THE BEHAVIOR OF CHROMIUM SPECIES INCORPORATED INTO ANODIC OXIDE-FILMSON BISMUTH

The behaviour of chromium species incorporated into anodic oxide films formed on bismuth in chromate solution has been shown to be strikingl y different from the behaviour of chromate species incorporated into a nodic oxide films on aluminium, tantalum and niobium. in the case of a nodic oxide films formed on bismuth, where the electric field within t he growing oxide is comparatively low, CrO42- anions do not dissociate to give cationic species, such as Cr6+ or Cr3+ ions, which subsequent ly migrate outwards as observed in anodic oxide films on aluminium, ta ntalum and niobium. Consequently, for anodic oxidation of bismuth, the incorporated CrO42- anions migrate inwards towards the metal/oxide in terface, as observed for PO43- and SO42- anions. These observations gi ve new insight into the role of the electric field, generally and loca lly, on the dissociation or non-dissociation of various structural uni ts within the growing oxide. Such information is of key importance in the progress towards the development of an integrated model of the ion ic transport processes involved in anodic oxide growth.