Oxidation and oxidation protection of Nd-Fe-B magnets

The corrosion behavior of Nd-Fe-B magnets was studied in oxidizing environments, including dry and humid air at 150°C and room temperature. The kinetics for oxidation of chloride free Nd-Fe-B magnets generally exhibit parabolic weight gain in the given environments, and show much slower
(\sim1/10)
oxidation rates than those of chloride contaminated Nd-Fe-B magnets. The oxidation rate of the magnets usually decreases as surface finish becomes more polished and clean. The oxidation rate of chloride free Nd-Fe-B magnets at 150°C is substantially reduced from that at room temperature by limiting the formation of iron oxide (or hydroxide) on the surfaces. In severe corrosion environments, such as aerated salt water baths, epoxy coated Nd-Fe-B magnets displayed excellent corrosion resistance.