The Use of Heating to Change the Crystallinity and Structure of Carbonated Calcium Hydroxyapatite

Abstract

Previous synthesis routes created apatite in low crystallinity and high crystallinity states, but a wider range will extend the design capabilities of apatities for hard tissue replacements. While high crystallinity apatites are more conventional, this work investigated lower crystallinity variations from an amorphous 10 state to low crystallinity apatite. Carbonated hydroxyapatite was prepared by precipitating an amorphous phase followed by crystallization at 650 ºC after a slow (5 ºC/min) and fast heating rate (60 ºC/min). The effect of processing conditions on crystallinity and structure changes was evaluated by thermal analysis, X-ray diffraction, transmission electron microscopy, Fourier transform infra-red and Raman spectroscopy. Furthermore, peak deconvolution of IR and Raman spectra resolved carbonate and 15 phosphate bands and revealed the carbonate and crystalline phase content in CHAp. Similar to precipitation of crystalline apatite, the crystallization at elevated temperature led to carbonate in both the phosphate and hydroxyl positions. Heating at 650 ºC provided a nanosized spherical hydroxyapatite containing carbonate controlled by the heating rate. This creates a mechanism for creating a large range in crystallinity with a greater resorption capability for regenerative medicine