Electrical materials practises(EMP)-A clear and Detail note about EMP

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         Lets divide them into topics and sub topics.every topic contains Introduction,materials,qualities,specifications,pros,cons and many more…

1.CLASSIFICATION OF ELECTRONIC ENGINEERING MATERIALS

  • Introduction:

Matter: Part of universe which is having certain mass and occupies some space is known as matter. It contains molecules. Molecules contain atoms.

Materials: It is a substance made from matter.

1.2Atomic structure:

Atoms are the smallest particles present in matter. Electrons, protons and neutrons present in all atoms are collectively known as fundamental particles. Neutron is absent in hydrogen atom.

Characteristics of Electron:

  • Electrons were discovered by J.J. Thomson.
  • Electrons are lightest fundamental particle.
  • The charge of an electron -1.602×10-19
  • The mass of an electron is 9.1094×10-24

Characteristics of Proton:

  • Protons were discovered by Gold stein.
  • Charge of proton is +1.602×10-19
  • Mass of proton is 1.672×10-24

Characteristics of Neutron:

  • Neutrons were discovered by Chadwick.
  • Charge of neutron is zero.
  • Neuron is least stable particle.

The atoms of all elements are composed of two parts.

  1. Nucleus: It is the central part of an atom which consists protons and neutrons. A proton has positive charge where as neutron has no charge. Obviously the nucleus of an atom as a positive charge.
  2. Extra Nucleus or orbital: It is the outer part of an atom which contains electrons only. The electrons are considered to be moving round the nucleus in different orbits or paths in the same way as the planets of the solar system round the sun. The electrons are not stationary particles. They move around the nucleus in different paths. Different atoms will have various number of electrons.

The number of electrons that can be accommodated in any orbit is given by the formula is 2n2.where ‘n’ is the orbital numbers (i.e. n=1, 2, 3, 4…….) and letter representing level or shell (i.e. K, L, M, N………..).

‘K’ level or 1st orbit contains =2×12=2 electrons.

‘L’ level or 2nd orbit contains =2×22=8 electrons.

‘M’ level or 3rd orbit contains =2×32=18 electrons.

‘N’ level or 4th orbit contains =2×42=32 electrons.

Under normal conditions the number of electrons is equal to the number of protons in an atom. Therefore the atom is neutral as a whole, the negative charge on the electrons cancelling the positive charge on the protons.

The number of protons or electrons in an atom called atomic number. It is denoted by ‘Z’.

The number which indicates the total number of protons and neutrons in an atom is called mass number. It is denoted by ‘A’.

Number of neutrons =A-Z.         Ex:   6C12

Number of protons = 6

Number of electrons = 6

Number of neutrons = 6

1.3 Electronic structure of the atom:

The distribution of electrons in various available orbitals in an atom is ground state is called electronic configuration.

Principal quantum number (n): It indicates the orbit number and these are denoted by K, L, M, N. The maximum number of electrons present in an orbit is 2n2.

Azimuthal quantum number (l): it indicates the number of sub shells present in a shell and shape of the orbital.

l=0 for s-sub shell

l=1 for p-sub shell

l=2 for d-sub shell

l=3 for f-sub shell

Aufbau’s principle: electrons enter into lower energetic orbitals before they enter into the higher energetic orbitals.

This principle is used in the calculation of relative energies of different orbitals on the basis of (n+l) value. Greater the (n+l) value more will be the energy of orbital.

Ex:      4s     3d

(n+l)     4       5 .so 3d is more energetic than 4s.if the (n+l) value is same for two orbitals the orbitals with low ‘n’ value has lower energy.

Example: 4s          3p

(n+l)     4+0=4       3+1=4.    The energy of 3p is less than 4s.

The relative energies of orbitals can also be obtained from molars diagram.

The orbitals are arranged in the increasing order of their energies

1s ‹ 2s ‹2p‹3s‹3p‹4s‹3d‹4p‹5s‹4d

Hund’s rule: Whenever degenerative orbitals are available for electrons the paring of electrons takes place only after all orbitals filled with one electron each. The orbitals having same energy are called degenerative orbitals

Ex: Nitrogen

7N14——-1S2S2  2P

According to this rule half-filled or completely filled orbitals are more stable than other configurations

1.4 Energy band diagram:

          Take aluminium its atomic number is 13 & electronic configuration is 1S2S2  2P3S2  3P1 it contains 3 electrons in the outer most orbital. The electrons in the outer most orbital are called valance electrons. These electrons are loosely bound their nucleus. And can be detached easily. this is because of the electrons in the inner orbital are tightly bound to the nucleus.

The no. of valance electrons is always less than 8.If the electrons added to the valance orbit to bring their total number 8 the atom become stable.

In a single silicon atom the electrons will be influenced by single nucleus where as in solid material consists of million of atoms. So electrons in a solid material are influenced not only by a single nucleus but by many adjacent nucleus.

In a isolated atom the electrons in a particular shell or orbit possess single energy. Where as in the case of solid materials the electrons present in the same orbit will have discrete range of energies.

The range of energies possessed by electrons in the same orbit is called energy band. Energy band structure consists of conduction band, valance band & forbidden gap.

  1. Valence Band:

The electrons in the outermost orbit of an atom are known as valence electrons. This band may be completely or partially filled.

  1. Conduction Band:

The band occupied by the free electrons is called conduction band.

  1. Forbidden Energy Gap:

In an atom the separation between conduction band and valence band is known as the forbidden energy gap.

1.5 Classification of materials:

The energy band structure determines the electrical behavior of solids. Based on the valance electrons solids are classified into 3 groups. i.e. conductors, insulators & semiconductors.

Conductors:

The atoms of some substances have less than one half of the maximum of eight valance electrons in its outer most orbit are called conductors.

    Ex: Copper, Aluminium.

  • No forbidden energy gap (i.e. EG=0Ev) between valence band and conduction band
  • So valence band and conduction band are overlapped
  • Very large number of free electrons is available.
  • Good conductorsof electricity.

Insulators:

The atoms of some substances have more than one half of the maximum of eight valance electrons in its outer most orbit are called insulators.

Ex: Wood, Plastic, rubber.

  • Insulators have full valance band & empty conduction band.
  • wide forbidden energy gap (EG =6Ev)
  • So in case of insulators a very large amount of energy must be supplied to cause an electron to cross from valance to conduction band.
  • bad conductorsof electricity

 

Semi Conductors:

The atoms of some substances have exactly one half of the maximum of eight valance electrons (i.e. 4 valence electrons) in its outer most orbit are called semi conductors.

Ex: Silicon, Germanium.

  • Narrow forbidden energy gap ( EG= l eV).
  • Partially filled valance and conduction band.
  • Electrical properties of semi conductors are intermediate between those of insulators and conductors.
  • neither good conductornor bad conductorsof electricity

 

  1.    a) Insulators                          (b) Conductors                       (c) Semi-conductors

1.6 Comparison of conductors, insulators & semi conductors:

S.NO Conductor Insulator Semi conductor
1. The materials which allow electrical current through them very easily are known as conductors. The materials which does not allow electrical current through them very easily are known as insulators. The materials which allow electrical current partially through them very easily are known as semi conductors
2. There are more free electrons to jump from one atom to another. No free electrons to jump from one atom to another. Few free electrons to jump from one atom to another
3. Good conductor of electricity. Bad conductor of electricity. Partial conductor of electricity.
4. The resistivity lies between 10-8 to 10-6Ωm. The resistivity lies between 1012 to 1018Ωm. The resistivity lies between 100to 102Ωm.
5. Electrical conductivity is very high. Electrical conductivity is negligible. Electrical conductivity is very less.
6. Number of valance electrons is less than 4. Number of valance electrons is more than 4. Number of valance electrons is equal to 4.
7. No forbidden gap between valance band & conduction band (EG=0ev). Wide forbidden gap between valance band & conduction band (EG>5ev). Narrow forbidden gap between valance band & conduction band (EG<5ev).
8. Very less energy is required for electrons to pass from valance band to conduction band. Very high energy is required for electrons to pass from valance band to conduction band.  High energy is required for electrons to pass from valance band to conduction band.
9. They have positive temperature coefficient of resistance. They have negative temperature coefficient of resistance. They have negative temperature coefficient of resistance.
10. Ex: copper,aluminium,tungsten , silver etc. Ex: paper,wood,glass, plastic etc. Ex: silicon,germanium,carbon etc.

