Efeito do teor de ferro na síntese de vitrocerâmicos de basalto

Abstract

Basalts, which cover about 70% of the Earth's surface, are igneous rocks originated from the cooling and solidification of magma on the Earth's surface. When the magma is cooled rapidly, it forms a glass. When cooled slowly, it crystallizes, totally or partially, forming several minerals. Products obtained from the melting of rocks have a wide market and can be considered the precursors of the glass ceramic technology. The glass-ceramic materials are ceramic materials, in which the crystalline phases are formed by controlled nucleation and crystallization of a base glass. These materials are promising due to the possibility of converting low-cost natural raw materials into products with excellent mechanical, thermal and chemical properties. Basalt glasses, when thermally treated, have the possibility of forming glass-ceramic materials if the Fe2O3/FeO ratio of the rock composition that originated it is greater than 0.5. In this work an FSG basalt was used to produce glass-ceramic materials by changing its chemical composition, by removing Fe2O3, by magnetic separation, and adding 5, 10 and 20% m. Fe2O3. To produce glassceramic the compositions were melted at 1500 °C for 1 h. A plateau of crystallization was applied at 950 °C for 3 h in the cooling step. Magnetic separation made it possible to reduce 13 %m. total Fe2O3 in the sample. Through the application of the petrurgical thermal treatment route, dendritic structures were obtained in the surface crystallization of the samples. With the increase of the iron content in the compositions there was an increase in the crystallization of the samples, observed by the thermal analysis, OM and SEM. It was concluded that all samples showed at least three different types of crystallization. On the surface, the predominant crystallization was dendritic, in the sample core the crystallization occurred in the form of small dots randomly distributed and, at the interface of the sample with the crucible, crystallization occurred heterogeneously, influenced by the chemical composition of the crucible. It was possible to verify the additive effect of the iron content in the crystallization of the glass-ceramic phases observed both in the amount and in the type of structure formed. The sample with reduced iron content was the only one that had a residual glass layer on the surface and did not show hematite in its structure. The samples show ed a Fe2O3/FeO ratio favorable to the formation of glass-ceramics, however it was observed that thetermination of this ratio is complex and the results were not conclusive. Thus, analyzes that evaluate the variation of the Fe2O3/FeO ratio throughout the entire heat treatment and not only the initial composition and the formed glass ceramic, could reveal its influence.