HIGH-PRESSURE SINTERING OF NANOCRYSTALLINE GAMMA-AL2O3

High-pressure sintering of nanocrystalline gamma-Al2O3 has been studie d over a temperature range of 923-1323 K and at a pressure of 1 GPa. T he gamma-Al2O3 to alpha-Al2O3 transformation temperature changed from 1473 K without pressure to similar to 1023 K at 1 GPa. Full density wa s obtained at 1273 and 1323 K in 10 min. The microhardness value of fu lly dense or-alumina with a grain size of 142 nm was found to be 25.3 +/- 0.8 GPa. The Hall-Fetch slope for the very fine grain size range i s different from that of the coarse-grained alumina.