František Krčma

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

A Plasma Surface Treatment of Polyester Textile Fabrics Used for Reinforcement of Car Tires

Polyester tire cord surfaces have been modified by plasma at low temperature and atmospheric pressure. The surface treatment has been executed by various nonequilibrium discharges, namely by barrier discharge, atmospheric pressure glow discharge and gliding arc. The polymeric multicord sewing threads treated by this procedure have been used in the same form as in industry, i.e., with the protecting oil films on their surface. The surface properties have been investigated by electron spin resonance spectroscopy and by measuring their contact angle with various liquids; partially the zeta potential measurements have been used, too. Further tests have been done at an industrial testing impregnation line using the common technology and conditions, on both plasma treated and untreated fibers. Finally, the standard H-tests and peel-tests have been used to characterize the fiber adhesion to usual testing rubbers.

The study of H2O2 generation by DC diaphragm discharge in liquids

The contribution gives results of hydrogen peroxide generation obtained in the DC diaphragm discharge in water solutions. Chemical active species, such as hydroxyl radicals and hydrogen peroxide are produced by the discharge. The dependencies of hydrogen peroxide concentration on high, voltage (magnitude and polarity), material of electrodes and dielectric diaphragm are studied for one electrolyte (NaCl) used for initial solution conductivity. The used dielectric diaphragms differ in material and they have various thickness.

Physical properties and chemical efficiency of an underwater dc discharge generated in He, Ar, N2 and air bubbles

A dc excited discharge generated in bubbles (He, Ar, Air, N2) in liquid phase is investigated in this work. Voltage/current characteristics and emission spectra of the discharge are recorded in the current range 10?30?mA. Electron density in the discharge is measured from Stark broadening of the H? line and is of the order of 2?6 ? 1020?m?3, depending on the feed gas. Estimation of electron temperature is carried out based on the balance of charged particles. Gas temperature is estimated by the slope of the Boltzmann plot and by the simulation of the OH band with different , and Tvib. Rotation temperature in the He discharge is 1200?K at I = 10?mA and linearly increases with current up to 1600?K. In the plasma of molecular gases the temperature is higher and almost constant at different currents. Chemical efficiency of the plasma is measured by the production of H2O2 and by the destruction of Direct Blue 106 dye. The highest energy consumption of H2O2 generation is achieved in the air discharge and it decreases up to 50% in the He plasma. Maximal efficiency of dye destruction is observed in the N2 plasma characterized by an energy consumption of dye decomposition of 0.86?g?kWh?1.

Diaphragm Discharge in Liquids: Fundamentals and Applications

Paper describes results of our research on DC diaphragm discharge creation in water solutions of electrolytes from the viewpoint of its principles, properties and applications. The thermal theory of discharge ignition in bubbles of evaporated solution has been confirmed by both high speed camera and sound records. Static current-voltage characteristics revealed a significant dependence of discharge breakdown on the solution conductivity. Determined breakdown parameters lay in the range of 900-1300 V and 40-100 mA, respectively, for NaCl solution conductivity varying from 150 to 1300 µS·cm -1 . Time resolved electrical characteristics showed a simultaneous appearance of current, voltage and sound oscillations as well as a light emission. Plasma diagnostics by optical emission spectroscopy confirmed formation of reactive species (hydroxyl, hydrogen and oxygen radicals) and excitation of metallic atoms presented in the solution. Moreover, rotational temperature was calculated from the obtained OH spectrum. Experiments focused on the diaphragm discharge applications are outlined in the paper. Results of hydrogen peroxide production, organic dye decomposition and treatment of humic acid solutions are compared from the viewpoint of experimental conditions.

Chemical Efficiency of

A dc underwater discharge generated in gas bubbles (air, Ar, He, and N2) in a NaH2PO4 · 2H2O solution is studied. It is shown that the maximal concentration of hydrogen peroxide produced in the discharge does not depend on gas composition. The energy efficiency of H2O2 production is, however, gas dependent, and the highest value of 2.95 g/kWh is obtained for air. The decomposition efficiency of the Direct Blue 106 dye, which is used as a model organic pollutant at an initial concentration of 20 mg/L, increases linearly with current in the investigated range (10-30 mA). A maximal dye decoloration of 65% is observed in a N2 discharge after 20 min of treatment at a current of 30 mA. Different mechanisms of dye decoloration by plasma are proposed and discussed.

