Sonochemical synthesis of nanostructured anatase and study of the kinetics among phase transformation and coarsening as a function of heat treatment conditions

In the present paper are investigated the microstructural, phase transformation and coarsening kinetics of nanometric anatase subjected to different heat treatment conditions. It is also demonstrated that nanostructured anatase can be produced by a novel methodology assisted sonochemical means with the following particles characteristics; an average particle size of 6.2 nm and a specific surface area of 300 m² g^-1. Sonochemically produced anatase subjected to heat treatments under ambient atmosphere conditions at temperatures from 773 K to 1073 K and times between 1 h and 72 h transforms only to rutile. Both rates, transformation to rutile and coarsening, increase with temperature. The critical size for the anatase particles to transform to rutile is temperature dependent. The coarsening kinetics, thus particle size, of the anatase and rutile investigated in this research can be predicted using exponential like equations. These equations are similar to the ones described in the LSW theory; in fact, the exponent changes as a function of time approaching 1/4 for times of 72 h of treatment. The characterization conducted in this research was assisted by means of Brunauer-Emmett-Teller (BET) method, thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The characterization results are given and discussed herein.