Preparation of Mullite Powder by Calcination of the Products Hydrothermally Treated from Mixed Alkoxide or Mixed Sol

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  • SUZUKI Matsuo
    Research Laboratory of Engineering Materials and Department of Materials Science, Tokyo Institute of Technology
  • HIRAISHI Shun-ichi
    Dainippon Ink and Chemicals, Inc.
  • YOSHIMURA Masahiro
    Research Laboratory of Engineering Materials and Department of Materials Science, Tokyo Institute of Technology
  • SOMIYA Shigeyuki
    Research Laboratory of Engineering Materials and Department of Materials Science, Tokyo Institute of Technology

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Other Title
  • 混合アルコキシド及び混合ゾルの水熱処理生成物の加熱焼成によるムライト粉末の調整
  • コンゴウ アルコキシド オヨビ コンゴウ ゾル ノ スイネツ ショリ セイセイ

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Abstract

Mullite powders were obtained by calcination of the products hydrothermally treated from mixed alkoxide or mixed sol, containing Al2O3:SiO2=3:2 (molar ratio). Pseudoboehmitelike phase, which contained both Al and Si components, was obtained by the hydrothermal treatment of mixed alkoxide or mixed sol, under 50MPa at 300°-400°C for 2h. The pseudoboehmite-like phase particles from alkoxide were finer and more homogeneous than those from sol. The reaction among Al2O3, SiO2 and H2O was promoted to form aluminosilicates by the hydrothermal treatment under 50MPa at 500°-600°C for 2h, using sol as a starting material. The products under these conditions were hydralsite (2Al2O3⋅2SiO2⋅H2O), AS (H)-II (5Al2O3⋅2SiO2⋅nH2O) and small amounts of mullite (3Al2O3⋅2SiO2-2Al2O3⋅SiO2). On the other hand, alkoxide as a starting material did hardly yield, these aluminosilicates by the hydrothermal treatment under the same conditions. The pseudoboehmite-like phase obtained under 50MPa at 300°C for 2h, was dehydrated to produce Al-Si spinel by calcination at 600°C for 1h, then was changed to mullite at 1300°C for 1h. The mullite particles from alkoxide were finer and more homogeneous than those from sol. Hydralsite and AS (H)-II, produced by the hydrothermal treatment of sol, were changed to mullite by calcination at the temperature as low as 800°C. Transmission electron microscope (TEM) detected granular mullite particles (Al2O3:SiO2=3:2, molar ratio) and acicular mullite particles (Al2O3:SiO2=2:1, molar ratio) in the powders obtained by calcination at 1300°C for 1h of the hydrothermally treated (600°C, 50MPa, 2h) product from sol.

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