ROOM-TEMPERATURE AC MICROPLASMA JET AT MEDIUM AND
ATMOSPHERIC PRESSURE FOR SURFACE TREATMENTS
J. C. Nascimento*; E. C. B. Aragão; G. J. P. Abreu; B. N. Sismanoglu
Instituto Tecnológico de Aeronáutica, Departamento de Física, São José dos Campos, SP, Brazil.
*Email-author: jananasci02@hotmail.com
Atmospheric pressure microplasma jet was developed to operated at open air with a range of gases with
lower power consumption (~ 5W, Irms = 12mA, Vrms = 600V. The stable microplasma jet operated in Ar,
He, O2, N2 and air at flow rates ranging between 1 and 15 liters/min is suitable for treatment of increased
surface area. For surface treatment the presence of metastable states of some gases used to produce the
microplasma, such as He (19.8eV), Ar (11.6 eV) and N2 (6.2 eV, generates high excited particles usefull
in applications. The optical modes temperature (excitation, rotational and vibrational) of the gas were
measured. A decrease of temperature from 110oC to 40oC was observed within 5 mm and furthermore the
temperature of the gas reaches the plasma jet at room temperature.
Keywords: Microplasma, optical emission spectroscopy, metastable.
Introduction
An ac atmospheric pressure microplasma jet with Cu or Mo spiral-type electrodes was
developed in this work. Its peculiarity is the ability to operate atomic and molecular
gases, including compressed air with lower power consumption (~ 5W, Irms = 12mA,
Vrms = 600V), smaller flow of gas (Φ = 1 to 15 liters/min) and good stability when glow
discharge is observed. The circular geometry used to develop the electrodes propitiates
the generation of low energy and stable microplasma jet operated in Ar, He, O2, N2 and
air at flow rates ranging between 1 and 15 liters/min, allowing expansion of the plasma
plume on the outer electrode with a diameter of about 2.5 mm and, consequently,
suitable for treatment of increased surface area. Furthermore, the device is absent of
dielectric parts which prevents contamination of the plasma. For surface treatment the
presence of metastable states of some gases used to produce the microplasma is
interesting, like He (19.8eV), Ar (11.6 eV) and N2 (6.2 eV). Optical measurements
allow us to infer the modes temperature (excitation, rotational and vibrational) of the
gas from the outer electrode along its axial position [1]. A decrease of temperature from
110oC to 40oC was observed within 5 mm and furthermore the temperature of the gas
reaches the plasma jet at room temperature.
Experimental part
The non-thermal low frequency (60 Hz) ac atmospheric pressure microplasma jet
(APMJ) could produce stable cold glow discharges from a number of gases as Ar, He,
N2, O2 and air. This APMJ was built as a pencil-type device, suitable for various
applications and research due to its low gas temperature and low cost materials in use,
such as a commercial neon-lamp transformer and air compressor (Fig. 1). The jet has a
visible radial diameter of approximately 1.5 mm with afterglow surrounding the jet, as
could be seen in Schlieren image.
Results and discussion
Current and voltage measurements at flow rate of 6 lmin-1 show sinusoidal wave forms
for flows of Ar, He, O2 + 1%Ar, N2 and air gases, with rms current and voltage
amplitudes of, respectively: a) 464 V, 10.4 mA; b) 410 V, 10,6mA; c) 515 V, 13 mA; d)
430 V, 11,8 mA and e) 456 V, 12.9 mA. The power absorbed by the plasma was,
respectively for these gases: a) 4.8 W; b) 4.1 W; c) 5.8W; d) 4.4 W and e) 4.9 W.
Optical measurements show the emission of important lines for bio-medical and surface
treatment applications, as O, N2, O3, N2+, N and OH. Electronic temperature (Te) was
estimated through Line Intensity Method. The average electronic temperature varies
between 0.50 to 0.70 eV for a range of gases flowing to generate the APMJ. The
Boltzmann plot method was applied to estimate the vibrational temperature (Tv) in the
plasma bulk using the second positive system N2 (C3u → B3g) for Δ = 2. The
temperature was in the range 0.35 to 0.57 K for the input power varying from 3 to 10
W, for all gases flow.
550
Ar
He
N2
O2+1% Ar
air
gas temperature (K)
500
450
400
350
300
gas temperature estimated from OH radicals
250
2
3
4
5
6
7
8
9
10
11
Power (W)
Fig. 1 – Schematic representation of the
Fig. 2 – Gas temperature as a function
microplasma
jet
and
the
schematic
representation of the electrical circuit (the inset
left represents the photograph of air plasma jet).
of the input power supplied to the
discharge (6 lmin-1 gas flow).
Conclusions
The gas temperature Tg was estimated from analysis of the OH (first order, ultra-violet, A 2Σ+, ν
= 0  X 2, ν’ = 0) rotational band (Fig. 2). A temperature decrease up to 40 oC was observed
up to 5 mm and beyond this the gas temperature reaches room temperature, so enabling the
APMJ to use in treatment of heat-sensitive surfaces such as biomaterials and polymers. The
difference between these three modes of temperature, Te  Tv  Tg, demonstrates the near PLTE
condition of this plasma source. The capacity of operation with molecular and atomic (noble)
gases, including air, is important for various technological applications, but the novelty of this
APMJ is the broadening of the plasma plume at the outer electrode with diameter of 2.5 mm
and, consequently, a higher surface area treatment.
References
[1] B. N. Sismanoglu et al., Spectroch. Acta Part B 64, 1287 (2009)
Acknowledgement: The authors acknowledge the financial support of the programs FAPESP,
CAPES and CNPq under Grant No. FAPESP/12/13064-4, CNPq/MCTI/SECIS 406035/2013-0,
CNPQ/310419/2012-3 DT, CAPES/88881.030340/2013-01.