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Tungsten
W-wolfram Atomic Number-74
1. Hard Metal
2. It can be drawn into very thin wires.
3. Melting point 3422°C
4. Used as filaments in incandescent lamps, and in electron tubes and also in heater.
Carbon
C atm no 6
Graphite 90% of carbon coal coke charcoal etc
1. High resistivity about 4600 micro ohm.cm
2. Negative tempt. Coefficient of resistance.
3. Pressure sensitive resistance material and has low surface friction.
4. This oxidised at about 300°C and is very weak.
5. Used as brush in electrical machines.
6. As components in electronics and communication equipments.
Nichrome
Nickel 75-78% chromium 20-30% manganese 1.5% and iron(balance)
1. Its resistivity is high.
2. Temperature coefficient of resistance is low.
3. Withstands high tempt for a long time.
4. Used as electric iron coil, furnace and heating elements.
Manganin
Copper 80% manganese17-18% nickel 1.5-2%
1. Resistivity 0.49 to 0.50 micro ohms.m
2. Low tempt. Coefficient of resistance(0.00015)
3. Melting point is 1020°C
4. Specific gravity is 8.19
5. Used for instruments shunts and for standard resistance.
Constantan
Copper 60% nickel 40%
1. It does not rust or corrode due to air , heat and moisture.
2. Resistivity is 49 micro ohm.cm
3. Specific gravity is 1.9
4. Melting point is 1300°C
5. Used for different types of rheostats, resistance wires, resistance boxes, arc lamps, motor starters, supporting wires for electric filaments.
Platinum
Pt atm no 78
1. It is non corroding.
2. Resistant to most chemicals.
3. Can be drawn into thin wires and strips.
4. Melting point 1775°C
5. Resistivity 10.5 micro ohm.cm
6. No oxidation.
7. Used for heating element in laboratory ovens and furnaces.
8. Used for platinum-rhodium thermocouples measurement of upto 1600°C.
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