(GS MATERIAL SCIENCE) Structure of atom and interatomic Bonding: electron proton neutron positron neutrino and antineutrino Stable particle Composed of matter (Physical substance) Tiny particles (atom) unstable particle mesons -particle unstable particle Deutron (i) Stable particle: Charge Mass 0.00054u  1 1.6  10 C uncharged 1.67  10 kg ~ proton mass 1.007274u  1 (a) electron –1.6  10 19 C 9.11 10 31 kg or 1 times mass 1836 of proton (b) Proton (c) Neutron 19 27 amu or u 1.00867u  1 Note: 1. Isotopes: Same atomic number, different mass number. 2. Isobars: Same mass number, different atomic number 3. Isotones: Same number of neutrons but different number of protons (or) mas number. 4. isoelectric: Atoms/molecules/ions having same number of . (ii) Unstable particles: ii) Unstable particles a) Positron: +1e b) Neutrono Antineutrino c) Mesons iii) Composite particles a) -particles: doubly charged He : uncharged  - meson ; heavy µ-meson; Light eithel + ve/-vely charged Note: z En = – 13.6   ev n 2 1. Energy of nth orbit : 2. Radius of nth orbit :  n2  rn  0.529   A  z  3. Orbital velocity is inversely proportional to n. 4. Orbital frequency is inversely proportional to n3. b) Deutron: + vely charged heavy hydrogen Periodic Table: Group number atomic number Element symbol Element name atomic weight (average) Electronegativity    ses ionization Energy   Electron gain Enthalpy  atomic radius  ses llic eta m n No ses ses  Atomic Radius  Electronegativity  Ionization Enthalpy  Electron Gain Enthalpy Period  ter rac a h c • Note: Ist transition series starts from the atomic number 21 [Sc] • Chemical Bonds: Bonds Primary bonds  Interatomic bonds  stable  Strong  Bond energy : 100 – 1000 kJ/mol Secondary Bonds Ionic Bond Covalent Bond Metallic Bond  Intermolecular bonds unstable weak Bond energy : 10 KJ/mol Note:   Of all the primary bonds, ionic is strongest and metallic weakest  Ionic solids are water soluble but covalent bonds are soluble in non-polar solvent.  Of all the secondary bonds, Hydrogen bond is strongest Bonds and their properties: Properties Ionic bond Covalent bond Metallic bond Secondary bond Mechanical Hardness increases with ionic charge; break by cleavage fracture; it is nondirectional bond. Very hard and brittle; break by cleavage fracture, it is a directional bond Tough and ductile, non-directional; can change shape permanently without breakking weaker than ionic or covalent bonds Soft; can be plastically deformed Electrical Insulators Semi conductors Electronic conductors Insulators Thermal Fairly high melting point, thermal insulators Very high melting point, good thermal insulators Modernately high melting po int, good heat conductors Low melting po int Optical Transparent coloured by absorption of ions Transparent or opaque,high refractive index Opaque and reflecting Transparent Examples Magnesia, calcite, NaCl, CaCl 2 Diamond, carborundum Sodium, iron copper Argon, paraffins ice Crystal Structure: Solid 1 Crystalline solids  periodically arranged atoms Definite geometric shape have sharp melting point anisotropic in nature Ex: NaCl 7. Crystal system and 14 bravais lattices Crystal Bravcis system Lattice 1. Cubic P, I, F 2. Non-crystalline camorphous) solid Non-periodically arranged atoms No definite geometric shape Melt over wide range of temp. Isotropic in nature Ex.: Glass abc       90 2. Rhom sohedral (Trigonal) P abc 3. Tetragonal P, I abc       90 4. Hexagonal P 5. Othor hom sic P, I, F, E abc       90 abc       90 6. Monoelinic P, E 7. Triclinic P abc abc       90     90,   120     90    P  Pr imitive  I  Bodycentre  F  Face centre  E  End Centre atomic radius () N CN APF Example 1. Simple cubic a/2 1 6 0.52 P0 2. BCC [ABAB] a 3 /4 2 8 0.68 Cr,  -fe, K, MO, W 3. FCC [ABCABC] 4 12 0.74 Al, Cu, Ag, Au, Ni, Pt, Pb 4. HCP [ABAB] a 2/4 a/2 6 12 0.74 Graphite, Zn, Mg 5. DC a 3 /8 8 4 0.34 Si, Ge, Sn Structure  Crystal imperfection: 1. O-dim ensional (point) defects : associated with Vaccancies interstitial atom impurities   substitutional atoms  frenkel defect  Schottky defect 2. 