Monitoring and measuring electrochemical behavior of engineering alloys by optical interferometry

Abstract

In a previous study, an optical corrosion meter was built based on a mathematical model relating to surface and bulk behaviors of metals in aqueous solution. The optical corrosion meter was established based on principles of holographic interferometry for measuring microsurface dissolution, i.e., mass loss, and on those of electrochemistry for measuring the bulk electronic current, i.e., corrosion current. The corrosion meter consists of an electrochemical cell in which the sample is immersed in aqueous solution. Furthermore, the corrosion meter has a holographic camera with a thermoplastic film for in situ processing holograms in order to obtain real-time holographic interferograms of the sample in the electrochemical cell. Results of the present work indicate that optical holography is a very useful technique for measuring the corrosion current density of different alloys in aqueous solutions. As a result, the corrosion current density of aluminium, stainless steel, low carbon steel, copper, and brass in 1M KCl, 1 M NaCl, 1 M NaOH, seawater and seawater solutions, respectively, were obtained. The obtained corrosion data from the optical corrosion meter (interferometric technique) were compared with corrosion data obtained on the same alloys in the specified solutions from the linear polarization method as well as from the weight-loss method. The comparison among the three techniques indicates that there is contrast in the results among the investigated alloys. In general, the new method of optical interferometry can be considered a more conservative method of corrosion measurement with respect to the linear polarization and weight-loss methods.