Bioactive Glass-ceramics Prepared by Hydrothermal Hot-Pressing

Bioactive glasses in the system Na₂O-CaO-SiO₂-P2O₅ are useful as implant materials for repairing bone because of their high bone-bonding ability. Their mechanical strength are, however in sufficient for bone substitutes under load-bearing conditions. The present study deals with preparation of the bioactive glass reinforced with rod-shaped crystals by hydrothermal hot-pressing (Fig. 1). The glass powders in the system Na₂O-CaO-SiO₂-P₂O₅ solidified by hydrothermal hot-pressing at 100 °C contained no crystalline phases. The solidified glass had about 86 % density. The Vickers hardness and the compressive strength of the solidified glass were 1 GPa and 150 MPa. The glass powders subjected to a hydrothermal treatment above 150 °C contained crystalline phases of NaCa₂HSi₃O₉ and Na₂Ca2Si₃O₉ (Fig. 2). The glass-ceramics prepared at 350 °C was almost pore free and homogeneously precipitated rod-shaped crystals with the length of about 3 μ;m and with the width of about 0.3 μ;m (Fig. 3). The Vickers hardness and the compressive strength of the glass-ceramics were 3 GPa and 460 MPa (Fig. 6). The fracture toughness K_IC was 2.5 ± 0.3 MPa^.m¹/₂, about five times that of the parent glass prepared by the conventional method. This high fracture toughness of glass-ceramics might be attributed to the crack defrection toughening and pull-out toughening with the rod-shaped crystals.