, Volume 3, Issue 9, pp 2363-2370

High-temperature thermodynamic properties of the chromium carbides determined using the torsion-effusion technique

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Abstract

The pressures of carbon monoxide in equilibrium with a Cr23C6-Cr2O3-Cr mixture and with a Cr7C3-Cr2O3-Cr23C6 mixture have been measured in the temperature range 1100 to 1300 K using the torsion-effusion technique. From the equilibrium data, the following equation for ΔGof of Cr23C6 (in cal per mole) has been calculated: ΔG f ° (±1200) = −77,000 - 18.3T (1150 to 1300 K) Combining the results of this study at temperatures between 1100 and 1300 K with those of Kelleyet al., 3 at temperatures between 1500 and 1720 K, the following equation for ΔGof of Cr7C3 (in cal per mole) has been determined: ΔG f ° (±400) = −35,200 - 8.7T (1100 to 1720 K) ) The above equation for ΔGof of Cr7C3 has been used to re-evaluate the equilibrium data of Kelleyet al., 3 and the following equation for ΔGof of Cr3C2 (in cal per mole) has been obtained: ΔG f ° (±400) = −16,400 - 4.4T (1300 to 1500 K) CHROMIUM reacts with carbon to form three carbides:1,2 Cr23C6, Cr7C3, and Cr3C2. The chromium carbides are of considerable technical importance because of their precipitation behavior in certain high-chromium steels and superalloys. A precise knowledge of their thermodynamic properties is essential for the understanding and the prediction of their chemical behavior in various environments.

This paper is based upon a thesis submitted by A. D. KULKARNI in partial fulfillment of the requirements of the degree of Doctor of Philosophy at the University of Pennsylvania.