Mercury cells anodes

Figure 4.5.19 depicts the schematics of the mercury cell anodes with an expanded titanium mesh [109]. Other types of mercury cell anodes use small diameter titanium rods or thin titanium blades. Electrical connection in the ceil is made through the boss using solid copper rods protected with a riser tube of titanium. A typical arrangement of anodes in a mercury cell is shown in Fig. 4.5.20. 

FIGURE 4.5.18. Configurations of mercury cell anodes (a) blade type (b) runner type (c) rod type (d) mesh type [106]. (Reprinted by permission of John Wiley Sons, Inc.)... 

Sconce illustrates a number of mercury-cell anodes ranging from flat horizontal plates to anodes with large numbers of grooves and holes. The value of e ranged from 0.06 to... 

Structure. The classical structure of anodes for this process still reflects the retrofitting concept used during the 1970s and the high current operations at ca. 10 kA/m. A typical mercury cell anode consists of a number of copper shafts, protected by either a permanently welded or removable titanium outer sleave, from which the current is distributed to the active surface over distributor bars (Fig. 68). 

The quick release of gas and the supply of fresh brine to the active surface are the major requirements of an mercury cell anode, and a wide range of designs have been built. The most common types are shown in Figure 69. The differences are more evident at current densities > 7 kA/m. The use of baffles on the back of the active surface to enhance the gas lift and aid the supply of brine to the active surface is also common [165]. 

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. 

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. 

Separation of the anode and cathode products in diaphragm cells is achieved by using asbestos [1332-21 -4] or polymer-modified asbestos composite, or Polyramix deposited on a foraminous cathode. In membrane cells, on the other hand, an ion-exchange membrane is used as a separator. Anolyte—catholyte separation is realized in the diaphragm and membrane cells using separators and ion-exchange membranes, respectively. The mercury cells contain no diaphragm the mercury [7439-97-6] itself acts as a separator. 

Recently it has been shown that the oxides of the platinum metals can have a higher corrosion resistance than the metals themselves , and have sufficient conductivity to be used as coatings for anodes, e.g. with titanium cores. Anodes with a coating of ruthenium dioxide are being developed for use in mercury cells for the electrolysis of brine to produce chlorine , since they are resistant to attack if in contact with the sodium-mercury amalgam. 

Another important primary battery is the mercury cell. It usually comes in very small sizes and is used in hearing aids, watches, cameras, and some calculators. The anode of this cell is a zinc-mercury amalgam the reacting species is zinc. The cathode is a plate made up of mercury(II) oxide, HgO. The electrolyte is a paste containing HgO and sodium or potassium hydroxide. The electrode reactions are... 

In the decomposer, deionized water reacts with the amalgam, which becomes the anode to a short-circuited cathode. The caustic soda produced is stored or evaporated, if higher concentration is required. The hydrogen gas is cooled by refrigeration to remove water vapor and traces of mercury. Some of these techniques are employed in different facilities to maximize the production of chlorine, minimize the consumption of NaCl, and also to prevent the buildup of impurities such as sulfate in the brine.26 The production of pure chlorine gas and pure 50% sodium hydroxide with no need for further concentration of the dilute solution is the advantage that the mercury cell possesses over other cells. However, the cell consumes more energy and requires a very pure brine solution with least metal contaminants and above all requires more concern about mercury releases into the environment.4... 

De Nora An electrolytic process for making chlorine and sodium hydroxide solution from brine. The cell has a mercury cathode and graphite anodes. It was developed in the 1950s by the Italian company Oronzio De Nora, Impianti Elettrochimici, Milan, based on work by I. G. Farbenindustrie in Germany during World War II. In 1958 the Monsanto Chemical Company introduced it into the United States in its plant at Anniston, AL. See also Mercury cell. 

A wide range of operating conditions and design philosophies affect mercury cell efficiency. For example, the fundamental distinction between a resaturation and a waste brine process influences the temperature and brine strength profile along the length of the cell and hence the overall efficiency. Another important factor is the quality of the brine. Impurities in the brine can cause base-plate deposits, which tend to reduce the anode/cathode gap. This gradual reduction in gap requires either manual or automatic adjustment and, eventually, the cell must be taken off-line and the thick mercury removed. 

One product that has been developed for mercury cells is a loose liner (Fig. 23.14), which is fitted on-site in the anode workshop and fastened with titanium nuts (Fig. 23.15). The riser tube is tightened using a Bakelite pressure plate. 

Two common types of button batteries both use a zinc container, which acts as the anode, and an inert stainless steel cathode, as shown in Figure 11.11 on the next page. In the mercury button battery, the alkaline electrolyte paste contains mercury(II) oxide, HgO. In the silver button battery, the electrolyte paste contains silver oxide, Ag20. The batteries have similar voltages about 1.3 V for the mercury cell, and about 1.6 V for the silver cell. 

Potassium hydroxide is produced commerically by electrolysis of a saturated solution of potassium chloride in brine using mercury cells consisting of a titanium anode and mercury cathode. Potassium reacts with mercury forming the amalgam which, on treatment with water, forms potassium hydroxide and hydrogen. 

Mercury cells, like dry cells, have a zinc anode and a use a mercuric oxide (HgO) cathode. The electrolyte is potassium hydroxide, KOH. These small, flat, metallic cells are widely used in watches, calculators, cameras, hearing aids, and other applications where small size is a premium. The reactions in the mercury cell are ... 

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