Electrolytic corrosion, copper

The Electrolytic Corrosion Test. Also developed for use on nickel—chromium and copper—nickel—chromium decorative automobile parts is the electrolytic corrosion (EC) test (44). Plated specimens or parts are made anodic in a corrosive electrolyte under controlled conditions for 2 min, and then tested for penetration to the substrate. 

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... 

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. 

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

Crevice corrosion occurs as a result of a non-uniform concentration of eletrolyte solution. The local electrode potential varies with the concentration of electrolyte corrosion currents (electron and ion migration) that occur in the metal and solution. For instance a piece of copper immersed in copper sulphate solution of varying composition, tends to be more positive in the region of high copper sulphate concentration due to the enhanced rate of deposition of Cu ions. A flow of electrons through the metal towards this region occurs and the ion deposition is a continuous process. As a result corrosion occurs in the metal where the solution concentration is at its lowest, and Cu ions pass into solution. 

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

Another corrosion mechanism, galvanic corrosion, is possible when two dissimilar metals such as copper and steel are connected together, whether buried or submerged. An electrolytic corrosion reaction will occur due to the difference in electrical potential between the two metals in contact with each other. This difference in potential produces a driving force, causing corrosion activity on the less noble of the two metals. Such galvanic couples must be avoided or isolated so that the possibility of corrosion damage is minimized. 

Are these corrosion cells common The answer is yes. Whenever a copper pipe service line is directly connected to a cast iron gas or water main, a galvanic cell is formed (Fig. 7.19) the soil is the electrolyte, the copper service line is the cathode, the iron (or steel) main is the anode, and the connecting circuit is completed by attaching the line to the main. Such cells may be relatively harmless when the anode or corroding metal occupies a much larger surface than the cathode so that the attack is spread out over a large area. 

Cells operating at low (2,80,81) and high (79,82) temperatures were developed first, but discontinued because of corrosion and other problems. The first medium temperature cell had an electrolyte composition corresponding to KF 3HF, and operated at 65—75°C using a copper cathode and nickel anodes. A later cell operated at 75°C and used KF 2.2HF or KF 2HF as electrolyte (83,84), and nickel and graphite as anode materials. 

Purification actually starts with the precipitation of the hydrous oxides of iron, alumina, siUca, and tin which carry along arsenic, antimony, and, to some extent, germanium. Lead and silver sulfates coprecipitate but lead is reintroduced into the electrolyte by anode corrosion, as is aluminum from the cathodes and copper by bus-bar corrosion. 

Copper is a galvanic metal and causes corrosion, in the presence of moisture, in nearby metals, such as cable sheathes, steel structure and water, gas or drain pipes, buried in its vicinity. With all such metafs. it forms a complete electrolytic circuit and corrodes them. Tinning may give protection against its galvanic effects but this is ati expensive proposition... 

In applying electrolytic protection, galvanized tubes can be installed downstream from copper components in water boilers without danger of Cu " -induced pitting corrosion. The protection process extends the application range for galvanized tubes with respect to water parameters, temperature and material quality beyond that in the technical regulations [16, 17]. 

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