Eco-friendly Surface Modification …
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and TiO 2 by plasma-assisted chemical vapour deposition technique, graffiti removal,
removal of paint and many more (Nehra 2008; Nema and Jhala 2015).
2.3.3 Atmospheric Pressure Glow Discharge
An atmospheric pressure glow discharge (APGD) is generated at a low voltage and
very high frequency, i.e. radiofrequency across parallel plate electrode setup which
is separated from each other by a few millimetres. The plasma-forming gas used is
usually helium since helium has a very low breakdown voltage and longer transition
time which help in extending the micro-discharge points on the insulating electrode.
The APGD is beneficial for material processing due to its capability for homogenous
treatment and stability of discharge, as it operates on a lower voltage than other
atmospheric pressure discharges. Moreover, the electrodes are not covered by any
dielectric material. The use of helium as the discharge gas limits its commercial
applicability in textile processing since it is costly and difficult to recover (Mather
2009; Nema and Jhala 2015).
2.3.4 Dielectric Barrier Discharge
A dielectric barrier discharge (DBD), also called as silent discharge, is produced
between two parallel electrodes where at least one of the electrodes is covered with
an insulating dielectric barrier. These discharge operate at atmospheric pressure,
typically in the range of 0.1–1 atm. A high AC voltage with an amplitude of the
order of 1–100 kV and frequency from a few kHz to MHz (corresponding to lower
RF—microwave range) is applied to the setup. A dielectric layer made of glass,
quartz, ceramic or polymer material, placed between the two metal electrodes, is the
characteristic of DBDs. The inter-electrode distance varies from a few mm to a few
cms depending on the processing requirement (Bogaerts et al. 2002). When the DBD
is powered with a high AC voltage, gases breakdown between the parallel plates in
filamentary mode, i.e. the discharge is constituted by a large number of individual tiny
breakdown filaments distributed uniformly over the entire dielectric layer, referred
to as micro-discharges or streamers. The use of dielectric as an insulating layer has
few advantages; firstly, it enables a continuous flow of current by avoiding glow to
arc transition and secondly, it creates random streamers by electron accumulation
on the electrode surface to ensure homogenous treatment of any surface (Nema and
Jhala 2015). DBD discharge differs from a classical discharge significantly, as in
classical discharge the electrodes are not covered with any dielectric layer; hence,
they come in direct contact with highly activated chemical species and thus causes
electrode etching and corrosion which is not the case in a DBD. Another major
point of difference is that DBD cannot be operated with a DC voltage due to the
presence of capacitive coupling which require an alternating current with time-lapse
to drive the displacement current (Nehra 2008). The dielectric barrier discharge has
become an important tool for surface modification of textiles at atmospheric pressure.
535
and TiO 2 by plasma-assisted chemical vapour deposition technique, graffiti removal,
removal of paint and many more (Nehra 2008; Nema and Jhala 2015).
2.3.3 Atmospheric Pressure Glow Discharge
An atmospheric pressure glow discharge (APGD) is generated at a low voltage and
very high frequency, i.e. radiofrequency across parallel plate electrode setup which
is separated from each other by a few millimetres. The plasma-forming gas used is
usually helium since helium has a very low breakdown voltage and longer transition
time which help in extending the micro-discharge points on the insulating electrode.
The APGD is beneficial for material processing due to its capability for homogenous
treatment and stability of discharge, as it operates on a lower voltage than other
atmospheric pressure discharges. Moreover, the electrodes are not covered by any
dielectric material. The use of helium as the discharge gas limits its commercial
applicability in textile processing since it is costly and difficult to recover (Mather
2009; Nema and Jhala 2015).
2.3.4 Dielectric Barrier Discharge
A dielectric barrier discharge (DBD), also called as silent discharge, is produced
between two parallel electrodes where at least one of the electrodes is covered with
an insulating dielectric barrier. These discharge operate at atmospheric pressure,
typically in the range of 0.1–1 atm. A high AC voltage with an amplitude of the
order of 1–100 kV and frequency from a few kHz to MHz (corresponding to lower
RF—microwave range) is applied to the setup. A dielectric layer made of glass,
quartz, ceramic or polymer material, placed between the two metal electrodes, is the
characteristic of DBDs. The inter-electrode distance varies from a few mm to a few
cms depending on the processing requirement (Bogaerts et al. 2002). When the DBD
is powered with a high AC voltage, gases breakdown between the parallel plates in
filamentary mode, i.e. the discharge is constituted by a large number of individual tiny
breakdown filaments distributed uniformly over the entire dielectric layer, referred
to as micro-discharges or streamers. The use of dielectric as an insulating layer has
few advantages; firstly, it enables a continuous flow of current by avoiding glow to
arc transition and secondly, it creates random streamers by electron accumulation
on the electrode surface to ensure homogenous treatment of any surface (Nema and
Jhala 2015). DBD discharge differs from a classical discharge significantly, as in
classical discharge the electrodes are not covered with any dielectric layer; hence,
they come in direct contact with highly activated chemical species and thus causes
electrode etching and corrosion which is not the case in a DBD. Another major
point of difference is that DBD cannot be operated with a DC voltage due to the
presence of capacitive coupling which require an alternating current with time-lapse
to drive the displacement current (Nehra 2008). The dielectric barrier discharge has
become an important tool for surface modification of textiles at atmospheric pressure.