EXPERIMENT

 

 

OBJECTIVE:

To classify materials into:

• Metals and non-metals.
• Metals and alloys.
• Ferrous and non-ferrous metals and alloys.

 

 

APPARATUS REQUIRED:

• Material specimens
• Grinding wheel
• Magnet
• Hot surface

 

 

PROCEDURE:

METALS AND NON-METALS: In order to classify the material specimens into metals and non-metals the following tests may be carried out:

• LUSTURE: By lustre of material we mean the ability of a surface to reflect light. In other words, lustre means how much does a surface shine. Normally we find that metals posses lustre whereas non-metals not. We may divide the specimens on the basis of lustre into metals and non-metals as follows:

 

METALS	NON-METALS
Copper	Glass
Zinc	Bakelite
Silver	Porcelain
Gold	Leather
Lead	Plywood
Nickel	Rubber
Muntz metal	PVC
Phosphor bronze	Polythene
Babbit metal	Cardboard
Cast iron	Thermocole
Galvanized iron	Sun-mica
Mild steel	Carbon
High carbon steel	–
High speed steel	–

 

• COLOUR AND TRANSPARENCY: Metals can be distinguished from non-metals to some extent by observing color and transparency of the materials. Color and transparency of some important materials are given below:

 

METALS	COLOR AND TRANSPARENCY
Copper	Typical reddish brown color
Zinc	Bluish white appearance
Silver	White color
Gold	Yellow
Lead	Bluish grey
Bronze	Pale yellowish
Nickel	Yellowish white
Cast-iron	Grey
Galvanized Iron	White
Steel	Typical steel grey color
High speed steel	Medium grey
Glass	Transparent
Polythene	Transparent
PVC	Transparent
Thermocole	Snow white
Bakelite	Deep brown
Rubber	Black or brownish
Porcelain	Whitish
Card-board	Straw color
Asbestos	Whitish
Leather	Light brown
Carbon	Black

 

• APPEARANCE AND TEXTURE:

Texture and general appearance of the materials can prove helpful in the identification of the materials.

 

METALS	NON-METALS
Cast iron is brittle in appearance.	Wood has long fibers and knots.
Galvanized iron can be easily recognized by geometric pattern of zinc on the surface of the iron.	Plywood is composed of layers.
–	Cork has holes in the surface.
–	Glass, porcelain and carbon are brittle.

 

• WEIGHT:

It is known that the weight of the same volume of various metals and alloys is different. The two characteristics namely density and specific gravity are sometimes useful in identifying the metals.

 

METALS	NON-METALS
Out of metals aluminum is relatively lighter in weight whereas lead is much heavier.	Out of non-metals asbestos, cardboard, plywood, wood, thermostat, leather and cork are lighter in weight.

 

Metals have high density as compared to non-metals.

 

• SOUND:

It has been observed that typical metallic sounds are produced by metals/alloys when struck or made to fall from a certain height. The following types of sounds are produced when we strike the specimens given below:

 

METALLIC SPECIMENS	SOUNDS PRODUCED
Aluminum	Dull sound
Lead	Dull sound
Copper	Dull sound
Brass	Slightly ringing sound
Mild steel	Slightly ringing sound
Bronze	School bell like sound
Gun metal	Ringing sound
Cast iron	Very dull sound
High carbon	Very high ringing sound
High speed steel	Low ringing sound
Non-metallic specimen	Usually very dull sound

 

• HARDNESS, BRITTLENESS AND BENDING:

We can have some idea of hardness of a material by feeling it whereas their relative hardness and ductility can be judged through bending. Following characteristics of the materials are worth noting for their identification.

• • • Cast iron cannot be bent.
    • Aluminum is good in bending.
    • Lead is very good in bending.
    • Copper is very good in bending.
    • Aluminum is soft in filing.
    • High carbon steel is very hard in filing.
    • High carbon steel is brittle.
    • Copper is soft in filing.
    • Mild steel is soft in filing.

 

• THERMAL AND ELECTRICAL CONDUCTIVITY:

Metals and non-metals can be distinguished to a large extent by the use of these properties. Metals are good conductors of heat and electricity whereas the non-metals are of normally bad conductors of heat and electricity.

Thermal conductivity of a material specimens can be tested by placing them in contact with a very hot surface on one end and sensing the temperature after sometime on the other end. In case of metals it will be seen that the metals heat up on the other end while in case on non-metals, normally the other end remain cold.

Similar property of electrical conductivity can be tested by placing the material in an electric circuit and measuring the current with the help of an electrical instrument. It is seen that the metals will allow the current to flow whereas the non-metals will resist the current flow indicating that they are bad conductors of electricity.

 

• SPARK TEST:

It is observed that many metals when rubbed against grinding wheel produce characteristics spark streams. Some examples are given below:

METALS	SPARK
Cast iron	Reddish color globules
Mild steel	Yellow straw with springs
Die steels	Dense yellow spring
High carbon steel	Dull and red color spark, spark moves with the wheel

 

FERROUS AND NON-FERROUS METAL AND ALLOYS: In order to distinguish ferrous and non-ferrous metals and alloys the use of a magnet is made. When the metallic specimen are brought near it we shall find that some of them which belongs to ferrous family gets attracted towards it. However, stainless steel, although belonging to ferrous family may not be attracted.

Non-metals are not attracted by the magnet.

 

METALS AND ALLOYS: There are hardly any test available by which it may be possible to identify pure metals from alloys. However from the knowledge we have gained so far we can give some examples of metals and alloys which are as follows:

 

METALS	ALLOYS
Copper	Bronze
Aluminum	Brass
Cast iron	Stainless steel
Nickel	Mild steel
Galvanized iron	High carbon steel