Alloys metals & non-metal class 10 science

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             ALLOYS

An alloy may be defined as homogeneous mixture of two or more metals, or a metal & a non-metal.
 The properties of any metal can be changed if it is mixed with some other metal or non-metal. This mixture is called ALLOYS.

Preparation of Alloys:

An alloy is generally manufactured by first melting the main Metal and then dissolving the other elements in it in a definite proportions. It is then cooled to room temperature.


Types of Alloys:

1. Ferrous Alloys:   An alloy in which iron is present as one of the constituents is known as a ferrous alloy.  For ex,  nickel steel (iron=96-98%, ni=4-2%) & manganese steel ( Fe=86%, Mn=13%, C=1%) etc.

2. Non ferrous Alloys:   An alloy which does not contain iron as one of the constituents is known as a non- ferrous alloy. For ex, brass ( cu= 80%, zn=20%), bronze( Cu=90%, Sn=10%), etc.

3. Amalgams:   An alloy which contains mercury as one of the constituents is known as amalgam. For ex, sodium amalgam, zinc amalgam, etc.

Alloying of Gold:

Purity of gold is expressed in carats. Pure gold, known as 24 carat gold, is very soft. It is, therefore, not suitable for making jewellery. It is allowed either with silver or copper to make it hard. 

Objectives of Alloy making:

Alloys are prepared in order to acquire certain specific properties which are not possessed by constituent elements. The main objectives of Alloy making are as follow:

1. To increase hardness:   when carbon is added to iron, its hardness increases. Thus hardened iron is known as steel. The hardness of steel increases with the increase in carbon content which varies between 0.05-1.5%.

2. To increase the resistance to Corrosion:   Stainless steel,  which is an alloy if iron, chromium & nickel, resists Corrosion.

3. To lower the melting point:   Solder, which is an alloy of tin & lead, has a lower melting point than either of its constituents. Thus, it is used for joining electrical wired together.

4. To increase the tensile strength:   Chrome steel, which is prepared by mixing iron & chromium has high tensile strength & thus, is used for making axels,  ball bearings, cutting tools such as files, etc. 

5. To reduce electrical conductivity:   Electrical conductivity of an alloy is less than that of pure metals. For ex. Copper is not a good conductor when it contains impurities.

6. To produce good casting:   Type metal which is an alloy of lead, antimony and tin, has good casting properties. Thus, it is used for making printing type.

7. To change chemical reactivity:   Sodium is a highly reactive metal. It's reactivity can be reduced by making its alloy with Mercury.

8. To change colour:   Aluminium is Silvery white where as copper is brown in colour but aluminium bronze, which is an alloy of aluminium & copper, had yellow colour & is used for making coins,  picture frames, cheap jewellery etc.

Some commonly used as alloys, their composition, properties & uses are given below: 



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