Contact Electric Resistance (CER) Technique for In-Situ Characterisation of Surface Films

In this paper a new in situ contact electric resistance (CER) technique for the measurement of electric resistance of surface films is described in detail. The applicability of this technique to characterise electrochemical phenomena is evidenced. Also the complementary nature of the CER technique to other electrochemical techniques is shown. The CER measurement enables monitoring of e.g. adsorption, oxide growth and reduction processes. It can also be applied at negative potentials where hydrogen evolution occurs and in electrolytes which contain a redox-couple having a significant exchange current density. The application areas of the CER technique include e.g. investigation of the role of adsorption in electrocatalysis, characterisation of conducting polymers, optimisation of electroplating processes, investigation of the effectiveness of inhibitors and monitoring of the kinetics of oxide growth in high temperature water. Correlation of CER results with practical corrosion phenomena such as weight gain and stress corrosion cracking susceptibility have been established. In this paper CER results on AISI 316 stainless steel in a borate buffer solution at 200°C are compared with a current-voltage curve and capacitance measurements in the same environment. As another example the electric resistance of the surface film on nickel and Inconel 600 are shown as a function of time in a high temperature (320°C) aqueous environment with varying dissolved hydrogen content.