Liquid treatments. Salt baths
Nitriding and nitrocarburizing - Industrial Processes and Practices

With the exception of non-activated baths, treatments in salt baths are always nitrocarburizing treatments resulting in ε-type combination layers and fairly shallow diffusion layers. These treatments are sometimes referred to as "treatments in ionic liquid media", insofar as the reactions take place after decomposition into ions of the compounds present (CNONa → CN ^- + Na ⁺ ).