Conversion of Monetite, CaHPO₄, To Apatites: Effect of Carbonate on the Crystallinity and the Morphology of the Apatite Crystallites

Abstract

Abstract The incorporation of carbonate in the apatite causes a decrease in crystallite size as demonstrated in precipitated apatites prepared at 37°C. Carbonate disturbs the crystallization of the growing apatite crystallites to such an extent that materials with more than 15 wt% CO3 gives an ‘amorphous’ x-ray diffraction pattern. The incorporation of carbonate in precipitates prepared at 100°C. causes a shortening of the a-axis and a lengthening of the c-axis which is proportional to the carbonate content, supporting the concept that in these apatites, CO 3 substitutes for PO 4 (11). X-ray diffraction linebroadening studies of CO 3 -apatites precipitated at 100°C and electron micrographs show that the size and shape of the crystallites change from long needles to smaller rods to tiny spheroids, depending upon the amount of CO 3 . Carbonate causes the bonding in the apatite to become weaker and more isotropic, which results in the small spheroidal crystals. This paper reports the effect of carbonate on lattice parameters and morphology of carbonate-apatites which have been prepared by the conversion of rnonetite, CaHPO 4 in hot carbonate solutions. The structural effects of CO 3 on the apatite is further reflected by the modification of the vibrations of the PO 4 groups in the infrared absorption spectra. The morphology of ‘amorphous’ CO 3 - containing apatitic precipitates and that of CO 3 ∼apatite with high CO 3 content (prepared at 100°C) is similar, i.e., spheroidal in shape, but greatly differing in crystallite size.