Spray freeze granulation of sub-micrometer α-alumina using ultrasonication

Granulation is a key factor towards improvement of the flowability of fine ceramic powders to make them suitable for industrial dry pressing. Controlled granulation of fine alumina particles with a primary particle size of ~150 nm was carried out using spray freeze drying, which led to the production of flowable granules with high crushability. The fracture surface of uniaxially die-pressed green bodies made from granules with density values of ≥50% of theoretical showed a uniform microstructure. Sintering experiments were performed using conventional single- and two-stage radiant heating methods followed by density and grain size measurement and characterisation of the final dense compacts to study the efficiency of two-stage sintering in grain growth elimination. The results have been compared with those of alumina bodies prepared using similar suspension by slip casting route.