The document discusses the size effects of nanoparticles including their physical properties, shapes, and applications. It states that nanoparticles less than 100 nm exhibit size-dependent properties not seen in bulk materials, such as higher strength. The properties of nanoparticles can change with temperature and pressure due to changes in crystal structure. Their large surface area to volume ratio gives nanoparticles additional properties like improved catalytic activity.
The document discusses several size-dependent properties of nanoparticles including shape, melting point, density, and specific surface area. As particle size decreases below 100nm, melting point decreases rapidly due to a higher percentage of surface atoms. Density may decrease or increase depending on the material. Specific surface area increases significantly with decreasing size. Nanoparticle shape depends strongly on factors like temperature, pressure and crystal structure, and may differ from the bulk material.
The document discusses several size-dependent properties of nanomaterials. As particle size decreases:
- Surface area to volume ratio increases, increasing surface and quantum effects
- Electronic structure changes from continuous bands to discrete energy levels
- Optical properties like absorption spectra and color are altered
- Reactivity and melting point decrease due to higher surface energy
- Magnetic and wetting properties change, with contact angle decreasing
- Density may increase or decrease depending on changes in cohesion and lattice constants
It describes how different properties of materials changes when reduced to nano. Property includes electrical, optical, mechanical, magnetic, thermal etc.
The document discusses how the surface-to-volume ratio affects the properties of nanomaterials. It explains that nanomaterials have an extremely high surface area to volume ratio compared to larger materials, meaning the surface plays a larger role in determining properties. Different shapes like spheres, cylinders, and cubes are examined, showing how their surface-to-volume ratios change with size. The large increase in surface area for a given volume is demonstrated by reducing a 10 micrometer particle to billions of 10 nanometer particles, increasing the surface area by a factor of 1000. The high surface-to-volume ratio is a key factor making nanomaterial properties dependent on surface effects.
The document discusses nanotechnology and provides definitions and explanations of key concepts. It begins by defining nanotechnology as the design, characterization, production and application of structures and systems through control of shape and size at the nanometer scale. It then explains that a nanometer is one billionth of a meter and provides examples to illustrate the nanoscale. The document goes on to summarize some of the unique physical properties of nanomaterials compared to bulk materials, including increased surface area to volume ratio and quantum confinement effects. It also briefly outlines some common synthesis methods like sol-gel processing and chemical vapor deposition.
Nanotechnology involves creating and manipulating materials at the nanoscale, between 1-100 nanometers. At this scale, materials exhibit unique properties due to increased surface area to volume ratio and quantum mechanical effects. Some examples include enhanced chemical reactivity, color changes with particle size, and size-dependent melting points and conductivity. The document provides background on nanotechnology and an overview of how properties change at the nanoscale.
There are several mechanisms for strengthening metals and alloys:
1. Grain refinement, where reducing grain size increases strength by creating more grain boundaries that impede dislocation movement.
2. Strain hardening occurs when plastic deformation increases dislocation density, requiring more stress for further movement.
3. Solid solution strengthening uses alloying to distort the crystal lattice, impeding dislocations. Interstitial atoms are especially effective.
4. Precipitation hardening forms coherent precipitates that strongly interact with dislocations. It involves solutionizing, quenching, and aging.
Lecture notes on Structure and Properties of Engineering Polymers
Course Objectives:
The main objective is to introduce polymers as an engineering material and emphasize the basic concepts of their nature, production and properties. Polymers are introduced at three levels; namely, the molecular level, the micro level, and macro-level. Through knowledge of all three levels, student can understand and predict the properties of various polymers and their performance in different products. The course also aims at introducing the students to the principles of polymer processing techniques and considerations of design using engineering polymers.
The document discusses several size-dependent properties of nanoparticles including shape, melting point, density, and specific surface area. As particle size decreases below 100nm, melting point decreases rapidly due to a higher percentage of surface atoms. Density may decrease or increase depending on the material. Specific surface area increases significantly with decreasing size. Nanoparticle shape depends strongly on factors like temperature, pressure and crystal structure, and may differ from the bulk material.
