14-04-2011, 03:21 PM
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1.INTRODUCTION
1.1 GREEN ENGINEERING:
Green Engineering is the design, commercialization and use of processes and products that are feasible and economical while:
Reducing the generation of pollution at the source.
Minimizing the risk to human health and the environment.
Green engineering embraces the concept that decisions to protect human health and the environment can have the greatest impact and cost effectiveness when applied early to the design and development phase of a process or product.
The principles of green engineering are as follows:
1) Engineer processes and products holistically, use system analysis and integrate environmental impact assessment tools.
2) Conserve and improve natural ecosystems while protecting human health and well being.
3) Use life cycle thinking in all engineering activities.
4) Ensure that all material and energy inputs and outputs areas inherently safe and benign as possible.
5) Minimize depletion of natural resources.
6) Strive to prevent waste.
7) Develop and apply engineering solutions, while being cognizant of local geography aspirations and cultures.
8) Create engineering solutions beyond current and dominant technologies; improve, innovate and invent (technologies) to achieve sustainability.
9) Actively include communities and stakeholders in development of engineering solutions.
1.2 NANOTECHNOLOGY
Nanotechnology is the engineering of functional systems at the molecular scale. This covers current work and concepts that are more advanced. In its original sense, nanotechnology refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, highly advanced products. Nanotechnology is often referred to as a general-purpose technology. That’s because in its mature form it will have significantimpact on almost all industries and all areas of society. It offers better built, longer lasting, cleaner, safer, and smarter products for the home, for communications, for medicine, for transportation, for agriculture, and for industry in general. Like electricity or computersbefore it,nanotechwill offer greatly improved efficiency in almost every facet of life. Butas a
general-purpose technology, it will be dual-use, meaning it will have many commercial uses and it also will have many military uses -- making far more powerful weapons and tools of surveillance. Thus it represents not only wonderful benefits for humanity, but also grave risks.
A key understanding of nanotechnology is that it offers not just better products, but a vastly improved means of production. A computer can make copies of data files -- essentially as many copies as you want at little or no cost. It may be only a matter of time until the manufacture of products becomes as cheap as the copying not only will allow making many high-quality products at very low cost, but it will allow making new nanofactories at the same low cost and at the speed. This unique (outside of biology, which is) ability to reproduce its own same rapid means of production is why nanotech is said to be an exponential technology. It represents a manufacturing system that will be able to make more manufacturing systems -- factories that can build factories -- rapidly, cheaply, and cleanly. The means of production will be able to reproduce exponentially, so in just a few weeks a few nanofactories conceivably could become billions. It is a revolutionary, transformative, powerful, and potentially very dangerous -- or beneficial – technology.
It is important to recognize some unique features about nanotechnology. First, it is the amalgamation of knowledge from chemistry, physics, biology, materials science, and various engineering fields. It epitomizes the concept of the whole being greater than the sum of theparts.
Second, nanoscale science and engineering span different scales. Nanostructures and nanoscale phenomena are generally embedded in micro- and macrostructures, and their interactions are important. The connection between scales—nano to micro to macro—is also a critical aspect of integration.
In addition, it is often difficult to isolate nanoscale phenomena as we do at customary scales. That is, thermal, electronic, mechanical, and chemical effects are often related to each other. By changing one, it is possible to influence the others. This, of course, emphasizes the need for interdisciplinary knowledge.
1.3 GREEN NANOTECHNOLOGY
Green nanotechnology is the development of clean technologies, "to minimize potential environmental and human health risks associated with the manufacture and use of nanotechnology products, and to encourage replacement of existing products with new nano-products that are more environmentally friendly throughout their lifecycle."
Nanotechnology is an emerging field that has great potential for use in commercial, defence and security applications. Nanomaterials and the manufacturing techniques used to create them, however, may pose adverse environmental, health and safety effects. One of the challenges facing this new industry is the design of nanomaterials and nano-manufacturing methods that provide maximum efficiency while minimizing these hazards. Merging green chemistry and nano-science will provide opportunities to meet these challenges and to develop sustainable technologies and materials.
