Plasma Chemistry and Plasma Processing (v.37, #1)

Quantum Chemical Approach for Determining Degradation Pathways of Phenol by Electrical Discharge Plasmas by Xiangru Fan; John B. McLaughlin; Artem Melman; Selma Mededovic Thagard (5-28).
This study uses density functional theory (DFT) simulations to predict the main pathways by which hydroxyl (OH) radicals oxidize phenol into monohydroxylated products during an electrical discharge directly in or contacting water. The calculated activation energies and reaction rate constants indicate that phenol ring H abstraction is less likely to occur than OH addition, which will be the fastest in the ortho and para positions. The chain propagation with molecular oxygen of such formed ortho and para radicals will result in the production of hydroquinone and catechol, which are, concurrently, the most likely products of phenol degradation by OH radicals. Electron transfer reactions between dihydroxycyclohexadienyl radicals and plasma oxidative species are another important reaction mechanism which may be contributing significantly to the formation of products. Good agreement between computed kinetic and experimental data demonstrates the feasibility of applying DFT to investigate chemical reaction mechanisms.
Keywords: Density functional theory; Electrical discharge; Phenol; Plasma

CO(B 1Σ+A 1Π) Angstrom System for Gas Temperature Measurements in CO2 Containing Plasmas by Yanjun Du; Keishiro Tamura; Sampson Moore; Zhimin Peng; Tomohiro Nozaki; Peter J. Bruggeman (29-41).
CO2 containing plasmas are of growing interest for greenhouse gas remediation and dry gas reforming. In this paper, we show that the optical emission spectrum of CO(B-A) transition can be used for gas temperature determination in CO2 containing plasmas. The study was performed in a packed-bed reactor and compared with previously published results for a MW discharge. The CO emission is mainly produced by direct electron excitation from ground state CO. The rotational temperature is determined by a fitting algorithm of the CO(B-A) (0-1) spectrum and the accuracy of the deduced rotational temperature is shown to be better than 30 K. Meanwhile, we also compared the results with the widely used Boltzmann plots of the CO(B-A) (0-1). The rotational lines corresponding to Q(18–24) yield accurately the gas temperature for spectra with a resolution in excess of 0.05 nm FWHM. Rotational lines with N < 18 cannot be used due to the overlap of rotational lines from different branches unless a spectral resolution of at least 5 pm is used.
Keywords: CO2 containing plasma; CO Angstrom system; Spectrum fitting; Gas temperature determination; Rotational spectroscopy; Dielectric barrier discharges (DBD)

It has been hypothesized that high-energy impact of very small silicon nanoparticles on a substrate may lead to epitaxial growth of silicon films at low substrate temperature. A possible means for producing such energetic nanoparticle fluxes involves pulsing an RF silane-containing plasma, and applying a positive DC bias to the substrate during the afterglow phase of each pulse so as to collect the negatively charged particles generated during the RF power on phase. We here report numerical modeling to provide a preliminary assessment of the feasibility of this scheme. The system modeled is a parallel-plate capacitively-coupled RF argon–silane plasma at pressures around 100 mTorr. Simulation results indicate that it is possible to achieve a periodic steady state in which each pulse delivers a controlled flux of nanoparticles to the biased substrate, that average particle sizes can be kept below 2–3 nm, that impact energies of the negatively-charged nanoparticles that are attracted by the applied bias can be maintained in the ~1 eV/atom range thought to be conducive to epitaxial growth without causing film damage, and that the volume fraction of neutral nanoparticles that deposit by low-velocity diffusion can be kept well below 1 %. The effects of several operating parameters are explored, including RF voltage, pressure, the value of the applied DC bias, and RF power on and off time during each pulse.
Keywords: Dusty plasmas; Silicon nanoparticles; Pulsed RF plasmas

