PRECIPITATION OF HYDROXYAPATITE THROUGH HYDROTHERMAL TREATMENT OF THE COMPOSITES IN THE CAO-P2O5-SIO2-B2O3 SYSTEM PREPARED BY SOL-GEL PROCESS

Six kinds of powders in the CaO-P2O5-SiO2-B2O3 system were prepared by a sol-gel process. The powders consisted of various Ca/P ratios: 1.50, 1.67 and 2.00. The composites were fabricated by firing the compressed powders at 1100 degrees C for 1 h. The relative densities (bulk densities/true densities) of the composites without B2O3 were only 65%, whereas those of the composites with 10 mol% of B2O3 were as high as 98%. When these composites with B2O3 were hydrothermally treated at 160 degrees C for 4-24 h in NH3 solution at a pH of similar to 10, the surfaces of the composites were homogeneously coated with whisker-like hydroxyapatite (HAp) particles. However, no HAp was found from the composites without B2O3 The bending strengths of the composites with B2O3 remained unchanged after the hydrothermal treatment.