0

Alloys of Copper and their Uses

  • Some of the alloys of copper are:

    (a) Cadmium copper alloy
    (b) Chromium copper alloy
    (c) Brass         
    (d) Bronze

    Cadmium Copper Alloy : 

    Cadmium is whitish in colour and similar to tin in appearance. It is present in traces with zinc ore. It is corrosion resistance. When maximum electrical conductivity in conjunction with high tensile strength is required, the alloy of cadmium copper with 0.55% to 1.04% of cadmium is used. The tensile strength of this type of alloy is about 65 kgf / sq. mm with 1% cadmium, the conductivity falls only to 94% to that of pure copper. For most purposes the alloy containing about 0.8% of cadmium is found to have most favourable combination of tensile and fatigue strength with good conductivity. The fatigue strength of alloy increases which is almost proportional to the cadmium content, but without the increase of brittleness. This is suitable for flexible telephone cords and trolley wires. This is also used as electrodes due to its hardness and high annealing temperature. This alloy is also used for switchgear contacts, commutator segments and conductor for overhead transmission lines. It is costlier than copper.



    Chromium Copper Alloy :

    Chromium is a hard and white metal. Where optimum conditions of a conductivity, strength and hardness in a casting are required, the chromium copper alloy is ideal. By simple heat treatment of alloy, the hardness can be increased to 100, tensile strength more than 40 kgf / sq.mm and conductivity 80% that of pure copper can be achieved. At higher temperatures, chromium copper alloys are far superior to any other copper alloys.

    Brass :

    Brass is an alloy of copper (Cu 60% to 80%) and zinc (40% to 20%). It has greater mechanical strength and wear resistant than copper but has considerably lower conductivity. It is malleable and ductile, can be casted, and is resistant to corrosion. It is used as current carrying structural material in plug points, socket outlets, switches, lamp holders, fuse holders, knife switches, sliding contacts for starters and rheostats etc. Its melting point is lower than copper. Some of the physical constants of Brass is shown in Table 2.1. The amount of copper in brass varies its properties.


    Percentage Composition

    Cu 60 + Zn 38 + Pb 1 + Sn 1
    Cu 67 + Zn 29 + Pb 3 + Sn 1
    Yellow Brass
    Cu 66 + Zn 34
    Specific Gravity
    8.3
    8.3
    8.3
    Young’s Modulus (kg/sq mm)
    9800
    9500
    7300
    Ultimate tensile strength  (kg/sq mm)
    56
    48
    54
    Hardness
    65
    50
    62.7
    Resistivity at 20o C in micro ohm-cm
    7.5
    6.78
    6.29
    Melting point (0o C)
    890
    840
    930












    When the alloy has 70% copper, it bears a clear golden yellow colour and is known as yellow brass or high brass, 80% of copper changes the colour to reddish and the metal becomes softer with more copper characteristics. Addition of zinc makes metal tougher and stronger.

    When the alloy contains 57 to 63% of copper and 43 to 37% of zinc, it is called MUNITZ metal. The metal is malleable, ductile, hard and corrosion resistant and is used for bolts, nuts, rods and tubes. Lead is added for better machinability. Tin or nickel improves the resistance to corrosion or wear. Welding rods, condensers, springs, bases and caps of valves are some of the application of brass.



    Bronze :

    Bronze is an alloy of copper and tin. Other materials like phosphorous, silicon, aluminium, berilium are alloyed with copper and is also called Bronze. The physical constants of a typical Bronze is shown in Table.

    TABLE - Physical Constants of a Typical Bronze


    Cu 88 + Sn 10 + P 2
    Temperature Co-efficient of resistance at 0o C
    0.0005
    Resistivity at 0o C
    17.8 micro ohm-cm
    Specific gravity
    8.89
    Ultimate tensile strength
    70 kg/sq mm
    Young’s Modulus
    9400 – 11000  kg/sq mm
    Melting point (0o C)
    950o C









    Phosphorous Bronze: It contains 10 to 15% of tin and upto 0.5% phosphorous. It has high tensile strength and elasticity but fairly low conductivity. Its resistivity is 6 to 12 micro ohms-cm and temperature co-efficient at 0°C is 10 x 10-4 /degree centigrade. This resistance to corrosion is due to dissimilar metals. Although the impurities of metals in copper decreases the conductivity, the conductivity of bronze containing 2% iron and 0.5% phosphorous can be increased to more than 90% by correct heat treatment. This is used for making current carrying springs, brush holders, knife switch blades etc.

