Determination of corrosion rate from electrode kinetic measurement

Electrode kinetic measurements provide a valuable technique for determining the corrosion rates of metals. The processes controlled by activation polarization are described by an exponential type of relation involving three unknowns. Corrosion behaviour of a metal can be fully described if these three parameters i.e. corrosion current, Ic and the two Tafel constants Beta/sub a/ and Beta/sub c/ are known. Experimentally the current density is measured as a function of the applied over relationship is such that an accurate determination of the three parameters by Ordinary Least Squares Fit is generally not possible. Various attempts have been made to simplify the equation using approximations. These are reflected in the well known methods such as Tafel Line Extrapolation and Linear Polarization. In Three Point and Four Point methods, selected data points are used which transform the original equation into similar relation such as a quadratic equation. Recently some computer based methods have been developed such as BETACRUNCH in which the method of averages is used. We have developed a new method to analyze experimental polarization data and determine the unknown parameters. We have formulated three independent relationships to solve for Ic, Ba and Beta/sub c/. In addition to the original version we have improved the methods by using some additional numerical approaches. These methods are robust and give accurate determination of Tafel constants and the corrosion current density for a wide range of systems. Using the suggested scheme, it is also possible to avoid data corresponding to very low and very high over potentials and yet obtain excellent results. These methods are less sensitive to experimental errors as compared to other existing methods. (author)