The effects of chromite ore on basalt based machinable glass-ceramics

Machinable glass ceramic materials are polycrystalline structures formed by controlled nucleation and crystallization heat treatment of glasses. Generally, nucleating additives are applied to the glasses to make more effective crystallization. Fine-grained microstructures are formed by efficient nucleation of crystals from whole body in the glass. This is the most important factor that strengthens the properties such as high strength, fracture toughness, impact resistance and abrasion. In the current study, machinable glass ceramics were produced by using natural raw materials chromite and basalt ores and the effects of composition changes on phase development, microstructure and machinability were investigated. The basalt and MgF2 powders were mixed in 90 and 10 wt.%, respectively. Three different compositions were prepared by adding 1 g, 3 g and 5 g chromite ore to this main composition. The prepared compositions were mixed in a dry condition in an alumina ball mill for 1 hour. These mixtures were melted in alumina crucible in an electric heated oven at 1500° C for 1 hour. After the melting process, it was cast into the graphite mold to produce bulk glass materials. Annealing process was performed at 600° C in order to eliminate internal stresses in the glasses. Differential thermal analysis (DTA) was applied to determine the glass transition and crystallization temperatures for the transition of glasses to glass-ceramics. As a result of the analysis, crystallization was carried out by heat treatment at 800, 900 and 1000 ° C. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) were used for characterization of glass ceramic samples. Hardness, fracture toughness and machinability tests were performed to determine mechanical properties. The results showed that all samples having flourphlgopite phase which provides machinability. Furthermore, chromite addition has a positive effect on crystallization properties of basalt based glasses.