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Nanomaterials
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Nanomaterials
Fullerenes
Carbon nanotubes
Fullerene chemistry
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Nanotechnology
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Nanomaterials are materials with morphological features smaller than a one tenth of a
micrometre in at least one dimension.[1] Despite the fact that there is no consensus upon
the minimum or maximum size of nanomaterials, with some authors restricting their size
to as low as 1 to ~30 nm, a logical definition would situate the nanoscale between
microscale (0.1 micrometre) and atomic/molecular scale (about 0.2 nanometers). See
Figure "Classification of nanostructured materials".
Contents
[hide]
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1 Fundamental concepts
2 Size concerns
3 Materials used in nanotechnology
o 3.1 Fullerenes
o 3.2 Nanoparticles
4 Chemical Processing of Ceramics
o 4.1 Microstructural uniformity
o 4.2 Sol-gel processing
5 Safety of Manufactured Nanomaterials
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6 See also
7 References
8 Other References
9 Further reading
10 External links
[edit] Fundamental concepts
An aspect of nanotechnology is the vastly increased ratio of surface area to volume
present in many nanoscale materials which makes possible new quantum mechanical
effects, for example the “quantum size effect” where the electronic properties of solids
are altered with great reductions in particle size. This effect does not come into play by
going from macro to micro dimensions. However, it becomes pronounced when the
nanometer size range is reached. A certain number of physical properties also alter with
the change from macroscopic systems. Novel mechanical properties of nanomaterials is a
subject of nanomechanics research. Catalytic activities also reveal new behaviour in the
interaction with biomaterials.
Nanotechnology can be thought of as extensions of traditional disciplines towards the
explicit consideration of these properties. Additionally, traditional disciplines can be reinterpreted as specific applications of nanotechnology. This dynamic reciprocation of
ideas and concepts contributes to the modern understanding of the field. Broadly
speaking, nanotechnology is the synthesis and application of ideas from science and
engineering towards the understanding and production of novel materials and devices.
These products generally make copious use of physical properties associated with small
scales.
As mentioned above, materials reduced to the nanoscale can suddenly show very
different properties compared to what they exhibit on a macroscale, enabling unique
applications. For instance, opaque substances become transparent (copper); inert
materials attain catalytic properties (platinum); stable materials turn combustible
(aluminum); solids turn into liquids at room temperature (gold); insulators become
conductors (silicon). Materials such as gold, which is chemically inert at normal scales,
can serve as a potent chemical catalyst at nanoscales. Much of the fascination with
nanotechnology stems from these unique quantum and surface phenomena that matter
exhibits at the nanoscale.
Nanosize powder particles (a few nanometres in diameter, also called nanoparticles) are
potentially important in ceramics, powder metallurgy, the achievement of uniform
nanoporosity and similar applications. The strong tendency of small particles to form
clumps ("agglomerates") is a serious technological problem that impedes such
applications. However, a number of dispersants such as ammonium citrate (aqueous) and
imidazoline or oleyl alcohol (nonaqueous) are promising solutions as possible additives
for deagglomeration.
[edit] Size concerns
Another concern is that the volume of an object decreases as the third power of its linear
dimensions, but the surface area only decreases as its second power. This somewhat
subtle and unavoidable principle has huge ramifications. For example the power of a drill
(or any other machine) is proportional to the volume, while the friction of the drill's
bearings and gears is proportional to their surface area. For a normal-sized drill, the
power of the device is enough to handily overcome any friction. However, scaling its
length down by a factor of 1000, for example, decreases its power by 10003 (a factor of a
billion) while reducing the friction by only 10002 (a factor of "only" a million).
Proportionally it has 1000 times less power per unit friction than the original drill. If the
original friction-to-power ratio was, say, 1%, that implies the smaller drill will have 10
times as much friction as power. The drill is useless.
For this reason, while super-miniature electronic integrated circuits are fully functional,
the same technology cannot be used to make working mechanical devices beyond the
