DOE Plasma Science Center 3rd Annual Meeting
Controlling Vibrationally Excited Nitrogen and Overall Plasma Chemistry with Surface Micro-discharge in Ambient Air
Yukinori Sakiyama and David B. Graves Department of Chemical and Biomolecular Engineering University of California at Berkeley
University of California, Berkeley
Outline
1. Surface micro-discharge (SMD) 2. Distribution of RONS at low-power • RONS in discharge layer and afterglow • Comparison with FTIR 3. Mode transition in afterglow • UV O3 measurement • Fitting model with N2 vibrational mode • Correlation with bactericidal effect 4. Concluding remarks
Plasma Science Center Predictive Control of Plasma Kinetics
SMD: discharge characteristics G. Morfill et al., New J. Phys. 11 (2009) 115019, T. Shimizu et al., New J. Phys. 13 (2011) 023026
SMD = surface micro-discharge (surface dielectric barrier discharge in ambient air at room temperature)
Cu (powered)
HV
image of emission
dielectric
~ 10 cm SS mesh (grounded)
RNS ROS
treated surface
Frequency: Voltage: Power: Distance to sample: Exposure time:
1-10 kHz 1-10 kVpp 2 0.01-1 W/cm 1-10 mm 1-1000 s
Plasma Science Center Predictive Control of Plasma Kinetics
SMD: anti-microbial effect Various microbes on agar plate G. Morfill ., New J. Phys. 11 (2009) 115019
untreated
E. coli on pig skin M. Pavlovich,, Plasma. Process. Polm. (submitted)
30 s
gram positive/negative bacteria, spores, viruses, etc… Plasma Science Center Predictive Control of Plasma Kinetics
SMD: multi-scale phenomena 1 ns
pulse excitation electron impact reactions
1 s
1 ms
1s
1000 s
charge transfer, recombination
Ozonizer Pollution control
neutral reactions applied voltage period gas diffusion
SMD for biomaterial treatment
exposure time
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Modeling: domain and equations • •
Humid air at 1 atm: 79% N2, 20% O2, 1% H2O (30% relative humidity) Gas temperature: 300 K
dp = 0.1 mm
discharge layer e
ROS, RNS
n p t
k j nr , j
pg
afterglow
dg = 10 mm
ng t
dp
j
ion
ROS, RNS
pg
D ( n p ng ) (d p d g ) / 2
k j nr , j j
pg dg
treated surface Plasma Science Center Predictive Control of Plasma Kinetics
Modeling: simulation procedure (solver: MATLAB) pls(=1 ns)
pulse-like electric field
E E0 exp{(t / pls ) 2 / 2} discharge layer (e, ion, neutral)
afterglow (neutral)
100 s for single cycle rep=100 s
Cycle-averaged reaction rates discharge layer (neutral)
afterglow (neutral)
for gas=1 s
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Modeling: humid air plasma chemistry •
53 species: electrons, 16 positive ions, 10 negative ions, and 26 neutrals
•
624 reactions 23 electron impact excitation/ionization 84 electron recombination/attachment/detachment 169 charge transfer and ion conversion 231 ion-ion recombination 116 neutral-neutral reactions
References • H.Matzing, Adv. Chem. Phys. 80 (1991) 315 • I. A. Kossyi, Plasma Sources Sci. Technol. 1 (1992) 207 • R. Atkinson, Atmos. Chem. Phys., 4 (2004) 1461 • M.Capitelli, “Plasma kinetics in atmospheric gases” (Springer, Berlin 2000) etc., etc., etc…. Plasma Science Center Predictive Control of Plasma Kinetics
Modeling: discharge layer at low power Power density: 0.05 W/cm2 Peak density: ~1019 m−3 Negative ions at 1000 s
Positive ions at 1000 s 8
8
total
-3
density [10 m ]
6
18
+
4
NxOy
+
Nx
2 0
+
Ox
+ OxHy
10
-9
10
-8
6 -
NOx
18
-3
density [10 m ]
total
4
electrons
2
-
Ox
OxHy -7
10 10 time [s]
-6
10
-5
10
-4
0 10
-9
10
-8
-7
10 10 time [s]
-6
10
-5
10
-4
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Modeling: neutrals still in transient after 1000 s Power density: 0.05 W/cm2 Peak density: > 1019 m−3
10
24
10
23
density
-3
[m ]
Cycle-averaged neutral density at 1000 s
10
22
10
21
10
20
10
19
Ox NxOy HxNyOz OxHy
1
2
3
4
5 6 7 89
10
