Hydrolysis of titanium alkoxides: Thermochemical, electron microscopy, SAXS studies

Hydrolysis of Ti(OR)(4) (R = Et, Pr-i, Bu-n) at various concentrations of t itanium alkoxides and ratios h = [H2O] /[Ti(OR)(4)] is studied in alcoholic medium by means of calorimetry, electron microscopy, SAXS, and chemical an alysis. The measured values for heat of hydrolysis of Ti(OR)(4) by excess w ater (-Delta H-h) at 298.15 K comprise 14.2, 64.9, 19.3 kJ/mol for R = Et, R = Et, Pr-i, Bu-n respectively. -Delta H-h increases drastically in the re gion of 0 <h <1 and demonstrates practically no changes with further increa se of h ratio. In the solid hydrolysis product with the composition TiOx(OR )(4-2x).y ROH, both x and y increase with increase of Ti(OR)(4) concentrati on in solution. Bushy network first formed in solution as a result of hydro lysis gradually structures with formation of well-shaped spherical particle s with diameters greater than or equal to0.2 mum. SAXS curves analysis in t he range of scattering vector values s = 0.07-4.26 nm(-1) for Ti(OBu)(4) hy drolysis products allows us to suggest their multilevel nature. Speculation s on the structure of titanium oxobutoxide were made on the basis of the we ll-known structural data for crystalline first hydrolysis products of Ti(OE t)(4) and Ti(O-i Pr)(4). It is suggested to perform hydrolysis of Ti(OBu)(4 ) with addition of water in two steps which allows us to decrease the rate of the solid precipitate formation, to regulate particles morphology in a w ide range and to obtain well-shaped spherical species more than one micron in size. The influence of the powder size distribution on the grain growth during ceramic sintering is discussed.