X-ray determination of crystalline hydroxyapatite to amorphous calcium-phosphate ratio in plasma sprayed coatings

A method to measure the amorphous calcium phosphate (ACP) content of plasma sprayed hydroxyapatite (HA) coatings is presented. The areas of the crysta lline peaks and the broad amorphous "hump" in an X-ray diffraction scan of a mixture of crystalline and amorphous HA can be fitted using conventional nonlinear least-squares methods. The weight fraction of the amorphous compo nent in a mixture of unknown proportions is obtained from the measured hump fraction using a linear expression requiring a single calibration constant . This calibration constant may be determined by applying the same sample p reparation, X-ray measurement, and least-squares fitting methods to a singl e standard of known (weighed) proportions as used to measure the unknown(s) . Application of this method to a set of 12 samples yields an "index of cry stallinity" for plasma sprayed HA coatings with an estimated standard devia tion of 1 wt % ACP across the entire compositional range. (C) 2000 John Wil ey & Sons, Inc.