Effect of solvent on formation characteristics of sol-gel aluminium titanate

摘要

Aluminium titanate, due to its low thermal expansion property, is considered to be one of the most important components in heat engine ceramics [1,2] and is usually synthesized by solid-state reaction between aluminium oxide and titanium oxide [3]. The formation temperature in such cases is above 1300 °C [3]. The main difficulty in preparation of this ceramic for commercial applications is its thermal instability in the region 1000-1200 °C [4]. One method indicated for successful stable aluminium titanate is to control the grain size below critical limits (1.5 mm). Sol-gel methods involving hydrolysis of aluminium and titanium alkoxides have been reported for the preparation of aluminium titanate [6]. Out of the several factors that might affect the formation characteristics, the effect of changing alumina source has already been studied [7]; where it was concluded that boehmite was the best alumina source for producing a low temperature aluminium titanate phase and for attaining a fine grained sintered microstructure, as compared with other sources like bayerite [A1(OH)3] and aluminium nitrate [A1(NO3)3]. In the synthesis of metal oxides by hydrolysis of metal alkoxides it has been reported that the nature of solvents, like butanol and ethanol, affect the shape and homogeneity of the particles in the final product [8, 9]. Generally, the medium has a consider-able effect on gelation in sol-gel systems [10]. Previous work on aluminium titanate precursor gel from titanium alkoxides and boehmite indicates that the solvent could influence the gelation characteristics [11]. The work reported here is further aimed at the possibility of finding out whether the solvent has any considerable effect on the formation characteristics of aluminium titanate from the precursor gel. Boehmite is selected as the source of alumina and titanium isopropoxide as the source of titania. The different solvent mixtures used are water, water-methanol, water-ethanol and water-isopropanol.