Neodymium Iron Boron magnets require a protective coating / surface finish to prevent corrosion of the magnet.
Moisture in the atmosphere is potentially enough to cause an uncoated NdFeB magnet to show signs of corrosion. Marine environments are particularly effective at making NdFeB magnets corrode. The process of corrosion is similar to rusting – the structure of the Neodymium Iron Boron magnets changes permanently resulting in a progressive loss in magnetic performance (the magnet will weaken; the magnet also breaks down into a powder during the corrosion process). Total magnetic failure is possible due to corrosion. To prevent this, the magnet is given a coating / surface finish.
There is a variety of surface finishes available. The application sometimes affects the choice of coating (e.g. gold plating is a noble element and is therefore chemically inert and ideal for many medical applications, rubber coating provides additional friction, etc).
The standard coating is a triple layer plating of Nickel-Copper-Nickel (Ni-Cu-Ni). Unless requested otherwise, this Ni-Cu-Ni coating is always applied to the magnets. It should be noted that the level of protection given by any coating depends on the environment the magnet will be subjected to and how the coating is looked after. If the coating is scratched or broken, it will not offer protection from moisture.
If moisture is sealed within the coating during the time of coating, the magnet may corrode from the inside out with little obvious signs of corrosion. The plating process is carried out on magnets that have been thoroughly cleaned and dried. Ideally the coatings should give a hermetic seal but the coating type may not make this possible. Not all coatings are hermetic i.e. some coatings may absorb water / let water through over long time period. In some circumstances, it may be beneficial to combine coatings to maximise corrosion protection (e.g. rubber coated zinc plating is used to assist magnet performance in marine environments).
The current range of coatings available is as follows:-
- Nickel-Copper-Nickel (Ni-Cu-Ni) [standard];
- Nickel (Ni);
- Zinc (Zn);
- Gold (Au);
- Silver (Ag);
- Tin (Sn);
- Titanium (Ti);
- Titanium Nitride (TiN);
- Parylene C;
- PTFE (also known as “Teflon®”; white, black, grey, silvery);
- Ni-Cu-Ni plus Epoxy;
- Ni-Cu-Ni plus Rubber;
- Zn plus Rubber;
- Ni-Cu-Ni plus Parylene C;
- Ni-Cu-Ni plus PTFE;
- Tin (Sn) plus Parylene C;
- Zinc Chromate;
- Phosphate Passivation; and
- Uncoated (bare – recommend vacuum packing as well).
Other coatings may be possible (e.g. we are currently experimenting with Aluminium coating at a R&D level). If you need a different coating, we can look into it.
It is not recommended to use the magnet without a protective layer (if a bare NdFeB magnet is required, we suggest it is vacuum packed to try to keep as much moisture away from the magnet as possible.
Some people may choose to add their own coatings when they have accidentally damaged the protective coating layer. Additional coatings used have included varnish, silicone sealant, lacquer and Hammerite® paint. Varying levels of success has been achieved from performing such secondary operations (we recommend such parts are cleaned and thoroughly dried before re-coating to prevent sealing in any moisture).