Our goals are to implement the principles of green nano-science to:
(1) Design environmentally benign nanoparticles, test for putative toxicity and redesign as necessary; we are developing methods to prepare libraries of functionalized metal nanoparticles in which the size, shape and functionality can be widely varied. We will study the accumulation of nanoparticles within organisms and the impacts of these nanoparticles on viability, gene expression and development. These data will be used to guide the development of more benign nanoparticles for a wide range of applications. The surface of these nanoparticles will be modified which will direct self-assembly, tune electronic or optical coupling, and further enhance the biologically safety of these nanoparticles.
(2) Develop greener methods for large-scale nanoparticle production through green nano-manufacturing technologies; we will identify acceptable nanoparticle formation reactions that can be carried out in a single solvent phase and that will permit control of particle size. From these studies we will scale up production and develop an integrated micro-reactor platform for deploying the single solvent phase chemistries. We are also exploring gas-phase production of ceramic nanoparticles in micro-reactors to produce materials that should expand our capabilities to produce novel devices for sensors and medicine.
(3) Discover efficient approaches for using nanoparticles in the development of novel nano-devices; Nanomaterials are driving innovation in optical and electronic devices, however, realizing the full potential of nanoscale matter in device technologies requires the integration of the nanoscale building blocks with other components of the device. Nanostructures can also be important precursors in the low-cost and greener manufacture of more traditional micro scaledevices and to exotic new materials. Thus, developing environmentally-benign assembly methods and identifying approaches to interface nanomaterials with macroscopic structures are being explored to produce greener, high-performance devices and nanostructured materials.
A marriage of nanotechnology with green engineering serves two important purposes.
First, emerging nanotechnologies could be made clean from start. It would be foolhardy to develop a new nanotechnology infrastructure from an old industrial model that would generateanother set of environmental problems. While nanotechnology will never be as green as Mother Nature, approaching a new nano approach to the technology’s development ultimately promises to shift society into a new paradigm that is proactive, rather than reactive, when it comes to environmental problems.
Second, green technologies that benefit the environment could use nanotechnology to boost performance. In other words, nanotechnology could help us make every atom count-for example, by allowing us to create ultra efficient catalysts, detoxify wastes, assemble useful molecular machines and efficiently convert sunlight to energy. It could potentially contribute for long term sustainability for future generations, as more green products and processes replace the old harmful and wasteful ones.
A huge amount of research and development activity has been devoted to nano-scale related technologies in recent years. The National Science Foundation projects nanotechnology related products will become a $1 trillion industry by 2015 [1]. Nano-scale technology is defined as any technology that deals with structures or features in the nanometer range or that are less than 100 nanometres, about one-thousandth the diameter of a human hair, and larger than
about 1 nm, the scale of the atom or of small molecules.
Below about 1 nm, the properties of materials become familiar and predictable, as this is the established domain of chemistry and atomic physics. It should be noted that nanotechnology is not just one, but many wide ranging technologies in many technical disciplines including but not limited to chemistry, biology, physics, material science, electronics, MEMS and self-assembly. Nano-structures have the ability to generate new features and perform new functions that are more efficient than or cannot be performed by larger structures and machines. Due to the small dimensions of nano-materials, their physical/chemical properties (e.g. stability, hardness, conductivity, reactivity,
optical sensitivity, melting point, etc.) can be manipulated to improve the overall properties of conventional materials. At nanometer scales, the surface properties start becoming more dominant than the bulk material properties, generating unique material attributes and chemical reactions. More fundamentally, the electronic structure of materials becomes size-dependent as the dimensions enter the nanoscale.
Delocalized electronic states as in a metal or a semiconductor are altered by the finite dimensions. Hence, the optical properties, including light absorption and emission behaviour, will be altered, the fact that nanoscale features are smaller
than the wavelength of visible photons also impacts light scattering, enabling the design of nanocrystalline ceramics that are as transparent as glass. Changes in the bonding at the surface of a nanoparticle will affect the electronic structure as well, and the implications for the reactivity of the surface can be significant. Beyond the electronic structure, nanostructuring can also affect transport properties markedly.