    Berilium Bronze: It is another alloy whose mechanical strength is higher than cadmium bronze and is also used for making current carrying springs, sliding contacts, knife switch blades etc.

    Silicon Bronze: It contains 90 to 96% of copper, 3 to 5% silicon, 0.5 to 2% manganese or zinc. It is resistant to corrosion and contains chemicals also. Soldering and brazing are not possible on this. This has more electrical conductivity than phosphorous bronze. This has very good tensile strength. It is used for boiler parts, aerial wires and spring materials.

    Aluminium Bronze: It contains 85 to 90% of copper, 6 to 8% aluminium, 3% iron and 0.5% tin. It has beautiful golden colour. It is light, strong and resistant to oxygen and chemical actions. It is brittle, strong, ductile and shock proof. It is used for gear drives, sliding parts, springs, brush holder frames, die castings, parts coming in touch with saline or sea water.

    Read more...
    0

    Block Diagram of Microcontroller 8051

  • Block Diagram of Microcontroller 8051


    CPU – The CPU (Central Processing Unit) comprising of ALU (Arithmetic and Logic Units) and Control units

    ALU - Arithmetic and Logic Unit performing the arithmetic and logical operations. These operations are multiplication, addition, subtraction, logical AND,OR etc. To do these operations one operand must be in Accumulator, and another may in B register or in general purpose register. The ALU operation results are mostly placed in A register. Some results are placed in B register too.

    OSC - Oscillator provides clock for controller operation .Crystal oscillator is used for providing perfect clock and stability. So this microcontroller uses crystal oscillator. For this purpose, the crystals linked to the pins are used.

    INTERRUPT CONTROLLER

    Microcontroller operation needs some interrupts. Here mainly five interrupts are used. The controller controls the operation interrupts. ie some interrupts may be allowed, some others are disabled and priority assigned and changed. The five interrupts are:

    BUS CONTROL

    In 8051, Address Bus has a width of 16 bits and Data Bus has a width of 8 bits. For both Address and data, lower byte address buses are used. The BUS control controls the BUS usage. There are 3 control signals: PSEN , EA, and ALE. The signals like Program Store Enable (PSEN), Address Latch Enable (ALE) and External Access (EA),  are used for external memory interfacing.



    ON CHIP RAM

    The 8051 has 4 kilobyte of inbuilt ROM. It is otherwise called program memory. Usually program-code is stored in ROM. To store program into ROM, programmer is needed. If more area is required in ROM, an external ROM may be connected. Maximum of 64kb ROM memory can be used.

    ON CHIP ROM

    The 8051 has an inbuilt of 128 byte RAM, some version have 256 byte and are used as data memory. If the system needs more memory, external RAM may be connected up to 64kb.In 128 byte RAM chip, 00h to 71Fh are the address range .In this range ,00H to 1FH are the general purpose registers . 20H to 2F are the bit Addressable area and rest of this is byte addressable .This is used as general purpose scratch pad. In 256 byte RAM chip, another 128 bytes are used for Special Function Registers.

    I/O PORTS

    There are four IO ports in 8051.These are named as P0, P1, P2, P3.All are bidirectional. Each port have its address, output driver, latch and input buffer. Each port is output by default. To make the port as input, it should be initialized by sending ‘1’ level in each pin.

    SERIAL PORT

    TXD and RXD are used for serial port. These pins are available in Port 3. To transmit data serially TXD pin is used. The RXD pin is used to receive data serially. Each pin has separate buffer registers named as SBUF.

