KINETICS OF THE PASSIVATION OF MOLYBDENUM IN SALT-SOLUTIONS AS INFERRED FROM IMPEDANCE AND POTENTIAL MEASUREMENTS

The oxide film formed on the molybdenum electrode in sodium salt solutions of different anions was found to thicken according to a logarithmic growth law. The rate of oxide film thickening in the respective solutions was in the order Na//3PO//4 greater than Na//2SO//4 greater than NaCl greater than NaNO//3. The equilibrium potential was found to be independent of anion concentration in the case of Cl** minus and NO//3** minus and was slightly dependent on the PO//4**3** minus and SO//4**2** minus concentrations. Complex plane analysis showed that the double-layer capacitance affects the measured capacitance and an electrical model was proposed to explain the alternating current behavior of the electrode-electrolyte interface.