Moving Boundary Simulation of Iron-Zinc Sacrificial Corrosion under Dynamic Electrolyte Thickness Based on Real-Time Monitoring Data

Abstract

The electrolyte film thickness condensation and evaporation is an important parameter for complexity of atmospheric corrosion. Atmospheric corrosion rate of zinc at the west coast of Singapore was measured for one year using an electrical resistance monitoring system. The analysis of the data reveals that significant corrosion rates only occur at specific hours on dry days. The beginning of this period corresponds to falling temperature and rising relative humidity resulting in the formation of a film of moisture on the zinc surface and the end corresponds to a point that this film dries as the temperature increases. This finding allowed the drying rate of the moisture film to be estimated for input into a moving boundary simulation model of the galvanic corrosion in scratched and zinc coating samples. The simulation results showed that the maximum corrosion rate occurs at electrolyte thickness of about 8 μm. Moreover, the simulation suggested that cut-edge is a more harmful defect than scratch, which was confirmed by the appearance of iron corrosion products on atmospheric exposed cut-edge samples whereas scratched samples were not corroded after one week of exposure. Finally, moving boundary simulation allowed to predict the changes to the geometry of the corroding electrodes.