The Nd-(Fe,Co)-B Powder Biencapsulation With Cu/epoxy Resin and Its Effect on Pitting Corrosion Resistance of Bonded Magnets

Abstract
In this chapter the effect of the Nd-(Fe,Co)-B powder particle biencapsulation with Cu layer on bonded magnetic materials corrosion behaviour has been investigated. Bonded magnets were prepared from nanocrystalline magnetic Nd11Fe77Co5B6 powder. Powder particles before consolidation were preliminary etched with oxalic acid and then coated with bilayer (powder biencapsulation). The powder surface was coated as a first with Cu layer during 1 or 5 minutes in copper plating bath and the second layer was thermosetting epoxy-resin. The polarization curves in phosphate environment with addition of chloric ions were determined. It has been established that the used biencapsulation method not always satisfactorily isolate individual particles of the powder and consequently, significantly inhibits corrosion processes of the final material, especially in passivating environment containing Cl-.
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