Influence of magnesia on the structure and properties of MgO-Al2O3-SiO2-F- glass-ceramics

Effects of MgO content (13.4-31.4 mol%) on the structure and properties of MgO-Al2O3-SiO2-F- glass-ceramics were investigated by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), infrared spectrophotometry (IR) and scanning electron microscopy (SEM). Results show that the main units of glass network structure are [SiO4] and [AlO4]. MgO contributes to the weakening of silica network and reduce the stability of glass structure. The main crystals of the MgO-Al2O3-SiO2-F- glass-ceramics are phlogopite, spinel, flur-pargrasite and forsterite. The increase of reheating temperature and MgO content are beneficial to the separation of phlogopite crystal, and cause an higher aspect ratio of the phlogopite phase, which improves the machinability of the glass-ceramics. Excellent machinability is obtained when MgO content is 31.4 mol% at the processing temperature of 1100 degrees C for 2 h. (C) 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved.