Preparation of submicrometer-sized porous spherical hydroxyapatite agglomerates by ultrasonic spray pyrolysis technique

Abstract

Microstructural changes during the heating of submicrometer-sized spherical hydroxyapatite (Ca10(PO4)6(OH)2: HAp) agglomerates were examined. The starting powder was prepared by the spray pyrolysi so f calcium phosphate (Ca/P ratio = 1.67) solution containing 0.0167­1.5mol·dm ¹3 Ca(NO3)2, 0.0100­0.9mol·dm ¹3 (NH4)2HPO4 and concentrated HNO3 at 600°C using an ultrasoni cv ibrator. The resulting powders were composed of spherical agglomerates; the agglomerate diameter was reduced with decreasing concentration of spraying solution. The mean diameter of agglomerates obtained by the spray pyrolysi so f solution with the lowest concentrations, i.e., 0.0167mol·dm ¹3 Ca(NO3)2 and 0.0100mol·dm ¹3 (NH4)2HPO4 (abbreviated as 0.0167/0.0100), was as small as 0.34µm. The spherical agglomerates became hollow following a heat treatment at 800°C for 10min. The incorporation of 0.015mol·dm ¹3 citri ca cid into 0.0167/0.0100 solution contributed to the formation of hollow spherical agglomerates following spray pyrolysis. Furthermore, the heat treatment of these agglomerates at 800°C for 10min increased the amount of pores with mean diameter of 0.2µm, due to the burn-out of residual carbon.