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Metal corrosion is a slow process of destruction of metal objects, after chemical reactions that occur on the surface of metals, alloys, under the action of the environment. Corrosion process is influenced by a number of internal and external factors.
Internal factors are those tied to metal, such as: steel structure, surface condition, presence at surface of protection films, etc. way of processing. Usually, pure metals does not corrode, in contrast, metals that contain various impurities, such as metals that have uses in technique, the very presence of these impurities favors corrosion.In the modern technique they are known various methods of protection against corrosion. Of these the most important and most common are:
- Choosing the appropriate materials for construction of various metal parts and equipment (especially for the chemical industry where one can find the most corrosive environments).
- Corrosion can be prevented using special substances called protease. In steel structures, the most used method of protection against corrosion is to isolate the surface material for the environment by a protective layer that can be metallic or organic -Metallic coating can be achieved by metallization and electroplating. Metallization is the process which one may cover a metal with an alloy of the metal.Thus, if a piece of steel is covered with aluminum and it is heated to a temperature less than melting temperatures of the two metals, it will form at the surface of steel object an alloy of iron and aluminum which is resisting to corrosion well. In the same way the iron may be covered with an iron-zinc alloy, if the iron object is held in zinc vapor.
1. Presence of impurities in metals: Speed of corrosion increases with
the presence of impurities in the metals because these impurities help
in setting up the voltaic cells.
2. Presence of electrolyte: Electrolytes present in water also increases
the rate of corrosion e.g. corrosion of iron in sea water takes place in
large extent than in distilled water because sea water contains salts i.e.
3. Position of metals in e.m.f. series: Highly reactive metals undergo
corrosion faster than least reactive metals. Reactivity of metals can be
found from the electrochemical series.
4. Presence of carbon dioxide in water: Presence of carbon dioxide in
natural water also increases the rusting of iron because it acts as an
electrolyte and increases the flow of electron from one place to
5. Presence of protective coating: When the iron surface is coated with
the metal, which is more reactive than the iron, then the rate of
corrosion is retarded e.g. when iron is coated with zinc, iron is
protected from rusting.
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