アルコキシド法より調製したベーマイト(AlO(OH))ゲルの加熱性状

抄録

The chemical properties of boemite gel prepared by alkoxy-method were studied by means of differential thermal analysis, thermogravimetric analysis and X-ray diffraction.
1) When boemite gel was heated in air at an atmospheric and reduced pressures, it was converted into a-Al₂O₃ via the following steps.
boemite gel→amorphous alumina→γ-A1₂O₃→θ-Al₂O₃→a-A1₂O₃
2) Boemite gel, in the case of sample weight 1 g, was easily converted into amorphous alumina gel by grinding in air, but this amorphous alumina gel did not change in spite of grinding for 250 hrs. On the other hand, the ground amorphous alumina gel was directly converted into α-Al₂O₃ at 990°C by heating.
3) In the conversion to α-Al₂O₃ through θ-Al₂O₃ from γ-Al₂O₃, the nucleation process may be the rate-determining step. The apparent activation energy for this process was about 115 kcal/mol.
4) Reactions of γ-Al₂O₃ and α-Al₂O₃ with ZnO were fitted to Dander's equation. At 850°C, the reaction rate constant of ZnO-γ⋅Al₂O₃ system was found to be about eighty six times as large as that of ZnO-a⋅Al₂O₃ system. The activation energies of ZnAl2O4 formation in ZnO-γ⋅Al₂O₃ system and ZnO-α⋅Al₂O₃ system were about 51 kcal/mol and 88 kcal/mol, respectively.