Alkoxide Hydrolysis and Preparation of TiO2Powders

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Abstract
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(OPri)4 in isopropanol, as well as the molar ratios of the reactants. Weight loss experiments showed the precipitated product to be metatitanic acid, TiO(OH)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 NH4OH (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 TiO(OH)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.

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