Phase composition of carbonyl iron-nickel powders

Abstract

1. A thermodynamic analysis is made of secondary reactions that may be responsible for contamination of carbonyl powders with carbon and oxygen. From a thermodynamic point of view, carbonyl iron-nickel powders may contain carbon in free form (carbon black) and in the form of cementite, Fe3C; the formation of nickel carbide, Ni3C, cannot be ruled out. Oxygen may be present in combined form as wustite, magnetite, and nickel oxide. 2. Carbonyl iron-nickel powders containing 20, 50, and 80% of nickel were analyzed for carbon and oxygen, and the phase condition of the contaminants was determined. 3. It was established by chemical phase analysis, and confirmed by x-ray diffraction and NGR methods, that much of the carbon in carbonyl iron-nickel powders is present in carbide form. 4. Oxygen in iron-nickel powders appears to be combined in the form of Fe3O4 (as revealed by x-ray structural analysis and an NGR study). 5. The relationship was established between the amount of carbon present in carbide form in iron-nickel powders and the latter's composition. It was found that, on passing from 20N to 80N powder, the amount of carbide-type carbon falls from 1.20 to 0.86%. 6. It is shown that the concentration of carbide-type carbon in an iron-nickel powder of a given composition is comparatively stable. When powder batches of the same composition exhibit total carbon content fluctuations attributable to the technological process of thermal decomposition, the fluctuations are due to variations in their carbon black content.