Copper-lead cells

In this cell, the following independent phases must be considered platinum, silver, gaseous hydrogen, solid silver chloride electrolyte, and an aqueous solution of hydrogen chloride. In order to be able to determine the EMF of the cell, the leads must be made of the same material and thus, to simplify matters, a platinum lead must be connected to the silver electrode. It will be seen in the conclusion to this section that the electromotive force of a cell does not depend on the material from which the leads are made, so that the whole derivation could be carried out with different, e.g. copper, leads. In addition to Cl- and H30+ ions (further written as H+), the solution also contains Ag+ ions in a small concentration corresponding to a saturated solution of silver chloride in hydrochloric acid. Thus, the following scheme of the phases can be written (the parentheses enclose the species present in the given phase) ... 

Block B shows the electrolytic copper recovery cell, which recovers metallic copper and regenerates sulfuric acid from the metal salts in the hot sulfuric acid pickle solution. It was originally felt that trace metals (zinc, tin, lead) would interfere with the recovery of pure copper. By controlling current density at 50 to 100 A/m 1 2 3, however, pure copper can be recovered while maintaining the copper concentration in the pickle bath at 15 g/L. 

Electrorefining can be used to purify a metal by using alternate electrodes of a pure and impure metal. Impurities oxidized at the anode, which is made of the impure metal, travel into solution. By arranging the cell appropriately, the ion of the metal to be purified is reduced on the pure metal cathode. For example, copper metal that contains lead and iron may be used as one electrode and pure copper as the other electrode in a cell. When the proper voltage is applied, copper, lead, and zinc will be oxidized and move into the electrolyte. Because copper is more easily reduced compared to zinc and lead, it will be plated out at the pure copper cathode. Therefore, this process effectively removes the zinc and lead impurities from the copper. 

Fig. 3.25. The Pask-Nuyken device for measuring simultaneously the conductivity and the UV spectrum of a reaction mixture. A mixing chamber, B conductivity cell with jacket, C graded-seal borosilicate glass-soda glass, D jacketed quartz cell, E copper leads to platinum electrodes Pt, F graded-seal borosilicate glass-quartz.

The other important factor to affect the operational conditions of the cell is the voltage increase between the carbon and copper lead. This problem has been solved individually in industry. For example, a 250 pm thick layer of nickel can be coated onto the upper part of the carbon anode using the atmospheric plasma spraying method.7 This electrode has been operated at 15 to 17 A dm-2 in a 1000 A scale industrial cell for 19 months. The cell voltage was 9.5 V and polarization did not occur with this electrode. Characteristic points of this new carbon electrode are low polarizability and no anode effect, and the concentration of carbon tetrafluoride contaminating the fluorine is below 2 ppm. 

A solution in 500 c.cs. water is made from 110 gms. potassium acetate, 26 gms. potassium carbonate and 28 gms. potassium bicarbonate, and poured into a lead cell or glass beaker, which need contain no anode chamber. The beaker should be placed in a basin of cold water, and the cathode should take the form of a thin lead pipe, with a copper connection soldered to it, wound in the form of a coil, and placed close to the inner walls of the beaker. Through this pipe a supply of cold water is run, so that the temperature is maintained at 25°—30° during the electrolysis. The anode is of platinum, and should be so arranged that it can be rotated. The current density is 20—25 amperes per sq. dcm., and the E.M.F. 7—8 volts. 

Copper is required for the activity of enzymes associated with iron metabolism, elastin and collagen formation, melanin production and the integrity of the central nervous system. It is required with iron for normal red blood cell formation. Copper is also required for bone formation, brain cell and spinal cord structure, the immune response and feather development and pigmentation. A deficiency of copper leads to poor iron mobilization, abnormal... 

Considerable selenium losses in wound exudates following severe burns have been recorded, and supplementation of a mixture of selenium, zinc, and copper leads to a reduction in respiratory infections." Supplementation, even in apparently selenium-adequate individuals, has some immune function stimulatory effects, including improvement in natural kfller cell activity and increases in IL-2 receptor expression." It has been speculated that the increased infection rates in acquired immunodeficiency syndrome (AIDS) patients may be related to selenium depletion and this may even influence the progression from human immunodeficiency virus (HIV) positivity to the AIDS syndrome. " ... 

When the compensation potential is determined using the Kenrick apparatus, the mercury streams down the center of the vertical tube and the HCl solution down its walls so that the Volta potential difference across the air gap is eliminated. In this system both the concentration of HCl and the pressure of hydrogen gas can be varied. It differs from cells (8.7.8) and (8.7.16) in that no attempt is made to balance the charge carriers on opposite sides of the cell. The Galvani potential difference measured between the two copper leads can be related to the electrochemical potentials of electrons in the mercury and platinum as follows ... 

Galvanic corrosion is an accelerated corrosion of a metal due to formation of a corrosion cell with a metal or non-metallic conductor that exhibits a higher corrosion potential. For example, if a water pipe made of zinc-coated steel (galvanized steel) is connected to a brass fixture and caution is not taken to electrically isolate the two metals, a corrosion cell is established (Figure 7.5). To simplify the situation, we have replaced, in Figure 7.5, the zinc-coated steel by pure zinc and the brass by copper. The cathodic reaction is the reduction of dissolved oxygen, which takes place on both metals. The corrosion cell formed between the zinc and the copper leads to an accelerated corrosion of zinc near the joint. 

A - Lav it e block 0 -B - Stainless steel block P -C - Teflon plus T -D - Stainless steel bolt S -E - Copper leads S2 -F - Springs Cu -G - Glass tube cell holder Gr -L - Platinum lead... 

Deposition corrosion is a special case of galvanic corrosion that takes the form of pitting. It occurs when particles of a more cathodic metal in solution plate out on an aluminum surface to set up local galvanic cells. The ions aggressive to aluminiim ate copper, lead, mercury, nickel, and tin, often referred to as heavy metals. The effect of heavy metals is greato in acidic solutions. In alkaline solutions, their solubility is much lower, resulting in less severe effects (Ref 27). 

Copper-containing lead alloys undergo less corrosion in sulfuric acid or sulfate solutions than pure lead or other lead alloys. The uniformly dispersed copper particles give rise to local cells in which lead forms the anode and copper forms the cathode. Through this anodic corrosion of the lead, an insoluble film of lead sulfate forms on the surface of the lead, passivating it and preventing further corrosion. The film, if damaged, rapidly reforms. 

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