Abstract
The gas equilibrium method of CH4/H2 has been widely used for measuring carbon potential. However, it has been reported that this method is not applicable at high temperatures since the equilibrium between CH4 and H2 is disturbed by the reaction of CH4 with moisture in the system. Nevertheless, this method should be applicable theoretically at high temperatures below which CH4 decomposition can be neglected because the equilibrium between CH4 and H2 reaches constant ratio in spite of the reaction. Since the role of moisture is to oxidize the sample during the measurements under the oxygen potential determined byPh 2 o/ph 2 ratio, the Gibbs free energies of formation of Mo2C and WC were successfully measured from 1173 to 1573 K by keeping the moisture level in the system low enough not to oxidize the sample. The experimental results are expressed by the following equations which were derived by least squares treatments of the data: Mo2C:ΔG = -68270 + 8.23T J mol-1 WC:ΔG = -52330 + 14.06T J mol-1 These values were in good agreement with those measured by M. Gleiseret al. for narrow tempareture ranges using the CO/CO2 gas equilibrium method.
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Iwai, T., Takahashi, I. & Handa, M. Gibbs free energies of formation of molybdenum carbide and tungsten carbide from 1173 to 1573 K. Metall Trans A 17, 2031–2034 (1986). https://doi.org/10.1007/BF02645000
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DOI: https://doi.org/10.1007/BF02645000