PASSIVE BEHAVIOR OF TIN

Quasi-steady (20 h stabilization) and transient polarization measurements coupled with capacitance and passive film thickness determinations (by cathodic reduction) have been performed on high-purity tin electrodes in a phosphate solution of pH 9.5 and 25-degrees-C. Over the potential range from -0.3 to 0.6 V (sce), tin exhibits an essentially potential independent steady-state passive current of about 20 nA cm-2. It also shows a steady-state passive film thickness, an inverse electrode capacitance and an initial Tafel slope which all increase linearly with the stabilization potential. The data yield interfacial charge densities and Volta potential profiles for passive tin electrodes, and they elucidate the ion transfer process occurring at the metal-oxide interface of such electrodes.