scales where frictional forces start to exceed the available power. So even though you
may see microphotographs of delicately etched silicon gears, such devices are currently
little more than curiosities with limited real world applications, for example in moving
mirrors and shutters. Surface tension increases in much the same way, thus magnifying
the tendency for very small objects to stick together. This could possibly make any kind
of "micro factory" impractical: even if robotic arms and hands could be scaled down,
anything they pick up will tend to be impossible to put down. The above being said,
molecular evolution has resulted in working cilia, flagella, muscle fibers and rotary
motors in aqueous environments, all on the nanoscale. These machines exploit the
increased frictional forces found at the micro or nanoscale. Unlike a paddle or a propeller
which depends on normal frictional forces (the frictional forces perpendicular to the
surface) to achieve propulsion, cilia develop motion from the exaggerated drag or laminar
forces (frictional forces parallel to the surface) present at micro and nano dimensions. To
build meaningful "machines" at the nanoscale, the relevant forces need to be considered.
We are faced with the development and design of intrinsically pertinent machines rather
than the simple reproductions of macroscopic ones.
All scaling issues therefore need to be assessed thoroughly when evaluating
nanotechnology for practical applications.
[edit] Materials used in nanotechnology
Materials referred to as "nanomaterials" generally fall into two categories: fullerenes, and
inorganic nanoparticles. See also Nanomaterials in List of nanotechnology topics
[edit] Fullerenes
Buckminsterfullerene C60, also known as the buckyball, is the smallest member of the
fullerene family.
Main article: Fullerene
The fullerenes are a class of allotropes of carbon which conceptually are graphene sheets
rolled into tubes or spheres. These include the carbon nanotubes which are of interest
both because of their mechanical strength and also because of their electrical properties.
For the past decade, the chemical and physical properties of fullerenes have been a hot
topic in the field of research and development, and are likely to continue to be for a long
time. In April 2003, fullerenes were under study for potential medicinal use: binding
specific antibiotics to the structure of resistant bacteria and even target certain types of
cancer cells such as melanoma. The October 2005 issue of Chemistry and Biology
contains an article describing the use of fullerenes as light-activated antimicrobial agents.
In the field of nanotechnology, heat resistance and superconductivity are among the
properties attracting intense research.
A common method used to produce fullerenes is to send a large current between two
nearby graphite electrodes in an inert atmosphere. The resulting carbon plasma arc
between the electrodes cools into sooty residue from which many fullerenes can be
isolated.
There are many calculations that have been done using ab-initio Quantum Methods
applied to fullerenes. By DFT and TDDFT methods one can obtain IR, Raman and UV
spectra. Results of such calculations can be compared with experimental results.
[edit] Nanoparticles
Main article: Nanoparticle
Nanoparticles or nanocrystals made of metals, semiconductors, or oxides are of particular
interest for their mechanical, electrical, magnetic, optical, chemical and other properties.
Nanoparticles have been used as quantum dots and as chemical catalysts.
Nanoparticles are of great scientific interest as they are effectively a bridge between bulk
materials and atomic or molecular structures. A bulk material should have constant
physical properties regardless of its size, but at the nano-scale this is often not the case.
Size-dependent properties are observed such as quantum confinement in semiconductor
particles, surface plasmon resonance in some metal particles and superparamagnetism in
magnetic materials.
Nanoparticles exhibit a number of special properties relative to bulk material. For
example, the bending of bulk copper (wire, ribbon, etc.) occurs with movement of copper
atoms/clusters at about the 50 nm scale. Copper nanoparticles smaller than 50 nm are
considered super hard materials that do not exhibit the same malleability and ductility as
bulk copper. The change in properties is not always desirable. Ferroelectric materials
smaller than 10 nm can switch their magnetisation direction using room temperature
thermal energy, thus making them useless for memory storage. Suspensions of
nanoparticles are possible because the interaction of the particle surface with the solvent
is strong enough to overcome differences in density, which usually result in a material
either sinking or floating in a liquid. Nanoparticles often have unexpected visual
properties because they are small enough to confine their electrons and produce quantum
