Thermodynamic study of nickel-molybdenum and nickel-chromium-molybdenum alloys by using solid oxide electrolytes

The thermodynamic properties of Mo and Cr have been determined in the f. c. c. phase region of Ni-Mo system and the Ni-corner of the Ni-Cr-Mo system, respectively. These properties are derived from the equilibrium electromotive force measurements using solid oxide electrolyte cells of the types: Mo, Mo0₂/Th0₂-Y₂0₃/Mo (binary alloy) , Mo0₂ and Cr , Cr₂0₃/Cr (ternary alloy) , Cr₂0₃ for Ni-Mo binary from 1123 to 1373 K and Ni-Cr-Mo ternary from 1173 to 1373 K, respectively.

In the f. c. c. phase region of Ni-Mo system, from 1123 to 1373 K, the Mo activity presents a positive deviation from ideality. The Mo activity decreases towards ideality as temperature increases.

In the f. c. c. phase region of Ni-Cr-Mo system, from 1173 to 1373 K, the Cr activity increases upon adding Mo into the Ni-Cr-Mo alloy. The Cr activity deviates negatively from ideality below five to ten atomic percent Cr and ten atomic percent Mo and positively above these compositions.