稀土Invar合金热力学性质研究

制备了稀土Invar（因瓦）合金YFe_(12-x)V_x（x＝1.6，2.0；2.4，2.8，3.2）和SmFe_(12－x_V_x（x=2.4, 2.8）采用电动势法以CaF_2单晶作为固体电解质，测定了钇和钐在相应合金中的活度．计算了偏摩尔自由能等热力学性质．测定温度对两类合金分别为920－1020 K和900－1000 K．

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

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.