Electrochemical behavior of rare earth magnet alloys in various solutions

It was found that passivation is not possible for all three kinds of rare earth magnet alloys, SmC05, Sm2TM17, and Nd-Fe-B in 1N sulfuric acid, Ringer's solution, and dilute (10 wt%) orthophosphoric acid, reaching a very high and steady anodic current density (0.1 - 1 A/cm at applied voltages E >1000 mV). Passivation is common for all three kinds of magnets in orthophosphoric acid. The content of rare earth element is the key factor determining the ability to passivate among the magnets. The passivated current density is least for the single phase alloys, SmCo5 and Nd-Fe-B; while the breakdown voltage of the passivated films is proportional to iron content of the magnet alloys. Galvanic current density of the coupled pairs between one of the magnet alloys and one of the biomedical alloys (amal-gam, Co-Cr and Ni2Cr alloys) was found to be within 3–12 A/cm in a solution of synthetic saliva. However a large value of 25 A/cm was observed between a Nd-Fe-B magnet and a Ni-Cr alloy. Detailed electrochemical data of the magnet alloys are given.