Thermal decomposition and mechanical properties of hydroxyapatite ceramic

Pure hydroxyapatite (HAP) ceramic and HAP composite ceramic with B2O3 were prepared by isostatic press forming and pressureless sintering. The relationships between thermal decomposition ratio and mechanical properties for pure HAP ceramic and the composite ceramic were investigated by means of FTIR, X-ray diffraction and three-point bending method. The results indicate that the decomposition ratio of pure HAP ceramic increases with ascending the sintering temperature and nearly reaches 80% at 1 350°C. For the HAP composite ceramic, the thermal decomposition is inhibited obviously due to the addition of B2O3. The added B atoms incorporate into the crystal lattice of HAP to form solid solution, resulting in an enlargement in the crystal spacing and an improvement in the binding strength of HAP crystal cell. Thermal decomposition ratio of HAP decreases but bending strength and fracture toughness are enhanced for HAP composite ceramics. However, when the added B2O3 is more than 5% (mass fraction), HAP decomposition is promoted and a steady β-TCP is formed due to the fact that when B atoms with higher negative electricity are combined with O, sp2 and a full-air p are formed, and those voids have a strong trend to intake of the outer electrons. So, it is very possible to occupy the place where HAP loses OH− or PO43−.