Electrochemical behavior of rare-earth magnet alloys in various solutions

Electrochemical behavior of rare earth magnet alloys SmCo₅, Sm₂TM₁₇, and Nd-Fe-B in various aqueous solutions was investigated. Although they are very reactive both in air and aqueous solutions, passivation is still possible in orthophosphoric acid. The ability to passivate, the passivated current density, and breakdown voltage of the passivated films were found to be related to the content of rare earth element, single- or multiple-phase state, and iron content of the alloys, respectively. Galvanic current density of the coupled pairs between one of the magnet alloys and one of the biomedical alloys (amalgam, Co-Cr, and Ni-Cr alloys) was found to be within 3-15 mu A/cm² in synthetic saliva. However a large value of 25 mu A/cm² between a Nd-Fe-B magnet and a Ni-Cr alloy was observed.