1- dim ensional (line) defects :  associated with dislocations Edge dislocation Screw dislocation  Mixed dislocation Note: 1. For edge dislocation, Burger, vector is perpendicular to the dislocation. 2. For screw dislocation, Burger vector is parallel to the dislocation. 3. Burger vector described the magnitude and direction of slip. 4. Slip is defined as the movement of block of atoms along certain crystallographic plane and direction. 3. 2-dimensioal (area) defects: – associated with faults – stacking faults – external faults Grain boundaries Tilt boundary Twin boundary Note: 1. A grain boundary is the imperfections that separate crystal or grains of different orientation in polycrystalline aggregate during crystallization 2. Average number of grains per inch at magnification of 100X is N = 2n–1; n = grain size number [Higher n indicates fine grain] 3. When the mismatch in orientation between adjacent boundaries is small (<10°), then it is called as tilt boundaries. 4. If the atoms on one side of the boundary is mirror image of atoms on the other side of the boundary then it is called as Twin boundary. 5. 3-dimensional (volume) defects: – associated with – Cracks – Pores – Foreign inclusions 6. Phase diagram: Gibbs phase rule: F = degree of freedom (it is the number of independent variables {P, T, composition} which can be varied independently without changing the number of phase in equilibrium. C = Number of components forming the system. P = Number of phases that coexist in a chosen system at equilibrium. 2 = Number of external factor (P, T). Note: 1. If phase diagram is plotted between T and percentage composition keeping P = const. then, F = C – P + 1. 2. F  0  P  c  1. 3. at triple point F  0 Types of phase diagram: (i) Unary phase diagram (ii) Binary phase diagram Type-I: Soluble in liquid as well as solid state. Note: 1. Solid solution  structure of solvent does not change  Substitutional solid solution: difference in atomic radii should be <15%  Interstitial solid solution: difference in atomic radii should be < 59% 2. Lever rule: It is used to find – Amount of each phase in the two region. Type-II Binary phase diagram – Soluble in liquid but partially soluble in solid state. Various types of phase diagram reaction: 1. Monotetic Reaction:   L 2  solid L1     2. Eutectic Reaction:   solid1  solid2 L     3. Eutectoid reaction:   solid2  solid3 solid1     4. Perictectic reaction:     solid2 L  solid1    5. Peritectoid reaction:     New solid solid1  solid2    Type-III Binary phase diagram  – soluble in liquid but completely insoluble in solid state. Fe-Fe3 C phase diagram 1. Fe – Fe3 C has four invariant reaction – Monotectic – Eutectic – Eutectoid – Peritectic 2. Fe – Fe3 C has 5 individual phases. (a) –ferrite: – BCC structure – soft and ductile – Chromium is used as stabilized – Carbon content is 0.025% @ 723°C. (b) –ferrite: – BCC – soft and ductile – carbon content is 0.09% @ 1493°C (c) Austenite (): – FCC – Soft, ductile, malleable, non magnetic – Nickel is used as stabilizer – Carbon content is 2% @1147°C and 0.8% @ 727°C (d) Comentite (Fe3C): – Complex orthorhombic crystal structure having 12 iron atoms and 4 carbon atoms per unit – Hard and brittle – Carbon content 6.67% (e) Lade burite [   Fe 3 C] : – Eutectic mixture of austenite and cementite – Observed in cast iron containing 4.3%C. (f) Pearlite [  Fe3 C] : – It is a mechanical mixture of 87% ferrite and 13% cementite. – Pearlite containing 0.8% C is known as eutectoid steel which makes steel more ductile. A0 : This temperature line lies in the bottom section of iron carbide diagram that is the 210°C temperature line. Here cementite changes from ferromagnetic to paramagnetic in nature. A1: It is the lower critical temperature. Here at 727°C temp erature austentine to pearlite Eutectoid transformation takes place. A2 : This indicates curie temp. that is 768°C below whi ch a ferrite is ferromagnetic in nature. A3 : This indicates upper critical temp. below which ferrites start to form from austenite. Acm: This indicates upper critical temperature below which cementite starts to form from austentine. Heat Treatment Objectives of heat treatment: 1. To remove internal stresses due to unequal contraction of castings. 