Thermal Plasma Processes and Nanomaterial Preparation
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100 A or more. It would be safe to assume a minimum requirement of 150 A current
source DC power supply. The load voltage—which incidentally varies depending
on the distance between the electrodes as well as the ambient gas and the electrode
material—could be typically 50–100 V.
3.4.3 Water Chiller
As detailed earlier, it is imperative that the synthesis chamber is maintained at around
room temperature in order to obtain nanosized particles. Due to high heat of the
plasma, the ambient temperature inside the synthesis chamber increases steadily. This
will result in the growth of the clusters to bigger size. Cooling the synthesis chamber
ensures the walls of the chamber are at low temperature resulting in sharp temperature
gradients and consequent arrest of the nanocluster growth. For this, a steady stream of
water is allowed to flow between the two walls of the chamber, thereby maintaining
the temperature of the chamber walls at ambient room temperature (or lower—as
required). So it is essential to have a water chiller of appropriate capacity to maintain
the temperature of production chamber. If the various flanges are sealed with neoprene
or viton “O” rings, then the flanges also need to be water cooled, lest the heat damages
the “O” rings.
4 Preparation of Various Nanostructures by Plasma
Process
4.1 Preparation of Oxide Nanostructures
For metal oxide nanoparticles the synthesis chamber can be done in ambient air. At
high temperatures, as that in plasma zone, the chemical reactivity is high and the metal
vapours form oxides easily. These then can be collected for analysis/application. In
the following sections, a brief of various metal oxides (both low as well as high
melting point materials) that have been synthesised, and their synthesis parameters
and properties of the obtained nanostructures are described in detail. Metal oxide
nanomaterials that are to be covered are: iron oxide and cobalt oxide (magnetic),
titanium dioxide (refractory) and zinc oxide (wide bandgap semiconductor).
4.2 Titanium Dioxide Nanoparticles
Titanium dioxide or titania (TiO 2 ) has wide application potential—especially in the
daily-use consumer products. They are used in cosmetics (as UV protection agent),
as pigments in paints, inks and so on (as an opacifier agent). Titania in nanosize is
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100 A or more. It would be safe to assume a minimum requirement of 150 A current
source DC power supply. The load voltage—which incidentally varies depending
on the distance between the electrodes as well as the ambient gas and the electrode
material—could be typically 50–100 V.
3.4.3 Water Chiller
As detailed earlier, it is imperative that the synthesis chamber is maintained at around
room temperature in order to obtain nanosized particles. Due to high heat of the
plasma, the ambient temperature inside the synthesis chamber increases steadily. This
will result in the growth of the clusters to bigger size. Cooling the synthesis chamber
ensures the walls of the chamber are at low temperature resulting in sharp temperature
gradients and consequent arrest of the nanocluster growth. For this, a steady stream of
water is allowed to flow between the two walls of the chamber, thereby maintaining
the temperature of the chamber walls at ambient room temperature (or lower—as
required). So it is essential to have a water chiller of appropriate capacity to maintain
the temperature of production chamber. If the various flanges are sealed with neoprene
or viton “O” rings, then the flanges also need to be water cooled, lest the heat damages
the “O” rings.
4 Preparation of Various Nanostructures by Plasma
Process
4.1 Preparation of Oxide Nanostructures
For metal oxide nanoparticles the synthesis chamber can be done in ambient air. At
high temperatures, as that in plasma zone, the chemical reactivity is high and the metal
vapours form oxides easily. These then can be collected for analysis/application. In
the following sections, a brief of various metal oxides (both low as well as high
melting point materials) that have been synthesised, and their synthesis parameters
and properties of the obtained nanostructures are described in detail. Metal oxide
nanomaterials that are to be covered are: iron oxide and cobalt oxide (magnetic),
titanium dioxide (refractory) and zinc oxide (wide bandgap semiconductor).
4.2 Titanium Dioxide Nanoparticles
Titanium dioxide or titania (TiO 2 ) has wide application potential—especially in the
daily-use consumer products. They are used in cosmetics (as UV protection agent),
as pigments in paints, inks and so on (as an opacifier agent). Titania in nanosize is