Read the text and say corrosion is.

Almost all metals and alloys subject to the action ofatmospheric air or other surrounding media (for example, sea water, soil, acid and alkali solutions, organic liquids, etc.) are gradually destroyed, beginning from the surface, and lose their initial appearance. This progressive destruction of a metallic surface exposed to an external aggressive (active) medium is called corrosion.

Experience shows that corrosive destruction depends mainly upon the following three factors: l) the chemical nature of the metal or composition of the alloy and their structures; (2) the chemical nature of the surrounding medium and the percentage of aggressive matter in metals (oxygen, moisture, acids, alkalis, etc.) and (3) the temperature of the surrounding medium.

As to its character, metal corrosion may be classified as: (1) uniform corrosion, in which the whole surface of the metal or alloy is corroded with equal intensiveness; (2) localised corrosion, in which only certain areas of the surface are attacked; (3) selective corrosion, where onlyseparate structural components of an alloy are affected and (4) intercrystalline corrosion, which involves destruction of the metal or alloy along its grain boundaries.

According to the mechanism of the corrosion process, it is necessary to distinguish between chemical and electrochemical corrosion.

Chemical corrosion conforms to the laws of chemical kinetics. A typical example of chemical corrosion is the oxidation and erosion of the valves of internal combustion engines by the incandescent products of combustion. A film of corrosion products, usually oxides, is formed on the surface of metal in the course of chemical destruction. In some cases this film may protect the underlying metal against further corrosion, i.е. make it more passive in respect to the surrounding medium.

Electrochemical corrosion occurs in the presence of liquids which are electrolytes containing free ions. The essence of electrochemical corrosion is that the atoms, on the surface of the metal in contact with the electrolytic solution, pass into the solution as ions and leave an equivalent quantity of electrons in the metal.

The principal corrosion protection methods applied in practice are: (1) alloying metals to obtain chemically inactive alloys of special composition; (2) forming oxide films on the surface of metal parts; (3) applying protective metallic coatings on the parts; (4) protecting the surface of’ metal with a coat of paint or lacquer.

2. Translate the following words and word-combinations from the text into Ukrainian: atmospheric air; sea water; soil; acid and alkali solutions; organic liquids; external aggressive (active) medium; the chemical nature of the metal; the composition of the alloy; the percentage of aggressive matter in metals; oxygen; moisture; acids; alkalis; the whole surface; equal intensiveness; certain areas of the surface; separate structural components; the laws of chemical kinetics; the valves of internal combustion engines; the incandescent products of combustion; electrolytic solution; the principal corrosion protection methods; paint; lacquer.

3. Write out the following word-combinations in English from the text: вплив оточуючого середовища; поступове руйнування; руйнування металу або сплаву вздовж меж зерен; хімічна корозія; електрохімічна корозія; плівка продуктів корозії; метал, який знаходиться знизу; подальша корозія; однакова кількість електронів у металі; легування металів; отримувати хімічно неактивні сплави певного складу; утворення оксидних плівок на поверхні металевих деталей; використання захисних покриттів; захист поверхні металу.

3. Which of the following statements are true/false?

1. Not all metals and alloys subject to the action ofatmospheric air or other surrounding media are gradually destroyed.

2. The progressive destruction of a metallic surface is called corrosion.

3. Chemical corrosion is closely connected with the laws of chemical kinetics.

4. Electrochemical corrosion takes place in the presence of liquids.

4. Choose the right variant.

1. Corrosive destruction depends mainly upon…

a) the chemical nature of the metal and the surrounding medium;

b) the temperature of the surrounding medium, the chemical nature of the metal or composition of the alloy;

c) the chemical nature of the surrounding medium and the percentage of aggressive matter in metals, the temperature of the surrounding medium and the chemical nature of the metal or composition (склад) of the alloy.

2. Metal corrosion may be classified as…

a) selective, intercrystalline, uniform corrosion.

b) uniform, localized, intercrystalline corrosion.

c) uniform, selective, localized, intercrystalline corrosion.

3. The principal corrosion protection methods applied in practice are…

a) alloying metals and protecting the surface of’ metal with a coat of paint or lacquer.

b) protecting the surface of’ metal with a coat of paint or lacquer, applying protective metallic coatings, forming oxide films on the surface, alloying metals.

c) forming oxide films on the surface of metal parts, applying protective metallic coatings.

6. Answer the following questions:

1. What process is called corrosion?

2. What factors does corrosive destruction depend upon?

3. How may metal corrosion be classified?

4. What is a typical example of chemical corrosion?

5. What is the essence of electrochemical corrosion?

6. What are the principal corrosion protection methods?

Student independent study: