Potential in the area of metal surface microroughness


I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Mathematical Models and Computing Experiment in Material Science - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2019, #21


A mathematical model was developed and the potential in the area of microroughness in the presence of cathodic polarization of the metal surface was calculated. On a square grid of discrete approximation of the model, the boundary points of the electrolyte are on the border with the metal (it is assumed that the height of the metal protrusion and its radius are equal). At these points, the dependence between the values of the polarization potential and the current density according to the cathode polarization curve is used. Their values were obtained at protection potentials –0,7; –1,1; –1,7 V. In all cases, the potential of the electrolyte above the microroughness area is practically zero and remains so in the upper part of the micronequality region (0.3 of its height at the protection potential is 0,7 V and 0,6 at –1,1; –1,7 V). The potential in the lower half of the lateral surface of the region (on the border with the metal) in all three cases is close to the protection potential. Almost all current flows from the region of the electrolyte to the metal protrusion through the lower part of the surface, whereas it almost does not pass through most of its upper half. Therefore, the results of the calculation show that on the upper surface of the microroughness area and in the electrolyte above it, the potential is zero. With such a geometry of the boundary between the electrolyte and the metal can be assumed that the corrosion is absent in natural conditions. The potential at the top of this region (microroughness) is close to zero even when the protection potential is equal to –1,7 V. However, the geometry of the microroughness is much more complex and needs additional research.