effects. For example gold nanoparticles appear deep red to black in solution.
The often very high surface area to volume ratio of nanoparticles provides a tremendous
driving force for diffusion, especially at elevated temperatures. Sintering is possible at
lower temperatures and over shorter durations than for larger particles. This theoretically
does not affect the density of the final product, though flow difficulties and the tendency
of nanoparticles to agglomerate do complicate matters. The surface effects of
nanoparticles also reduces the incipient melting temperature.
[edit] Chemical Processing of Ceramics
[edit] Microstructural uniformity
In the processing of fine ceramics, the irregular particle sizes and shapes in a typical
powder often lead to non-uniform packing morphologies that result in packing density
variations in the powder compact. Uncontrolled agglomeration of powders due to
attractive van der Waals forces can also give rise to in microstructural inhomogeneities.
[2] [3]
Differential stresses that develop as a result of non-uniform drying shrinkage are directly
related to the rate at which the solvent can be removed, and thus highly dependent upon
the distribution of porosity. Such stresses have been associated with a plastic-to-brittle
transition in consolidated bodies, [4] and can yield to crack propagation in the unfired
body if not relieved.
In addition, any fluctuations in packing density in the compact as it is prepared for the
kiln are often amplified during the sintering process, yielding inhomogeneous
densification. [5] [6] Some pores and other structural defects associated with density
variations have been shown to play a detrimental role in the sintering process by growing
and thus limiting end-point densities. [7] Differential stresses arising from inhomogeneous
densification have also been shown to result in the propagation of internal cracks, thus
becoming the strength-controlling flaws. [8]
It would therefore appear desirable to process a material in such a way that it is
physically uniform with regard to the distribution of components and porosity, rather than
using particle size distributions which will maximize the green density. The containment
of a uniformly dispersed assembly of strongly interacting particles in suspension requires
total control over particle-particle interactions. Monodisperse colloids provide this
potential. [9] [10] [11]
Bulk microstructure of a colloidal crystal composed of submicrometre amorphous
hydrated colloidal silica. SEM Micrograph: R.M. Allman III, UCLA (1983)
Monodisperse powders of colloidal silica, for example, may therefore be stabilized
sufficiently to ensure a high degree of order in the colloidal crystal or polycrystalline
colloidal solid which results from aggregation. The degree of order appears to be limited
by the time and space allowed for longer-range correlations to be established. [12] [13] Such
defective polycrystalline colloidal structures would appear to be the basic elements of
submicrometre colloidal materials science, and, therefore, provide the first step in
developing a more rigorous understanding of the mechanisms involved in microstructural
evolution in inorganic systems such as polycrystalline ceramics.
[edit] Sol-gel processing
Main article: Sol-gel
[edit] Safety of Manufactured Nanomaterials
Nanomaterials behave differently than other similarly-sized particles. It is therefore
necessary to develop specialized approaches to testing and monitoring their effects on
human health and on the environment. The OECD Chemicals Committee has established
the Working Party on Manufactured Nanomaterials to address this issue and to study the
practices of OECD member countries in regards to nanomaterial safety.[14]
While nanomaterials and nanotechnologies are expected to yield numerous health and
health care advances, such as more targeted methods of delivering drugs, new cancer
therapies, and methods of early detection of diseases, they also may have unwanted
effects. [15] Increased rate of absorption is the main concern associated with manufactured
nanoparticles.
When materials are made into nanoparticles, their surface area to volume ratio increases.
The greater specific surface area (surface area per unit weight) may lead to increased rate
of absorption through the skin, lungs, or digestive tract and may cause unwanted effects
to the lungs as well as other organs. However, the particles must be absorbed in sufficient
quantities in order to pose health risks.[16]
As the use of nanomaterials increases worldwide, concerns for worker and user safety are
mounting. To address such concerns, the Swedish Karolinska Institute conducted a study
in which various nanoparticles were introduced to human lung epithelial cells. The
results, released in 2008, showed that iron oxide nanoparticles caused little DNA damage
and were non-toxic. Zinc oxide nanoparticles were slightly worse. Titanium dioxide
