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1) Discuss the classification of nanomaterials based on their origin, phase composition and dimension. a) Natural nanomaterials and (b) Artificial nanomaterials Natural nanomaterials are those which are obtained naturally. Examples:- Carbon-nanotubes and fibers Artificial nanomaterials are those which are synthesized in laboratories Examples:- Au/Ag np system and Gold nanoparticles, Polymeric nanocomposites. Phase composition Single-Phase solids Crystalline, amorphous particles and layers, etc. Multi-phase solids Matrix composites, coated particles, etc. Multi-phase system Colloids, aerogels, ferrofluids, etc. Q…exlain Electrodeposition:- By carefully controlling the number of electrons transferred, the weight of material transferred can be determined in accordance with Faraday’s law of electrolysis. This states that the number of moles of product formed by an electric current is directly proportional to the number of moles of electron supplied. Since the quantity of electricity passed (measured in coulombs) is current (amps) x time (sec) and Faraday’s constant F (96485 coulombs is currently the most accurate estimate) is the charge per mole of electrons (1 mole of electrons = 96485 coulombs), then the number of moles of electron is charged supplied/F. Specific Advantages of electro-deposition for the synthesis of the nano scale materials:- a. Rapidity b. Low cost c. Free from porosity d. High purity e. Industrial applicability e. Higher deposition rates. h. Easy to control alloy composition. k. No Postdeposition treatment. Q.. Types of carbon nanotubes:- (i) Single-walled:- Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube length that can be many millions of times longer.They exhibit electric properties that are not shared by the multi-walled carbon nanotube (MWNT) variants. The most basic building block of these systems is the electric wire. (ii) Multi-Walled:- Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of graphite. This is especially important when functionalization is required to add new properties to the CNT. Applications: 1. Structural Composite Applications:- The exceptional strength of nano carbon tubes benefits several sporting goods applications based on carbon fiber composites. 2. Coating applications:- A network of very thin conductive structures such as nanocarbon tubes given also new possibilities in thin film technology such as antistatic transparent and conductive coatings with permanent conductivity, better mechanical properties and chemical resistance.. 3. Reinforced Elastomers:By addition of 5-10% of multi-wall nano carbon tubes will give you similar level of stiffness and strength in high performance elastomers along with improved elasticity. 4. Conductive Plastics:- The use of nano carbon tubes for antistatic and conductive applications in polymer is already a commercial reality.This explains the lower content needed for a given resistivity. Particle sizing by laser diffraction:- Laser diffraction has become one of the most commonly used particle sizing methods, especially for particles in the range of 0.5 to 1000 microns. It works on the principle that when a beam of light (a laser) is scattered by a group of particles, the angle of light scattering is inversely proportional to a particle size (smaller the particle size, the larger the angle of light scattering). It is also a very fast, reliable and reproducible technique and can measure over a very wide size range Chemical vapour deposition:- it gives rise to high-quality films and it is applicable to large-scale production. This technique is widely used in the fabrication of epitaxial films toward various GaN-based optoelectronic devices, and similar trend might be expected for future applications of ZnO. Pulsed Laser Deposition:- In the pulsed-laser deposition (PLD) method, high power laser pulses are used to evaporate from a target surface such that the stoichiometry of the material is preserved in the interaction. As a result, a supersonic jet of particles (plume) is directed normal to the target surface. The plume expands away from the target with a strong forward directed velocity distribution of different particles. The ablated species condense on the substrate placed opposite to the target. Sol-Gels:- The sol-gel process is a wet-chemical technique used primarily for the fabrication of materials starting from a chemical solution which acts as the precursor for an integrated network (or gel) of either discrete particles or network polymers. Ball milling:- ball milling is better described as mechanical crushing. In this process, small balls are allowed to rotate around the inside of a drum and drop with gravity force on to a solid enclosed in the drum. Ball milling breaks down the structure into nanocrystallites. The significant advantage of this method is that it can be readily implemented commercially. Ball milling can be used to make a variety of new carbon types, including carbon nanotubes Vapor condensation:- This approach is used to make metallic or metal oxide ceramic nanoparticles. It involves evaporation of solid metal followed by rapid condensation to form nanosized clusters that settle in the form of a powder. Various approaches to vaporize the metal can be used and variation of the medium into which the vapor is released affects the nature and size of the particles. Inert gases are used to prevent oxidation when creating metal nanoparticles, whereas a reactive oxygen atmosphere is used to produce metal oxide ceramic nanoparticles. The main advantage of this approach is low contamination levels. Final particle size is controlled by variation of parameters such as temperature, gas environment and evaporation rate.
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