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.
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–
rusting causes enormous economic problem and is reason why extensive measures
of rusting/corrosion protection have to be developed
1.1 RUST IN HISTORY
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.
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.
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.
very useful domestically, it is also the metal of war, slaughter and
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
most widely used metal, such as in vehicles motorcycles, bicycles, machineries,
pipelines, bridges and girders for
Iron being a special element corrodes; its corrosion is know as “rusting” and
is of special significance.
PROPERTIES OF 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.
It is a silvery solid
It is malleable
It is ductile
Has a meeting point of 15300c
It conducts electricity e.t.c
Reaction with air: When
iron is exposed to moist air, it
rust, due to the formation of hydrated iron (III) Oxide (Fe203. XH20) 4FE(S) +302(g)+2xH20
Reaction with steam : When
steam is passed over red-hot
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
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
metal in the world , rusting is the most common type of corrosion.
Iron rusts by combining with oxygen in the presence of water
brown hydrated iron (iii) oxide (commonly known as rust), Fe2 03.XH20
RUST: Is a general term used for describing iron oxides.
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
to produce brown hydrated iron (iii) oxide
Reaction of iron and chloride, in an environment deprived