Formation of iron-nitrides by the reaction of iron nanoparticles with a stream of ammonia

Iron-nitride formation by reaction of iron particles of various grain sizes (20 nm to I mu m) with an ammonia stream was studied to examine correlatio n between the nitrogen content in the product and dissociation extent of th e ammonia. Dependence of the nitridation reaction on the grain size was inv estigated in the same conditions by fixing mass of reactant, pow rate and t emperature (723 K). It was found that nanoparticles enhance ammonia dissoci ation and that the product was therefore of lower nitrogen content than tha t of coarse particles. This result is understood as follows: The larger spe cific surface of nanoparticles has enhanced ammonia dissociation occurring on the surface in parallel with nitridation and then reduced the chemical p otential of nitrogen in the gas phase surrounding the nanoparticles in equi librium. (C) 1999 Acta Metallurgica Inc.