ALLOYS (SUBSTITUTIONAL SOLID SOLUTIONS)
- An alloy is a homogenous mixture of 2 or moremetal (or a metal and a non-metal).
- brass is the alloy of Cu and Zn.
- bronze is an alloy of Cu and Sn.
- solder is an alloy of Pb and Sn.
- Amalgam is the alloy of Hg with other metal.
PREPARATION OF ALLOYS
Alloy is usually prepared by first melting
the primary metal and tehn dissolving the other elements in it in a definite
proportions. It is then cooled to room temperature.
OBJECTIVE/ PURPOSE OF ALLOY MAKING
Alloys are used to prepare certain specific
properties, which is not possessed by constituent elements. These objectives
are :-
To increase hadrness:-pure iron is very
soft and stretches easilywhen hor but when carbon (.o5-1.5%) is added to iron,
its hardness increase . this hardeneded iron is called steel.
To increase tensile strength:- chrome
steel is prepared by mixing iron and
chromium. It has a high tensile strength then its constituent metals. It is
used for making axles, ball bearings and cutting tools such as files etc.
To increase resistance to corrosion:- when
iron is mixed with nickeland chromoium , it became stainless steel, which is
hard and does not rust. Thus resists corrosion.
To reduce electrical conductivity:- electrical
conductivity of an alloy is less than that of pure metals ex;- brass( an alloy
of Cu and Zn0 and bronze (alloy of Cu and Sn) and not good conductors of
electricity but pure copper si an excellent conductor of electricity and used
for making electrical ciruits .
To lower the MP :- solder , an alloy of
tin(50%0 and lead (50%) has a lower MP than either of its constituent metal
(tin and lead ). It is thus, used for welding electrical wires together.
To modify chemical reactivity:- the
reactivity of sodium can be reduced by maing its alloy with liuid i.e. amalgam.
To produce good casting
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