Argentum Solutions, Inc.
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David C. Silverman |
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Much of corrosion, especially of metals and alloys, is electrochemical in nature. Electrochemical measurements, therefore, play a major role in corrosion assessment and prediction. The reference electrode is one of the foundations of the electrochemical measurement. All measured voltages (potentials) are the difference between two values. In an electrochemical measurement, one of these voltages must be constant. Then, the changes in the measured voltage reflect changes in the interaction between the metal and its environment, changes in corrosion behavior. The purpose of the reference electrode is to create a fixed potential against which the potential of the test (or working electrode) is measured. Since the reference electrode is so critical to electrochemical measurements, a basic understanding of its characteristics is necessary in order for the corrosion practitioner to be able to assess the validity of any electrochemical measurement. Many reference electrodes exist. The choice of which to use often depends on the environment being examined. The key requirement for potential measurements in corrosion is a reference that has a stable potential under the conditions in which it is being used. Another requirement is that the measurement must be made at "zero" current (actually an extraordinarily low current). A high impedance voltmeter is the necessary device for such a measurement. Reference electrodes have been reviewed in the literature. Perhaps the most extensive review of the more important laboratory reference electrodes is that provided in "Reference Electrodes - Theory and Practice", D. J. G. Ives and G. J. Janz, Academic Press, 1961. This reference itself is fairly old but most of the information provided remains relevant. Though modern reference electrode technology has tended to emphasize making the electrodes themselves more robust and offering faster response, the chemical knowledge behind the commonly used reference electrodes has tended to remain as it was in this earlier reference. This tutorial summarizes several areas that are important in understanding the principles behind the reference electrode response for those more commonly used in corrosion related electrochemical measurements. The areas covered are:
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David C. Silverman, Ph.D. - Primary Consultant |