    TIMER/COUNTER

    There are two types of counter/timer in 8051.These counter/timers are name as Timer/Counter 0 and Timer/Counter 1. Each one can be used as either Timer or Counter. 16 bit timer register are used for counting in timer operation or counter operation. Clock pulses are counted in Timer operation and external events are counted in counter operation.

    Read more...
    0

    Properties of Conducting Materials

  • PROPERTIES OF CONDUCTING MATERIALS:

    1. Conductivity (σ) :

    The conductivity (σ) is the reciprocal of electrical resistivity of the material. The units of conductivity are mhos/cm. It is the property of a material due to which the electric current flows easily through the material. In other words it provides an easy path to the flow of electric current through the material.

    2. Tensile Strength :

    Strength of a material is defined as the ability to resist load without failure. Tensile strength is therefore tie ability of the material resist a stretching (tensile) load without fracture. Therefore the tensile strength gives an indication of the conductor limit within which it has to be used and beyond which excessive deformation or fracture takes place. It is expressed in load per unit cross sectional area. (tonnes / cm2).

    3. Ductility :

    It is the ability of the material to be deformed plastically without rupture under tensile load. A ductile material can be drawn out into a fine wire without fracture and can also be bent, twisted or changed in shape without fracture. Gold, silver, copper, aluminium, nickel, tin, lead etc., are ductile materials.

    4. Corrosion Resistance :

    Corrosion is a gradual process in a material due to electro-chemical attack. Due to the chemicals present in the atmosphere and if the material is exposed, the metal is generally converted into an oxide, salt or some other compound, thus the metal- does not serve the purpose it is intended to. It may also occur in elevated temperature in media which are inert when near or below the room temperature.



    5. Effect of Alloying on Resistivity :

    Any impurity whether metallic or non-metallic increases resistivity. The effect of metal impurities on resistivity of a given metal is dependent on the nature of alloy formed. When the metal differs widely in atomic volumes and melting points the alloy comprises of crystals of both metals. Such alloys are called mechanical mixtures. The resistivity and temperature co-efficient of resistivity in these alloys vary linearly with percentage content of impurity.

    When the atomic volumes of both do not differ by more than 15% the alloy comprises of single crystal in structure in which the crystal lattice accommodates the atoms of both metals. This is called solid solution alloy. In this type of alloy, the resistivity increases and temperature co-efficient decreases upon certain percentage of impurity content. After this, if the impurity is increased the resistivity decreases and temperature co-efficient increases.

    When the metals combine chemically, it is called chemically combined alloy. The variation of resistivity and temperature co-efficient of resistivity with percentage of impurity content is very complicated. The alloying will increase the mechanical strength to a considerable extent and the material will become hard.

    6. Effect of Alloying on Mechanical Properties :

    Addition of even a small percentage of certain alloys improves mechanical and physical properties. Some of the effects are summarized below:

    (a) Copper : It increase the strength and hardness and lowers the ductility. It also increases the corrosion resistance.

    (b) Aluminium: It acts as de-oxider and restricts grain growth and aids nitriding.

    (c) Lead : It increases machinability.

    (d) Nickel : It increases tensile strength without sacrificing ductility. Increases toughness lowers the co-efficient of thermal expansion. Increases hardness slightly and decreases rusting.

    (e) Tungsten : Carbide forming tendency high inhibits grain growth and considerably increases cohesive force.

    (f) Silicon : Improves magnetic permeability and electrical resistivity. Increases the resistance to oxidization. Raises the ultimate strength. Acts as a ferrite strengthener.

    (g) Chromium : Increases strength and hardness without affecting ductility. Increases wear and corrosion resistance. Increases the critical temperature and improves toughness.

    (h) Manganese : Lowers melting point of iron decreases critical temperature increases the hardenability of steel.

    (i) Cobalt : Imparts excellent magnetic properties, increases hardness in high speed steel.

    7. Solderability :

    Solder is a fusible alloy used to join the surfaces of metals. The property is useful at places where the two pieces of metals are to be joined as in the case of wires.

