Effect of special phase separation on microstructure and property of glass-ceramics

Glass-ceramics were prepared in a K₂O-MgO-Al₂O₃- B₂O₃-SiO₂-F system doped with different amounts of Ca, P and F, in a percentage of fluorapatite. The batches were melted at 1 500 °C and annealed at 580 °C for 1.5 h. The glass-ceramics with different microstructures and properties were obtained after heat treatment of the glass with special phase separation. The X-ray diffraction and scanning electron microscopy analysis show that flake-shaped fluorophlogopite and needle-like fluorapatite appear in the crystal glass and that needle-like fluorapatite assumed a distinct distribution, both random and oriented, due to the special phase separation. Moreover, for the apatite-oriented samples, machinability in direction parallel to needle-like apatite is inferior to the opposite direction. However, the machinability for the glass-ceramics with random apatite distribution lay somewhere in between.