(Bio)Plasma Chemistry

Wouter Van Gaens, Annemie Bogaerts

PLASMANTUniversity of Antwerp, Belgium

Plasma to Plasma! Workshop, Jan 2013

Plasma medicine applications Microdischarge Non-LTE plasma at atmospheric pressure Large interest in plasma jets Usually noble gas mixing with ambient air Both physically and chemically complicated processes

1. Introduction

NOBLE GASPLASMA

MIXING ZONE

Aim of this work Insight in chemical phenomena (generally valid ?!?) Simple model = low computational load Mainly qualitative study Implement humid air chemistry set with argon coupling Reduced chemistry set (can be used in higher level models ?!?)

1. Introduction

NOBLE GASPLASMA

MIXING ZONE

Other important/relevant humid air reaction chemistry modelling, i.a.:

Kogelschatz et al (1988) & Kossyi et al (1992) : Dry air NIST Standard reference data (‘90-’00): Humid air

Combustion and atmospheric chemistry community (Herron, Atkinson, Tsang et al) Gentille and Kushner (1995): Humid air

Plasma remediation of NxOy

Liu, Bruggeman, Iza and Kong (2010): He/H2O General biomedical applications, hydrogen peroxide generation

Iza et al (‘10): He/O2/H2O Plasma medicine, RF discharges

Sakiyama et al (2012): Humid air Plasma medicine, surface micro discharge

Babaeva and Kushner (2013): Humid air Plasma medicine, DBD filaments and fluxes towards wounded skin

1. Introduction

Recent review: X Lu et al, Plasma Sources Sci. Technol. 21 (2012) 03400)

2. Typical plasmajet configurations

Recent review: X Lu et al, Plasma Sources Sci. Technol. 21 (2012) 03400)

2. Typical plasmajet configurations

Device of our choice:Prof. P. Bruggeman, Eindhoven Univ. of Technology

• Needle electrode (Ø ± 0.5 mm)

• Coaxially inserted in dielectric tube (inner Ø ± 1.8 mm)

• Needle tip 1.9 mm from nozzle exit

2. Typical plasma jet configurations

10 mm 3 m

m

Operating conditions:

• 6.5 Watt dissipated power• RF discharge• Ar gas feed 2 slm• Possibility of oxygen

admixture

2. Typical plasma jet configurations

9 mm 3 m

m

0D model ‘GlobalKin' Prof. M. J. Kushner, University of Michigan, US

3. Model

Species kineticsBoltzmann solver(*)

Electron energy equation(*) can be called very frequently with changing background gas composition!!!!!!!

0D fluid model ‘GlobalKin' Prof. M. J. Kushner, University of Michigan, US

3. Model

Species kineticsBoltzmann solver(*)

Electron energy equation

(*) can be called frequently, for example with changing background gas composition

Power input!

3. Model Assumptions to obtain ‘semi-empirical’ model

1) Pseudo-1D simulation (to give idea of “distance to nozzle”) Volume averaged element moving along the plasmajet stream > imaginary

cylinder Moving speed flow velocity & ̴ Ø cylinder (1cm ≈ 1msec) No radial transport (high flow speed) / no axial drift & diffusion flux

3. Model Assumptions to obtain ‘semi-empirical’ model

2) Humid air diffusion Ar replaced by N2/O2/H2O Mixing speed fitted to literature values and 2D fluid simulation calculation

Ellerweg et al (2012) Reuter et al (2012)

2D Fluid flow model

3. Model Assumptions to obtain ‘semi-empirical’ model

3) Tgas evolution Fitted to measurements TU/e (Tg, radially averaged) Self consistent Tgas calculations by model only accurate in first few mm!

Why ‘device specific’ plasma chemistry study (≠ more general approach)? Pdeposition as function of plasma jet position unknown > plasma

properties matched to experiment Tgas evolution device specific: crucial for chemistry (eg. NOx and O3)

Broad parameter study: more general chemical info

3. Model

4. Reaction chemistry set Extended Ar/N2/O2/H2O chemistry set

85 implemented species!

