This work was done in order to investigate the ion exchange reaction between ~-Agl and B"-alumina and to develop a new technique for thermodynamic investigations by the EMF method using the B-alumina solid electrolyte. The following galvanic cell was assembled, and the EMF measurements were carried out in the temperature range of 325-806 K Mo, Na(s, l)l~"-aluminalAg + AgI, MoThe cell was kept at 626 K for 43 days, and an ion exchange reaction between ~-AgI and B"-alumina was allowed. The ion exchange reaction was confirmed by a change in the EMF. Electrodes were then shorted at 626 K through a resistor six times, and Na of a known quantity was transferred to the cathode. After each shorting, the cell's EMF was measured at various temperatures. Nal was finally formed at the cathode after the cell shortings, and then the EMF agreed with that of the cell in which Ag + AgI + Nal was used as the cathode. The ion exchange between Ag + ion in the ~-AgI and Na + ion in the ~"-alumina crucible proceeded smoothly by the retention of the cell at temperatures higher than 657 K. By conducting the experiment over a period of five months, equilibrium EMF's for the following two kinds of three-phase coexistences above 657 K were obtained: (i)solid Ag + solid AgI + liquid (Ag-Na)I and (ii) solid Ag + solid NaI + liquid (Na-Ag)I.In our previous studies (1-3), the following cells were assembled, and EMF measurements were made Mo, Na(s, 1)lB"-aluminalAg + AgI + NaI, Mo[I]and Mo, Na(s, 1)lB"-aluminalAg + AgI + ~"-alumina, Mo[II]Cell [I]'s EMF's were accurately determined, and the values were used as a measure of the degree of ion exchange in the cathode of cell [II]. In order to investigate the ion exchange between Ag + ion in ~-AgI and Na + ion in B"-alumina powder, the Na content in the cathode was changed by shorting the electrodes through a resistor. The experimental results revealed the occurrence of an ion exchange reaction between ~-AgI and ~"-alumina powder and the formation of NaI. The shorting electrode method also formed NaI, which was not a starting material. If an appropriate mixing ratio of the ~-Agl and B"-alumina powders was chosen, NaI may be formed in the cathode by the spontaneous ion exchange reaction between a-AgI and B"-alumina powder. This work was done to evaluate the ion exchange reaction between a-AgI and B'-alumina and to establish "shorting electrodes method" and "spontaneous ion exchanging method" for EMF measurements using B-alumina (B-and B"-alumina) solid electrolyte. For this purpose, the following cell was assembled and the EMF measurements were made using these two methods Mo, Na(s, 1)lB"-aluminalAg + AgI, Mo[III]
Experimental PrincipleIt was found in our previous works (2, 3) that the ion exchange reaction between Ag § ion in a-AgI and Na § ion in ~"-alumina can occur (i) between a-AgI and IY'-alumina powders in the cathode of cell [II] and (ii) between a-AgI powder in the cathode and ~"-alumina crucible used as a solid electrolyte. The ion exchange reaction is represented by * Electrochemical Soc...