This paper presents a review of multielectrode array systems and sensors for electrochemical studies and corrosion monitoring. Uncoupled multielectrode arrays [also called wire beam electrodes (WBEs)] for corrosion studies were reported in 1991. Coupled multielectrode arrays were first reported in 1996 for studying the spatiotemporal electrochemical behavior and corrosion processes, and in 1997 for mapping localized corrosion. More recently, coupled multielectrode array sensors (CMASs) have been used for real-time measurement of localized corrosion rates. The various application examples for the CMAS probes, including quantitative localized corrosion monitoring in aqueous solutions, wet gases, oil/water mixtures, salt deposits, biodeposits, soil, concrete, and undercoatings were reviewed. Some of the limitations of the multielectrode array systems are discussed.
A multielectrode system is an integrated device that has multiple electrodes. In this paper, a multielectrode system is called a coupled multielectrode system if the electrodes in it are connected together through an external circuit and these electrodes are essentially at the same potential. A multielectrode system is called a multielectrode array if the electrodes in it are spatially arranged in a regular pattern (e.g., 4×4, or 10×10 array). The coupled multielectrode systems were reported for corrosion detection in concrete nearly two decades ago, and for crevice corrosion measurements nearly 13 years ago. The concept of multielectrode arrays was first reported, in the uncoupled form, 15 years ago for corrosion studies. The first published coupled multielectrode array was used for studying the spatiotemporal electrochemical behaviors and corrosion processes of iron in sulfuric acid solutions 10 years ago. Because the electrodes in a multielectrode array can be arranged in any given pattern and each of electrodes is addressable, the coupled multielectrode arrays have been widely used by researchers to study the corrosion processes, especially the localized corrosion processes, of metals.
Recently, coupled multielectrode arrays have been used as sensors [called coupled multielectrode array sensors (CMASs)] for online and real-time monitoring of corrosion in laboratories and industrial fields. Because a CMAS does not require the presence of bulk electrolytes, CMAS probes have been used to quantitatively measure the localized corrosion of metals not only in aqueous solutions, but also in wet gases, oil/water mixtures, salt deposits, biodeposits, soil, concrete, and undercoatings. CMAS probes were also used for real-time monitoring of the performance of cathodic protection systems. In addition to the real-time measurement of the quantitative rate of localized corrosion, such as pitting and crevice corrosion, CMAS probes have also been used to measure the average corrosion rates. This paper presents a summary of the development of the coupled multielectrode array systems, with a focus on the applications of CMASs in laboratories and industrial fields. Some of the limitations of the coupled multielectrode array systems are also reviewed.
COUPLED MULTIELECTRODE SYSTEMS FOR CORROSION DETECTIONS
One of the devices described by Schiessl in a U.S. patent issued in 1991, and in a patent application initially filed in Germany in 1988 appeared to be the first coupled multielectrode system for corrosion monitoring (Figure 1). This coupled multielectrode system consisted of multiple steel anodes that were composed of materials similar to the reinforcement material and a corrosion-resistance cathode. Both the anodes and the cathode were embedded in a concrete structure. The steel anodes were spaced from one an
