The influence of MgF2 content on the characteristic improvement of machinable glass ceramics

The influence of MgF2 on the various properties like crystalline behavior, microstructure phases, hardness etc. in the SiO2-Al2O3-MgO-K2O-B2O3 glass system has been investigated. Three batches of glass system were synthesized and characterized by differential scanning calorimetry (DSC), coefficient of thermal expansion (CTE), X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) equipped with energy dispersion X-ray spectroscopy (EDS). DSC study reveals that with the increase in MgF2 content the glass transition temperature (T-g) and first crystallization peak temperature (T-p(I)) decreased whilst the second crystallization peak temperature (T-p(II)) slightly increased. The CTE of the glasses is found to be in the ranges 634-6.40 x 10(-6) K-1 (50-400 degrees C). The activation energy (E-c) and frequency factor (v) both increase with increasing MgF2 content. The three-dimensional crystal growth is observed. The mica crystals are identified as fluorophlogopite, the predominant crystal phase for all the three glass specimens heat treated at 1050 degrees C. Vickers hardness values decrease with increasing amount of fluorine content and it gives better machinability. (C) 2015 Elsevier B.V. All rights reserved.