A high-density and fine-grainded alumina was fabricated at low temperature by $α-Al_{2}O_{3}$ seeding in boehmite through colloidal process.
Because of zeta-potential difference between α-alumina and boehmite, flocculation experiments were done at first by varying pH in the slip to mix seed and boehmite homogeneously. And then ultrasonic treatment was taken to diminish the agglomerates which prohibit densification during sintering. So increasment of relative density with respect to that of untreated was shown through all temperature range in this experiment.
Green compacts were prepared by centrifugal casting of slip. Above pH 7, mass segregtion between α-alumina seed and boehmite was not found. Pore size distribution and mean pore size of the green compacts was very narrow and 6. 9nm, respectively. As solid contents in slip was increased, green density was slightly decreased due to high viscosity.
Sinltered density above 99% of theoretical could be obtained with 3wt% seed contents of 0.1㎛ mean size and boehmite of 160 ㎡/g sintered at 1400℃ for 1 hr. A number of pores were shown to be entraped in grain interiors at lower seed contents, and large grains were observed by grain growth at higher seed contents. Therefore optimum seed content was considered as about 3wt%. When the mean size of the seed particles went larger to 0.3㎛, in contrast to Messing's data, full density could be achieved more efficiently than the finer seed. This is due to the higher green density and the dispersity improved by large difference of the particle size between boehmite and seed particles which made the entrapping of seed particles in boehmite matrix easy during flocculation. In the case of using boehmite powders with higher surface area (230 ㎡/g), fully dense bodies could be obtained even with smaller seed contents because of the dispersity improved by high viscosity in slip and smaller particle size effect during sintering.
