The electrical double layer capacitance at the interface of a platinum electrode and oxide melts in the systems CaO-SiO₂, CaO-SiO₂-Al₂O₃ and CaO-Al₂O₃ was measured by an AC impedance method.
The results obtained are as follows:
(1) Capacitance-Potential curves (C-E curves) measured at various frequencies (0.2∼2.0 kHz) were similar to those for Na₂O-SiO₂ previously investigated.
(2) There were two minima and a hump on the C-E curves extrapolated to an infinite frequency.
(3) The maximum capacitance on the C-E curves increased with increasing CaO concentration and temperature.
(4) The maximum on the C-E curves for CaO-Al₂O₃ melts was larger than those for CaO-SiO₂ and CaO-SiO₂-Al₂O₃.
(5) The minimum capacitances extrapolated to infinite frequency increased with increasing CaO concentration and temperature, and the effect of temperature was more pronounced for basic slags.
(6) The minimum capacitance on the anodic branch was in the vicinity of 100 mV (vs Pt), indicating adsorption of oxygen ions on the surface of the Pt electrode.
(7) The span of E for adsorption or desorption of oxygen ions extended 250 to 300 mV and was independent of slag composition.