The Thermal Changes in Gels of the SiO2–Al2O3–In2O3–H2O System

Abstract

Abstract The synthesized coprecipitated gels in the SiO2–Al2O3-In2O3n-π*–H2O system showed an allophane-like pattern in the DTA except for the indium-rich gels. The exothermic peak temperature in the DTA was lowered from 980 to 940 °C with an increase in the indium content, while that on mixed gels was scarcely lowered at all. A new small exothermic peak around 880 °C in the DTA was observed in the coprecipitated gels with more than 11.93 wt% of In2O3; it was considered to be due to the structural change in the gels which arose from the formation of the indium (III) oxide. The firing products of the coprecipitated gels were identified as mullite, indium (III) oxide, and indium (III) silicate. The mullite formed in the coprecipitated gels included indium ions at 900 °C, accompanied by an increase in its unit cell volume, while the indium ions were almost entirely removed from the mullite lattice at 1200 °C.