Fabrication, characterization, and modeling of high-pressure/low-temperature sintering of nanocrystalline titania

A model to predict the densification and grain growth of n-TiO{dollar}sb2{dollar} during high pressure/low temperature sintering has been developed. In this model, the densification is predicted by a modified grain boundary diffusion creep model during the intermediate stage sintering and by a modified grain boundary diffusion model that governs migration from interparticle boundaries to pores during the final stage sintering. The rate equations for densification during both stages are affected by the increasing driving force and the decreasing diffusivity with high pressure. During sintering, the concurrent grain growth is modeled with a pore-controlled mechanism. The model suggests that grains grow little during intermediate stage sintering, but experience rapid growth during final stage sintering. Moreover, grain growth during densification is minimized by the high pressure. Finally, the models demonstrate that the phase transformation during sintering significantly increases the densification rate.; Bulk n-TiO{dollar}sb2{dollar} samples with a relative density as high as 95% and a grain size {dollar}{dollar}98%; whereas the grain size of the anatase phase always increased with temperature. The decrease of the rutile grain size with temperature at constant pressure can be explained in terms of the competition between nucleation and growth processes with increasing temperature. All of the experimental observations are in agreement with the proposed sintering theory.