Freeze granulation: Powder processing for transparent alumina applications

se of freeze granulated powders is successfully used as an industrially viable alternative to loose powder sintering for transparent polycrystalline lumina (PCA). Freeze granulation with narrow granule size distribution was realized after suspension condition optimization, with very good owability and regular spherical shapes. The key factors are low viscosity slurries linked to the complex interactions between the organic processing dditives and their interaction with dopant ions in solution. Real in-line transmittances (RITs) of 52% were achieved by pulsed electric current intering (PECS) of dry pressed green bodies from doped granulated powders. This is the first example of a high RIT (>50%) alumina produced rom simple dry pressing of a granulated powder. The results indicate that higher granule solid loads and lower organic additive concentrations ive better RITs after PECS. Aging of the powder slurry before freeze granulation proves a crucial step for the optical performance of the final ransparent PCA. 2012 Elsevier Ltd. All rights reserved.