Electric melting has been widely applied to glass melting in glass industries. However, there are few experimental data concerning the reaction at electrode-molten glass interface.
In this paper, the electrochemical behavior such as anodic dissolution, passivation and cathodic deposition was investigated for nickel and molybdenum in a molten silicate glass of the composition 16Na2O·12CaO·72SiO2 in wt% at 1300 and 1400°C, respectively. Linear potential sweep voltammetry was carried out at various potential sweep rates (5-0.002V/sec) up to ±5V by using a platinum electrode as reference and auxiliary in Ar gas atmosphere. Moreover, the metal-glass interface after polarization was analysed by EPMA.
On cathodic potential sweep of Ni, silicate anions were easily reduced to silicon element and a kind of nickel silicide layer covered the electrode surface. Since the nickel silicide has high electrical resistance, its formation made the measurement of voltammogram difficult at slower sweep rates. The anodic voltammogram of Ni at 3.0V/sec showed a large current peak around 1.2V (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 passive layer on the Ni electrode. The occurrence of NiO layer with 15μm thickness on the Ni electrode has been confirmed by EPMA when Ni was oxidized at 3V for 3min. On cathodic polarization of Mo, Mo formed molybdenum silicide layer with high electrical resistance. The thickness of layer and the ratio of Si/Mo in the layer increased with increasing cathodic potential. The pronounced current peak was observed around 0.4V on anodic voltammogram of Mo, followed by a stationary current up to 4V at 3.0V/sec. The current peak was accompanied by a discernible shoulder at 1.0V/sec and split into three peaks at slower sweep rates than 0.05V/sec due to the formation of molybdenum oxides such as MoO2, Mo2O5 and MoO3. At slower sweep rates a stationary current with many small irregular was found, which can be attributed to the volatilization of MoO3. The occurrence of a stationary current indicates that the layer is made up by a stable oxide like MoO2 and the surface of Mo electrode is covered almost perfectly with the oxide layer.
