The degradation of polymer-bonded Nd-Fe-B magnets (abstract)

The susceptibility of Nd-Fe-B magnet powders to oxygen and chloride ions is well known, however, the interactions between magnet alloy powders and polymeric binders in bonded magnets can also lead to severe irreversible losses. The losses observed for polymer-bonded Nd-Fe-B magnets in some cases can be more substantial than the losses due to oxidation or corrosion alone. The aging characteristics of polymer-bonded magnets have been examined with respect to time, temperature, alloy treatment, particle size, molding method, and polymer composition. Each sample was evaluated for magnetic properties after thermal aging. The chemical effects of oxygen, chloride ions, and various polymers on Nd-Fe-B alloys and the resulting changes in magnetic properties can be very different, but all can lead to significant losses and each degradation process (oxidation, corrosion, or polymer-alloy interactions) exhibits a different magnetic hysteresis ''signature.'' The irreversible losses stemming from these processes can be alleviated through the use of passivating coatings