 

1.7 Effect of impurities in resistance of conductors:

Resistance (R):

  • It is directly proportional to its length i.e.RL
  • Inversely proportional to its area of crossection i.e. RL/A
  • Depends upon the nature of the material and temperature.

R∝L/A    or    R=ρ L/A Ω

Where ρ (rho) is a constant of proportionality and is known as resistivity.

               Resistivity (ρ): The resistance offered between the two opposite faces of a given material is having one meter length and one square meter as area of crossection is called resistivity.

If L=1m, A=1m2 then R=ρ

Alloying is another factor which affects the resistivity of a material. Alloying is the process in which impurity (a small quantity of some other metal) is added to the base metal. For example brass is an alloy of copper & zinc. Where copper is the base metal and zinc is the impurity.

Pure metals like copper, aluminium possess low resistivity any impurity whether metallic or non metallic increases their resistivity. The influence of various impurities on the resistivity of conductors depends on the metals.

ρx=Ax (1-x)

Where x is the % of impurities and A is the constant which depends on the base metal & the impurity. For dilute solution, x<1, the above equation reduces to

ρx=Ax

1.8 CLASSIFICATION OF CONDUCTING MATERIALS:

Conducting materials used in electrical engineering can broadly classify into two groups.

  • Low resistivity or high conductivity materials.
  • High resistivity materials.

Low resistivity materials:

These materials should have the least possible electrical resistivity and are used for making conductors. These materials are used in applications where the power loss and voltage drop is low.

Ex: silver, copper, aluminium

Requirements of low resistivity materials:

  • Low resistivity i.e. high conductivity
  • Low temperature coefficient of resistance.
  • High mechanical strength.
  • Good solder ability.
  • Resistance to corrosion.
  • Low power loss & voltage drop.
  • No brittleness.
  • Low contact resistance.
  • High ductility & malleability.
  • Good flexibility.
  • Low cost.\

High resistivity materials:

These materials are mostly alloy of different metals which are also conductors of electricity. These are used for elements of heating devices, filaments of incandescent lamps, loading rheostats.

Ex: Tungsten, nichrome, carbon, platinum, manganin.

Requirements of high resistivity materials:

  • High resistivity i.e. low conductivity
  • Low temperature coefficient of resistance.
  • High mechanical strength.
  • High melting point.
  • No tendency for oxidation.
  • Should not be brittle.
  • Ductility & malleability.
  • Able to dissipate more heat per unit volume.

1.9 Commonly used metals:

Some of the commonly used metals in electrical & electronics fields are

  • Copper
  • Aluminium
  • Silver
  • Tungsten
  • Tin
  • Brass
  • Bronze
  • Nickel etc.

1.10 Mechanical (or) physical properties of materials:

The important physical properties of materials are given below.

  • Density: It is defined as the ratio of mass to the volume

Units of density is kg/m3

  • Stress: Stress is defined as load applied per unit area.

Units of stress is N/m2

  • Strain: The ratio of change in length to the original length during application of load.
  • Strength: Strength is the ability of material to with stand to external load without fracture.
  • Ductility: Ductility is the ability of a material undergo considerable plastic deformation before fracture under tensile load. Ductile materials can drawn into thin wires.
  • Malleability: The ability of a material undergo plastic deformation under compressive load. Malleable materials can drawn into thin sheets.
  • Hardness: It is defined as the resistance of a metal to deformation. A hard metal resist wear and cutting.
  • Wear resistance: It is theproperty of material of items by virtue of which they protect themselves against the rubbing action of another item in their contact.
  • Impact resistaance: The ability of material to resist (sudden shock) loads without fracture is called impact resistance.
  • Fracture: It is the separation of a solid into two or more parts under the action of stresses.
  • Toughness: The ability of material to resist fracture is called toughness.
  • Fatigue: The ability of material to resist cyclic loads over a specified time or number of cycles without fracture is called fatigue strength.

 

1.11 Electrical properties of copper:

 

The electrical properties of copper are

Conductivity (σ): conductivity is a measure of how well a material accommodates the movement of an electric charge. Its unit is mho/meter.

                            σ =5.95×107 mho/meter

Resistivity (ρ): The resistance offered between the two opposite faces of a meter cube of the material is called resistivity.

ρ =AR/L

                        Where A=area of cross-section.

R=resistance.

L=length.

Its unit is ohm meter.

ρ =1.724 x 10-8 Ωm

Temperature Coefficient of Resistance (α0): The temperature coefficient of resistance of a conductor is the increase in resistance per ohm original resistance per 0C rise in temperature.

α0=(Rt-R0)/R0t

Its value is 4.29×10-3/0c

Solderability: It is the property of a material which when joined should have minimum contact resistance.

 

1.12 Physical properties of copper:

  • Copper is the second best conductor of electricity.
  • Its conductivity is 100%.
  • It is reddish brown colour.
  • It is malleable & ductile.
  • Its melting point is 10840
  • Its boiling point is 25950
  • Temperature coefficient of resistance at 200C is 0.00429/0
  • It is highly resistant to corrosion.
  • It is non magnetic.
  • Annealed copper has soft in nature, high conductivity & its hardness (H) range is 40 to 65HV, tensile strength(R) is 200 to 250N/m2.
  • Hard drawn copper has hard and low conductivity & its hardness (H) is 110HV, tensile strength(R) is 360N/m2.

Applications:

  • Copper is used for making wires of cables for transmission lines and distribution of electric power and for motor, generator windings.
  • It is used for high voltage underground cables.
  • Hard drawn copper is used for over Head conductors.
  • Annealed copper is used for insulated conductors in low voltage power cables.
  • It is used for making bus bars.

1.13 Properties of aluminium:

  • Electrical conductivity is next to copper.
  • It is soft and silvery coloured metal.
  • It is malleable & ductile.
  • Its melting point is 6550
  • Its boiling point is 20570
  • Temperature coefficient of resistance at 200C is0.0038/0
  • It is highly resistant to corrosion.
  • It is non magnetic.
  • It cannot be solder or welder easily.
  • It is cheap and readily available.
  • It is much lighter than copper.

Applications:

  • It is used in overhead transmission lines, domestic wires.
  • For making capacitor foils.
  • Well suited for cold atmospheric conditions.
  • It is used for making bus bars.

1.14 General electrical properties of aluminium:

The electrical properties of aluminium are

Conductivity (σ): conductivity is a measure of how well a material accommodates the movement of an electric charge. Its unit is mho/meter.

                            σ =3.77×107 mho/meter

Resistivity (ρ): The resistance offered between the two opposite faces of a meter cube of the material is called resistivity. Its unit is ohm meter.

ρ =AR/L

                        Where A=area of cross-section.

R=resistance.

L=length.

ρ =2.65 x 10-8 Ωm

Temperature Coefficient of Resistance (α0): The temperature coefficient of resistance of a conductor is the increase in resistance per ohm original resistance per 0C rise in temperature.

