
Impact of Nanoscale on Material Properties
Explore how nanotechnology alters material properties through reduced grain size, increased defect density, and unique surface characteristics. Nanomaterials exhibit distinct mechanical, electrical, and magnetic behaviors due to their fine-grained structure, influencing their applications in various fields.
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Presentation Transcript
Nanotechnology 1 25/10/2016
Scale at which Surfaces and Interfaces Play a Large Role in Materials Properties and Interactions Why should the material behaviour vary so significantly by a mere reduction in grain size? Nanostructured materials are composed of grains and grain boundaries. Nanometre-sized grains contain onlyafew thousands of atoms within each grain. A large number of atoms reside at the grain boundaries, as shown in Figure (3). As the grain size decreases, there is a significant increase in the volume fraction of grain boundaries or interfaces and triple junctions, as shown in Figure (4). With increase in defect density, or in other words, when the fraction of atoms residing at defect cores like dislocations, grain boundaries and triple junctions becomes comparable with that residing in the core, the properties of the material are bound to be governed to a large extent by defect configurations, dynamics mechanical and chemical properties of nanomaterials are significantly altered duetodefectdynamics. and interactions. Hence the 2 25/10/2016
The elastic modulus of nanomaterials can be significantly different from that of bulk alloys, due to the presence of increased fraction of defects. Nanocrystalline ceramics are tougher and stronger than those with coarse grains. Nano-sized metals exhibit significant increase in yield strength and the toughness decreases. It has also been shown that electrical, optical and magnetic properties are influenced by the fine-grained structure of these materials. As the technical capability to tailor and modulate dimensions at the nanoscale has improved greatly it has become possible to realise the fascinating properties of nanostructures 3 25/10/2016
Figure (3):- nanomaterial. The black circles indicate atoms in the grain, while the white circles indicate atoms at the grain boundaries. The hypothetical structure of a 4 25/10/2016
Figure (4):- boundaries) and triple junctions with decrease in grain size of nanomaterials. Increase in the intercrystalline region (grain 5 25/10/2016
So, the changing in the properties of the materials when it become in nanoscale can be summarised by:- (i) Large fraction of surfaceatoms; (ii) High surfaceenergy; (iii) Spatial confinement; (iv) Reduced imperfections, which do not exist in thecorresponding bulk materials. 6 25/10/2016
Therefore ,due to their small dimensions, nanomaterials haveextremelylargesurfacearea to volume ratio, which makes a large to be the surface or interfacial atoms, resulting in more surface dependent material properties. Especially when the sizes of nanomaterials are comparable to length, the entire material will be affected by the surface properties of nanomaterials. This in turn may enhance or modify the properties of the bulk materials. 25/10/2016 7
Large surface area also makes nanostructured membranes and materials ideal candidates for water treatment and desalination .It also helps support functionalization of nanoscale material surfaces (adding particles for specific purposes), for applications ranging from drug delivery to clothing insulation. Reduced imperfections are also an important factor in determination of the properties of the nanomaterials. Nanosturctures and Nanomaterials selfpurification process in intrinsic material defects will move to near the surface upon thermal annealing. perfection affects the properties of nanomaterials. Due to their nanometer size, nanomaterials are already known to have many novel properties. Many novel applications of the nanomaterials rose from these novel properties have also beenproposed. favors impurities of a that the and This increased materials 8 25/10/2016
Important terms :- Catalyst: chemically take part in the reaction but results in increase in rate of reaction by decreasing theactivationenergy a substance that does not Colloid: a homogenous suspension of a dispersoid in a continuous medium; it may beasolid, liquid orgas 9 25/10/2016
Principleof Nanotechnology Classification of Nanomaterials Nanomaterials have extremely small size which having at least one dimension (100 nm or less). Nanomaterials can be nanoscale in one dimension (e.g. surface films), two dimensions (e.g. strands or fibres), or three dimensions (e. g. particles). They can exist in single, fused, aggregated or agglomerated forms with spherical, tubular, and irregular shapes. Common types of nanomaterials include nanotubes, dendrimers, quantum Nanomaterials have applications in the field of nano technology, and displays different physical chemical characteristics from normal materials (i.e., silver nano, carbon nano tube, fullerenet, carbon nano, dots and fullerenes. 25/10/2016 silica). 10
According to Siegel, Nanostructured materials are classified as Zero dimensional, one dimensional, two dimensional, threedimensional nanostructures. Nanomaterials are materials which are characterized by an ultra fine grain size or by a dimensionality limited to 50nm. Nanomaterials can be created with various modulation dimensionalities as defined by Richard W. Siegel , zero, one, two and three dimensions asshown in theabove Figure 1. 11 25/10/2016
Figure 1: Classification of Nanomaterials (a) 0D spheres and clusters (b) 1D nanofibers, wires, and rods (c) 2D films, plates, and Networks (d) 3D nanomaterials. 12 25/10/2016
Considering the three dimensions, we can classify each system by the numberof dimensionsthatare not in the nanometricrange: 0-dimensional systems: in these materials pores have all three dimensions in nanometric range and, often, have spherical shapes and are directly connected with the external ambient. They are generally used to store single molecules, stabilized inside cavities by three-dimensional interactions with the walls. An example of this typeof materials arezeolites. 1-dimensional systems: these materials are formed by parallel channels of micrometric length, often organized in regular patterns (such as hexagonal). Channels could be straight or curved, isolated or communicating, but generally they retain the same pattern along all the material. Materials with nanochannels could be used as nanoreactors, as diffusion systems in purifying membranes or for gasstorage. Anexampleof this type iscarbon nanotubesCNTs. 13 25/10/2016