Abstract
Characterization of the Ag/AgCl electrode is a necessary step toward its application as a chloride sensor in a highly alkaline medium, such as concrete. The nucleation and growth of AgCl on Ag in 0.1 M HCl was verified through cyclic voltammetry. Ag anodization was performed at current densities, determined by potentiodynamic polarization in the same (0.1 M HCl) medium. The morphology and microstructure of the AgCl layers were evaluated via electron microscopy, while surface chemistry was studied through energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. At current density above 2 mA/cm2, the thickness and heterogeneity of the AgCl layer increased. In this condition, small AgCl particles formed in the immediate vicinity of the Ag substrate, subsequently weakening the bond strength of the Ag/AgCl interface. Silver oxide-based or carbon-based impurities were present on the surface of the sensor in amounts proportional to the thickness and heterogeneity of the AgCl layer. It is concluded that a well-defined link exists between the properties of the AgCl layer, the applied current density and the recorded overpotential during Ag anodization. The results can be used as a recommendation for preparation of chloride sensors with stable performance in cementitious materials.
Highlights
IntroductionTime needed for establishing a dynamic equilibrium at the sensor/environment interface
The determination of the chloride content in reinforced concrete (RC) structures is important for the assessment of the probability of chloride-induced corrosion of steel reinforcement
The morphology and microstructure of the AgCl layers were evaluated via electron microscopy, while surface chemistry was studied through energy-dispersive spectroscopy and X-ray photoelectron spectroscopy
Summary
Time needed for establishing a dynamic equilibrium at the sensor/environment interface. As with each electrochemical process of this kind, the anodization regime will affect the produced layer thickness, surface morphology and ionic/electron conductivity, respectively [5, 10] These features of the AgCl layer may subsequently be reflected in the electrochemical response of the sensor [20], especially in alkaline medium. This enabled the inner morphology of the AgCl layer to be well observed This procedure and sequence were chosen for the purpose of clear differentiation of the AgCl layers’ formation on identically handled Ag substrates, but in conditions of different anodization regime (various current density, ‘‘Ag anodization: preparation of Ag/ AgCl sensors’’ section). The relative concentrations of various chemical species were determined by normalization of the peak areas to their photoionization cross sections, calculated by Scofield [29]
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