Because molten salts resemble an aqueous solution, if carefully selected and designed, electrolysis can meritoriously be performed on the melt to extract metals from compounds that are impossible or less effective to do than with aqueous systems. In as much as both systems defined the Redox potential the same way, the metamorphosis is predominantly the reference potential. In this regard, the Standard Hydrogen Electrode (SHE) is predominantly considered as the reference potential and pH measurements are universal for aqueous systems. However, in molten salt systems, the reference potential can only be designated from what is available in the melt: F(melt)/F₂(g), K(melt)/K(element), and even a Ag electrode specially inserted. Similarly, pO^2- from the composition of the molten salt can be a substitution for pH of the aqueous system. This results in potential-pO^2- (E-pO^2-) diagrams that, in many ways, resemble E_H-pH diagrams but are different in detail. This paper presents the thermodynamic considerations and method of constructing an E-pO^2- diagram for neodymium metals from their oxides.

Acknowledgements

Research was sponsored by the Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-15-2-0020. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.