Sintering and crystallization of La2O3-doped Al2O3 aerogels from chemically modified aluminum alkoxide

Sintering and crystallization of low-density La2O3-doped Al2O3 aerogels prepared from Al-alkoxide chemically modified with ethyl acetoacetate were investigated. Isothermal sintering experiments showed that the sintering mechanism of Al2O3 aerogels is surface diffusion. The specific surface areas (SSA) of Al2O3 aerogels heat-treated at 1000 to 1200 degrees C were greatly increased by the addition of 1-2 mol% La2O3. The crystalline phase of Al2O3 aerogels with 1 mol% La2O3 is theta-Al2O3 with heat-treatment at 1200 degrees C, while that of non-doped Al2O3 aerogels is alpha-Al2O3 with small surface area, Addition of more than 5 mol% La2O3 caused crystallization of La-containing crystalline phases, and the SSA of these aerogels was smaller than that of Al2O3 aerogels with 1-2 mol% La2O3. Addition of small amount of La2O3 prevented aerogels from sintering through surface diffusion, wkiIe the addition of more La2O3 caused nucleation of La-containing crystals. (C) 1998 Elsevier Science B.V. All rights reserved.