Abstract
The effects of protection potentials for aluminum in 0.5N NaCl solutions as functions of the potential turning from anode to cathode and all values of pH of the solutions were reported in the preceding paper.
The protection potentials of aluminum were always constant independent of pH values when the border potentials turning from anode to cathode were constantly regulated in 0.5N NaCl solution of pH=4-6, at which an oxide film was produced on the surface of aluminum.
The protection potentials in 0.5N NaCl solutions of pH=4, 5.5, and 6 at the up-down border potentials of+50mV (vs. SCE) were -1.45V (vs. SCE), -1.47V (vs. SCE), and -1.39V (vs. SCE), respectively; and the potentials of these solutions at the up-down border potentials of about -500mV (vs. SCE) were -1.20V (vs. SCE), -1.37V (vs. SCE), and -1.20V (vs. SCE), respectively.
In the same way, the protection potentials of aluminum in 0.5N NaCl solutions of pH=8 and 10 were affected by the border potentials, but were independent of pH values when the up-down border potentials were regulated, on the assumption that Al2O3⋅H2O was formed on the surface of aluminum at the time when the aluminum was put in the solutions.
The protection potentials in 0.5N NaCl solutions of pH=8 at the up-down border potential of+50mV (vs. SCE) and about -500mV (vs. SCE) were -1.36V (vs. SCE) and -1.16V (vs. SCE), respectively; and the potentials in these solutions of pH=10 at the above border potentials were -1.35V (vs. SCE) and -1.16V (vs. SCE), respectively.
The approximate flowing currents of aluminum at the above up-down border potentials were nearly constant independent of pH values.
In 0.5N NaCl solutions of pH=12, the protection potentials of aluminum were nearly constant, about -1.8V (vs. SCE), independent of the up-down border potentials.
