Low-temperature nitriding of iron through a thin nickel layer

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We present a new method for nitriding iron at low temperatures. First, iron is coated with a thin layer of nickel (∼36 nm), after which it is exposed to an NH3 atmosphere at temperatures below 300 °C. Underneath the nickel layer ε-Fe3−xN is formed at temperatures as low as 225 °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.