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 x 1) were hot pressed to produce dense hydroxyapatite-tricalcium phosphate (HAP/TCP) biphasic materials. Ceramics hot pressed at 1100°C were composed of an homogeneous distribution of the HAP and β-TCP grains with an average size of 0.2 μm. Grain growth was observed for TCP loading >70 wt%. The strength exhibited a maximum of σf=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 Ringerʹs 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°C, grain growth was observed and the mechanical properties were decreased. This was explained by the allotropic transformation α/β of TCP.