The Structure of Al₂O₃-SiO₂ Gels Derived from Aluminium Nitrate and Tetraethylorthosilicate

Abstract

Al₂O₃-SiO₂ gels were synthesized by the sol-gel method using aluminium nitrate and tetraethylorthosilicate in various organic solvents. By calcining the dry gels, aluminium ion could be incorporated into SiO₂ gel networks. By increasing heat treatment temperature, the coordination number of aluminium ion changed from six to four. At around 1000°C mullite crystals precipitated. The temperature of mullite precipitation should depend on the homogeneity of the dry gels. The presence of five-coordinated aluminium ions was confirmed between 400° and 800°C, as in accordance with the gels derived from silicon-aluminium alkoxide. The proportion of the five-coordinated aluminium ions was reduced by hydration in an autoclave.