EFFECT OF METAL COUPLING

ON THE RUSTING OF

IRON

CERTIFICATEThis is to certify that the project / Dissertation entitled “EFFECT OFMETAL COUPLING ON THE RUSTING OF IRON” is a bonafide work done by Master EKANSH WAGADARE of class XII -SCIENCE Session 2016-17 in partial fulfillment of CBSE’s AISSCE Examination 2016-17 and has been carried out under my direct supervision 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 INTERNAL

➜  I undertook this Project work , as the part of my XII-Physics 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

➜ Mrs. FAIZA. ➜ I am very much thankful to our principal Dr. RAJESH

SHARMA 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

RUSTING OF

METALS

➜ 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

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.

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.

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 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.

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.

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.

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

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.

ASSOCIATED REACTIONSThe 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 oxygen𝑶𝟐 + − + 𝟒𝒆 𝟐𝑯𝟐 ⟶ −𝑶 𝟒𝑶𝑯Because it forms hydroxide ions, this process is strongly affected by the presence of acid. Indeed, the corrosion of most metals by oxygen isaccelerated at low pH.

Providing the electrons for the above reaction is the oxidation ofiron that may be described as follows:

⟶ 𝑭𝒆 𝑭𝒆𝟐+ + −𝟐𝒆The following redox reaction also occurs in the presence of waterand is crucial to the formation of rust:𝟒𝑭𝒆𝟐+ + 𝑶 𝟐 ⟶ + + −𝟒𝑭𝒆𝟑 𝟐𝑶𝟐In addition, the following multistep acid-base reactions affect thecourse of rust formation:𝑭𝒆𝟐+ + 𝟐𝑯𝟐 ⟶ ( )𝑶 𝑭𝒆 𝑶𝑯 𝟐 + +𝟐𝑯𝑭𝒆𝟑+ + 𝟑𝑯𝟐 ⟶ ( )𝑶 𝑭𝒆 𝑶𝑯 𝟑 + +𝟑𝑯as do the following dehydration equilibria:𝑭𝒆( )𝑶𝑯 𝟐 ⟶ + 𝑭𝒆𝑶 𝑯𝟐𝑶𝑭𝒆( )𝑶𝑯 𝟑 ⟶ ( ) + 𝑭𝒆𝑶 𝑶𝑯 𝑯𝟐𝑶𝟐𝑭𝒆𝑶( ) ⟶ 𝑶𝑯 𝑭𝒆𝟐𝑶𝟑 + 𝑯𝟐𝑶

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 − 𝒙𝑶 /𝒙 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 +, both of which 𝑪𝒂𝟐serve 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 + ions and hydroxyl ions. Formation of Fe2+ 𝑭𝒆𝟐ions and hydroxyl ions are indicated by blue and pink patchesrespectively.

RUSTING ALL AROUND.

OBSERVATION

COLOUR OF THE PATCH NAILS RUST

IRON-ZINC

IRON-MAGNESIUM

IRON-COPPER

IRON-NAIL

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.

Thanks!