Free energy of formation of Mo2C and the thermodynamic properties of carbon in solid molybdenum |
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Authors: | L. L. Seigle C. L. Chang T. P. Sharma |
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Affiliation: | (1) Materials Science and Engineering Dept., State University of N.Y., Stony Brook, N.Y.;(2) General Electric Co., San Jose, CA;(3) General Instruments Corp, Hicksville, NY |
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Abstract: | The activity of C in the two-phase region Mo+Mo2C has been obtained from the C content of iron rods equilibrated with metal+carbide powder mixtures. From this activity data the free energy of formation of α-Mo2C has been determined as ΔG f o (α-Mo2C) (1270 to 1573 K)=−47,530−9.46T±920 J/mol. This is in good agreement with the expression obtained from gas-equilibration studies by Gleiser and Chipman, ΔG f o (α-Mo2C) (1200 to 1340 K)=−48,770−7.57 J/mol, but both our and Gleiser and Chipman's values are about 10 pct lower than those of Pankratz, Weller and King calculated from ΔH f,298 o andC p vs T data. With the aid of available data for the solid solubility of C in Mo, the thermodynamic properties of C in the terminal solid solution have been calculated as J/mol, J/mol and , the excess entropy ofC in the solid solution assumingC is in the octahedral interstices =43.4±8.2 J/deg.-mol. |
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