Corrosion of Neodymium Magnets in Polyligand Solutions

We present the results of investigation of the corrosion behavior of rare-earth neodymium magnets doped with cobalt and dysprosium in media that contain ammonium and pyrophosphate ions and belong to the class of complex electrolytes intended for electrodeposition. We use the methods of cyclic and linear voltammetry, chronoamperometry, chronopotentiometry, and the weight method. In polyligand ammonium-pyrophosphate solutions, the corrosion potential of a magnet occupies an intermediate position between the values typical of pyrophosphate and ammonium solutions and the corrosion current is lower. The weight losses of doped magnets in polyligand solutions without currents decrease as a result of alkalization. It is shown that, in the presence of currents, the weight losses are minimal near the stationary potential and increase both in the case of anodic dissolution of the magnet and in the presence of cathodic degradation caused by hydrogen release. Under the conditions of periodic variations of the potential of the magnet near its stationary value realized in the course of formation of the multilayer coating, the weight losses become much lower and equal to 0.42 mg/(cm 2 · h) . The potential of a doped magnet immersed in a polyligand electrolyte for the deposition of (Cu–Ni)/(Ni–Cu) multilayer coatings corresponds to the potential range (– 0.8–(– 0.7 V)) of deposition of compact copper layers. The current density of contact exchange almost attains its maximum value of 0.95 mA/cm 2 for the first minute and almost completely decays after 40 min.