Page 214 - Chemistry ICSE Class X

200 ICSE Chemistry – 10
Alloys

One of the most important properties of metals is their ability to form
ůůŽLJƐ ĂƌĞ ĂůƐŽ ĐĂůůĞĚ ƐŽůŝĚ ƐŽůƵƟŽŶƐ͘ alloys.
ͻ
>Žǁ ŵĞůƟŶŐ ĂůůŽLJƐ ĂƌĞ ĐĂůůĞĚ fusible What is an alloy
alloys͘ ^ƵĐŚ ĂůůŽLJƐ ĂƌĞ ďĂƐĞĚ ŽŶ
ŵĞƚĂůƐ ƐƵĐŚ ĂƐ ďŝƐŵƵƚŚ͕ ůĞĂĚ͕ ƟŶ͕ ĞƚĐ͘ A homogeneous mixture of a metal with other metals or with a nonmetal
is called an alloy.
ƒ Brass is an alloy of two metals — copper and zinc.
dŚĞ ĂůůŽLJ ŝŶ ǁŚŝĐŚ ŽŶĞ ŽĨ ƚŚĞ ŵĞƚĂůƐ ŝƐ ƒ Steel is an alloy mainly of one metal and one nonmetal — Iron (metal)
ŵĞƌĐƵƌLJ ŝƐ ĐĂůůĞĚ amalgam͘ dŚƵƐ͕ ĂŶ and carbon (nonmetal).
ĂŵĂůŐĂŵ ŝƐ an alloy of mercury͘
ŽŵŵŽŶůLJ ƵƐĞĚ ĂŵĂůŐĂŵƐ ĂƌĞ njŝŶĐͲ What is the purpose of making an alloy
ŵĞƌĐƵƌLJ͕ ƐŽĚŝƵŵͲŵĞƌĐƵƌLJ ĂŵĂůŐĂŵƐ͘
ͻ #P CNNQ[ KU OCFG VQ OQFKH[ CP[ URGEKſE RTQRGTV[ QH KVU OCLQT EQORQPGPV
ůůŽLJƐ ĂƌĞ ĐŽŵŵŽŶůLJ ƉƌĞƉĂƌĞĚ ďLJ For example,
ŵĞůƟŶŐ ƚŚĞ ƌĞƋƵŝƌĞĚ ĐŽŵƉŽŶĞŶƚ ƒ To modify the appearance and colour
ŵĞƚĂůƐ ŝŶ ƚŚĞ ĚĞƐŝƌĞĚ ƌĂƟŽ ĂŶĚ ƒ To modify the chemical reactivity
ĂůůŽǁŝŶŐ ƚŚĞ ŵŽůƚĞŶ ŵĂƐƐ ƚŽ ƐŽůŝĚŝĨLJ͘
ƒ To modify the melting point
ƒ To modify casting ability
ƒ To increase resistivity
ƒ To increase hardness

How do the properties of alloys differ from those of major
component in them
The properties of alloys are different from those of their constituent metals.
For example,
ƒ The electrical conductivity of an alloy is lower than that of the pure
metals. That is why, the conductivity of impure copper is lower than
that of pure copper.
ƒ Nichrome has high resistivity.
ƒ Alloys usually are harder than the constituent metals. For example.
Š duralumin (an alloy of aluminium, copper, magnesium and
manganese),
Š magnalium (an alloy of aluminium and magnesium) are much
A bronze statue harder and stronger than aluminium.
ƒ The presence of small amount of carbon (0.1% to 1.5%) in iron makes
'ŽůĚ ŝƐ ƚŚĞ ŵŽƐƚ ŵĂůůĞĂďůĞ ĂŶĚ ĚƵĐƟůĞ it harder and stronger.
ŵĞƚĂů͘ 'ŽůĚ ƵƐĞĚ ŝŶ ŵĂŬŝŶŐ ũĞǁĞůůĞƌLJ ŝƐ
ƵƐƵĂůůLJ ĂůůŽLJĞĚ ǁŝƚŚ ĐŽƉƉĞƌ ĂŶĚ ƐŝůǀĞƌ͘ Š Brass is harder than both copper and zinc.
dŚĞƐĞ ĂůůŽLJƐ ƌĞƚĂŝŶ ŐŽůĚĞŶ ĐŽůŽƵƌ ďƵƚ Š Carboloy (an alloy of tungsten, carbon, cobalt) is as hard as
ĂƌĞ ŚĂƌĚĞƌ ƚŚĂŶ ƉƵƌĞ ŐŽůĚ͘ diamond.
dŚĞ ƉƌŽƉŽƌƟŽŶ ŽĨ ŐŽůĚ ŝŶ ĂůůŽLJĞĚͲŐŽůĚ ŝƐ ƒ Alloying iron with nickel and chromium makes it corrosion-resistant.
ĞdžƉƌĞƐƐĞĚ ŝŶ carats͘ WƵƌĞ ŐŽůĚ ŝƐ
Ϯϰ ĐĂƌĂƚƐ͘ ƒ The melting point of alloys may be higher or lower than the parent
dŚĞ ĂůůŽLJƐ ĐŽŵŵŽŶůLJ ƵƐĞĚ ĂƌĞ metal. Solder (an alloy of lead and tin) has lower melting point
ϵ ĐĂƌĂƚƐ͕ ϭϴ ĐĂƌĂƚƐ ĂŶĚ ϮϮ ĐĂƌĂƚƐ͘ (180°C) than both the metals. [Lead (327°C), Tin (232°C)] Solder is
dŚĞƐĞ ĂůůŽLJƐ ƚŚƵƐ ĐŽŶƚĂŝŶ ϵ ƚŚ͕ ϭϴ ƚŚ used for welding electric wires.
Ϯϰ Ϯϰ ƒ Bell metal is more sonorous than copper.
ĂŶĚ ϮϮ ƚŚ ƉĂƌƚ ŽĨ ƉƵƌĞ ŐŽůĚ͕
Ϯϰ ƒ Sodium amalgam is less reactive than sodium.
ƌĞƐƉĞĐƟǀĞůLJ͘
ƒ Alnico (an alloy of aluminium, nickel, cobalt) can lift heavy masses.
ƒ Aluminium bronze (an alloy of aluminium and copper) has golden
&ƵƐĞ ŵĞƚĂů ŝƐ ĂŶ ĂůůŽLJ ĐŽŶƚĂŝŶŝŶŐ ĐŽƉƉĞƌ yellow colour.
ĂŶĚ ƟŶ͘
Some important alloys of some common metals are listed below: