Dissolution of metallic materials in the pseudopassive state in alkaline media

This review article presents examples of the intense dissolution of aluminum, silicon, tungsten, molybdenum, zinc, cadmium, tantalum, and niobium in alkaline electrolytes when these metals are in a pseudopassive state.The pseudopassive state of metals differs significantly from the passive state.Unlike the transition of metals to the passive state, which is characterized by a considerable decrease in the dissolution rate and a positive shift of the free corrosion potential, the pseudopassive state is associated with a high dissolution rate and considerable negative free corrosion potentials.A common feature of the passive and pseudopassive states is a nearly constant current density during anodic polarization of metallic samples, which in many cases indicates chemical dissolution of the surface film and its rapid, almost instantaneous, reduction.However, while the chemical dissolution rate in the passive state is low, it becomes significantly higher in the pseudopassive state.The high dissolution rate of metallic materials in the pseudopassive state serves as the primary mechanism of electrochemical and chemical polishing of metals.