SINTERING EFFECTS ON THE STRENGTH OF HYDROXYAPATITE

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