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Formation of La2(SO4)3-Al2(SO4)3 Solid Solution and Phase Transition of Alumina Formed by Thermal Decomposition

Keiji DAIMON*, Hiroki TOMIMATSU, 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 solutions of La2(SO4)3 and Al2(SO4)3 were prepared by rapidly drying mixed aqueous solutions using micro-wave heating. The La3+ ion is soluble into the anhydrous aluminum sulfate crystal lattice up to about 6 mol%. On heating the thermal decomposition starts at 830 °C for the pure Al2(SO4)3, while at 760 °C for 6 mol% La2(SO4)3 contained Al2(SO4)3. The anhydrous aluminum sulfate solid solution thermally decomposes into the η-Al2O3 without any other crystalline phases. The LaAl11O18 is formed after heating the desulfurized product at 1300 °C without forming LaAlO3 when the content of La2O3 is less than 6 mol%. The La3+ doping increases the stability of η-Al2O3 at high temperatures. The phase transformation of alumina takes place above 1350 °C when the amount of La2O3 is 5 mol%.


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