Hi, need to submit a 1500 words paper on the topic Materials and Corrosion. Very often corrosion results in the formation of oxides and salts and the overall physical properties of the materials affected by corrosion are changed rendering the material useless in most cases. The major types of corrosion are discussed in the following paragraphs.
The most important feature of this type of corrosion is the contact with a stagnant solution which takes place in interstices, near seals, and in cervices made for nuts and rivet heads. The metals and alloys used in chemical plants and other industrial applications are covered with passive films of protective coatings in order to prevent contact with high concentrations of Cl- and H+ ions. When such places are left unclean for long durations after long usages of the plant, sand, and other substances also get deposited near metals and alloys which prevent the proper application of protective coatings. In such a scenario the crevices and interstices are more likely to come in direct contact with corroding media. The corroding fluids which commonly contains high concentrations of chloride ion are likely to get accumulated in the crevices made for nuts, rivets or any other type of hole. The prolonged contact with such chemical fluids starts the oxidation of the metals. The direct contact with aerated chloride rich media creates a differential aeration cell which destroys the passivity of the material. The oxidized metal starts dissolving into the chemical which is in contact with the metal, in the presence of oxygen and the prolonged contact can corrode the material completely.
The best way to prevent crevice corrosion is to prevent crevices. This can be done by using welds in place of bolts and rivets in joints. The design of various components should be done in such a way that there is always a drainage mechanism for the accumulating fluid so that the harmful corroding liquids do not come in contact with the metals for a long duration of time. . .