2. To improve machinability 3. To improve electrical and magnetic properties 4. To improve mechanical properties like tensile strength, ductility, hardness, shock resistance etc. 5. To improve corrosion resistance. Heat treatment process: (I) Annealing: Purpose: 1000 900 A3 Acm 0.8 1. Reduce residual stress, hardness 2. Increase ductility and toughness 3. To refine grain size i.e. uniform grain structure results. (II) Normalizing: Purpose: (i) Increase the strength of medium carbon steel. (ii) Improve machinability of low carbon steel. (iii) It is less ductile than annealed steel. (iv) Improve mechanical and electrical properties (III) Hardening: Purpose: (i) Produces extreme hardness (ii) Maximum tensile strength (iii) Minimum ductility (iv) Materials are too brittle Note: (1) g o lin t co Fas Moderate Austenite (2) Martensite = = Cooling Slo w co ol in g Martensite @lo Bainite [C in ferrite] Heat Treatment Pearlite [87% ferrite 13% cementite] Structure is body centred tetragonal Very strong and brittle. mp w te Martensite @ high temp Spheroidite (3) During heat treatment of steel, the hardness of various structures in increasing orders is spherodite < pearlite < martensite (4) Spheroidizing: – Used for high carbon steel (C > 0.6%) – This type of heat treatment produces comentite in the form of globulus particles (Spheroids) from pearlite. Purpose: 1. Good machnability 2. High ductility 3. Maximum softness Quenching media for hardening: Quenching media 1. Mineral Oils Application – used in hardening alloy steels – Very fine pearlite structure is produced 2. Water (or) aqueous solution of NaOH or NaCl (Brine) – used for quenching carbon and low allow steel 3. Air – Martensite structure is produced – Used for rails, pipes etc. – fine pearlite structure is produced Note: (1) Brine solution provides fastest cooling amongst all. (2) Martempering: [stepped quenching] → Austenite is converted to martensite (3) Austempering: Austenite is converted to Bainite. IV. Tempering: Purpose: 1. Residual stresses are relieved 2. Ductility is improved 3. Toughness is increases 4. Decreased hardness. 5. Improve strength 6. Reduce brittleness 7. Increase wear resistence 900 A A3 B 723° C D 0.8 % wt of c A = Normalising B = Annealing (or) Hardening C = Spheroidising (or) process annealing D = Tempering Case hardening (1) Hard surface = case provides hard wear resistance Soft core provides toughness (2) Mild steels cannot be hardened by quenching, so their strength is increased by case hardening. (I) Chemical heat treatment of steel (a) Carburising: (a) Pack carburising: – – (b) BaCO Carburising mixture: 50% charcoal + 20% 1444442 4444433 + 5% CaCO3 + 5 – 12% Na2CO3. Heating time  6 – 8 hours @ 950°C Energizer Gas carburising: – heated in the medium of gases containing CO + hydrocarbon such as CH4, propane, butane @950°C for 3–12 hrs. (c) Liquid carburising: 950C  dipped in molten state bath containing 20% NaCN. Work piece  (d) Nitriding:   (500  600)C (1) Work piece   hardest case on steel. NH atmosphere 3 (2) Cooled in the spring of ammonia. (e) Cyaniding: Work piece  immersed in molten cyanide bath containing 20 – 30% NaCN, 25 – 50% NaCl, 25 – 50% Na2CO3 for 30 – 90 minutes Note: Hardness of steel greatly improves with cyaniding. (f) Carbonitriding: Work piece is heated in the mixture of ammonia and hydrocarbon to a temp. 850°C for 2–10 hrs. (II) Induction Hardening:   (III) austentic range. Quenched immediately to form martensite. Flame hardening:    (I) The heating effect is due to eddy