Preparation of dense nanocrystalline Bi2O3-HfO2-Y2O3 ceramic by microwave plasma sintering

Processing of nanocrystalline Bi2O3-HfO2-Y2O3 ceramic having high density has been investigated and reported in this paper. Nanopowders of mixed bismuth oxide, hafnia and yttrium oxide have been prepared by a reverse titration chemical coprecipitation from Bi3+, Hf4+ and Y3+ containing aqueous solution. The high density, nanocrystalline Bi2O3-HfO2-Y2O3 ceramic has been synthesized by microwave plasma sintering. The XRD results of grain growth behavior indicates that growth of both δ-Bi2O3 and c-HfO2 crystallites obeys the parabolic rate law, expressed as (D–D0)2 = Kt, during sintering process. After sintering at 700 °C for 60 min, the relative density of the samples sintered by microwave plasma has been found to be greater than 97%, and the samples exhibit considerably finer microstructure with an average size between 60 and 70 nm and equiaxed morphology and better density comparing with that of samples sintered by conventional pressureless sintering. In addition, mechanical properties of nanocrystalline Bi2O3-HfO2-Y2O3 ceramic has been improved greatly compareing with nanocrystalline Bi2O3-Y2O3 ceramic.