Nanomaterials Unit 3 PowerPoint PDF

UNIT-3 Nanomaterials Introduction: Nanotechnology is the manipulation of atoms & molecules at nano scale (1-100nm) To produce devices, structures, system etc. The materials having at least one dimension in nano scale is called as nanomaterials  When the bulk is converted to nano size then thes...

UNIT-3 Nanomaterials Introduction: Nanotechnology is the manipulation of atoms & molecules at nano scale (1-100nm) To produce devices, structures, system etc. The materials having at least one dimension in nano scale is called as nanomaterials  When the bulk is converted to nano size then these nano material have extended properties & tremendous use  The study of nanomaterials is called nano science Properties: Physical & chemical properties of nano materials is different than bulk materials of same composition, due to spatial arrangement of molecules  So results in different electrical, energetic, chemical, & catalytical properties  The surface to volume ration increases hence chemical reactivity increases also it affects the strength and electrical properties.  The quantum confinement is observed at nanoscale that changes the optical, electronic & magnetic properties of material, the band gap increase as the size of material is decrease to nano size. Size Dependent Properties: Particle size vs. Surface Area Particle size α 1/surface area With decrease in particle size surface are of particle increases, this relation brings out remarkable changes in physical & chemical properties of Surface Chemistry of Materials material Due to increased surface area, nanomaterial posses greater surface energy & are less thermodynamically stable. There is difference in the properties of atom/molecules present in surface & bulk. The surface atom/molecules have enhanced reactivity & greater tendency to agglomerate. Various physical properties viz., thermal, optical, mechanical etc are dependent on the electronic state of material Electronic Properties:  Electronic properties generally depends upon energy level, types of bonding, energy bands, energy gaps & fermi levels. o The electrons over in quantified level in any isolated solid. If the distance between atoms is less, electron orbital interact with each other, that’s leads to broadning of energy levels to form energy bands. o Internal bands (narrow) are formed by inner shell, while the electron in external shell form valence band. o The electron in excited state form conduction band. o Difference between the valance & conduction band is known as energy gap o In metal energy gap is zero, in semiconductor it is small & large in case of insulator o The max. energy for electron at absolute zero temp. is called Fermi level (fermi energy) o The physical properties are generally governed by the electrons that have energy higher than fermi energy The band gap decreases when the particle size is decreased & energy gaps gradually convert into discrete molecular electronic levels. Mechanical Properties:  nanomaterials have crystalline size in 1-100nm & have numerous grain boundaries.  these grain boundaries determine the mechanical properties of nanomaterials  Mechanical properties are enhanced by reducing the grain size, as grain size have no defect in them  This crystalline nature of nano materials is maintained hence mechanical properties like tensile strength, stress, compression, Tg etc are enhanced. Fullerenes: Third allotrope (crystalline) of carbon Contains alternate hexagonal & pentagonal rings Hollow sphere (bucky ball), ellipsoid/tubes (nanotubes)  C60 (Buckminster) contains 12 pentagon & 20 hexagons  Structure is similar to graphite & having hybridization between sp2 & sp3  molecule is symmetrical, with all bond length equal  Brittle, soft weak, covalent material like properties  Electrically insulator Types of fullerenes:  Buckyball cluster o less than 300 Carbon atoms o Smallest Bucky ball is C20 o Found in soot of coal o most abundant is C60 Characteristic of fullerenes:  Highly symmetrical, sp2 in C60  Chemically stable, heat stable  Reactive due to pi- electrons electron delocalisation  Water insoluble, soluble in toluene & CS2  Non toxic  Nanotubes o Hollow cylindrical tubes, with few nm to micron diameter o with single & multiple walls Carbon Nanotubes (CNT): Also called bucky tubes  Have great length, electrical & thermal properties  Useful in nanoelectronics, optics & material science Types: Single walled nanotubes (SWNT): diameter ~1nm, million length  The structure is formed as graphene sheet is wrapped  Types: zigzag & armchair Multiwalled nanotubes (MWNT): Multi layered  Russian Doll model: Characteristic of CNT: Strength: Strongest & stiffest due to covalent sp2 bonds. Hardness: Too hard to compress. Kinetics: Movement of tubes occurs without friction, creating automatic bearing (molecular ) nanotechnology Thermal: Good thermal conduction, but insulator along the tube axis Application of nanomaterials: In medicine: Diagnostics: Magnetic NP (nanoparticle), bound to suitable antibody & are used to label molecules, structure or microrganism eg: GNP (Gold NP) are use for DNA sequencing Drug delivery: Amount of drug consuption & side effect can be reduced by depositing the activated NP in the targated areas. Tissue Eg: FeNP/GNP