Influence of powder pre-treatments and milling on dispersion ability of aqueous hydroxyapatite-based suspensions

The rheological properties and the dispersion stability of highly concentrated aqueous hydroxyapatite (HAP) powder suspensions in the presence of an anionic polyelectrolyte dispersant have been investigated. Dispersed suspensions with high content of HAP powder (up to 75 wt.%) and low viscosity were obtained. HAP suspensions with solids loading as high as 75 wt.% could be prepared following a slow process of increasing the solids weight fraction in steps of 3 wt.%, starting from 66 wt.%. After each increment of solids, ball milling was conducted for periods of 6 h, which then increased up to 24 h with solids loading increasing. Zeta potential measurements were conducted on HAP powders evaluate the influence of calcination on surface-charge properties of the particles. It was concluded that both aqueous ball milling and calcining enhance the repulsive interaction forces between particles, like the presence of the dispersant.