Injection moulded hydroxyapatite ceramics

The injection moulding of hydroxyapatite (HA) and properties (relative density, shrinkage, microstructure, thermal strength and phase composition) of HA ceramics sintered at temperatures of 1373–1773 K were studied. Particles of oval shape and size of 0.5 μm were most suitable for injection moulding. Polymer/HA mixture contained 63 vol% of the HA powder. Maximum relative density (98.7%) and shrinkage (16%) of HA ceramics were obtained at a sintering temperature of 1523 K. Maximum flexural strength (60 MPa) of HA ceramics occurred at a sintering temperature of 1473 K. The strength of these ceramics decreased at sintering temperatures higher than 1473 K. Loss in strength was owing to the grain growth and decomposition of HA ceramics. The relationship between grain size and strength is described by the equation: σ = 53.3d1/2. The calculated activation energy of grain growth obtained was 215 kJ mol−1 K−1. The decomposition of HA to α-tricalcium phosphate was important at temperatures greater than 1573 K.