    8. Brittleness:

    It is opposite to the property of toughness and is the tendency of a metal to break on receiving a hammer blow. The brittle material has a poor resistance to shock loads.

    Read more...
    0

    Atomic Structure of Elements

  • Classification of Materials:

    Any electrical equipment has to use materials which serve the purpose under arduous conditions without loosing the reliability which is an essential condition. If therefore becomes necessary to have a thorough knowledge of materials and its characteristic quantities with respect to its role. The parameters of the material are temperature, pressure, frequency, reaction to atmosphere, ageing, stress, fatigue etc. The variable parameters are established from experimental results and only those which are of importance are reflected in the respective topics.

    It is possible that a material which are used for electrical engineering application are also used for mechanical, civil etc., and when it falls under electrical engineering materials, its properties and behaviour to its role in electrical engineering forms the prime importance. For example, copper is used both for electrical and also for refrigeration and air conditioning. Electrical properties of copper are of interest in electrical engineering materials whereas in refrigeration and air conditioning the point of interest is different.

    At the time of designing of electrical machines and equipment a designer has to take all precautions to select the right type of material for each component of his product. To fulfill this requirement, he should have a thorough knowledge and understanding of the properties and behaviors of electrical engineering materials. Materials used for electrical applications may have limitations and it would be dangerous if its usability is not studied thoroughly for the conditions of requirements. For example, the maximum working temperature of material is fixed by experimental results and if in its role in electrical equipment exceeds this limit; it would fail sustaining heavy damage to the equipment itself.

    The factors such as cost, availability, feasibility for manufacture without involving complicated process and its peripheral conditions should be kept in mind before selecting any material to serve a purpose or role in the equipment.



    Atomic Structure of Element

    To understand the behavior of a material as a conductor, insulator or semi-conductor, it is necessary to study their atomic structure. Every material is thought to be made of smallest and tiny indivisible particles which are not further divisible and is called an Atom. Every element has number of atoms in it. An atom of any element consists of:

    (a) electrons which are negatively charged, light in weight and movable.
    (b) protons which are immovable
    (c) neutrons have no charge but heavy and immovable.

    Each electron has a negative electrical charge of 1.602 x 10-19 Coulombs and protons within the nucleus have a positive charge of the same magnitude. Since opposite charges attract, a force of attraction exists between the oppositely charged electrons and nucleus. The force of attraction is balanced by the centrifugal force due to the motion of the electrons around the nucleus. Compared to the mass of nucleus, electrons are very tiny particles having negligible mass and therefore can be considered as having no mass. The nucleus of an atom is largely a cluster of protons and neutrons. A neutron has no charge at all. For a given atom, the number of protons in the nucleus is equal to the number of orbiting electrons.

    In an atom, the number of negatively charged electrons is always equal to the positively charged protons contained in the nucleus. These electrons fall within orbits that are clearly defined for all types of material. Due to some external force if a negatively charged electron move out of the orbit, another adjacent electron takes its place. The electrons in any orbit are normally balanced as shown in Figure.

    Sample Atomic Structure

    For a more complex atom, the number of electrons is needed to balance the electrical charge and so the orbit increases to accommodate the electrons. For example, in a Hydrogen atom only one electron exists and the electron occupy in a single orbit. Similarly in the helium atom the two electrons share the same orbit. But in the Lithium atom there are three electrons and therefore the number of only two electrons can occupy in the first orbit. The pattern of orbits are set even in the more complex atoms. The first, the innermost orbit can have maximum of two electrons and the last or the outermost orbit has a maximum of eight electrons. Orbits between the innermost and outermost may contain various numbers of electrons but the outermost never exceed eight electrons. The properties are determined by the number of electrons in the outermost orbit and are classified as conductors, insulators, and semi-conductors depending on the number of electrons in the outermost orbit.

