Application of gravity electrode to the analysis of iron-pitting corrosion under vertical gravity field

Vertical gravity field effect on iron-pitting corrosion in chloride solution was examined, and a new method for analyzing pitting corrosion with gravity electrode was proposed, i.e., in this method, instead of a potential step, a gravity field step is applied to an electrode system, so that this method is superior to the measurement for pitting corrosion in natural state. After a vertical gravity field is imposed, a number of minute convection cells, which control the corrosion rate, are formed on the electrode surface. In view of the interaction between the convection cells and nonequilibrium fluctuations from corrosion, pitting corrosion state of passivated metal can be analysed; i.e., the coverage of passive films, and the corrosion rate on the active sites without passive films can be obtained (in the present case, 0.531 A m−2). In experiments under vertical gravity fields, the change of the corrosion potential of iron in NaCl solution increased in proportion to the 1/3rd power of gravitational acceleration. At the same time, the corrosion rate also increased in proportion to the 1/3rd power of gravitational acceleration. These results strongly suggest that there is no interference between nonequilibrium fluctuation accompanying the pitting corrosion and gravitational convection cells induced in a vertical gravity field.