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Presentation - Corrosion of metals and methods of protection against corrosion

The text of this presentation

Chemistry lesson on the topic "Corrosion of metals and methods of protection against corrosion"
Prepared by the teacher of chemistry of the secondary school of the State Enterprise "Republican Rehabilitation Center for Children and Adolescents" Lepesbayeva Sandugash Kairatovna

Lesson Objectives:
to form students' understanding of the mechanism of corrosion processes, their consequences and methods of protection against corrosion; develop the ability to work with reference summary, observe, draw conclusions; educate an emotional attitude to the phenomenon being studied.

Cast iron
Alloy of iron with carbon (2-4%)
Steel
Alloy of iron with carbon (less than 2%)
Used in mold casting
By adding alloying elements improves the quality

In the III BC, a lighthouse was built on the island of Rhodes in the form of a huge statue of Helios. The Colossus of Rhodes was considered one of the seven wonders of the world, but it lasted only 66 years and collapsed during an earthquake. At the Colossus of Rhodes, the bronze shell was mounted on an iron frame. Under the influence of humid, salt-saturated Mediterranean air, the iron frame collapsed.

What is the symbol of Paris? - Eiffel Tower. She is incurably ill, rusts and collapses, and only constant chemotherapy helps to fight this deadly disease: she was painted 18 times, which is why her weight of 9000 tons increases by 70 tons each time.

Corrosion - a red rat, Gnawing on scrap metal. V. Shefner
Every year, up to ¼ of the produced iron is “lost” in the world ...

A.N. Nesmeyanov
To know is to win!

Journey through the realm of the "Red Devil"
Art. Informational
Art. experimental
Art. Practical

destruction of metals and alloys under the influence environment.
Corrosion

Types of corrosion
By the nature of the destruction, continuous (general): uniform, uneven local (local): point, spots, ulcers, subsurface, through, etc.

Types of corrosion
solid dotted

Ulcerative intergranular

Chemical corrosion
- the metal is destroyed as a result of its chemical interaction with an aggressive environment (dry gases, non-electrolyte liquids).
Formation of scale during the interaction of iron-based materials at high temperature with oxygen: 8ē 3Fe0 + 2O20 → (Fe+2Fe2+3)O4-2
Video fragment
Laboratory experience - glowing copper wire

Electrochemical corrosion
- in the electrolyte environment, an electric current arises when two metals come into contact (or on the surface of one metal having a heterogeneous structure); - corrosion resembles the work of a galvanic cell: there is a transfer of electrons from one part of the metal to another (from metal to inclusion).
Video fragment

The Fe2+ ions formed at the anode are oxidized to Fe3+: 4Fe2+ (aq) + O2 (g) + (2n + 4)H2O (l) = 2Fe2O3 nH2O (solid) + 8H+ (aq)
Corrosion of metal in humid air

Iron slightly corroded in water; in pure water, corrosion proceeds more slowly, since water is a weak electrolyte.
Let's compare the results of experiments No. 2 and No. 5

The addition of NaCl to water enhances the corrosion of Fe. the addition to the NaCl-NaOH solution, as can be seen from experience, on the contrary, weakened the corrosion, there was little rust.
Let's compare the results of experiments No. 1 and No. 2

That. The corrosion rate of a given metal depends on the composition of the surrounding medium. Some components of the metal-washing medium, in particular Cl- - ions, enhance the corrosion of metals, other components can weaken corrosion. Corrosion of Fe is weakened in the presence of OH- - ions.

In both cases, Fe is in the same solution, but in one case it is in contact with zinc, while in the other it is not. In test tube No. 2, the brown precipitate is rust, and in test tube No. 4, the white precipitate is Zn (OH) 2 it comes into contact with zinc.
Let's compare the results of experiments No. 2 and No. 4

Zn is oxidized as a more active metal
BUT (-)
split off from its atoms
move to the surface of Fe and restore
K(+)Fe

In both cases, Fe is in the same solution, but in one case it is in contact with copper, while in the other it is not. Corrosion occurred in both test tubes and a brown rust precipitate appeared. There was less rust in test tube No. 2 than in test tube No. 3. Conclusion: Thus, the corrosion and rusting of iron is greatly enhanced when it comes into contact with copper.
Let's compare the results of experiments No. 2 and No. 3

BUT (-)
K(+)Cu
The reaction of oxygen dissolved in water with iron leads to the formation of brown rust.

