SYNTHESIS OF TITANIUM-DIOXIDE PARTICLES IN SUPERCRITICAL CO2

Spherical particles of titanium dioxide, anatase, were prepared in a s upercritical carbon dioxide medium from titanium alkoxides and water, The dissolution of the alkoxide and stabilization of water dispersions in supercritical CO2 were found to be required for the formation of s pherical particles, An anionic fluorinated surfactant was used to stab ilize water dispersions in supercritical CO2. This could not be realiz ed with hydrocarbon-based surfactants. The solubility of titanium alko xides in CO2 appears to parallel their vapor pressure which is depende nt on the oligomerization of the unhydrolyzed all;oxides. The polydisp ersity in particle sizes is due to nucleation occurring simultaneously with particle growth, owing to changes in the degree of supersaturati on during the transition from the liquid to I-he supercritical state.