I nvestigatory ProjectCLASS: XIth

SUBJECT: CHEMISTRYROYAL GONDWANA PUBLIC

SCHOOL

NAME: KRISHNA YADAV

AcknowledgementAim IntroductionMechanism of corrosion of metal

Methods of Prevention of Corrosion of metals

Aim of this Project Apparatus ProcedureObservation Conclusion

CONTENTS

ACKN

OWLE

DGEM

ENT 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.

AIM:STUDY OF THE EFFECT

OFMETAL COUPLING ON

THERUSTING OF IRON

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

INTR

OD

UCT

ION

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.

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.

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.

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.Methods of Prevention of Corrosion and RustingSome 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 PROJECTIn 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.

Apparatus1) Two Petri dishes 2) Four test-tube 3) Four iron nails 4) Beaker 5) Sand paper 6) Wire gauge 7) Gelatine 8) Copper, Zinc and Magnesium strips 9) Potassium ferricyanide solutions

10) Phenolphthalein

PROCEDURE1) 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 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 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.

S.No.

Metal Pair Colour of the Patch

Nails Rust or not

1 Iron-Zinc Pink No2 Iron-

Copper Blue Yes

3 Iron-Magnesium

Pink No

4 Iron-Nail Blue Yes OBSERVATION

CONCLUSIONIt 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.