Starting from the elementary corrosion reactions on a passive metal surface a model is developed for the origin of electrochemical noise. The ion currents flowing at the electrochemical reactions are described by the electrons remaining in the metal and then interpreted as a measuring signal. The measurable sum current is composed of the superimposition of the electron currents of the partial reactions. Due to the in-homogeneity of the metal surface, local metal dissolutions take place in preferential areas until the area is consumed or repassivated after short times. The short-time surplus of free electrons leads for every metal dissolution event to a current transient, which itself consists of the partial currents of the elementary anodic and cathodic reactions. Due to the different reaction speeds, there are temporary charge disequilibria and thus measurable noise transients. In model calculations the influence of the diffusion of the oxygen on the sum signal as well as the variation of the anodic current is shown. Furthermore, the results show that a measurable noise signal can only arise under certain conditions. This signal arisen directly at the metal surface is not, however, ascertainable without further amplification. In the measurement amplifiers filter stages play an important role for signal conditioning. The influence of the measuring technique is shown at the filtration of a simulated test signal in different frequency domains. It is discussed how the signal distortion affects the detectability of the partial reactions described at the beginning and in which way the noise signal is estimated. Indications for the layout of suitable measuring parameters are given.
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