INFLUENCE OF INTERPARTICLE FORCES ON THE RHEOLOGICAL BEHAVIOR OF PRESSURE-CONSOLIDATED ALUMINA PARTICLE SLURRIES

The stress relaxation behavior of alumina powder compacts, consolidate d from aqueous slurries by pressure filtration, is reported. The inter particle forces were controlled prior to consolidation by changing the pH from 3 to 9 and by adding different amounts of salt (0.1 to 2.0M N H4Cl) to slurries maintained at pH 4. Disk-shaped bodies were rapidly compressed to an axial strain of 2%, and the resulting stress relaxati on data were monitored as a function of time. For bodies formed from d ispersed slurries (pH less-than-or-equal-to 4 without added salt), the stress relaxation behavior consisted of an irreproducible mixture of plastic and elastic response. The initial stress and the stress retain ed afterlong relaxation periods were highest for bodies formed with fl occed slurries (pH 9). For bodies formed with coagulated slurries (pH 4 with added salt), the initial stress increased with the addition of 0.1 to 0.5M salt, but the bodies behaved plastically, with more than 9 0% of the initial stress relaxing within a short period. These results are consistent with a short-range, repulsive interparticle force that lowers the attractive force between particles. They also suggest that interparticle forces in consolidated bodies can be controlled in a wa y that should prove useful in preventing damage that occurs during pro cessing and reshaping operations.