CORROSION-ELECTROCHEMICAL BEHAVIOR OF AN AIR-EXPOSED Zr–Mn–Cr–Ni–V ALLOY

Abstract

Scanning electron microscopy and X-ray microanalysis found a dendritic structure and chemical inhomogeneity of the ZrMnCrNiV alloy. The corrosion mechanism for alloy without exposure and with exposure in air for 7 and 15 days, followed by aging in a 30% KOH solution is the same: corrosion originates at the interphase boundary and propagates along it, which is typical of pitting corrosion. In the case of preliminary exposure of the alloy in air, its surface has a greater number of pittings, but all of them are smaller in area and depth, which makes the corrosion process more uniform. In hydrogenation–dehydrogenation of this alloy, even more uniform distribution of smaller corrosion areas is observed. Studies of the corrosion resistance of this alloy in a KOH solution carried out by atomic adsorption spectrometry showed that the alloy powder exposed in air had higher corrosion resistance compared to the unexposed powder. Corrosion-electrochemical studies of the alloy conducted in the anode region by the method of polarization curves determined that the corrosion rate for alloy without and with exposure in air is controlled by the rate of formation of passivating films. The most prolonged area of passivation was observed in the alloy exposed in air for 15 days. It show sufficient corrosion resistance in a 30% KOH solution. The studies of the cyclic resistance of electrodes pressed from the alloy powder exposed for 10 days, with a discharge to reach the potential difference E = –1.0 V and E = –0.8 V, demonstrated the effect of oxidation processes during hydrogenation-dehydrogenation on cyclic resistance. It is found that there is a time limit for exposing the alloy in air (as an ingot and/or powder), after which the cyclic resistance deteriorates.