General Corrosion in Aqueous Media

Copper, being a noble metal, has good resistance to corrosion. A thin adherent film of cuprous oxide and cupric carbonate is formed due to corrosion. Passivation is not a prominent process. The dissolved copper in solution affects the electrode potential such that the increase in velocity of the solution in contact with the metal results in increasing attack of the metal. Thus cuprous oxide is produced under dynamic flow of the solution. The thickness of the oxide film is about 500 nm. 

Depending upon the composition of the water, other products may be formed. Typically the dissolved species in water such as chloride, sulfate or carbonate, present in small concentrations, give rise to the chloride, sulfate or carbonate compounds of copper. 

The corrosion rates of copper in soft waters are greater than in hard waters since calcium carbonate precipitation in hard waters retards the corrosion rate of copper. Typically the corrosion rate of copper in distilled water is about 0.051-0.16 mm/yr and in rapid flowing conditions can be as high as 0.26 mm/yr. 

The corrosion rate of a totally immersed copper sample in seawater is about 0.02-0.07 mm/yr and at half-tide the rate is 0.02-0.1 mm/yr. In this respect the corrosion resistance of copper is 2-5 times greater than mild steel under total immersion conditions and even greater under half-tide conditions. The copper loses its corrosion resistance in seawater of velocities greater than 1 m/s and the rate of dissolution is such that toxic copper species produced are beneficial in that they are used in marine antifouling agents. 

Copper alloys C44300, C44500, C61300, C68700, C70600 and C71500 series are more corrosion resistant than copper in natural waters. In general these alloys contain corrosion-resistant metals such as nickel or metals such as iron and aluminum, which 

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General corrosion is the most common form of corrosion. This can be uniform (even), quasi-uniform, or uneven. General corrosion accounts for the greatest loss of metal or material. Electrochemical general corrosion in aqueous media can include galvanic or bimetallic corrosion, atmospheric corrosion, stray current dissolution, and biological corrosion (Table 1.1). 

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