α0= (Rt-R0)/R0t

Its value is 3.8×10-3/0c

1.15 Reasons for preferring aluminium for overhead lines:

            Aluminium is preferred transmission of electrical power through overhead lines because

  • The metal is cheap.
  • It has high conductivity.
  • It is lighter than copper.
  • It has good ductility and malleability.
  • It has higher tensile strength.

1.16 Uses of conductors:

          Some of the uses of conductors are given below:

  • Wires
  • Cables
  • Windings of generators and transformers
  • Over head conductors
  • Bus bars
  • Heating elements
  • Resistors

 

1.17 Iron:

  • The electrical conductivity is 1.044×107mho/
  • Its resistivity is 9.579×10-8Ωm.
  • It has temperature coefficient of resistance is 0.0065/0
  • Its melting point is 15380
  • Its boiling point is 28620

Applications:

  • It is used in generators, electric motors.
  • It is used for transformers.
  • It is used in loud speakers.
  • It is used in electrical & induction stoves.

1.18 Corrosion:

               Corrosion refers to the ultimate destruction of the metal due to its reaction with the surrounding environment.

Ex: Rusting of iron.

Prevention of corrosion of conductors:

  • Proper selection and designing of materials.
  • Cathodic protection.
  • Use of corrosion inhibitors.
  • Application of protective coatings.

1.19 Anodization of aluminium:

          Anodization is a process to electrolytically coat a metallic surface with a protective oxide.

The anodic coating consists of hydrated aluminium oxide and is considered resistant to corrosion. The anodized coating is hard, durable, will never peel under normal conditions.

The anodization process consists of 5 steps:

  1. Cleaning
  2. Pre treatment
  3. Anodizing
  4. Colouring
  5. Sealing
  6. Cleaning: It removes fabrication oils and by soaking the work in water based solution containing mild acids and alkalies along with detergents.
  7. Pre treatment: Used for decorative purposes to improve the appearance of surface prior to the anodizing step. The most common pretreatments are etching, desmutting.

Etching: Etching in caustic soda (NaoH) prepares the aluminium for anodizing by chemically removing a thin layer of aluminium.

Desmutting: Rinsing in an acidic solution removes unwanted surface alloy consistent particles not removed by the etching process.

  1. Anodizing: Produces the actual coating acting as the positive electrode, a directly current is passed through the item to be anodized while submerged in a bath of water and acid. (Sulphuric, phosphoric, chromic) used as electrolyte.

The water breaks down, liberating oxygen at the surface of the item, which the combines with the aluminium to form the coating a transparent porous layer of aluminium oxide.

  1. Colouring: This process produces various colours while providing a more resistant coating than anodizing.
  2. Sealing: The pores on the surface of the finished pieces need to be closed before the anodized item is placed into service. If left unsealed, surfaces could have poor corrosion resistance.

1.20 Uses of anodization:

  • Protects satellites from harsh environment of space.
  • It is used in ceilings, floors, escalators.
  • Motor vehicle components.
  • Food preparation equipment.

1.21 Silver:

       Properties:

  • It is highly malleable and ductile.
  • It has highest conductivity i.e.106%.
  • It has high resistant to corrosion.
  • It has high tensile strength.
  • Its melting point is 9610
  • Its boiling point is 21620

 

Applications:

  • It is used for silver electro plating.
  • It is used for making bowls, trays and dishes.
  • It is used in electrical instruments.

1.22 Zinc:

       Properties:

  • It is highly malleable.
  • It has good electrical conductivity.
  • It has high resistant to corrosion.
  • It has medium hardness.
  • Its melting point is 4190
  • Its boiling point is 9070

Applications:

  • It is used as container for dry cells.
  • As an alloy element for manufacturing brass.
  • Used as a protective zinc coating.
  • Zinc oxide is used in the preparation of ointments, lotion and cosmetics.

1.23 Gold:

       Properties:

  • It is highly ductile and malleable.
  • It has high electrical and heat conductivity.
  • It has high resistant to corrosion.
  • It has tensile strength.
  • Its melting point is 10630
  • Its boiling point is 29700

Applications:

  • It is used for jewellery.
  • It was used earlier in coins and medals.
  • It is used as a powder in ayurvedic medicines.

 

2.PROPERTIES AND APPLICATIONS OF INSULATING MATERIALS

2.1 Introduction:

            The materials which prevent the flow of electrons through them are known as insulating materials.

Insulation materials offers high resistance to the flow of electric current even to pass a few milli amperes of current through it and requires very high voltage of the order of KV or MV. The insulation strength of the material depends mainly on the dielectric strength.

Dielectric materials are those which are used to store electrical energy and having insulating properties. The dielectric strength of the insulating materials depends on various parameters such as pressure, temperature, humidity, nature of applied voltage.

Typical examples of solid, liquid and gaseous insulators are

Solids: sulphur, rubber.

Liquids: petroleum oils, silicon oils synthetic carbons.

Gaseous: air,CO2,  hydrogen ,SF6(sulphur hexa fluoride).

2.2 Electrical properties of insulating materials:

          The various electrical properties of insulating materials are

  • Insulation resistance
  • Dielectric strength
  • Dielectric loss

Insulation resistance: It is the property of an insulating material by virtue of which a material opposes the flow of electric current. For an insulating material its value should be as high as possible. If a voltage of ‘V’ volts is applied to an insulator when ‘I’ amperes of current is flowing through it then the insulation resistance ‘R’ in ohms.

R=V/I

            Insulation resistance is categorized in to 2 types.

  1. Volume resistance
  2. Surface resistance

Volume resistance: It is the resistance offered to the current IV, which flows through unit cube of a material. It is measured in ohm-m.Volume resistance can be expressed as

                        RVV L/A

Where ρV=volume resistivity

L=length of the material in m.

A=area of cross-section in m2.

Thus if L=1m,A=1m2 then RVV

Surface resistance: It is the resistance offered to the current IS which flows over the surface of the insulating material. Surface resistance is numerically equal to the resistance of a unit square over the surface of the insulating material. It is expressed in ohm/sq.m.

Dielectric strength: The maximum voltage that the material can withstand without breakdown is called dielectric strength. It depends on the pressure, temperature, humidity, nature of the applied voltage.

Dielectric loss: The loss appearing in the form of heat due to reversal of electric stresses compelling molecules rearrangement is known as dielectric loss.

2.3 Factors effecting insulation resistance:

  1. Temperature: Insulation resistance decreases with the rise of temperature and is very much affected by temperature variations.

 

  1. Moisture: Surface resistance of the insulation decreases if exposed to moisture and causes insulation breakdown.
  2. Voltage: Insulation resistance decreases with the increase in applied voltage.
  3. Age: As the insulation serves for long years, its resistance will decrease with the age of service.

2.4 Classification of insulating materials:

          Insulating materials can be classified depending upon

  • The thermal withstandability
  • The physical state such as solid, liquid and gaseous
  • Structure of the material such as cellulose, fibrous
  • Organic or inorganic compounds
  • Process of manufacture(natural or synthetic)

2.5 Thermal classification of insulating materials:

          The performance of the insulating material depends on its operating temperature. Thus the insulating materials are grouped into different classes depending on temperature limits.

Insulation classes Maximum permissible temperature
Y 900
A 1050
E 1200
B 1300
F 1550
H 1800
C Above 1800

 

Class Y insulation:

  • Withstands a temperature of up to 90°C.
  • Typically made of paper, Cotton, silk, rubber and similar organic materials without impregnated or without immersed in any oil.

Class A insulation:

  • Withstands a temperature of up to 105°C.
  • Same as class ‘y’ material, but immersed in oil, also included enameled wire, varnished paper, laminated wood etc.

