Electrochemical investigation of the passive behaviour of biomaterials based on Ag–Sn and Cu–Zn–Al in carbonate buffer in the absence and presence of chloride

Abstract

The electrochemical behaviour of biomaterials based on Cu-Zn-Al (cubic Cu 3 Zn phase) and Ag-Sn (orthorhombic Ag 3 Sn and hexagonal Ag 4 Sn phases) alloys was investigated in carbonate buffer solutions (pH 9.66) in the absence and presence of chloride, using different electrochemical techniques. Analyses of the open circuit potential and the potentiodynamic polarisation curves showed that the passivation domain and the corrosion parameters depend on alloy composition and chloride concentration. Chronoamperometric studies showed that passivation kinetics and corrosion of the passive film are both well described by a linear ln(i) versus ln(t) relation. The passive film formed on the Ag-Sn alloy is less susceptible to corrosion when compared to the Cu-Zn-Al system. The impedance data obtained in the passive region for the Cu-Zn-Al alloy showed that the passive layer is compact. In contrast, the impedance data obtained for the Ag-Sn alloy showed that the passive layer is formed by a compact oxide layer covered by a porous oxide gel layer.Mott-Schottky analysis showed that the passive film formed on the Cu-Zn-Al alloy behaves as a p-type semiconductor.

Impact of pH and temperature on the electrochemical and semiconducting properties of zinc in alkaline buffer media

“…This behavior points to an increase in the polarization resistance of the barrier passive layer on zinc surface as the pH of its contact electrolyte is increased. 20,27 The results of polarization are in good consistency with the behavior of OCP and EIS measurements indicating that buffer carbonate/bicarbonate solution with higher pH value facilitates the formation of a more resistive passive lm on Zn metal with better barrier protection. 3.1.2 Effect of temperature.…”

“…The results in Table 6 reveal continuous increase in the negative value of E FB with the increase in the alkalinity of the medium, being À0.170 V at pH 9.2 and reaching À0.282 V at pH 9.8. This trend indicates lowering in the overpotential for the charge transfer reaction at the semiconductor passive lm/ electrolyte interface and suggests a more facile lm growth on zinc surface in the most basic buffer medium 5,16,27 in good (Table 6), but it decreases with the temperature rise 39 ( Table 7). This could be correlated to a change in the lm thickness (d), being increased with pH and decreased with the increment of formation temperature, as proven from the values of the lm thickness (d) estimated from the impedance data using eqn (4) and illustrated by the bar diagram in Fig.…”

“…Electrochemical impedance spectroscopy (EIS) is a non-destructive powerful technique for studying corrosion and passivation phenomena and can be used to probe in real time any differences in the electrode behavior due to surface modication. [25][26][27][28] Fig. 3a and b presents the impedance spectra of Zn electrode as Bode and Nyquist plots traced aer 30 min from electrode immersion in the test buffer solutions of pH 9.2, 9.4, 9.5 and 9.8.…”

“…30 Due to surface heterogeneity of solid electrode resulting from surface roughness and formation of porous layers, a constant phase element (CPE) is commonly used to replace the capacitance (C) in real electrochemical process, which mainly depends on a non-ideal capacitance behavior. 27,30 The impedance of the CPE is dened as:…”

Characterization of electrodeposited undoped and doped thin ZnO passive films on zinc metal in alkaline HCO3−/CO32− buffer solution

“…This behavior hints to a decrease in the corrosion susceptibility of the metal substrate owing to an increase in the protective efficacy of the formed passive lm with increasing its processing V a value. 36,37 Based on the parallel plate capacitor model, the capacitance of the interface is related to the passive lm thickness (d f ) according to the following relation: 28,38,39 C t ¼ 33 0 A/d f (5) where 3 is the dielectric constant of the passive lm (8.5 for ZnO), 40 3 0 is the permittivity of the free space (8.854 Â 10 À14 F cm À1 ) and A is the geometric surface area of the electrode. Eqn (5) indicates a reverse correlation between C t and d f which points towards a direct increase in the lm thickness (d f ) with increasing the anodizing voltage (V a ) as depicted in Fig.…”