title: Transformation mechanism of different chemically precipitated apatitic precursors into beta-tricalcium phosphate upon calcination.
abstract: The Ca-deficient apatite (CDHA) was prepared from the precursors of (CH3COO)2Ca x xH2O, Ca(NO3)2 x 4H2O and H3PO4, (NH4)H2PO4 to investigate the transformation mechanism of beta-tricalcium phosphate (beta-TCP). X-ray diffraction analysis shows that the development of beta-TCP is not via direct reaction between Ca and P for all the different combinations between Ca and P precursors. The activation energy of beta-TCP formation with (NH4)H2PO4 as precursor was higher than that with H3PO4. Following the Johnson-Mehl-Avrami equation, the reaction kinetics of beta-TCP phase formation is found one-dimension growth with interface-controlled and diffusion controlled growth depending on the annealing temperature. There exists a transition between 750 degrees C and 825 degrees C, and the transition rate from interface-controlled to diffusion-controlled growth is precursor-dependent.
mesh_terms: D001031:Apatites / Q000737:chemistry*; D002118:Calcium / Q000378:metabolism*; D002130:Calcium Phosphates / Q000737:chemistry* / Q000494:pharmacology; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction
chemical_list: D001031:Apatites; D002130:Calcium Phosphates; C485817:beta-tricalcium phosphate; C018392:tricalcium phosphate; D002118:Calcium