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 like zinc, magnesium or aluminium rusting is prevented but if on the other hand, it is coupled with less electro –positive metals like copper, the rusting is facilitated.

2. Acknowledgement
Aim
Introduction
Mechanism of corrosion of
metal
Methods of Prevention of
Corrosion of metals
Aim of this Project
Apparatus
Procedure
Observation
Conclusion
CONTENTS

3. ACKOWLEDGEMENT
I would like to take this
opportunity to thank my Teacher
whose unstinted support,
Guidance and Encouragement has
enabled me to complete this
Project.
I would like to Thank our Lab-
Assistant for co-operation.

4. AIM:
STUDY OF THE EFFECT
OF
METAL COUPLING ON
THE
RUSTING OF IRON

5. 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. 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.
INTODUCTION

6. 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.

7. 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.

8. 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 behaves
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 interact to form, i.e.,
hydrated
ferric
oxide.

9. Methods of Prevention of Corrosion and
Rusting
Some of the methods used: -
1) Barrier Protection: In this method, a
barrier film is introduced
between iron surface
and atmospheric air. The
film is obtained by
painting, varnishing etc.
2) 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.
AIM OF THIS PROJECT

10. Apparatus
1) Two Petri dishes
2) Four test-tube
3) Four iron nails
4) Beaker
5) Sand paper

11. 6) Wire gauge
7) Gelatine
8) Copper, Zinc and Magnesium strips
9) Potassium ferricyanide solutions
10) Phenolphthalein
PROCEDURE
1) At first we have to clean the surface of
iron nails with the help of sand paper.
2) 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
Mg Zn Cu

12. a fourth nail in Petri dishes so that they are
not in contact with each other.
3) 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.
4) Keep
the
covered
Petri
dishes for
one day or
so.
5) The
liquids set to a
gel on cooling.
Two types of

13. 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
colourless phenolphthalein to pink.

14. S.No. Metal Pair Colour
of the
Patch
Nails Rust
or not
1 Iron-Zinc Pink No
2 Iron-
Copper
Blue Yes
3 Iron-
Magnesium
Pink No
4 Iron-Nail Blue Yes

15. 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.