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 p ressure consolidated, saturated, alumina powder bodies, were determined wit h uniaxial compression experiments of cylindrical specimens at a fixed disp lacement rate. Five different alpha-Al2O3 powders, from the same manufactur er, were used. The slurries were dispersed at pH 4 and then either coagulat ed with additions of NH4Cl to produce weakly attractive particle networks w ith short-range repulsive potentials or flocculated at the isoelectric poin t (iep = pH 9). These slurries were consolidated by pressure filtration usi ng pressures ranging from 2.5 to 150 MPa. Larger particles packed to higher relative densities when compared to smaller particles. Blocky particles pa cked at a lower relative density when compared to particles with roundish s urfaces. Bodies were plastic when consolidated below a critical consolidati on 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-partic le contacts per unit volume at a given relative density. Namely, for a give n applied pressure, larger forces exist between larger particles because of the smaller number of contacts per unit volume relative to smaller particl es. (C) 1999 Elsevier Science B.V. All rights reserved.