Acknowledgement Certificate Introduction Resistance to corrosion Aim Materials Required Theory Procedure Observations Conclusions Precautions Protection from corrosion Biblography

I am using this opportunity to express my gratitude to everyone who supported me throughout the course of this project.I am thankful for their aspiring guidance, invaluably constructive criticism and friendlyadvice during the project work. I am sincerely grateful to them for sharing their truthful andilluminating views on a number of issues related to the project.I would like to express my special thanks of gratitude to my teacher Mr.Najumudeen as well as ourprincipal Mr.Krishnamoorthy who gave me the golden opportunity to do this wonderful project on the topic“Effect of Metal Coupling on Corrosion”, which also helped me in doing a lot of Research and I came to know about so many new things I am really thankful to them.Secondly I would also like to thank my parents and friends who helped me a lot in finalizing this projectwithin the limited time frame.

P. Reshop nandaClass : XII-A6

• Corrosion is the gradual destruction of materials (usually metals) by chemical reaction with their environment.

• Corrosion is a serious problem of some metals like iron, zinc, aluminium and alloys like brass which are commonly used in day to day life.

• Basically , this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen.

• Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal.

• Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common.

• Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.

EXAMPLES OF CORROSION

• Some metals are more intrinsically resistant to corrosion than others .

• There are various ways of protecting metals from corrosion (oxidation) including painting, hot dip galvanizing, and combinations of these.

• Gold nuggets do not naturally corrode, even on a geological time scale.

• The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. 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 have long been valued. More common "base" metals can only be protected by more temporary means.

Metals resistance to corrosion:

• Beakers-15• Iron sheets of 2• Aluminium rods of 2• Brass rods of 2• Zinc sheets of 2• Measuring cylinders• Chemical Balance• Weight Box.

• Hydrochloric acid and • Sodium hydroxide.

1. Mix 9 ml. of conc. HCl with 241 ml. of water to form 250 ml. of solution.

2. Take this solution in seven different beakers.3. Mark each beaker serially from 1 to 7.4. Take the weights of three iron sheets, three

aluminium rods, three brass rods and three zinc sheets.

5. Now keep iron sheets, aluminium rods, zinc sheets and brass rod in separate beakers

6. Then take iron + brass, iron + aluminium, iron + zinc, aluminium + zinc and brass + zinc and keep them in different beakers.

7. Allow the reactions to occur for 24 hours. 8. Note the maximum and minimum temperatures.9. Now at the end of reaction take out the metals and

keep them in sun for sometime so that they get dried up quickly

10. Take the weights of each specimen and note the difference.

11. Similarly repeat 1,2,3,4,5,6,7 and 8 steps in a basic solution.

Sl.No

Specimen (with acid) Initial weight(in gm)

Final weight(in gm)

1 Brass 8 5

2 Iron 8 6

3 Zinc 8 6.50

4 Aluminium 8 7.10

5 Aluminium + Iron 15 12.30

6 Brass + Zinc 15 13.00

7 Iron + Zinc 15 14.10

These experiments are done under acidic condition

Sl.No

Specimen (with base) Initial weight(in gm)

Final weight(in gm)

1 Brass 8 5.80

2 Iron 8 6.20

3 Zinc 8 7.10

4 Aluminium 8 7.60

5 Aluminium + Iron 15 12.90

6 Brass + Zinc 15 13.60

7 Iron + Zinc 15 14.40

These experiments are done under basic condition

• The rate of corrosion observed in acidic medium or the mass consumed during the corrosion is in the decreasing order from brass to aluminum. Brass has the highest corrosion rate while aluminiumhas the least corrosion rate.

Brass > Iron > Zinc > Aluminium

• When coupling of these metals was done each couple showed some difference in their corrosion with respect to each metal kept aloneIron + Aluminium couple has the highest rate of corrosion while iron +Zinc couple has the lowest rate of corrosion.Rate of corrosion of each couple is in the order of

Iron + Aluminium > Brass + Zinc> Iron + Zinc

• Rate of corrosion in basic medium is in the decreasing order from Brass to Aluminium.

The order of rate of corrosion is as below:

Brass > Zinc >Iron > Aluminium

• When these metals were coupled the rate of corrosion was in the decreasing order from

Brass+ Aluminium > Brass + Zinc >

Iron + Aluminium

• Temperature and time of reaction were constant i.e., temperature was 21° C and time of reaction was 24 hours.

• Corrosion is a serious problem of some metals like iron, zinc, aluminium and alloys like brass which are commonly used in day to day life.

• Apart from reducing the life of articles made up of these metals or alloys the chemical substances formed out of corrosion have serious public health problems.

• Replacement of machines or their parts and many other articles in industrial and public dealing lead to huge expenditure.

• Hence, how to reduce or avoid corrosion of articles made up of metals or alloys has been a major subject of study in the field of chemistry and electro-chemistry.

• The study of the rate of corrosion of different metals or alloys showed gradual decrease in their masses in acidic medium. The decrease is in the order of brass, iron, zinc, aluminium.

• The present experiments are in full agreement with the well known electro-chemical reaction. Some of the typical reactions as occur with iron are illustrated.

• The reactions at respective electrodes are:

At cathode: Fe Fe + 2e.

in acid the equilibrium is

HCl H + Cl .

At anode:

The water which is in equilibrium

H O H + OH.

2

2

Here the Fe2+ cation will readily take Cl and form FeCl . While H of acid will be reacting withanother H+ of water and will form H gas. While OH. Anion will also react with some of the iron and will form Fe(OH) which is observed in the form of

rust.

3

3

2

• The e.m.f of these metals are in the order of Al:Zn:Fe .

The values are e.m.fAl Al3 + 3e- 1.66VZn Zn2 + 2e- 0.76V Fe Fe 2 + 2e- 0.44V

Brass which is an alloy of zinc and copper has the e.m.f. 0.42V during the forward reaction or oxidation reaction. While in backward reaction the e.m.f. value is 0.42. This is because during oxidation reaction the e.m.f values of zinc and copper are .0.76 and+ 0.34, respectively. That is why the value differs.

• In acid there are replaceable H ions which react with metals and H2 gas is evolved. This is because all the metals are highly electronegative in nature. When these two come in contact they react very easily and form stable compounds. Thus the rate of corrosion is very high. The rate of corrosion in basic medium is very less as compared to acidic medium.

• This is shown because of following factors:(i) Ex: sodium hydroxide .NaOH which is in equilibrium with Na and OH. ions.

NaOH Na + OH

When NaOH comes in contact with water the two ions immediately dissociate. The hydrates Na+ ions will take the H+ ion.The electropositive characters here will be the main factor in the slow rate of corrosion. Na being more electropositive than the metal mentioned above, most of OH ions will be taken by Na when compared to the other metals

i.e., the rate of corrosion is slow with Na+ \ Fe2+ || OH\OH- While H+ + electron = H H + H = H2 gas.

-+

+

+ -

+

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.

Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. Cathodic protection systems are most commonly used to protect steel, water, and fuel pipelines and tanks; steel pier piles, ships, and offshore oil platforms.

Anodic protection impresses anodic current on the structure to be protected (opposite to the cathodicprotection). It is appropriate for metals that exhibit passivity (e.g., stainless steel) and suitably small passive current over a wide range of potentials. It is used in aggressive environments, e.g., solutions of sulfuric acid.

galvanization

Cathodic protection

1. XII class Chemistry NCERT Books

2. iCBSE.com

3.XII class Chemistry Practical Book

4.Photos from Google images.

5.More Information from Wikipedia..