Class E insulation:

  • Withstands a temperature of up to 120°C.
  • Enameled wire insulations, cotton and paper laminated with formaldehyde bonding (HCHO), epoxy resisns, polythene, synthetic resin enamels.

Class B insulation:

  • Withstands a temperature of up to 130°C.
  • Mica, fiberglass (alkali free alumino boro silicate) Bakelite, polyster enamel and similar inorganic materials impregnated.

Class F insulation:

  • Withstands a temperature of up to 155°C.
  • Same as class ‘B’ but impregnated.

Class H insulation:

  • Withstands a temperature of up to 180°C.
  • Same as class ‘B’ but impregnated with (silicon rubber) silicon containing no organic fibrous materials.

Class C insulation:

  • Withstands a temperature of above 180°C.
  • Same as class ‘B’ impregnated with suitable non organic like Teflon (poly tetra flouro ethylene).

2.6 properties of insulating materials:

Wood:

            Properly seasoned and impregnated wood is cheap and good insulating material.

 

Properties:

  1. It is cheap
  2. It is seasonally available
  3. Easily available
  4. Easily fabricated
  5. It is hygroscopic
  6. It’s density is 0.5 to 1 gm m/cm3
  7. Its tensile strength is 700 to 1300 kg m/cm3
  8. It is temperature dependent
  9. It absorbs moisture looses mechanical properties
  10. It uses as insulating material. It is impregnated in oil
  11. Low voltage application

 

Applications:

            It is used in switch boxes, terminal boxes, capping, electrical poles, slot wedges in motors and generators windings, handles for tools, and high voltage and low voltage Winding transformer in sealing.

 

Cardboard:

 

Properties:

  1. Short fiber sheets
  2. Similar to paper except in thickness
  3. It is denser and low flexible
  4. Insulation resistance is 107Ωm
  5. Its dielectric strength is 50 KV/mm
  6. It’s density is 0.5 to 1 gm m/cm3
  7. Passing wood pulp through heavy machines called calendars

 

Applications:

Separators in transformers, slot wedges, slot linings

Asbestos:

            Natural fibrous mineral with large fiber

Properties:

  1. It can withstand a temperature of 4000C
  2. Its dielectric strength is low about 3 to 5 KV/mm
  3. It is hygroscopic hence it is used after impregnation
  4. It is strong and flexible
  5. It has good tensile strength

 

 Applications:

  1. It is used in the form of boards and sleeves in heating devices like ovens, electric iron etc
  2. It is used as arcing barrier in switchgear and circuit breakers.
  3. It is used in coils, windings and insulation in motors and generators
  4. It is used as insulation in transformers
  5. It is used as insulation in wires and cables under high temperature conditions
  6. It is used in panel board construction for switches
  7. It is used for covering roofs of the buildings

Mica:

            It is a mineral compound of silicate aluminum with silicates of soda, potash and magnesia.

Properties:

  1. It is strong, tough, flexible and right material
  2. It is non-hygroscopic
  3. It is not effected by acids, alkalies and chemicals
  4. Its dielectric strength is 40 to 150 KV/mm
  5. It can withstand high temperature of about 5000C
  6. It releases water heated at high temperature
  7. It can easily split into thin sheets
  8. It is fire proof
  9. It possess very good insulating properties

 

Applications:

  1. It is used in electrical heating devices such as electric iron, toaster, electric heaters for insulation purpose
  2. It is used in spark plugs of motor vehicles
  3. It is used in capacitors
  4. It is used in coil frames and slot insulation in electrical machines
  5. Mica in the form of tape is used for taping the stator coils of high voltage alternators

Ceramics:

            Ceramic insulating materials are produced from pulvarised (powdered) silicates Sio2 and other metal oxides by forming and then baking. This is called sintering process. In sintering process the raw materials powdered and mixed and formed into required shape and then baked to 50 to 900C temperature.

Ceramics are 3 types

  1. Insulation porcelain: Clay, quartz, feldspar (It contains alumino silicate mineral that contain calcium, sodium. Potassium)
  2. High Frequency porcelain: clay, quartz, barium carbonate(BaCo3)
  3. Steatite: Clay, talc[hydrated magnesium silicate H2Mg3(Sio3)4], magnasite(MgCo3)

 

 Properties:

  1. It is mechanically hard and strong
  2. Its dielectric strength is 24 KV/mm
  3. It can be easily moulded to any shape
  4. It is non hygroscopic
  5. It is not effected by chemical action except by strong acids and alkalies
  6. It can withstand high temperature of about 10000C to 18000C
  7. It can easily split into thin sheets
  8. It has very high resistivity of the order of 1011 to 1016Ωcm at 200C

 

Applications:

  1. Insulators used in transmission and distribution lines
  2. Plugs, sockets and fuse units
  3. Telephone insulators
  4. Heat resistance elements in heating appliances
  5. Discs for electric stoves, electric kettles to insulate heating conductors
  6. High temperature appliance like furnace
  7. Equipments for high frequency systems and where thermal shock resistance is desired
  8. Capacitors and transistors

Glass:

            It is thermo plastic inorganic materials obtained by fusion of different oxides and then by cooling in such away that it doesn’t contain crystals. But remain in amorphous state. The different raw materials are sand (Sio2), soda (Na2Co3), potash (K2Co3), chalk (CaCo3), magnesite (MgCo3), Dolamite (CaCo3.MgCo3), feldspar.

Properties:

  1. It is normally transparent, brittle and hard
  2. It has high dielectric strength of the order of 25 KV/mm to 50 KV/mm
  3. Its resistivity is 106 to 1015Ωm
  4. It has dielectric loss
  5. It has good mechanical strength
  6. It is resistant to most of the chemicals
  7. It is hygroscopic
  8. It is difficult to manufacture as it requires very high temperature

 

Applications:

  1. It is used as dielectric in capacitors
  2. It is used as insulating device in fuse bodies
  3. It is used as line insulators in transmission and distribution lines upto 25 KV
  4. It is used in vaccum tubes, electrical lamps
  5. It is used for making scientific instrument parts and containers etc
  6. It is used in chemical industry due to transparency
  7. It is used for those applications where working temperature above 1800C
  8. It is used in radio and TV tubes, electrical lamps ,laminated boards etc

 

2.7 Thermoplastic and thermosetting resins:

            Plastics: A high molecular weight polymer which can be moulded into any shape by applying heat and pressure.

Two types on the basis of heat treatment

  1. Thermoplastics
  2. Thermosetting

 

Thermoplastics:

            Plastics which are softened on heating and hardened on cooling are called thermoplastics.

Ex: Polyethylene, PVC, cellulose acetate

Thermosetting:

Plastics which are hardened on heating and cannot be softened by applying heat and pressure are called thermosetting.

Ex: Bakelite, silicon resin, epoxy resin, polyamide (RCONH2), nylon

 

 

 

 

2.8 Differences between thermoplastic and thermosetting resins:

 

Thermoplastics Thermosetting
1. Plasticity is reversible 1. Plasticity is irreversible
2. Addition polymerization (no elimination of byproducts) 2. Condensation polymerization (elimination of byproducts)
3. Linear in shape 3. Cross linked in shape
4. Low molecular weight 4. High molecular weight
5. Weak, soft and less brittle 5. Strong , hard and more brittle
6. Soluble in organic solvents 6. Insoluble in organic solvents
7. These are reclained from the waste 7. These are not reclained from the waste
8. Ex: PVC, polyethylene, cellulose acetate 8. Ex: Bakelite, silicon resin, epoxy resin

 

2.9 Polyvinyl chloride (PVC):

            It is addition polymerization, less molecular weight, linear in shaped. It is obtained from the combination of acetylene (C2H2) With HCl in the presence of catalyst peroxides at the temperature of 500C.