currents flowing in the surface of work piece up to Oxyacetylene torch is used to produce a temperature of 2400–3500°C Austenite is converted to martensite. Testing of materials. Ductility testing: (a) Close bend test (b) Angle bend test (c) 180° bend test (II) Impact testing (Toughness test) (a) Izod test → cantilever type (b) Charpy test → beam type (III) Hardness test: (a) Brinell hardness test: Specification: Load (P) D d D = 10 mm ± 0.0045 mm  3000 kg  hard material  P =  1500 kg  int ermediate hardness 500 kg  soft material  15 sec  for ferrous metals T =   30 sec  for softer metals. BHN = (b) P D  D  D2  d2   2  Vicker’s hardness test: It uses a diamond square based pyramid indenter with 136° angle between opposite faces. Load varies from 5kg – 120kg in increment of 5kg. VHN = 1.854 (c) P d2 Rockwell hardness test: Dial A to H and K with 9 scales. B & C scales are mostly used B scale → for soft metal → steel ball indenter C scale → for hard metal → diamond cone as indenter Note: It is a non-destructive testing. Non-destructructive testing [NDT]: (i) (ii) (iii) (iv) (v) Visual inspection Magnetic particle inspection Ultrasonic testing Liquid - penetration test X-ray /  -ray testing. Magnetic properties of materials: (i) Pm = Pm(orbit)  Pm(spin)  Pm(nuclear )  Pm(spin) (ii)  = M = r  1 H Magnetic material: (a) For diamagnetic material:  H  M  m  1  r  0 Ex : Si, Ge, Au etc (b) Paramagnetic material: (i) at H = 0; M = 0 at H 0; M 0 m = +ve (ii) (c) r  1 (iii) It follows curie law: m = (iv) Above curie temperature it’s M = 0. Ferromagnetic material: (i) Mainly d-block elements exhibit ferro-magnetism. (ii) Pm = Pm(spin) (iii) at H = 0; Bresidual = 0M (iv) It follows curie-weiss law; m = (d) C T (v) Above curie temp.; it becomes paramagnetic (vi) Ex: Fe, Co, Ni (vii) Exhibit hysteris. Anti ferromagnetic: (i) (e) C T m = 0 (ii) 0 = 1 (iii) Follows neel’s law, m = (iv) T > N  Paramagnetic. C T  N Ferrimagnetic material: → Antiparallel and equal dipole moments → Above curie temp., converts to paramagnetic. Ex: Ferrites → Suitable for high frequency application. Electric and magnetic characteristics of ferrites: (i) High resistivity (ii) Low dielectric loss (iii) High permeability (iv) High curie temp. (v) Mechanically hard and brittle. (v) Low eddy current losses. Types of ferrites: (I) Hard ferrites:   Used to make permanent magnet These are having (i) Higher curie temp. (ii) High coercive force (iii) High residual magnetism i.e., wide B-H curve. (iv) High permeability.   (II) Sr ferrites 14243 Ex: Ba and exhibit semiconductor behaviour Application: Small motors, TV tube focusing magnet. Soft Ferrites: → These are having    Ex: High permeability Low coercive force Narrow B-H loop. Mn – Zn ferrites Ni – Zn ferrites Application: Core of inductors and transformers. (III) Rectangular loop ferrites: → Ex: Mg – Mn ferrites Cu – Mn ferrites → (IV) Application: For magnetic memory storage in HDD, floppy etc.  -wave ferrites/Garnets: Ex: Mn – ferrites Ni – ferrites Appl: For Gyrator, circulater, isolater etc. Magnetostriction: →  Change in the dimension of a magnetial material when it is magnetized. Longitudinal magnetastriction –  Transverse magnetostriction –  Note: Change in the dimension is in the direction of Change in the dimension is in the perpendicular direction of Volume magnetostriction Humming sound in transformer is due to magnetostriction. Soft / Hard magnetic materials: (a) Soft magnetic material: Characteristics: (1) Low retentivity, coercivity and hystrisis loss. (2) High permeability and magnetic saturation (3) Hysterisis curve is tall and thin. Ex: Silicon steel, soft iron, Fe-Si alloy. Note: Si ses DC resistivity,  ses area of hysterisis. Appl.: (1) Used in mfd. power transformer @ 50 – 60 Hz. (2) Fe – Ni alloy → 36% Ni used for high frequency application. → 50% Ni used for magnetic memory. → 77% Ni used for current transformer  45% Ni  Permalloy     79% Ni  Superalloy   Loss  