Preparation and Characterization of Nickel Substituted Fe5C2

摘要

Nickel can be substituted into Fe5C2 to the extent of 20 atomic percent. Samples were prepared by codecomposition of mixed nitrates followed by reduction at 290 C in a 9:1 H2:CO atmosphere. Confirmation of the limit of substitution was made by both magnetic and x-ray analysis. It has been shown by a number of investigators that the catalytic activity of iron catalysts, used to reduce CO by hydrogen, was related to the extent of carbide formation. Fournier et al. reported that the phases Fe5C2 and Fe were detectable both from x-ray diffraction patterns and from thermomagnetic curves taken from products which were quenched after 10 minutes of reaction time (at maximum activity). It was shown that the active catalysts formed from both Fe2O3 and metallic iron contain Fe5C2. Catalyst deactivation is most probably associated with unreactive graphite which is formed during the methanation process. There have been no reports concerning the crystallographic or magnetic properties of the system Fe5-xNixC2. Since Fe5C2 shows a Curie point at 246 C, any substitution of nickel into the phase could be determined by changes in the Curie point. Furthermore, the optimum solubility of nickel into Fe5C2 could be determined from x-ray diffraction studies of members of the system Fe5-xNixC2. Since pure nickel does not appear to carbide under Fisher-Tropsch conditions, it should be present as a separate phase when maximum solubility is achieved.