    Electronic Configuration :

    The positively charged proton and the negatively charged electron are equal in magnitude and is equal to 1.6 x 10-19 Coulomb. The mass of the proton or neutron is 1.672 x 10-27 kg whereas the mass of an electron is 9.107 x 10-31 kg. Therefore, a proton is 1836 times heavier than an electron. The orbit in which the electrons revolve is called shell. Different shells have different planes. The number of electrons in each shell can accommodate 2n2 where n is the number of shell counting from the innermost shell. A sample shell configuration is shown in Fig.

    Taking an example, potassium has 19 protons in the nucleus and 19 electrons in the orbit. Its atomic number is therefore 19. Applying the formula 2n2, the number of electrons in the orbit is given by

    (a) innermost orbit (K shell) 2n2 = 2 X 12 = 2 electrons
    (b) second orbit (L shell) 2n2 = 2 X 22 = 8 electrons

    The balance is nine. Third orbit (M shell) can occupy 2 x 32 = 18 electrons but there are only nine electrons. For a stable condition even number of electrons should be present in the shell. Therefore, 8 electrons occupy M shell and the remaining one in the N shell.

    Take the case of Germanium where the atomic number is 32. It contains 32 electrons in the orbit. Apply the same formula, the number of electrons in each shell is as follows :

    K shell = 2n2 = 2 x 12 = 2 electrons
    L shell = 2n2 = 2 x 22 = 8 electrons
    M shell = 2n2 = 2 x 32 = 18 electrons

    and the balance is four electrons which is even in number occupy in the N shell.

    Atomic Structure of Elements:

    Atomic
    Element
    Proton
    Electrons per level
    K
    L
    M
    N
    O
    P
    Q
    1
    Hydrogen (H)
    1
    1






    2
    Helium (He)
    2
    2






    3
    Lithium (Li)
    3
    2
    1





    5
    Boron (B)
    5
    2
    3





    6
    Carbon (C)
    6
    2
    4





    7
    Nitrogen (N)
    7
    2
    5





    8
    Oxygen (O)
    8
    2
    6





    10
    Neon (Ne)
    10
    2
    8





    11
    Sodium (Na)
    11
    2
    8
    1




    12
    Magnesium (Mg)
    12
    2
    8
    2




    13
    Aluminium (Al)
    13
    2
    8
    3




    14
    Silicon (Si)
    14
    2
    8
    4




    15
    Phosphorous (P)
    15
    2
    8
    5




    16
    Sulphur (S)
    16
    2
    8
    6




    17
    Chlorine (Cl)
    17
    2
    8
    7




    18
    Argon (A)
    18
    2
    8
    8




    19
    Potassium (K)
    19
    2
    8
    8
    1



    24
    Chromium (Cr)
    24
    2
    8
    12
    2



    26
    Iron (Fe)
    26
    2
    8
    14
    2



    27
    Cobalt (Co)
    27
    2
    8
    14
    3



    28
    Nickel (Ni)
    28
    2
    8
    16
    2



    29
    Copper (Cu)
    29
    2
    8
    18
    1



    30
    Zinc (Zn)
    30
    2
    8
    18
    2



    32
    Germanium (Ge)
    32
    2
    8
    18
    4



    33
    Arseni (As)
    33
    2
    8
    18
    5



    34
    Selenium (Se)
    34
    2
    8
    18
    6



    36
    Krypton (Kr)
    36
    2
    8
    18
    8



    47
    Silver (Ag)
    47
    2
    8
    18
    18
    1


    48
    Cadmium (Cd)
    48
    2
    8
    18
    18
    2


    50
    Tin (Sn)
    50
    2
    8
    18
    18
    4


    51
    Antimony (Sb)
    51
    2
    8
    18
    18
    5


    74
    Tungsten (W)
    74
    2
    8
    18
    32
    12
    2

    78
    Platinum (Pt)
    78
    2
    8
    18
    32
    16
    2

    79
    Gold (Au)
    79
    2
    8
    18
    32
    18
    1

    80
    Mercury (Hg)
    80
    2
    8
    18
    32
    18
    2

    82
    Lead (Pb)
    82
    2
    8
    18
    32
    18
    4




    Read more...

    Subscribe