\hbox{H}_{2}\hbox{O}_{2}

In this work, the reaction kinetics in argon flowing afterglow with nitrogen addition was studied by optical emission spectroscopy. The DC flowing post-discharge in pure argon was created in quartz tube at the total gas pressure of 1000 Pa and discharge power of 60 W. The nitrogen was added into the afterglow at the distance of 9 cm behind the active discharge. The optical emission spectra were measured along the flow tube. The argon spectral lines and after nitrogen addition also nitrogen second positive system (SPS) were identified in the spectra. The measurement of spatial dependence of SPS intensity showed a very slow decay of the intensity and the decay rate did not depend on the nitrogen concentration. In order to explain this behavior a kinetic model for reaction in afterglow was developed. This model showed that C (3)Πu state of molecular nitrogen, which is the upper state of SPS emission, is produced by excitation transfer from argon metastables to nitrogen molecules. However, the argon metastables are also produced at Ar2(+) ion recombination with electrons and this limits the decay of argon metastable concentration and it results in very slow decay of SPS intensity.

Production and Decomposition of Organic Compounds Under Action of DC Underwater Discharge in Gas Bubbles

A new low-temperature plasma surface modification of advanced polyester tire cord at atmospheric pressure was tested. Plasma surface treatment was performed in the barrier discharge plasmas (BDPs, atmospheric pressure glow discharge (APG) and plasma of gliding are (Glid Arc). The surface properties were characterized by the electron spin resonance spectroscopy (ESR), measurements of the contact angle of various polar and non-polar liquids with polyester cords, H-test, peel test and partially by zeta potential measurements. Further tests have been performed at an industrial testingimpregnation line where the common technology was applied on both plasma treated and untreated fibres. The standard H-test and peel-tests were used to characterize the adhesion of the fibre to usual testingrubbers.

Study of argon flowing afterglow with nitrogen injection

The low-temperature low-pressure hydrogen based plasmas were used to study the influence of processes and discharge conditions on corrosion removal. The capacitive coupled RF discharge in the continuous or pulsed regime was used at operating pressure of 100-200 Pa. Plasma treatment was monitored by optical emission spectroscopy. To be able to study influence of various process parameters, the model corroded samples with and without sandy incrustation were prepared. The SEM-EDX analyzes were carried out to verify corrosion removal efficiency. Experimental conditions were optimized for the selected most frequent materials of original metallic archaeological objects (iron, bronze, copper, and brass). Chlorides removal is based on hydrogen ion reactions while oxides are removed mainly by neutral species interactions. A special focus was kept for the samples temperature because it was necessary to avoid any metallographic changes in the material structure. The application of higher power pulsed regime with low duty cycle seems be the best treatment regime. The low pressure hydrogen plasma is not applicable for objects with a very broken structure or for nonmetallic objects due to the non-uniform heat stress. Due to this fact, the new developed plasmas generated in liquids were applied on selected original archaeological glass materials.

Plasma Surface Treatment of Textile Fibres for Improvement of Car Tires

The reaction kinetics in nitrogen flowing afterglow with mercury vapor addition was studied by optical emission spectroscopy. The DC flowing post-discharge in pure nitrogen was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 130 W. The mercury vapors were added into the afterglow at the distance of 30 cm behind the active discharge. The optical emission spectra were measured along the flow tube. Three nitrogen spectral systems--the first positive, the second positive, and the first negative, and after the mercury vapor addition also the mercury resonance line at 254 nm in the spectrum of the second order were identified. The measurement of the spatial dependence of mercury line intensity showed very slow decay of its intensity and the decay rate did not depend on the mercury concentration. In order to explain this behavior, a kinetic model for the reaction in afterglow was developed. This model showed that the state Hg(6 (3)P1), which is the upper state of mercury UV resonance line at 254 nm, is produced by the excitation transfer from nitrogen N2(A ³Σ(u)⁺) metastables to mercury atoms. However, the N2(A ³Σ(u)⁺) metastables are also produced by the reactions following the N atom recombination, and this limits the decay of N2(A ³Σ(u)⁺) metastable concentration and results in very slow decay of mercury resonance line intensity. It was found that N atoms are the most important particles in this late nitrogen afterglow, their volume recombination starts a chain of reactions which produce excited states of molecular nitrogen. In order to explain the decrease of N atom concentration, it was also necessary to include the surface recombination of N atoms to the model. The surface recombination was considered as a first order reaction and wall recombination probability γ = (1.35 ± 0.04) × 10(-6) was determined from the experimental data. Also sensitivity analysis was applied for the analysis of kinetic model in order to reveal the main control parameters in the model.