Determination of the zero-charge ph value of a passive iron surface in aqueous solution

摘要

Two techniques of measurement of pH(0), which represents the pH of solution at which the total charge of passive metal electrode surface is zero have been developed. The procedures are based on the use of acid-base equilibria between oxide on electrode surface and solution. In the former technique, the pH of the drop of solution that is applied onto the electrode surface is measured. At pH(0), the pH of the drop does not change in time. In the latter procedure, the potential of a passive electrode that is immersed into solutions with various pH values is measured. pH(0) has been measured on a passive iron electrode. The pH(0) values measured by the two procedures are similar. Comparison of pH(0) of passive electrode and various oxides one to determine the composition of a passive film. The introduction of surface-active ions Ba2+ and Cl- to the solution leads to a shift of pH(0) values and electrode potential in opposite directions.