The corrosion of a metal increases sharply if it comes into contact with some other, less active metal, i.e., located in the electrochemical series of metals to the right of it. But corrosion slows down if the metal comes into contact with another metal located to the left in the electrochemical series of metal voltages, i.e., more active.

Corrosion protection
- Isolation of the metal from the environment - - Changing the environment

barrier protection
- mechanical isolation of the surface when using surface protective coatings: non-metallic (varnishes, paints, lubricants, enamels, gumming (rubber), polymers); metal (Zn, Sn, Al, Cr, Ni, Ag, Au, etc.); chemical (passivation with concentrated nitric acid, oxidization, carburization, etc.)

barrier protection

What surface protective coating was used in this case? Which group of surface protective coatings does it belong to?
Video fragment
barrier protection

Change in the composition of the metal (alloy)
Protective protection - the addition of powder metals to the coating material, which create donor electron pairs with the metal; creating contact with a more active metal (for steel - zinc, magnesium, aluminum).
Under the action of an aggressive environment, the powder of the additive gradually dissolves, and the base material does not corrode.

Rivets or plates of a more active metal are attached to the main structure, which are subject to destruction. Such protection is used in underwater and underground structures.

transmission electric current in the direction opposite to that which occurs during the corrosion process.
Change in the composition of the metal (alloy)
electrical protection

AT Everyday life man is most often found with zinc and tin coatings of iron. Sheet iron coated with zinc is called galvanized iron, and plated with tin is called tinplate. The first is used in large quantities on the roofs of houses, and tin cans are made from the second.
Change in the composition of the metal (alloy)
Video fragment

Introduction of alloying additives into the metal: Cr, Ni, Ti, Mn, Mo, V, W, etc.
Change in the composition of the metal (alloy)
alloying

Changing the environment
inhibition
The introduction of substances that slow down corrosion (inhibitors): - for acid corrosion: nitrogen-containing organic bases, aldehydes, proteins, sulfur-containing organic substances; - in a neutral environment: soluble phosphates (Na3PO4), dichromates (K2Cr2O7), soda (Na2CO3), silicates (Na2SiO3); - at atmospheric corrosion: amines, nitrates and carbonates of amines, esters of carboxylic acids.

In which test tube did the nail not rust and why?
Changing the environment

Changing the environment
Deaeration - removal of substances that cause corrosion: water heating; passing water through iron shavings; chemical removal of oxygen (for example, 2Na2SO3 + O2 → 2Na2SO4).

Think and explain (homework)
1. A plate of Zn and a plate of Zn, partially covered with Cu, were placed in a solution of hydrochloric (hydrochloric) acid. In which case is the corrosion process more intense? Motivate your answer by making electronic equations of the corresponding processes.
2. How does the atmospheric corrosion of nickel-plated iron proceed if the coating is broken? Compose the electronic equations of the anode and cathode processes.

1. I worked in the lesson 2. I worked with my work in the lesson 3. The lesson seemed to me 4. My mood 6. The material of the lesson was actively / passively satisfied / dissatisfied with the short / long became better / became worse understandable / not understandable useful / useless interesting / boring
Reflection

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The word corrosion comes from the Latin "corrodo" - "gnaw" (Late Latin "corrosio" means "corrosion"). Corrosion is caused by the chemical reaction of a metal with environmental substances occurring at the interface between the metal and the medium. Most often, this is the oxidation of a metal, for example, with atmospheric oxygen or acids contained in solutions with which the metal comes into contact. Metals located in the voltage series (activity series) to the left of hydrogen, including iron, are especially susceptible to this.

Chemical corrosion t Fe+ 3 SO O 2 Fe 2 (SO 4) t Fe + 3 Cl 2 2 FeCl t Zn + O 2 2 ZnO Corrosion occurs in a non-conductive medium. For example, the interaction of a metal with dry gases or liquids - non-electrolytes (gasoline, kerosene, etc.)