The document discusses several size-dependent properties of nanomaterials. As particle size decreases:
- Surface area to volume ratio increases, increasing surface and quantum effects
- Electronic structure changes from continuous bands to discrete energy levels
- Optical properties like absorption spectra and color are altered
- Reactivity and melting point decrease due to higher surface energy
- Magnetic and wetting properties change, with contact angle decreasing
- Density may increase or decrease depending on changes in cohesion and lattice constants
It describes how different properties of materials changes when reduced to nano. Property includes electrical, optical, mechanical, magnetic, thermal etc.
The document discusses how the surface-to-volume ratio affects the properties of nanomaterials. It explains that nanomaterials have an extremely high surface area to volume ratio compared to larger materials, meaning the surface plays a larger role in determining properties. Different shapes like spheres, cylinders, and cubes are examined, showing how their surface-to-volume ratios change with size. The large increase in surface area for a given volume is demonstrated by reducing a 10 micrometer particle to billions of 10 nanometer particles, increasing the surface area by a factor of 1000. The high surface-to-volume ratio is a key factor making nanomaterial properties dependent on surface effects.
The document discusses nanotechnology and provides definitions and explanations of key concepts. It begins by defining nanotechnology as the design, characterization, production and application of structures and systems through control of shape and size at the nanometer scale. It then explains that a nanometer is one billionth of a meter and provides examples to illustrate the nanoscale. The document goes on to summarize some of the unique physical properties of nanomaterials compared to bulk materials, including increased surface area to volume ratio and quantum confinement effects. It also briefly outlines some common synthesis methods like sol-gel processing and chemical vapor deposition.
Nanotechnology involves creating and manipulating materials at the nanoscale, between 1-100 nanometers. At this scale, materials exhibit unique properties due to increased surface area to volume ratio and quantum mechanical effects. Some examples include enhanced chemical reactivity, color changes with particle size, and size-dependent melting points and conductivity. The document provides background on nanotechnology and an overview of how properties change at the nanoscale.
There are several mechanisms for strengthening metals and alloys:
1. Grain refinement, where reducing grain size increases strength by creating more grain boundaries that impede dislocation movement.
2. Strain hardening occurs when plastic deformation increases dislocation density, requiring more stress for further movement.
3. Solid solution strengthening uses alloying to distort the crystal lattice, impeding dislocations. Interstitial atoms are especially effective.
4. Precipitation hardening forms coherent precipitates that strongly interact with dislocations. It involves solutionizing, quenching, and aging.
Lecture notes on Structure and Properties of Engineering Polymers
Course Objectives:
The main objective is to introduce polymers as an engineering material and emphasize the basic concepts of their nature, production and properties. Polymers are introduced at three levels; namely, the molecular level, the micro level, and macro-level. Through knowledge of all three levels, student can understand and predict the properties of various polymers and their performance in different products. The course also aims at introducing the students to the principles of polymer processing techniques and considerations of design using engineering polymers.
The experiment measured mechanical properties of annealed and unannealed brass rods as well as borate glass rods of varying compositions. It found that annealing decreased the yield strength of brass rods by increasing grain size and reducing dislocation density. Borate glass became more brittle at lower alkali concentrations due to being below its glass transition temperature. Young's modulus was measured through tensile testing, 3-point bending, and measuring speed of sound, with varying results found between annealed and unannealed brass.
This document discusses the classification and properties of nanomaterials. It begins by describing the different types of nanomaterials based on dimensionality - zero-dimensional, one-dimensional, two-dimensional, and three-dimensional. It then explains how the physical and chemical properties of nanomaterials, such as melting point, band gap, mechanical strength, and optical absorption, are dependent on their size and shape due to increased surface area and quantum effects. The document concludes by discussing how electrical conductivity and other electronic properties are also influenced by the nanoscale dimensions.
This document discusses nanomaterials and nanotechnology. It defines nanomaterials as materials with structured components less than 100nm in at least one dimension. It describes four main types of nanomaterials: carbon-based, metal-based, dendrimers, and composites. The properties of nanoparticles differ from bulk materials due to their high surface area to volume ratio and quantum confinement effects. Nanoparticles are synthesized using top-down or bottom-up approaches such as sol-gel methods, chemical vapor deposition, and pulsed laser deposition. Nanotechnology has applications in areas like energy, electronics, medicine, and consumer goods.
Nanoparticles are structures with sizes in the nanometer range that are made up of collections of bonded atoms. They exist commonly in nature and can be physically manufactured through various production methods that involve vaporizing atoms and allowing them to condense into clusters. The properties of nanoparticles, such as their structure, reactivity, and optical properties, are strongly dependent on their size at the nanoscale. Methods for producing physically manufactured nanoparticles include energetic vaporization, seeded supersonic nozzle sources, and gas-aggregation cluster sources. Potential applications utilize properties of nanoparticles deposited at low or high energies on surfaces.
The document discusses the mechanism of size reduction through crushing and grinding. It explains that size reduction is done to increase surface area for reactions, improve leaching efficiency, and for other purposes. The key points are:
1. Size reduction depends on factors like the material's internal structure, hardness, and the process used. It involves opening existing cracks or creating new surfaces.
2. Only a small fraction (0.1-2%) of the energy supplied is used to create new surface area. The type of force applied and how force is applied affects energy efficiency.
3. Materials have a "grind limit" where little additional size reduction occurs despite continued grinding. Crack propagation is important to size reduction.
The equilibrium crystal shapes of nanoparticles depend on the anisotropy of the surface energy and can be predicted by the Wulff construction. For supported nanoparticles, the Wulff-Kaichew construction is used, which truncates the shape based on the adhesion energy between the particle and substrate. Deviations from these predicted shapes can occur due to factors like strain from lattice mismatches or kinetic effects during non-equilibrium growth conditions.
This document summarizes key concepts from an AP Chemistry unit on the states of matter, including liquids, solids, and phase changes. It discusses intermolecular forces like hydrogen bonding and London dispersion forces. It describes the properties of liquids and different types of solids, focusing on crystalline solids, metallic bonding, and using X-ray diffraction to analyze solid structures.
Introduction to Mechanical Metallurgy (Our course project)Rishabh Gupta
The document summarizes key concepts in materials science and engineering. It discusses:
1. The importance of selecting high quality materials for better product design and performance.
2. The four main components in materials science - processing, structure, properties, and performance - and how they interrelate.
3. The main classes of materials - metals, ceramics, polymers, composites, semiconductors, and elastomers - and some of their key characteristics.
4. Crystal structures of metals and how they are classified based on atomic packing efficiency. Factors that determine a material's density are also covered.
This document provides an overview of liquids and solids in advanced chemistry, covering topics such as intermolecular forces, the liquid and solid states, vapor pressure and phase diagrams, molecular solids, ionic solids, metallic structures, carbon and silicon networks, and vapor pressure and state changes. Key sections discuss properties of liquids and solids, intermolecular forces, the liquid state, types of solids including molecular, ionic and atomic solids, metallic bonding models, carbon and silicon network structures, and phase diagrams.
This document provides an overview of liquids and solids, discussing intermolecular forces, the liquid and solid states, different types of solids including molecular, ionic, atomic and network solids, and the structures and bonding of metals and carbon/silicon network solids. Specific topics covered include dipole-dipole forces, hydrogen bonding, London dispersion forces, liquid properties, crystalline and amorphous structures, metallic bonding models, metal alloys, and silicates.
The document discusses crystallinity in polymers. Crystallinity affects the optical, mechanical, thermal and chemical properties of polymers and can range from 10-80% depending on the polymer, making them semi-crystalline. A polymer's structure and intermolecular forces influence its ability to form crystals. Crystallinity can be estimated using different analytical methods like x-ray scattering, dilatometry, and comparing crystalline and amorphous peak areas. Crystallinity contributes to the strength of many polymeric materials.
The properties of nanomaterials depend on their small size, with dimensions typically between 1 to 100 nanometers. As size decreases, the surface area to volume ratio increases, altering physical properties like melting point. Nanomaterials also exhibit unique electrical properties due to quantum confinement effects, where energy levels become discrete. Their optical, magnetic, chemical and mechanical properties also change at the nanoscale, making nanomaterials useful in applications like hydrogen storage, catalysis, and superplastic materials.
Metallic materials can undergo elastic or plastic deformation when stressed. Plastic deformation is permanent and corresponds to the movement of dislocations on an atomic scale. Several mechanisms can strengthen materials by impeding dislocation movement, such as grain refinement, solid solution strengthening, and strain hardening. Grain refinement strengthens materials by introducing more grain boundaries that act as barriers to dislocation motion. Solid solution strengthening occurs when alloying elements are added, which impose lattice strains and interact with dislocations. Strain hardening makes metals stronger through plastic deformation, which increases dislocation density and hinders their movement.
