I have little to do with chemistry and my only background is the inorganic chemistry I learned at school when I was 13-14 years old.

I need to have a basic understanding of the nitrating process (for an automation engineering application, more precisely an automated furnace used for nitrating iron or steels parts with the purpose of improving their mechanical and chemical properties).

A few things are not so clear for me:

  1. What is the chemical formula of the iron lattice mixed with nitrogen atoms (see the picture)?
  2. What is the unwanted white layer that I understand forms on the surface of the metal part treated with dissociated ammonia?
  3. What is this dissociated ammonia?

Gas nitriding

Gas nitriding


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  • $\begingroup$ (1) Natrium is the Latin name for sodium, hence the elemental symbol Na. (2) What "white layer"? -- Do you mean the iron atoms that are shown as white circles? $\endgroup$ – MaxW Apr 7 at 19:15
  • $\begingroup$ Nitrogen, sorry! The "white layer" is not shown in the picture. $\endgroup$ – Robert Werner Apr 7 at 20:33

Steels are nitrided in ammonia gas at 900 to 1050 F ; It forms a very hard , very thin ( < 0.01 ") hard layer of iron nitride . An addition of aluminum alloy to the steel ( 0.5 to 1.0 % ) enhances the nitriding. Nitriding is applied typically to cutting tools like drill bits and wearing surfaces. At higher temperatures "carbo-nitriding " is done where C and N are diffused into the steel surface. The "white layer" is something seen in a metallographic sample at high magnification -100 x and higher. It is undesirable and apparently unidentified as the ASM handbooks refer to it as only "white layer" ; they give procedures to remove it if necessary . The white layer should be thin , even compared to a 0.005 " thick layer of nitride. Plain ammonia or dissociated ammonia may be used with slightly different procedures.

  • 1
    $\begingroup$ ah... yes. I overlooked the "cation" Gas nitriding in the OP's post. So the picture is for creating a layer of iron nitride, not using Fe as a catalysts in reaction between hydrogen and nitrogen to make ammonia. $\endgroup$ – MaxW Apr 7 at 21:38
  • $\begingroup$ No guesses regarding what the chemical composition of the white layer might be? $\endgroup$ – Night Writer Apr 8 at 10:43

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