SiO_2-Al_2O_3-H_2O系化合物の加熱分解生成物のキャラクタリゼーション : アロフェンの場合

概要

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The evolved phases of spinel-type phase, mullite and cristobalite formed by calcining allophane, a clay mineral mainly composed of SiO2, Al2O3 and H2O, were characterized by various methods. Spinel-type phase was assigned to be γ-Al2O3 from the results of the lattice constants, infrared spectra, specific gravities and alkali extraction. Its chemical composition was considered to be nearly pure Al2O3 with little substitution of SiO2. Mullite formed by calcining at 975°-1050°C contained an excess amount of Al2O3 over the composition 3 Al2O3⋅2SiO2. On the other hand, mullite obtained at 1075°-1500°C developed prismatic shaped crystals which grew with increasing calcination temperature, and the composition was nearly 3Al2O3⋅2SiO2. The lattice constants of cristobalite formed in calcined specimens were larger than those of pure ones, suggesting a possibility of substitutions of Al2O3 and Fe2O3 for cristobalite. More than 2% of Al2O3 and more than 1% of Fe2O3 are detected on cristobalite particles by an analytical transmission electron microscopy. Allophane was concluded to decompose firstly into γ-Al2O3 and amorphous SiO2 with a little amount of mullite by calcination, which react to form mullite and that the remaining amorphous SiO2 crystallizes into cristobalite at higher temperature.
社団法人日本セラミックス協会の論文
1985-11-01