EFFECTS OF ADDITION OF POLYACRYLIC AMMONIUM ON COLLOIDAL PROCESSING OF ALPHA-ALUMINA

Effects of addition of polyacrylic ammonium (shorten as PAN) on the rheological properties of aqueous alumina suspensions, pore size distributions and sintering behavior of consolidated powder compacts were studied to reduce fluctuation of microstructure and density in powder processing. It was possible to prepare a highly concentrated fluid alumina suspension of approximately 63 vol% solids by controlling the electrosteric stabilization effect of negatively charged polymer which was adsorbed onto alumina surface. Combustion of adsorbed polymer at 1000-degrees-C formed continuous narrow pore size distributions in the alumina compacts with 60.2 to 67.2% T.D., depending on solids content of suspensions. The densification of high-density alumina compacts proceeded at low sintering temperatures through disappearance of closed pores which were formed at around 92-95% T. D. The low-density compacts were densified at high temperatures without significant formation of closed pores. The texture of sintered alumina was strongly affected by the pore size distribution of the starting alumina compact, which greatly depended on the consolidation processes of powder (i.e., filtration or doctor blade method) and the electrosteric effect of added polymer in suspension stage. Addition of PAN was effective in achieving a fine microstructure of narrow grain size distribution.