Phase-transformation Kinetics of TiO_2 in-TiO_2/(O'+beta')-Sialon Multi-phase Ceramics

摘要

TiO_2/(O'+beta')-Sialon multiphase ceramics with different phase composition of TiO_2 were prepared by pressureless sintering under high-purity N_2 atmosphere with (O'+beta')-Sialon powder and nano TiO_2 (anatase) powder as raw materials, Yb_2O_3 or Tb_2O_3 as additive. For each sample, the weight percentage of anatase in TiO_2 was calculated from XRD data and the kinetics of anatase-rutile transformation was investigated, wherein the emphasis was placed on the influence of Yb_2O_3 and Tb_2O_3. The results indicate that the added Tb_2O_3and Yb_2O_3 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 Yb_2O_3 or Tb_2O_3 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, C_A=kt~(1/2)+C, is valid for the samples containing Tb_2O_3. In the two cases, the effect of the additive content on the transformation can be perfectly reflected by the apparent rate constant.