Characterisation of the rheological properties and zeta potential of a range of hydroxyapatite powders.

The effect of precipitation temperature, i.e. particle morphology on the rheological properties of a hydroxyapatite (HA) slip was investigated and compared to a commercial HA (batch P120 supplied by Plasma Biotal, Tideswell, Derbyshire, UK). The commercial HA was highly crystalline and had a particle size much larger than the HA precipitated at 60 and 80 degrees C. With no deflocculant addition, the commercial HA had a viscosity much higher compared to the precipitated HA as expected. The commercial HA and the HA precipitated at 60 degrees C showed similar pseudoplastic behaviour, but the HA precipitated at 80 degrees C showed Newtonian behaviour. This was explained by the HA precipitated at 80 degrees C having mean particle size of 82.24 nm, but a much wider particle size distribution. This is confirmed by the electrophoretic mobility measurements which show that the HA precipitated at 80 degrees C has a much lower zeta potential at a 0 wt% addition of deflocculant. Because of the wider particle size distribution, the need to add deflocculant is much reduced.