Cherginets V. Physico-chemical regularities of acid-base interactions on the background of molten halides of s-elements

Object of investigation: reactions of oxide ion exchange in molten salts. Purpose: finding regularities of running chemical interaction with the participation of oxide compounds in ionic solvents based on alkali (Na, K, Cs) and alkaline earth (Ca, Sr, Ba) metal halides. Methods: potentiometric titration, atomic-emission spectral analysis, X-ray phase analysis, isothermal saturation and sequential addition method. Some common regularities of effect of anion and cation composition of the ionic solvent, its acidity and temperature on running Lux acid-base reactions (oxoacidity) on the background of melts based on alkali and alkaline earth halides were stated. The generalized definition of acids and bases of the solvent system was introduced. The “oxobasicity index” was proposed as a measure of acidic properties of ionic melts and the methods for its determination were substantiated. Using this parameter common acidity scales of the ionic melts based on alkali and alkaline metals halides at 600, 700 и 800оС are constructed. Polythermal studies of equilibria with the participation of carbonate ion dissociation and oxide solubility the ionic melts based on alkali and alkaline earth metal halides were performed. The dependence of the dissociation constant of carbonate vs. reverse temperatures has been shown to possess the slope close to that of the corresponding carbonate decomposition. The oxide solubility changes in 600-800 оС temperature range has been found to agree with the Shreder-Le Chatelier equation. The solubility of alkaline metal oxides and oxides of 3d-elements (Mn, Co, Ni, Cu, Zn) and Pb in melts based on alkali and alkaline earth metal halides was found to increase with the cation radius, the melt acidity and the decrease of halide ion radius. The reversibility of Pt(O2)|ZrO2(Y2O3) membrane oxygen electrode in the halide melts was studied. The plot of e.m.f. vs. oxide ion concentration was shown to consist of two linear parts with slopes of 1,15 RT/F at low oxide ion concentrations and 2,3 RT/F athigh concentrations of O2–. The change of the position of this point of inflection with the increase if the melt temperature and acidity increase agrees with the existence of so-called peroxide function of gas oxygen electrodes. A degree of application: the methods of determination of common content of oxygen were applied in the manufactures of scintillation single crystal growth.