Hysteresis phenomenon in a reaction system of nanocrystalline iron and a mixture of ammonia and hydrogen.

During nitriding of nanocrystalline iron and reduction of iron nitrides with NH3/H2 mixtures, at the stationary states a hysteresis phenomenon is observed where two phases coexist, according to the extended phase rule of Gibbs due to the presence of an additional degree of freedom associated with the size of the nanocrystallites. Nanocrystallites transform from the biggest ones to the smallest due to differences in energy demand.