High Resistivity or Low Conductivity Conducting Material

Materials having high resistivity or low conductivity are very useful for some electrical engineering products and applications. These material are used to manufacture the filaments for incandescent lamp, heating elements for electric heaters and furnaces, space heaters and electric irons etc.

Required Properties in High Resistivity or Low Conductivity Conducting Material

The following properties are required in high resistivity or low conductivity conducting material–

• High resistivity.

• High melting point.

• High mechanical strength.

• High ductility, so that can be drawn in the form of wire easily.

• High corrosion resistance mean free from oxidation.

• Low cost.

• Long life or durable.

• High flexibility.

Some of Materials having High Resistivity or Low Conductivity are listed below

1. Tungsten

2. Carbon

3. Nichrome or Brightray B

4. Nichrome V or Brightray C

5. Manganin

Tungsten

Tungsten is produced by very complicated processes from rare ores or from tungstic acids. Some facts about tungsten are listed below-

• Very hard.

• Resistivity is twice to aluminum.

• High tensile strength.

• Can be drawn in the form of very thin wire.

• Oxidize very quickly in the presence of oxygen.

• Can be used up to 2000oC in the atmosphere of inert gases (Nitrogen, Argon etc.) without oxidation.

Properties of Tungsten

Properties of tungsten are listed below-

• Specific weight : 20 gm/cm3

• Resistivity : 5.28 µΩ -cm

• Temperature coefficient of resistance : 0.005 / oC

• Melting point : 3410oC

• Boiling point : 5900oC

• Thermal coefficient of expansion: 4.44 × 10-9 / oC

Uses of Tungsten

1. Used as filament for incandescent lamp.

2. As electrode in X- ray tubes.

3. The great hardness, high melting and boiling points make it suitable for use as electrical contact material in certain applications. It is having high resistance for destructive forces produces during operation of electrical contacts.

Carbon

Carbon in widely used in electrical engineering. Electrical carbon materials are manufactured from graphite and other forms of carbon.

Properties of Carbon

• Resistivity : 1000 – 7000 µΩ – cm

• Temperature coefficient of resistance : – 0.0002 to – 0.0008 /oC

• Melting point : 3500oC

• Specific gravity : 2.1gm /cm3

Uses of Carbon

Carbon is having following applications in electrical Engineering

1. Used for making pressure sensitive resistors, which are used in automatic voltage regulators.

2. Used for manufacturing the carbon brushes, which are used in DC machines. These carbon brushes improve the commutation as well as reduce the wear and tear.

3. For making filament of incandescent lamp.

4. For making electrical contacts.

5. For making resistors.

6. For making battery cell elements.

7. Carbon electrodes for electric furnaces.

8. Arc lighting and welding electrodes.

9. Component for vacuum valves and tubes.

10. For makings parts for telecommunication equipment.

Nichrome or Brightray B

Composition of Nichrome or Brightray B

Properties of Nichrome or Brightray B

• Resistivity : 1.10 µΩ -cm

• Temperature coefficient of resistance : 0.0002 /oC

• Melting point : 1350oC

• Specific gravity : 8.24 gm /cm3

• High resistance to oxidation

Uses of Nichrome or Brightray B

Used in making tubular heaters and electric irons.

Nichrome V or Brightray C

Composition of Nichrome V or Brightray C

Properties of Nichrome V or Brightray C

• Resistivity : 40 µΩ – cm

• Temperature coefficient of resistance : 0.0001 /oC

• Melting point : 1400oC

• Specific gravity : 8.4gm /cm3

• High resistance to oxidation

Uses of Nichrome V or Brightray C

Used in making heating elements for electric heaters and furnaces.

Manganin

Composition of Manganin

Properties of Manganin

• Resistivity : 40 µΩ -cm

• Temperature coefficient of resistance : 0.0001 /oC

• Melting point : 1400oC

• Specific gravity : 8.4gm /cm3

• High resistance to oxidation

Uses of Manganin

Manganin is having following applications in electrical Engineering.

1. Used in making electric heating elements and in electric furnaces.

2. As the manganin is having very low temperature coefficient of resistance, therefore it is used to make the standard resistances and in measuring instruments.

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