Many metals (for example, aluminum) during corrosion are covered with a dense, oxide film, which does not allow oxidizing agents to penetrate into deeper layers and therefore protects the metal from corrosion. When this film is removed, the metal begins to interact with moisture and oxygen in the air.

Electrochemical corrosion Corrosion occurs in a conductive medium (electrolyte) with the appearance of an electric current inside the system. Metals are not homogeneous and contain various impurities. When they come into contact with electrolytes, some parts of the surface act as anodes, others as cathodes.

Let us consider the destruction of an iron sample in the presence of a tin impurity. 1. In an acidic environment: On iron, as a more active metal, in contact with the electrolyte, the processes of oxidation (dissolution) of the metal and the transition of its cations to the electrolyte occur: Fe 0 - 2 e \u003d Fe 2+ (anode) At the cathode (tin) occurs reduction of hydrogen cations: 2H + + 2e H 2 0 iron ions (Fe 2+) go into solution

2. In an alkaline or neutral environment: Fe 0 - 2e Fe 2+ (at the anode) O H 2 O + 4e 4OH - (at the cathode) ________________________________________________________ Fe OH - Fe (OH) 2 4 Fe (OH) 2 + O 2 + 2H 2 O = 4 Fe (OH) 3 (Rust)

1. Sanding the surfaces of the product so that moisture does not linger on them. 2. The use of alloyed alloys containing special additives: chromium, nickel, which at high temperatures form a stable oxide layer on the metal surface (for example, Cr 2 O 3). forks, spoons), machine parts, tools.

3. Application of protective coatings Non-metallic - non-oxidizing oils, special varnishes, paints, enamels. True, they are short-lived, but they are cheap. Chemical - artificially created surface films: oxide, nitride, silicide, polymer, etc. For example, all small arms and parts of many precision instruments are burnished - this is the process of obtaining the thinnest film of iron oxides on the surface of a steel product.

Metallic is a coating with other metals, on the surface of which stable protective films are formed under the action of oxidizing agents. Application of chromium - chromium plating, nickel - nickel plating, zinc - zinc plating, etc. A chemically passive metal - gold, silver, copper - can also serve as a coating.

4. Electrochemical methods of protection 4. Electrochemical methods of protection * Protective (anodic) - a piece of a more active metal (protector) is attached to the protected metal structure, which serves as an anode and is destroyed in the presence of an electrolyte. Magnesium, aluminum, zinc are used as a protector in the protection of ship hulls, pipelines, cables and other steel products.

The introduction of substances - inhibitors that slow down corrosion. Examples of the use of modern inhibitors: during transportation and storage, hydrochloric acid is perfectly "tamed" by butylamine derivatives, and sulfuric acid - by nitric acid; volatile diethylamine is injected into various containers. Inhibitors act only on the metal, making it passive in relation to the environment. More than 5 thousand corrosion inhibitors are known to science. Removal of oxygen dissolved in water (deaeration). This process is used in the preparation of water entering boiler plants. 5. Special treatment of the electrolyte or other environment in which the protective metal structure is located

Corrosion of metals

teacher of chemistry and biology, SBEI NPO RO PU No. 61 named after the Hero of the Soviet Union Vernigorenko I.G.

- find out what corrosion is, its types, mechanism (on the example of iron corrosion), methods of protection against corrosion;

To develop the ability to perform an experiment, draw conclusions from what they saw, compose oxidation and reduction half-reactions based on the position of metals in the electrochemical series of voltages.

Lesson Objectives

• - reactions that occur with a change in the oxidation states of elements are called ....
• The element that increases the oxidation state as a result of the reaction is called ...
• The process of adding electrons is called....
• The redox process that occurs on the electrodes during the passage of a direct electric current is called ...
• cathode charged...
• process is going on at the anode...
• during the electrolysis of a melt of potassium bromide at the cathode, ...
• during the electrolysis of a melt of potassium hydroxide, gaseous ...
• Determine the oxidizing agent and reducing agent in the reaction scheme:

Zn + AgNO 3 – Zn(NO 3 ) 2 + Ag

Chemical dictation

Currently, we are witnessing the destruction of architectural structures and structures. Monuments (buildings and sculptures) made of limestone or marble catastrophically suffer from acid rain.

