2. CERTIFICATE
This is to certify that the project / D issertation entitled “EF F ECT OF
M ETA L COU P LING ON TH E R U STING OF IRON” is a bonafide work
done by Master SRI KANNAN of class XII -A Session 2022-23 in partial
fulfillment of CBSE’s A ISSCE Examination 2022---23 and has been
carried out under my direct superv ision and guidance .
This report or a similar report on the topic has not been submitted for
any other examination and does not form a part of any other course
undergone by the candidate.
… … … … … … … … … … … … … … … … … … … … …
PRINCIPAL EXTERNAL IN T E R N A L
3. I undertook this Project work , as the part of my XII-Chemistry
project .I had tried to apply my best of knowledge and experience
gained during study and class work experience.
I would like to extend my sincere thanks and gratitude to my teacher
Mr.Sakthivel Murugan.
I am very much thankful to our principal Mr.Sakthivel Murugan for
giving valuable time and moral support to develop this project.
I would like to take the opportunity to extend my sincere thanks and
gratitude to our parents for being a source of inspiration and
providing time and freedom to develop this project.
AKNOWLEDGEMENT
5. ➜ Introduction
➜ Mechanism of corrosion of metal
➜ Electrochemical Mechanism(rusting)
➜ Methods of Prevention of Corrosion
➜ Economic Effect
➜ Aim of this project
➜ Requirements
➜ Procedure
➜ Observation
➜ Conclusion
➜ Bibliography
INDEX
6. INTRODUCTION
Metal corrosion is the most common form of
corrosion. The corrosion occurs at the surface of the
metal in forms of chemical or electrochemical
reactions. This process significantly reduces the
strength, plasticity, toughness and other mechanical
properties of the metallic material. However, because
of the metal and its alloys is still the most important
pipe and structure materials, the cost of corrosion
grows significantly with the growth of industries. Thus
many scientists focus on the research of corrosion
control in order to reduce the cost of replacing the
rusting metal material.
7. Nowadays, there are mainly two corrosion control
methods that are very popular in the world. One is
impressed current and another is sacrificial anode
cathode protection system. In this project, we will
focus on the mechanism and application of the
sacrificial anode cathode protection
system.
8. MECHANISM OF CORROSION OF METAL
General Principle of Corrosion: Reaction is the
fundamental reaction during the corrosion process,
which the electron can flow from certain areas on the
metal surface to other areas through a solution which
can conduct electric currents. Basically, both anodic
and cathode reactions have to balance each other out,
resulting in a neutral reaction. Both anodic and
cathodic reactions occur simultaneously at the same
rates. What’s more, the site of these electrodes may
consist of either two different kinds of metals, or they
may be on different areas of the same piece of metal,
resulting a potential difference between the two
electrodes, so that the oxidation reaction of the metal
at the anode and formation of negative ions at the
cathode can take place at the same time.
9. Similar electrical potentials may also be developed
between two areas of a component made of a single
metal as result of small differences in composition or
structure or of differences in the conditions to which the
metal surface is exposed. That part of a metal which
becomes the corroding area is called the “anode” ; that
which acts as the other electrode of the battery is called
“cathode” which does not corrode, but is an important
part of the system. In the corrosion systems commonly
involved, with water containing some salts in solution as
the electrolyte. Corrosion may even take place with pure
water, provided that oxygen is present. In such cases
oxygen combines with the hydrogen generated at the
cathode, removing it and permitting the reaction to go on.
10. RUSTING: AN ELECTROCHEMICAL
MECHANISM
Rusting may be explained by an electrochemical
mechanism. In the presence of moist air containing
dissolved oxygen or carbon dioxide, the commercial
iron behave as if composed of small electrical cells. At
anode of cell, iron passes into solution as ferrous ions.
The electron moves towards the cathode and form
hydroxyl ions. Under the influence of dissolved oxygen
the ferrous ions and hydroxyl ions into form, i.e.,
hydrated ferric oxide.
11. METHODS OF PREVENTION OF CORROSION
AND RUSTING
Some of the methods used:-
➜Barrier Protection: In this method, a barrier film is
introduced between iron surface and atmospheric air.
The film is obtained by painting, varnishing etc.
➜Galvanization: The metallic iron is covered by a layer of
more reactive metal such as zinc. The active metal losses
electrons in preference of iron. Thus, protecting from
rusting and corrosion.
12. AIM OF THIS PROJECT
In this project the aim is to investigate effect of the metals
coupling on the rusting of iron. Metal coupling affects the
rusting of iron. If the nail is coupled with a more electro-
positive metal rusting is prevented but if on the other
hand, it is coupled with less electro –positive metals the
rusting is facilitated.
