Mechanical behavior of saturated,consolidated, alumina powder compacts: effect of particle size and morphology on the plastic-to-brittle transition

The effects of particle size and morphology on the mechanical behavior of pressure consolidated, saturated, alumina powder bodies, were determined with uniaxial compression experiments of cylindrical specimens at a fixed displacement rate. Five different α-Al₂O₃ powders, from the same manufacturer, were used. The slurries were dispersed at pH 4 and then either coagulated with additions of NH₄Cl to produce weakly attractive particle networks with short-range repulsive potentials or flocculated at the isoelectric point (iep=pH 9). These slurries were consolidated by pressure filtration using pressures ranging from 2.5 to 150 MPa. Larger particles packed to higher relative densities when compared to smaller particles. Blocky particles packed at a lower relative density when compared to particles with roundish surfaces. Bodies were plastic when consolidated below a critical consolidation pressure; above this pressure, the body was brittle. Bodies formed with large particles were brittle at a lower consolidation pressure. The effect of particle size is discussed with respect to the number of particle–particle contacts per unit volume at a given relative density. Namely, for a given applied pressure, larger forces exist between larger particles because of the smaller number of contacts per unit volume relative to smaller particles.