Liquid-feed flame spray pyrolysis of nanopowders in the alumina-titania system

We report here the synthesis of (TiO2)(x)(Al2O3)(1-x) nanopowders with molar ratios that span the TiO2-Al2O3 composition range. The nanopowders were synthesized using liquid-feed flame spray pyrolysis (LF-FSP) of mixtures of N(CH2CH2O)(3)TiOiPr (titanatrane isopropoxide) and N(CH2CH2O)(3)Al (alumatrane) dissolved in the appropriate molar ratios in alcohols used as solvent and fuel. Ethanol, methanol, and butanol were used in an attempt to regulate the flame temperatures, particle sizes, and size distributions, as well as to influence the phase(s) produced in selected mixed-phase materials produced at x = 0.5. The as-produced powders were characterized in terms of phase, size, specific surface area, composition, and morphology by BET, XRD, SEM, TEM, and TGA-DTA. At compositions close to Al2O3, the delta phase is the primary phase observed. As the compositions approach x = 0.5, a combination of rutile, alpha-Al2O3, and Al2TiO5 is observed. Pure titania powders consist of 90:10 mixtures of anatase and rutile; however, doping with x = 0.05 of alumina results in 40:60 anatase/rutile mixtures and nearly pure rutile phase at x = 0.15. The source of this latter phase transformation can be explained in terms of Al3+ substituting for Ti4+ ions in the anatase lattice forcing the phase transformation as found in highly defective TiO2. No effect of flame temperature as a function of fuel was observed.