Characterization of the transformation from calcium-deficient apatite to beta-tricalcium phosphate

The structural changes that occur during the transformation of a Ca-deficie nt apatite, prepared by a wet chemical method, to beta-TCP were investigate d. X-ray diffraction (XRD) analysis of as-prepared samples and samples calc ined at temperatures between 500 and 1100 degrees C showed that the transfo rmation occurs over the temperature range 710-740 degrees C, under non-equi librium conditions. The change in crystallite size with increasing calcinat ion/sintering temperature was studied by XRD using the Scherrer formula. Fo urier transform infra-red (FTIR) analysis indicated considerable structural change in samples above and below this temperature range. Changes were obs erved in the hydroxyl, carbonate and phosphate bands as the calcination tem perature was increased from 500 to 1100 degrees C. Even once a single beta- TCP phase is obtained at 740 degrees C there remains a considerable amount of structural change at temperatures between 740 and 1100 degrees C. This e ffect was illustrated by an unusual change in the lattice parameters of the beta-TCP structure and significant changes in the phosphate bands of the F TIR spectra as the calcination temperature was increased. The results obtai ned in this study show that the combined experimental techniques of XRD and FTIR are excellent complimentary methods for characterizing structural cha nges that occur during phase transformations. (C) 2000 Kluwer Academic Publ ishers.