Corrosion and Oxidation (Coursework Sample)

6.12.10 Corrosion Environments
Corrosive environments include the atmosphere, aqueous solution, soils, acids bases inorganic solvents, molten salts, liquid metals, and last but not least, human body. On a tonnage basis, atmospheric corrosion account for the greatest loss. Moisture containing dissolved oxygen is the primary corrosive agent, but other substances, including Sulphur compounds and sodium chloride also contribute. This is especially tome of marine atmospheres, which are highly corrosive because of the presence of sodium chloride. Dilute sulphuric acid solution (acid rain) in industrial environment can also cause corrosive problems, metals commonly used for atmospheric applications include alloys of aluminum and copper and galvanized steel.
Water environments can also have a variety of compositions and corrosion characteristics; fresh water normally contains dissolved oxygen, as well as other minerals several of which account for hardiness.
Sea water contains approximately 3.5% salt (pre-dominantly sodium chloride). Sea water is generally more corrosive than fresh water frequently producing pitting and crevice corrosion. Cast iron steel, aluminum, copper, brass and some stainless steels are generally suitable for fresh water use, whereas titanium, brass, some bronze, copper nickel alloys and nickel- chromium- molybdenum alloys are highly corrosive resistant in sea water.
Soils have a wide range of compositions and susceptibilities to corrosion. Compositional variables include moisture, oxygen, salt content, alkalinity and acidity as well as the presence of various forms of bacteria. Cast iron and plain carbon steels both with and without protective surface coating s are found most economical for underground structures.
6.13 Corrosion Prevention
General techniques used include material selection, environmental alteration, design