Corrosion

©Purnendu Kartikay1

Index

Certificate III

Acknowledgements IV

Aim V

Apparatus V

Theory VI-VII Corrosion Mechanism of Corrosion

Procedure VIII

Observations IX

Result X

Conclusion XI

Addendum XII

Bibliography XIII

Project Evaluation Performa XIV

©Purnendu Kartikay2

Certificate

This is hereby to certify that the original and genuine investigation work has

been carried out to investigate about the subject matter and the related data

collection and investigation has been completed solely, sincerely and

satisfactorily by Purnendu Kartikay of CLASS XII A, Rajkiya Pratibha

Vikas Vidyalaya, Lajpat Nagar, New Delhi 110 024 regarding his project

titled “Corrosion in metals”.

Teacher’s Signature

Name __________________.

©Purnendu KartikayIII

Acknowledgements "There are times when silence speaks so much more loudly than words of praise to only as good

as belittle a person, whose words do not express, but only put a veneer over true feelings, which

are of gratitude at this point of time."

I would like to express my sincere gratitude to my chemistry mentor Mrs. Amita Puri , for her vital support,

guidance and encouragement -without which this project would not have come forth. I would also like to express

my gratitude to my brother Amit Chandra for his support during the making of this project

©Purnendu KartikayIV

Aim

To study the rate of corrosion in different metals.

Apparatus 12 inches (30.5 cm) of silver wire

12 inches (30.5 cm) of steel wire

12 inches (30.5 cm) of zinc wire

12 inches (30.5 cm) of copper wire

12 inches (30.5 cm) of aluminum wire

Small pair of wire cutters

10 clear drinking glasses (preferably identical), or 10 test tubes and a test tube rack

A pen or fine-point marker

Small pieces of paper or labels for the glasses or test tubes

10 pencils

Transparent or masking tape

Liquid measuring cup

A tablespoon measure

A funnel

Distilled water

Table salt (NaCl)

©Purnendu KartikayV

Theory

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactionswith its surroundings. In the most common use of the word, this means electrochemical oxidation of metalsin reaction with an oxidant such as oxygen. Formation of an oxide of iron due to oxidation of the iron atomsin solid solution is a well-known example of electrochemical corrosion, commonly known as rusting. This type of damage typically produces oxide(s) and/or salt(s) of the original metal. Corrosion can also refer to other materials than metals, such as ceramics or polymers, although in this context, the term degradation is more common.

Mechanism of Corrosion

The mechanism of corrosion can be explained by taking the example of rusting of iron. The theory is called electrochemical theory because it explains the formation of rust on the basis of the formation of electrochemical cells on the surface of metal.

The formation of rust on the basis of this theory is explained in the following steps:

(i) The water vapours on the surface of the metal dissolve CO2 and O2 from the air. Thus the surface of the metal is covered with the solution of CO2 in water that is carbonic acid (H2CO3)

H2O + CO2 H2 CO3

This acts as an electrolytic solution of the cell. The carbonic acid and water dissociate to small extent as follows:

H2CO3 2H+ + CO23

- (1)

H2O H+ + OH– (2)

(ii) Iron in contact with the dissolved CO2 and O2 undergoes oxidation as follows:

Fe Fe2+ + 2e- (Eo = 0.44V) (3)

Thus the sites where the above reaction takes place act as anodes. As a result of the above reaction, iron is converted into ferrous (Fe2

+) ions.

(iii) The electrons lost by iron are taken up by H+ ion present on the surface of the metals which were produced by the dissociation of H2CO3 and H2O. Thus H+ ions are converted into H atoms.

H+ + e- H (4)

These H atom either react with the dissolved oxygen or oxygen from the air to form water.

4H + O2 2H2 O (5)

©Purnendu KartikayVI

Multiplying eqn.(4) with 4 and adding to eqn.(5), the complete reduction reaction may be written as

O2 + 4H+ + 4e- 2H2O (Eo= 1.23 V) (6)

The dissolved oxygen may take up electrons directly to form OH- ion as follows:

O2 + 2H2O + e- 4OH- (7)

The sites where the above reactions take place act as cathodes.

Multiplying equations (3) by 2 and adding to equation (6)

2Fe(s) + O2(g) + 4H+ (aq) 2Fe2+ (aq) + 2H2O(l); Eocell= 1.67V

It may be mentioned here that if water is saline, it helps in the flow of current in the miniature cell and hence enhances the process of corrosion.

