Sinter-crystallization in the diopside-albite system part II. Kinetics of crystallization and sintering

The formation of intragranular pores, induced by diopside crystallization in diopside-albite glasses, was highlighted in a previous study and here confirmed by SEM observation. The sinter-crystallization kinetics of four glass compositions, labelled G1, G2, G3 and G2-Cr, characterized by the formation of induced crystallisation porosity, P-CR, was investigated. The activation energies of crystallisation, E-C, and sintering, E-S, were evaluated by differential thermal analysis (DTA) and by contact differential dilatometer in non-isothermal conditions, respectively. The results highlighted that the kinetics of the crystallization process was not influenced by the P-CR formation and that the E-C values are in agreement with the corresponding activation energies of viscous flow. The sintering was evaluated up to 24% linear shrinkage of the samples. In the initial stage of the densification, up to 8% shrinkage, the measured E-S values are comparable for all glasses while, between 9 and 24% shrinkage, E-S increase as a function of the crystallisation ability of each glass. Bulk nucleation occurred in G2-Cr: the rate of phase formation resulted to be higher, the densification was inhibited by the formation of 6 +/- 3 wt.% diopside and significant open porosity remained in the sintered glass-ceramic. (c) 2005 Elsevier Ltd. All rights reserved.