| Hydrolysis of titanium isopropoxide was studied under controlled
conditions in presence of dry isopropanol. The alkoxide-water interaction
presumably proceeded via several intermediate reactions with
soluble products; at an advanced stage of reaction, the products of
hydrolysis became insoluble, marked by a sudden appearance of
uniform turbidity. The rate of hydrolysis, leading to the ultimate
formation of an insoluble species, was found to be dependent on the
concentration of water and Ti(0Pri)4 in isopropanol, as well as the
molar ratios of the reactants. Weight loss experiments showed the
precipitated product to be metatitanic acid, Ti0(0H)2• Thermal
analysis showed a broad endotherm at around 135°C, corresponding
to the loss of water, to be the only thermal effect; separate calcination
and X-ray diffraction studies showed that formation of anatase
from the amorphous precursor took place around the same temperature.
No thermal effect was obtained for the anatase-rutile transformation.
However, on treatment of the precipitated powder with
NH.OH (used as a dispersant of the particles), an exothermic effect
was noted at about 355°C; this was explained to be due to the breakdown
of surface-exchanged NH4 ion and partial oxidation of NH3•
Electron microscopic studies showed that the initial amorphous
Ti0(0H)2 was extremely fine (at least 0.1-0.2 micron), which increased
in size on calcination and crystallization to a maximum of
0.5 micron, though agglomeration was a major problem in determining
the particle size distribution. |
