Contamination of the electrolyte

Figure 8.1—Principle of zone electrophoresis. Each compartment is separated by a membrane to avoid contamination of the electrolyte by secondary products formed at the electrodes. The size and the sign of the charge carried by each species depends on the chemical medium in which they are found. The experiment can be carried out at constant current, constant voltage or constant power.

These solid electrolytes do conform to the conditions laid out in Wagner s theory and many important applications cein be foreseen which would require devices based on such solid electrolytes. Some of these applications aire of the open circuit variety such as solid electrolyte emf sensors for high temperature environments where contamination of the electrolyte may be a problem. But many other applications will be of the closed circuit variety and to a large extent this aspect has not been negotiated very rigorously in the traditional theory. Significant extensions of the traditional theory will have to be made before the performance characteristics of fuel cells and high temperature steam hydrolyzers can be successfully analyzed via the theory of mixed conduction in solids. 

Finally, the most important concerns regarding alloys as substitutes for Pt in fuel cell electrodes include the potential leach and contamination of the electrolyte membrane with cations coming from the dissolution of the base-metal therefore, the design of new catalysts requires not only optimizing the catalytic activity but also analyzing the stabihty of the Pt and non-Pt elements under proton exchange fuel cell conditions. 

In space applications, the advantages of greater mechanical simplicity mean that this approach is now used. However, for terrestrial applications, where the problem of carbon dioxide contamination of the electrolyte is bound to occur, renewal of the electrolyte must be possible. For this matrix-type cell, this would require a complete fuel cell rebuild. Also, the use of asbestos is a severe problem, as it is hazardous to health, and in some countries... 

Contamination of the Electrolyte with Ash Entrained with Coal... 

Eor the negative electrolyte, cadmium nitrate solution (density 1.8 g/mL) is used in the procedure described above. Because a small (3 —4 g/L) amount of free nitric acid is desirable in the impregnation solution, the addition of a corrosion inhibitor prevents excessive contamination of the solution with nickel from the sintered mass (see Corrosion and corrosion inhibitorsCorrosion and corrosion control). In most appHcations for sintered nickel electrodes the optimum positive electrode performance is achieved when one-third to one-half of the pore volume is filled with active material. The negative electrode optimum has one-half of its pore volume filled with active material. 

Figure 19-1 shows the experimental setup with the position of the steel test pieces and the anodes. The anodes were oxide-coated titanium wires and polymer cable anodes (see Sections 7.2.3 and 7.2.4). The mixed-metal experimental details are given in Table 19-1. The experiments were carried out galvanostatically with reference electrodes equipped to measure the potential once a day. Thus, contamination of the concrete by the electrolytes of the reference electrodes was excluded. The potentials of the protected steel test pieces are shown in Table 19-1. The potentials of the anodes were between U(2u-cuso4 = -1-15 and -1.35 V. 

Most oxygen trim systems interpose an additional link in the air/gas ratio controller. Others use an additional valve. Most types are based on the zirconia cell installed in the flue, while others use paramagnetic or electrolytic cell methods. The zirconia type has the advantage that there is no time lag in sampling, nor is there a risk of contamination of the sample. 

Electrolytic cells are constructed of materials that can withstand the action of the electrolytes and of the electrode products. The cell may be of the open type or may be partially or fully closed, depending on the requirement of handling the electrode products. Some of these cells will be described while dealing with the production of specific metals. Very stringent requirements are imposed when considering the design of electrolytic cells for the deposition of refractory and reactive metals. Most of such metals are produced by using molten salt electrolytes. These metals are prone to atmospheric contamination at the electrolysis temperature, and it is thus necessary to operate the cell under an inert atmosphere. 

An account of cell features should make a reference to the diaphragm. The diaphragm used in some electrolytic processes is essentially constituted of a separator wall, though this allows the free passage of the electric current. It performs the important function of preventing the products of electrolysis formed at the anode from coming into contact with those formed at the cathode so as to avoid, as far as feasible, either secondary reactions which would lower the current efficiency, or contamination of the products which would diminish their value. 

With the progress of electrolysis the concentration of aluminum (and of other base impurities) increases as a result of this the contamination of the cathode deposit also increases. A stage may be reached when the contamination exceeds acceptable limits, thereby calling for a premature termination of electrolysis. It is for this reason that it is desirable to purify and recycle the electrolyte wherever possible so that electrorefining could be conducted for extended periods, without having to contend with the problem of excessive contamination. 

There are a few reports of poly(naphthalene) thin films. Yoshino and co-workers. used electrochemical polymerization to obtain poly(2,6-naphthalene) film from a solution of naphthalene and nitrobenzene with a composite electrolyte of copper(II) chloride and lithium hexafluoroarsenate. Zotti and co-workers prepared poly( 1,4-naphthalene) film by anionic coupling of naphthalene on. platinum or glassy carbon electrodes with tetrabutylammonium tetrafluoroborate as an electrolyte in anhydrous acetonitrile and 1,2-dichloroethane. Recently, Hara and Toshima prepared a purple-colored poly( 1,4-naphthalene) film by electrochemical polymerization of naphthalene using a mixed electrolyte of aluminum chloride and cuprous chloride. Although the film was contaminated with the electrolyte, the polymer had very high thermal stability (decomposition temperature of 546°C). The only catalyst-free poly(naphthalene) which utilized a unique chemistry, Bergman s cycloaromatization, was obtained by Tour and co-workers recently (vide infra). 

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