How to avoid hot corrosion

Although corrosion problems cannot be completely remedied, it is estimated that corrosion-related costs can be reduced by more than 30% with development and use of better corrosion control technologies. Corrosion control measures include corrosion inhibitors, cathodic protection, and coatings (Priyantha et al., 2003). Corrosion of metals occurs when they come in electrical contact with a corrosive environment. Therefore metallic corrosion can be prevented by either changing the metal or altering the environment or by separating the metal from the environment as shown in Fig. 7.7 (Narayan, 1983). 

The deposition of molten salt on the surface of alloys results in accelerated corrosion for components used in boilers and gas turbines. In general, alloying 

Choice of substrate metal is usually governed by cost, weight and general physical, mechanical or fabrication properties and these factors will normally dictate a very limited number of possible materials, none of which may be ideal in resisting the corrosive enviromnent that will be encountered in service. Ideally a protective metal coating should exclude completely the corrosive environment from the substrate metal and, if this can be achieved, only the resistance of the coating metal itself to that corrosive enviromnent needs to be considered (Shreir, 1976). 

For adequate corrosion protection of a metal in an aggressive environment, it is important to select materials and techniques that are compatible. For example, addition of an organic inhibitor (e.g. pyridines, pyrimidines, quinolines) is sufficient to mitigate corrosion of metals in many corrosive media. However, these inhibitors have shown only limited success due to solubility and/or thermal stability problems in high-temperature, concentrated salt solutions such as in chemical heat pumps (Priyantha et al., 2003). 

The first and foremost question which comes into our mind is why coatings Simply, it can be answered that coatings can achieve the following  

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