1) At high temperatures, grains in metals and ceramics can undergo grain boundary sliding to accommodate deformation. For this to occur without void formation, the rates of diffusional creep and grain boundary sliding must be balanced.
2) Grain boundary sliding is usually accommodated by diffusion, either through the lattice (Nabarro-Herring creep) or along grain boundaries (Coble creep). The overall creep rate is governed by the slower of these sequential processes.
3) Restricting grain boundary sliding, such as with second phase particles, causes the creep rate to be described by the usual equations for diffusional creep instead of grain boundary sliding models.
This document discusses nanostructures, their synthesis, and surface modification techniques. It defines nanostructures as having at least one dimension between 1-100 nm. Nanostructures are classified based on dimensionality as 0D, 1D, 2D, and 3D. Common synthesis methods include physical vapor deposition, chemical vapor deposition, and thermal spraying. Surface modification is done to change properties like reactivity, roughness, and corrosion protection. Common modification techniques are thermal spraying, PVD, and CVD.
Matter and energy exist in various forms and interact in many ways. Nano materials are materials that have at least one dimension sized between 1 to 100 nanometers. They exhibit different properties than bulk materials due to greater surface area to volume ratio and quantum effects. Nanotechnology involves designing and engineering structures at the nanoscale to utilize these size-dependent properties. Nano materials find applications in industries such as electronics, energy, medicine, and more.
This document discusses size reduction and comminution. It outlines the objectives of size reduction such as improving flow properties and increasing surface area. It examines how material properties like brittleness, toughness, and hardness influence size reduction. Different size reduction methods are described, including cutting, compression, impact, attrition, and combined impact/attrition. Specific equipment like ball mills, hammer mills, and fluidized mills are discussed in terms of how they achieve size reduction through impacts and attrition. Factors that influence particle size distribution changes during milling are also covered.
breakfast importance in the health sectorJaved Iqbal
The document discusses healthy breakfast options for children. It recommends that breakfast include starchy carbohydrates like wholegrains for energy, at least one portion of fruit or vegetables for nutrients, and optionally a source of protein or dairy. Unhealthy options to limit include those high in sugar, salt, and saturated fat like pastries. A healthy breakfast provides nutrients and fiber to help children feel full and perform well throughout the morning. The document provides examples of balanced breakfasts and encourages including foods from the different food groups per nutrition guidelines.
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The experiment measured mechanical properties of annealed and unannealed brass rods as well as borate glass rods of varying compositions. It found that annealing decreased the yield strength of brass rods by increasing grain size and reducing dislocation density. Borate glass became more brittle at lower alkali concentrations due to being below its glass transition temperature. Young's modulus was measured through tensile testing, 3-point bending, and measuring speed of sound, with varying results found between annealed and unannealed brass.
This document discusses the classification and properties of nanomaterials. It begins by describing the different types of nanomaterials based on dimensionality - zero-dimensional, one-dimensional, two-dimensional, and three-dimensional. It then explains how the physical and chemical properties of nanomaterials, such as melting point, band gap, mechanical strength, and optical absorption, are dependent on their size and shape due to increased surface area and quantum effects. The document concludes by discussing how electrical conductivity and other electronic properties are also influenced by the nanoscale dimensions.
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Nanoparticles are structures with sizes in the nanometer range that are made up of collections of bonded atoms. They exist commonly in nature and can be physically manufactured through various production methods that involve vaporizing atoms and allowing them to condense into clusters. The properties of nanoparticles, such as their structure, reactivity, and optical properties, are strongly dependent on their size at the nanoscale. Methods for producing physically manufactured nanoparticles include energetic vaporization, seeded supersonic nozzle sources, and gas-aggregation cluster sources. Potential applications utilize properties of nanoparticles deposited at low or high energies on surfaces.
The document discusses the mechanism of size reduction through crushing and grinding. It explains that size reduction is done to increase surface area for reactions, improve leaching efficiency, and for other purposes. The key points are:
1. Size reduction depends on factors like the material's internal structure, hardness, and the process used. It involves opening existing cracks or creating new surfaces.
2. Only a small fraction (0.1-2%) of the energy supplied is used to create new surface area. The type of force applied and how force is applied affects energy efficiency.
