Mercury cells steel base

A typical mercury cell is shown in Figs 3.3 and 3.4. It consists of a large, shallow trough, dimensions 15 m x 2 m x 0.3 m, with a steel base which slopes slightly from end to end so that the mercury can flow along the bottom of the cell. The coated, expanded titanium DSA anodes (see Fig. 3.1), each of approximate dimensions 30 cm X 30 cm, enter the cell from the top and are arranged parallel to the mercury surface with an anode-cathode gap of about 1 cm. The cell will have about 250... 

In all these cells, the mercury flows over a sloped (by 1.0-2.5%) steel base, and the flanged sidewalls are rubber-lined. The cell cover is steel lined with rubber or titanium on the underside or made of rubberized fabrics, and is fixed to the side walls by clamps. 

FIGURE 5.8. Cross section of the DeNora mercury cell [71]. (a) Cell base (steel) (b) Side wall (rubber-lined steel) (c) Lifting gear (d) Transverse support (e) Lengthwise support (f) Anode carrier (g) Anode rod (h) Anode surface (i) Adjustment motor (k) Bus bar G) Flexible anode current strap (m) Multilayer cell cover (n) Service walkway (o) Intercell bus bar (p) Switch (q) Insulator (r) Switch drive (s) Support. (With permission from John Wiley Sons, Inc.)... 

Electrosynthesis is based on the use of an electrochemical cell and a requisite for this technique is the use of electroactive moleeules, for example thiophene, pyrrole and aniline among organic monomers. The experimental setup is based on a galvanic cell, a potent ostat and two electrodes [206], as schematized in Fig. 1.18. The monomer is solubilized typically into organic solvents or in aqueous media and usually an electrolyte (e.g. lithium perchlorate or tetrabutylammonium acetate) is added. Platinum, carbon rods, magnesium, mercury, stainless steel can be used as electrodes and the electrosynthesis can be carried out with constant potential or constant current. The choice of the electrodic material, its shape and size play a cmcial role in many electrochemical reactions. 

The mercuric oxide-zinc (mercury) cell for miniature applications is usually based on the familiar button construction using a compressed cathode of mercuric oxide and graphite (added for conductivity) in a plated steel can. The cell seal is supported by a cathode sleeve, on top of which is placed a synthetic separator and an electrolyte absorbing pad. The electrolyte is a solution of potassium hydroxide. The amalgamated zinc anode is added and the cell sealed with a polymeric gasket and a metal top cap. 

Selection. The widely used cathode materials iaclude Hg, Pb, Al, Zn, Ni, Fe, Cu, Sn, Cd, and C. Because of mechanical iaconvenience, mercury is not an attractive electrode material for large cells. The preferred material is lead or an amalgam. Because Pb is soft and has a tendency to deform, however, it presents some mechanical problems. The problems can be overcome by hot dip or electroplating on steel, copper, or other rigid base material. 

Subcategory A encompasses the manufacture of all batteries in which cadmium is the reactive anode material. Cadmium anode batteries currently manufactured are based on nickel-cadmium, silver-cadmium, and mercury-cadmium couples (Table 32.1). The manufacture of cadmium anode batteries uses various raw materials, which comprises cadmium or cadmium salts (mainly nitrates and oxides) to produce cell cathodes nickel powder and either nickel or nickel-plated steel screen to make the electrode support structures nylon and polypropylene, for use in manufacturing the cell separators and either sodium or potassium hydroxide, for use as process chemicals and as the cell electrolyte. Cobalt salts may be added to some electrodes. Batteries of this subcategory are predominantly rechargeable and find application in calculators, cell phones, laptops, and other portable electronic devices, in addition to a variety of industrial applications.1-4 A typical example is the nickel-cadmium battery described below. 

Metrohm and BAS have also introduced improved DME models capable of operating in the SMDE mode. The Metrohm electrode (Fig. 14.6b) has a needle valve and small-bore capillary. Much of it is pneumatically controlled. The BAS version (Fig. 14.6c) is called the controlled growth mercury electrode (CGME). It is based on the work of Kowalski, Osteryoung, and coworkers [30]. Its features include a low-resistance electrical contact to the mercury thread in the capillary via a stainless steel tube and a fast response valve. The fast valve has allowed unique experiments to be performed where precise control of mercury drop growth during the experiment is desirable [31-33]. The BAS (Fig. 14.7), EG G Princeton Applied Research (Fig. 14.8), and Metrohm (Fig. 14.9) electrodes offer this easy and reproducible drop renewal in fully equipped cell stands. 

Experimental. All photodimerizations were carried out in a stainless steel fixed volume cell (1.75 cm ID with a 1.0 cm path length) with sapphire windows under the irradiation of a Hanovia medium pressure mercury lamp filtered through water and Pyrex for a 13.5 hour exposure. The cell and lamp assembly have been described previously (31). For selected runs a custom built 0.9 mL variable-volume pump was connected to the cell and the pressure was varied to determine the exact location of the phase boundary, based on light scattering measured in a Cary 2290 UV-Vis spectrophotometer (Varian Inst.). The spectrophotometer was also used to measure the concentrations of the monomeric cyclohexenone before and after reaction. 

If the mercury pump stops, the steel cathode base of the cell is exposed to electrolyte, and hydrogen evolves to form an explosive mixture with the chlorine in the cell. 

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