Silver-iron cells

Silver—Iron Cells. The silver—iron battery system combines the advantages of the high rate capabiUty of the silver electrode and the cycling characteristics of the iron electrode. Commercial development has been undertaken (70) to solve problems associated with deep cycling of high power batteries for ocean systems operations. 

Fig. 13. Charge—discharge characteristics of a nominal 140-A-h silver—iron cell where the charge (-) is at 25 A for 8 h, A represents a 0.25 A float...

Since cadmium and iron are relatively insoluble in concentrated alkaline electrolytes, the hfe of the silver-cadmium and silver-iron cells is therefore limited by the rate of silver migration through the various layers of the separator system. Failure (internal short circuit) occurs when a metallic bridge is established through the separator between positive and negative electrodes. Multiple layers of separator are used to extend the life capability, however, at the expense of higher internal resistance. 

The silver half-cell half-equation is multiplied through by 2 before it is added to the iron(iii)/iron(ii) halfequation. This is done to make the number of electrons equal, so they cancel to generate the ionic equation ... 

The overall electrochemical cell reactions for the sUver-zinc, sUver-cadmium, and silver-iron systems, all of which use aqueous solutions of potassium hydroxide (KOH) for electrolyte, can be summarized as follows ... 

The separator system and the solubility of the active materials play critical roles in determining the wet and cycle lives of the silver-based cells. The separator must have a low electrolytic resistance for discharges at high rates, yet it must have high resistance to chemical oxidation hy the silver species as well as low permeability to colloidal silver, zinc, cadmium, or iron. 

Cells consist of porous sintered silver electrodes and high rate iron electrodes. The latter are enclosed with a seven-layered, controUed-porosity polypropylene bag which serves as the separator. The electrolyte contains 30% KOH and 1.5% LiOH. 

The cell shown in Figure 19-16 can serve as an example for calculations using Equation. One cell contains aqueous 1.00 M iron(in) chloride in contact with an iron metal electrode, and the other cell contains 1.00 M KCl in contact with a silver-silver chloride (AgCl/Ag) electrode. The half-reactions for these electrodes follow ... 

A galvanic cell can be constructed from a silver-silver chloride electrode in contact with a solution containing chloride anions and an iron electrode in contact with a solution containing iron(IIt) cations. 

Glyoxal-based fixatives work faster than formalin. Small biopsies may be ready to process after only an hour while properly grossed larger specimens are ready in about 6h. Structural detail is remarkable in its clarity (Fig. 12.9). Red blood cells are lysed, but that rarely presents a problem. Eosinophilic granules are reduced in prominence (see below). Special stains work well, except for tests for iron (the mildly acidic pH is detrimental) and the silver detection methods for Helicobacter pylori. Most notably, glyoxal-fixed tissues retain strong immunoreactivity for most antigens. The chemistry behind most of this is known. 

The two half-cells in a galvanic cell consist of one iron electrode in a 1 mol/L iron(II) sulfate solution, and a silver electrode in a 1 mol/L silver nitrate solution. 

Having identified the main features of electrochemistry, the remainder of this chapter will focus on the use of electrolytic cells and will use as examples the electrodeposition (or electroplating) of metals such as copper, zinc, iron, chromium, nickel and silver. The chapter will also consider the electrochemistry of some organic molecules. Electroanalysis will not be considered since a full description is not within the scope of this chapter. Eor those interested readers, there is a review on the topic [2],... 

Electroplating is achieved by passing an electric current through a solution containing dissolved metal ions as well as the metal object to be plated. The metal object acts as a cathode in an electrochemical cell, attracting metal ions from the solution. Ferrous and nonferrous metal objects are typically electroplated with aluminum, brass, bronze, cadmium, chromium, copper, iron, lead, nickel, tin, and zinc, as well as precious metals such as gold, platinum, and silver. Common electroplating bath solutions are listed in Table 7-1. 

Zinc has been nscd for ages to coat iron pails and pipes to prevent them from rusting — "galvanized iron. Zinc is also a part of many alloys (German silver and brass) and is important in the making of dry-cell batteries. 

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