Corrosion protection of Nd–Fe–B magnets by bismaleimide coating

Abstract

Enhancement of coercivity for Nd-Fe-B thin films by the infiltration of Nd-Cu alloy cap layer J. Appl. Phys. 110, 023903 (2011) Demagnetizing effects in granular hard magnetic bodies J. Appl. Phys. 109, 093901 (2011) Dysprosium-saving improvement of coercivity in Nd-Fe-B sintered magnets by Dy2S3 additions J. Appl. Phys. 109, 083916 (2011) Effect of surrounding air region size on finite element modeling for permanent magnetic solenoids J. Appl. Phys. 109, 07A757 (2011) The effect of doping element Zr on anisotropy and microstructure of SmCo7xZrx J. Appl. Phys. 109, 07A748 (2011) Additional information on J. Appl. Phys. Samples of Nd-Fe-B were coated with bismaleimide ͑BMI͒, a resin which is well known for its desirable barrier, mechanical, and thermal properties but has not been used as a coating material. The performance of BMI-coated samples ͑average coating thickness ϳ15 m͒ was compared with commercial epoxy-coated samples ͑average coating thickness ϳ20 m͒ in a series of tests. In the copper-accelerated acetic acid-salt spray test, the epoxy-coated samples failed badly ͑damaged area Ͼ50%͒ within 20 h while the BMI-coated samples showed no sign of failure up to 200 h. Using the cross-cut tape test for adhesion strength ͑ASTM D 3359͒, the commercial epoxy coatings suffered 25% area detachment while for the BMI coatings, no detachment was observed. The scratch resistance of the BMI coatings, measured in terms of scratch depth in the pin scratch test, was about 1.5 that of the commercial epoxy coatings, and the Vickers hardness was higher by a factor of about 2.5. When magnetized under the same magnetizing field, there was no significant difference in the magnetization obtained among bare, epoxy-coated, and BMI-coated samples. These results suggest that BMI coatings are excellent for protection of the Nd-Fe-B magnets against corrosion and function better than the commonly used epoxy resin.

Corrosion Behaviour of a Silane Protective Coating for NdFeB Magnets in Dentistry

“…In the presence of an electrolyte solution, different electrochemical potentials promote galvanic corrosion, mainly within Ndrich phase. Low corrosion resistance causes mechanical deterioration, modification of the magnetic properties, and release of cytotoxic agents [2][3][4].…”

Multi-layered electroless Ni–P coatings on powder-sintered Nd–Fe–B permanent magnet

“…This is because polymers are, in general, prone to moisture attack and mechanical scratch, which will weaken the adhesion between coating and the base material. Among polymeric coatings, BMI seemed to be able to provide the best protection [4] but the material itself is brittle and difficult to prepare. Its adhesion has to be improved by an extra layer of undercoat [4], so the advantage of simplicity and low cost of polymer resin coating is, to a certain degree, lost.…”

“…Among polymeric coatings, BMI seemed to be able to provide the best protection [4] but the material itself is brittle and difficult to prepare. Its adhesion has to be improved by an extra layer of undercoat [4], so the advantage of simplicity and low cost of polymer resin coating is, to a certain degree, lost. Generally polymeric coatings are considered more suitable for applications in less stringent conditions such as low temperature and low humidity environment.…”

“…To overcome this problem, a lot of research work on the protective coating on Nd-Fe-B magnet has been carried out [2][3][4][5][6][7][8]. The coating material can be generally categorized into two groups: polymers, including epoxy resin [2,3] and bismaleimide (BMI) resin [4], and metals [2,[5][6][7][8]. Generally epoxy coating is easy to apply and less costly.…”

Metallization and APPJ treatment of bismaleimide

“…They are used for pre-pegs and laminates for the electronic industry, printed circuit boards, diamond wheels and tools, heavy duty insulation and electrical insulation, high temperature applications, glass, aramid and carbon fibre reinforced composite, aerospace and military applications [1,2,3]. BMI coating has been used for the corrosion protection of Nd-Fe-B magnets [4]. Thin ceramic coatings Silica coatings has been deposited on bismaleimide (BMI) polymeric substrates as reinforcements or extenders and their Vickers microindentation has been performed which showed cracking [5,6].Siliconized epoxy-phosphorus based bismaleimide coating systems using diglycidylether terminated poly (dimethylsiloxane) (DGTPDMS) and phosphorus-containing bismaleimide (PBMI) as chemical modifiers for epoxy resin has been developed [7].BMI is used to improve the thermomechanical properties of the parent resin [8].…”