Analyse des elektrochemischen Potentialrauschens zur Untersuchung des korrosiven Angriffs auf dünne Schutzschichten am Beispiel von Kohlenstoff auf Aluminium

In the present work the electrochemical potential noise was examined. Therefore the statistic analysis by means of the Fast Fourier Transformation (FFT) was used. This analysis technique was applied to coated aluminium surfaces. A procedure for the analysis of the electrochemical potential noise was established. During the investigations the transferability of the results of the pure metal on the coated surfaces was in the centre of attention. This required the set-up of an electrochemical measuring device for the collection of fast fluctuations in potential. This was attached to a system for data acquisition with a fast data acquisition card and a large memory. The constructed measuring system and the developed software were examined with a precision power supply unit and a function generator for its accuracy. In the further process of the work the constructed measuring system was used to perform several series of investigations on uncoated aluminium surfaces. Here the influence of the temperature, the surface quality of the aluminium samples (polishing degree) and the concentration of chloride ions in the corrosive medium were examined. Further samples with differently thin carbon layers were provided by a sputtering plant and examined both with polarization measurement as well as with the new method of the analysis of the electrochemical potential noise. As the results showed, pitting corrosion of aluminium induces low frequency potential fluctuations with large amplitudes. This shows up in the FFT diagrams in a rise in the low frequency range. The fluctuations arise from crack / heal processes of the oxide from the local dissolution of the oxide, by anion attacks and from the nascence of hydrogen in the holes. These processes start in the porosities of the coating as well as at ranges where the layers adhesion fails. A higher rate of these events leads to a higher rise frequency in the FFT diagram. Here new investigation possibilities are offered for the corrosion of layer / substrate systems with the technology of the statistic analysis of the electrochemical noise.