Effect of Crystallisation Degree on Hardness of Basaltic Glass-Ceramics

The dependence of hardness of basaltic glass-ceramics on their crystallisation degree has been explored by means of differential scanning calorimetry, optical microscopy, X-ray diffraction, and Vickers indentation. Different degrees of crystallisation in the basaltic glasses have been obtained by varying the temperature of heat treatment. The change of the relative degree of crystallisation with the heat treatment temperature can be described by an empirical model established in this work. The predominant crystalline phase in the glass has been identified as the pyroxene augite. The hardness of the augite crystals is in the range of the hardness of a similar pyroxene, i.e., a pure diopside crystal. The hardness of diopside has been both measured and calculated. The calculation has been done by considering the strength of each individual bond and the amount of bonds per volume, i.e., by using first principle calculations. It is found that the hardness of the glass phase decreases slightly with an increase in the degree of crystallisation, while that of the augite phase drastically decreases.