THE CORROSION BEHAVIOR OF SPUTTER-DEPOSITED AMORPHOUS COPPER TANTALUM ALLOYS IN 12-M HCL

Cu-Ta alloys containing 44-91 at% tantalum are amorphous and are spontaneously passive showing almost the same low corrosion rate as that of tantalum metal. Formation of a single fcc Cu phase alloy supersaturated with tantalum of up to 21 at% of tantalum is not effective in enhancing the corrosion resistance in aggressive 12 M HCI. The passive films on the amorphous alloys and tantalum metal consist only of Ta2O5. The passive films on Cu-28Ta and Cu-36Ta alloys consisting of a mixture of microcrystalline fcc Cu phases in the amorphous matrix are composed of TaO2OH and are thicker and less protective in comparison with the Ta2O5 film. Polarization at potentials higher than potentials for oxygen and chlorine evolution prevents the formation of the tantalum-enriched passive film on the amorphous Cu-Ta alloys and results in sharp increase in the anodic current.