Thermally activated step for densification and creep of high-porosity MgO compacts in the intermediate sintering stage

High porosity MgO compacts were sintered in the temperature range 1283-1350 K, under the action of weak uniaxial loads of 3.3 +/- 0.4 kPa. Isothermal densification and creep rates were found to be significantly different expo nentially decreasing functions of density. The pore size and the pore distr ibution of samples heated at two different temperatures of 1283 K and 1333 K have turned out to be the same when the relative densities are equal. A c ommon activated step with an average apparent activation enthalpy equal to 480 +/- 40 kJ per mole has been experimentally established for both densifi cation and weak load creep. The obtained results are consistent with the mo del used to explain the nature of the creep phenomena in high porosity MgO compacts when weak uniaxial loads are applied. These results also suggest t hat both pore growth and grain growth processes obey the same thermal activ ated mechanism. If this is true, as data of Wong and Pask suggest. The rate -limiting step for intermediate stage grain growth might be different from that applying in the final stage of sintering. (C) 1999 Elsevier Science Li mited. All rights reserved.