Densification and grain growth during pressureless sintering of TiO2 nanoceramics

Anatase titania nanopowders with mean particle sizes of 7, 15, 26 and 38 nm synthesized by sol–gel method were used to sinter bulk TiO2 nanoceramics. The relative densities and average grain sizes of the TiO2 nanoceramics were studied as a function of the compaction pressure on green sheet, sintering temperature, and mean particle size of the starting TiO2 nanopowders. The relative density of the TiO2 nanoceramics increases rapidly and average grain size increases slowly with increasing sintering temperature below 800 °C. Sintering at higher temperatures above 800 °C enhances the densification of the TiO2 nanoceramics and leads to a increase of the grain size. Bulk TiO2 nanoceramics with an average grain size of less than 60 nm and relative density over 95% was obtained by a phase-transformation-assisted pressureless sintering at a relatively low temperature (800 °C).