Processing and characterization of sinter-crystallized basalt glass-ceramics

In this work, basalt from the Serra Geral Formation, Brazil, was used to prepare a glass frit from which glass-ceramics were produced by the sinter-crystallization process. After different heat treatments in an inert atmosphere, properties were evaluated, as well as their relationship with the obtained microstructure. The results show that bulk density, hardness and crystallinity index increased with the treatment time up to the final temperature, with highest values for the longest heat treatment (6.5 h), respectively 2.39 g/cm3, 74.8% and 9.81 GPa. However, a shorter heat treatment (2.5 h) at the same final temperature resulted in comparable values (respectively, 2.38 g/cm3, 72.3% and 9.68 GPa). As such, isothermal steps at intermediate crystallization temperatures have no relevant influence on the final microstructure. Thus, for this basalt, nucleation is a very fast process and crystal growth is likely rather limited and little improved by intermediate crystallization heat treatment steps.