1729. KELLEY, K. K., BOERICKE, F. S., MOORE, G. E., HUFFMAN, E. H., AND BANGERT, W. M. Thermodynamic Properties of Carbides of Chromium. Bureau of Mines Tech. Paper, vol. 662, 1944, 43 pp.; Chem. Abs., vol. 38, 1944, p. 6183.

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Literature Abstracts

Describes preparation of carbides of Cr, and records some observations of the general properties of the carbides. Reports low-temperature specific-heat measurements in the temperature range 51°-298° K. for the carbides that are true compounds (Cr₃C₂, Cr₇C₃, and Cr₄C) and for the mixed carbide Cr₅C₂. The corresponding entropies are computed. High-temperature heat-content measurements from room temperature up to the limiting temperatures of available containers are reported for Cr₃C₂, Cr₇C₃, Cr₄C, and Cr₂O₃. Analytical representations of the results are given. C reduction of solid Cr₂O₃ takes place in four distinct, reversible reaction steps in which Cr₃C₂, Cr₇C₃, and Cr₄C are the intermediate compounds. Results of the equilibrium measurements obtained with described apparatus and methods are reported for each reaction step. The various data are correlated satisfactorily and thermodynamic values and functions are derived for the Cr carbides. Each carbide of Cr at temperatures below its melting point is stable with respect to decomposition into (1) the elements, (2) any lower carbide and C, and (3) any higher carbide and Cr. The intermediate carbide, Cr₇C₃, is stable with respect to decomposition into Cr₃C₂ and Cr₄C.