Nanomaterials PDF

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...

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 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 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 Chemistry Surface & chemical of Materials properties of 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 increases 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 & bond angle 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 Characterstic 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 Carbon Nanotubes/Bucky tubes o Hollow cylindrical tubes, with few nm to micron diameter o with single & multiple walls Also called bucky tubes  Have great length, electrical & thermal properties  Useful in nano-electronics, optics &  Carbon Nanotubes (CNT): Types: Single walled nanotubes (SWNT): diameter 1 nm and of million length  The way the graphene sheet is wrapped is denoted by (n, m) called the chiral vector. Multiwalled nanotubes (MWNT): Multi layered  Russian Doll model:  Parchment model : haracteristic 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. Eg: FeNP/GNP for cancer treatment. Tissue repair: Nanotech can help in repair & regenerate damage 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 needles. 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 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 emmissive display panel using CNT  Nomfet (Nanoparticle organic memory field-effect 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 Nanomaterials in Catalysis:  Nanoparticles of metal, semiconductors, oxides and others are widely used for chemical reactions.  Use of nano particles provides large surface are to volume ratio.  Increase contact area between the reactants arises.  Gold (Au) is a noble metal, but nano size gold particle are effective catalyst, lowers reaction tempreature and making reaction more efficient.  Au/TiO2, Au/MgO  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 Lubricants function to: (Purpose of using lubricant) 1.Keep moving parts apart [ By putting a thin film of lubricant between moving parts (hydrodynamic lubrication)] 2.Reduce friction [lubricant to surface friction is less than surface to surface friction]. Lubricants may contain additives known as friction modifiers which may bind to metal surface. 3.Protect against wear [ By keeping the moving parts away, by having anti-wear additives or extreme pressure additives]. 1.Transfer heat [liquid Lubricant has high specific heat, it circulates to and from the cooler part of system] 2.Carry away contaminants and debris[Have capacity of carrying away internally generated debris and external contaminants, sometimes contain detergent] 3.Prevent corrosion [It contains anti-corrosive additives] 4.Seal gasses [it gives air tight seal between moving parts] Classification of Lubricants based on physical properties. 1. Gaseous: Steam air, technical gases, steam and liquid metal vapours 2. Liquid: Mineral oil, water, Lanolin (corrosion inhibitor), Vegetable (natural) oil, 3. Solid: Graphite, MoS2, Boron nitride, PTFE (teflon) 4. Semisolid: Grease, Na, Al, Ca, Li based grease 5. Metals/alloys: Lead, tin, zinc alloy Additives used for Lubricants 1. Antioxidants (amines, zinc dithiophosphate to prevent the oxidation of lubricating oil) 2. Corrosion inhibitor: It forms a thin film on the surface of material and protect it from corrosion. Esters, carboxylic acids. 3. Viscosity index modifier: With increase in temperature the viscosity of oil decrease, thus a modifier (polymer) is used that will increase viscosity of oil with temperature. Acrylate polymer 1. Fire and flash points (determine volatility and fire resistance) Pensky Marten’s apparatus (Direct method of heating) Abel’s Closed cup apparatus (Indirect method of heating and water is used as a medium for heating the lubricant)  2. Cloud and pour points (determine suitability of lubricants in cold conditions) 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 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.