Low Cost Compact Nanosecond Pulsed Plasma System for Environmental and Biomedical Applications by Muhammad Arif Malik; Karl H. Schoenbach; Tarek M. Abdel-Fattah; Richard Heller; Chunqi Jiang (59-76).
Nanosecond pulsed non-thermal atmospheric-pressure plasmas are promising for numerous applications including air and water purification, ozone synthesis, surface sterilization, material processing, and biomedical care. However, the high cost of the nanosecond pulsed power sources has hindered adaptation of the plasma-based technologies for clinical and industrial use. This paper presents a low cost (<100US$) nanosecond pulsed plasma system that consists of a Cockcroft–Walton high voltage charging circuit, a compact nanosecond pulse generator using a spark gap as switch, and a plasma reactor. The nanosecond pulse power source requires only a 12 V DC input, hence is battery operable. Through the optimization of the experimental parameters, pulses with a peak voltage >10 kV, a 3 ns rise time (10 to 90 %), and a 10 ns pulse duration (full width at half maximum) at a pulse repetition rate of up to 500 Hz were achieved in the present study. It has been successfully tested to power three different plasma reactors to form pulsed corona discharges, dielectric barrier discharges, and sliding discharges. The energy efficiency of such a nanosecond pulsed sliding discharge system was assessed in the context of ozone synthesis using air or oxygen as the feed gas, and was found comparable to a previously reported non-thermal plasma system that used commercial high voltage pulsed power sources. This study demonstrated that this low-cost nanosecond pulsed power source can prove to be an energy efficient and simple supply to drive various non-thermal atmospheric-pressure plasma reactors for environmental, medical and other applications.
Keywords: Cockcroft–Walton voltage multiplier; Nanosecond pulsed power; Non-thermal plasma; Ozone synthesis; Energy efficiency

A Portable Plasma Sterilizer by ChangMing Du; Chao Shang; Ting Wang; ZiMing Li; Xin Yang; HaiTian Chen; Ya Liu; Kui Wang (77-97).
An atmospheric microplasma jet system powered by an commercial transformer is developed for investigating the sterilizing efficiency of Escherichia coli in different conditions. The device can be hand-held and operated in the open air. The effect of carrier gas, gas flow rate, distance and treatment time of inactivation is studied. According to the experiment, plasma jet is able to inactivate all the bacteria on the surface in 20 s when the air flow rate is 5 L/min and the distance is 2.0 cm. Besides, the sterilization efficacy with different carrier gas follows an order as bellow: N2 > air > O2 > Ar. The measurements of malondialdehyde content, protein leakage quantity and Mg content are performed as well. In addition, the SEM after plasma treatment reveals that the integrity of E. coli cells is damaged and intracellular particles are excreted into the extracellular space. With discussions upon the mechanisms of surface sterilization, it is found that during the treatment of microplasma, it is mainly the etching actions of electrons and ions on the bacilli that kill the E. coli. Chemical effects rather than physical ones that are responsible for inactivation. Furthermore, the experiment results suggest that there may be better sterilization effect with gas mixture as carrier gas.
Keywords: Microplasma jet; Sterilization; Escherichia coli

Softening Hard Water Using High Frequency Spark Plasma Discharge by Talie Zarei; Shahriar Mirpour; Hamed Nikmaram; Mahmood Ghoranneviss; Sahar Mirpour; Davoud Dorranian (99-114).
Effects of high frequency spark plasma discharge as a time efficiency method in order to softening the natural hard water has been investigated experimentally. A very hard water sample with 331 ± 19 mg/l of CaCO3 hardness was used. The current and voltage of each spike was about 9.6 A and 3.5 kV respectively at 16 kHz frequency with 35 μs pulse width. Hard water was treated for 2, 4, 6, and 8 min. The concentration of CaCO3, Ca2+ ions, Mg2+ ions and pH as well as water conductivity was controlled before and after treatment. The concentration of CaCO3 dropped by 70%, after 8 min treatment. During the treatment, the pH had a fluctuation about 1.5 and finally remained in neutral state. Also the elemental composition, crystalline structure and morphology of the precipitates were identified. Molecular dynamics simulation revealed that the ozone and hydroxyl play important roles in the softening of the hard water.
Keywords: High frequency spark plasma; Hard water; Precipitation; Calcium; Magnesium

Hydrogen-rich synthesis gas was produced by pulsed dc plasma submerged into ethanol–water mixtures using an original system with a coaxial geometry. The ignition of the discharge is immediately followed by production of hydrogen and after a short time necessary for filling the outlet tubing a flame can be ignited. No auxiliary gas was used for the reforming process. The synthesis gas containing up to 60% of hydrogen was formed, at the outflow rate of 250 sccm at the average power as low as 10 W. The hydrogen production efficiency corresponds to 12 kWh/kg H2.
Keywords: Plasma discharge in liquid; Hydrogen production; Synthesis gas; Ethanol reforming; Pulsed plasma

