Bulk to Nanomaterials

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 8, Issue 1, January 2018)

122

Bulk to Nanomaterials

Dr. Ujjwal Kumar Bhaskar

1_{Department of Physics, Sreegopal Banerjee College, Bagati, Magra, Hooghly, PIN-712148}

Abstract— In the present article the hot focus nano-structured materials are presented in terms of their key features, classifications, method of preparations and application as well as their adverse effect on living beings in popular ways. The nanomaterials are the ultra fine particles of bulk material in nanometer dimension (1nm - 100nm). The nanomaterials behave in different way from their bulk counter part because of large surface area which makes them highly reactive. This lucrative character makes the nanomaterials a core focus in present day in industrial and commercial applications. The article emphasis on the synthesis, applications and hazards of manmade industrial nanomaterials.

Keywords— Nanocrystalline, Ball-milling, Nanoparticle, Composite, Nanotube.

I. INTRODUCTION

The nanomaterials are extraordinary for their extremely small feature size and have the potential for wide-ranging industrial, biomedical and electronic home applications. The nanomaterials in general can be metals, ceramics, polymeric materials, or composite materials. The ultra fine particles having grain size in the range of 1-100 nm are in general known as nanomaterials. The unit of nanometer (10-9 m) derives its prefix nano from a Greek word meaning dwarf or extremely small. There are three to five atoms can be lined in a span of one nanometer. The nano-structured world lies in the midway between the scale of atomic and quantum phenomena, and the scale of bulk materials. The properties of the nanomaterial are greatly governed by the laws of atomic physics and quantum mechanics, rather than the traditional behaviours of the bulk materials. The widespread interest in nanomaterials although grows in recent years but the concept was raised over 40 years ago. The nanomaterials have actually been produced and used by humans for hundreds of years - the beautiful ruby red color of some glass is due to gold nanoparticles trapped in the glass matrix and the colourations effect in peacock’s feather, silky nature of lotus leaf is actually due to presence naturally occurring of nanomaterials [1, 2].

In present days, the nanomaterials have been a core focus of nanoscience and nanotechnology which is an ever-growing multidisciplinary field of study attracting tremendous interest, investment and have entered a commercial application, exploration and effort in world

wide research and development . Nanoporous materials as

a subset of nanostructured materials possess unique surface, structural, and bulk properties that underline their important uses in various fields such as ion exchange, separation, catalysis, sensor, biological molecular isolation and purifications. Nanoporous materials are also of scientific and technological importance because of their vast ability to adsorb and interact with atoms, ions and molecules on their large interior surfaces and in the nano-sized pore space. These offer new opportunities in areas of including chemistry, guest-host synthesis and molecular manipulations and reaction in the nanoscale for making nanoparticles, nanowires and other quantum nanostructures [3, 4].

II. RADICAL CHANGES AT THE NANO SCALE LEVEL

When scientists synthesize nanomaterials in the laboratory, everything we understand about a material at a macroscopic level changes at a glance. Color, chemical properties, conductivity - it all changes. At the nanoscale level, the quantum properties of materials overpower its bulk properties and stuff gets unusual. The graphite and carbon nanotubes are familiar due to honeycomb (graphene) structure; however, the simple structural change from sheets to tubes changes carbon from one of the softest elements (graphite) to one of the strongest (carbon nanotubes). Gold nanoparticles trade their glossy yellow glitter for a dark reddish shade [3]. The numerous differences between nanoscale and macroscale materials have flung the door wide open for new technology and applications. From medicine to energy to information technology, the nanomaterial revolution is coming.

III. IMPORTANT FEATURES

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IV. DIFFERENT ROUTES TO SYNTHESIZE NANOMATERIALS

The nanomaterials synthesized in different physical and chemical routes which can be classified in two broad categories.

4.1. Top-down method:

a) Mechanical milling or Ball-milling.

The ball-milling or mechanical milling is one of the easiest way to synthesize nannomaterials of different kinds from bulk materials. The researchers from different parts of world uses this method to synthesize nano-structured materials like nano-nitrides (TiN, TiCN, TiSiN, TiAlN, TiNiN) [5] , nano-carbides (TiC, TiAlC, TiNiC) [6], quantum dots (ZnS, ZnTe, CdS, CdTe, CdZnS) [7], nano-ferites [8].

