Biocorrosion behavior of hydroxyapatite/bioactive glass plasma sprayed on Ti6A14V

Abstract

Biocorrosion behavior and changes in morphology and phases of hydroxyapatite (HA), bioactive glass (BG) and HA/BG coatings in Hank's physiological solution is investigated. Results showed that as-coated BG had the roughest surface, while as-coated HA had the smoothest surface. The HA/BG coating was comprised of both bubble-shaped particles of BG and small irregular-shaped particles of HA. Low intensity X-ray diffraction (XRD) peaks of CaO, β-TCP and Ca 4P 2O 5, besides the major apatite peaks, were observed in HA and HA/ BG coatings. BG coating had an essentially amorphous structure. When HA and HA/BG were immersed in Hank's solution for 30 days, most of the minor phases dissolved. When BG coating was immersed, both apatite and SiO 2 peaks gradually rose. A sudden drop and recovery in OCP occurred to BG and HA/BG but not to HA. Anodic polarization showed that passivation and film breakdown occurred to all three coatings. Passivation started approximately from 200, 300 and 400 mV(SCE) for HA, HA/BG and BG coatings, respectively. The three coatings had similar critical current densities. The released calcium ion concentration was found the highest in HA-tested solution, while the concentrations of sodium and silicon were the highest in BG-tested solution. The drop-and-rise phenomenon was also observed in the FT-IR spectra of immersed HA and HA/BG coating. These FT-IR results are consistent with the XRD results reported earlier.