Hydroxyapatite suspensions as precursors of pieces obtained by gelcasting method

The aim of this work was to prepare slurries of hydroxyapatite (OHAp) with a high content of solids, which is necessary for shaping pieces by the gelcasting method. For this purpose different studies were carried out using powders of OHAp calcined at temperatures ranging between 600 and 1200 °C and several dispersants. Surface area, porosity and chemical composition of OHAp powders played a fundamental role in the viscosity of slurries. The highest concentration of solid was obtained with OHAp calcined at 1200 °C. The best dispersant was selected in a first stage, by electrophoretic measurements and sedimentation studies and, finally, by rheological measurements. The concentration of dispersant which provides the minimum viscosity, depended on the calcination temperature of the OHAp. A great increased of viscosity took place for time of slurries preparation higher than 30 min. Milling of powder for 20 h was necessary to improve the rheological behaviour of the slurries. Finally, ceramic bodies were prepared from fluid slurries containing 60 vol.% of solids and the mechanical properties were evaluated.