Cathodes amalgam cathode

Polyfluorobenzyl alcohols are one class of fluorinated starting materials for medicinal and agricultural usage. Practical electrochemical methods for the product-selective synthesis of polyfluorobenzyl alcohols have been developed [79, 80], 2,3,4,5,6-Pentafluorobenzoic acid is reduced selectively to 2,3,4,5,6-pentafluorobenzyl alcohol at amalgamated lead, zinc and cadmium cathodes in aqueous sulfuric acid solutions, while 2,3,5,6-tetrafluorobenzyl alcohol can also be obtained selectively by using the non-amalgamated cathodes in solutions containing small amounts of a quartemary ammonium salt [79],... 

This issue has been investigated using amalgam cathodes, and the indications are that the cryptand has negligible influence on the rate of incorporation of a sodium ion into the amalgam (Chen et ai, 1991 Doan et al, 1991). One of the most interesting applications of the cryptands is that they increase the mobility of dipositive ions in polymer electrolytes (Chen and Shriver, 1991). 

Nitric acid dissolved in sulphuric acid is reduced eleetrolytieally at an amalgamated cathode almost exclusively to hydroxylamine, although such a cathode has a distinct electrolytic reducing action on hydroxylamine sulphate. On the other hand, nitric acid is reduced almost completely to ammonia at a copper cathode which is effective only at... 

The computed value E1 indicates the theoretical decomposition voltage of sodium chloride in a solution with unit activity of both sodium and chloride ions if a reversible insoluble anode and a reversible amalgam cathode which contains 0.206 per cent of Na are used (at a temperature of 25 °0). 

Many lithium salts, such as lithium perchlorate and the halides, are soluble in nonaqueous solvents. The reduction potential of Li depends on the electrode and the solvent. At a mercury cathode amalgam formation takes place, whereas formation of lithium metal occurs at platinum in aprotic media. Lithium metal is less reactive than sodium, and in some solvents sodium attacks the solvent whereas lithium is unreactive. A small water content in an aprotic solvent may react with lithium (or Li may react with hydroxyl ions formed at the cathode) to form lithium hydroxide, which may cover the electrode with an insoluble, insulating layer. 

Using a Pb amalgam, cathode production of Pb-alkali-metal alloys from aq alkalichloride is possible. The electrolysis is performed at ca. 40°-80°C. The Pb-alkali-metal alloy is separated from the amalgam on cooling. Residual Hg is evaporated Formation of Li-Pb compounds during electrolysis of LiOH solns at a Pb cathode is inferred from measurements. ... 

Udupa, H.V.K. Rotating Amalgamated Cathode for the Preparation of Salicylaldehyde Bulletin De L Academie Polonaise Des Sciences Serne De Sciences chimiques Volume IX, No. 2, 1961... 

Silver oxide cells were developed in the 1960s. These cells use silver oxide mixed with carbon (to increase the electronic conductivity of the material) as cathode, amalgamated pellet zinc powder as anode, and a solution of potassium hydroxide or sodium hydroxide with dissolved zin-cates in water as electrolyte. Permion (a radiation graft of methacrylic acid onto a polyethylene membrane) is used as separator. The cell reactions are... 

The sodium amalgam cathode product of the electrolyzer of the mercury cell is the chief difference between this and the diaphragm cell. The production of sodium hydroxide from this stream uses a separate set of electrochemical reactions conducted in a decomposer or denuder. This unit is usually located below the electrolyzer so as to allow gravity feed of the sodium amalgam from the electrolyzer to the top end of the decomposer (Fig. 8.4). Deionized water is fed into the bottom of the decomposer to provide countercurrent flows of sodium amalgam and water. Mercury, stripped (or denuded) of sodium, is continuously drawn off the bottom of the decomposer, and a hot solution of 50-70% sodium hydroxide in water, plus hydrogen gas, from the top. 

To avoid getting into diffusion-limited regimes arising from the solubility limitations, the amalgam should be stirred sufficiently to reduce the thickness of the diffusion layer. However, impurities such as Mg2+ in the brine can deposit on the amalgam cathode as Mg(OH)2 retarding the convection of the amalgam. Hence, brine purity becomes an important issue in mercury cell operations. 

Weston cell (cadmium cell) A type of primary voltaic cell, which is used as a standard it produces a constant e.m.f. of 1.0186 volts at 20°C. The cell is usually made in an H-shaped glass vessel with a mercury anode covert with a paste of cadmium sulphate and mercury(l) sulphate in one leg and a cadmium amalgam cathode covered with cadmium sulphate in the other leg. The electrolyte, which connects the two electrodes by means of the bar of the H, is a saturated solution of cadmium sulphate. In some cells sulphuric acid is added to prevent the hydrolysis of mercury sulphate. It is named after Edward Weston (1850-1936). 

