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 degrees C. Underneath the nickel layer epsilon-Fe3-xN is formed at temperatures as low as 225 degrees C, while uncovered iron samples show a large uptake of oxygen after the same treatment. The nickel layer prevents the oxidation of iron by impurities in the NH3 gas, and acts as a catalyst for the decomposition of NH3. After decomposition the atomic nitrogen diffuses through the nickel layer towards the iron. With the process described, pore-free iron nitrides can be formed at low temperatures