Cuprous anodic oxidation

Lamache M, Bauer D (1979) Anodic oxidation of cuprous sulfide and the preparation of nonstoichiometric copper sulfide. Anal Chem 51 1320-1322. 

Copper Corrosion Inhibitors. The most effective corrosion inhibitors for copper and its alloys are the aromatic triazoles, such as benzotriazole (BZT) and tolyltriazole (TTA). These compounds bond direcdy with cuprous oxide (CU2O) at the metal surface, forming a "chemisorbed" film. The plane of the triazole Hes parallel to the metal surface, thus each molecule covers a relatively large surface area. The exact mechanism of inhibition is unknown. Various studies indicate anodic inhibition, cathodic inhibition, or a combination of the two. Other studies indicate the formation of an insulating layer between the water surface and the metal surface. A recent study supports the idea of an electronic stabilization mechanism. The protective cuprous oxide layer is prevented from oxidizing to the nonprotective cupric oxide. This is an anodic mechanism. However, the triazole film exhibits some cathodic properties as well. 

Native copper ore is crushed, concentrated by washing with water, smelted, and cast into bars. Oxide and carbonate ores are treated with carhon in a smeller. Sulfide ore treatment is complex, hut. in brief, consists of smelling to a matte of cuprous sulfide, ferrous sulfide, and silica, which molten matte is treated in a converter by the addition of lime and air is forced under pressure through the mass. The products are blister copper, ferrous calcium silicate slag, and SO . Refining is conducted by electrolysis, and the anode mud is treated to obtain the gold and silver. See Fig. I. 

Other methods of formation are the addition of sodium carbonate to a solution of cupric sulphate and sodium chloride reduced with sulphurous acid,9 and that of an alkaline solution of sodium potassium tartrate to a solution of cuprous chloride and sodium chloride.10 At temperatures below 350° C. copper reacts with nitrous oxide to form cuprous oxide above this temperature the product is cupric oxide.u Cuprous oxide is also formed at the anode in the electrolysis of a solution of cupric sulphate,12 and by heating cupric oxide in steam. 

Cupric oxide, CuO.—This oxide is obtained as a black, amorphous powder by igniting cupric hydroxide, carbonate, or nitrate.7 It is also formed on copper anodes in electrolytic oxidation.8 The amorphous oxide can be converted into lustrous, cubic tetrahedra by heating with potassium hydroxide,9 the crystalline variety being also produced by ignition to redness in a platinum crucible of a small amount of cuprous chloride.10... 

K. Fischbeck and E. Einecke found that the cathodic polarization of ferrous, cuprous, calcium, and magnesium chromites produces chromic acid, whilst the other chromites are unaffected, and natural chrome ironstone behaves in a like manner, but other commercial chromites are reduced on cathodic polarization, and yield chromic acid on anodic polarization. Chromites behave as an intermediate electrode. 0. Unverdorben observed that chromyl fluoride, prepared by heating a mixture of fluorspar, lead chromate, and sulphuric acid, when passed into water, furnishes an aq. soln. of this oxide. The soln. was treated with silver nitrate, and the washed precipitate of silver chromate decomposed by hydrochloric acid. A. Mans said that anhydrous sulphuric acid or fuming sulphuric acid is not suited for the preparation because of its volatilization with the chromyl fluoride. 

These problems can be alleviated by electrolyzing, for example, a mixed solution of HCl and CuCl2 [38-40], The anode reaction is still the oxidation of chloride ion. The cathode reaction becomes the reduction of the cupric ion to cuprous ... 

A system based on a copper redox system [55] is a combined electrolytic and catalytic process carried out in a three-compartment cell. The cell consists of a central packed bed anode of graphite separated by an ion exchange membrane from a packed cathode bed of copper on one side, and on the other side a packed bed of Cu which acts as an absorber. In the absorption chamber the copper, after first being oxidised to cuprous oxide, is responsible for the oxidation of SO2 to sulphuric acid. 

The ceils are operated on a batch basis cuprous oxide falls from the anodes to the bottom of the tanks. At suitable intervals, the electrolysis is stopped, the residual electrodes removed for remelting, and the Cu O-NaCI slurry is agitated and pumped out of the cell for external separation of CujO<... 

As already stated, the pH of the solution alters the potential difference between the anodic and cathodic reactions and this is reflected in the plating rate which increases with pH. This is in agreement with the theoretical principles outlined earlier. The limit to which the pH can increase is determined by the value at which precipitation occurs. Large variations in pH may cause fine precipitates to form (e.g. nickel phosphite, cuprous oxide) and these may act as seed crystals for the complete reduction of the plating solution. 

Cupronickels (90/10 that contains 10% nickel or 70/30 with 30% nickel or Monel 400) have been used for many years in applications where sea water has been involved, for their good corrosion resistance. This fitness for purpose is specifically because of the cupronickels passive cuprous oxide (CU2O) film, which retards both the anodic dissolution of the alloy and the rate of oxygen reduction [7]. Based on studies by Gouda et al. and reported by Lee et al. [8], alloy 400 (= Monel 400 containing 66.5% nickel, 31.5% copper, and 1.25% iron) is much more susceptible to SRB-induced MIC compared to 70/30 cupronickel or brass. 

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