Abstract
In the previous paper, the electrochemical phenomena of Ni and Mo in a molten silicate glass of the composition 16 Na2O·12 CaO·72 SiO2 in wt% were investigated. In this paper, W, Cr, Fe, SUS 304 and Inconel 600 were chosen as the objects to be measured. Anodic dissolution, passivation and cathodic deposition for these metals were investigated by linear potential sweep voltammetry at various potential sweep rates (5-0.05V/sec) with platinum reference and auxiliary electrodes in Ar gas atmosphere or in air. Moreover, the metal-glass interface after polarization was analysed by EPMA.
On cathodic potential sweep of every metal investigated here, silicate anions were easily reduced to silicon element and a kind of silicide layer covered the electrode surface. Since the silicide has high electrical resistance, its formation made the measurement of voltammogram difficult at slower sweep rates.
The anodic voltammogram of W at 3V/sec showed a large current peak around 1.7V (relative to Pt reference). The peak potential shifted to more cathodic direction with decreasing sweep rate. The current peak was attributed to the formation of a passsive layer on the W electrode. The occurrence of tungsten oxide layer with 30μm thick on the W electrode was confirmed by EPMA. The oxide layer seemed to be made up by WO3. The broad current peak was observed on anodic voltammogram of Cr due to the formation of chromium oxide Cr2O3. There was no peak on the anodic current-potential curve for the Fe electrode and Fe dissolved rapidly and easily. Both SUS 304 and Inconel 600 were subject to passivation by oxide film formation of Cr2O3 and NiO on anodic polarization.
