Engineers and technologist engage themselves in the design and manufacturing of machine like latches, engines, motors, generators, bulldozers etc. And in the fabrication of vehicles like aircraft, trains, automobiles. When we analyze the products of engineering industry for their constituent materials, we find that the materials that are primarily used are solids, fluids like water, oil and steam. But solid with their properties manipulated with the variety of ways dominate the industry. Solid materials may be conveniently grouped into four different groups. It is possible to be conversant with the thousands of engineering materials, unless we are guided by some broad and some generalization. This book deals with such materials that are commonly used in electrical engineering field. The decision upon the broad classification of materials in this book is done by first listing the functions of electrical engineering materials.
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TYPE
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PROPERTIES
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TYPICAL EXAMPLES
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METALS
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Typical metallic cluster ,high thermal and electrical conductivity ductile, high strength corrosion, resistance is poor , positive temperature coefficient
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Steel copper aluminium iron etc.
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Non metallic inorganic materials (also referred as ceramics)
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No cluster high strength even at high temperature excellent resistance to oxidation and corrosion good thermal and electrical insulator brittle.
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Oxide (Sio2, MgO, Al2O3, BaTiO3 ) silicate borides, nitrides, carbides.
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Organic polymers
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Easy to fabricated, good insulators, light in weight, good corrosion resistance, low strength, negative temperature resistance
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Generally synthetic organic compounds rubber (natural polymer).
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Composite (combination of above various verities of materials
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Many unusual combinations of properties can be accomplished by the suitable design of a composite.
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Strong carbon fifers embedded in plastics, concrete, wood (naturally occurring composite.)
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(1) To transmit electricity.
(2) To resist the flow of electricity except in a particular direction
(3) To store electrical energy.
(4) (A) to transfer electrical energy from one circuit to another,
(B) To change the form of energy,
(5) To change nature and level of electrical signals.
Analyzing the above, a function classification of electrical engineering materials can be made as follows:
(1) The materials which, allow the CURRENT to pass through them, are called conducting materials. These have very low electrical resistance and available in large variety having diverse properties. The conducting materials should be able to withstand high temperatures and on the other hand should have minimum power loss even when carrying large Nichrome currents. Examples: copper, aluminium, silver, gold, tungsten, platinum, tantalum, bronze, brass, steel, lead, mercury etc.
(2) The materials which obstruct the flow of current without any appreciable power loss are classified as insulating materials. These have very high electrical resistance and are available in large variety. Examples: rubber, Glass, Asbestos, Bitumen, Wood, etc.
(3) The materials, which store electrical energy, are classified as dielectric materials. They increase the capacitance or charge storage ability of a capacitor. Examples: air, mica, ceramic, plastic etc.
(4) The materials which provide a path to the magnetic flux are classified magnetic materials. Many electrical engineering devices such as inductors, transformers, rotating machines and ferrite antennas are based on utilizing the magnetic properties of materials. Examples: iron, high carbon steel, tungsten steel, cobalt steel, barium ferrite, chromium steel etc.
(5) The material which possess electrical resistivity in between the conducting and insulating materials are classified as semiconductor materials. They are used for the manufacturing of devices like diode, transistors, rectifier etc. Examples: silicon, germanium, graphite, diamond, selenium, silicon, carbide, gallium phosphate, gallium arsenide, cadmium sulphide, etc.