The rapid and accurate measurement of electrochemical phenomena is of considerable importance for a wide range of studies like corrosion, effectiveness and life of surface coatings, battery testing, electrode kinetics, double-layer studies etc. Of these, corrosion and surface treatments are discussed in detail in this work, although the basic mechanisms are broadly similar for all the applications.
It is possible to measure the corrosion rate by direct analytical methods like weight loss measurements etc; but, because the corrosion process is very slow, these methods are time consuming and inefficient. Further, they are restricted to systems in which the products formed by corrosion do not form adherent layers. As the processes under consideration (corrosion and surface treatments) are electrochemical in nature, it is possible to analyze them using electrical methods, based on faraday’s laws, which relate the change in mass per unit area to the current flow.
The advantages of this approach are a relatively short measuring time, high accuracy and the possibility of monitoring the process continuously. The major disadvantage of this approach is that the system under investigation has to be perturbed from its normal state by an external signal, which inevitably changes the properties of the system. The perturbation itself can be due to an AC or DC signal and it is primarily with AC methods.
The DC technique is widely used for corrosion rate measurement. But this method generally requires large perturbation signal and can infact fail when the corrosion process is taking place in a low conductivity medium. AC methods are finding increasing applications in electrochemical research because only small perturbation signals, which do not disturb the electrode properties, are used and can be investigated in low conductivity media.
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