3. Materials have a "grind limit" where little additional size reduction occurs despite continued grinding. Crack propagation is important to size reduction.
The equilibrium crystal shapes of nanoparticles depend on the anisotropy of the surface energy and can be predicted by the Wulff construction. For supported nanoparticles, the Wulff-Kaichew construction is used, which truncates the shape based on the adhesion energy between the particle and substrate. Deviations from these predicted shapes can occur due to factors like strain from lattice mismatches or kinetic effects during non-equilibrium growth conditions.
This document summarizes key concepts from an AP Chemistry unit on the states of matter, including liquids, solids, and phase changes. It discusses intermolecular forces like hydrogen bonding and London dispersion forces. It describes the properties of liquids and different types of solids, focusing on crystalline solids, metallic bonding, and using X-ray diffraction to analyze solid structures.
Introduction to Mechanical Metallurgy (Our course project)Rishabh Gupta
The document summarizes key concepts in materials science and engineering. It discusses:
1. The importance of selecting high quality materials for better product design and performance.
2. The four main components in materials science - processing, structure, properties, and performance - and how they interrelate.
3. The main classes of materials - metals, ceramics, polymers, composites, semiconductors, and elastomers - and some of their key characteristics.
4. Crystal structures of metals and how they are classified based on atomic packing efficiency. Factors that determine a material's density are also covered.
This document provides an overview of liquids and solids in advanced chemistry, covering topics such as intermolecular forces, the liquid and solid states, vapor pressure and phase diagrams, molecular solids, ionic solids, metallic structures, carbon and silicon networks, and vapor pressure and state changes. Key sections discuss properties of liquids and solids, intermolecular forces, the liquid state, types of solids including molecular, ionic and atomic solids, metallic bonding models, carbon and silicon network structures, and phase diagrams.
This document provides an overview of liquids and solids, discussing intermolecular forces, the liquid and solid states, different types of solids including molecular, ionic, atomic and network solids, and the structures and bonding of metals and carbon/silicon network solids. Specific topics covered include dipole-dipole forces, hydrogen bonding, London dispersion forces, liquid properties, crystalline and amorphous structures, metallic bonding models, metal alloys, and silicates.
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The properties of nanomaterials depend on their small size, with dimensions typically between 1 to 100 nanometers. As size decreases, the surface area to volume ratio increases, altering physical properties like melting point. Nanomaterials also exhibit unique electrical properties due to quantum confinement effects, where energy levels become discrete. Their optical, magnetic, chemical and mechanical properties also change at the nanoscale, making nanomaterials useful in applications like hydrogen storage, catalysis, and superplastic materials.
Metallic materials can undergo elastic or plastic deformation when stressed. Plastic deformation is permanent and corresponds to the movement of dislocations on an atomic scale. Several mechanisms can strengthen materials by impeding dislocation movement, such as grain refinement, solid solution strengthening, and strain hardening. Grain refinement strengthens materials by introducing more grain boundaries that act as barriers to dislocation motion. Solid solution strengthening occurs when alloying elements are added, which impose lattice strains and interact with dislocations. Strain hardening makes metals stronger through plastic deformation, which increases dislocation density and hinders their movement.
1) At high temperatures, grains in metals and ceramics can undergo grain boundary sliding to accommodate deformation. For this to occur without void formation, the rates of diffusional creep and grain boundary sliding must be balanced.
2) Grain boundary sliding is usually accommodated by diffusion, either through the lattice (Nabarro-Herring creep) or along grain boundaries (Coble creep). The overall creep rate is governed by the slower of these sequential processes.
3) Restricting grain boundary sliding, such as with second phase particles, causes the creep rate to be described by the usual equations for diffusional creep instead of grain boundary sliding models.
This document discusses nanostructures, their synthesis, and surface modification techniques. It defines nanostructures as having at least one dimension between 1-100 nm. Nanostructures are classified based on dimensionality as 0D, 1D, 2D, and 3D. Common synthesis methods include physical vapor deposition, chemical vapor deposition, and thermal spraying. Surface modification is done to change properties like reactivity, roughness, and corrosion protection. Common modification techniques are thermal spraying, PVD, and CVD.
