Applicability of the Levich Equation for a Two-Phase Solution in the Rotating Disk Electrode System

The mass-transter characteristics of a two-phase system formed by mixing a fixed quantity (20 v/v%) of organic solvent with an aqueous ferricyanide electrolyte solution in an RDE system were studied. The Levich eqution, I₁ = 0.62 nFAC_bD^2/3v^?1/6_ω^1/2, was found to be applicable to the two-phase system with only a minor modification in the angular velocity (ω) at Reynolds numbers between 3–5 × 10⁴. The experimental results indicate that the interfacial tension is the most important variable for the two-phase system. One group of organic solvents with smaller interfacial tension, such as benzene or toluene, needs a modification of the Levich equation by replacing the observed angular velocity (ω_o) with the true angular velocity (ω_t) which was observed to be 1.1 times the observed angular velocity. For the other group with larger interfacial tension, such as n-hexane or cyclohexane, there is no need to modify the observed angular velocity. In other words, the Levich equation may be expressed as I₁ = 0.65 nFAC_bD^2/3v^?1/6ω^1/2 for two-phase solution if the interfacial tension is smaller than 37.0 dyne/cm.