影响。其次，研究了新的加速扩散常数的化合物，发现了Al-B-C化合物。这些化合物降低了烧结和晶粒生长温度，也使我们能够使用复杂的热等静压（HIP）制备完全致密的碳化硅。第三，我们研究了碳化硅和金属硼化物复合材料，并表征了晶粒生长和致密化行为。最后，根据这些结果，我们尝试利用相变诱导的材料输运和扩散加速晶粒生长来制备多孔材料。我们采用两种不同晶体结构的碳化硅和我们已经发现的Al-B-C添加剂，原始粉末表现出由表面能加速的初始晶粒生长，然后由于晶体转变而最终大晶粒生长。我们成功地制造了具有约50%孔隙率和100 MP强度的强多孔碳化硅材料，这些材料适合于环境使用。

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.