Matter and energy exist in various forms and interact in many ways. Nano materials are materials that have at least one dimension sized between 1 to 100 nanometers. They exhibit different properties than bulk materials due to greater surface area to volume ratio and quantum effects. Nanotechnology involves designing and engineering structures at the nanoscale to utilize these size-dependent properties. Nano materials find applications in industries such as electronics, energy, medicine, and more.
This document discusses size reduction and comminution. It outlines the objectives of size reduction such as improving flow properties and increasing surface area. It examines how material properties like brittleness, toughness, and hardness influence size reduction. Different size reduction methods are described, including cutting, compression, impact, attrition, and combined impact/attrition. Specific equipment like ball mills, hammer mills, and fluidized mills are discussed in terms of how they achieve size reduction through impacts and attrition. Factors that influence particle size distribution changes during milling are also covered.
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Introduction to Computational chemistry-Javed Iqbal
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LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
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accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
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Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
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You will hear from Liz Willett, the Head of Nonprofits, and hear about what Walmart is doing to help nonprofits, including Walmart Business and Spark Good. Walmart Business+ is a new offer for nonprofits that offers discounts and also streamlines nonprofits order and expense tracking, saving time and money.
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𝐃𝐢𝐬𝐜𝐮𝐬𝐬 𝐭𝐡𝐞 𝐄𝐏𝐏 𝐂𝐮𝐫𝐫𝐢𝐜𝐮𝐥𝐮𝐦 𝐢𝐧 𝐭𝐡𝐞 𝐏𝐡𝐢𝐥𝐢𝐩𝐩𝐢𝐧𝐞𝐬:
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1. NAST 613 : ELEMENTS OF MATERIALS SCIENCE AND
PHYSICAL PROPERTIES OF NANOSTRUCTURED
MATERIALS
SIZE EFFECT OF NANOPARTICLES
Course Instructor : Dr. A.Subramania
SUBMITTED BY,
MUGILANE.N
M.TECH 1ST YEAR
NANOSCIENCE &
TECHNOLOGY
2. SIZE
⚫ Nanoparticles are the simplest form of structures
with sizes in the nm range.
⚫ The physical properties of materials are dependent
on the dimensions of the material – its properties
(e.g. conductivity, elasticity, etc.) are scalable with
respect to the amount of atoms in the material.
⚫ There are basically two types of size-dependent
effects:
⚫ Smoothly scalable ones which are related to the
fraction of atoms at the surface.
⚫ Quantum effects which show discontinuous
behaviour due to completion of shells in systems
with delocalised electrons.
3. PROPERTY APPLICATION
Single magnetic domain
Small mean free path of electrons in
a solid
Size smaller than wavelength
High & selective optical absorption
of metal particles
Formation of ultra fine pores due to
superfine agglomeration of particles
Uniform mixture of different kinds of
superfine particles
Grain size too small for stable
dislocation
Magnetic recording
Special conductors
Light or heat absorption,
Scattering
Colours, filters, solar
absorbers, photovoltaics,
photographic material,
phototropic material
Molecular Filters
R&D of New Materials
High strength and hardness
of metallic materials
4. PROPERTY APPLICATION
Large specific surface area
Large surface area, small heat
capacity
Lower sintering temperature
Specific interface area, large
boundary area
Superplastic behaviour of ceramics
Cluster coating and metallization
Multi-shell particles
Catalysis, sensors
Heat-exchange materials
Combustion Catalysts
Sintering accelerators
Nano-structured materials
Ductile ceramics
Special resistors,
temperature sensors
Chemical activity of
catalysts, Tailored Optical
elements
Surface/ Interface
5. SHAPE
⚫Small structures or Nanoparticles are not
just the fragments of bulk materials.
⚫There can be entirely different structures as
well as bond and bond strength in
Nanomaterial.
have
⚫Temperature and pressure also
profound effect on the crystal structure.
6. EXAMPLE : Silicon crystal
Experiments suggests that the shape of small size clusters are quite different
7. ⚫Even though some may acquire bulk crystalline
structure, lattice parameters may not be the same
as in the bulk material.
⚫For Example, X-Ray diffraction patterns of ZnS
that as small as 1.4 nm particles had liquid like
disorder.
⚫However larger nanocrystals of ZnS indeed
show same sphalerite structure (cubic structure)
as in the bulk.