Grube s horizontal mercury cell more closely resembled the standard salt electrolyzers and had an asbestos diaphragm between the electrodes in order to isolate the amalgam cathode from sulfuric acid. This cell produced pure caustic soda free of chloride ions from its amalgam decomposer. However, voltage and energy consumption still was high ( 4,000 kWhr t NaOH). 

Formation of the alkane is believed to require a strongly acidic electrolyte and the highest yields have been obtained using lead, zinc, and zinc-amalgam cathodes/ t In contrast, low yields of the 1,2-diol (VIII) have been isolated... 

Thus of the separated reference anodes, the mercurous sulphate electrode is even somewhat superior to the calomel electrode because of its lower polarizability. As reference cathodes, amalgam electrodes have proved to be best. 

Si-based cells. The Weston standard cell (cell 22.5) uses a Cd/Hg amalgam cathode, but use of this cell is declining. Cadmium is toxic and environmental legislation in the European Union and US in particular has led to a reduction in its use. Cadmium used in NiCd batteries can be recycled, but its use in other areas is expected to decrease. 

The overpotential of sodium on the amalgam cathode is caused by the limited diffrision rate of the liberated sodium atoms into the amalgam, but it is small compared to the chlorine overvoltage. 

Samarium, europium and ytterbium can readily be removed from lanthanon mixtures by reductive extraction from a buffered acidic solution into a dilute (0.5% or less) sodium amalgam, Marsh (1957), or by electrolyzing an alkaline citrate solution with a lithium amalgam cathode, Onstott (1955, 1956). Europium can be obtained especially pure from such amalgams by treatment with cold concentrated HCl, which causes precipitation of sparingly soluble EuC. 2H2O, Hulet et al. (1972), by the common-ion effect. Both Sm(II) and Yb(II) are rapidly oxidized by hydronium ion to the very soluble trihalides, but oxidation of Eu(II) in the absence of oxygen proceeds slowly. 

Sodium hydroxide is manufactured by electrolysis of concentrated aqueous sodium chloride the other product of the electrolysis, chlorine, is equally important and hence separation of anode and cathode products is necessary. This is achieved either by a diaphragm (for example in the Hooker electrolytic cell) or by using a mercury cathode which takes up the sodium formed at the cathode as an amalgam (the Kellner-Solvay ceW). The amalgam, after removal from the electrolyte cell, is treated with water to give sodium hydroxide and mercury. The mercury cell is more costly to operate but gives a purer product. 

L. radius, ray) Radium was discovered in 1898 by Mme. Curie in the pitchblende or uraninite of North Bohemia, where it occurs. There is about 1 g of radium in 7 tons of pitchblende. The element was isolated in 1911 by Mme. Curie and Debierne by the electrolysis of a solution of pure radium chloride, employing a mercury cathode on distillation in an atmosphere of hydrogen this amalgam yielded the pure metal. 

Chloiine is pioduced at the anode in each of the three types of electrolytic cells. The cathodic reaction in diaphragm and membrane cells is the electrolysis of water to generate as indicated, whereas the cathodic reaction in mercury cells is the discharge of sodium ion, Na, to form dilute sodium amalgam. 

Overvoltages for various types of chlor—alkali cells are given in Table 8. A typical example of the overvoltage effect is in the operation of a mercury cell where Hg is used as the cathode material. The overpotential of the H2 evolution reaction on Hg is high hence it is possible to form sodium amalgam without H2 generation, thereby eliminating the need for a separator in the cell. 

Fig. 7. Mercury cathode electroly2er and decomposer (11) 1, brine level 2, metal anodes 3, mercury cathode, flowing along baseplate 4, mercury pump 5, vertical decomposer 6, water feed to decomposer 7, graphite packing, promoting decomposition of sodium amalgam 8, caustic Hquor exit 9, denuded mercury 10, brine feed 11, brine exit 12, hydrogen exit from decomposer 13, chlorine gas space 14, chlorine exit 15, wash water.

In the case of the alkaline manganese dioxide cell, only high quaUty synthetic manganese dioxide, typically an EMD (224), is used and graphite is the cathode. The anode is an amalgamated 2inc. Potassium hydroxide serves as the electrolyte and the reaction can be summari2ed as follows ... 

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