Plasma sprayed hydroxyapatite (HA) has been used extensively as surface coatings on metallic implants. These biomedical implants are generally made of biocompatible stainless steels, CoCr alloys, or Ti alloys. The coatings have been shown to promote bone fixation and osteoconductivity. However, there are some concerns related to the formation of large particle debris during the resorption of the coating. To overcome this situation coatings formed by smaller features are required. Solution precursor plasma spraying (SPPS), has been reported to produce submicron/nanocrystalline structured coatings from relatively inexpensive precursors. These nanocrystalline HA coatings may improve the resorption of the coating in the body, avoiding the irritant effect of large particles which may be seen in current thermal sprayed HA coatings.

 

In this work was studied and compared the suitability of two different liquid precursors of HA as feedstock for the air plasma spray (APS) coating technique. The precursors were organic (calcium nitrate tetrahydrate and triethyl phosphite) and inorganic (calcium nitrate tetrahydrate and ammonium dihydrogen phosphate) sol-gel solution precursors employed in previous work to produce thin films by a dipping technique. We report on the formation and the characteristics of the coatings so formed on Ti6Al4V substrates as a function of the spraying parameters. The presence of crystalline and amorphous phases was assessed by X-ray diffraction analysis. The surface chemical composition of the coatings was obtained by X-ray photoelectron spectroscopy. The microstructure of both types of coatings was characterized by scanning/transmission electron microscopy in order to identify the different submicron/nanocrystalline features. The suitability of the technique and the precursor to coat biomedical implants is discussed in terms of the results obtained.