Machinable calcium pyrophosphate glass-ceramics

Glass-ceramics containing a large amount of calcium pyrophosphate (β–Ca₂P₂O₇) crystal were prepared via crystallization and sintering; compacts of a calcium phosphate glass powders with a composition of 60CaO · 30P₂O₅ · 5TiO₂ · 5Na₂O (in mol%) were heated for 3–6 h at 850 °C in air. The compacts were densified by the viscous flow of the glassy phases during heating. The calcium phosphate glass-ceramics were found to show a bending strength of approximately 100 MPa, and they were easy to machine, as confirmed by a drilling test using a conventional carbide tool. The machinability is thought to arise from the microstructure consisting predominantly of the interlocking and platelike β–Ca₂P₂O₇ precipitated in the glass.