Densification of single-grain vs. multi-grain zirconia powders

To study hot-pressing densification rates of single-grain and multi-grain zirconia powders, spray-dried granules of ZrO 2 -3%Y 2 0 3 (D(10-90) = 35-90 μm) were densified at 1400 °C. Ball milling was utilized to break up the inter-agglomerate bridges. The resulting powder represented the multi-grain particle (MGP). Single-grain particle (SGP) of comparable grain size was obtained by intensive ball milling of the dense granules to the grain size (-0.35 μm diameter). To compare the densification behavior of these powders, specimens of each powder were hot-pressed in a SiC die at 1350 °C for 1 hour. The highest density was achieved by hot pressing MGP screened to +75 pm. The MGP densities by particle creep of the polycrystalline powder controlled by the diffusion distance on the order of the grain size while the SGP is thought to densify primarily by pressure-assisted sintering, i.e., diffusion along the neck between particles. The difference in final density reflects the initially higher packing density of the MGP powder.