Metals
Metals are opaque, lustrous elements that are good conductors of heat and electricity.

Properties of Metals
(i) Physical Properties
(ii) Mechanical Properties

Physical Properties
1. Weight: Weight varies from metal to metal.
2. Structure: If metals are broken and their construction is examined, they look different from one another.
3. Colour: Every metal has different colour. Ex: Copper-red, Aluminium-white
4. Conductivity: Metals that allow free passage of electricity and heat through them are called conductors. Conduction of each metal is different.

5. Fusibility: It is the property of metal to change its state from solid to liquid on being heated to a certain temperature. Temperature at which metal turns into liquid is called melting point. Each metal has different melting point.
6. Magnetization: It is the property of metal to become a magnet. It is not necessary that each metal should possess ability of magnetization. Each metal has different magnetism.

Mechanical Properties
1. Elasticity: On application of external force/energy/weight the metal acquires elasticity (deforms) and regains its original shape on removal of external force. Plasticity: Metal undergoes permanent deformation on application of certain magnitude of force.
2. Brittleness: It’s the property of metal to resist deformation. On application of external force/weight/energy, metal is broken into pieces and turn into powder.
3. Ductility: Metal can be drawn into thin wires without breaking (hammered thin or stretched into wire).
4. Toughness: Metal does not break on heavy impact (hammer blows) or bending. On heating, metal tends to lose its toughness.
5. Hardness: metal does not easily bend or break and has potential to cut or scratch another metal. Hardness decreases when a metal is heated. Ex: steel is harder than copper/aluminium.
6. Malleability: Metal can be beaten into sheets without heating. Forging and rolling can be done without heating.
7. Tenacity: Metal may stand a pull and does not break. Maximum pull that a metal can bear without breaking is called tensile strength. Tenacity is the property of metal to bear the effect of tensile forces.

Types of Metals
(i) Ferrous Metals
(ii) Non-ferrous Metals

Ferrous Metal Non-ferrous Metal
Metals contain high iron and carbon Metals do not contain iron or carbon
This is of black and brown colour These are found in different colours
The melting point is high The melting point is low
Catches rust Doesn’t catch rust
Can be magnetized Cannot be magnetized
Brittle in cold state Brittle in hot state
These are rigid and strong Comparatively less strong and soft
Not costly Costly
Ex: pig iron, wrought iron, cast iron, mild steel, nickel etc. Ex: copper, zinc, aluminium, gold, silver etc.


Pig Iron
$\displaystyle \small \bullet$ Iron mixture obtained from mines is called ore. This is not pure because it contains other materials such as oxygen, sulphur etc.
$\displaystyle \small \bullet$ Blast Furnace is used to extract pig iron.
Iron ores: magnetite, hematite, limonite, carbonite.
Coke: The carbon from the coke in the form of carbon monoxide combines with the iron ore to reduce it to iron.
Flux: This is used to lower the melting point of the ore, and it combines with the non-metallic portion of the ore to form a molten slag.
$\displaystyle \small \bullet$ Pig-iron is refined and remelted and used to produce other varieties of iron and steel.

Cast Iron
$\displaystyle \small \bullet$ It is made out of pig iron
$\displaystyle \small \bullet$ Cupola furnace is used to obtain cast iron.
$\displaystyle \small \bullet$ The carbon content ranges from 2 to 4%
$\displaystyle \small \bullet$ It cannot be forged since it is brittle. It breaks on striking.
$\displaystyle \small \bullet$ Types of cast iron:
Grey cast iron
This is widely used for the casting of machinery parts and can be machined easily.
White cast iron
White cast iron cannot be welded.
Malleable cast iron
Malleable cast iron has increased ductility, tensile strength and toughness when compared with grey cast iron. Used for making hubs, brake-pedal, elbows of pipe, sockets
Nodular cast iron
This has good machinability, castability, resistance to wear, low melting point and hardness

Wrought Iron
$\displaystyle \small \bullet$ Made by melting white pig iron in puddling furnace.
$\displaystyle \small \bullet$ It is the purest form of iron. It contains 99.9% of iron.
$\displaystyle \small \bullet$ When heated, wrought iron does not melt but becomes soft.
$\displaystyle \small \bullet$ Used for making chain, draw boxes, hooks, wires, sheets and rivet etc.

