PREPARATION AND CHARACTERIZATION OF CALCIUM HYDROXYAPATITE FROM FORCED HYDROLYSIS OF Ca(OH) 2 -TRIPHOSPHATE-HCl MIXED SOLUTION

The effects of hydrochloric acid (HCl) on the formation of calcium hydroxyapatite (HAp) particles produced by aging Ca(OH)2 and sodium triphosphate (sodium tripolyphosphate, Natpp: Na5P3O10) mixed solution at 100C for 18 h were examined. The effect of addition of urea was also investigated. In the absence of HCl, the spherical secondary particles with ca. 60 nm in diameter composing by aggregation of spherical primary particles with ca. 20 nm in diameter were produced. Similar aggregated secondary spherical particles were formed up to HCl concentration ([HCl]) of 8 mM. On the contrary, the particles produced at [HCl]≥12 mM were elongated to c-axis and exhibit aggregated rod-like shape, though those produced at [HCl]=20 mM were spherical aggregates with ca. 20 nm in diameter. All the particles produced at [HCl]≤16 mM were HAp, though the sample produced at 20 mM was amorphous. The specific surface areas of the samples were ranged among 84-98 m/g and were fairly agreed with the estimated value of spherical primary particle with 20 nm in diameter. The in situ IR spectra of the HAp particles exhibited very small bulk OH band at 3570 cm. This result indicated that the HAp particles are produced by aggregation mechanism and OH ions along with c-axis in the poorly crystallized primary particles were disordered. The HAp particles with Ca/P molar ratio larger than theoretical value of 1.67 were not exhibited surface P-OH groups at 3656 and 3683 cm. However, the addition of urea produces CaCO3 (calcite) together with HAp and no single HAp crystal was produced. It was revealed that forced hydrolysis reaction of tpp was accelerated by HCl and aggregated secondary spherical particles with unique structure and high specific surface area were obtained. (Received Oct. 8, 2013; Accepted Jan. 16, 2014)