The NdFeB magnets require a protective coating / surface finish to minimize the effects of corrosion. Iron within the structure can ‘rust’ which causes a permanent structural change in NdFeB which results in a permanent weakening of the magnetic performance – the worst case scenario is a total loss of magnetism.
A NdFeB magnet kept in dry conditions will not corrode and will retain its performance theoretically for ever (if not subjected to excessive heat, radiation or strong external magnetic fields). If the conditions are wet, it is recommended that alternative magnets be considered for use of that the magnet design try to protect the magnet from moisture (e.g. encasing, modified coatings such as zinc plus rubber, etc). The plating / surface finish should be hermetic for best corrosion protection – scratched or damaged surfaced may render the affected region more prone to corrosion. Marine environments (salt sprays, sea water) are particularly corrosive and far from ideal for NdFeB. In critical applications where corrosion and magnet failure are unacceptable, magnets such as ferrite or SmCo may be more suitable. Please note that any claims that a NdFeB magnet will not corrode is misleading. It is claimed that higher Hci magnets resist corrosion better although the empirical results are not so conclusive (a trend suggesting an improvement in corrosion resistance exists but it is not guaranteed). It is the application and the overall design that determines how well the magnet will perform in damp environments.
