Reversible nitrogen absorption and desorption on rare earth–iron intermetallic compounds

Abstract

Nitrogen absorption and desorption characteristics on rare earth–iron intermetallic compounds, R 2Fe 17 and RFe 7, were performed. These intermetallic compounds absorbed nitrogen into their crystal lattices by heating in NH 3 or N 2 gas at 573–773 K to form the interstitial-type metal nitrides. The nitrogen stored in the metal nitrides was reversibly released by a successive heat treatment in a stream of H 2 gas at 523–723 K. The nitrogen absorption and desorption properties of RFe 7 was superior to that of R 2Fe 17 because of the ease of nitrogen diffusion due to the difference of crystal structure between them. The nitrogen absorbed in the lattice of both compounds exists as an atomic state, so that the nitrogen desorbed from the compounds readily reacted with hydrogen to form ammonia during the nitrogen desorption.