Solid state galvanic cells

Let us investigate the steady state behavior of multicomponent crystals exposed to uniform but non-hydrostatic stresses. We first introduce some ideas on the thermodynamics of such solids (which will be discussed in more detail in Chapter 14). Solid state galvanic cells can be used to perform the appropriate experiments. 

Equation (8.67) can be integrated. If demixing is sufficiently small, a linearized version can be used. jy is found by measuring the electrical current in the solid state galvanic cell depicted in Figure 8-9. Experiments in this area are scarce. For recent reports see [D. Dimos et al. (1988) C. Reinke (1995)]. 

Figure 10-4, Solid state galvanic cell which establishes the oxygen potential at the metal/oxide interface b.

A solid state galvanic cell consists of electrodes and the electrolyte. Solid electrolytes are available for many different mobile ions (see Section 15.3). Their ionic conductivities compare with those of liquid electrolytes (see Fig. 15-8). Under load, galvanic cells transport a known amount of component from one electrode to the other. Therefore, we can predetermine the kinetic boundary condition for transport into a solid (i.e., the electrode). By using a reference electrode we can simultaneously determine the component activity. The combination of component transfer and potential determination is called coulometric titration. It is a most useful method for the thermodynamic and kinetic investigation of compounds with narrow homogeneity ranges. For example, it has been possible to measure in a... 

Solid oxides and fluorides satisfy the same conditions, and when used as electrolyte for forming solid state galvanic cells they are referred to as Solid Electrolytes. ... 

Use of Solid State Galvanic Cells In Metal Extraction and Refining... 

Ramasesha, S.K. and Jacob, K.T. (1989) Studies on nonisothermal solid state galvanic cells - effect of gradients... 

Determination of the standard molar Gibbs free energies of formation of the silicates of cobalt and nickel by solid-state galvanic cells involving the CaF2-based composite electrolyte, J. Chem. Thermodyn., 32, (2000), 931-935. Cited on pages 243, 244,437. 

Hotzel G. and Weppner W., Application of fast ionic conductors in solid state galvanic cells for gas sensors. Solid State Ionics, 18/19, 1223-1227, 1986. 

The basic element for the investigation of wiistite Fei jO (5 = deviation from ideal stoichiometry) is the solid-state galvanic cell... 

Solid state galvanic cells 9.2.1. General introduction... 

The general conclusion to be drawn from this specific examples is that solid state galvanic cells with solid electrolytes can be used primarily to measure free energies of reactions. From this, it is often possible to deduce the difference in chemical potentials (or the ratios of activities) of components of the participating phases. 

Before discussing further interesting applications of solid state galvanic cells, let us first examine the thermodynamic and electrical processes which occur in these cells in the light of the general transport theory of solids. We shall then be better able to understand the applications. 

Application of the general transport theory to solid state galvanic cells Let us once again consider, as a specific example, the cell Pt/FeO, Fe3 04/Zr02(-1-Me0)/Fe304, Fe203/Pt... 

Fig. 9-6. Variation of the electrical, chemical, and electrochemical potentials in the solid state galvanic cell illustrated in Fig. 9-5. The variation of the concentration of electrons is also shown. The transport number of the ions, in the electrolyte is equal to one.

Since the electrons and the electron holes in the crystal are in equilibrium with one another, the concentration of electron holes will vary inversely as the concentration of electrons throu the relationship e + h = 0. As a result, electron hole conduction will occur in the electrolyte when the oxygen potential is high. In this case, the term must be included in the bracketed expression of eq. (9-15). By substituting eq. (9-15) into eq. (9-13), we then obtain an expression for the emf of a solid state galvanic cell when the oxygen potential at the electrodes is different, and when mixed ionic and electronic conduction occurs in the electrolyte. This equation reads ... 

In this section we shall discuss some typical applications of solid state galvanic cells in the study of solid state reactions. The use of these cells to obtain thermodynamic data has already been discussed. For example, the emf of the galvanic cell [24]... 

Fig. 9-7. Schematic diagram of a solid state galvanic cell to measure the tarnishing rate constant for NiS.

Fig. 9-9. Reaction rate and super-saturation during the reaction Ag2+ S-f-H2(g)-(2 + 5)Ag-h H2S, measured with a solid state galvanic cell of the type Ag/AgI/ Ag2+.S/H2(g)/Pt.

These few examples of the application of solid state galvanic cells in the field of solid state reactions can only present a very limited view of this important area of solid state science. The examples were chosen primarily in order to demonstrate the principles according to which solid state research in thermodynamics and kinetics should be conducted with the use of electrochemical tools and methods. Such measurements are only possible because of the existence of suitable solid electrolytes. The most important of these are Zr02(-f CaO) and Th02(+Y2 03) for oxygen, silver halides and Ag4Rbl5 for silver, copper halides for copper, some glasses in which certain ions are dissolved, and p — Al2 03(-hNaO) for sodium. 

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