Spray-pyrolyzed hydroxyapatite thin-film coatings

Hydroxyapatite (HA) thin-film coatings have been deposited on sheet substrates of a commonly used biomaterial (Ti6Al4V) using the spray pyrolysis technique. For this, a 0.042 M calcium spraying solution was prepared by dissolving calcium acetylacetonate hydrate in N,N-dimethylformamide, and phosphoric acid (H3PO4) was used as the source of phosphorous with different volume concentrations in deionized water. Both the solutions were supplied simultaneously and in parallel during the deposition of the coatings. The coatings were deposited at substrate temperatures of 425 and 525 °C. The use of 0.27% (volume) solution of H3PO4 resulted in coatings with stoichiometry close to that of the HA. The chemical composition, surface morphology and structure of the HA coatings were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The characteristics of the coatings thus observed are presented and discussed. The high purity of the coatings was revealed by XPS, confirming the presence of Ca, P and O as the main constituents, with a Ca/P ratio of about 1.3. Some carbon, inherent to the precursors used, was also detected by XPS. The XRD patterns obtained suggested preferred (113) and (321) crystal orientations in the coatings.