Resistance to localized corrosion of metallic substrates with glass-ceramic containing sol gel coatings for biomedical applications

C. GARCÍA,; P. GALLIANO; S. CERÉ

MATERIALS LETTERS

Elsevier

Año: 2003 vol. 57 p. 1810 - 1814

0167-577X

CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spontaneously form passiveoxide films when immersed in physiological environments. The stresses resulting from the use of the prosthesis can causefracture and abrasion of the oxide film that covers the surface. This can result in crevice corrosion, with the correspondingdecrease in pH leading to severe attack. Protective coatings deposited onto the metals would minimise the release of metallicions from the substrate and the incorporation of bioactive particles would enable the adhesion to the bone tissue.This work describes the electrochemical behavior of CrCoMo alloys (F75) as cast, covered by a hybrid silica coatingobtained by sol–gel. The silica sol–gel coating contains bioactive glass ceramic and vitreous particles of the system CaO–SiO2–P2O5 previously obtained by fusion, crystallization and milling. The performance of the alloy with and without coating isevaluated in simulated body fluid (SBF) pH 7.31 at 37 jC. As cobalt base alloys are susceptible to crevice attack, coated piecesare also tested in SBF acid solution (pH 0.7) in order to simulate the acidic media and the high chloride concentrations thatdevelop when a crevice is formed. The electrochemical behavior has been evaluated by potenciodynamic polarization andelectrochemical impedance spectroscopy. It was found that for both pH conditions the samples coated with double layer of glassceramic particles showed lower passive current densities than those with monolayers. The coating improves the protectionpotential of the base material in the neutral solution. Besides, in the acidic solution, all the samples remain passive but theprotection potential shifts to potentials more active than those measured in the neutral SBF