Plasma Synthesis of Nanoparticles for Nanocomposite Energy Applications Page: 4 of 12
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plasma , laser ablation , chemical vapor condensation , spray pyrolysis ,
electrospray , and plasma spray .
Solution processing is a wet chemical synthesis approach that can be used to generate
nanoparticles by gelation, precipitation, and hydrothermal treatment . Size distribution of
semiconductor, metal, and metal oxide nanoparticles can be manipulated by either dopant
introduction  or heat treatment . Better size and stability control of quantum-confined
semiconductor nanoparticles can be achieved through the use of inverted micelles , polymer
matrix architecture based on block copolymers  or polymer blends , porous glasses ,
and ex-situ particle-capping techniques [24,25]. Additional nanoparticle synthesis techniques
include sonochemical processing, cavitation processing, microemulsion processing, and high-
energy ball milling. In sonochemistry, an acoustic cavitation process can generate a transient
localized hot zone with extremely high temperature gradient and pressure . Such sudden
changes in temperature and pressure assist the destruction of the sonochemical precursor (e.g.,
organometallic solution) and the formation of nanoparticles. The technique can be used to
produce a large volume of material for industrial applications. In hydrodynamic cavitation,
nanoparticles are generated through creation and release of gas bubbles inside the sol-gel
solution . Rapidly pressurizing in a supercritical drying chamber and exposing to cavitational
disturbance and high-temperature heating would mix the sol-gel solution. The erupted
hydrodynamic bubbles are responsible for nucleation, growth, and quenching of the
nanoparticles. Adjusting the pressure and the solution retention time in the cavitation chamber
can control particle size. Microemulsions have been used for synthesis of metallic ,
semiconductor [29,30], silica , magnetic, and superconductor nanoparticles . By
controlling the very low interfacial tension (-10- mN/m) through the addition of a co-surfactant
(e.g., an alcohol of intermediate chain length), these microemulsions are produced
spontaneously without the need for significant mechanical agitation. The technique is useful for
large-scale production of nanoparticles using relatively simple and inexpensive hardware .
Finally, high-energy ball milling (mechanical attrition), the only top-down approach for
nanoparticle synthesis, has been used for the generation of magnetic , catalytic , and
structural nanoparticles . The technique, which is already a commercial technology, has
been considered dirty because of contamination problems from ball-milling processes. However,
the availability of tungsten carbide components and the use of inert atmosphere and/or high
vacuum processes have reduced impurities to acceptable levels for many industrial
applications. Common drawbacks include the low surface area, the highly polydisperse size
distributions, and the partially amorphous state of the as-prepared powders.
Achieving Monodispersed Nanoparticles
One of the most challenging problems in synthesis is the controlled generation of
monodispersed nanoparticles with size variance so small that size selection by centrifugal
precipitation or mobility classification is not necessary. Liquid processes have produced the
most monodisperse particles, but typically theses processes are high dilution and, hence, not
particularly cost effective. Gas-phase synthesis is one of the best techniques for controlled
generation with respect to size monodispersity, typically achieved by using a combination of
rigorous control of nucleation-condensation growth and avoidance of coagulation by diffusion
and turbulence as well as by the effective collection of nanoparticles and their handling
afterwards. Plasma gas-phase (chemical and physical) synthesis has the best potential to
produce nanoparticles with a narrow and tight size distribution in a very short time. More
attention should focus on plasma gas-phase synthesis technology development.
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Kong, Peter C. & Kawczak, Alex W. Plasma Synthesis of Nanoparticles for Nanocomposite Energy Applications, article, September 1, 2008; [Idaho Falls, Idaho]. (digital.library.unt.edu/ark:/67531/metadc897497/m1/4/: accessed February 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.