Electrolytic corrosion of copper

D 3482 Test Method for Determining Electrolytic Corrosion of Copper by Adhesives... 

ASTM D3482-90 (2000) Standard practice for determining electrolytic corrosion of copper by adhesives. 

Alloys of lead and thallium 2 are distinctive in that they have higher melting points than either component. The amount of thallium varies from 3 to 65 per cent. The alloy containing 10% thallium, 20% tin, and 70% lead is resistant to the corrosive action of mixtures of sulfuric, nitric, and hydrochloric acids. This alloy is especially recommended for use as anode for the electrolytic deposition of copper, in which its corrosion is less than one-fifth that of lead alone. 

External corrosion of copper hot water tubing underslab has resulted in a great deal of construction defect litigations due to this type of corrosion cell [17]. Oil and gas well casings also experience similar cell attack. The pipe at some depth below the surface is at a higher temperature since temperature increases with depth and thus becomes the anode. The cooler pipe near the surface and the surface piping make up the cathode, the soil is the electrolyte, and the pipe is the electrical connection. 

Galvanic corrosion is the enhanced corrosion of one metal by contact with a more noble metal. The two metals require only being in electrical contact with each other and exposing to the same electrolyte environment. By virtue of the potential difference that exists between the two metals, a current flows between them, as in the case of copper and zinc in a Daniell cell. This current dissolves the more reactive metal (zinc in this case), simultaneously reducing the corrosion rate of the less reactive metal. This principle is exploited in the cathodic protection (Section 53.7.2) of steel structures by the sacrificial loss of aluminum or zinc anodes. 

There is an accelerating trend away from the use of lead-containing solders in contact with potable water. The effects of galvanic corrosion of one of the substitute alloys (Sn3%Ag) in contact with a number of other metals including copper have therefore been studied . The corrosion of tin/Iead alloys in different electrolytes including nitrates, nitric and acetic acids, and citric acid over the pH range 2-6 were reported. The specific alloy Pb/15%Sn was studied in contact with aqueous solutions in the pH range... 

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

For long lengths of anode it is sometimes necessary to extrude one material over another to improve a particular characteristic. Thus titanium may be extruded over a copper rod to improve the longitudinal conductivity and current attenuation characteristics of the former lead alloys may be treated similarly to compensate for their poor mechanical properties. It should he noted that these anodes have the disadvantage that, should the core metal be exposed to the electrolyte by damage to the surrounding metal, rapid corrosion of the former will occur. 

Test methods for determining electrolytic corrosion with electrical insulating materials Method for determination of resistance to intergranular corrosion of austenitic stainless steels copper sulphate-sulphuric acid method (Moneypenny Strauss test) Specification for electroplated coatings of tin/lead alloys... 

Beryllium is obtained by electrolytic reduction of molten beryllium chloride. The element s low density makes it useful for the construction of missiles and satellites. Beryllium is also used as windows for x-ray tubes because Be atoms have so few electrons, thin sheets of the metal are transparent to x-rays and allow the rays to escape. Beryllium is added in small amounts to copper the small Be atoms pin the Cu atoms together in an interstitial alloy that is more rigid than pure copper but still conducts electricity well. These hard, electrically conducting alloys are formed into nonsparking tools for use in oil refineries and grain elevators, where there is a risk of explosion. Beryllium-copper alloys are also used in the electronics industry to form tiny nonmagnetic parts and contacts that resist deformation and corrosion. 

DEZINCIFICATION. A form of electrolytic corrosion observed in sume brasses where the copper-zinc alloy goes into solution with subsequent redepnsition of the copper. The small red copper plugs thus formed in the brass are usually porous and of low strength. In recent years, the term dcziticilicalion lias also been applied in a more general sense to signify any metallic corrosion process that dissolves one of the components from an alloy. 

Copper is by far the cheapest and most convenient material for use in making such a cell. Other metals such as magnesium, nickel, and monel metal have been used. Although there is some corrosion of the vessel and diaphragm, and some copper fluoride is formed in the electrolyte, this does no harm, but if, after a number of regen-... 

Such a view was confirmed by many detailed experiments in the first half of this century. These experiments included direct studies of the rate and products of the corrosion of a metal as a function of the electrolytic conduction of the moist film. They also involved an imaginative extrapolation from experiments on energy-producing electrochemical cells, in which, e.g., separate pieces of zinc and copper were immersed in an electrolytic solution, to a situation in which an actual piece of impure (copper-containing) zinc decayed when brought into contact with a film of moisture that contained dissolved electrolyte. 

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