Microstructure and mechanical properties of a nucleant-free basaltic glass-ceramic

The crystallisation kinetics of magnetite from basalt glass was studied using glass samples prepared by melting basaltic rocks from the Serra Geral Formation, without the addition of the nucleating agent, using differential scanning calorimetry under isothermal conditions. The temperature of maximum nucleation rate for magnetite was determined as 650 C. Upon further heating to 860 C, a second phase crystallises, which was identified by X-ray diffraction as a pyroxene (augite, Ca(Mg,Fe)SiO). The best mechanical properties were exhibited by a glass-ceramic nucleated at 650 C for 0.5 h and further heat-treated at 860 C for 1 h. The basalt glass-ceramic exhibited a fine grain and homogeneous microstructure, with high hardness and reasonable resistant to NaOH attack.