caused only DNA damage. Carbon nanotubes caused DNA damage at low levels. Copper
oxide was found to be the worst offender, and was the only nanomaterial identified by the
researchers as a clear health risk.[17]
In October 2008, the Department of Toxic Substances Control (DTSC), within the
California Environmental Protection Agency, announced its intent to request information
regarding analytical test methods, fate and transport in the environment, and other
relevant information from manufacturers of carbon nanotubes.[18] The term
"manufacturers” includes persons and businesses that produce nanotubes in California, or
import carbon nanotubes into California for sale. The purpose of this information request
will be to identify information gaps and to develop information about carbon nanotubes,
an important emerging nanomaterial.
DTSC is exercising its’ authority under California Health and Safety Code, Chapter 699,
sections 57018-57020.[19] These sections were added as a result of the adoption of
Assembly Bill AB 289 (2006). They are intended to make information on the fate and
transport, detection and analysis, and other information on chemicals more available. The
law places the responsibility to provide this information to the Department on those who
manufacture or import the chemicals.
DTSC anticipates issuing a formal information request letter in January 2009. Interested
individuals are encouraged to visit their website for the latest up-to-date information at
http://www.dtsc.ca.gov/TechnologyDevelopment/Nanotechnology/index.cfm.
[edit] See also
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Ceramic engineering
Ceramics processing
Colloid
Colloidal crystal
List of emerging technologies
Nanostructures
Nanotechnology
Nanocomposite
Printed electronics
Sol-gel
Transparent materials
[edit] References
1. ^ Cristina Buzea, Ivan Pacheco, and Kevin Robbie "Nanomaterials and
Nanoparticles: Sources and Toxicity" Biointerphases 2 (1007) MR17-MR71.
2. ^ Onoda, G.Y., Jr. and Hench, L.L. Eds. (1979). Ceramic Processing Before
Firing (Wiley & Sons, New York).
3. ^ Aksay, I.A., Lange, F.F., Davis, B.I. (1983). "Uniformity of Al2O3-ZrO2
Composites by Colloidal Filtration". J. Am. Ceram. Soc. 66: C-190.
4. ^ Franks, G.V. and Lange, F.F. (1996). "Plastic-to-Brittle Transition of Saturated,
Alumina Powder Compacts". J. Am. Ceram. Soc. 79: 3161.
5. ^ Evans, A.G. and Davidge, R.W. (1969). "Strength and fracture of fully dense
polycrystalline magnesium oxide". Phil. Mag. 20: 373.
6. ^ Evans, A.G. and Davidge, R.W. (1970). "Strength and fracture of fully dense
polycrystalline magnesium oxide". J. Mat. Sci. 5: 314.
7. ^ Lange, F.F. and Metcalf, M. (1983). "Processing-Related Fracture Origins in
A12O3/ZrO2 Composites II: Agglomerate Motion and Crack-like Internal
Surfaces Caused by Differential Sintering". J. Am. Ceram. Soc. 66: 398.
8. ^ Evans, A.G. (1987). "Considerations of Inhomogeneity Effects in Sintering". J.
Am. Ceram. Soc. 65: 497.
9. ^ Allman III, R.M. and Onoda, G.Y., Jr. (1984). Ceramic Science Group, IBM
T.J. Watson Research Center.
10. ^ Allman III, R.M. (M.S. Thesis, UCLA, 1983). Structural Variations in
Colloidal Crystals.
11. ^ Mangels, J.A. and Messing, G.L., Eds. (1984). "Microstructural Control
Through Colloidal Consolidation". Advances in Ceramics: Forming of Ceramics
9: 94.
12. ^ Whitesides, G.M., et al. (1991). "Molecular Self-Assembly and Nanochemistry:
A Chemical Strategy for the Synthesis of Nanostructures". Science 254: 1312.
13. ^ Aksay, I.A., et al. (2000). "Self-Assembled Ceramics". Ann. Rev. Phys. Chem.
51: 601.
14. ^ “Safety of Manufactured Nanomaterials: About,” OECD Environment
Directorate, OECD.org, 18 July 2007
<http://www.oecd.org/about/0,3347,en_2649_37015404_1_1_1_1_1,00.html>.
15. ^ Small Sizes that Matter: Opportunities and Risks of Nanotechnologies, Joint
report of the Allianz Center for Technology and the OECD International Futures
Programme, ed. Dr. Christoph Lauterwasser, OECD.org 18 July 2007
<http://www.oecd.org/dataoecd/37/19/37770473.pdf> (28).
16. ^ Small Sizes that Matter: Opportunities and Risks of Nanotechnologies, Joint
report of the Allianz Center for Technology and the OECD International Futures
Programme, ed. Dr. Christoph Lauterwasser, OECD.org 18 July 2007
<http://www.oecd.org/dataoecd/37/19/37770473.pdf> (30-32).
17. ^ Chemical & Engineering News Vol. 86 No. 35, 1 Sept. 2008, "Study Sizes up
Nanomaterial Toxicity", p. 44
18. ^ Nanotechnology web page. Department of Toxic Substances Control. 2008.
http://www.dtsc.ca.gov/TechnologyDevelopment/Nanotechnology/index.cfm.
19. ^ Chemical Information Call-In web page. Department of Toxic Substances
Control. 2008.
http://www.dtsc.ca.gov/PollutionPrevention/Chemical_Call_In.cfm.
[edit] Other References
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Hench, L.L., and West. J.K., The Sol-Gel Process, Chem. Rev., Vol.90, p.33 (1990)

