Corrosion protection of Nd-Fe-B permanent magnets by organic coatings

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Corrosion protection of Nd-Fe-B permanent magnets by organic coatings

 

Author: Li, Tak-wing Danny
Title: Corrosion protection of Nd-Fe-B permanent magnets by organic coatings
Year: 1999
Subject: Permanent magnets -- Corrosion
Protective coatings
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Applied Physics
Pages: 74, [3] leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1511597
URI: http://theses.lib.polyu.edu.hk/handle/200/2184
Abstract: Nd-Fe-B permanent magnet is one of the most important permanent magnets in the world. The excellent magnetic properties cause the magnet to be widely used in commercial products. However, the corrosion resistance in humid environment of the magnet is undesirable and this largely limits its scope of applications. The present project aims at using organic coatings as protective coatings, to protect the surface of the magnet from corrosive environments, hence improving its corrosion resistance and extending its service life. Three different primers and one enamel were employed as a simplex protective coating for the magnet. The corrosion resistance of duplex coating constructed from the three primers (undercoat) & the enamel (topcoat) were also studied. Salt spray test and electrochemical impedance spectroscopy were used to evaluate the corrosion resistance of these coatings. Zinc yellow chromate primer and red lead primer were found to provide good corrosion protection for Nd-Fe-B magnet. Zinc yellow chromate with a coating thickness of 123um and red lead primer with coating thickness of 119um remained intact in salt spray chamber for over 250 hours and 200 hours respectively. However, red lead primer is toxic in nature; therefore, zinc yellow chromate was recommended to be the best choice. The corrosion resistance of zinc yellow chromate was significantly improved by a synthetic enamel topcoat in duplex coating. The effective thickness for simplex paint coating was found to be above 100um. Besides, the hardness of the paints showed a direct relation with the corrosion protection performance.

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