Properties:

  1. It is hard and less flexible
  2. It never gets corrosion
  3. It is less weight and is cheap
  4. It has high resistance to chemical action
  5. Its insulation resistance is 1012 to 1013Ωm
  6. It cannot withstand very high temperature
  7. It is normally transparent, brittle and hard
  8. Its dielectric strength is 15 KV/mm to 30 KV/mm
  9. It is obtained in different colours
  10. It is slightly hygroscopic
  11. It has good electrical, mechanical properties

 

Applications:

  1. It is used as insulation for wires and cables
  2. It is used in making toys
  3. It is used as insulation for dry batteries
  4. PVC insulated cables are commonly used for low and medium voltage domestic applications
  5. PVC has widely used in clothing.PVC fabric is water resistant. So it used in coats, shoes, jackets, aprons and bags
  6. Resistant to corrosion outdoor uses such as window frames ,water and garden furniture
  7. Wiring and cables used in house hold goods such as cookers, refrigerators and also office equipment such as computers
  8. It is used as insulation for wires in aircraft, radio, communication, and television

 

2.10 Applications of Nylon:

            It is condensation polymerization involves elimination of molecules. It has crossed linked and high molecular weight. It is a polyamide formed from adipic acid [HOOC-(CH2)4-COOH] or hexamethylene dicarboxylic acid and hexamethylene diamine [H2N-(CH2)6-NH2]

Properties:

  1. Nylon has good elasticity
  2. Nylon fabrics have low absorbency
  3. It does not affected by alkalies but affected by strong acids
  4. It has high tensile strength
  5. Easy to wash
  6. Chemically stable
  7. Its dielectric strength is 15 KV/mm
  8. Insulation resistance is 1012Ωm

Applications:

  1. Nylon high strength fiber. So it is used for making fishing nets, ropes, parachutes
  2. Making fabrics is textile industry
  3. It is used for plastic for making machine parts
  4. Furniture, locks, hangers, chairs
  5. Used for tyres for vehicles
  6. Nylon threads are used for surgical applications

 

 

         3.Properties and applications of magnetic materials

 

3.1 Introduction:

                        A magnet is a material or object that attracts iron pieces and produces a magnetic field around it. Magnetism is the property of a magnetic. The magnetic field is invisible. The magnetic materials create a magnetic field around them in which energy transformation is taken place. They provide a path for the magnetic flux.

Magnetic materials play an important role in the field of electrical engineering. They are used for making magnetic circuits in electro magnets, machines, relays, transformers. In all rotating machines the electro mechanical energy conversion is takes place through the magnetic field. The energy storing capacity of the magnetic field is nearly 25,000 times greater than that of electric field.

Magnets have two opposite kinds of magnetic poles namely north pole ‘N’ and south pole ‘S’ like poles repel each other but unlike poles (N-S) attract each other. Magnetic poles always available in pairs there is no isolated single pole.

Magnets may be natural or artificial. Natural magnets are formed from the iron ores and are obtained from mines which are comparatively weak and hence have no practical uses. Artificial magnets are made from iron, nickel, cobalt, steel or alloy materials and used in all electrical machines and equipments.

The magnets may be classified into permanent or temporary magnets depending on their ability to retain magnetism.

Permanent magnets retain their magnetism for a long time and have retentivity power these are mainly prepared from steel which is generally much harder than soft iron. They are used in small dc motors, telephone receiver.

Temporary magnets are made temporary by passing direct current through a coil of wire wound over iron or steel pieces. These magnets losses most of their magnets where dc source is removed and have low retentivity power.

 

 

3.2 Classification of magnetic materials:

            According to their relative permeabilities the magnetic materials are classified into 4 groups.

  1. Dia magnetic materials
  2. Para magnetic materials
  3. Ferro magnetic materials
  4. Ferri magnetic materials
  1. Dia magnetic materials:

The relative permeability of these materials are slightly less than unity.

These materials are slightly magnetized when placed in a strong magnetic field and act in the direction opposite to that of the applied magnetic field. They are repelled by a magnet. They don’t retain the magnetic properties when field is removed.

Ex: Silver, copper, gold, bismuth, zinc, mercury, lead, sulphur etc.

  1. Para magnetic materials:

The relative permeability of these materials are slightly greater than unity.

These materials are slightly magnetized when placed in a strong magnetic field and act in the direction of the magnetic field. They are weakly attracted by a magnet.

Ex: Aluminium, platinum, oxygen, tin, magnesium, lithium.

  1. Ferro magnetic materials:

The relative permeability of these materials are much greater than unity and are dependent on field strength. These materials are strongly attracted by a magnet. The relative permeability varying from several hundreds to many thousands. They are able to retain the magnetic properties after the external field has been removed.

Ex: Iron, nickel, cobalt, steel, and some of their alloys.

  1. Ferri magnetic materials:

Ferri magnetism is observed only in compounds such as ferrites in which the magnetic moments of neighbouring ions are antiparallel and unequal in magnitude. These substances behave like Ferro magnetic materials. The relative permeability of these materials is greater than one. A large magnetization is produced on applying a small magnetic field.

Ex: Ni ferrite, manganese ferrite

 

3.3Soft and hard magnetic materials:

            Ferro magnetic materials can be easily magnetized at low magnetic field is called soft magnetic materials and also these materials can be demagnetized at low magnetic field.

 Ex: Silicon steel, nickel iron alloy

Ferro magnetic materials the magnetization occurs only when high magnetic field is called hard magnetic materials. Ferro magnetic materials are difficult to magnetize but once magnetized it is difficult to demagnetize.

 Ex: Tungsten steel, chromium steel, cobalt steel

 

3.4 Differences between soft and hard magnetic materials:

 

Soft magnetic materials Hard magnetic materials
1. Easy to magnetize and demagnetize 1. Difficult to magnetize and demagnetize
2. Retentivity power is small 2. Retentivity power is more
3. Used for making temporary magnets 3. Used for making permanent magnets
4. Does not effected by impurities 4. Impurities increases the strength of the hard magnetic materials
5. Small hysteresis area 5. Large hysteresis area
6. Low hysteresis loss 6. Large hysteresis loss
7. Susceptibility and permeability is too large. 7. Susceptibility and permeability is low
8. Coercivity and retentivity values are less 8. Coercivity and retentivity values are large
9. Magnetic energy stored is less 9. Magnetic energy stored is high
10. Eddy current loss is less 10. Eddy current loss is high
11. Low BH product 11. High BH product

 

3.5 Some definitions:

            Magnetic field:

The space or region around the magnetic material which magnetic effects can be observed is known as magnetic field. It is represented as magnetic lines of force.

 

Magnetic lines of force:

The magnetic field around a magnet is invisible; hence the field is represented by a imaginary lines of force. These lines forms closed loop and always starting from North Pole & ends at South Pole. These lines of force never intersect to each other.

Magnetic flux (ϕ):

The total no of lines force in a magnetic field is know as magnetic flux. It is measured in webers.

1 Weber = 108lines

Magnetic flux density (B):

It is defined as magnetic flux per unit area. It is measured by weber/m2 or Tesla

Magneto motive force:

            It is the force which drives the flux through a magnetic circuit

Magnetic field strength (H):

            It is defined as the flux exerted by a magnet on another magnet to either attract or repel it

H = Mmf/main length

Permeability (µ):

            It is the property of a material which allows flux freely through it.

µ=B/H

Residual magnetism:

The magnetic flux density which still remains in a magnetic material even when the magnetizing force is completely removed is known as residual magnetism.

Retentivity:

            It is the ability of a magnetic material to retain magnetism in it even after the removal of magnetic force.

Coercivity:

            The force required to demagnetize the iron piece.