repair: for can Nanotech cancer help in repair & regenerate damage treatment. tissue (tissue engineering). It can replace organ transplant or artificial implant surgeries Transdermal drug delivery: Nano protrusions on patches, can be fixed on skin like plaster. These carries drug dose, act as tiny In electronic & communications: Principle aim to develop 3D confined quantum structure electronic devices (quantum wire, quantum dot) Quantum well laser for telecommunication High electron mobility transistors (HEMT), low noise  Microwave application, laser emitting for data communication & senor coding Three-dimensional (3D) structure or bulk structure: No quantization of the particle motion occurs, i.e., the particle is free. Two-dimensional (2D) structure or quantum well: Quantization of the particle motion occurs in one direction, while the particle is free to move in the other two directions. One-dimensional (1D) structure or quantum wire: Quantization occurs in two directions, leading to free movement along only one direction. Zero-dimensional (0D) structure or quantum dot (sometimes called “quantum box”): Quantization occurs in all three directions. Consumer Products: Computer hardware  display devices  Mobile & communication products  Audio products  camera & films etc. Advance uses:  Transistors from CNT  Memory chips with density 1 Tb/sq inch  High speed transistors (from single atom thick graphene film)  Light weight nano emmessive display panel using CNT  Nomfet (Nanoparticle organic memory field-effect transistor) In energy Science: Zeolite (nano porous crystalline solid) are used for oil refining. They have well defined molecular structure (molecular sieves). Helps in petrol yield  Quantum dot can be used as light emission source, due to smaller size than wavelength of light they do not scatter light & enhance optical efficiency  Electrode material can be changed by nano-structuring, imparts nano-texture to improve electrical performance of battery  Energy production can be brought about using nanomaterial as clean & high efficiency energy sources (eg: LEDs)  Solar cells can be integrated from nano crystal of semiconductors coated with light absorbing dye, emmiting electron and from nanostructured diamond thermal cells that capture heat & light, emitting high energy electron  Ultraporous nanomaterial are used to store hydrogen at high density for fuel cell powered cars In catalysis: Hetrogeneous catalyst are now a days are used which have nano size (active material attached to porous support)  nanoparticle of metal, semiconductor, oxides & other compounds are generally used  Use of nano sized material generally provide large surface to volume ratio  Hence due to large surface area more contact is between the reactant and the catalyst and more effective is the catalyst (eg: GNP)  They also lower the reaction temperature, making reaction more energy efficient  Nanoparticle of transition metals oxide show catalytic properties, which can be enhanced by NP like gold & platinum 4 main catogeries: o Gold based (Au/TiO2, Au/MgO) o Other metal based (Cu, Rh) o Platinum/Pd based (eg: Pt/Pd/Ni) o Nanosized metal particle dispersed in polymer (eg: Cu/polymer, Pt/polymer)  Limitation: Low thermal stability Liquid crystals & Their Applications:  Crystalline solids /materials exhibit long range periodic order of their constituent atoms or molecule in 3D  Their exist another state between the two states called Liquid state/ mesogenic state  They consist order of arrangement like solid & randomness in position like the liquid phase.  These are more closer to liquid state than solid state because to change from solid to LC state needs more heat as compared to change of LC into liquid state.  Characteristic: Rod like molecular structure Rigidness of the long axis, with flexible ends Strong Dipoles Easily polarizable substituents Types of Liquid Crystals Nematic liquid Crystals:  Most common of liquid crystal phase  Constituents have no positional order, but long range orientational order  “Nematos” in Greek means thread, they look like thread when viewed through polarized light  Flow like normal liquid  Low viscosity  Turbid  Anisotropic Smectic liquid Crystals:  Do not flow as normal liquid  Found at lower temperature than nematic liquid crystal  Molecules are arrange in well defined layers that can slide over one another like soap  “Smetos” in Greek mean soap  Molecule are free to move in layer, movement between layer is less  Molecule are layered parallel or tilted relatively Application of liquid Crystals:  Used in detection of tumors (indicated by colour change)  In electronic industry, any breakage in circuit can be detected  In thermostrips & disposable thermometers  Optical imaging  Detection of radiation or pollution in atmosphere  LCD are used in watches, calculators, TV, sign board, computers, etc  Used in non destructive testing of material under stress  Low molecular mass liquid crystals are used in erasable optical disks & light modulators for colour electronic imaging Composites  Low density  High strength & stiffness  good abrasion  Impact resistance  Corrosion resistance One or two distinct components combines to form a new class of materials suitable for structural application  Matrix  Dispersed phase