L. Keller et Wa. Dollase, X-ray determination of crystalline hydroxyapatite to amorphous calcium-phosphate ratio in plasma sprayed coatings, J BIOMED MR, 49(2), 2000, pp. 244-249
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.