Phase-Transformation Kinetics of TiO2 in TiO2/(O′+β′)-Sialon Multi-Phase Ceramics
TiO2/(O′+β′)-Sialon multiphase ceramics with different phase composition of TiO2 were prepared by pressureless sintering under high-purity N2 atmosphere with (O′+β′)-Sialon powder and nano TiO2 (anatase) powder as raw materials, Yb2O3 or Tb2O3 as additive. For each sample, the weight percentage of anatase in TiO2 was calculated from XRD data and the kinetics of anatase-rutile transformation was investigated, wherein the emphasis was placed on the influence of Yb2O3 and Tb2O3. The results indicate that the added Tb2O3 and Yb2O3 serve the significant function of inhibition and promotion on the phase transformation, and the effects are enhanced and attenuated with increasing additive content, respectively. For the sample without additive, the transformation process follows apparent first-order kinetic model. The addition of Yb2O3 or Tb2O3 results in completely different transformation kinetic law. For the samples with Yb2O3 added, the transformation is an apparent second-order reaction, whereas a unique kinetic model, CA=kt1/2+C, is valid for the samples containing Tb2O3. In the two cases, the effect of the additive content on the transformation can be perfectly reflected by the apparent rate constant.
Wei Pan and Jianghong Gong
J. Yang, X. X. Xue, L. M. Pan, M. Wang, T. Qiu, "Phase-Transformation Kinetics of TiO2 in TiO2/(O′+β′)-Sialon Multi-Phase Ceramics", Key Engineering Materials, Vols. 336-338, pp. 2318-2321, 2007