Reluctance:

            It is the opposition offered by the material to the flux.

Curie point:

            As the magnetic material is heated its molecules vibrate and get out of a alignment there by reducing the magnetic strength of the magnetized substance. The ‘H’ decreases with rise in temperature.

The temperature at which the vibrations of the molecular magnets become so random and out of alignment as to reduce magnetic strength to zero is called Curie point. It is the critical temperature above which a Ferro magnetic material becomes Para magnetic material.

 

 

 

Material Curie temperature
Iron 1043K
Cobalt 1400K
Nickel 631K
Silicon iron 961K

 

3.6 Properties of magnetic materials:

            Some of the important properties of magnetic materials are

  1. Magnetic permeability
  2. Reluctivity
  3. Retentivity
  4. Coercivity
  5. Hysteresis loss
  6. Magnetization curve
  7. Demagnetization curve
  8. Magnetic field intensity
  9. Curie temperature
  10. Magnetic flux density

 

3.7 Effect of temperature on magnetism:

            Diamagnetic materials not temperature dependent. Para and Ferro magnetic materials decrease with increasing temperature.

Paramagnetic substance obey curie law

=C/T

Where C-Curie constant

T-Temperature

With increasing temperature the alignment is more difficult anddecreases.

 

3.8 Hysteresis and hysteresis loss:

            The phenomenon of lagging of flux density ‘B’ behind the magnetizing force ‘H’ in magnetic materials subjected to cycles of magnetization is known as magnetic hysteresis.

If the given unmagnetized iron piece is magnetized first in one direction and then in the other direction and finally demagnetize it then the piece is said to go through one cycle of magnetization.

Take an unmagnetized bar of iron AB on which a solenoid is wound uniformly and a dc source is connected. When the field intensity is gradually increased by increasing the current in the solenoid. Then the magnetic flux density ‘B’ also increases until saturation point ‘a’ is reached and curve is ‘oa’.

Now if the current is gradually reduced to zero the flux density is also reduces but it does not follow the earlier path, rather it stops at point ‘b’. This means that at this point even through current in the coil is zero, some flux density exists. This is called residual magnetism (ob).

To demagnetize the magnetic bar ‘AB’ the magnetizing force ‘H’ is reversed by reversing the direction of flow of current in the solenoid. When ‘H’ is increased in the reverse direction the flux density starts decreasing and becomes zero and the curve flows the path ‘bc’. Thus residual magnetism of the force dc in opposite direction. The portion ‘oc’ is called coercive force.

If the current in solenoid is further increased in the reverse direction the flux density increased (portion cd) i.e. iron bar magneties in the reverse direction till it saturation.

Once again if the current is reduced to zero the flux density reduces and the curie follows the path ‘de’. The portion de corresponds to residual magnetism in the reverse direction.

In order to neutralize the residual magnetism (oe) the current should be applied in the positive direction (i.e. original direction).The curve flows the path ‘ef’ and further follows ‘fa’ to complete the loop ‘abcdefa’.

Thus when a magnetic material is subjected to one cycle of magnetization the BH curve forms a closed loop called hysteresis loop.

 

 

 

Hysteresis loss:

            When a magnetic material is magnetized in first in one direction and then in the other in repeated cycles of magnetization it results in hysteresis loss. It is due to the friction between the molecules of the materials as they are shifted in direction by the magnetizing force. Hysteresis loss is a power loss and it appears in the form of heat. Hysteresis loss is equal to the energy consumed in magnetizing and demagnetizing a magnetic material.

Formula for hysteresis loss:

      L= length of the iron bar

A=area of cross-section of the iron bar

N=number of turns

B= flux density

When the current passing through the coil changes the flux induced in the iron bar also changes and emf will be produced.

e=N dϕ/dt

=N dBA/dt

=NA db/dt

Now H=NI/L

So the power =e x I watt

=NAdB/dt HL/N

=HAL dB/dt .dt

=HALdB joule

Wh=ALHdB joule

HdB=Area of the BH loop

Hysteresis loss also be calculated theoretically by applying Steinmetz law

Wh=Bm1.6fv watt

Wh=ƞ steinmetz hysteresis coefficient

V=volume of the magnetic material

F=frequency

Bm=maximum flux density

3.9 Factors affecting the hysteresis loss:

  1. Area of cross-section of the material
  2. Magnetic flux density
  3. Length of the material
  4. Number of turns of wire of solenoid

 

3.10 Use of laminations for reducing eddy current loss:

            When a magnetic material is subjected to a changing magnetic field an emf induced according to faraday’s law. Since magnetic material is conducting, these emfs circulate current within the body of the material. These circulating current are known as eddy currents. Eddy currents are not used for doing any work. Heat is generated due to circulating currents and hence power loss in the material. This loss is called eddy current loss. The both hysteresis loss and eddy current loss in a magnetic material are called core losses or iron losses.

To reduce the eddy current loss the magnetic material is laminated or solid core is splitting into thin sheets in the plane parallel to the magnetic field. Each lamination is insulated from the other by a fine layer of insulation. This arrangement reduces the area of each section and hence the induced emf. It also increase the resistance of eddy current paths .since the area through the current can pass is small. Using silicon steel as the core material this loss can be minimized as it is having high value of resistivity.

We=Bm2f2t2v  watt

We=Ke Bm2f2t2v  watt

Where Ke is coefficient of eddy current, its value depends upon nature of the material

Bm is maximum flux density in wb/m2

                t is the thickness of lamination in m

f is frequency in hertz

v is volume of magnetic material in m3

3.11 Silicon sheet steel:

            When silicon is alloyed with steel it is called silicon steel. Pure iron is added with small quantity of silicon of about 0.5% to 5% by weight in order to reduce eddy current loss.

This is used for transformer core plates, rotating machines electro magnets and relays. It increases permeability.

Silicon steel has narrow hysteresis loop low hysteresis loss and heat produced is also low.

Addition of 2% silicon,1% manganese and 0.4 to 0.6% carbon with steel has good tensile strength is used for poles of motors and transformer core plates.

With silicon more than 5% steel is brittle and 14% silicon contact steel is used in chemical industries due to high corrosion resistance.

 

3.12 Cold Rolled Grain Oriented steel (CRGO steel):

The Ferro magnetic materials have a crystal structure. Every crystal of a Ferro magnetic substance has a particular direction along which it offers high permeability and most easily magnetized.

For easily magnetization the crystal direction of electrical sheet steel should be so oriented that their axes are parallel to the direction in which the external field is applied. Thus can be achieved by carefully controlling the rolling and annealing of silicon iron sheet.

By means of special rolling process and intermediate annealing a structure is obtained in which grain orient themselves very accurately in the direction of rolling such sheets are grain oriented.

These days the oriented is done by rolling under cold conditions. These magnetic materials are called cold rolled grain oriented silicon steel. Hysteresis loss reduces as a result of grain orientation.

CRGO silicon steel is widely used for making transformer cores. By using CRGO the magnetizing current required by transformer is low.

If not used CRGO it would need a certain amount of magnetizing force to establish flux in the core.

Where CRGO steel is used to build transformer cores the core must be assembled in such a manner that the crystal direction is parallel to the flux path other with core will offer low permeability rather than high permeability.

 

4. Properties and applications of special purpose materials

 4.1 Introduction:

Alloying:

            Alloying is the process in which impurity (a small quantity of some other metal) is added to the base metal.

For example brass is an alloy of copper and zinc where copper is the base metal and zinc is the impurity.

Pure metals like copper, aluminium possess low resistivity, any impurity whether metallic or nonmetallic increases their resistivity. The alloyed metals acquire proper like higher mechanical strength which are needed for certain special applications.

