Electrical and Electronics Engineering Materials Electrical and Electronics Engineering Materials Electrical Engineering Third Semester

Detailed Contents Classifications of materials Properties of conductors Properties of semiconductors Properties of insulators Classification based on atomic structure and energy band Copper and its properties Aluminium and its properties High resistivity materials Superconductors Semiconductors

Classification of materials Classification of Conducting ,semi conducting and insulating materials based on atomic structure Classification of Conducting ,semi conducting and insulating materials based on energy bands A conductor of electricity is a material or substance which allows to flow of electric current when subjected to a potential difference Gold ,silver, copper and Aluminium are conductors. A material or an object that does not easily allow heat, electricity, light, or sound to pass through it. Air, cloth and rubber are good electrical insulators Semiconductor has a conductivity between that of an insulator and conductor example silicon and germanium

Properties of conductors Resistance of conductor is very low or negligible. The electric filed inside the conductor is zero The charge density inside the conductor is zero High conductivity Casted, forged, rolled, drawn and machined Malleable and Ductile Positive temperature coefficient of resistance.

Properties of Semiconductor Conductivity lies between conductor and insulator. They are negative temperature coefficients of resistance. Resistivity is high Adding of impurity result in increased conductivity. Small forbidden energy band of 1ev approx.

Properties of Insulators High resistance High dielectric strength They are rigid , tough and strong Low permittivity Low dissipation factor Least thermal expansion High thermal strength

Classification based on atomic structure

Classification based on energy bands

Classification of conducting material as low resistivity and high resistivity materials Low resistance materials Copper, Aluminium, steel, Silver, Gold, Platinum , copper alloys Brass, Bronze. High resistivity materials manganin, constantan, Nichrome, mercury, platinum, carbon and tungsten

Copper and its properties A good electrical conductor A good thermal conductor Corrosion resistant Antibacterial Easily joined Ductile Tough Non magnetic Easy to alloy Recyclable Catalytic

Properties of Aluminium It is silver- white in colour It posses high ductility It has high thermal and electrical conductivity It has high contact resistance High reflectivity for light rays It can be rolled into thin sheets and drawn into wires

Copper alloys Brass, Bronze An alloy is a combination of metals Brass and bronze are both alloys of copper -- that is, they are ``solid solutions," or mixtures of copper with another metal. The main difference between brasses and bronzes is that brass is mostly made of copper and zinc while bronze is mostly made of copper and tin.

High resistivity material properties 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.

Superconductors and their applications Superconductivity is a phenomenon of exactly zero electrical resistance when cooled below a characteristic critical temperature Superconducting magnets are used in MRI (Magnetic Resonance Imaging) which is a way of looking at the soft Low and high field magnets for Nuclear Magnetic Resonance (NMR) parts of the body. Industrial magnets for materials magnetic separation

Semiconductors A solid substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects Most common materials commercially used as semiconductors are germanium (Ge) and silicon (Si) because of their property to withstand high temperature Semiconductors show negative temperature coefficient Semiconductor in its pure form is called as intrinsic semiconductor Impure semiconductors are called extrinsic semiconductors

Extrinsic Semiconductors Types N-type and P-type semiconductors N-type semiconductor majority carriers are electrons and minority carriers are holes. It is formed by adding pentavalent impurity e.g. P. As, Sb P-type semiconductor majority carriers are holes, and minority carriers are electrons. These are formed by adding trivalent impurity e.g. B, Al Ba

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