78
C. Balasubramanian
and an arc column is created between the electrodes. For this to be done, either both
the electrodes or at least one of the electrodes has to be movable. (ii) The electrodes
need not be made to touch each other, if there is provision for a high-frequency starter
in the power supply—it would be sufficient to bring the electrodes closer to initiate
the arc followed by the plasma plume. The second option is helpful in cases where
the arcing need to be created between two soft metal electrodes.
The power supply that is generally used for plasma torch (transferred as well as
non-transferred) is a constant current DC power source. The power supply ratings
are chosen, taking into consideration the materials to be evaporated—higher current
for high melting point materials. Typically, the current could vary from few tens of
amperes to hundreds of amperes. The load voltage could be few tens of volts. A
large current is required as the material evaporation from the anode depends on the
resistive heating given by I
2 R, where I is the current and R is the resistance. A larger
voltage would, on the other hand, support a long arc column.
The non-transferred arc assumes its name as the “job” material is not part of
the electrical circuitry. So even if the material of interest is insulating in nature,
it can be used for making nanostructures. On the other hand, in a transferred arc
plasma, the material of interest is very much a part of the electrical circuitry and
is, as described above, the anode itself. Both transferred and non-transferred arc
plasmas have advantages and disadvantages: A non-transferred can be used both
for conducting and insulating materials, whereas the transferred can be used only
for electrically conducting materials. On the other hand for a transferred arc, the
efficiency of the electrical power applied versus the power that is effectively used in
evaporating the material is more than 90%, whereas the best efficiency that can be
obtained from a non-transferred torch would not exceed 75% (more likely around
65%).
3 Synthesis of Nanomaterials
For synthesis of nanomaterials, both non-transferred as well as transferred arc
plasma/torch can be used. In the following sections both the techniques would be
discussed. However, more emphasis and details would be related to transferred arc
plasma route of nanomaterial synthesis.
3.1 Non-transferred Plasma Process for Synthesis
of Nanostructures
There are numerous published literatures on the synthesis of nanomaterials, using
either of the plasma types. In a non-transferred type, as briefly mentioned earlier in
Sect. 4.1, two possible mechanisms exist.
C. Balasubramanian
and an arc column is created between the electrodes. For this to be done, either both
the electrodes or at least one of the electrodes has to be movable. (ii) The electrodes
need not be made to touch each other, if there is provision for a high-frequency starter
in the power supply—it would be sufficient to bring the electrodes closer to initiate
the arc followed by the plasma plume. The second option is helpful in cases where
the arcing need to be created between two soft metal electrodes.
The power supply that is generally used for plasma torch (transferred as well as
non-transferred) is a constant current DC power source. The power supply ratings
are chosen, taking into consideration the materials to be evaporated—higher current
for high melting point materials. Typically, the current could vary from few tens of
amperes to hundreds of amperes. The load voltage could be few tens of volts. A
large current is required as the material evaporation from the anode depends on the
resistive heating given by I
2 R, where I is the current and R is the resistance. A larger
voltage would, on the other hand, support a long arc column.
The non-transferred arc assumes its name as the “job” material is not part of
the electrical circuitry. So even if the material of interest is insulating in nature,
it can be used for making nanostructures. On the other hand, in a transferred arc
plasma, the material of interest is very much a part of the electrical circuitry and
is, as described above, the anode itself. Both transferred and non-transferred arc
plasmas have advantages and disadvantages: A non-transferred can be used both
for conducting and insulating materials, whereas the transferred can be used only
for electrically conducting materials. On the other hand for a transferred arc, the
efficiency of the electrical power applied versus the power that is effectively used in
evaporating the material is more than 90%, whereas the best efficiency that can be
obtained from a non-transferred torch would not exceed 75% (more likely around
65%).
3 Synthesis of Nanomaterials
For synthesis of nanomaterials, both non-transferred as well as transferred arc
plasma/torch can be used. In the following sections both the techniques would be
discussed. However, more emphasis and details would be related to transferred arc
plasma route of nanomaterial synthesis.
3.1 Non-transferred Plasma Process for Synthesis
of Nanostructures
There are numerous published literatures on the synthesis of nanomaterials, using
either of the plasma types. In a non-transferred type, as briefly mentioned earlier in
Sect. 4.1, two possible mechanisms exist.