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C. Balasubramanian
for surface modifications, bio-medical applications and so on. The heat generated
in thermal plasma can reach thousands of Kelvin depending on the plasma current
applied. The high heat energy not only helps in melting, evaporation and so on,
but also promotes higher chemical reactions. Nanoparticle synthesis which involves
evaporation, nucleation and growth also employs high temperature plasma. Plasma
torch and arc plasma are used for synthesis of nanoparticles. A detailed report on the
use of various plasmas for synthesis of nanostructures is given by Siegmann et al.
(2008).
Low-temperature plasma, on the other hand, is used extensively in surface modifications of various materials, including polymers, textiles and so on. It is also
used to grow nanocrystalline films or 2-D nanostructures as well as nanocomposites (Tsai et al. 2009). It is also used to make nanopatterns on substrates. Plasmaenhanced chemical vapour deposition (PECVD), magnetron sputtering processes are
all examples of low-temperature plasma, which are used effectively for nanostructure
formations. Basically, the high kinetic energy of the charged particles in plasma is
used to knock out surface atoms or atom clusters to impart changes to the surface
roughness leading to changes in the surface properties and surface chemistry. The
kinetic energy of the charged particles can also be used to break chemical bonds and
then graft it with atoms of other elements, thereby imparting different functionality
to the original surface.
In this chapter the focus would be exclusively on the properties, types and applications of thermal plasmas—with particular emphasis on nanomaterial synthesis.
2.2 Thermal Plasma Processes
2.2.1 Transferred and Non-transferred Plasma
Nanoparticles by thermal plasma can be prepared by two methods: either by
transferred arc torch method or by non-transferred arc torch method.
In the non-transferred torch (as shown in Fig. 1) method, an electric arc is struck
between the central cathode rod (typically water cooled tungsten) and the coaxially
placed anode (typically water-cooled copper). This arc is extended outside of the
nozzle by a strong gas draft (also known as plasma forming gas). The length of the
extended arc (plume) can reach up to tens of centimetres long, depending on the gas
flow rate and the voltage applied between the electrodes. The material of interest
(whose nanostructure is to be formed) is either placed in a crucible at the plume
end or it can be introduced in powder form between the electrodes along with the
plasma-forming gas jet.
If it is placed in a crucible, the heat from the plume would evaporate the material
which subsequently leads to nucleation, growth and condensation. If, on the other
hand, the material is introduced in powder form, the powder comes directly in contact
with the core of the plasma (which has a significantly higher temperature than at the
C. Balasubramanian
for surface modifications, bio-medical applications and so on. The heat generated
in thermal plasma can reach thousands of Kelvin depending on the plasma current
applied. The high heat energy not only helps in melting, evaporation and so on,
but also promotes higher chemical reactions. Nanoparticle synthesis which involves
evaporation, nucleation and growth also employs high temperature plasma. Plasma
torch and arc plasma are used for synthesis of nanoparticles. A detailed report on the
use of various plasmas for synthesis of nanostructures is given by Siegmann et al.
(2008).
Low-temperature plasma, on the other hand, is used extensively in surface modifications of various materials, including polymers, textiles and so on. It is also
used to grow nanocrystalline films or 2-D nanostructures as well as nanocomposites (Tsai et al. 2009). It is also used to make nanopatterns on substrates. Plasmaenhanced chemical vapour deposition (PECVD), magnetron sputtering processes are
all examples of low-temperature plasma, which are used effectively for nanostructure
formations. Basically, the high kinetic energy of the charged particles in plasma is
used to knock out surface atoms or atom clusters to impart changes to the surface
roughness leading to changes in the surface properties and surface chemistry. The
kinetic energy of the charged particles can also be used to break chemical bonds and
then graft it with atoms of other elements, thereby imparting different functionality
to the original surface.
In this chapter the focus would be exclusively on the properties, types and applications of thermal plasmas—with particular emphasis on nanomaterial synthesis.
2.2 Thermal Plasma Processes
2.2.1 Transferred and Non-transferred Plasma
Nanoparticles by thermal plasma can be prepared by two methods: either by
transferred arc torch method or by non-transferred arc torch method.
In the non-transferred torch (as shown in Fig. 1) method, an electric arc is struck
between the central cathode rod (typically water cooled tungsten) and the coaxially
placed anode (typically water-cooled copper). This arc is extended outside of the
nozzle by a strong gas draft (also known as plasma forming gas). The length of the
extended arc (plume) can reach up to tens of centimetres long, depending on the gas
flow rate and the voltage applied between the electrodes. The material of interest
(whose nanostructure is to be formed) is either placed in a crucible at the plume
end or it can be introduced in powder form between the electrodes along with the
plasma-forming gas jet.
If it is placed in a crucible, the heat from the plume would evaporate the material
which subsequently leads to nucleation, growth and condensation. If, on the other
hand, the material is introduced in powder form, the powder comes directly in contact
with the core of the plasma (which has a significantly higher temperature than at the