(iv)The ferrous ions formed react with the dissolved oxygen or oxygen from the air to form ferric oxide as follows:

4Fe2+ + O2 + 4H2 O 2Fe2 O3 + 8H+(aq)

Ferric oxide then undergoes hydration to form rust as follows:

Fe2 O3 + x H2O Fe2O3.xH2O (Hydrated ferric oxide (Rust))

Rust is a non-sticking compound i.e., it does not stick to the surface; it peels off exposing fresh iron surface for further rusting.

©Purnendu KartikayVII

Procedure1. Using the pen or marker, mark ten labels or small pieces of paper as follows:

o water + silver

o salt water + silver

o water + steel

o salt water + steel

o water + zinc

o salt water + zinc

o water + copper

o salt water + copper

o water + aluminum

o salt water + aluminum

2. Glasses or test tubes were set on a table or counter so as it could be easily observed.

3. A marked label or a piece of marked paper was stuck on each glass or test tube. All labels were front-faced to

facilitate easy visibility.

4. Using the measuring cup and funnel, five glasses or test tubes were filled with distilled water.

5. 8 ounces (240 ml) of water was mixed with 1 tablespoon of salt. It was stirred until the salt is completely

dissolved.

6. The other five glasses or test tubes were filled with the salt water solution, mixing more water and salt as

needed.

7. One end of each piece of wire around a pencil was wrapped, so that when the pencil rests across the top of the

glass, the wire hangs to the bottom.

8. Each wire was observed for 15 days.

©Purnendu KartikayVIII

ObservationsObservations of metal wire suspended in distilled water:Day Iron (Fe) Aluminum (Al) Copper (Cu) Zinc (Zn) Silver (Ag)1 No change No change No change No change No change

2 No change Formation of brownish layer starts No change Corrosion started No change

3 Corrosion gradually increases No change Slightly Corrosion No change

4 Slightly Corrosion Corrosion continues No change Corrosion continues No change

5 Gradually increasing

The process of corrosion continues at a Constant rate…..

No change The process of corrosion continues at a slow rate………

No change

6 Corrosion continues Corrosion stopped &Formation of oxide layer started

Corrosion started No change

7 Corrosion increases Corrosion gradually increases

No change

8 The process of corrosion continues at a Constant rate……………………………..

Oxide layer is forming Corrosion gradually increases at constant rate………………………………………………………………………………………………………………………

No change

9 Oxide layer is formed completely Corrosion gradually increases

No change

10 No change occurs after

the formation of oxide

layer is completed.

Corrosion started

11 Corrosion continues Slightly Corrosion

12 Corrosion continues The process of corrosion continues at a Constant rate.

13 Corrosion process is almost completed.

Corrosion continues

14 Corrosion continues

15 Corrosion process is completed.

Corrosion process is not completed.

Corrosion process is almost completed.

Corrosion process is not completed.

Observations of metal wire suspended in salt water:Iron (Fe) Aluminum (Al) Copper (Cu) Zinc (Zn) Silver (Ag)

1 No change Corrosion started No change No change No change2 Corrosion started Corrosion gradually increases No change Corrosion started No change3 Corrosion gradually increases The process of corrosion continues

at a fast rateNo change Corrosion gradually

increasesNo change

4 The process of corrosion continues at a fastrate……………………………………………………………………………………………………………

Corrosion started Corrosion gradually increases at a constant rate……………………

No change5 Corrosion stopped &

Formation of oxide layer startedCorrosion gradually increases at a constant rate……………………………………..

No change6 No change7 Oxide layer is forming No change8 Oxide layer is formed completely Corrosion

started9 No change occurs

after the formation of oxide layer is completed.

Corrosion continues10 Corrosion process is almost

completed1112 Corrosion process is completed. Corrosion

continues1314 Corrosion process is

completed.15 Corrosion process is not completed.

Corrosion process is not completed.

©Purnendu KartikayIX

Result Corrosion is an electrochemical process. For a corrosion reaction we need (1) a metal that can be oxidized, (2) oxygen, and (3) water. The process of corrosion can be facilitated by adding a salt to the water (such as sodium chloride, sea salt). Aluminum is corrodes fastest among Iron, Zinc, Copper, Silver, i.e. the speed of corrosion depends on

reactivity of metals; the more reactive metal corrodes easily or lower the Standard electrode potential higher the speed of corrosion.

Aluminum corrodes till the certain interval of time and then it forms oxide layer which prevents the further corrosion.

©Purnendu KartikayX

ConclusionThus summarizing, for a corrosion reaction we need (1) a metal that can be oxidized, (2) oxygen, and (3) water. The reaction can be facilitated by adding a salt to the water (such as sodium chloride, sea salt). The salt increases the conductivity of the water, and thus enhances the electron transfer. This is the reason why cars rust so much faster in the winter (plenty of water, salt on the roads). Another way to enhance the corrosion of metals is to increase the acidity of the solution; the increased availability of H+ ions not only increases conductivity, but also promotes the reduction reaction. Finally, temperature is also a factor: at higher temperatures metals corrode faster.