⚫ It has been observed that there is a lattice
contraction of nearly 1% for 1.4 nm ZnS
Nanoparticles.
8. ⚫With increase in temperature the disordered
structure of small particles of ZnS were found
to transform to wurtzite (hexagonal) structure.
⚫The chemical capping often used in the
synthesis of nanoparticles, gets removed and
the particles tend to agglomerate or coalesce
forming larger particles.
⚫For structural transformation the nanoparticles
require larger pressure and depends upon the
particle size.
10. EXAMPLE : CdSe Nanocrystals
CdSe nanoparticles of 2 to 4 nm size required 4.9Gpa to 3GPa
pressure to transform them from wurtzite to rock salt structure.
Bulk CdSe needs just 2.0Gpa for the same transformation
11. EQUILIBRIUM SHAPE
⚫ The equilibrium crystal shape is the shape obtained
by minimizing the total surface free energy for a fixed
crystal volume.
⚫ The key factor for calculating the equilibrium shape
of a cluster is the cohesive energy of the atoms in a
given geometry
WULFF POLYHEDRON:
⚫ Cluster is made by assembling atoms, treated as
spheres with varying levels of order.
⚫ This assembly of spheres cannot give rise to another
sphere.
⚫ The shape and nature of polyhedron depend on the
binding energy of the atoms.
12. Wulff’s Plot -A Wulff Plot is a polar plot of the
surface free energy as a function of orientation
and fundamentally, the shape of a nanocrystal in
equilibrium.
13. ⚫The construction criterion satisfies the
following rule: If a face is characterised by
Miller indices hkl and has area S, then
Ƴhkl/Rhkl = constant
⚫If there is no anisotropy, as in the drop model
where we have ƳhklShkl= ƳS, we simply obtain
Ƴ/R = constant
This is the equation for a
sphere because R must be
constant. If the need for
faces is taken into account,
the construction become
much more difficult
14. MELTING POINT
A decrease in the bonding energy would result in
a lower melting temperature.
Melting starts at the surface of a material.
Surface atoms contribute to a lowering of the
melting temperature of the particle.
16. The change in melting temp. dependence thus as 1/R
The melting temperature decreases rapidly for clusters with diameter
below 5nm.
According to this model a cluster with radius 2nm has melting
temperature of 880K
17. SPECIFIC SURFACE AREA
applied to
⚫Specific surface area is measure
granular or granulate solids.
⚫It is the surface area per unit mass.
⚫It is important because many physical and
chemical process takes place at the surface of
solids.
⚫Unit : square meters per gram.
⚫Denoted by the symbol S.
⚫The general expression for this specific surface
area per gram S is
19. Specific surface area depends on the shape...
Scub = 1.24Ssph . So a cube has 24% more specific surface than a
sphere with the same volume.
General expression for the shape dependence of the area: volume
ratio,
20. Dependence of the surface
area S(L/D) of a cylinder on
its length :diameter ratio
L/D
Specific surface areas of
GaAs spheres, long
cylinders (wires) and
thin disks as a function
of their size.
21. DENSITY
⚫Density can be generally varied by changing the
pressure or the temperature.
⚫It has been observed that density changes with
the change in the thickness of the layer in nm
range.
⚫ Mass density of Cu, Cr, TiN film on MgO was
found to be lower than the corresponding bulk
value.
⚫ SiO2, SiC on stainless steel showed increase in
density.
⚫ Cu, Ag, Au showed no significant change.
22. Density varies with the size…
The density decreases with the reduction in size but not in
quantitative agreement with the results reported.
24. Image of Don Quixote become
invisible at temperature < 341K
25. THERMAL PROPERTIES
⚫ Nanocrystalline materials expected to have lower thermal
conductivity compared to conventional material.
In nanocrystalline materials, size become comparable to mean
free path of phonons.
Phonon scattering
Phonon confinement and
Quantization effects of phonon.
• The use of nanofluids to enhance the thermal transport is
another promising application the thermal properties of
nanomaterials.
•
26. ELASTIC PROPERTIES
⚫ Elastic modulus is of material is proportional to the bond
strength between the atoms or molecules.
• Structure independent and dependent on temperature and
defect concentration.
• A large increase in vacancy and other defect concentrations
can be treated as equivalent to higher apparent temperature.
• If the temperature is increased, the mean separation between
the atoms increase and modulus decreases.