Word corrosion comes from the Latin corrodere, which means to corrode. Corrosion called the spontaneous process of destruction of materials and products from them under the chemical influence of the environment.

Corrosion

A) gases (O 2 ,SO 2 , H 2 S, Cl 2 , NH 3 , NO, NO 2 , H 2 O-steam, etc.); soot is an adsorbent of gases;

B) electrolytes: alkalis, acids, salts;

B) Cl ions - , air humidity;

D) macro- and microorganisms;

E) stray electric current;

G) heterogeneity of metals.

Causes of corrosion

CORROSION - RUSTY RAT,

gnaws on scrap metal,

TO SHEFNER

4Fe + 6H 2 O+3O 2 = 4Fe(OH) 3

Corrosive processes

Corrosion

Chemical

Electrochemical

Types of corrosion

Corrosion of metals

By the nature of the destruction

According to the type of corrosive environment

By processes

Electrochemical

Uniform

Soil

Uneven

Chemical

Liquid

atmospheric

Classification

Chemical corrosion is caused by the interaction

metals with dry gases or liquids,

non-conductive electric current

It usually flows

Corrosion products are formed directly at the points of contact of the metal with an aggressive environment.

with increased

temperatures

Corrosive media

The rate of the corrosion process is determined not only by the nature of the metal, but also by the properties of the resulting products.

oxide film

Durable, protective

loose

Al 2 O 3 , ZnO, NiO, Cr 2 O 3, TiO 2

FeO, Fe 2 O 3 , Fe 3 O 4

Chemical corrosion

Electrochemical corrosion is carried out by

electrochemical reactions that take place

on the surface of the metal in contact

with an electrolyte solution. She is accompanied

the occurrence of an electric current

Contact corrosion example

Li, K, Ba, Ca, Na, Mg, Al, Mn, Zn, Cr, Fe, Ni, Sn, Pb, H 2 , Cu, Hg, Ag, Pt, Au

Weakening of restorative properties, activity

Electrochemical series of voltages of metals

CONTINUOUS

does not pose a particular danger to structures and apparatus, especially in cases where the loss of metals does not exceed technically justified standards. Its consequences can be relatively easily accounted for.

LOCAL

metal losses are small. The most dangerous is pitting corrosion (the formation of through lesions, pitting cavities - the so-called pittings. Local corrosion is favored by sea water, salt solutions, in particular halide salts (sodium chloride, magnesium chloride, etc.). The danger of local corrosion lies in the fact that, by reducing the strength of individual sections, it sharply reduces the reliability of structures, structures, and apparatus.

Corrosion of metals

We lower the zinc granule into the solution of hydrochloric acid. We observe the evolution of hydrogen.

Zn + 2HCl = ZnCl 2 + H 2

The reaction proceeds rapidly at first, and then gradually slows down. This is due to the fact that zinc ions go into solution and form a layer of positively charged ions near the metal surface. This layer is a barrier that prevents the penetration of similarly charged hydrogen ions to the metal surface. In addition, when zinc is dissolved, electrons accumulate in its crystal lattice, which hinder the further transition of surface zinc ions into solution. This leads to a slowdown in the interaction of zinc with acid.

Experience number 1.

We touch the zinc with a copper wire - the dissolution of zinc increases.

This is explained as follows: in the series of voltages of metals, copper is located behind hydrogen and does not interact with acids, in which hydrogen ions are the oxidizing agent. Therefore, free electrons do not accumulate in the crystal lattice of copper. When these two metals come into contact, the free electrons of zinc pass to copper and reduce hydrogen ions:

2H + + 2e = H 2 0

In this case, along with chemical processes (electron recoil), electrical processes also occur (transfer of electrons from one metal to another).

