Dispersion and slip casting of hydroxyapatite

The dispersibility in deionized water of hydroxyapatite (HA) synthesized by a high-temperature (1000 degreesC) solid-state reaction between tricalcium phosphate and calcium hydroxide was investigated as a function of the pH o f the medium and the quantity of two dispersing agents (A = inorganic, B = organic) added to the slips. Although pH modification had a negligible effe ct on dispersibility, both of the dispersing agents produced a good dispers ion at considerably higher concentrations (>2 wt% of HA). At optimum amount s (2-4 wt%) of the dispersing agents, the slips showed near-Newtonian flow behavior up to 45 wt% solids loading and non-Newtonian behavior at > 50 wt% . By the optimal addition of dispersing agents and conditioning by ball mil ling, 60-67 wt% (32-39 vol%) solids-loaded HA slips could be cast into plas ter molds to produce 50%-58% dense green bodies, which, in turn, sintered t o 90%-94% density in the temperature range 1300 degrees -1400 degreesC. The sintered HA exhibited a three-point flexural strength of 40-60 MPa and a h omogeneous microstructure, with interspersed microporosities.