|An important achievement in the
field of nanocrystalline powders and sintered
magnets based on Nd-Fe-B was the improvement of
the intrinsic corrosion resistance by introducing
small amounts of additives such as ZrO2. ZrO2 reacts
with free Nd in the grain boundary phase and Nd2O3 and ZrB2 phases are
formed. The sensitivity of the grain boundaries
is diminished and consequently the corrosion
resistance is improved.
To further improve the chemical stability of the
sensitive powders we developed and patented a
coating procedure for the powders by using
long-chain fatty acids or silanes.
The mechanism of the chemical
With this method a chemical bond between the
powder's surface and a surface-active agent is
formed (Figure) and a thin organic layer on the
surface allows for the free handling of the
powder under atmospheric conditions. This is of
special importance for industrial use.