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Tuesday, 5 October 2021

Classification of Materials based on Energy Band Diagram

Classification of Materials:


Any electrical device must use materials that will serve the function under extreme conditions without sacrificing reliability. As a result, a thorough understanding of materials and their characteristic amounts in relation to their role is required. Temperature, pressure, frequency, response to the atmosphere, ageing, tension, and fatigue are some of the material's parameters. The variable parameters are determined by experimental results, and only those that are relevant are reflected in the specific topics.


It is possible that materials used in electrical engineering applications are also used in mechanical, civil, and other applications. However, when it comes to electrical engineering materials, the properties and behaviour of the material in relation to its role in electrical engineering takes priority. For example,  Copper is utilised in refrigeration and air conditioning as well as electrical applications. Copper's electrical characteristics are important in electrical engineering materials, even though they're not as important in refrigeration and air conditioning.


When designing electrical machines and equipment, a designer must take all precautions to choose the appropriate material for each component of his product. He must have a thorough knowledge and grasp of the characteristics and behaviours of electrical engineering materials to meet this criteria. Materials used in electrical applications may have restrictions, and it would be dangerous if their suitability for the conditions of needs was not thoroughly investigated. For example, the maximum working temperature of a material is determined by experimental results, and if it is exceeded in its role in electrical equipment, it will fail, causing severe damage to the equipment.


Before selecting any material to serve a purpose or role in the equipment, focus on aspects such as cost, availability, feasibility of manufacture without involving complicated processes, and its peripheral characteristics.


Classification of Materials based on Energy Band Diagram:



The energy band diagram of a conductor, semiconductor, and insulator is shown in the figure. Since the forbidden zone between the valence band and the conduction band is so large in an insulator, it requires additional extra energy for electrons to become free and migrate towards the conduction band. Because there is no prohibited gap between the valence and conduction bands in a conductor, electrons from the valence band can easily pass into the conduction band even with low applied energy.

Energy Band Diagram for Conductor, Insulator, and Semi-Conductor

Comparison of Conducting Materials :


A conductive material containing less than four electrons in its last orbit and has a negligible or zero forbidden band. Consider three distinct elements, each with a different number of orbits. Consider the case of gold. Copper and silver. The configurations of respective shells are listed in the table.


Shell configuration of Gold, Silver, and Copper

Shell

K

L

M

N

O

P

Gold

2

8

18

32

18

1

Silver

2

8

18

18

1

Copper

2

8

18

1

 

Since there is just one electron in the last orbit, Gold has a lower energy level to detach the electrons from the last orbit than silver or copper because the bondage decreases as the orbit level increases. As a result, gold is a superior conductor to silver. Similarly, because the valence electron occupies the 'O' shell in silver and the 'N' shell in copper, the energy required to remove the electron from the final orbit in silver is less than in copper. The higher the energy level required to remove the electron from the final orbit, the lower the conductivity and the higher the resistivity. Any conducting material is graded on this basis.

 

Free electrons flow at a random velocity in conducting materials. The temperature affects the magnitude of velocity. Electrons in a conductor acquire a regular velocity when an electric field is applied. The resultant drift current is 0 when there is no electric field.

 

General Classification of Electrical Engineering Materials :

 

The materials are divided into three basic categories based on the energy level principle. Conductor, insulator, and semi-conductor are the three types of materials. Some of the conducting materials can also operate as magnets. In the same way, insulators can be employed as dielectric materials. Materials can be categorized into five categories based on their applications. They are:

 

(a) Conducting material: There are less than four valence electrons in the outermost orbit. The total energy required to detach one electron is directly proportional to the material's resistance. The more the energy required to detach, the higher the resistivity, and vice versa. Conductive materials include silver, copper, aluminum, brass, carbon, and others.

 

(b) Magnetic material: Some conducting materials can be magnetized or attracted to a magnet. Magnetic materials, such as Iron, Cobalt, Steel, and others, provide a channel for magnetic flux. Many alloys have significant magnetic characteristics, such as Cobalt steel and Cadmium steel. They are used to make magnetic circuits in relays and transformers, among other things, in addition to forming a medium for energy conversion in static and dynamic equipment.


(c) Insulators: These materials have more than four valence electrons in their outermost orbit and have significant resistance to current flow. Solids, liquids, and gases have resistivities ranging from 1012 to 1018 ohm meter. They're utilized in situations when a charged conductor needs to be separated, such as in an electric iron element where nichrome wire is isolated using mica. Some of these substances can also be utilized as dielectrics.

 

(d) Dielectric material: Dielectric materials are used to store electric energy and are made of insulating materials. They are characterized as insulating materials that can sustain an electric field with minimal power dissipation. Mica, oil, and paper are examples of dielectric materials.

 

(e) Semi-conducting material: Semiconducting materials are neither conducting nor insulating because they have four valence electrons in the outermost orbit. However, act unusually. It is a crystalline solid with a modest resistivity ranging from 1 to 100 Ω – m. Over a portion of the temperature range, these materials have a negative temperature coefficient. Germanium, Silicon, and other materials that fail this test are employed in electronic circuits as capacitors, rectifiers, and other components.

 

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