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

The morphology of reduced and stabilized ammonia synthesis catalyst, which is produced by reduction of magnetite, has been studied using optical microscopy with polarized light and transmission electron microscopy. The combined use of these techniques has revealed micrometer size regions of different pore structure within the reduced magnetite grains. One of these structures consisting of parallel sheets of bcc-iron is described. Both the sheets and the space between them are of typical thickness, 15 nn. The orientation of iron in the sheets is related to the former magnetite crystal lattice by a rotation of 45 degrees about one of the three (100) axes. This (100) axis, common to both magnetite and iron, is normal to the iron sheets. The sheet-like iron regions display large scale magnetic domains with in-plane magnetization within the sheets. (C) 1995 Academic Press, Inc.