Freed from excess electrons, zinc is oxidized again:

Zn 0 – 2e = Zn 2+

In addition, surface zinc ions are no longer held by the electrostatic attraction of electrons and are distributed throughout the solution, so zinc dissolves faster in contact with copper. Thus, the increased corrosion of zinc in contact with copper is explained by the appearance of a short-circuited galvanic cell. In which zinc acts as the anode, and copper as the cathode.

Experience number 2.

We connect the copper and zinc plates in HCl solution with a conductor, we observe the evolution of hydrogen on the copper plate.

Anode (Zn): Zn 0 – 2e – Zn 2+

Cathode (Cu): 2H + + 2e – H 2 0

Similarly, corrosion of metals occurs, which are heterogeneous and contain impurities. In the presence of an electrolyte, some parts of the metal surface play the role of an anode, while others play the role of a cathode.

Metal atoms are oxidized at the cathode: Me 0 –ne = Me n+

In this case, excess electrons remain on the metal. The role of the anode is performed by a more active metal.

At the cathode, the electrons that come from the anode are accepted by some oxidizing agent. In acids, hydrogen ions act as an oxidizing agent. In a neutral environment, dissolved oxygen predominantly acts as an oxidizing agent, then the process proceeds at the cathode: O 2 + 4e + 2H 2 O = 4OH -

Experience number 3.

1. Alloying of metals, i.e. obtaining alloys that are resistant to corrosion.

2. Isolation of metal from the environment is achieved by using protective coatings. There are three types of coatings: (varnishes, paints, enamels); chemical coatings (phosphate, oxide, nitride); metal (nickel plating, chrome plating, tin plating - tin coating). There are cathodic and anodic coatings. If the metal to be protected is coated with a less active metal, then it is a cathodic coating, such as tin-plated iron. If the integrity of the cathode coating is violated, a galvanic cell appears, in which the anode - iron is destroyed, and the cathode - tin - remains protected. If the metal to be protected is coated with a more active metal, then this is an anode coating, for example, iron is coated with zinc. If the integrity of the anode coating is violated, a galvanic cell appears, where the anode - zinc - is destroyed, and the cathode - iron - remains protected.

Protective protection. To the protected metal structure

attach sheets (protectors) of a more active metal. The protector is destroyed, protecting the protected metal. This method protects underground pipelines and tanks, ship hulls and ship propellers in sea water.

4. Changing the properties of an aggressive environment. It is achieved in two ways: 1) removal from aggressive environments of substances that enhance the corrosion of metals, for example, oxygen by boiling; 2) adding to the aggressive environment substances that slow down corrosion (inhibitors).

Methods for protecting metals from corrosion .

A zinc plate is lowered into a vessel with inhibited hydrochloric acid. The reaction does not occur. Inhibitors can be urea, sodium sulfite, sodium thiosulfate, sodium nitrite, phosphates, carbonates, silicates.

Experience number 4.

Test questions:

1. Define the corrosion of metals.

2. What types of metal corrosion do you know.

3. What contributes to the corrosion process?

4. Consider the corrosion process when iron comes into contact with a more active metal. Write the equations for oxidation and reduction reactions.

4. Knowing what corrosion is and what contributes to it, suggest ways to combat corrosion of iron products as the most common.

5. What methods of corrosion control do you know?

6. Protective protection is of particular interest. What is its action based on? What is its disadvantage?

7. What is cathodic protection based on?

Consolidation of knowledge

It's easier to destroy than to build. Losing is much easier than finding. Fighting corrosion is not easy, but it is possible. And one of the many proofs of this is the Eiffel Tower (slide 38), which was built with the expectation that it would last thirty years and be demolished. And for the second century now she has adorned Paris with herself ...

Lesson summary

1. For household needs, you need to purchase two iron buckets. In the hardware store there were two buckets of two types: galvanized (iron coated with zinc) and tinned (iron coated with tin). Which of these buckets will last longer? What kind of buckets do you prefer? Give a reasoned answer.

2. You are a locksmith. A copper rivet was placed on a steel part (steel mainly contains iron and carbon up to 2%). Do you know what will break first: the part or the rivet? Give a reasoned answer.

3. Sheets of a more active metal (zinc, magnesium) are welded to the walls of the steam boiler, the ship's hull. Which metal will break down first? Give a reasoned answer.

