CRYSTALLIZATION OF TITANIA IN LIQUID-MEDIA AT HIGH-TEMPERATURES

Amorphous titania gels were prepared by the hydrolysis of TiCl4 in a m ixed 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 degrees C associat ed with the crystallisation of anatase and, in the liquid media, XRD s howed the formation of anatase at temperatures as low as 140 degrees C . The kinetics of crystallisation in water, n-hexane, and methanol cou ld 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 powder s, prepared in water-methanol mixtures, were sintered in air for 5 h a t 800-1200 degrees C. The sinterability of powder prepared in water wa s poorer than that prepared in the organic solvent but the results sho wed 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.