Chemistry Form 4: Chapter 9 - Making of Alloy

An alloy is a mixture of two or more elements with a certain fixed composition in which metal is the major component.

The making of alloy is:

• To increase the strength and hardness of a pure metal.
• To prevent corrosion.
• To improve the appearance of a pure metal.

Pure Metal

·     Pure metal is made up of one type of atoms that are in same size. Therefore, when a force is applied, the layers of atoms can slide over one another. Thus, metals are ductile or can be stretched. ·     There are some empty spaces in between the pure metal atoms. When a metal is knocked or pressed, groups of atoms may slide and then settle into new positions. Thus, metals are malleable or can be shaped.

Alloy

·     Some of the spaces between the metal atoms are filled up by the foreign atoms which may be bigger or smaller than the original metal atoms. ·     The presence of foreign atoms disrupts the orderly arrangement or the pure metal. ·     The layers of metal atoms are prevented from sliding over one another easily. This makes alloys stronger and harder than pure metals.

Examples of alloy

Alloy	Composition
Steel	99 %   iron     +   1 %  carbon
Stainless steel	74 %   iron  +  18 % chromium  + 8 % nickel
Bronze	90 %   copper   +   10 %  tin
Brass	70 %  copper   +   30 %   zinc
Magnalium	70 %  aluminium   +   30 %   magnesium
Duralumin	95 %  aluminium   +  4 %  copper    +  1 %   magnesium
Pewter	97 %  tin   +    3 %  lead and antimony
Solder	50 %   tin   +    50 %  lead
cupronickel	25 %  copper    +    75 %  nickel