Passivation of a CoCrMo PVD Alloy with Biomedical Composition under Simulated Physiological Conditions Studied by EQCM and XPS

Abstract

Kinetics of passive film growth on a CoCrMo biomedical alloy have been studied using the Electrochemical Quartz Crystal Microbalance technique (EQCM) in phosphate buffer solution at room temperature and 37 • C. CoCrMo layers were deposited on the quartz crystals by physical vapor deposition (PVD) reaching a dense and compact deposition film with fine-grain structure. EQCM measurements were performed under potentiodynamic and potentiostatic conditions (at applied passive and transpassive potentials). Furthermore, ex-situ X-ray Photoelectron Spectroscopy (XPS) analysis of the each tested sample was performed at the end of the electrochemical test. The use of EQCM allows distinguishing between electrochemical oxidation, passive and transpassive dissolution and passive film growth. In the passive domain the passive film thickness stabilizes within 200 to 400 s after an initial fast growth. The increase in current at the onset of the transpassive domain does not affect the passive dissolution rate. Only at higher potential dissolution rate increases due to the dissolution of Cr(VI), Co(III) and Mo(VI) species. The observed constant mass loss rate at transpassive potentials indicates that the passive film at these potentials is cracked or porous. Increasing temperature accelerates the mass loss through the oxide/electrolyte interface enhancing the passive and transpassive dissolution and increasing the thickness of the oxide film. CoCrMo alloys are one of the most important metallic materials used in orthopedic implants.1-3 Their use is based on their excellent mechanical properties (wear and hardness) and the high resistance to corrosion in physiological media which is related to the spontaneous formation of an oxide film that protects the metal from the surrounding environment. This layer has a high Cr content (mainly Cr 2 O 3 and smaller amount of Cr(OH) 3 ) with a minor contribution of Co and Mo oxides. [4][5][6][7] One of the most important issues in the use of this metallic biomaterial is passive dissolution which has been considered one problem for the long term durability of the implants and for the adverse effects that can cause metal ion release (physiological effects, toxicity, carcinogenicity and metal allergy). [8][9][10][11][12] The properties of the oxide film may change depending on the physico-chemical conditions (i.e. temperature, potential, etc.) and the adsorption of organic species present in body fluids such as proteins. [13][14][15] Furthermore, there is an increasing interest in the study of interfacial behavior of proteins in the human body as a result of problems associated with bacterial growth 16,17 and metal dissolution. 18, 19Considerable insight into the corrosion behavior of CoCrMo biomedical alloys has been obtained using conventional electrochemical techniques such as potentidynamic curves, cyclic voltammetry measurements, potentiostatic tests and Electrochemical Impedance Spectroscopy (EIS). 5,6,[20][21][22][23][24] The Electrochemical Quartz Crystal Microbalance (ECQM) is known to b...

Electrochemical behavior of near-beta titanium biomedical alloys in phosphate buffer saline solution

“…It has been reported that the capacitance of the film (C film ) is related to the quality and the thickness of the passive film [31][32][33][34]. Figure 10b shows the relation between C film and i pp of the different alloys at the studied potentials.…”

“…The interface equilibrium the potential drop in the of the passive film formation, adapted from [33].…”

Electrochemical Quartz Crystal Microbalance and X-Ray Photoelectron Spectroscopy study of cathodic reactions in Bovine Serum Albumin containing solutions on a Physical Vapour Deposition-CoCrMo biomedical alloy

“…Thus, working electrodes of 23 mm 2 surface area were covered by a CoCrMo coating of 1.5 mm thickness. The deposition procedure of CoCrMo layer on quartz crystal and crystal characterization has been described in detail elsewhere [17].…”

“…An Ag/AgCl reference electrode (0.195 V versus SHE) and a gold wire counter electrode were used. More details on the experimental set-up can be found in previous work [4,17].…”

“…Surface analysis by X-Ray Photoelectron Spectroscopy (XPS) was used to characterize surface composition after polarization. A similar protocol was previously used for investigating adsorption of protein at passive potentials [17].…”