 

4.2 Need for alloying:

  1. To modify appearance and colour.

Aluminium bronze (Al+Cu) is bright yellow.

  1. To modify chemical activity.

Sodium amalgam (Na+Hg) is less reactive than sodium.

  1. To increase hardness and tensile strength.

Brass (Cu+Zn) is hardened than copper.

  1. To increase resistance to electricity.

Nichrome (Ni+Fe+Cr) has more resistance to electricity than copper.

  1. To lower the melting point.

Solder (Pb+Sn) has lower melting point than lead or tin.

  1. To modify the casting ability.

Type metal (Pb+Sn+Sb) expands on solidification and easily casting.

  1. To increase resistance to corrosion.

Stainless steel (Fe+Cr+Ni+C) is a good corrosion resistant.

 

4.3 Alloys used in electrical engineering:

            Some of the alloys used in electrical engineering are

  1. Manganin
  2. Nichrome
  3. Eureka
  4. Solder
  5. Silicon bronze

 

4.4 Low resistivity copper alloys:

            Brass and bronze are some of the low resistivity copper alloys.

Brass:

Different types:

  1. Lead brass
  2. Iron brass
  3. Tin brass
  4. Manganese brass

Properties:

  1. It is an alloy of copper(60% to 80%) and zinc (205 to 40%)
  2. It has high tensile strength but has a lower conductivity
  3. It can be welded and soldered easily
  4. It has high resistant to corrosion
  5. It can be drawn into wires easily
  6. It is cheaper than copper
  7. Its resistivity is 7.5µΩcm
  8. It has high melting point of 8900C

Applications:

                        Used as current carrying structural material in plug points, socket outlets, switches, lamp holders, sliding contacts for starters and rheostats

 

 

Bronze:

            Bronze is an alloy of copper and tin.

Different types:

  1. Phosphorous bronze
  2. Silicon bronze
  3. Aluminium bronze
  4. Leaded bronze

 

Properties:

  1. It is an alloy of copper and Tin
  2. It has high tensile strength
  3. It is very hard and brittle
  4. It has high resistant to corrosion better than brass
  5. It is ductile

Applications:

            It is used in springs, gears & bearings, marine engineering, boiler fittings making bells

4.5 Cadmium copper:

Pure unalloyed copper is soft & ductile and usually contain approximately 0.7% impurities. Cadmium copper alloys are considering high copper alloys they contain 98 to 99% copper & 0.1 to 1.5 % cadmium & minor amounts of other material. When copper is added to copper the material becomes more resistant to softening.

Properties:

  1. It has almost double the mechanical strength and wear resistant of pure copper
  2. With stand temperature as high as 1500C
  3. By adding cadmium improves its hardness, wear resistance, fatigue strength

Applications:

  1. Telephone drop wires, catenary stand for railway overhead electrification
  2. Electrical components such as contact strips
  3. They can withstand high temperature. So they are used in both domestic and automotive radiators and fittings
  4. It is used for tralley wire because it is extremely resistant to corrosion
  5. It is used as soldering applications to join components in automobile and truck radiators

 

4.6 Beryllium copper:

Copper beryllium alloys are used for their strength and good electrical ,thermal conductivity.

They are 2 groups of copper beryllium alloys.

  1. High strength alloys
  2. High conductivity alloys

High strength alloys contain 1.6 to 2 % beryllium and approximately 0.3% cobalt.

High conductivity alloys contain 0.2% to 0.7% beryllium and higher amounts of nickel and cobalt.

Properties:

  1. It is ductile
  2. It is resistant to corrosion
  3. It can be heated to improve its strength, durability and electrical conductivity
  4. It has highest mechanical strength

Applications:

  1. Used as electrical equipment such as switch and relay blades, control bearings
  2. Housings for magnetic sensing devices
  3. Non sparking applications
  4. Resistance welding systems

 

 

4.7 Bimetals:

          A bimetal is made of two metallic strips of unlike metals alloy with different coefficients of thermal expansion.

When heated the element bends so that the metal with the greater coefficient of expansion is on the outside of the arc formed while that with smaller coefficient is on the inside.

When cooled the element bends in the other direction.

Alloy of iron and nickel with low coefficient of thermal expansion are used as one element of the bimetallic strip.

The other elements consists of materials having high value coefficient of thermal expansion those are iron, nickel, eureka, brass etc.

 

Applications:

  1. Bimetallic strips are used in electrical apparatus and in devices such as relays and regulators
  2. The bimetal element cuts off or regulates the supply voltage at the predetermined value of the current or temperature
  3. A bimetal relay can be used for overhead protection of electric motors
  4. In order to maintain a constant temperature in a heat a bimetallic regulator may be used

 

4.8 Soldering materials:

            Soldering is an alloy of two or more metals of low melting point which is used to join two or more pieces of metals.

The melting point of a solder is lower than the materials to be joined.

The molten metal joins the pieces of metals is known as soldering.

The common solder is an alloy of tin and lead. i.e. 50% lead and 50% tin.

The lead-tin solder serves to join copper, bronze, brass, tinned iron, zinc etc.

These are 2 types of solders.

  1. Soft solders (melting point lower than 4000C)
  2. Hard solders (melting point higher than 4000C)

Soft solders:

            It as composed of lead and tin in various proportions.

It is used for joining copper, bronze, brass and other such metals.

Due to poor mechanical strength the joints made by such solders not be subjected to mechanical stresses.

The most important applications of soft solder is in electronic devices for soldering electrical connections.

Hard solders:

It is an alloy of copper and zinc. In metals at a very high temperature. It is used for joining brass, copper, iron and steel.

The hard solder is called brazing solder. When applied to copper, iron, brass etc and silver solder when applied to silver, gold.

Hard solder is in the power applications for making permanent connections for joining metals such as copper, silver, gold and alloys such as brass.

 

4.9 Fuse materials:

            A fuse is a protective device which consists of a thin wire or strip which metals when a particular value of current flowing through it is exceeded.

These are placed in semi enclosed porcelain holders or totally closed cartridges. Ratings of fuses depend upon the type of load current.

The main factor of a fuse is to protect the circuit from current due to over load or short or circuit.

A fuse is a protective device which consists of a thin wire or strip. This thin wire is called the fire wire and is placed in series with the current it has to protect, so that circuit current flows through it.

When the current is too large, the temperature of the wire or strip will increase till the wire metals that breaking the circuit.

The function of a fuse wire is

  1. To carry the normal working current safety without heating
  2. To break the circuit when the current exceeds the limiting value

Most commonly used materials for fuse wire are lead, tinned copper, zinc, tin, silver, lead-tin alloy (Pb 37% and Sn 63%) silver alloys and copper alloys.

Fusible alloys having melting point in the range of 600C  to 2000C and made of bismuth, cadmium, lead and tin in various proportions.

