SINTERING EFFECTS ON THE STRENGTH OF HYDROXYAPATITE

Mechanisms underlying temperature-strength interrelations for dense (>95% dense, pores closed) hydroxyapatite (HAp) were investigated by comparative assessment of temperature effects on tensile strength, Weibull modulus, apparent density, decomposition (HAp:tricalcium phosphate ratio), dehydroxylation and microstructure. Significant dehydroxylation occurred above similar to 800 degrees C. Strength peaked at similar to 80 MPa just before the attainment of closed porosity (similar to 95% dense). For higher temperatures (closed porosity), the strength dropped sharply to similar to 60 MPa due to the closure of dehydroxylation pathways, and then stabilized at similar to 60 MPa. At very high temperatures (>1350 degrees C), the strength dropped catastrophically to similar to 10 MPa corresponding to the decomposition of HAp to tricalcium phosphate and the associated sudden release of the remaining bonded water.