2
3
time
4
[s]
5 6 7 89
100
2
3
4
5 6 7 89
1000
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10
21
10
19
10
17
N2O
Simulation at 100 [s] H2
H2O2
O3
HNO3 NO3
HNO2 NO2
N2O5
10
4
10
2
10
0
10
-2
FTIR measurement (qualitative comparison) 0.12
IR beam
200 scans for 60-120 [s]
transmittance [-]
density
-3
10
23
density [ppm]
[m ]
Modeling: distributions of neutrals
O3
0.08 0.04
N2O
0.00 400035003000 2500
HNO3 HNO3 N2O5 N2O5
2000 1500 wave number
HNO3
1000 [cm ] -1
500
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Outline
1. Surface micro-discharge (SMD) 2. Distribution of RONS at low-power • RONS in discharge layer and afterglow • Comparison with FTIR 3. Mode transition in afterglow • UV O3 measurement • Fitting model with N2 vibrational mode • Correlation with bactericidal effect 4. Concluding remarks
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Gas-phase ozone: modulation by power density UV 254 nm
• power density: 0.03-3 W/cm2 • gas gap: ~10 mm • temporal resolution: 1 s
concentration [ppm]
5000 4000 3000 2000 1000
Intermediate power (0.25 W/cm2)
Low power: “ozone-mode” (0.025 W/cm2)
ozone-mode in SMD (our study) High mode” Highpower: power:“nitrogen “nitrogenoxides oxide mode” (2.64 (2.64W/cm W/cm22))
0
U. Kogelschatz, Ozone Sci. 367 0 20 et al.,40 60 Eng. 10 80(1988)100
120
time [s] Plasma Science Center Predictive Control of Plasma Kinetics
Mode transition: N2 vibrational state Ref: M. Capitelli, “Plasma kinetics in atmospheric gases” (Springer, Berlin 2000)
e
O3
O
N2 N2(v)
NO2
NO
v > 12 Energy transfer efficiency 1.0
10 10
-2
10
-4
0.2
10
-6
0.0
10
-8
F (v >12)
Qv / Qttl
0.8
0
0.6 0.4
0
2 4 6 8 mean electron energy [eV]
10
Cumulative distribution function (v >12)
2000
4000 Tv
6000 [K]
8000
10000
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Mode transition: simplified fitted model discharge layer
mixed layer
afterglow
R1: O + O 2 M O3 M R2: N 2 (v) O NO N R3: O3 NO NO 2 O 2
diffusion loss
R4: O NO + M NO 2 M
Governing equations dnO3 nO3 k1nM nO nO2 k3nNO nO3 dif dt dnNO n k2 nN 2 (v) nO k3nNO nO3 k4 nO nNO nM NO dt dif nN 2 (v) nN 2 Fv 12
2 unknown variables • nO3 and nNO 3 fitting parameters • nO, Tvmax, v
12 v nN 2 exp( ) kTv
Tv Tg Tvmax {1 exp(t / v )} Plasma Science Center Predictive Control of Plasma Kinetics
Mode transition: O3 model and NxOy mode fitted parameters: nO = 8×1017 m−3, Tvmax = 5000 K, v = 2 s concentration [ppm]
8000
O3
800
v
600
6000
Tv
4000 400
Tv
nO
NO
2000
200 0
0
5
10
ozone mode
15 time [s]
20
25
0 30
Vibrational temperature [K]
1000
nitrogen oxides mode
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[-]
3
1500
2
1000
1
500
0 0.001
0
[ppm]
2000
Intermediate Low power 0.1 High power (< (>power 1.0 Wcm Wcm22)) Wcm2) O33:: low increase ••(0.1-1.0 O O3: quenched L-R: increase •• L-R: low • L-R: high Avg O3 for 30s
4
Log reduction
Gas-phase ozone: bactericidal activity on agar plate
0.01 0.1 1 2 power density [W/cm ]
• •
ozone is not responsible for inactivation? Nonlinear reaction on lipid membrane?
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Concluding Remarks 1. We developed multi-scale model of SMD. Our simulation results at low power (0.05 W/cm2) shows good agreement with our FTIR measurement. 2. We presented one example of modulating plasma chemistry in SMD. The modulation is achieved by controlling distribution functions of electrons and neutrals through pulsing of electric field.
Plasma Science Center Predictive Control of Plasma Kinetics
Acknowledgements Prof. G. Morfill (Max-Planck Institute) Dr. T. Shimizu (Max-Planck Institute) Prof. D. Clark (UC Berkeley) M. Pavlovich (Ph.D. candidate, UC Berkeley) H.-W. Chang (Ph.D. candidate, National Taiwan University)
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