Electrochemical Behavior Research Of Metal Corrosion Under Thin Electrolyte Lay

Electrochemical corrosion of the metal under thin electrolyte layer is one of the most important features of atmospheric corrosion. It will form thin electrolyte layer on the metal surface, because of evaporation, agglomeration and capillary condensation, adsorption or chemical coagulation caused by temperature and climate changing. The thickness and the dispersion of the film will vary with the changing of the weather conditions and the alternation of day and night. In the 1940s, Tomashov reported that the rate of metal corrosion under thin electrolyte layer is influenced by the thickness of the water film. Since the qualitative relationship between the water film thickness and the atmospheric corrosion rate has been proved by the following experiments. But, the metal corrosion behavior should be studied quantitatively in order to research the mechanism of atmospheric corrosion. So using the electrochemical methods to study the metal corrosion under thin electrolyte layer is necessary. And it also has great significance to develop appropriate electrochemical testing equipment, testing technique and data analytic method.In this paper, the control of water film thickness and its influences were researched. Finally, the satisfactory devices of water film thickness control and measuring were established. The water film thickness can be controlled to meet the requirements for electrochemical testing, and the measuring error of thickness was less than 2μm.Using Kelvin Probe as reference electrode, polarization testing method was made on electrochemical measurements on electrode covered with thin electrolyte layer. And impedance testing method was also established by using micro-elctrodes technology. The two testing methods established can effectively measure the electrochemical features of metal under thin electrolyte layer. The experimental results can be explained by traditional electrochemical methods and also can be compared with the results measured in the solution.The features of polarization and impedance of metal corrosion under thin electrolyte layer were primarily analyzed. The corrosion behavior was simply evaluated by analyzing the diffusion-limiting current of oxygen, anodic polarization current, solution resistance and other electrochemical parameters.The differences of corrosion behavior of carbon steel under thin electrolyte layer by changing the concentration of Na₂SO₃ were primarily studied using Kelvin probe reference electrode and impedance method. The results showed that not the anode reaction but the cathode reaction was influenced by changing the concentration of Na2SO3. At the same thickness, the corrosion rate of carbon steel firstly increased and then decreased with increasing of the concentration of Na2SO3 solution.