LOW-TEMPERATURE NITRIDING OF IRON THROUGH A THIN NICKEL LAYER

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.