Problem of corrosion and its prevention

Most of the materials used in the construction for bleaching equipment, are corroded due to free chlorine dioxide gas evolved during bleaching process. Various approaches have been suggested to minimise the evolution of chlorine dioxide gas and corrosion problem. 

The ammonium salts appear to act by neutralising chlorite solutions. Moreover, they appear to improve bleaching at 100 C. 

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Ordinary corrosion is the redox process by which metals are oxidized by oxygen, O2, in the presence of moisture. There are other kinds, but this is the most common. The problem of corrosion and its prevention are of both theoretical and practical interest. Corrosion is responsible for the loss of billions of dollars annually in metal products. The mechanism of corrosion has been studied extensively. It is now known that the oxidation of metals occurs most readily at points of strain (where the metals are most active ). Thus, a steel nail, which is mostly iron (Section 22-7), first corrodes at the tip and head (Figure 21-11). A bent nail corrodes most readily at the bend. 

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