Effect of impurities on the corrosion behaviour of neodymium

Corrosion studies on highly textured Nd–Fe–B sintered magnets

“…6 shows the current density-potential curves, potentiodynamically recorded in phthalate buffer, which reveal a characteristic behaviour of active dissolution (U corr up to ∼100 mV) followed by stable passivation (∼100-1200 mV) and oxygen evolution (>1200 mV). It has to be emphasized that under anodic conditions the main contribution to the measurable total dissolution current density is attributed to the preferential dissolution of the less noble Ndrich intergranular phase and only smaller contributions are due to the oxidation of the residual phases [3]. Corresponding with the more active state under free corrosion conditions, the parallel magnet side exhibits slightly higher current densities in the active dissolution regime, which may be well attributed to the discussed enhanced dissolution tendency of this side of the aligned Nd 2 Fe 14 B grains.…”

“…The principal corrosion process of isotropic microcrystalline sintered as well as of nanocrystalline hotpressed magnets with Nd-rich composition in aqueous environments has been well established [3][4][5][6]. It comprises the preferential dissolution of the highly reactive intergranular Nd-rich phase (Nd 4 Fe) phase, the absorption of atomic hydrogen causing embrittlement of the material and finally the loosening and detachment of ferromagnetic Nd 2 Fe 14 B grains from the magnet surface.…”

Effect of DyF3 on the corrosion behavior of hot‐pressed Nd–Fe–B permanent magnets

“…The ferromagnetic Nd 2 Fe 14 B phase is surrounded by a Nd-rich phase. In aqueous solution, the Nd-rich phase dissolves preferentially due to its high oxidative reactivity and the galvanic coupling with the Nd 2 Fe 14 B phase [18][19][20][21][22][23][24][25]. Furthermore, hydrogen, which can evolve during the corrosion reaction is partially absorbed by the solid material and causes volume expansion.…”

“…Various additives were investigated regarding their effect on the corrosion behavior. For example, Co [20,22,[37][38][39], Cr [18], Cu [38,40] Al, Ga [38,41] change the composition of the intergranular Nd-rich phase and reduce its corrosion susceptibility.…”

Effect of rare earth metals addition on the corrosion behaviour of crystalline Co–Ni alloys in alkaline solution

“…Rare earth elements are among the most electrochemically active metals, the standard potentials for RE 3+ /RE systems being À2.6 to À2.0 V [28]. It has been established that transition metal alloys containing relatively high amounts (20 mass %) of rare earth elements suffer strongly from corrosion attack both in acidic and neutral media [29][30][31], but very little information is available for the corrosion behaviour in an alkaline environment [32].…”