The effect of additive (SiO2, MgO, and CaO) in the hardness and crystal phase of basalt glass-ceramics

The purpose of this research is to increase added value and maximize the potential for abundant availability of local basalt. The utilization of basalt needs to be a major concern in Indonesia. The additive effects on the crystallization and hardness of basalt glass-ceramics were studied. Eight specimens were modified by SiO2 (10 and 20 wt.%), MgO (5 and 8 wt.%), and CaO (7 and 10 wt.%). After melting at 1200°C for 2h, it was quenched with pH 7 water at room temperature. The nucleation temperature was kept at 600°C for 1hr and the crystallization temperature at 1050°C for 3:h. According to the XRF results, the chemical composition of basalt glass-ceramics consist of 35-41.9 SiO2 + 12.21-25.9 Al2O3 + 9.6-16.4 Fe2O3 + 17.4-24.0 CaO+3.06-5.27 MgO by percent weight. In addition to the base crystal phase (anorthite, olivine, and pyroxene), diopside and cristobalite formed as the effect of the additive. The highest hardness of basalt glass-ceramics was 564 Hv0.1N, an increase of 50.4% compared with raw basalt. From the analysis of variance (ANOVA), the increase in hardness effect by SiO2 content had a 68% contribution and a P-value of 0.02.