P. Mukundan

Sol–gel synthesis of nanosized anatase from titanyl sulfate

Nanosized titanium oxide with anatase structure holding high surface area has been synthesized by the sol–gel route from an aqueous solution of titanyl sulfate. A stable titania sol with extremely narrow range of particles having an average size of 30 nm has been obtained. The crystalline anatase particles have average particle size of 5–10 nm and specific surface area of 375–104 m2 g−1 between the calcination temperature 200–600 °C. The powders were characterized by XRD, FTIR, TGA/DTA and N2 adsorption analysis.

Phase transformation in sol–gel titania containing silica

Abstract Titanium dioxide containing 5–10% silica has been prepared by the co-hydrolysis of titanium isopropoxide at pH 4 in presence of TEOS in different solvents such as methanol, ethanol and water. The resultant gels have been analyzed by BET surface area measurements and thermal analysis. Addition of 5% silica to TiO2 increases initial surface area of 89 to 188 m2/g. As the amount of silica is further increased to 10%, the surface area is further increased to 203 m2/g. The composition containing TiO2–10% SiO2 in ethanol medium achieved the highest specific surface area 232 m2/g while the corresponding sample in methanol had 217 m2/g. Addition of silica has further resulted in considerable increase of anatase–rutile transformation temperature >800°C. Addition of methanol and ethanol to titania–silica systems enhances the formation of rutile phase. This phase transformation has been followed by X-ray powder diffraction data and further, through impedance measurements on the precursor gel pellets heated to various temperatures and the latter has been presented as a very simple and convenient tool to study phase transformation in titania ceramics.

Synthesis of thermally stable, high surface area anatase-alumina mixed oxides

Mixed oxides containing anatase and 5-20 mol% alumina have been synthesized from a precursor sol containing acetic . acid modified titanium isopropoxide and boehmite AlOOH . The resultant oxides retain considerable anatase phase at 10008C and have specific surface area many times higher than that of pure titania. A composite precursor containing titania-20 mol% alumina after calcination at 4508C, has a specific surface area as high as 318 m 2 rg compared to a value of 100 m 2 rg for pure titania prepared under identical conditions. The uniform dispersion of the nanoparticles of alumina in the titania gel matrix causes reduction in the anataseranatase contact points and thus results in a decrease of nucleation sites leading to increase in thermal stability of anatase phase. The high surface area and porosity could arise from the highly branched acetate polymeric gel. The sintered density of compacts derived from mixed oxides is also brought down considerably compared to pure titania counter parts. q 2000 Published by Elsevier Science B.V. All rights reserved.

Effect of precursor pH on the formation characteristics of sol-gel mullite

Abstract Mullite precursor gel of stoichiometric composition 3Al 2 O 3 · 2SiO 2 has been prepared by reacting boehmite sol and tetraethyl orthosilicate (TEOS) in a stoichiometric ratio. The pH of the preparation medium was varied from pH 3.5–8. The sol to gel transformation of the precursor was studied using optical microscopy. Phase formation characteristics of the heated gels studied from X-ray frequencies indicate that the precursor gel prepared under low pH conditions forms crystalline mullite at 1250°C. However at higher pH conditions α-Al 2 O 3 was the major phase. The mullite phase was also formed but the α-Al 2 O 3 phase was retained even at high temperatures (1500 °C). The results show that the pH of the precursor at the time of gelation can highly influence the gelation characteristics, mullite formation and microstructural features.

Low temperature sintering of seeded aluminium titanate precursor gels

Abstract Aluminium titanate has been prepared by thermal decomposition of a precursor gel formed by the controlled flocculation of a homogeneous mixture of boehmite and titanium isopropoxide sols. The effect of aluminium titanate seed nuclei, with average size less than 0.25 mm, on the phase formation, densification and microstructure development is reported. The results indicate enhanced densification kinetics for the seeded precursor. Such gels after calcination at 1000 °C for 2 h were sintered to densities of ~ 96% at 1300 °C for 30 min. Nearly complete formation of the aluminium titanate phase was achieved under the present experimental conditions. A simultaneous densification and phase formation from a liquid phase assisted titania rich precursor is suggested. On the other hand the unseeded gels could achieve only

Development of Porous Alumina from Engineered Boehmite Xerogel Containing Different Solvent Media

An attempt to study the effect of solvents in the development of porous alumina from engineered boehmite xerogel has been made. Boehmite powder was dispersed at pH-3 to get a stable boehmite sol. The excess water was evaporated and the resultant gel was dried at 60oC to get a xerogel. The xerogel was refluxed using methanol, ethanol and isopropanol, washed and dried. The gel samples were characterized using TGA and FTIR. The results show more interaction of methanol with the gel matrix. The specific surface area and total pore volume of calcined samples are presented. The nitrogen adsorption studies of the samples calcined at two different temperatures are also presented and discussed.