VOLTAMMETRIC, OPTICAL, AND SPECTROSCOPIC EXAMINATION OF ANODICALLY FORCED PASSIVATION OF COBALT-TUNGSTEN AMORPHOUS-ALLOYS

Passivation and corrosion of thin layers of amorphous Co-W alloys were examined using potentiometry with linear current change, voltammetry, and anodic current pulsation. The state and the composition of the an odized alloy surface were determined by x-ray diffraction, electron mi croprobe spectroscopy, and optical microscopy. Investigations performe d in noncomplexing electrolytes indicated that passive layers on the a lloy are easily formed and are stable in acidic solutions. They can be formed also in alkaline solutions, under conditions of larger current . In neutral solutions an effective protecting layer cannot be obtaine d during anodization. In this pH range, selective oxidation of cobalt takes place, and amorphous tungsten is formed on the surface. The tung sten layer is loose and does not protect the base metal against furthe r dissolution. Prolonged application of anodic current to the amorphou s layers, at any pH, leads to appearing of cracks on the surface. The behavior of amorphous and polycrystalline, homogeneous alloys were com pared also.