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Noble metal coatings are commonly employed to improve corrosion resistance of metals in the electronic and jewellery industry. The corrosion resistance of electroplated goods is currently determinate with long, destructive and almost subjective interpretation corrosion tests in artificial atmosphere. In this study we present the application of electrochemical analysis to obtain fast and numerical information of the antiaging coating. We performed open circuit potential (OCP) and corrosion current measurement; we employed also the electrochemical impedance spectroscopy (EIS), commonly applied to organic or passivated metal with high-impedance, to find the best option for noble low-impedance coating analysis. For comparison, traditional standardized tests (damp heat ISO 17228, salt spray ISO 9227 and sulphur dioxide ISO 4524) were also performed.

Abstract:The passivation of metal electrodes covered by self-assembled monolayers of long-chain thiols is well known. The disappearance of the voltammetric peak of redox species in solution is a classical test for the formation of full layers of thiols. Similar studies on semiconductors are still very limited. We used silver surfaces covered by an ultrathin layer of CdS as substrate for self-assembling of n-hexadecanethiol (C 16 SH), and we compared the experimental results with those obtained by using the bare silver surface as substrate. The strong insulating effect of C 16 SH deposited on Ag(III) is shown by the inhibition of the voltammetric peak of Ru(NH 3 ) 6 3+/2+ . On the contrary, the voltammogram obtained on CdS-covered Ag(III) is very similar to that obtained on the bare Ag(III) electrode, thus suggesting that the presence of CdS exerts a contrasting effect on the passivation of the silver electrode. A crucial point of our work is to demonstrate the effective formation of C 16 SH monolayers on Ag(III) covered by CdS. The formation of full layers of C 16 SH was strongly suggested by the inhibition of the stripping peak of Cd from the CdS deposit covered by C 16 SH. The presence of C 16 SH was confirmed by electrochemical quartz crystal microbalance (EQCM) measurements as well as by Auger electron spectroscopy (AES) analysis.

The overall goal of this work is the use of COMSOL Multiphysics® in the modelling of the current density distributions for the electrodeposition of Aluminium coatings from Ionic Liquids baths. The local current distribution is strongly dependant on the conductivity, on the distribution of concentrations and on the geometry of the galvanic cell, such a calculation can only be performed by the numerical solution of the PDE’s governing the system. This work approach is to exploit computational techniques based on the well-known FEA (Finite Elements Analysis) to obtain stationary and dynamical solutions of such problem. The ability to predict the local current density on an electrode is crucial to eventually evidence portions where the deposition may be invalidated.

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