79% Ni  Mu  metal  (b) Hard magnetic material: [Permanent magnet] Charactristics: (1) High  , coercive force, curie temp, hysterisis loss (2) Ramanent flux density Application: Permanent magnet, focusing magnets in TV tubes. Hard magnetic materials are: (4) (1) Carbon steel – 98% Fe, 10% Mn, 0.37°C ; Compass needle (2) Tungsten steel – Fe, W, C, Cr. ; DC – Motor. (3) AlNiCO – Al, Ni, CO → Permanent magnet Platinum cobalt – 77% Pt 23% Co (5) Aloemax – 55% Fe 11% Ni 22% Co 8% Al 4% Cu (6) Hycomax – 50% Fe 21% Ni 20% Co 9% Al Magnetic Anisotropy: If material is having direction dependent magnetic properties then material is said to be magnetically anisotropy and this property of material is called anisotropy. There are 3 methods to include magnetic anisotropy in a materials: (I) Cold working: In this method, material is cooled down using cold rollers. This method induces magnetic anisotropic in direction of rolling. (II) Magnetic annealing: It is the process of heating and slow cooling in the presence of magnetic field. (III) Magnetic quenching: It is the process of heating and test cooling in the presence of magnetic field. In this method, material is cooled down to curie temp. in order to induce anisotropy. Conducting materials: (1) J = E ; ohm’s law  = ne2  ;   conductivity m  ne e ;  e  mobility of [cm² / v–s] ; as T  ;   . [Metals shows PTC] (2)  (3) Mattheisein’s Rule: 1 T = ralloy ar Lin e Constant rr T QD Debye temperature (4) Thermoelectric effect: Seeback effect Peltier effect Thomson effect Fe Zn Cu Au Ag Pb Al Hg Pt Constantan (i)  @ Cold junction (ii) Super conductivity:  – R  O at T  TC   – Diamagnetic  Ex : Hg @ 4.2 K – H  HC  Commercial superconductors: Tc V3Ga → 16.8 K Nb3Sn → 18.5 K  Nb3Ge → 23.2 K Meissner’s effect: The repulsion of magnetic flux from the interior of a piece of super conducting material, as the  material under goes to the transition to the super conducting phase is known as meissner’s effect. Critical magnetic field: HC H0 Super -conductor Normal TC T   T 2  HC  H0 1       TC      Silsbee’s rule: The maximum current allowed is IC to retain super conductivity.  Types of super conductor: Type - I Type - II (a) Ideal super conductor. and exhibits diamagnetic nature at super conductivity Non-ideal/ hard super conductor (b) Critical field and transition temp. are low Critical field and transition temp. are high (c) Exhibit complete meissner's effect and follows silsbee rule. Exhibit incomplete meissner's effect and shows some deviaton from silsbee's rule. (d) Transition state is sharp. Transition state is gradual. –M –M Vortex region Super conducting Normal state H HC Super conducting state r Normal state HC1 H HC2 r Vortex Super conducting Super conducting Normal state H H HC Ex: Pb, n, Zn  Normal state Ex: Nb3Al, NbTi, Nb3Sn Semiconductors: Eq.: (1) For semiconductor. Si T = 0°K T = 30°K 1.21 eV 1.1 eV Semiconductor exhibits NTC. Ge 0.78 eV 0.72 eV Note: (2) (i) Width of energy band depends on Temp. (ii) Si is more sensitive to temp. variation as compared to Ge. For metals: – (3) Both CB and VB overlaps. For insulater – EG  5eV @ T = 0°K Insulator Note: (1) Semiconductor @ T = 300°K Conductor Extrinsic semiconductor: Do na to ra A P, n = p = ni m s, ) (N D , Sb n ta Pe Bi le n va n > ni P < ni @ equilibrium: n p = n i n < ni P > ni @ equilibrium: np = n i 2 tom ta Intrinsic simiconductor 2 (B, Al, Ga, In, Tl) Trivalent atom Note: (1) (2) N-type (or) P-type are always neutral. ni2  A0T3 eEGO /KT ni Ge  ni si N-type semiconductor C.B. P-type semiconductor. C.B. EC ED EC EA EV EV V.B. V.B. @ T = 0°K (Insulator) @ T = 0°K (Insulator) N-type semiconductor P-type semiconductor. EC ED EC EA EV EV @ T = 300°K (conductor) @ T = 300°K (conductor) Note: (1) Temperature coefficient of resistance of doped semiconductor may be +ve/–ve depending upon level of doping. (2) When alloying is done for group III–V elements, the crystalline structure is formed of the type