Sinter-crystallization in the diopside–albite system: Part II. Kinetics of crystallization and sintering

Abstract

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.