• Thus, the nanomaterials by virtue of their high defect
concentration, may have considerably lower elastic properties in
comparison to bulk materials.
27. E.O.Hall and N.J.Petch have derived the following relation,
famously known as Hall-Petch relation between yield
strength (σy) and grain size (d):
Hall-Petch relation
where σ
i is the ‘friction stress’, representing the overall resistance
of the crystal lattice to dislocation movement,
k is the ‘locking parameter’ that measures the relative hardening
contribution of the grain boundaries and d is the average grain
diameter
29. Fracture Mechanisms
At higher temperatures the yield strength is lowered and the
fracture is more ductile in nature
At lower temperatures the yield strength is greater and
the fracture is more brittle in nature
This relationship with temperature has to do with atom
vibrations. As temperature increases, the atoms in the
material vibrate with greater frequency and amplitude. This
increased vibration allows the atoms under stress to slip to
new places in the material ( i.e. break bonds and form new
ones with other atoms in the material). This slippage of
atoms is seen on the outside of the material as plastic
deformation, a common feature of ductile fracture
30. When temperature decreases however, the exact opposite is true.
Atom vibration decreases, and the atoms do not want to slip to new
locations in the material. So when the stress on the material
becomes high enough, the atoms just break their bonds and do
not form new ones. This decrease in slippage causes little plastic
deformation before fracture. Thus, we have a brittle type fracture
So, temperature determines the amount of brittle or
ductile fracture that can occur in a material.
31. DISLOCATION DENSITY
⚫ Another factor that determines the amount of brittle or
ductile fracture that occurs in a material is dislocation
density.
⚫ The higher the dislocation density, the more brittle the
fracture will be in the material.
⚫ The idea behind this theory is that plastic deformation comes
from the movement of dislocations. As dislocations increase in a
material due to stresses above the materials yield point, it
becomes increasingly difficult for the dislocations to move
because they pile into each other.
⚫ So a material that already has a high dislocation density can
only deform but so much before it fractures in a brittle manner
32. Grain size
As grains get smaller in a material, the fracture becomes more
brittle. This phenomena is do to the fact that in smaller grains,
dislocations have less space to move before they hit a grain
boundary. When dislocations can not move very far before
fracture, then plastic deformation decreases. Thus, the material's
fracture is more brittle.
Dislocation movement is temperature dependent. Their motion
(slip) occurs by sequential bond breaking and bond reforming .
The number of dislocations per unit volume is the dislocation
density, in a plane they are measured per unit area.
The growth of grain size with temperature can occur in all
polycrystalline materials. It occurs by migration of atoms at grain
boundaries by diffusion, thus grain growth is faster at higher
temperatures
33.
34. ⚫ creep is the tendency of a solid material to slowly move or
deform permanently under the influence of stresses.
⚫ It occurs as a result of long term exposure to high levels of
stress that are below the yield strength of the material. Creep
is more severe in materials that are subjected to heat for long
periods, and near melting point. Creep always increases with
temperature.
⚫ The effects of creep deformation generally become
noticeable at approximately 30% of the melting point for
metals and 40–50% of melting point for ceramics.
⚫ Small grain size lowers creep resistance and
⚫ Large grain size increases creep resistance.
CREEP
35. SINTERING
above
It is based on atomic diffusion. Diffusion occurs in any material
absolute zero but it occurs much faster at higher temperatures
Sintering in practice is the control of both densification and grain growth.
Densification is the act of reducing porosity in a sample thereby making it
more dense.
Grain growth is the process of grain boundary motion and Ostwald ripening
to increase the average grain size.
Many properties (mechanical strength, electrical breakdown strength, etc.)
benefit from both a high relative density and a small grain size
36. Sintering occurs by diffusion of atoms through the microstructure.
The different paths the atoms take to get from one spot to another
are the sintering mechanisms.
The six common mechanisms are:
Surface diffusion – Diffusion of atoms along the surface of a particle
Vapor transport – Evaporation of atoms which condense on a
different surface
Lattice diffusion from surface – atoms from surface diffuse through
lattice
Lattice diffusion from grain boundary – atom from grain boundary
diffuses through lattice
Grain boundary diffusion – atoms diffuse along ground
boundary Plastic deformation – dislocation motion causes
flow of matter