A comparative study on the corrosion behavior of NdFeB magnets in different electrolyte solutions

摘要

Sintered NdFeB magnets possess excellent magnetic properties. However, the corrosion resistance property of NdFeB is very poor due to its multiphase microstructure consisting of matrix phase Nd{sub}2Fe{sub}14B, Nd-rich phase, and B-rich phase. The corrosion behavior of NdFeB magnets in sodium hydroxide (NaOH), sodium chloride (NaCl), nitric acid (HNO{sub}3), and oxalic acid (H{sub}2C{sub}2O{sub}4) solutions was investigated by immersion and electrochemical tests. HNO{sub}3 is the strongest corrosive electrolyte compared with the other three solutions. The increase in HNO{sub}3 concentration can accelerate the corrosion of NdFeB magnets. NaCl belongs to medium corrosion electrolyte. A NaCl concentration of 0.5 M shows the severest corrosive feature in comparison with other concentrations of NaCl solution. NdFeB hardly suffers corrosion in NaOH and H{sub}2C{sub}2O{sub}4 solutions owing to the formation of passivation films on the surface of magnets. Based on the corrosion behavior of NdFeB in different electrolytes, the possible corrosion mechanisms are discussed.