Spark Plasma Sintering of Nano-crystalline Ceramics

Spark Plasma Sintering (SPS) has been successfully applied in the sintering of nanocrystalline BaTiO3 and γ-Al2O3 in order to reach fully dense nanostructured ceramics at moderate pressure and temperature. BaTiO3 compacts with densities exceeding 97% and grain size of 50 nm have thus been prepared at temperatures not exceeding 850 oC using a uniaxial pressure of 100MPa. The selection of sintering temperature is critical for the purpose of minimizinggrain growth and there is a demarcation temperature (820 oC) between normal and abnormal grain growth for the nanocrystalline BaTiO3 powder used in this study. Fully dense α-Al2O3 compacts containing grains of the size 300nm or less were consolidated from high-purity γ-Al2O3 powders without the use of additives or seeds. The transition temperature of γ-Al2O3 to α-Al2O3 can be lowered to 960 oC when γ-Al2O3 powder is compacted in the SPS apparatus. The possible mechanisms related to this low transition temperature and to the sintering of both BaTiO3 and γ-Al2O3 are discussed with special reference to the effect of the pulsed electric field generated by the pulsed electrical current used to heat the sample