4.1.1. Merits of Ball-milling:

The merits of ball-milling are- i) It is single step single pot method, ii) No sophisticated instruments are required, iii) With in short duration of time large quantity of nanocrystalline materials can be synthesized, iv) No hazardous chemicals are required. Only elemental powders in stoichiometric ratio are required to prepare the nanocrystalline materials of desired chemical composition, v) The particle size can be made down to ~ 3nm – 4nm, vi) Synthesis of new equilibrium phases with severe localized plastic deformation of the materials can be achieved, vii) Alloying and complete solid solubility of materials can be done, viii) Solid state amorphization of materials can be achieved, ix) Reduction of metal oxides by hydrogen /carbon is possible.

4.1.2. Demerits of ball-milling:

There are different demerits of the ball-milling. i) The nanocrystalline materials may contaminate from grinding media, ii) Stickiness of nanomaterials during dry grinding, iii) Excessive amount of heat generates during ball-milling of material to be ground, iv) Combustible liquids with boiling point <1200C can not be used in this method.

4.2. Bottom-up method:

In bottom-up method the nanocrystalline materials are synthesized from molecular level to nano-structured level by using the following methods.

a) Sol-gel, b) Chemical vapor deposition technique, c) Chemical Co-precipitation, d) Plasma spraying.

The above methods are not so user friendly to synthesize nanomaterials because of following reasons.

i) Costly and sophisticated instruments are required, ii) Life hazardous chemicals are necessary to synthesize nanocrystalline materials, iii) It is a time consuming method.

V. CLASSIFICATION OF NANOMATERIALS

Nano-structured materials can be classified in a number of ways. They can be arranged according to chemical composition (individual elements such as silver or carbon, alloys or other chemical compounds), size (diameter, length) or shape (wires, tubes, particles, combinations). Additionally, they can be classified according to their various properties (surface area, electrical or thermal conductivity, strength, optical properties, etc). However, at present nanomaterials could be prearranged into four types [9]. (i) Carbon Based Materials, (ii) Metal Based Materials, (iii) Dendrimers, (iv) Composites.

Carbon Based nanomaterials are composed mostly of carbon, most commonly, they takes the form of a hollow spheres, ellipsoids, or tubes. Spherical and ellipsoidal carbon nanomaterials are referred to as fullerenes, while cylindrical ones are called nanotubes. These particles have many potential applications, including improved films and coatings, stronger and lighter materials, and applications in electronics.

Metal Based nanomaterials include quantum dots (QDs), nanogold, nanosilver and metal oxides, such as titanium dioxide. A quantum dot is a closely packed semiconductor nanocrystal comprised of hundreds or thousands of atoms, and whose size is on the order of a few nanometers to a few hundred nanometers. The optical properties of QDs change with the changing the size of nanoparticles.

Dendrimers: These nanomaterials are nanosized polymers built from branched units. The surface of a dendrimer has numerous chain ends, which can be tailored to perform specific chemical functions. The three-dimensional dendrimers contain interior cavities into which other molecules could be placed and they may be useful for drug delivery.

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VI. PROPERTIES OF NANOMATERIALS

Mechanical properties: The large amount of grain

boundaries in bulk materials made of nanoparticles allows extended grain boundary sliding leading to high plasticity [9].

Catalytic Properties: Due to their large surface area, nanoparticles made of transition metal oxides exhibit interesting catalytic properties. In special cases, catalysis may be enhanced and more specific by decorating these particles with gold or platinum clusters [9] .

Optical Properties: Distributions of non-agglomerated

nanoparticles in a polymer are used to tune the refractive index of materials. In addition to such a process may produce materials with non-linear optical properties. Gold or CdSe nanoparticles in glass lead to red or orange coloration. Semi-conducting nanoparticles and some oxide-polymer nanocomposites exhibit fluorescence showing blue shift with decreasing particle size [2].

