Composite orthopedic and dental implants consisting of metallic substrates plasma-spray coated with hydroxylapatite (HA), are currently used in reconstructive surgery. It is believed that the crystalline form of the calcium phosphate ceramic, the presence of contaminant phases, and the degree of crystallinity affect its biological properties.
X-ray diffraction has been employed to characterize the contaminants and percent crystallinity in biological and sintered synthetic HA. However, application to plasma-sprayed coatings is complicated by the potential presence of several crystalline contaminant phases, an amorphous component, and possible instability during grinding or inhomogeneity of the coatings.
The external standard method of x-ray diffraction quantitative analysis is developed for HA plasma-sprayed coatings. A data collection and reduction strategy to allow separation of contaminant phases and the amorphous fraction is presented. Examples of applications to a variety of coating samples, typical of those in current use, are presented. Repeatability and accuracy are demonstrated with powder mixtures of known composition. Detection limits and sources of error are discussed.