Unit 3 Corrosion

Ex.1 learn the new words.

corrosion - коррозия	electrochemical oxidation- электромеханическое окисление
disintegration- дезинтеграция, распад	oxide of iron – оксид железа
rusting- ржавление, коррозия	structural alloy - конструкционный сплав
uniformly – однородно, равномерно	immersed - погруженный
humidity - влажность	exposed surface – открытая, незащищенная поверхность
salinity - соленость	fluctuation - колебание
amplify - усиливать	gasket – прокладка, набивка
crack – трещина	seal - изоляция
sulfuric acid - серная кислота	seam – шов, стык, рубец
deterioration – ухудшение, износ	to be subject to – быть подверженным чему-либо
plating - обшивка	enamel - эмаль
painting - окраска	aerospace - воздушное и космическое пространство
treatment - обработка	roller - валик
brush- кисть, щетка	flexible - удобный, гибкий
polyurethane - полиуретан	coating - покрытие
durable - долгопрочный	do for - разрушать; убираться; быть достаточным
slip resistant – не скользящий	waterfront – порт, береговая линия
merely – по крайней мере	solid solution - твёрдый раствор

Ex.2 Read and translate the text.

Corrosion

Corrosion is the disintegration of an engineered material into atoms due to chemical reactions with its surroundings. This means electrochemical oxidation of metals in reaction with oxygen. Formation of an oxide of iron in solid solution is a well-known example of electrochemical corrosion, commonly known as rusting. Corrosion can occur in other materials, such as ceramics or polymers.

Many structural alloys corrode merely from exposure to moisture in the air. Corrosion can form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. There are different types of corrosion: galvanic corrosion, pitting corrosion, crevice corrosion, microbial corrosion, high temperature corrosion etc.

Galvanic corrosion¹ occurs when two different metals electrically contact each other and are immersed in an electrolyte. Galvanic corrosion is of major interest to the marine industry where water can contact pipes or metal structures.

Factors such as relative size of anode, types of metal, and operating conditions (temperature, humidity, salinity) will affect galvanic corrosion.

Pitting corrosion². Certain conditions, such as low concentrations of oxygen or high concentrations of species such as chloride can re-form a passivating film. All of the surface will remain protected, but tiny local fluctuations will degrade the oxide film in a few critical points. Corrosion at these points will be greatly amplified, and can cause corrosion pits of several types, depending upon conditions. This problem is especially dangerous because it is difficult to detect before a part or structure fails.

Crevice corrosion³ occurs in spaces to which the access of the working fluid from the environment is limited. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.

Microbial corrosion³ is promoted by microorganisms. It can apply to both metals and non-metallic materials, in both the presence and lack of oxygen. Sulfate-reducing bacteria⁴ produce hydrogen sulfide, causing sulfide stress cracking. In presence of oxygen, some bacteria directly oxidize iron to iron oxides and hydroxides, other bacteria oxidize sulfur and produce sulfuric acid causing biogenic sulfide corrosion.

High temperature corrosion is chemical deterioration of a material under very high temperature. This non-galvanic form of corrosion can occur when a metal is subject to a high temperature atmosphere containing oxygen, sulfur or other compounds. For example, materials used in aerospace, power generation and even in car engines have to resist high temperature in which they may be exposed to an atmosphere containing potentially highly corrosive products of combustion.

Plating, painting, and the application of enamel are the most common anti-corrosion treatments. They work by providing a barrier of corrosion-resistant material between the damaging environment and the structural material that is often cheaper, tougher, and easier-to-process. It is often wise to plate with a more active metal such as zinc or cadmium. Painting either by roller or brush is more desirable for tight spaces; spray would be better for larger coating areas such as steel decks and waterfront applications. Flexible polyurethane coatings can provide an anti-corrosive seal with a highly durable slip resistant membrane.

Notes to the text

1. galvanic corrosion – гальваническая коррозия

2. pitting corrosion – точечная коррозия

3. crevice corrosion – щелевая коррозия

4. Sulfate-reducing bacteria – сульфатвосстанавливающие бактерии, железобактерии

Ex.3 Read and translate international words.

Application , polyurethane, anti-corrosive, membrane, temperature, atmosphere, barrier, product, bacteria, disintegration, Formation, electrochemical, galvanic, electrically, contact, metal structure, concentration, microorganism, process, electrolyte, deposit, spray, zinc, cadmium, steel, hydroxide, stress, critical, oxide.