Nanoscale features that are smaller than or comparable to the wavelengths or mean-free paths of phonons (quanta of lattice vibrations) or electrons permit the design of materials with thermal and electrical conductivity that may be outside the range accessible with ordinary materials. The most significant nano-structures investigated to date are made from single atomistic layers of carbon. These structures include hollow ball shaped “Bucky balls” (Fullerene - C60), carbon nanotubes (CNTs) and graphene sheets which have a very interesting range of mechanical, thermal and electrical properties. It should also be noted that even though the environmental and health effects of nano-scale structures are poorly understood at this time, nano-scale-based technologies are already being used in some industrial applications. A series of nano-materials, including metal nanoparticles and nano-powders, magnetic fluids, nano-adhesives, nanocomposite polymers, and nanocoatings (anti-fog, antireflective, wear and scratch resistant, dirt repellent, biocide, etc.) are being introduced for potential application in the automotive market.
Metal nanoparticles are being considered for potential use in catalytic converters since the catalytic reactivity is significantly enhanced due to the increased surface area and altered electronic structure of the metal nanoparticle.
Coolants utilize nanoparticles and nano-powders to increase the efficiency of heat transfer and potentially reduce the size of the automotive cooling equipment. Some manufacturers are currently using nanomagnetic fluids in shock absorbers to increase vibration control efficiency. Wear-resistant, hard surface nano-coatings are being investigated for applications in bearings, cylinders, valves, and other highly stressed areas.
Nano-layers of semiconducting materials provide high efficiency electronic components and systems with a longer lifetime. Sensors based on nanolayer structures are used in engine control, airbag, anti-lock brake and electronic stability program systems. Nanoparticles also support the optimization
of conventional components like batteries, catalysts, solar cells or fuel cells.
The most promising automotive applications of nanotechnology include the following:
• Improved materials with CNTs, graphene and other nanoparticles/structures
• Improved mechanical, thermal, and appearance properties for plastics
• Coatings & encapsulates for wear and corrosion resistance, permeation barriers, and appearance
• Cooling fluids with improved thermal performance
• Joining interfaces for improved thermal cycle and crack resistance
• Metal alloys with greater mechanical strength
• Metal matrix and ceramics with improved mechanical properties
• Solder materials with crack resistance or lower processing temperature
• Displays with lower cost and higher performance
• Batteries for electric vehicles and fuel cells with improved energy capacity
• Automotive sensors with nano-sensing elements, nanostructures and nano-machines
• Hybrid electric vehicles using electrical interconnects for high-frequency and high-power applications
• Electrical switching including CNT transistors, quantum transistors, nano-electro-mechanical switches, electron emission amplification, and more efficient solar cells
• Self-assembly using fluid carriers
2.THE ROLE OF MECHANICAL ENGINEERING IN NAN
Itis fair to ask what the role of mechanical engineering in nanotechnology will be. In fact,quite abit of nano scale science and engineering is already performed by mechanical engineers.
For example, mechanical engineershave been essential in developing instruments such as nano indenters and atomic force microscopes, which are used for mechanical testing, nano scale imaging, and metrology. Issues of feedback control of such systems are unique because of the nano scale precision required in positioning and the ability to measure forces down to piconewton levels.
Mechanical engineering issues extend to instruments for nanoparticle and aerosol detection and characterization, as well as to various forms of nanoscale imaging. Magnetic data storage technology already has many features that fall well into the nanometer size range, and requires mechanical engineering knowledge and expertise to further its development.
It is important to recognize some unique features about nanotechnology. First, it is the amalgamation of knowledge from chemistry, physics, biology, materials science, and various engineering fields. It epitomizes the concept of the whole being greater than the sum of the parts.
Second, nanoscale science and engineering span different scales. Nanostructures and nanoscale phenomena are generally embedded in micro- and macrostructures, and their interactions are important. The connection between scales—nano to micro to macro—is also a critical aspect of integration.
In addition, it is often difficult to isolate nanoscale phenomena as we do at customary scales. That is, thermal, electronic, mechanical, and chemical effects are often related to each other. By changing one, it is possible to influence the others. This, of course, emphasizes the need for interdisciplinary knowledge.
There are many concepts in mechanical engineering that are critical in the development of nanotechnology. It is incumbent upon mechanical engineers to provide depth in these areas.
At present, nanotechnologists can create simple structures, like this silicon carbide tower.
One of the most important issues related to nanotechnology is systems integration and packaging. Researchers have been able to study individual nanostructures and have even synthesized building blocks such as nanoparticles and nanowires. But how do we integrate these building blocks in a rational manner to make a functional device or a system? This step requires design based on the understanding of nanoscale science, and on new manufacturing techniques.