Some metals corrode more easily than others. This is a function of their redox potential, or their ability to donate electrons... In any case, materials such as magnesium, zinc, aluminum, and chrome corrode more easily than iron. Materials such as tin, lead, copper, silver and gold corrode less easily than iron.

In case we noticed that aluminum was in the list of easily corroding materials, this is no mistake. However, this material has the pleasant property that its oxide (aluminum oxide) forms a protective layer around the aluminum, so that no more oxygen can permeate. Hence, many people are under the somewhat incorrect impression that aluminum doesn't "rust"...

©Purnendu KartikayXI

Addendum

Prevention of corrosionCorrosion can be prevented by a number of ways. Some of these are explained below:

1. Barrier Protection: - The metal surface is not allowed to come in contact with moisture, oxygen and carbon dioxide. This can be achieved by the following methods:

(i) The metal surface is coated with paint which keeps it out of contact with air; moisture etc. till the paint layer develops cracks.

(ii) By applying film of oil and grease on the surface of the iron tool and machinery, the rusting of iron can be prevented since it keeps the metal surface away from moisture, oxygen and carbon dioxide.

(iii) The metal surface is coated with non-corroding metals such as nickle, chromium, etc. (by electroplating) or tin, zinc, etc. (by dipping the iron article in the molten metal). This again shuts out the supply of oxygen and water to iron surface.

(iv)The metal surface is coated with phosphate or other chemicals which give a tough adherent insoluble film which does not allow air and moisture to come in contact with iron surface.

2. Sacrificial Protection: - Sacrificial protection means covering the metal (let be M) surface with a layer of metal which is more active (electropositive) than the metal M and thus prevents the metal M from losing electrons. The more active metal loses electrons in preference to metal M and converts itself into ionic state. With the passage of time, the more active metal gets consumed but so long as it present there, it will protect the metal M from corrosion and does not allow even the nearly exposed surface of metal M to react.

For example Zinc is most often used for covering iron with more active metal galvanization. The layer of zinc on the surface of iron, when comes in contact with moisture, oxygen and carbon and carbon-dioxide in air, a protective invisible thin layer of basic zinc carbonate ZnCO3 Zn(OH)2 is formed due to which the galvanized iron sheets lose their luster and also tends to protect it from further corrosion.

Iron can be also coated with copper by electro-deposition from a solution of copper sulphate or with tin by dipping into molten metal. Now if the coating is broken, iron is exposed and iron being more active than both copper and tin, is corroded, Here iron corrodes more rapidly than it does in the absence of tin.

3. Electrical Protection: - Cathodic Protection. The metal (let M) object to be protected from corrosion is connected to a more active metal either directly or through a wire. The metal M object acts as cathode and the protecting metal acts as anode. The anode gradually used up due to the oxidation of the metal to its ions due to loss of electrons. Hydrogen ions collect at the metal M cathode and prevent the rust formation. The metal M object gets protection from rusting as long as some of the active metal is present. Magnesium, zinc and aluminum are widely used for protecting iron objects from rusting which are called sacrificial anodes.

Magnesium is often employed in the cathodic protection of iron pipes buried in the moist soil, canals, storage tanks etc. Pieces of magnesium are buried along the pipeline and connected to it by the wire.

4. Using anti-rust solutions: These are alkaline phosphate and alkaline chromate solutions. The alkalinity prevents availability of hydrogen ions. In addition, phosphate tends to deposit an insoluble protective film of iron phosphate on the iron. These solutions are used in car radiators to prevent rusting of iron parts of the engine.

©Purnendu KartikayXII

Bibliography

Books Title Publisher

Chemistry Part 1 (Text book for class XII) NCERT

Chemistry Laboratory Manual (Class XII) Araya Publication

Corrosion Control (3rd Edition) Butterworth-Heinemann

Websites

www.wikipedia.org

www.infoplease.com

www.cbse.nic.in

www.researchguides.case.edu

©Purnendu KartikayXIII

PROJECT EVALUATION PERFORMASCHOOL’S NAME: - Rajkiya Pratibha Vikas Vidyalaya.

Lajpat Nagar, New Delhi

STUDENT’S NAME: - Purnendu Kartikay.

STUDENT’S ID.:- 20040001179.

ROLL No.:- 9711986.

CLASS: - 12th (Science).

STUDENT’S ADDRESS: - M-154, Saurabh Vihar, New Delhi 110044.

E-Mail Address: - [email protected]

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