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

Abstract

A method to measure the amorphous calcium phosphate (ACP) content of plasma sprayed hydroxyapatite (HA) coatings is presented. The areas of the crystalline 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 component 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 preparation, X-ray measurement, and least-squares fitting methods to a single 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 crystallinity" for plasma sprayed HA coatings with an estimated standard deviation of 1 wt % ACP across the entire compositional range.

Multifunctional hydroxyapatite and poly(d,l-lactide-co-glycolide) nanoparticles for the local delivery of cholecalciferol

“…The mean crystallite size (D) of the powders calculated from the half-width (β 1/2 ) of the XRD reflection of the (002) plane (2 θ =25.9°) using the Scherrer equation was 12.5 nm. The degree of crystallinity of HAp could be facilely determined from its XRD pattern [20]. Similar in appearance to that obtained by different researchers [17,19,21], the diffractogram shown in Fig.…”

Calcium orthophosphates

“…This method is based on a rapid quenching of melted calcium orthophosphates occurring, e.g., during plasma spraying of HA 270 - 272 . A plasma jet, possessing very high temperatures (5,000–20,000°C), partly decomposes HA.…”

Bioceramic Materials

“…Recent investigations with highresolution synchrotron radiation have suggested that the atmospheric plasma spraying of stoichiometric HAp results initially in a reversible dehydroxylation to form OAp with c 0 = 0.6902(3) nm (see Scheme 10.1 , Step 2). Indeed, a quantitative estimation of the amorphous content according to the method of Keller and Dollase (2000) revealed ACP contributions of 25% (plasma power 11 kW) and 40% (plasma power 24 kW), respectively ( Figure 10.13 ). Figure 10.12 shows the XRD pattern of HAp powder (average grain size 120 µ m) when plasma -sprayed (plasma power 11 and 24 kW; total plasma gas fl ow rate 50 slpm; powder feed rate 18 g min − 1 ; spray distance 100 mm; translation speed 30 m min − 1 ) onto a Ti6Al4V target plate.…”

“…Figure 10.12 shows the XRD pattern of HAp powder (average grain size 120 µ m) when plasma -sprayed (plasma power 11 and 24 kW; total plasma gas fl ow rate 50 slpm; powder feed rate 18 g min − 1 ; spray distance 100 mm; translation speed 30 m min − 1 ) onto a Ti6Al4V target plate. (Keller and Dollase, 2000 ) to determine the ACP content of a plasma -sprayed hydroxyapatite coating Figure 10.14 Scattering vector Q = 4 π sin Θ / λ of synchrotron radiation diffraction profi les of as -sprayed hydroxyapatite coatings showing the vicinities of the (002) and (004) Figure 10.15 Schematic model of the thermal decomposition of a spherical hydroxyapatite particle subjected to high temperature in a plasma jet. However, the strongly elevated background between about 25 and 35 o 2 Θ suggest the existence of considerable amounts of amorphous calcium phosphate.…”