13. REQUIREMENTS
➜ Two Petri dishes
➜ Four test-tube
➜ Four iron nails
➜ Beaker
➜ Sand paper
➜ Wire gauge
➜ Gelatin
➜ Copper, Zinc and Magnesium strips
➜ Potassium ferricyanide solutions
➜ Phenolphthalein
14. PROCEDURE
At first we have to clean
the surface of iron nails
with the help of sand
paper.
After that we have to
wind zinc strip around
one nail, a clean copper
wire around the second
and clean magnesium
strip around the third
nail.
Then to put all these
three and a fourth nail
in Petri dishes so that
they are not in contact
with each other.
Then to fill the Petri
dishes with hot agar-
agar solution in such a
way that only lower half
of the nails are covered
with the liquids.
Keep the covered Petri
dishes for one day or
so.
The liquids set to a gel
on cooling.
Two types of patches
are observed around
the rusted nail, one is
blue and the other pink.
Blue patch is due to the
formation of potassium
Ferro-ferricyanide
where pink patch is due
to the formation of
hydroxyl ions which
turns colorless
phenolphthalein to pink.
15. ASSOCIATED REACTIONS
The rusting of iron is an electrochemical process that begins
with the transfer of electrons from iron to oxygen. The iron
is the reducing agent(gives up electrons) while the oxygen
is the oxidizing agent (gains electrons). The rate of
corrosion is affected by water and accelerated by
electrolytes, as illustrated by the effects of road salt on the
corrosion of automobiles.
The key reaction is the reduction of oxygen
𝑶𝟐 + 𝟒𝒆− + 𝟐𝑯𝟐𝑶 ⟶ 𝟒𝑶𝑯−
Because it forms hydroxide ions, this process is strongly
affected by the presence of acid. Indeed, the corrosion of
most metals by oxygen is
accelerated at low pH.
16. Providing the electrons for the above reaction is the
oxidation of
iron that may be described as follows:
𝑭𝒆 ⟶ 𝑭𝒆𝟐+ + 𝟐𝒆−
The following redox reaction also occurs in the presence of
water
and is crucial to the formation of rust:
𝟒𝑭𝒆𝟐+ + 𝑶𝟐 ⟶ 𝟒𝑭𝒆𝟑+ + 𝟐𝑶𝟐−
In addition, the following multistep acid-base reactions
affect the
course of rust formation:
𝑭𝒆𝟐+ + 𝟐𝑯𝟐𝑶 ⟶ 𝑭𝒆(𝑶𝑯)𝟐 + 𝟐𝑯+
𝑭𝒆𝟑+ + 𝟑𝑯𝟐𝑶 ⟶ 𝑭𝒆(𝑶𝑯)𝟑 + 𝟑𝑯+
as do the following dehydration equilibria:
𝑭𝒆(𝑶𝑯)𝟐 ⟶ 𝑭𝒆𝑶 + 𝑯𝟐𝑶
𝑭𝒆(𝑶𝑯)𝟑 ⟶ 𝑭𝒆𝑶(𝑶𝑯) + 𝑯𝟐𝑶
𝟐𝑭𝒆𝑶(𝑶𝑯) ⟶ 𝑭𝒆𝟐𝑶𝟑 + 𝑯𝟐𝑶
17. From the above equations, it is also seen that the corrosion
products are dictated by the availability of water and oxygen.
With limited dissolved oxygen, iron(II) containing materials are
favored, including FeO and black lodestone or magnetite
(𝑭𝒆𝟑𝑶𝟒). High oxygen concentrations favor ferric materials with
the nominal formulae 𝑭𝒆(𝑶𝑯)𝟑 − 𝒙𝑶𝒙/𝟐.
The nature of rust changes with time, reflecting the slow rates
of the reactions of solids.
Furthermore, these complex processes are affected by the
presence of other ions, such as 𝑪𝒂𝟐+, both of which serve as
an electrolyte, and thus accelerate rust formation, or combine
with the hydroxides and oxides of iron to precipitate a variety
of Ca-Fe-O-OH species. Onset of rusting can also be detected
in laboratory with the use of ferroxyl indicator solution. The
solution detects both 𝑭𝒆𝟐+ ions and hydroxyl ions. Formation
of Fe2+ ions and hydroxyl ions are indicated by blue and pink
patches
respectively.
20. CONCLUSION
It is clear from the observation that coupling of
iron with more electropositive metals such as zinc
and magnesium resists corrosion and rusting of
iron. Coupling of iron with less electropositive
metals such as copper increases rusting.