Dislich, H., Glass. Tech. Berlin., Vol.44, p.1 (1971), Angew. Chem. Int. Ed., Vol.10,
p.363 (1971)

Matijevic, E., et al., JCIS, Vol.44, p.95 (1973); JCIS, Vol.50, p.567 ((1975); JCIS,
Vol.61, p.302 (1976); J. Inorg. Nucl. Chem., Vol.35, p.3691 (1973)

Matijevic, E., Monodispersed Colloids: Art and Science, Langmuir, Vol.2, p.12 (1986)

Mukherjee, S. P. and Zarzycki, J., Microstructures and Crystallization Behavior of Gels
in the System La203-Si02, J. Am. Ceram. Soc., Vol.62 (1979)

Brinker, C.J. and Mukherjee, S.P., J. Mat. Sci., Vol.16, p.1980 (1981)

D.W. Schaefer, J.F. Joany and P. Pincus, Macromol., Vol.13, p.1280 (1980).

Carturan, G., Gottardi, V., Graziani, M., Physical and Chemical evolutions occurring in
glass formation from alkoxides of silicon, aluminum and sodium, J. Non-Cryst. Solids,
Vol. 29, p. 41 (1978)

Kamiya, K., Sakka, S., Mizutani, M., Glasses prepared from metal alcoholates, Res. Rep.
Fac. Eng., Mie Univ., Vol.2, p.87 (1977), Preparation of silica glass fibers and
transparent silica glass from silicon tetraethoxide, Yogyo KyokaiShi, Vol. 86, p.553
(1978),

S. Sakka and K. Kamiya, J. Non-Cryst. Sol., Vol.42, p.403, (1980)

Yamane, M., Aso, S., Sakaino, T., Preparation of a gel from metal alkoxide and its
properties as a precursor of oxide glass, J. Mat. Sci., Vol. 13 (1978), Low temperature
synthesis of a monolithic silica glass by the pyrolysis of a silica gel, J. Mat. Sci., Vol.14,
p. 607 (1979)

Yoldas, B.E., J. Mat. Sci., Vol. 12, p.1203 (1977), Monolithic glass formation by
chemical polymerization, J. Mat. Sci., Vol.14, p.1843 (1979)