Some advantages & differences compared to other models:1. complex waterclusters2. Argon implementation (less expensive)3. Rot/Vib excited states (partially) included

Ground State Excited ChargedAr Ar(4S), Ar(4P), Ar2* (a 3Σ+

u) e-, Ar+, Ar2+, ArH+

N2, N N2,rot, N2,vib, N2(A 3Σ+u), N2 (a' 1Σ-

u), N(2D) N2+, N3

+, N4+, N+

O2, O3, O O2,rot, O2,vib, O2 (a 1Δg), O2 (b 1Σ+g), O(1D) O2

+, O4+, O+, O-, O2

- , O3-

NO, NO2, N2O, NO3, N2O3, N2O4, N2O5 N2Ovib NO+, NO2+, NO2

-, NO3-

NH, HNO, HNO2, HNO3, HNO4 H+, H2+, H3

+,H2, H, H2O, H2O2, HO2, OH H*, H2,rot, H2,vib, H2*, OH (A) H2O+, H3O+, H2O2

-, OH+, H-,OH-

WaterclustersH5O2

+, H7O3+, H9O4

+, H11O5+, H13O6

+, H15O7+, H2NO2

+, H4NO3+, H6NO4

+

4. Reaction chemistry set

Extended Ar/N2/O2/H2O chemistry set 1885 reactions! (can be reduced to ± 400 reactions)

278 electron impact & 1596 heavy particle reactions (692 dry air)

recombinations; 14%

electron de-tachment; 2%

momentum trans-fer; 17%

dissociation; 8%ionisation; 15%deexcitation; 10%

electron at -tachment; 12%

excitation; 22%chemical

change; 30%

charge ex-change; 6%

electron de-tachment; 2%

cluster reactions; 15%

Penning ionisation; 3%

physical quenching;

17%

radiative decay; 1%

ion recom-bination;

26%

5. Validation Calc. [O3] vs. experim. [O3] by TU/e (2% O2 admixture) Relatively good qualitative agreement Detailed discussion in upcoming paper!

Agreement for [O], [NO] and [OH] (literature) for similar devices.

6. Output reaction chemistry model Similar conditions as for TU/e

plasmajet device, except no O2 admixture

Very rapid chem/phys quenching of energetic Ar states by air

Fast charge exchange by Ar ions

Strong [e-] drop due to efficient dissociative electron attachment of air

6. Output reaction chemistry modelBiomedically active species

O2(a), O3, NO, N2O, H2O2, HNO3 predicted to be very long living species

1-1000 ppm

N < H < O in lifetime and density, but ‘distance of treatment’ is crucial!

O into O3 if Tgas low/ into NOx if Tgas high

Plasma becomes electronegative due to electron attachment in the far effluent

6. Output reaction chemistry model Water cluster formation

Complex mechanism by implementing reaction rates (≠ Arrhenius form) by Sieck et al (2000)

Dominant positive charge carrier

Water cluster size gradually increasing in time

NO+ clusters less abundant

6. Output reaction chemistry model Example of parameter variation: 300K

Large changes in densities (up to order of magnitude)

Changes in chemical pathways less drastic!

Less NO, much more O3 in far effluent

Faster recombination of radicals like O, H into OH, HO2

Favors HNO3 formation! (though net less NOx)

Chemical pathway changes taken into account in reduced chemistry set!

Rel. ∆[X] vs. [X] with fitted Tg profile cfr. experiment

8. Conclusions & Outlook• Large amount of chemical data studied• Argon implementation• Semi-empirical model (validation)• More detailed chemical pathway analysis will be given in upcoming paper• Idem ditto for effect of power, air humidity & flow speed on chemistry• Reduced chemistry set

Acknowledgments: Prof. Dr. M. J. Kushner Flemish Agency for Innovation by Science and Technology Computer facility CalcUA Prof. P. Bruggeman of Eindhoven University of Technology for providing experimental data

Thank you for your attention!

Questions?