Effect of drying conditions during synthesis on the properties of hydroxyapatite powders

The effect of the drying conditions during the hydroxyapatite (HAp) powder synthesis on the size and microstructure was studied. The starting materials were agitated in water, dried at 60-150 degrees C, and heat-treated at 720 degrees C. The heat-treated HAp powders were crystalline, and their particle sizes decreased with an increase in the drying time, but were independent of the drying temperature. For a 3 day drying period, it was 1.61 microm, and 0.55 microm for 21 days. The surface zeta potential of the HAp powder with a long drying period was more negatively charged than that from the short drying period. The average primary particle sizes of the HAp powders seem to be almost equivalent, and so the drying period may be related to the dispersibility of the primary particles, and may lead to a small HAp particle size.