Steel
$\displaystyle \small \bullet$ Carbon content is from 0.15%-1.5%. Due to excessive carbon, it is harder and tougher.
$\displaystyle \small \bullet$ Contains other impurities like sulphur, phosphorus etc. which cannot be separated.
$\displaystyle \small \bullet$ Types of Steel
(i) Plain Carbon steel
(ii) Alloy steel

Plain Carbon Steel
In this carbon and iron is mixed.
Types of Plain carbon steel according to the percentage of carbon
Low carbon steel
$\displaystyle \small \bullet$ Also called mild steel
$\displaystyle \small \bullet$ Carbon is 0.15-0.25%
$\displaystyle \small \bullet$ Used for making nuts, bolts, rivets, sheets, wires, T-iron, angle iron etc.
Medium carbon steel
$\displaystyle \small \bullet$ Carbon is 0.25-0.5%
$\displaystyle \small \bullet$ Due to excess carbon, it is harder and tougher than mild steel
$\displaystyle \small \bullet$ Used for making high tensile tubes, wires, agricultural implements, connecting rods, cam shafts, spanners, pulleys etc.
High carbon steel
$\displaystyle \small \bullet$ Carbon content is 0.5-1.5%
$\displaystyle \small \bullet$ It is very hard and tough
$\displaystyle \small \bullet$ It acquires permanent magnetic properties
$\displaystyle \small \bullet$ Used for making pointed tools, springs, dye pumps, files, cutleries, cold chisels, press die etc.

Alloy Steel
Steel is mixed with alloying elements like vanadium, manganese, tungsten etc.
Types of Alloy Steel
Low alloy steel
$\displaystyle \small \bullet$ It has low percentage of alloying metals
$\displaystyle \small \bullet$ Used in manufacturing of parts of aeroplane and camshaft etc.
High alloy steel
$\displaystyle \small \bullet$ It has high percentage of alloying metals
$\displaystyle \small \bullet$ Types of High alloy steel
High Speed Steel: It is also called high tungsten alloy steel because it has more quantity of tungsten.  It is used for cutting tools, drills, cutters, reamers, hacksaw blades etc.
Nickel Steel: Contains carbon and nickel. This is used for making rivets, pipes, axle shafting, parts of buses and aeroplanes.
Invar steel: Contains cobalt and nickel. It is mainly used for making precious instruments.
Vanadium Steel: It has strength to bear sharp jerks. It is mainly used to manufacture of tools.
Manganese Steel: It is also called special high alloy steel. It is not affected by magnet. It is used in grinders and rail points etc.
Stainless Steel: It is used for making knives, scissors, utensils, parts of aeroplane, wires, pipes and gears etc.
Silicon Steel: It is used for manufacturing electric motors, generators, lamination of transformers.  
Cobalt Steel: Toughness and tenacity is high. It has magnetic property therefore used to make permanent magnets.

Non-ferrous Metals
1. Copper
$\displaystyle \small \bullet$ Best conductors of heat and electricity
$\displaystyle \small \bullet$ Reddish brown colour
$\displaystyle \small \bullet$ It is malleable and ductile
$\displaystyle \small \bullet$ Used in wires, cables, windings of generators and transformers, overhead conductors, bus-bars, alloyed with gold for making ornaments
2. Aluminium
$\displaystyle \small \bullet$ Ores are Bauxite and Cryolite
$\displaystyle \small \bullet$ Good conductors of heat and electricity
$\displaystyle \small \bullet$ Light grey colour
$\displaystyle \small \bullet$ It is malleable and ductile
$\displaystyle \small \bullet$ Used in aircraft industry, used for making windows, doors, furniture, home appliances, wires, utensils, pipes, rods, sheets, parts of machines, heating appliances, parts of automobile engines
3. Zinc
$\displaystyle \small \bullet$ Ore is sphalerite
$\displaystyle \small \bullet$ Electrical conductivity is almost half of copper
$\displaystyle \small \bullet$ Bluish white colour
$\displaystyle \small \bullet$ It is malleable and ductile at high temperatures (1250C)
$\displaystyle \small \bullet$ Used for galvanizing steel parts and wires to protect against rusting
4. Lead
$\displaystyle \small \bullet$ Soft bluish grey colour
$\displaystyle \small \bullet$ It is malleable and ductile
$\displaystyle \small \bullet$ Used for coating electric cables, acid proof chambers, soldering, fuses, water pipes, roofings etc.
5. Tin
$\displaystyle \small \bullet$ Good conductors of heat and electricity
$\displaystyle \small \bullet$ Bluish white colour with lustre
$\displaystyle \small \bullet$ It is malleable and ductile
$\displaystyle \small \bullet$ Used as protective coating on steel sheets, domestic brass utensils
$\displaystyle \small \bullet$ Used for production of food containers

