CHAPTER ONE

1.0 Introduction

Rusting is the corrosion of iron which is the most widely used structural metal. Most of it is used in making steel. The wide range of products made from steel includes all types vehicles, machinery pipeline, bridges and reinforcing rods and girders for construction  purposes.

Rusting  is due to electrochemical reaction, it require the presence of both air i.e oxygen and water. Like the electrochemical cell, electrons given up from anode of an iron atom flow (through metal ) to cathode and reduces the oxygen being  dissolved  in the water layer to  give OH-  

Therefore, rusting causes enormous econom ic problem and is reason why extensive measures of rusting/corrosion protection have to be developed

1.1 RUST IN HISTORY

To the great majority of people, corrosion means rust, an almost universal object of hatred. `Rust' is, of course, the name which has more recently been specifically reserved for the corrosion of iron, while `corrosion' is the destructive phenomenon which affects almost all metals.     Although iron was not the first metal used by man, it has certainly been the most used, and must have been one of the first with which serious corrosion problems were obtained. It is not, therefore, surprising that the terms corrosion and rust are almost synonymous. 

The great Roman philosopher, Pliny, AD 23-79, wrote at length about ferrum corrumpitur, or spoiled iron, for by his time the Roman Empire had been established as the world's foremost civilization, a distinction due partly to the extensive use of iron for weaponry and other artifacts. 

The Romans must have been vexed by the susceptibility of iron to rust, for, in true scientific fashion, Pliny asked himself the question: why should iron corrode more easily than other metals? Lacking the ability to investigate the problem experimentally, he arrived at the metaphysical solution that it is because iron is both the best and the worst of man's servants. 

Although very useful domestically, it is also the metal of war, slaughter and brigandage. 

In other words, Pliny considered the rusting of iron to be a punishment of the gods, as the metal allows itself to be used for swords an other war purposes.

1.2 Iron : Is the second most abundant metal found in earth’s crust after aluminum and it is the most common metal that is found around us, therefore, its corrosion is of special significance. 

Iron is an alloy of steel i.e a mixture of iron and carbon and it

is the most widely used metal, such as in vehicles motorcycles, bicycles, machineries, pipelines, bridges and girders for

construction purposes etc.

Iron being a special element corrodes; its corrosion is know as

“rusting” and is of special significance.

PROPERTIES OF IRON 

Iron has chemical and physical properties which some of it react with oxygen and water to produce rust and which enable it to be useful for many purposes. 

PHYSICAL PROPERTIES

• It is a silvery solid 

• It is malleable

• It is ductile 

• Has a meeting point of 15300c

• It conducts electricity e.t.c

CHEMICAL PROPERTIES

• Reaction with air: When iron is exposed to moist air, it

gradually rust, due to  the formation of hydrated iron (III) Oxide (Fe203. XH20)

4FE(S) +302(g)+2xH20                2Fe203.xH2O(Rust)

• Reaction with steam : When steam is passed over red-hot

iron fillings, iron (ii) diiron (iii) oxide and hydrogen are produced 

3Fe(s) ¬+ 4H20(G)  = Fe3304(s) + 4h2(g)

• Reaction with non-metals:- When heated, iron readily

combines with chlorine to give iron (iii) chloride. 

2Fe(s) + 3cl2(g)            2Fecl3 (s) 

1.3 Rusting: Is the corrosion of iron. As iron is the most widely

used metal in the world , rusting is the most common type of corrosion. 

Iron rusts by combining with oxygen in the presence of water

to from brown hydrated iron (iii) oxide (commonly known  as rust), Fe2 03.XH20

RUST:  Is a general term used for describing iron oxides.

The terms is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture.

FORMS OF RUST

• Reaction of iron and oxygen in the presence of water or air

moisture to produce  brown hydrated iron (iii) oxide 

• Reaction of iron  and chloride, in an environment deprived of oxygen 

2.1 FACTORS THAT SPEED UP RUSTING 

• Presence of electrolytes:- Acid solutions make rusting go faster.

In industrial areas where air is seriously polluted, there are high concentrations of carbon dioxide, sulfur dioxide and nitrogen dioxide. These gases dissolve in rain water to give "acid rain", which makes iron objects rust faster. 

Sodium chloride also makes iron rust more quickly. For example, the iron objects by seashore, where seawater has a high salt content, amounting to about 3.6% in the Atlantic and Pacific Oceans. The thin water film on iron surface contains dissolved sodium chloride from sea spray. This greatly increases conductivity of the solution, due to a higher concentration of ions. As a result, special "seawater rust" is formed which actually very strongly corrosion is inducing. 

Presence of soluble salts other than sodium chloride may also assist rust