High Temperature Electrochemical Determination of the Thermodynamic Stability of the Iron-Rich, Iron-Niobium Intermetallic Phase

Abstract A non-stationary technique of e.m.f. measurements after polarization of solid galvanic cells, previously applied to the determination of the standard free energy of formation of metal oxides, has been extended to intermetallic phases. The chief condition of applicability of this technique to intermetallic compounds is that the rates of recombination of the cathodic reduction products to yield the stable intermetallic phase be high as compared with that of chemical oxidation at the interface with the solid intermediate electrolyte, due to oxygen impurities in the gas phase. In particular, the solid electrolytic cell: (y values expressing the ε-phase iron-rich boundary compositions according to different authors investigations) was examined. Values of the standard free energy of formation of Fe7-yNb2 from the elements, ranging between -3.77+0.72-10-3 T and -5.66+1.09 · 10-3 T kcal/atom were found.