We present a new method for nitriding iron at low temperatures. First,
iron is coated with a thin layer of nickel (similar to 36 nm), after
which it is exposed to an NH3 atmosphere at temperatures below 300 deg
rees C. Underneath the nickel layer epsilon-Fe3-xN is formed at temper
atures as low as 225 degrees C, while uncovered iron samples show a la
rge uptake of oxygen after the same treatment. The nickel layer preven
ts the oxidation of iron by impurities in the NH3 gas, and acts as a c
atalyst for the decomposition of NH3. After decomposition the atomic n
itrogen diffuses through the nickel layer towards the iron. With the p
rocess described, pore-free iron nitrides can be formed at low tempera
tures. (C) 1997 American Institute of Physics.