Acta Phys. -Chim. Sin. ›› 1994, Vol. 10 ›› Issue (03): 276-280.doi: 10.3866/PKU.WHXB19940315

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Investigation on the Thermodynamic Properties of Invar-type Alloys Containing Rare Rarth Metals

Xu Jian-Ming, Wang Chang-Zhen, Sui Zhi-Tong   

  1. Northeastern University, Shenyang 110006
  • Received:1993-02-16 Revised:1993-06-15 Published:1994-03-15
  • Contact: Wang Chang-Zhen


The invar-type alloys of YFe_(12-x)V_x (x=1.6, 2.0, 2.4, 2.8, 3.2) and SmFe_(12-x)V_x (x=2.4, 2.8) were prepared by melting elements in water cooled crucibles in a small are furnace with a magnetic stirring appratus. The activity and the relative partial molar Gibbs free energy of the Yttrium and Samariam in the alloys were determined by the emf method using the single crystal of CaF2 as a solid electrolyte at temperatures of 920-1020 K and 900-1000 K, respectively. The galvanic cell used can be expressed as
Mo|RE, REF_3|CaF_2|REF_3, REF_(12-x)V_x|Mo
The overall cell reaction is RE(S)=RE(alloys). The relative partial molar free energy of RE in alloy is equal to the free energy change of the cell reaction, ΔG_(RE)=ΔG=-3FE. If pure solid phase RE is chosen as the standard state, then ΔG_(RE)=RT Ina_(RE), a_(RE)=exp(-3FE/RT).
The experimental result shows that the activity of Y in alloys are larger than that of Sm in alloys, the SmFe_(12-x) alloys are therefore more stable.

Key words: Rare earth, Invar-type alloys, Thermodynamic properties, Activity, Electromotive force method