The influence of aluminium oxide content on the formation of barium containing fluormica glass-ceramics.

The effect of varying the aluminium oxide content on the nucleation and cry stallisation behaviour of barium containing fluormicas was investigated in order to develop novel, high strength, and machinable glass-ceramics. Nine glasses were synthesised and characterised by thermal analysis, microscopic and spectroscopic methods. Reduction of aluminium oxide allowed charge-bal ancing cations of magnesium oxide to adopt a network-disruptive role in the glass; this also increased the tendency of these glasses to bulk nucleate. The substitution of barium in the interlayer sites of these fluormicas dis rupted their microstructural formation, to produce ionically disordered bar ium fluormicas. Magic Angle Spinning Nuclear Magnetic Resonance spectroscop y confirmed the formation of fluorophlogopite with a minor percentage of co rdierite crystal phase. These glasses have been successfully cast into mono liths and an investigation into their machinability and physical properties is continuing.