Electrochemical measurements, like potentiodynamic methods, to examine the materials' susceptibility to corrosion, were found to be inappropriate in electrolytes exhibiting low ionic conductivity. This limitation is due to the high resistance of the electrolyte, which requires a voltage supply outside of the capabilities of standard electrochemical equipment. Electrochemical impedance spectroscopy enables one to study the polarisation resistance regardless of the conductivity of the electrolyte, i.e. measurements in non-polar, low conductivity liquids like biofuel. In this study the corrosion behaviour of stainless steel AISI 420 (DIN 1.4034) exposed to biofuel was evaluated by applying the impedance spectroscopy technique. An applicable reference electrode for these fuels was developed, whereas the distance between the working and the reference electrode had to be minimized and kept constant. Even small variations in distance were found to have a significant influence on the results. In addition, the water and chloride contents of the fuel were varied in the investigation. The materials variables were the structure of the surface and the heat treatment conditions. The results of the measurements were compared with the results of immersion testing. The test samples were immersed for one week under the same conditions as those in the impedance tests.
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