Classification: 2 levels  1st level Matrix constituent OMCs (Organic matrix composites) MMCs (Metal matrix composites) CMCs (ceramic matrix composites)  2nd level Reinforcement form Fiber reinforced composites: Discontinuous & continuous fibers Laminar composites: Structural composites, have high isotropic strength Particulate composites: Particles, like flakes or powder eg; concrete, wood particle board  Fiber reinforced plastics  composites of fiber & polymer matrix  fiber are source of strength, polymer matrix glue the fiber together  fillers & modifiers are added to smoothen the properties Common reinforce agents: Al, aluminum oxide, aluminium silica, asbestos, graphite, glass etc. Polymer matrix: acrylonitrile butadiene, nylon, PE, PP, PET, polyester, polyurethane, epoxy etc. Applications  In cars n aircrafts, due to light weight  making bridges (graphite epoxy), due to strength  cars & boats, due to corrosion resistance  archery bows, due to flexiblity  armors, due to high strength  building insulation, automobile compartment, due to thermal resistance Conducting Polymers Poly(p-phenylene) Trans Polyacetylene  Lubricants A lubricant is a substance introduced to reduce friction, decrease the wear and improve the efficiency by forming a film two between moving surfaces Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other Asperity deformation, creates welded junction, which carry entire load between the surfaces. 1. Sliding (kinetic) 2. Rolling friction Lubricants function to: (Purpose of using lubricant) 1. Keep moving parts apart [ By putting a thin film of lubricant between moving parts. Reduces friction, heat generation, operating noise & vibrations. 2. Reduce friction [lubricant to surface friction is less than surface to surface friction]. Reduce surface friction, heat generation and formation of wear particles 3. Protect against wear [ By keeping the moving parts away, by having anti-wear additives or extreme pressure additives]. 4. Transfer heat [ Gas & Liq. both transfer heat. Liquid lubricant has high specific heat so they are much effective , it circulates to and from the cooler part of system. High flow system carry away lot of heat & reduces thermal stress ] 5. Carry away contaminants and debris[ Have capacity of carrying away internally generated debris and external contaminants that get introduced into the system to a filter Classification of Lubricants based on physical properties. 1. Gaseous: Steam air, technical gases, steam and liquid metal vapours 2. Liquid: Mineral oil, water, Lanolin (derive from sheep wool grease) (corrosion inhibitor), Vegetable oil (natural- plant & animal)(canola, palm, castor) 3. Solid: (use under high temp)Graphite, MoS2, Boron nitride, PTFE (teflon) 4. Semisolid: Grease, (soaps of Na, Al, Ca, Li) based grease 5. Metals/alloys: Lead, tin, zinc alloy Additives used for Lubricants 6. Antioxidants At elevated temp, lubricating oil gets oxidized (amines, zinc dithiophosphate to prevent the oxidation of lubricating oil) 7. Corrosion inhibitor: It forms a thin film on the surface of material and protect it from corrosion. Esters, carboxylic acids. Additives used for Lubricants gents: Carbon particles can coat and spoil diesel engine components. D maintain a suspension of carbon particles always, extending the lubric ulphonates, phosphonates of Na, Ca, Mg aming additives: Added to have proper flooding of lubricants at the p nd in pump operation. Dimethysiloxanes. nity additives: Certain fuels have higher S content form SO2 and SO3 nts, causes corrosion. Ca, Mg and other metal ions with organic acid su lkylbenzene sulphonates or alkyl silicates.  1. Fire and flash points (determine volatility and fire resistance) oint is the lowest temp. at which the lubricating oil gives off enough vapors to ig t burn, when a small flame is brought near it. Fire point is the lowest temp. at wh pors of the oil burn continuously for at least 5 sec. when a tiny flame is brought n ubricant should have flash point above the temp at which it is to be used. In mos e points are 8-10% higher than flash point  2. Cloud and pour points (determine suitability of lubricants in cold conditions) Pour Point The temp at which oil ceases to flow or pour. Lubricant used in machine working at low temp. should possess low pour point Cloud Point The Cloud Point of a fluid is the temperature at which dissolved solids are no longer completely soluble, precipitating as a second phase giving the fluid a cloudy appearance. The temp at which it becomes cloudy or hazy. Aniline point: The lowest temperature at which equal volume of aniline and a solvent (as gasoline) is just completely miscible to each other. [ below that temperature the two phase are separated from each other] High aniline point means higher percentage of paraffinic hydrocarbons and lower percentage of aromatic hydrocarbon. For a lubricant to be called good it should have high aniline point 1.Thick film or Fluid Film or Hydrodynamic Film 2. Thin Film or Boundary Lubrication : system operated at slow speed, high contact pressure, slightly rough surfaces, hydrodynamic lubrication fail. Solid, greases are good for boundary not liquid 3. Extreme Pressure Lubricant: Chlorinated ester, Sulphurized oil, tricresyl phosphate (added to mineral oil)