Method of protecting magnetic powders and densified permanent magnets of the Fe Nd B type from oxidation and atmospheric corrosion

摘要

The invention concerns a method of protecting magnetic powders and permanent magnets containing at least one rare earth, at least one transition metal and boron from oxidation and atmospheric corrosion, by the introduction of gaseous fluorine during the grinding of the powders. It is characterized in that the fluorine is introduced by a mixture of F2+N2 during the fine grinding of the powders, the mixture containing from 1 to 100 ppm (by volume) of fluorine, and preferably from 1 to 10 ppm. The powders thus obtained are far less reactive and the densified magnets are far more resistant to atmospheric corrosion than non fluorinated powders and magnets obtained therefrom.