A quick and inexpensive method was developed to determine the crystallinity of hydroxylapatite coatings using X-ray diffraction for the purpose of production control.
Crystalline hydroxylapatite powder, when sprayed onto a substrate with thermal spraying, forms a mostly two phase material consisting of crystalline hydroxylapatite and amorphous material and very likely some trace impurities. The term crystallinity of a thermal sprayed hydroxylapatite coating is defined as the weight percentage of crystalline hydroxylapatite material to the total amount of material in the coating. With X-ray diffraction of the coating, the integrated crystalline hydroxylapatite peak intensity between 25° and 40° (2⊖) is measured and divided by the same integrated intensity of a 100% crystalline hydroxylapatite standard. The ratio between both is called the crystallinity of the hydroxylapatite coating. The method is calibrated using crystallinity standards which have been made by mixing 100% crystalline hydroxylapatite powder with 100% amorphous powder in different ratios.