非化学计量金属间化合物DO3型Fe3Al热力学性质

用以CaF2单晶为固体电解质的电池电动势(EMF)法测定了720～850 K温度区间内(－)Pt|Ir|Al_0.85Sn_0.15,Na₃AlF₆|CaF₂|Al_xFe_1－x(x=0.23～0.33),Na₃AlF₆|Ir|Pt(＋)电池电动势,通过DO₃型Fe₃Al的粉末化以及选用富Al合金Al_0.85Sn_0.15作为参比电极,使电池反应较快地达到热力学平衡,EMF测量前后工作电极的X射线衍射分析证明没有化学变化发生.计算了DO₃型Fe₃Al非化学计量金属间化合物均相范围内组元Al的活度及Al的偏摩尔热力学函数ΔG_Al、ΔH_Al、ΔS_Al ,基于Gibbs-Duhem方程计算了DO₃型Fe₃Al中另一组元Fe的活度和偏摩尔Gibbs自由能.计算了750 K时DO₃型Fe₃Al相中Al的扩散热力学因子,在化学计量比成分(xAl=0.25)附近Fe₃Al相中Al扩散的热力学因子达到最大值.

Thermodynamic Properties of Nonstoichiometric Intermetallic Compounds Fe3Al with DO3 Structure

The electromotive force(EMF) values of the cell (－)Pt|Ir|Al_0.85Sn_0.15, Na₃AlF₆|CaF₂|Al_xFe_1－x(x=0.23～0.33), Na₃AlF₆|Ir|Pt (＋) were measured between 720 K and 847 K using solid galvanic cells with a single-crystal CaF₂ electrolyte. For attaining quick thermodynamic equilibrium of the cell, Al_0.85Sn_0.15 alloy was used as the reference electrode and DO₃-Fe₃Al was powdered. It was confirmed that there was no chemical transformation in the working electrode by X-ray diffraction experiments before and after EMF measurement. The Al activities in Fe₃Al with DO₃-ordered nonstoichiometric intermetallic compounds were derived. The partial molar thermodynamic functions ΔG_Al、ΔH_Al、ΔS_Al of Al were calculated. The activities and partial molar Gibbs energies of Fe in the Fe-Al alloys were derived by Gibbs-Duhem equation. The thermodynamic factor in diffusion of aluminum in the Fe₃Al phase at 750 K was calculated, and showed a maximum at a composition near the stoichiometric proportion (xAl=0.25).