Calcium phosphate apatites with variable Ca/P atomic ratio III. Mechanical properties and degradation in solution of hot pressed ceramics

Calcium deficient hydroxyapatite powders Ca10-x(PO4)(6-x)(HPO4)(x)(OH)(2-x)(0 less than or equal tox less than or equal to1) were hot pressed to produce dense hydroxyapatite-tricalcium phosphate (HAP/TCP) biphasic materials. Ceramics hot pressed at 1100 degreesC were composed of an homogeneous distribution of the HAP and beta -TCP grains with an average size of 0.2 mum. Grain growth was observed for TCP loading > 70 wt%. The strength exhibited a maximum of sigma (f) = 150 MPa for 90/10 (w/w) HAP/TCP and it dropped for smaller and greater amounts of TCP. This value was twice that of pure HAP. When placed in Ringer's solution, only the surface of biphasic compounds was degraded after 60 days of immersion with a preferential etching of the TCP phase. After hot pressing at 1200 degreesC, grain growth was observed and the mechanical properties were decreased. This was explained by the allotropic transformation alpha/beta of TCP. (C) 2001 Elsevier Science Ltd. All rights reserved.