Essay Effect of Ph Level on Corrosion Rate
Substances with a pH less that 7 are considered to be acidic and substances with pH equal to or greater than 7 to be basic or alkaline. Thus, a pH of 2 is very acidic and a pH of 12 very alkaline. However, it is technically possible to have very acidic solutions with a pH lower than zero and concentrated caustic solutions with a pH greater than 14. Such solutions are in fact typical of many ore extracting processes that require the digestive power of caustics and acids.
Low pH acid waters accelerate corrosion by supplying hydrogen ions to the corrosion process. Although even absolutely pure water contains some free hydrogen ions, dissolved carbon dioxide (CO2) in the water can increase the hydrogen ion concentration. Dissolved CO2 may react with water to form carbonic acid (H2CO3) as shown in equation. where Keq is the reaction equilibrium expressed as a ratio.
Carbonic acid subsequently dissociates in bicarbonate and carbonate ions as expressed respectively in the following equations:
Rusting of iron consists of the formation of