Compaction and sintering behaviour of glass-alumina composites

The effects of Al2O3 additions on the compaction and sintering behaviour of a leadborosilicate glass (LG) have been investigated. LG powder was prepared by melting, fritting and milling a glass of the composition: 77PbO, 10B(2)O(3), 10SiO(2), 2Al(2)O(3) and IP2O5 (wt.%). The mean particle sizes of the powders were: LG, 6.5 mum and Al2O3, 3.3 mum The compaction behaviour of LG-Al2O3 powder mixtures can be represented by a new compaction equation: [(D-g - D-0)/(1 - D-0)] = (P/P-f)(n), where D-g is the relative green density, D-0 the relative tap density and n and Pr are material constants. The exponent pi decreases from 0.192 to 0.065 as the Al2O3 content is increased from 0 to 100 vol.%. The Frenkel equation for isothermal shrinkage has been found to be valid. It is shown that in the glass matrix composites the minimum sintering temperature can be determined by measuring the dilatometric deformation temperature. The presence of Al2O3 in excess of 15 vol.% has been found to strongly retard the sintering kinetics. An addition of 45 vol.% Al2O3 increases the activation energy for sintering from 67 to 112 kcal mol(-1). The presence of Al2O3 particles also induced a partial crystallisation in LG matrix. (C) 2001 Elsevier Science B.V. All rights reserved.