CRYSTALLITE SHAPE AND IRON LATTICE ORIENTATION IN THE AMMONIA-SYNTHESIS CATALYST

The morphology of reduced and stabilized ammonia synthesis catalyst, w hich is produced by reduction of magnetite, has been studied using opt ical microscopy with polarized light and transmission electron microsc opy. The combined use of these techniques has revealed micrometer size regions of different pore structure within the reduced magnetite grai ns. One of these structures consisting of parallel sheets of bcc-iron is described. Both the sheets and the space between them are of typica l thickness, 15 nn. The orientation of iron in the sheets is related t o the former magnetite crystal lattice by a rotation of 45 degrees abo ut one of the three (100) axes. This (100) axis, common to both magnet ite and iron, is normal to the iron sheets. The sheet-like iron region s display large scale magnetic domains with in-plane magnetization wit hin the sheets. (C) 1995 Academic Press, Inc.