ON THE CAPACITANCE OF PLATINUM ELECTRODES IN Na2O-SiO2 MELTS.

The capacitance of platinum electrodes in Na//2O-SiO//2 melts was measured by the alternating current bridge method in order to obtain information on slag-metal interfacial structure. The results obtained are as follows: Capacitance-potential curves measured by various frequencies (0. 2 similar 2. 0 kHz) have the maximum capacitance in the vicinity of minus 200 similar minus 300 mV(vs Pt) and two minimum capacitances on both sides of the maximum capacitance, and abruptly rose above 200 mV on the anodic side and under minus 400 similar minus 500 mV on the cathodic side. The capacitance-potential curve obtained by extrapolating to infinite frequency is parabolic with a hump at the natural electrode potential. Oxygen ions in melts is adsorbed onto the platinum electrode surface in the vicinity of the natural electrode potential indicating the minimum capacitance on the anodic side for various frequencies. Adsorption-desorption reaction of oxygen ion occurs in the vicinity of the potential indicating the maximum capacitance ( minus 300 similar minus 450 mV). The platinum surface is stripped by oxygen ions over the range of minus 300 to minus 450 mV and is occupied by Na** plus ion. The minimum capacitance extrapolated to infinite frequency and the maximum capacitance for several frequencies increase with increasing concentration of Na//2O in slag.