ZnS (Zinc blende). Hall effect: – Used to find:   n-type / P-type  Conductivity  Carrier concentration Mobility 2 2 2 + VH – – d w Note: B W N-type/metal Voltage  mv 1 v (1) VH = RH (2)  ve ; P  type RH =   ve ; N  type, int rinsic semiconductor  (1) 1 e 1 The fermi level represents the energy state at which 50% probability of finding an electron EF  n2/3 ; n = number of free es/volume. (2) EC ED EA EF = N-type EF = intrinsic EF = P-type EV  P–type E EF /KT exist: Note: 1 Fermi-dirac probability function f(E): f(E) = → VH + 1 Formulated (compound and alloyed) semi conducting materials. (I) Gallium Arsenide (GaAs). Uses: (a) Switching and parametric diodes (b) Semiconducto lasers (c) Tunnel diodes (d) Hot electron diodes (II) Indium Antimonide [InSb] Uses: (a) Infrared detectors (b) Laser diodes (c) Infrared filter material (d) Hall effect devices (e) Tunnel diodes (f) Transistors. (III) Cadmium sulphide [Cds] Uses: (a) As constituent of cathode ray. (b) To record modulating light intensity on sound track. (c) As on-off light relay in digital and control circuits. (IV) Silicon carbide [SiC] Uses: (a) High temp. rectifiers (b) High temp. transistors. Applications of few semiconductor device. (1) Junction diodes: Rectifier, clipper, clamper (2) Zener diodes: Voltage regulator (3) Transient condition diode: These are: (i) Schottky diode (ii) Varactor diode (4) Bipole Junction transitor (BJT) : Amplifier (5) Field Effect Transistor (FET) : Amplifier (6) Metal oxide semiconductor (FET) : Digital circuits. (6) Opto electronic devices: These are: – Photodiodes – Photocells – LED – Optical fibres – Solar cells (7) Negative conductance microwave devices: These are: – Tunnel diode – Gunn diode – Impatt diode (8) Power devices: These are: – P–n–p–n diode – Silicon controlled rectifier (SCR) Polymers: Polymers are gigantic molecules (or) macromolecules which is formed by repeated linking of the small molecules called monomers that are covalenthy bonded together. The average molecular weight of polymer varies from 10,000 to more than 10,00,000 gm/mole. Polymerisation: The process by which a monomer is converted into polymer under specific condition. The reaction may be initiated by initiater i.e., a catalyst. Note: (1) Ex: Homopolymer : When the repeating units along a chain are of some type, A A A A A (2) Copolymer : Two or more different monomer subunits linked to create a polymer chain. Ex: (1) Block copolymer : A (2) Random copolymer : (3) Alternate copolymer : (4) Graft copolymer : A A A A B B Classification of polymer: (I) Based on source: (a) Natural polymers (b) Semi-synthetic polymers (c) Synthetic polymers (II) Based on structure: (a) Linear polymer (b) Branched polymer A B B A B A A A B B A B A B B A B A A A B A B A B A A A A B B B B A A A (c) Cross-linked polymer (d) Network polymer (III) Based on polymerisation: (a) Additional polymers (b) Condensation polymers Characteristics of polymers: (1) Low density (2) Good corrosion resistance (3) Good mould ability (4) Economical (5) Low mechanical properties (6) Can be produced transparent or in different colours. (7) Low coefficient of friction (8) Poor tensile strength. Classification of plastics: Thermoplastics Thermosetting plastics (1) They have long chains of polymers which are not cross linked. They have long chains of polymers which are cross linked. (2) They become soft on heating. Hence they can be moulded on heating and under pressure. Once set or mould it does not become soft on further heating i.e., the cannot be remoulded on heating (3) They are used for making: (i) Buckets (ii) Pipes (iii) Carry bags (iv) Toilet goods (v) toys They are used for hot temperature application such as: (i) Utensil handle (ii) Body of socket and plug (iii) Furniture (iv) Telephone body (v) Automobile parts. (4) Ex: Polyethlene, Polyestyrene, Nylon etc. Ex: Bakelite, malamine (5) Formed by addition polymerisation. Formed by condensation polymerisation