Prochazka,, S. and Klug, S.J., Infrared-Transparent Mullite Ceramic, J. Am. Ceram.
Soc., Vol.66, p.874 (1983)

Sonuparlak,B., et al., Sol-Gel Processing of Infrared Transparent Mullite, Adv. Ceram.
Mater., Vol.3, p.26347 (1988)

Donkai, N., et al., Preparation of Transparent Mullite-Silica Film by Heat-Treatment of
Imogolite J. Mat. Sci., Vol. 27, p.6193 (1992)

Ikesue, A., et al., Fabrication and Optical Properties of High Performance
Polycrystalline Ceramics of Solid State Lasers, J. Am. Ceram. Soc, Vol. 78, p. 1033
(1995), Polycrystalline Lasers, Optical Materials, Vol. 19, p.183 (2002)

Tachiwaki, T., et al., Novel Synthesis of YAG leading to Transparent Ceramics, Solid
State Communications, Vol. 119, p. 603 (2001)

Rabinovitch, Y., et al., Transparent Polycrystalline Neodymium-Doped YAG, Optical
Materials, Vol.24, p.345 (2003)

Wen, L.,et al., Synthesis of Nanocrystalline Yttria Powder and Fabrication of
Transparent YAG Ceramics, J. European Ceramic Soc., Vol. 24, p. 2681, (2004)

Pradhan, A.K., et al., Synthesis of Neodymium-doped YAG Nanocrystlalline Powders
Leading to Transparent Ceramics, Materials Research Bulletin, Vol. 39, p. w1291 (2004)

Jiang, H., et al., Transparent Electro-Optic Ceramics and Devices, Proc. SPIE, Vol.
5644, p.380 (2005), www.bostonati.com/whitepapers/SPIE04paper.pdf

Huie, J.C. and Gentilman, R., Characterization of Transparent Polycrystalline YAG
Fabricated from Nanopowders, Window and Dome Technologies and Materials IX, Proc.
SPIE, Vol. 5786, p.251 (2005)

Barnakov, Y. A., et al., Simple Route to Nd:YAG Transparent Ceramics, Materials
Research Bulletin, Vol. 35, p. 238 (2006)

Barnakov, Y.A., et al., The Progress Towards Transparent Ceramics Fabrication, Proc.
SPIE, Vol. 6552, p.111 (2007)

Yamashita, I., et al., Transparent Ceramics, J. Am. Ceram. Soc., Vol. 91, p.813 (2008)

Xaiodong Li,et al., Transparent Nd:YAG Ceramics Fabricated Using Nanosized γAlumina and Yttria Powders, Vol.92, p.241 (2008)
[edit] Further reading
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
Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing by C. Jeffrey
Brinker and George W. Scherer, Academic Press (1990)
Sol-Gel Materials: Chemistry and Applications by John D. Wright, Nico A.J.M.
Sommerdijk
Sol-Gel Technologies for Glass Producers and Users by Michel A. Aegerter and
M. Mennig
Sol-Gel Optics: Processing and Applications, Lisa Klein, Springer Verlag (1994)
Sol-Gel: A Low temperature Process for the Materials of the New Millenium, Jean
Phalippou(2000) http://www.solgel.com/articles
Silica Glass from Aerogels, Michael Prassas (2008)
http://www.solgel.com/articles/april01/aerog.htm
[edit] External links

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Safety of Manufactured Nanomaterials: OECD Environment Directorate
Assessing health risks of nanomaterials summary by GreenFacts of the European
Commission SCENIHR assessment
International Liposome Society
Textiles Nanotechnology Laboratory at Cornell University
IOP.org Article
Nano Structured Material
AGAPAC - Advanced GaN Packaging EU FP7 project using nanomaterial
composites to enhance the thermal management of GaN electronic devices
Retrieved from "http://en.wikipedia.org/wiki/Nanomaterials"
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