Attachment between mercury and argon bubbles in aqueous KF solutions

The attachment between mercury and argon bubbles in aqueous solutions was studied using a mercury electrode by varying the polarization potential of mercury and the KF concentration (5 × 10^-4-1 M). The polarization potential of mercury was converted into the potential of the Stern plane, ψ_δ. There were two critical potentials, negative ψ^-_δ and positive ψ⁺_δ, between which mercury and single bubbles show spontaneous attachment upon contact. In a more negative potential range than ψ^-_δ, there was strong repulsion, while in a more positive potential range than ψ⁺_δ, repulsion was relatively weak. The negative values of ψ^-_δ decreased with increasing KF concentration with a sign reversal at KF concentrations higher than 1 × 10^-2 M, and the positive values of ψ⁺_δ also decreased with increasing KF concentration; the range of ψ_δ of mercury for spontaneous attachment became narrow with increasing KF concentration, that is the lower the concentration the easier the attachment, in contrast to the prediction of the colloid stability theory. The trend of ψ^-_δ in a dilute KF concentration range (< 10^-2 M) was interpreted in terms of the heterocoagulation theory with the negative Hamaker constant for mercury-bubble in water. Zeta potentials (ζ_B) of bubbles in aqueous KF solutions assessed using ψ^-_δ with the aid of the heterocoagulation theory showed anomalous behavior at high KF concentrations.