Morphological Evolution of Corrosion Pits on the (200) and (211) Surfaces of Tantalum Foil

As an extremely passive metal, tantalum is often used as an additive element in corrosion-resistant alloys. Although the electrochemical corrosion mechanisms of these tantalum-based alloys have been extensively studied, however, the corrosion properties of the tantalum metal itself have received little attention. In this study, we developed a numerical simulation model to qualitatively describe the propagation of corrosion pits on different crystal surfaces of tantalum. The morphological characteristics of the corrosion pits predicted by the model are in high agreement with those observed those observed experimentally, indicating the validity of the model. Due to the difference in crystallographic orientation, the corrosion pits on the surface of (200) have a square shape while those on the surface of (211) have an inverted triangle shape. Although the dimensions of the two types of pits are close, the square pit is more likely to develop deeper and thus the (200) surface exhibits a higher specific surface area. Therefore, the present work provides a reference for the fabrication of etched foils for tantalum electrolytic capacitors.