3 International Conference on Frontiers of Plasma Physics and Technology Trends in plasma applications R. Barni Centro PlasmaPrometeo Bangkok 5 March 27
Plasma processing Trends towards atmospheric pressure: Most industrial processes are performed in open air or at atmospheric pressure. Many materials do not like to be exposed to vacuum. Processes are integrated in a chain with an almost continuos feeding of the materials to be treated. So atmospheric plasma are more compatible with existing industrial processes Moreover: processes are faster (higher density of neutral radicals, if not ions) easily scalable to large areas processing region is well confined
Atmospheric pressure plasmas in nature On earth: lightning, thunderbolt (storms, volcano eruptions) Mankind activity: Electrical discharges B.Franklin (1747)
Atmospheric pressure plasmas in laboratory Arc discharge: thermal plasma (T gas ~T ~T e ~5-1 K) Corona discharge: cold diffuse plasma micro-discharges discharges: intermittent plasma (streamers) Applications: : plasma torch waste, coatings,, cutting Corona treatment: Adhesion, painting
Laboratory and experimental setup PlasmaPrometeo Center (24) Plasma sources and diagnostics Controlled gas-phase DBD reactor Evacuated chamber Surface Diagnostics: AFM, FIB/SEM, FT-IR
Electrical characteristics: Voltage across the gap: HV probes, large bandwidth (PS-615A, 75 MHz) microdischarge current Large bandwidth, high sensitivity (home-mademade Rogoski coils) Diagnostics Voltage [KV] Voltage [KV] Time [µs] 24 26 28 3 32 8 3 6 4 2 2-2 1-4 -6-8 8 4 6 4 2 2-2 -4-2 -6-8 -4 1 2 3 4 5 6 Time [µs] Current [ma] Current [ma]
Diagnostics Optical tecniques: Intensità (a.u.) 5 4 3 2 1 2 3 4 5 6 7 8 Lunghezza d'onda (nm) Atmospheric pressure DBD Low pressure Glow discharge Oxygen Intensity ratio.1.9.8.7.6.5.4.3.2 Emission spectra radical identification Advanced tools LIF, Stark,, fast cameras Vibrational temperature (K) 33 32 31 3 29.1. Intensity ratio O (777.4) / N2 (357) 1 12 14 16 18 2 Power (W) 28
Modeling Chemical kinetics of the gas-phase in a microdischarge Chemical reactor model cylindrical channel (R s, L) radial diffusion longitudinal uniform (n, T) slow flowrate -> mixing along the channel (well-mixed reactor) dn dt k = Density balance equations 22 species (1 neutral, 12 ions) 194 reactions rates 15 wall recombination processes i,j K i+ j k n i n j - i,j K i+ k j n i n k D D k i - n k + (1 S 2 2 i ) Bi(w) k Λ i Λ n i
Modeling Density (cm^-3) 1 2 Chemical Composition of an Air streamer 1 19 1 18 1 17 1 16 1 15 1 14 1 13 1 12 1 11 1 1 1 9 1 8 1 7 1 6 1 5 Chemical kinetics of a dbd in air (streamer regime) 1 4 1E-1 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3.1.1 Streamer development Time (s) N N2 O O2 O3 NO N2O NO2 H 2 partial pressure (1-6 mbar) / H α line intensity (a.u.) Chemical kinetics of a spark discharge in Ar/CH4 1..8.6.4.2 P (H 2 ) I (H α ) Repetition rate. 5 1 15 2 ν = 2 ν AC Mean spark current (ma).3.2.1. H2 conversion efficiency (percentage)
Silk: Applications: technology goal remove sericin Process: selective removal pure fibroin fibres Plasma: etching O 2 remove/crack sericin Untreated Plasma treated Chemical degumming
Leathers: Applications: technology goal obtain printability Process: modify wettability dye fixed on surface Plasma: dbd in air/helium -OH, OH,-COOH grafting Untreated Plasma treated Photographic film
Applications: PET films: technology goal optical properties Process: modify roughness reflectivity changes Plasma: dbd in air surface etching 4. 3.5 energy dose 15.4 J cm -2 untreated sample Reflectivity (%) 3. 2.5 2. 1.5 1. treated.5 untreated Untreated Plasma treated. 5 6 7 8 9 1 wavelength (nm)
Applications: Percentage (%) Energy: Process: Plasma: 6 5 4 3 2 1 CO CO2 H2 O2 CH4 technology goal fuel reformer Percentage (%) 6 5 4 3 2 1 pure methane hydrogen production CO CO2 H2 O2 H 2 rich mixtures spark in CH 4 /air H 2 production O/C ratio 1.2 total flow Γ=2 l/min 1 2 3 4 5 discharge current (ma)..2.4.6.8 1. 1.2 1.4 1.6 1.8 2. 2.2 O/C ratio
Applications: Paper: technology goal improve packaging Process: modify wettability hydrorepellncy Plasma: N 2 /HMDSO dbd siloxane film 3 25 2 W ater A bsorption [C obb 6 ] U ntreated surface Low pressure plasma atmospheric pressure plasma 7 6 g/m 2 5 4 3 2 Untreated Plasma treated 1 e 1 e 2 e 3 e 4 e 5
Applications: 1 Transmittance (%) 8 6 4 2 FIB section and imaging 4 35 3 25 2 15 1 5 Wavenumber k (cm -1 ) FT-IR spectra of HMDSO film on PET (Si-O-Si, Si, Si-CH3, CHx) Estimated thickness: 12 nm
Conclusions Plasma processing: is a dry and eco-friendly technology (deserve spreading) atmospheric pressure discharges widen application field of plasmas processes should be brought at atmospheric pressure (polymerization, pattern, nanopowder) Contribution from basic plasma physics research: development of advanced diagnostics (electrical, optical) modeling of the discharge processes (breakdown, sustainement, regimes, chemistry)