Processamento e desempenho mecânico de vitrocerâmicos obtidos a partir do basalto da Serra Gaúcha

Abstract

One of the main formations of igneous rocks of the western countries, denominated Serra Geral Formation (FSG), is located in the south of Brazil and extends over a significant part of the territory of the State of Rio Grande do Sul, forming the Gaúcho Plateau. These rocks, like basalts and dacites, have been used for centuries as pavement, structural elements in buildings, ornamental rocks, among others. The possibility of melting these rocks and turning them into glass-ceramic materials makes them high-value technological materials, but they are not yet manufactured in Brazil. The basalts may be melted at temperatures close to 1200 °C and if cooled to a sufficiently high rate, form glasses. Heat treatments with temperature and time control transform the glasses into glass-ceramics with defined microstructures, which will directly influence the properties of the final product. In this work, the mechanical properties of the FSG basalt glass ceramics were evaluated as a function of the microstructure. The basaltic rock, without addition of nucleating agents was fused and quenched in metallic molds. Thermal treatments were conducted at 1070 °C for 40 min, 6 h and 36 h. The microstructural characterization indicated that the time of heat treatment at the crystallization temperature of the glass controls the crystallinity index and the size of the crystals of the glass ceramic. Phase like magnetite (FeO.Fe2O3), labradorite sodium anorthite) ((Ca,Na)(Al,Si)4O8) and pyroxene (augite) (Ca,Na)(Mg,Fe,Al,Ti),Al)2O6) were identified by XRD. Both the bulk density and KIC of the glass ceramic increased and were linearly dependent on the IC. The heat treatment of 36 h resulted in the highest CI, 64%, the highest apparent density 2.90 g/c hardness, the highest value was found for the heat treatment of 6 h, 7.34 GPa. Thus, it can be concluded that for longer treatment times, both CI and crystal size increased and influenced directly the propagation of cracks through the material and, therefore, the production of glass-ceramics with controlled microstructure from basalt of the Rio Grande do Sul is technically feasible. [resumo fornecido pelo autor]