Magnetic Properties: In magnetic nanoparticles, the energy of magnetic anisotropy may be so small that the magnetization vector fluctuates thermally; this is called superparamagnetism. Such a material is free of remanence, and coercitivity. Touching the superparamagnetic particles loose this special property by interaction, except the particles are kept at distance. Combining particles with high energy of anisotropy with superparamagnetic ones leads to a new class of permanent magnetic materials [9].

VII. 7.APPLICATIONS

The unique properties of these various types of purposely produced nanomaterials give them novel electrical, catalytic, magnetic, mechanical, thermal, or imaging features that are highly desirable for applications in commercial, medical, military, and environmental sectors [10].

Next-Generation Computer Chips: The microelectronics

industry demands the miniaturization of chip size, where the elements of the circuits, such as transistors, resistors, and capacitors, are reducing in size by using smart nanomaterials. However significant reduction in their size, the microprocessors, which contain these components, can run much faster, thereby enabling computations at far greater speeds.

Phosphors for High-Definition TV: The resolution of a television, or a monitor, depends greatly on the size of the pixel. The resolution improves with the increase of the pixel density of the monitors.

Nanocrystalline Zinc Selenide (ZnSe), Zinc sulfide (ZnS), Cadmium Sulfide (CdS), and Lead Telluride (PbTe) synthesized by the sol-gel techniques plays crucial roll for improving the resolution of monitors.

Tougher and Harder Cutting Tools: Tools for cutting and trimming made out of or coated with nanocrystalline materials, such as Tungsten carbide (WC), Tantalum carbide (TaC), and Titanium carbide (TiC), Titanium nitride (TiN) synthesize by mechanical alloying (MA) are much harder, much more wear-resistant, erosion-resistant, and last longer than their conventional (large-grained) counterparts.

Better Insulation Materials: Nanocrystalline materials synthesized by the sol-gel technique result in foam like structures called "aerogels." These aerogels are porous and extremely lightweight; yet, they can bear loads equivalent to 100 times their weight. Since they are porous and air is trapped at the interstices, aero gels are currently being used for insulation in offices, homes, etc.

Elimination of Pollutants: Due to their enhanced chemical

activity, nanocrystalline materials can be used as catalysts to react with harmful and toxic gases such as carbon monoxide and nitrogen oxide in automobile catalytic converters and power generation equipment to prevent environmental pollution arising from burning gasoline and coal.

High-Power Magnets: It has been shown that magnets made of nanocrystalline Yttrium-Samarium-Cobalt grains possess very unusual magnetic properties due to their extremely large surface area. Typical applications for these high-power rare-earth magnets include ultra-sensitive analytical instruments, and magnetic resonance imaging (MRI) in medical diagnostics.

High Energy Density Batteries: Nickel-metal hydride (Ni-MH) batteries made of nanocrystalline nickel and metal hydrides made it best candidates for far less frequent recharging and to last much longer because of their large grain boundary (surface) area and enhanced physical, chemical, and mechanical properties.

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International Journal of Emerging Technology and Advanced Engineering

125 Ductile, Machinable Ceramics: Nanocrystalline ceramics, such as silicon nitride (Si3N4) and silicon carbide (SiC) have been used successfully in automotive applications such as high-strength springs, ball bearings and valve lifters due to its good formability and machinabilty along with excellent physical, chemical, and mechanical properties. They are also used as components in high-temperature furnaces because of high melting point.

Nanomaterials in Aviation Industry: The growth and

success of the Aviation Industry depends largely on factors ranging from reduction of weight, use of smart materials

with multidimensional properties, eco-friendly low

consumption fuels, faster and highly responsive

communications systems, extended and safe life, less or no repairs spare parts and many more. The aircraft

components made of high strength low fatigue

nanocrystalline materials greatly increase its life span. The light weight high strength carbon nanocomposite fiber offer a significant reduction in the grain size over conventional materials which in turn increase fatigue life by an average of 200-300%. Moreover light weight aircrafts can fly faster and more efficiently with less aviation fuel. The spacecrafts operated at elevated-temperature (such as rocket engines, thrusters, and vectoring nozzles) require high strength light weight heat resistant nanocomposite materials and nanomaterials are perfect candidates for spacecraft applications, as well.