4. One iron plate is coated with magnesium and the other with copper. On which plate does rust form when the integrity of the coating is violated? Give a reasoned answer.

Creative tasks.

Textbook "Chemistry" for the professions of NPO and SPO technical cycle O.G. Gabrielyan, I.G. Ostroumov, M., "Academy" 2014, 256 p. Page

Workbook "Metals and non-metals": crossword puzzle No. 1 p. 27;

Homework

slide 2

slide 3

slide 4

slide 5

slide 6

Target

Investigate the effect of environmental factors on the degree of rusting of metals. Hypothesis If iron is placed in an alkaline environment, then the corrosion rate will decrease.

Slide 7

Tasks

1. To study the essence of corrosion, its types and methods of protection against corrosion. 2. To investigate the dependence of the corrosion rate on the presence of oxygen. 3. To investigate the effect of electrolytes on the corrosion process. 4. Investigate the effect of inhibitors on the corrosion process.

Slide 8

Significance of corrosion

1. Causes serious environmental consequences: leakage of oil, gas, and other chemical products. 2. Unacceptable in many industries: aviation, chemical, oil and nuclear engineering. 3. Negatively affects the life and health of people.

Slide 9

Corrosion is a heterogeneous process that occurs at the metal-environment interface. As a result of corrosion, metals oxidize and turn into stable compounds - oxides or salts, in the form of which they are found in nature.

Slide 10

In the case of chemical corrosion, the metal interacts directly with the oxidizing agent in the environment. As a result of this, the metallic bond is destroyed, and the metal atoms are combined with the atoms and groups of atoms that make up the oxidizers. 2Fe0+3Cl20→-2Fe+3Cl3 3Fe+2O2→Fe3O4 Chemical corrosion.

slide 11

Electrochemical corrosion

This type of corrosion occurs most often and is a process of interaction of metals and alloys with electrolytes, accompanied by the spontaneous appearance of galvanic pairs "cathode - anode". Anode on iron(+) Cathode on copper(-)Fe 0-2e=Fe2+2H++2e=2H0 →H20

slide 12

factors causing corrosion

1. Oxygen and moisture of the atmosphere 2. Carbon dioxide and sulfur dioxide contained in the atmosphere 3. Sea water 4. Ground water

slide 13

Experiment #1 The role of oxygen in the process of iron corrosion. In test tube No. 1-zh. nail + water by half. In test tube No. 2-zh. nail + water completely. In test tube No. 3-zh. nails-water + oil.

Slide 14

slide 15

slide 16

Experiment number 2. Influence of electrolytes on the corrosion process. In a glass No. 1-zh. nail + water. In a glass No. 2-zh. nail + sodium chloride solution. In a glass No. 3-zh. nail + copper + sodium chloride solution. In a glass No. 4-zh. nail + aluminum + sodium chloride solution.

Slide 17

Slide 18

Slide 19

Experiment #3 Influence of inhibitors on the corrosion process. In test tube No. 1 - well. nail + sodium hydroxide solution. In test tube No. 2 - well. nail + sodium phosphate solution. In test tube No. 3 - well. nail + sodium dichromate solution.

Slide 20

slide 21

Based on the results of the research, the following conclusions were drawn:

1. Corrosion of iron increases dramatically in the presence of oxygen. 2. Corrosion of iron increases dramatically if it comes into contact with a less active metal, but corrosion slows down if iron comes into contact with a more active metal. 3. The corrosion rate depends on the composition of the environment surrounding the metal. Chloride ions increase the corrosion of iron. 4. Corrosion of iron is weakened in the presence of hydroxide ions, phosphate ions and chromate ions.

Metals have an enemy that leads to huge
irretrievable losses of metals, annually completely
about 10% of the iron produced is destroyed. By
according to the Institute of Physical Chemistry of the Russian Academy of Sciences, each
the sixth blast furnace in Russia is running in vain - the entire
the smelted metal turns into rust.
That enemy is corrosion.

