The structure of the mercury-electrolyte interphase in the presence of thiourea

Abstract

Some recent results on the adsorption of thiourea from aqueous NaF solutions at mercuryelectrodes are analyzed. It is shown that the adsorbed molecules behave as if they constituted a two-dimensional imperfect gas. The constants of the adsorption isotherm are interpreted in terms of a simple model, from which is obtained by two methods the dielectric constant of the inner part of the double layer. The dielectric constant is independent of the surface concentration of thiourea, but dependent upon the charge on the mercury, being about 12 when this is zero and falling to 8 when it is — 12 μC/cm 2 . The thickness of the inner region is constant at about 4 Å in the absence of thiourea, but increases to about 5 Å at the highest surface concentrations studied. The total capacity of the inner layer as a function of charge and thiourea concentration can also be interpreted using this model.