Better and Future Weapons: Conventional guns, such as cannons, 155 mm howitzers, and multiple-launch rocket system (MLRS), utilize the chemical energy of gun powder in which the penetrator can be propelled is approximately 1.5-2.0 km/sec. In ultramodern weapons the ectromagnetic launchers (EML guns) or rail guns use the electrical energy and the concomitant magnetic field (energy) to propel the penetrators /projectiles at velocities up to 10 km/sec. The greater the energy, the greater is the damage inflicted on the target. In order to satisfy these requirements, a nanocrystalline composite material made of tungsten, copper, and titanium diboride is being used as a potential candidate. This nanocomposite possesses the requisite electrical conductivity, adequate thermal conductivity, excellent high strength, high rigidity, hardness, and wear/erosion resistance. This results in longer-lasting, wear-resistant, and erosion-resistant rail guns which can be fired more frequently and often than their conventional counterparts.

Longer-Lasting Satellites: The satellites which are being used for both defense and civilian applications, utilize thruster rockets to remain in or change their orbits (orbit correction) due to a variety of factors including the influence of gravitational forces exerted by the earth and other celestial bodies. The life of these satellites depends on the amount of fuel it can carry on board. It is the fact that more than 1/3 of its fuel is wasted by these repositioning thrusters due to incomplete and inefficient combustion of the fuel such as hydrazine. The reason behind the incomplete and inefficient combustion is that the onboard igniters wear out quickly and cease to perform

effectively. The nanomaterials like nanocrsytalline

tungsten-titanium diboride-copper composite are the potential candidates for enhancing the life and performance igniters.

Medical applications:Nanoparticles used as drug and gene

delivery (core shell structure), bio detection of pathogens and proteins, separation and purification of biological molecules and cells, and detection of functions of all vital organ systems, vascular circulation condition.

Anti-microbial: Nanocrystalline silver used as an

antimicrobial agent for the treatment of wounds, burn dressing that is coated with nanocapsules containing antibiotics and wood & textile fibers preservation. Nanoparticle creams contain nitric oxide gas, which is known to kill bacteria.

Nanotechnology to reduce water pollution: Gold tipped carbon nanotubes used to trap oil drops polluting water. Iron oxide nanoparticles used to clean arsenic from water of wells.

UV-Attenuating Coatings: -Nano sized Zink oxide (ZnO) used as UV protective coatings.

VIII. NANOMATERIALS AND ENVIRONMENTAL ISSUES

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International Journal of Emerging Technology and Advanced Engineering

126 Size is the key factor. Silver nanoparticles are being used in toothpastes, soaps and face creams, food packaging, clothing, household appliances, disinfectants and wound dressings. Silver nanoparticles have a strong ability to kill 650 different bacteria. However it may also kill beneficial bacteria in ecosystem [13 - 15]. Experiments so far have also shown possible harmful effects on invertebrates and fish, including effects on behaviour, reproduction and development. There is less research to date on soil systems and terrestrial species, and it is not clear whether laboratory results relate to what may happen out in the real world. But we hope for new pollution free world.

IX. SOCIAL RESPONSIBILITY

Potential impact of nanomaterials on human health is often anticipated but in reality often not quantified. This relative lack of evidence has led both to articulation of public concern and commitment by public policy-makers to strengthen the regulatory environment. The manufacturers of nanomaterials based health products, home appliances and beauty products should mention the size of nanomaterials used in the products and possible side effects may arise in that size range of particles. In actual situation the manufactures is always drumming the quality of products. Peoples must be careful before using the particular nanomterials based products [16]. The policy makers should build-up strong environment policy to protect environment and living beings from any kind of pollution may arise out of nanomaterials and there should be provision of tough punishment.

X. CONCLUSIONS

It is an important issue that in near future the products of engineered nanomaterials cover and swallow us. We must use the time and cost saving characteristics of nanomaterials and at the same time there should be minimum awareness regarding its dark sides. So many researches are going on throughout the glob for

characterizations and possible applications of

nanomaterials.

The international organizations must initiate worldwide research projects regarding use and safety assessment of nanomaterials for unbiased and holistic knowledge.

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