Self-propagating high-temperature synthesis of nonstoichiometric wüstite

Abstract

This paper describes the self-propagating high-temperature synthesis (SHS) of nonstoichiometric FexO (x=0.833–1), with particular focus on the effects of nonstoichiometric Fe content and diluent addition on the phase of the SHS product. In the SHS process, the raw materials Fe, NaClO4 (oxidizer), and NaCl (diluent) were thoroughly mixed in the desired ratio by ball milling, and the lower surfaces of the disk-shaped green compacts were subsequently electrically ignited to produce FexO through the propagation of the sustainable exothermic reaction. X-ray diffraction analysis showed that the SHS products comprised double phases of FexO and Fe3O4. The peaks of products with 0.947≤x≤1.00 shifted to lower angles in comparison to those of the product with x=0.833 attributed to the lattice parameter distortion of the crystal structure because of the Fe defects. In the presence of the NaCl diluent, the raw materials were converted to high-purity FexO powders during the SHS process. Without the NaCl diluent, the lattice parameter of SHS Fe0.947O corresponded to the theoretical lattice parameter. Nonstoichiometric compounds of FexO (0.942≤x≤0.952) were obtained through SHS without additional external heating.