Auxiliary electrolytes

The auxiliary electrolyte is generally an alkali metal or an alkaline earth metal halide or a mixture of these. Such halides have high decomposition potentials, relatively low vapor pressures at the operating bath temperatures, good electrolytic conductivities, and high solubilities for metal salts, or in other words, for the functional component of the electrolyte that acts as the source of the metal in the electrolytic process. Between the alkali metal halides and the alkaline earth metal halides, the former are preferred because the latter are difficult to obtain in a pure anhydrous state. In situations where a metal oxide is used as the functional electrolyte, fluorides are preferable as auxiliary electrolytes because they have high solubilities for oxide compounds. The physical properties of some of the salts used as electrolytes are given in Table 6.17. 

Figure 18.3—Principle of ISE measurement of fluoride ions in solution using a double junction reference electrode. The reference electrode is inserted into a separate chamber that contains the auxiliary electrolyte in order to avoid osmosis of KC1 into the sample solution. Also, 1 M KN03 can be used for F , Cl, CN or Ag+ determination. The measurement involves the use of a high impedance millivoltmeter (pH meter type). A version of an all-solid fluoride electrode is shown on the right.

The advantage of the processes mentioned above lies in the fact that no special devices are needed in the column to control output of the product. However, in case auxiliary electrolytes are needed in the process again, it becomes necessary to separate them from the solution leaving column I and from the resin leaving column II and this presents certain difficulties. 

Min, B.-K. and Choi, S.-D. (1995) SO2-sensing characteristics of Nasicon sensors with Na2SO4-BaSO4 auxiliary electrolytes. Sens. Actuators B, 95,209-15. 

Polymerization runs are reported in the same patent, where Cr-, Fe-, V-, Mn-, Ni-, Co-, Mo-, Zr- acetylaeetonates and titanyl-acetyl-acetonate are employed. Electrolyses were carried out using CH2CI2 as solvent and AICI3 as auxiliary electrolyte, between A1 electrodes with concentric electrode symmetry. A teflon-coated magnetic stirring bar was provided for agitation of the electrolysis cell. Electrolyses, at constant current, were performed until the desired concentration of methylenebis(dichloroaluminium) was reached... 

Dyes Organic auxiliaries Inorganic auxiliaries Electrolytes NaCl,Na2S04... 

The temperature dependence of the e.m.f. of cells including tellurium iodides was determined Agl was used as an auxiliary electrolyte the chemical po-... 

Experimmtal results are shown in Fig. 39 together with the calculated curve IE2 — E,. Crosses rqn sent measurements with a cell arrangement without auxiliary electrolyte ... 

In TSP, a solution of the sample and an auxiliary electrolyte (usually ammonium acetate) passes through a heated capillary to enter the pumped ion chamber (1-10 Torr). A supersonic beam of charged droplets emerges at the entrance of the chamber, which is heated to aid the desolvation of Ore droplets. TSP produces essentially equal numbers of positively and negatively charged droplets the droplet charge is determined by the electrolyte ion... 

Min B-K, Choi S-D (2003) SO -sensing characteristics of Nasicon sensors with Na SO -BaSO auxiliary electrolytes. Sens Actuators B 93 209-213... 

FIGURE 9.16. Dc polarization technique for the determination of the partial ionic conductivity of mixed conductors by blocking the electronic current with an auxiliary electrolyte. Probes are used to measure the gradient of the electrochemical potential of the mobile ions. The stoichiometry of the mixed conductor is controlled by a reversible electrode (or by applying another auxiliary electrolyte with a counter electrode and the application of a voltage) that defines the activities at the right-hand side. 

For the measurement of the chemical diffusion coefficient D, an auxiliary electrolyte is used both to measirre the flux of ions into and out of the sample and to determine the concentration of the mobile species at the interface with the electrolyte. The rate-determining factor is assumed to be the diffusion of species within the mixed conducting solid and not the transport of ions across the interface. The change in the double layer charge at the interface must also be small compared to the charge transported into or out of the bulk of the sample. In order to verify this assnmption, typical valnes for the double layer capacities may be assumed and, better, samples with different lengths shonld be employed. 

Auxiliary electrolyte for one component n-phase equilibrium for n phases Auxiliary electrolyte for stoichiometrically variable component... 

Electrons blocked by auxiliary electrolyte, reversible electrode Reversible electrode, small weight changes... 

Reversible electrode, practically total conductivity Auxiliary electrolytes Auxiliary electrolyte, various signals... 

Contacts. Usually, good mechanical contacts to a soHd are best accomphshed by a liquid. Examples are the sodium/suUur and the zebra batteries where the solid electrolyte acts as a separator between two Hquid phases. In the case of the zebra battery [6], an auxiliary electrolyte, NaAlCU (which is Hquid at the operating temperature of the battery), is employed to provide the contact between the solid sodium electrolyte, Na/j8" alumina, and the positive electrode, NiCh. It is especially difficult to prepare all-soHd-state batteries - except possibly thin-film batteries with good contacts - because of differences in the thermal expansion coefficients of the different materials and because the appHcation of high temperatures may result in undesirable side reactions including the evaporation of alkaline oxides. Employment of binders may minimize the mechanical contact problem but may increase the electrical resistance and may lead to slow reactions with the organic component of the binder. 

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