The title subject is studied by galvanostatic E-t curves on 20 h stabilized passive tin electrodes in weakly alkaline phosphate solution (pH 9.5) at 25-degrees-C. These curves generally exhibit a small initial superpolarization ascribed to transient changes in the surface density of kinks (s) by the current density (j) applied. Obedience is found to the Cabrera-Mott equation for irreversible metal ion transfer from kink sites in the metal surface and to the oxide film. For the steady-growth kink density and the ion transfer valence, it is found that d log s/d log j = 0.5 and n = 2, respectively. No space-charge effect is seen in passive films growing at rates up to 100 muA cm-2 (the highest current applied).