Corrosion Behaviour of Hafnium in Buffer Solutions as Revealed by Impedance and Potential Measurements

The growth of thin oxide films (2·0–8·0 nm) on hafnium immersed in aqueous buffer solutions of pH 1–12 has been followed by means of capacitance and potential measurements. Capacitance measurements show that the corrosion reaction film exerts an action on the behaviour of the metal, in that it determines the magnitude of the open-circuit corrosion potential.In the early stages of oxide film growth, the potential of the hafnium electrode was found to decrease by 59 mV/unit increase in pH, whereas in the final stages the potential decreased by 20–30 mV/unit increase in pH. The reason for the deviation from the 59 mV/unit increase in pH in the final stages of oxide film growth may be connected lvith non-uniform oxygen supply, or with variation of the conducting properties of the oxidefilm with its thickness.