SINTERING OF NANOPHASE GAMMA-AL2O3 POWDER

The sintering of ultrafine gamma-Al2O3 powder (particle size approxima te to 10-20 nm) prepared by an inert gas condensation technique was in vestigated in air at a constant heating rate of 10 degrees C/min. Qual itatively, the kinetics followed those of transition aluminas prepared by other methods. Measurable shrinkage commenced at approximate to 10 00 degrees C and showed a region of rapid sintering between approximat e to 1125 degrees and 1175 degrees C followed by a transition to a muc h reduced sintering rate at higher temperatures. Starting from an init ial density of approximate to 0.60 relative to the theoretical value, the powder compact reached a relative density of 0.82 after sintering to 1350 degrees C. Compared to compacts prepared from the as-received powder, dispersion of the powder in water prior to compaction produced a drastic change in the microstructural evolution and a significant r eduction in the densification rate during sintering. The incorporation of a step involving the rapid heating of the loose powder to approxim ate to 1300 degrees C prior to compaction (which resulted in the trans formation to alpha-Al2O3) provided a method for significantly increasi ng the density during sintering.