Formation of MgSO4-Al2(SO4)3 Solid Solution and Thermal Decomposition into the Spinel Solid Solution

Keiji DAIMON*, Kazuki HAYASHI, Takashi MATSUBARA, Yasuo HIKICHI and Toshitaka OTA

Department of Materials Science and Engineering, Nagoya Institute of Technology; Gokiso-cho, Showa-ku, Nagoya-shi 466-8555 Japan
Ceramics Research Laboratory, Nagoya Institute of Technology; 10-6-29, Asahigaoka, Tajimi-shi 507-0071 Japan

Solid solution of MgSO4 and Al2(SO4)3 was prepared from mixed aqueous solutions by rapid dry using micro-wave heating. The Mg2+ ion is soluble into the anhydrous aluminum sulfate crystal lattice over a wide range up to near the equimolar composition of MgSO4 and Al2(SO4)3. The anhydrous aluminum sulfate solid solution, at first, thermally decompose into the mixture of η-Al2O3 and MgSO4. The crystalline spinel phase appears at the second step of the thermal decomposition. The lattice parameters of the spinel changes linearly with the Mg content ranging from 0.5 to 0.8 at the fraction of MgAl2O4/(MgAl2O4+Al2O3). The produced nonstoichiometric spinel solid solutions must be metastable because the stable region of the composition of the spinel solid solutions is very narrow at the heating temperature employed to the thermal decomposition.

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