THE ELECTROCHEMICAL HYDROGENATION OF NDFEB SINTERED ALLOYS

The absorption of hydrogen by NdFeB alloys in aqueous solution has bee n investigated using de electrochemical methods and x-ray diffraction. Immersion of the NdFeB alloy in 0.1 M H2SO4 results in the formation of the Nd2Fe14BH27 hydride phase as indicated by x-ray diffraction ana lysis. The hydrogen entering the NdFeB lattice is believed to result f rom the preferential acid dissolution or etching of the Nd-rich phase. The hydrogen absorption and desorption behavior of sintered NdFeB all oys, (NdDy)(15)Fe78.3Al0.7B6 and (NdDy)(15)Fe67Co5V4Al2B7, have been c ompared with that of a LaNi5 alloy utilizing an electrochemical techni que. LaNi5 is capable of absorbing extremely high quantities of hydrog en as a metal hydride. The level of hydrogen absorbed by the three all oys was compared by ''charging'' electrodes of each alloy in 6 M KOH a t a constant cathodic current, followed by a constant anodic ''dischar ge'' current. An arrest in the resulting potential versus time curve d uring discharge indicates the oxidation of the hydride, i.e., of absor bed hydrogen, formed during the cathodic charging process. Results ind icate that both NdFeB alloys absorb hydrogen in aqueous solution. Simi lar experiments performed on a set of samples with varying total rare- earth (TRE) content showed that the amount of hydrogen absorbed is pro portional to TRE content. Anodic potentiodynamic polarization after ch arging shows that the corrosion rate increases as the level of absorbe d hydrogen increases.