The densification mechanism of hydroxyapatite particles during spray pyrolysis with variable carrier gas rates of flow.

Abstract

The densification mechanism of hydroxyapatite particles during spray pyrolysis with varying carrier gas flow rates was investigated. A calcium phosphate solution with a Ca/P ratio of 1.67 was prepared by dissolving calcium nitrate tetrahydrate and diammonium hydrogen phosphate in deionized water followed by the addition of nitric acid. Hydroxyapatite particles were then synthesized by spray pyrolysis at 1500°C with carrier gas flow rates of 10, 30, and 50 L/min, respectively. The lower the carrier gas flow rate, the smaller and denser the as-prepared hydroxyapatite particles. Consequently, the lower flow rates produced particles with higher sinterability at 1100°C. The results can be explained in terms of the nucleation and growth mechanism based on the degree of supersaturation of hydroxyapatite in a droplet, which was dependent on the evaporating speed of nitric acid and water. The practical implication of these results is that highly sinterable hydroxyapatite powders can be synthesized via spray pyrolysis by reducing the carrier gas flow rate in a fixed temperature environment.