Chemistry Reference
In-Depth Information
10
7
10% O
2
D
1
= 14 min
10
6
10
5
10
4
4% O
2
D
1
= 9 min
10
3
D
2
= 90 min
10
2
10
1
10
0
0.7% O
2
D
2
= 150 min
D
1
= 2.4 min
10
-1
D
2
= 17 min
10
-2
0
50
Exposure time (min)
100
FIGURE 8.25
IC of
Bacillus atrophaeus
spores observed in the flowing afterglow of a
microwave sustained discharge (pressure 667 Pa, power 100 W, frequency 2.45 GHz, volume
of afterglow-chamber 20 l) in N
2
/O
2
gas mixtures. Data points: mean of CFU/object; error
bars: rms deviation; solid lines: least square fits. (From Boudam, M.K., Moisan, M., Saoudi,
B., Popovici, C., Gherardi, N., and Massines, F., Bacterial spore inactivation by atmospheric-
pressure plasmas in the presence or absence of UV photons as obtained with the same gas
mixture,
J. Phys. D Appl. Phys.
, 39(16), 3494-3507, 2006. With kind permission from the
Institute of Physics.)
As a result, a 20 times higher power density necessary for equivalent inactivation of
spot-contaminated samples was investigated. Similar effects of the initial microbial
load were studied by means of plasmas at atmospheric pressure (e.g., [122]).
In atmospheric pressure discharges, under specific operation conditions, the UV
photons can be the dominant biocidal agents as well [105]. However, in most of the
plasmasdrivenatatmosphericpressure,nosufficientdoseofUVemissionisproduced
(in most atmospheric air plasmas, there is almost no radiation below 300 nm, see, e.g.,
[123]). In Figure 8.26, antimicrobial treatment of spot-contaminated polyethylene
strips(about3 10
6
MO/cm
2
)bymeansofplasmajets
∗
inargonatatmosphericpressure
are given.
In previous studies, the generation of UV and VUV radiation as well as ROS
has been investigated by means of optical spectroscopy in similar arrangements
[125]. ROS (O, O
3
, NO, OH) are formed by excitation of air compounds, mixed into
the expanding argon gas from the surrounding air. UV radiation above a wavelength
∗
The plasma jet configuration used in the experiment consists of a nozzle made of ceramics (inner
diameter of outlet about 7 mm) and a concentric needle electrode. The argon gas flows through the
nozzle (gas flow of 20slm) and the RF voltage (power: 20W) is coupled to the center electrode via a
matching network. The grounded electrode is a ring placed at the nozzle outlet. The plasma is generated
in the nozzle starting from the point of the needle electrode and expands into the surrounding air outside
the nozzle. Depending on the gas flow rate and the applied power, the plasma jet has a length of up to
10 mm measured from the nozzle outlet and a diameter of about 8mm.
