THE THERMOKINETIC INSTABILITY OF THE SURFACE-COVERING LAYERS DURING HIGH-RATE ANODIC-DISSOLUTION CONTROLLED BY MASS-TRANSFER

Anodic dissolution of copper is experimentally studied in nitrate solu tions (0.220 A cm(-2)) in a cell with chaotic electrolyte agitation. T he study is conducted at different electrode configurations, specifica lly: (a) a stationary disk electrode and (b) a model of large artifici al pitting. The experimental results are utilized to show that the act ivation of anodic dissolution and the loss of stability of the surface -covering layers in one case and the absence of the latter in the othe r can be attributed to different heat exchange conditions. It is confi rmed experimentally that activation in the (a) case is observed under the condition T-s > T-s(c), where T-s(c) represents a critical surface temperature corresponding to transition to thermokinetic instability. The (b) case, on the other hand, is characterized by passivation, whi ch occurs at the same current densities, because T-s < T-s(c). It is d emonstrated that the loss of stability of surface layers comprising di ssolution products, which is observed at T greater than or equal to T- s(c), is associated with the kinetic (thermofluctuation) nature intrin sic to the strength of the solids.