Abstract
In the previous paper, the results of the studies on anodic dissolution, passivation and catholic deposition of some metals such as Pt, Ni and Fe in molten sodium diborate glass had been reported.
In this paper, the electrochemical behaviors of other electric conductive materials such as Co, graphite, W and Cr were investigated in the same melt by the linear potential sweep method and potential step chronoamperometry. Current-potential curves were obtained at various potential sweep rates (5∼0.5V/sec) and various potential spans between 0 and 5V for anodic polarization and between 0 and -4V for cathodic polarization. All the measurements were carried out under N2 atmosphere at 900°C.
By anodic potential sweep of a Co electrode, the current-potential curve having a large current peak at ca. 1V was obtained. Such a passivation phenomenon may be explained with the oxide film formation on the electrode surface by the reaction, Co+O2-=CoO+2e. By applying higher potential than 3V, a plateau accompanied by small vibrating waves resulting from the oxygen gas evolution was observed on the current-potential curve. A graphite electrode showed a S-shape current-potential curve by anodic polarization in the same way as Pt. Graphite acted as an insoluble electrode, but a marked gas evolution was observed at the anodic potential more than 3V. A W electrode readily dissolved, and no peak was observed. A Cr electrode showed a broad and weak current peak during anodic polarization. As the current density for the Cr electrode on applying further potential was as small as the value for Pt, it seemed that Cr acted as an insoluble electrode.