Fuse materials:

  1. Copper
  2. Aluminium
  3. Lead
  4. Cadmium
  5. Bismuth
  6. Tin
  7. Silver

Properties:

  1. Low resistivity
  2. Low melting point
  3. Free from corrosion

Applications:

  1. These are used for protection purpose
  2. These are used for high speed operations

4.10 Some alloys:

  1. Manganin:

                        Properties:

  1. This metal is an alloy of copper (86%), manganese (12%) and nickel (2%)
  2. Its melting point is 1020C
  3. Its resistivity at 200C is 48µΩcm
  4. It is easy to drawn into thin wires
  5. Working temperature is low (600C to 700C)
  6. Temperature coefficient of resistance is 0.00015/0C

Applications:

  1. It is used in making wire wound precision resistance for measuring instruments
  2. Resistance boxes
  3. Standard resistance coils
  4. Eureka or constantan:

                        Properties:

  1. This metal is an alloy of copper (60%) and nickel (40%)
  2. It is silver like in appearance
  3. Its melting point is 13000C
  4. Its resistivity is 49µΩcm
  5. It is drawn into thin wires
  6. Working temperature is 5000C
  7. Temperature coefficient of resistance is 0.00002/0C
  8. It is rust proof does not corrode

 

 

 

Applications:

  1. It is used in loading rheostat, resistance wires and starters for electric motors
  2. Resistance element in resistance boxes
  3. Resistance element in field regulators
  4. Arc lamps
  5. Supporting wires for electrical filament
  6. Nichrome:

            Properties:

  1. This metal is an alloy of copper (75% to 78%) of nickel, chromium (20% to 30%), 1 to 1.5% manganese and little percentage of iron
  2. It is also silver white appearance
  3. Its resistivity is 100×10-8Ωcm
  4.   Working temperature is 11000C
  5. Temperature coefficient of resistance is 0.0001/0C
  6. It has good mechanical and thermal properties

Applications:

It is used in making heating elements for electric heaters, electric ovens, electric iron, room heaters, electric furnace etc

 

4.12 Applications of carbon:

  1. It is used for brushes in electrical machines
  2. It is used as component in electronic equipment i.e. carbon resistors etc
  3. It is used in carbon arc lamps, battery cell elements in projectors and in microphones
  4. For anode grids of vaccum tubes
  5. Carbon arcing tips are in circuit breaking

4.13 Ferrites:

            Ferrites are usually non conductive ferri magnetic ceramic compounds derived from iron oxides such as hematite (Fe2O3), magnetite (Fe3O) as well as oxides of other metals.Ferrites can be divided into two types based on the magnetic coercivity.

  1. Soft ferrites
  2. Hard ferrites

Properties:

  1. Soft ferrites have low coercivity means the materials magnetization can easily reverse direction without dissipating much energy (Hysteresis loss)
  2. High resistivity prevents eddy currents in the core
  3. Low losses at high frequency
  4. Examples for soft ferrites are manganese zinc ferrite (Mn Zn Fe2O4),nickel zinc ferrite ( Ni Zn Fe2O4)
  5. Hard ferrites are high coercivity and very resistant to become demagnetized
  6. Examples for hard ferrites are cobalt ferrite (CoFe2O4),barium ferrite

Applications:

  1. Ferrites cores are used in electronic inductor, transformers and electro magnets where high electrical resistance and low eddy current losses.
  2. Ferrite powders are used in the coating of magnetic recording tapes
  3. Ferrite particulars are also used as a components radar -absorbed materials.
  4. Radio magnets used in loud speakers
  5. Soft ferrites are used in the cores of RF transformers and microwaves
  6. Hard ferrites are used in household products such as refrigerator magnets
  7. Recording heads in tape recorders

 

4.13 Neodymium magnets:

Neodymium is a rare earth metal component (mixed metal) which can be used to create powerful magnets. Neodymium magnets are strongest one. Because of their strength neodymium magnets are used in a broad range of applications.

Typical composition of neodymium

 

Neodymium(Nd) 29 to 32%
Iron(Fe) 64.2 to 68.5%
Boron (B) 1 to 1.2%
Aluminium(Al) 0.2 to 0.4%
Niobium (Nb) 0.5 to 1%
Dysprosium(Dy) 0.8 to 1.2%

 

 

 

Applications:

            Neodymium magnets are so strong their uses are

1.It is used in computer hard drive magnets,microphones,head phones, loud speakers

  1. Motors (Ex: washing machines, vaccum cleaners)
  2. Generators (turbo generators, wind turbines)
  3. Used in jewellery
  4. Alternators, switches, relays, meters
  5. The security industry uses them for alarms, switches and security systems
  6. Neodymium magnets are often used in machines made for the health industry

 

4.14 Silicon rubber:

            Silicon rubber is an elastomer composed of silicon itself a polymer containing silicon together with carbon, hydrogen and oxygen. Silicon rubbers are widely used in industries and there are multiple formulations.

Silicon rubber is generally non-reactive stable and resistant to extreme environments and temperature from -550C TO 3000C while still maintaining its useful properties. Due to these properties and its ease of manufacturing and shaping, silicon rubber can be found in a wide variety of products.

Properties:

  1. It is stable polymer
  2. Excellent service life and less production cost
  3. Silicon rubber compounds are simple to mix and donot contain flammable
  4. Elongation, tear strength, dielectric strength, thermal conductivity, fire resistance for superior to organic rubbers
  5. It does not react with chemicals

Applications:

  1. Circuit boards in computers, cell phones, and VCD, DVD players all depend on silicon based materials
  2. Silicon rubber is an essential component in providing proper insulation for computer and technical wiring in medical field
  3. It is used in automotive application, cooking, baking, and food storage products
  4. It is used in sportswear, footwear
  5. Used in home repair and hardware with products

 

4.15 Graphene:

            Graphene is pure carbon in the form of a very thin, nearly transparent sheet, one atom thick. It is remarkably strong for its very low weight (100 times stronger than steel) and it conducts heat and electricity with great efficiency.

 

 

Applications:

  1. Graphene mixed with vanadium oxide can create battery cathodes that recharge 20 sec and retain more than 90% of their capacity even after 1000 cycles of use
  2. It could even be used for unbreakable smart phones where users can soon twist and bend their phones
  3. It is very strong, stiff and very light
  4. Due to its electrical conductivity it could even be used to coat aircraft surface material to prevent electrical damage
  5. Mega fast uploads we are taking a whole tera bit in just one second
  6. Lower cost display screens in mobile devices. The use of grapheme instead of indium not only reduces the cost but eliminates the use of metals in the LED
  7. Components with higher strength to weight ratio
  8. Ultra capacitors with grapheme better performance than batteries

 

4.16 Applications of nano materials:

Nano technology devices are one dimensional & two dimensional

One dimensional: Such as small thin films

Two dimensional: Such as tubes & wires

  1. Used in cosmetics application (Ex:sunscreen lotions)
  2. Nano composite materials: Nano tubes and nano layer are used a reinforced fillers not only to increase mechanical properties but also into implement new properties
  3. Nano coatings: Surface coating with nano meter thickness of nano material can be used to improve properties like wear and scratch resistant
  4. Hand cutting tools: Mill machines tools made using nano composities have more wear and corrosion resistant
  5. More performed paint using nano particles to improve paint properties
  6. Display: New class of display using carbon nano tubes as emission device for the next generation of monitor and television (FED field emission display)
  7. Using nano technology may be provide more efficient light weight, high energy density batteries

 

4.17 Super conductivity:

            One of the most interesting and unusual properties of solids is that certain metals and alloys exhibits almost zero resistivity (i.e. infinite conductivity) when they are cooled to sufficiently low temperature. This phenomenon is called super conductivity.

The temperature at which the transition from normal state to super conducting state takes place on cooling in the absence of magnetic field is called the critical temperature (Tc) or the transition temperature.

Super conducting state of metal mainly depends on temperature and strength of the magnetic field. Super conducting disappears if the temperature raised above the Tc.

At the temperature Tc in the absence of any magnetic field, the material is in super conducting state.

When a weak magnetic field is applied to a super conducting at a temperature below transition temperature Tc, the magnetic flux lines are expelled. The substance acts as an ideal diamagnetic. This effect is called meissner effect.

Applications of super conductors:

  1. Super conducting generators are very smaller in size and weight when compared to conventional generators
  2. It is used in transmission lines and transformers .Since resistance is almost zero. So power loss during transmission is negligible
  3. Super conducting materials are used for producing very high magnetic fields of the order of 50 Tesla
  4. Super conductors are used to perform logic and storage functions in computers
  5. It is used for fast electrical switching

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