Ion Selectivity of Beta‐Alumina during the Coulometric Titration of Liquid Pb‐Na Alloys

Abstract

The ion selectivity of 8-and 8"-alumina during the coulometric titration of a liquid Na-Pb alloy was investigated using a double galvanic cell Mo, Na(1) I ~-, or ~"-alumina 1Pb-Na(1), Mo [I] Mo, Pb-Na(1) I ~"-alumina IAu + Au2Na(s), Mo [I'] where Pb-Na(1) was used as the common electrode. Sodium was coulometrically titrated through the ~-or 8"-alumina electrolyte to cell [I] both ways and EMF's were measured. It was found that no reaction occurs between the Pb-Na alloy and the 8-and 8"-alumina and only Na was transferred in the 8-and ~"-alumina during the coulometric titrations. Thermodynamic stabilities of ~-and ~'-alumina in both liquid Pb and liquid PbCI~ are discussed based on the thermodynamic data.Beta-alumina (g-, and ~"-alumina) is a typical Na § ion conductor. The crystal structures of ~-and ~"-alumina differ from each other and the difference is characterized by the structures of spinel block and conduction plane. Betaalumina has been applied as a solid electrolyte for various kinds of investigations in the materials science and metallurgy fields. A typical application in metallurgy is the measurement of the thermodynamic properties of liquid alloys (1-15), as shown in Table I. Using the beta-alumina solid electrolyte, the in situ preparation of the liquid alloy with a desired composition is possible by means of a coulometric titration. The coulometric titration method has also been applied in several investigations (4-8, 10-14) as shown in Table I. In these investigations, coulometric titration was carried out only in the direction from pure Na to the Na-M(M = Cd, Ga, In, Sn, Cs, Hg, T1, Pb, Bi) alloys in order to change the liquid alloy composition. Therefore, the ion selectivity during the coulometric titration was not known. Fray (16, 17) used Ga § and In § to purify Ga and In, respectively. A small amount of alloying elements other than Ga and In passed through the Ga § and In+-~-alumina. Na § ions in the single-crystals of 8-and 8"-alumina can be completely ion exchanged by Pb 2 § ion (18-21) with the ionic conductivity of the pb2 § the highest of all the divalent ~"-alumina (19). Na § ions in the polycrystaUine ~"-alumina also can be easily ion exchanged by Pb z § ion in a molten salt (22,23).This study was undertaken to obtain information on the stability of ~-and ~"-alumina involved in the application of the purification and separation of liquid alloys. As a first step, the ion selectivity of polycrystalline ~-and ~"-alumina during the coulometric titration experiments was investigated using a galvanic cell with a liquid Pb-Na alloy electrode. ExperimentalExperimental principle.--The following double galvanic cell was assembled and the EMF's were measured Mo, Na(1) I ~-, or ~"-alumina IPb-Na(1), Mo [I] Mo, Pb-Na(1)l ~"-alumina IAu + Au2Na(s), Mo [I']The Pb-Na was used as the common electrode. Sodium was transferred between the Na and the Pb-Na electrodes by the coulometric titration.Regarding the reaction between beta-alumina and Pb-Na alloy during the coulometric titration experiment, t...

Thermodynamic properties of dilute solutions of various elements in liquid lead

“…The values of the electromotive force of the circuit, reported for dilute solutions, are close to the results of other studies. According to [38], the values of ln γ Na are in good agreement with the earlier obtained results [35] (Fig. 2).…”

“…The Pb-Na system exhibits signifi cant negative deviations from the ideal behavior. In [35][36][37][38], the thermodynamic properties of dilute sodium solutions in lead were studied by the electromotive-force method.…”

“…However Saboungi et al did not fi nd compositions at which γ ∞ Na were constant. Itoh and Kozuka [38] paid primary attention to the behavior of β-and β''-alumina in a coulometric variation of the composition of a Pb-Na alloy at a temperature not exceeding 410°C. The values of the electromotive force of the circuit, reported for dilute solutions, are close to the results of other studies.…”

“…Na on the composition in the Pb-Na system at 400°C according to (1) [35], (2) [36], and (3) [38]. properties of the system were fi rst examined in [46].…”

The Fast Silver Ion Conducting Solid-State Electrolytes for Deriving Thermodynamic Data

“…They are commonly used in electrochemical cells to measure chemical potentials of gases, liquids and solids. Detailed theory and practical applications of the solid electrolytes have been discussed in many review papers [3,6,[13][14][15][16][17][18][19][20][21][22]. Figure 3 shows ionic conductivity of some of the solid electrolytes in different temperature regions.…”