Materials Science Forum, Vol.416-4, 54-59, 2003
Characterization of sintered NdFeB magnets after phosphating in alkaline and acidic environments
Despite their excellent magnetic properties NdFeB permanent magnets are highly susceptible to corrosion. Conversion coatings, such as phosphating, have been evaluated as promising methods for corrosion control of these types of magnets. In the present work, alkaline and acid solutions have been used for phosphating a NdFeB commercial magnet. Characterization of the phosphate layer formed in alkaline solution (pH>8) of Na2HPO4, was carried out by Auger Electron Spectroscopy (AES), Energy Dispersive X-ray analysis (EDX), and Electrochemical Impedance Spectroscopy (EIS). AES and EIS results showed that the layer formed in the alkaline solution was not protective. On the other hand, the phosphate layer formed in the acid solution (3,8