Ex.4 Mach the word stems in column A with the suffixes in column B.

corro -	–ics
disintegra -	–ive
surround -	–able
dur -	–gen
hydro-	–ing
ceram -	–sion
moist -	–ous
differ -	–ize
damag -	–tion
danger -	–ment
environ-	–ure
oxid-	–ent
volt-	–age

Ex.5 Answer the questions about the text.

1. Is corrosion a disintegration of an engineered material into atoms due to chemical reactions with its surroundings. 2. What electrochemical process do we call corrosion? 3.Why do many structural alloys corrode ? 4. When does galvanic corrosion occur? 5.Which factors affect galvanic corrosion? 6. Where does crevice corrosion occur? 7.What is microbial corrosion promoted by? 8.Does lack of oxygen slow down the corrosion? 9. In what branches of technology do materials have to resist high temperature ? 10.What are methods of anti-corrosive treatment?

Ex.6 Translate the following sentences paying attention to underlined words.

1.Passivation is extremely useful in alleviating corrosion damage, but care must be taken not to trust it too thoroughly. 2. Chemicals that inhibit corrosion include some of the salts in hard water, chromates, phosphates, polyaniline, other conducting polymers and a wide range of specially-designed chemicals that resemble surfactants. 3. At the end of the treatment, the pores are allowed to seal, forming a harder-than-usual surface layer. 4. Any corrosion products of gold or platinum tend to decompose spontaneously into pure metal, which is why these elements can be found in metallic form on Earth, and is a large part of their intrinsic value. 5. Climbing equipment is available in a wide range of anodized colors. 6. In order for galvanic corrosion to occur, an electrically conductive path and an ionically conductive path are necessary. 7. Whilst being resilient, anodized coating must be cleaned frequently. 8. On the other hand, sometimes unusual conditions can bring on passivation in materials that are normally unprotected, as the alkaline environment of concrete does for steel rebar.

Ex.7 Read the following determinations. Use this information in short dialogues.

Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact and immersed in an electrolyte. The same galvanic reaction is exploited in primary batteries to generate a voltage.

Pitting corrosion is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with limited diffusion of ions.

Crevice corrosion is a corrosion occurring in spaces to which the access of the working fluid from the environment is limited. These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.

Sulfate-reducing bacteria obtain their energy by oxidizing organic compounds or molecular hydrogen H2 while reducing sulfates to sulfides, especially to hydrogen sulfide. In a sense, they "breathe" sulfate rather than oxygen. Sulfate-reducing bacteria can be traced back to 3 billion years ago and are considered to be among the oldest forms of bacteria.

Ex.8 In each sentence choose the correct alternative. Consult the text in exercise 2. Translate the sentences.

1. Formation of an oxide of iron in solid solution is a well-known example of electrochemical corrosion, commonly/personally known as rusting. 2. Many structural alloys corrode only/merely from exposure to moisture in the air. 3. Corrosion can form a pit or crack, or it can extend across a wide area uniformly/totally corroding the surface. 4. Problem of pitting corrosion is actually/especially dangerous because it is difficult to detect before a part or structure fails. 5. Flexible polyurethane coatings can provide an anti-corrosive seal with a highly/extremely durable slip resistant membrane. 6. Galvanic corrosion occurs when two different metals mechanically/electrically contact each other and are immersed in an electrolyte. 7. In presence of oxygen, some bacteria entirely/directly oxidize iron to iron oxides and hydroxides.8. Materials used in aerospace, power generation and even in car engines have to resist high temperature in which they may be exposed to an atmosphere containing potentially/absolutely corrosive products of combustion.

Ex.9 Translate the text into English.

Корро́зия — это самопроизвольное разрушение металлов в результате химического или физико-химического взаимодействия с окружающей средой. В общем случае это разрушение любого материала, будь то металл или керамика, дерево или полимер. Причиной коррозии служит термодинамическая неустойчивость конструкционных материалов к воздействию контактирующей с ними среды. Например, коррозия железа в воде, которую называют ржавчиной.

В повседневной жизни для сплавов железа чаще используют термин «ржавление». Менее известны случаи коррозии полимеров. Применительно к ним существует понятие «старение». Например, старение резины из-за взаимодействия с кислородом или разрушение некоторых пластиков под воздействием атмосферных осадков, а также биологическая коррозия. Скорость коррозии, как и всякой химической реакции, очень сильно зависит от температуры. Повышение температуры на 100 градусов может увеличить скорость коррозии на несколько порядков.

Ex.10 Retell the text “Corrosion”.