Date of Award
Doctor of Philosophy
Materials Science and Engineering
Solid electrolyte electromotive force cells have been used to determine the Gibbs free energies, enthalpies, and entropies of formation of binary intermediate phases in the Y-Fe and Y-Co systems. Solid CaF(,2) was used as the electrolyte, and EMF meas- urements were made over the temperature range 850 K to 1271 K with electrochemical cells of the type Y, YF(,3)(VBAR)CaF(,2)(VBAR)YF(,3), M, YM(,c) or Y, YF(,3)(VBAR)CaF(,2)(VBAR)YF(,3), YM(,a), YM(,b) where M = Fe or Co, and M and YM(,c) or YM(,a) and YM(,b) are neighboring phases in the Y-M equilibrium diagram. The data indicate that, at a given stoichiometry, the Gibbs free energy of formation becomes more negative in progression from Y-Fe to Y-Co;The experimental values for the Gibbs free energies of formation of the Y-Fe and Y-Co intermediate phases at 973 K are compared with those of the Th-Fe, Th-Co, Th-Ni, La-Co, and La-Ni systems. Examination of the trend shows that there is an empirical correlation between the Gibbs free energy of formation and the total number of valence electrons in these alloy systems;The experimental enthalpies of formation of the equiatomic alloys in the Y-Fe and Y-Co systems are compared with the theoretical pre- dictions of the Miedema and Watson-Bennett models. Experimental data for the Y-Fe system favors the Watson-Bennett approximation;in the case of the Y-Co system, however, both predictions are acceptable approximations to the experimental value; *DOE Report IS-T-1125. This work was performed under Contract W-7405-eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
P. Ramanathan Subramanian
Subramanian, P. Ramanathan, "Thermodynamics of formation of intermediate phases in the yttrium-iron and yttrium-cobalt systems " (1984). Retrospective Theses and Dissertations. 8219.