Laser optical interferometry as a zero resistance ammeter: fundamental and applications

Abstract

It is well known that electronics instrumentation, i.e. Ammeter, Potential-meter, have been used for years to measure electrochemical properties of metallic electrodes in aqueous solutions. One of the disadvantages of using electronic instruments for the measurement of electrochemical properties is the invasive nature of those instruments to the electrochemical systems of the metallic electrodes in aqueous solutions. In recent works published elsewhere [1–16], it has been shown that laser optical interferometry can be used as an optical transducer to characterize the electromagnetic field, i.e. phase and amplitude of the reflected light waves of a surface of a metallic electrode moving further away from the light source, which develops as a result of the electron conduction in metallic electrodes in aqueous solutions due to the anodic reaction, corrosion processes, between the electrodes and the aqueous solutions. The characterization of such electromagnetic field (phase and amplitude of the reflected light waves of a surface) and a mathematical correlation of the electromagnetic field to any electrochemical properties, i.e. corrosion current density, double layer capacitance, alternating current impedance, and so on, would lead to the measurement of the electrochemical properties by optical interferometry, by the non-invasive method. In the present work, the corrosion current density of a pure Copper (99.8% Cu), an Aluminum–Brass alloy (76% Cu, 22% Ni, and 2% Al), and a Stainless steel (UNS No.304 Stainless steel, 19% Cr, 9% Ni, 0.45% Mn, and rest Fe) were obtained in natural seawater, respectively. Also, the corrosion current density of the same Stainless steel (UNS No.304 stainless steel, 19% Cr, 9% Ni, 0.45% Mn, and rest Fe) was obtained in 1 M NaCl solution. The obtained corrosion data from the optical interferometry technique, as a zero resistance ammeter were compared with corrosion data obtained on the same alloys in the specified solutions from an electronic zero resistance ammeter as well as from the linear polarization method. The comparison among the three techniques indicates that there is contrast in the results among the investigated alloys. In general, the results of the optical interferometry were found in agreement with the electronic zero resistance ammeter as compared with the linear polarization method. As a result, the optical interferometry can be considered as a useful zero resistance Ammeter for measuring the corrosion current density of metallic electrodes in aqueous solutions at the open circuit potential of the electrodes in the aqueous solutions.