2352. NAESER, G. [Heat of Formation of the Iron Carbide Fe3C.] Mitt. Kaiser-Wilhelm-Inst. Eisenforsch. Düsseldorf, vol. 16, No. 1, 1934, p. 1-7; Chem. Abs., vol. 28, 1934, p. 2985.
Review of measurements of heat of formation of Fe3C shows very variable values between positive and negative maximum. It was determined again from amorphous C and a-Fe at room temperature by converting the carbide (under separation of C) and the pure Fe into the iodide and chloride, respectively. From both methods, the heat of formation was found to be +8±0.25 kcal. per mol., which corresponds to 4.66±1.4 cal. per gm. cementite, 47.8±1.5 cal. per gm. Fe, 668±20 cal. per gm. C. The heat of combustion of finely distributed amorphous C on disintegration of carbide was found to be 107.9 kcal. per mol. The heat of reaction in the formation of FeS from a-Fe and rhombic S was 23.89±1.16 kcal. per mol. The final result is that the heat of formation of Fe3C lies in the range of +8 to –4 kcal. per mol. according to the state of C and decreases with increasing graphitization. 46 refs.