Effects of mechanical activation of inorganic gels on their thermal behavior. 1. Crystallization process of titania gels

The influence of mechanical pretreatment on the crystallization from amorphous titania hydrogel to anatase was studied. The temperature of crystallization, T_crys, determined by the DTA exothermic peak, decreased by 18 and 44 K on grinding for 3 hr by the rotation and vibration ball-mill, respectively. Preliminary ordering of anatase in ground gels was detected by Raman spectroscopy and selected area electron diffractometry, before any X-ray diffraction peak appeared. It is suspected that the decrease in T_crys by mechanical activation is attributed to the above precursory ordering. By applying mechanical stress, the sudden weight loss was observed at T_crys. This suggests that a small amount of hydroxyl groups and NH⁺₄ may block the long-range ordering of TiO₆ structural units.