The problem of protecting metals from corrosion
arose almost at the very beginning of their
use. People tried to protect
metals from weathering with
with the help of fats, oils, and later
coated with other metals and, before
all, low-melting tin (tinning). AT
writings of the ancient Greek historian Herodotus
(V century BC) there is already a mention of
the use of tin to protect iron from
corrosion.

In the III BC on the island of Rhodes was built
lighthouse in the form of a huge statue of Helios.
The Colossus of Rhodes was considered one of the seven wonders of the world,
however, it lasted only 66 years and collapsed during
earthquakes. At the Colossus of Rhodes bronze
shell was
mounted on
iron frame.
Under the action of wet
saturated with salts
mediterranean air
the iron frame collapsed.

In the 20s of the twentieth century. commissioned by a millionaire
The luxury yacht “Call of the Sea” was built.
Even before entering the open sea, the yacht is completely
out of order. The reason was the contact
corrosion. The bottom of the yacht was sheathed in copper-nickel alloy, and the rudder frame, keel and other
parts are made of steel. When the yacht was
launched into the water. A gigantic
galvanic cell, consisting of a cathode, a steel anode and an electrolyte - marine
water. As a result, the ship sank without making any
one flight.

What is a symbol
Paris? –Eiffel
tower. She is incurable
sick, rusty and
collapses and only
constant
chemotherapy helps
fight with it
deadly disease:
she was painted 18 times, why
its weight is 9000 tons
every time
increases by 70 tons.

Corrosion is the destruction of metals and
alloys under the influence of the environment
environment. The word corrosion comes from
Latin corrodere, which means
fret.

Types of corrosion

Chemical corrosion

Chemical corrosion -
this interaction
metals with dry
gases and liquids -
non-electrolytes.
This kind of corrosion
turbines are exposed
furnace fittings and parts
internal engines
combustion.

Electrochemical corrosion

Electrochemical
corrosion is everything
cases of corrosion
the presence of water and
liquids -
electrolytes.

essence of corrosion.

Corrosion is made up of
two processes:
chemical is
donating electrons and
electrical is
electron transfer.

Patterns of corrosion:

1. If connected
two different metals
then corrosion
exposed only
more active and
until he is completely
will not collapse, less
active protected.

Patterns of corrosion:

2. Corrosion rate
the more than
further apart
in a series of voltages
located
connected
metals.

Corrosion chemistry.

Corrosion protection methods.

One of the most common
ways to protect metals from corrosion
is applied to their surface
protective films: varnish, paint, enamel.

Widespread method of protection
metals from corrosion is coating them
layers of other metals. Covering
metals themselves corrode with little
speed, as they are covered with dense
oxide film. Produce coating
zinc, nickel, chromium, etc.

Coating with other metals.

In everyday life, people most often
meets with coatings of iron with zinc and
tin. sheet metal, coated
zinc is called galvanized iron,
and covered with tin - tinplate. First
in large quantities goes to the roof
houses, and from the second they make
cans.

Corrosion protection methods.

Create alloys with
anticorrosive
properties. For this
into base metal
add up to 12%
chrome, nickel,
cobalt or copper.

Corrosion protection methods.

Line-up change
environment. For
corrosion inhibition
introduced
inhibitors. it
substances that
slow down the speed
reactions.

Corrosion protection methods.

The use of inhibitors is one of the effective
ways to combat corrosion of metals in various
aggressive environments (atmospheric, in sea water, in
coolants and salt solutions, in
oxidizing conditions, etc.). Inhibitors are
Substances capable of slowing down in small quantities
the flow of chemical processes or stop them.
The name inhibitor comes from lat. inhibere that
means to stop, stop. It is known that
damascus masters for scale and rust removal
used solutions of sulfuric acid with additives
brewer's yeast, flour, starch. These impurities were
one of the first inhibitors. They didn't let the acid
act on weapon metal, resulting in
only scale and rust were dissolved.

Electrical protection.

1. Tread protection.
to the main structure
attached
rivets or plates
from a more active
metal, which
exposed
destruction. Such
protection is used in
underwater and underground
structures.

Electrical protection.

2. Passing
electric current
in the direction,
opposite
the one who
occurs in the process
corrosion.