Ferromagnetism carbides

Dav] Davenport, E.S., Bain, E.C., Transformation of Austenite at Constant Subcritical Temperatures , Transactions Amer. Inst, of Mining and Met. Eng. Iron and Steel Div, 117. (1930) [1932Takl] Takei, T., On flie Ferromagnetic Carbides in Molybdenum Steels , Kinzoku no Kenkyu, 9, 97-124 (1932) (Phase Diagram, Experimental, 5)... 

Pichler and Merkel (24) investigated the composition of iron catalysts at various stages of pretreatment and synthesis by chemical and thermo-magnetic analysis. Copper-free iron catalysts, carburized at 325°C. before medium-pressure synthesis, were virtually completely transformed to a ferromagnetic higher iron carbide with a Curie point of 265°C., whose formula corresponded to approximately Fe2C. 

Carburization of copper promoted (20% Cu) iron catalysts at 220-230°C. yielded not only the 265°C. Curie point carbide, but also a second ferromagnetic iron carbide whose Curie point was 380°C. 

Magnetic methods are, like x-ray diffraction, a tool for gaining structural information. These methods have been used to measure the effective dispersion of a paramagnetic oxide such as chromia gel or chromia supported on alumina and to determine oxidation states and bonding types under conditions where other procedures are difficult or inapplicable. Magnetic methods are useful also in the identification and estimation of ferromagnetic components such as iron carbide in Pischer-Tropsch or synthetic ammonia catalysts. 

Carbides and nitrides of Fe, Co, and Ni are ferromagnetic as their parent metals. The other compounds which are paramagnetic, show typically lower susceptibilities compared to the pure metals. 

Those substances which exhibit ferromagnetism are limited to the metals iron, cobalt, and nickel, to certain oxides and carbides containing these elements, and to a small number of miscellaneous substances con-... 

The product gave x-ray lines for cobalt carbide, but no cobalt metal. The amount of cmbon taken up corresponded closely to that required for the formation of CotC. However, the sample showed a small d ree of ferromt etism and it was assumed that this was due to a few per cent of ct-cobalt, although there is some uncertainty in this procedure because cobalt carbide itself appears to be slightly ferromagnetic. 

Carbides coexist with the metallic ferromagnetic phases. This is unfavorable for the mechanical properties. The Curie temperature of the r phase decreases with increasing C content to a constant value (see Fig. 4.3-71) according to the phase diagram. 

Cementite. Cementite is an iron carbide with the chemical formula FCjC. At room temperature, cementite is a hard, brittle, and ferromagnetic material with a Curie temperature of 210°C. It is formed by chemical reaction between iron and excess carbon. Three distinct origins must, however, be distinguished ... 

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