Trends in plasma applications

Transcription

1 3 International Conference on Frontiers of Plasma Physics and Technology Trends in plasma applications R. Barni Centro PlasmaPrometeo Bangkok 5 March 27

2 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

3 Atmospheric pressure plasmas in nature On earth: lightning, thunderbolt (storms, volcano eruptions) Mankind activity: Electrical discharges B.Franklin (1747)

4 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

5 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

6 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] Time [µs] Current [ma] Current [ma]

7 Diagnostics Optical tecniques: Intensità (a.u.) Lunghezza d'onda (nm) Atmospheric pressure DBD Low pressure Glow discharge Oxygen Intensity ratio Emission spectra radical identification Advanced tools LIF, Stark,, fast cameras Vibrational temperature (K) Intensity ratio O (777.4) / N2 (357) Power (W) 28

8 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

9 Modeling Density (cm^-3) 1 2 Chemical Composition of an Air streamer 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 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/CH P (H 2 ) I (H α ) Repetition rate ν = 2 ν AC Mean spark current (ma) H2 conversion efficiency (percentage)

10 Silk: Applications: technology goal remove sericin Process: selective removal pure fibroin fibres Plasma: etching O 2 remove/crack sericin Untreated Plasma treated Chemical degumming

11 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

12 Applications: PET films: technology goal optical properties Process: modify roughness reflectivity changes Plasma: dbd in air surface etching energy dose 15.4 J cm -2 untreated sample Reflectivity (%) treated.5 untreated Untreated Plasma treated wavelength (nm)

13 Applications: Percentage (%) Energy: Process: Plasma: CO CO2 H2 O2 CH4 technology goal fuel reformer Percentage (%) 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 discharge current (ma) O/C ratio

14 Applications: Paper: technology goal improve packaging Process: modify wettability hydrorepellncy Plasma: N 2 /HMDSO dbd siloxane film W ater A bsorption [C obb 6 ] U ntreated surface Low pressure plasma atmospheric pressure plasma 7 6 g/m Untreated Plasma treated 1 e 1 e 2 e 3 e 4 e 5

15 Applications: 1 Transmittance (%) FIB section and imaging Wavenumber k (cm -1 ) FT-IR spectra of HMDSO film on PET (Si-O-Si, Si, Si-CH3, CHx) Estimated thickness: 12 nm

16 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)