Cells sealed

Liquid samples are analyzed in one of two ways. For nonvolatile liquids a suitable sample can be prepared by placing a drop of the liquid between two NaCl plates, forming a thin film that typically is less than 0.01 mm thick. Volatile liquids must be placed in a sealed cell to prevent their evaporation. 

Miniature zinc—mercuric oxide batteries may be made with either KOH or NaOH as the electrolyte. Cells having KOH operate more efficiently than those having NaOH at high current drains (Eig. 12) because of the higher conductivity of KOH. On the other hand, batteries with KOH are more difficult to seal, cells with NaOH are more resistant to leakage. 

Fig. 21. Retention of discharge capacity of miniature zinc—air battery having an unopened sealed cell after storage at 20°C (-) projected data (21).

Some manufacturers add a small (10—20% of the positive loading) amount of cadmium to positive plates as an antipolar mass to prevent some of the problems of reversal in sealed cells. This practice may, however, create as many problems as it solves in that positive capacity is reduced proportionally to the quantity of antipolar mass added. 

Cell Assembly. The methods for cell assembly, starting with the processed plaques depend on whether the cells are to be vented or sealed. For vented cells, processed plaques are usually compressed to 85 —90% of their processed thickness allowing sufficient porosity for electrolyte retention and strengthening the plate stmcture. For sealed cells, sizing of the negative plaques is usually avoided because maximum surface area is important to oxygen recombination. 

Tlie piismatic sealed cells are not self-supporting and are nomiaUy used in battery operation where the battery case is used to constrain cell cases because internal cell pressures in the range of 690 kPa (100 psi) are common. 

By far the majority of sealed cells are of the small cylindrical self-supporting type in the familiar "C," and "D" commercial sizes such as that... 

Tlie cover assembly usually contains a safety v ent. Tlie most common type consists of a steel or nickel diaphragm built into the cov er and a bent point cut from the cov er. At a certain internal cell pressure, the diaphragm niov es to the bent point and is pierced. Some cylindrical sealed cells use one or more temiinal feed-throughs employing glass-to-metal or ceramic-to-metal techniques. 

For increased power requirements, electrode constructions have been developed which bring the electronic conductors in closer contact with the active material particles first, around 1930, the sinter electrode [110], recently in sealed cells largely replaced by the nichel-foam electrode, and then, around 1980, the fiber structure electrode [111]. In order to take full advantage of their increased perform-... 

Demountable cells can be disassembled and may or may not use a spacer. Without a spacer, the liquid sample is simply applied to one salt plate, and the second plate is positioned over the first to smear the liquid out between the plates. Such a method cannot be useful for quantitative analysis because the pathlength is undefined and not reproducible. Also, the two salt plates may be positioned in the path of the light without a frame if there is a way to hold them there. If a spacer is used, it is positioned over one of the plates. The sample is applied to this plate in the cutout space in the spacer reserved for it, and the second plate is then positioned over the first with both spacer and sample in between. There are no inlet and outlet ports since the sample is not introduced that way. However, the plates, with sample, are placed in a frame, or holder, similar in appearance to the sealed cell, but without the ports. See Figure 8.18. Such a cell is also undesirable for quantitative analysis because of the difficulty in obtaining an identical pathlength each time the cell is reassembled. 

What are the differences between a sealed cell, a demountable cell, and a sealed demountable cell for liquid sampling ... 

Sealed cell, 2) demountable cell, and 3) sealed demountable cell. 

The rate was enhanced using ultrasound when carried out in a semi-sealed cell, which minimised the effects of ultrasonic degassing. An optimum acoustic power was found when using a source at a frequency of 20 kHz. 

In sealed cells, which are the most important kind of Ni-Cd batteries, the gas (H2 and O2) evolution accompanying discharge should be minimized. This can be achieved by incorporation of antipolar mass - cadmium hydroxide in the positive electrode. In this case overdischarge results in reduction of Cd(OH)2 to Cd, instead of hydrogen evolution [348]. On the other hand, oxygen evolved on the positive electrode during overcharging can react with cadmium [348] ... 

The state of charging, mainly of sealed cells, can be studied using galvanos-tatic methods [353] and electrochemical impedance spectroscopy [354-356] (see reviews [357, 358]). The battery behavior was analyzed using electronic network modeling [359, 360]. 

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