Sinter-crystallisation in the diopside–albite system: Part I. Formation of induced crystallisation porosity

The sinter-crystallisation was investigated in three model glasses (G1, G2 and G3) belonging to the diopside–albite system and forming between 30 and 60% diopside, respectively. The effect of bulk crystallisation on the sintering was studied by the addition of 0.7 wt.% Cr2O3 as nucleating agent to the G2 glass.The degree of sintering was evaluated by the variation of the apparent density while the crystallisation, by the increasing of the absolute density. The structure and morphology of the sintered glass-ceramics was observed by SEM-BSE.The results highlighted that the densification is not influenced by the variation of the composition among the three glasses but is inhibited by the diopide formation in G2-Cr where bulk nucleation takes place. It was shown that, due to the volume variation related to the diopside crystallisation, a spherical intragranular pores were formed in the glass-ceramics. The amounts of this porosity, named induced crystallisation porosity, increased as function of the crystallisation trend.