Non-ferrous Alloys
1. Brass
$\displaystyle \small \bullet$ It is an alloy of copper and zinc
$\displaystyle \small \bullet$ It can be easily machined.
$\displaystyle \small \bullet$ It is also corrosion-resistant.
$\displaystyle \small \bullet$ Used for making motor car radiator core and water taps etc.
2. Bronze
$\displaystyle \small \bullet$ Alloy of copper, tin and zinc
$\displaystyle \small \bullet$ It can be easily machined with sharp tools
3. Babbit metal
$\displaystyle \small \bullet$ Babbit metal is an alloy of lead, tin, copper and antimony.
$\displaystyle \small \bullet$ It is a soft, anti-friction alloy, often used as bearings.

Insulators
$\displaystyle \small \bullet$ These are the materials which offer very high resistance to the flow of current and make current flow very negligible or nil.
Properties:
$\displaystyle \small \bullet$ High specific resistance to reduce the leakage currents to a negligible value.
$\displaystyle \small \bullet$ Good dielectric strength (breakdown  or puncture on application of high voltage).
$\displaystyle \small \bullet$ Good mechanical strength, in tension or compression
$\displaystyle \small \bullet$ Non-absorption of moisture, when exposed to damp atmospheric condition.
$\displaystyle \small \bullet$ Ex: Mica, Rubber, Dry cotton, Varnish, Asbestos, Gutta parcha, Porcelain, Glass, Wood dry, Plastic, Ebonite, Fibre, Empire cloth, Leathroid paper, Millimax paper, P.V.C., Bakelite, Shellac, Slate, Paraffin Wax

Insulators Uses in electric field
Mica In elements or winding
Rubber Insulation in wires
Porcelain Overhead lines insulators
P.V.C. Wire insulation
Bakelite Switch etc. making, for insulation


Rubber
Rubber is an elastic material.
Classification of rubber
Natural rubber: It is obtained from the secretion of plants. Sulphur is added to rubber and the mixture is heated. This process is called vulcanising. By this process, stronger, harder and more rigid rubber is obtained. Rubber is moisture-repellent and possesses good electrical properties.
Hard rubber: By increasing the sulphur content and prolonged vulcanization, a rigid rubber product called hard rubber or ebonite is obtained. It possesses good electrical and mechanical properties. It is used for battery containers, panel boards, bushing, ebonite tubes, etc.
Synthetic rubber: This is similar to natural rubber and is obtained from thermoplastic vinyl high polymers. Ex: Nitrite butadience rubber, Butyl rubber, Hypalon rubber, Neoprene rubber, Silicon rubber etc. Silicon Rubber is used to make insulation for power cables and control wires

Timber
Classification:
Softwood:
$\displaystyle \small \bullet$ Trees with needle leaves are softwood
$\displaystyle \small \bullet$ The wood contains resins and turpentines.
$\displaystyle \small \bullet$ Fibres are straight.
$\displaystyle \small \bullet$ Tough for resisting tensile stresses.
$\displaystyle \small \bullet$ Because of its cheapness it is used for low grade furniture, doors and windows for cheap type of houses.
$\displaystyle \small \bullet$ Used as fuel.
Hardwood:
$\displaystyle \small \bullet$ Trees with broad leaves are hard-wood
$\displaystyle \small \bullet$ The wood generally contains a large percentage of acid.
$\displaystyle \small \bullet$ It is difficult and hard to work with.
$\displaystyle \small \bullet$ It resists shearing stress.
$\displaystyle \small \bullet$ Used for high quality furniture such as chairs, tables, sofas, dewans, beds, etc.
$\displaystyle \small \bullet$ Used for door, window frames for high quality houses as they can take good polish and painting finish.