Crystallisation of titania in liquid media at high temperatures

Amorphous titania gels were prepared by the hydrolysis of TiCl₄ in a mixed solution of ammonia, water, and methanol at room temperature and their crystallisation behaviour in air and on heat treatment in water, n-hexane, and methanol, was examined over a range of temperatures. In air, DTA analysis showed an exothermic peak at 370°C associated with the crystallisation of anatase and, in the liquid media, XRD showed the formation of anatase at temperatures as low as 140°PC. The kinetics of crystallisation in water, n-hexane, and methanol could be adequately described by the surface chemical reaction controlled shrinking core model with activation energies of 89.1, 88.0, and 206 kJ mol^-1, respectively. The rate of crystallisation was much faster in water than in n-hexane or methanol. Compacts of crystallised powders, prepared in water-methanol mixtures, were sintered in air for 5 h at 800-1200° C. The sinterability of powder prepared in water was poorer than that prepared in the organic solvent but the results showed that the addition of the requisite amount of water to the organic solvent was useful in promoting crystallisation without impairing the sinterability of the powder.