Oriented apatite glass-ceramics by extrusion

In the system SiO2 - Al2O3 - P2O5 - CaO - K2O - F-., glass-ceramics with needle-like apatite were produced. By means of subsequent extrusion, oriented glass-ceramics with needle shape apatite have been produced at temperatures corresponding to viscosities in the range of 10(7) to 10(8) dPas. The needle shape apatite crystals are oriented with their c-axes parallel to the extrusion direction. The degree of orientation was studied by means of XRD measurements. The influence of crystal alignment on the mechanical properties was studied. Vickers indentations show a decrease in the crack length perpendicular to the extrusion axis, whereas cracks, introduced parallel to the extrusion axis are longer. Hence, the K-\ c - values calculated show anisotropy.