Some Considerations in Establishing Thermodynamic Activities from High Temperature EMF Measurements*

Guy R. B. Elliott
1976 ECS Proceedings Volumes  
Various sources of uncertainty and error in establishing thermodynamic properties from experimental data are discussed and evaluated. These problems reflect experimental difficul ties, the frequent absence of necessary data, some dubious assumptions in the absence of data, certain fallacies when simple models are combined with thermodynamic manipulations to correlate limited or imprecise data, and some ill-chosen methods of describing data. Effects of metal solubility in molten salts, of
more » ... ns between electrolyte and metal, of experi mental errors, and of poor models are considered. I. INTRODUCTION Certain kinds of molten salt emf measurements surpass most aqueous emf measurements in precision, accuracy, stability, reliability of tem perature coefficients, and versatility in the systems which can be stu died --many sources of aqueous system uncertainty can be avoided with molten salts. Specifically, measurements taken at room temperature with aqueous solutions often need correction for nonequilibrium effects, e. g., continuing side reaction with the water component of the solutions, strains and concentration gradients in the solids, and effects of de posited surface films. Frequently molten salts and molten metals can be reacted to equilibrium, except, of course, for the concentration gradients across the salt bridges. As corollary, certain aspects of electrochemical behavior which cannot be studied in aqueous solutions can be detected and analyzed in molten systems. This paper describes the results of some such analyses we have carried out; it deals with problems which can be met and with solutions to these problems. Many of our examples use data from our own labora tory because that is the work we know best. Other equally important problems upon which we have done little work are discussed in other papers of this symposium, and elsewhere. Areas of our research interest include (a) the structure of liquid and solid alloys, (b) the validity of usual solution models in light of such structure, (c) the development of better models and the reconcil iations of the newer models with established models of proven validity, (d) solution metastability, (e) treatment of the effects arising from the solubility of metals in their salts, primarily where significant electronic conductivity is not introduced, (f) correction for the
doi:10.1149/197606.0442pv fatcat:tzkysy4chnhw5g67osdl2bgbeq