Hydrogen Peroxide Formation by Electric Discharge with Fine Bubbles by Yui Hayashi; Noriharu Takada; Wahyudiono; Hideki Kanda; Motonobu Goto (125-135).
Pulsed discharge plasma is typical oxidation technology for disposing organic compounds in aqueous solutions. When this electrical discharge plasma was applied in water, it may produce hydrogen peroxide (H2O2) without any catalyst or chemical agent. In order to increase H2O2 production by electrical discharge plasma in water, fine bubbles were introduced into the electrical discharge plasma in this experiment. Bipolar pulsed voltages were applied to cylindrical electrodes in the water while Ar or O2 bubbles were introduced, generating a pulsed discharge plasma. The introduction of the bubbles seemed to enhance the dissociation of water molecules and increased H2O2 formation, especially with O2 bubbling. Dissolved oxygen in the water contributed to H2O2 formation by pulsed discharge plasma with the bubbles, while dissociation of water molecules was the cause of H2O2 formation by pulsed discharge plasma without bubbles. More H2O2 was formed by pulsed discharge plasma with O2 bubbles, because the amount of dissolved oxygen in the water increased upon bubbling with O2.
Keywords: Hydrogen peroxide; Discharge plasma in water; Fine bubble

Comparison of Gasoline-Ranged n-Alkanes Conversions Using Dielectric Barrier Discharge: A Kinetic Study by Shuiliang Yao; Shan Weng; Qi Jin; Zuliang Wu; Boqiong Jiang; Xiujuan Tang; Hao Lu; Jingyi Han; Yaqun Cao; Xuming Zhang (137-148).
Here, we compared the conversion of gasoline-ranged n-alkanes (C6–C9) using dielectric barrier discharge. For an energy density of ~68 J/L and an initial n-alkane concentration of ~230 ppm, when carbon number increased from 6 to 9, the energy efficiency of n-alkane conversion increased from 117 to 240 mmol/kWh, CO x selectivity decreased from 46 to 20%, and ozone concentration increased from 216 to 240 ppm. The effect of energy density and initial n-alkane concentration were also investigated. The understanding of initial step of conversion was greatly aided by a proposed kinetic model. The pathways of consecutive reactions from the initiation to products were also discussed.
Keywords: n-Alkane; Dielectric barrier discharge; Energy efficiency; Kinetic study; Conversion product

OES and GC/MS Study of RF Plasma of Xylenes by Szetsen Lee; Shiao-Jun Liu (149-158).
The radio-frequency discharge of xylene isomers was monitored with optical emission spectroscopy (OES). It was found that the meta isomer showed relatively stronger excimer to monomer intensity ratio than the other two isomers. OES also indicates the formation of xylyl (methylbenzyl) radicals. The reaction products of low pressure xylene plasmas were analyzed by gas-chromatography mass spectrometry (GC/MS). It showed that the main composition of the reaction products was 1,2-di-p-tolylethane (DPTE), regardless the types of xylene isomers used. It is known that o- and m-xylyl radicals can undergo rearrangement and convert to p-xylyl radicals. Similar to the cases in benzene and toluene plasmas, the recombination reaction between two p-xylyl radicals is believed to be responsible for the formation of DPTE. Density functional theory calculations suggest that the direct conversion of xylene excimers to DPTE is unlikely.
Keywords: Xylene; Monomer; Excimer; GC/MS; OES

ZnO nanoparticles with and without 8 mol % Ce dopant were synthesized by precipitation method and the prepared samples were treated with various types of non-thermal plasma in order to study their effects on the morphology and photocatalytic activity of the samples. As-prepared Ce-doped ZnO has a hexagonal wurtzite structure and the crystal system was not changed by the plasma treatment. The morphology of Ce-doped ZnO was changed from spherical particle to flower and rod-like shapes by the plasma treatment. The particle size of the treated Ce-doped ZnO is smaller in comparison with that of untreated sample. The photodegradation of methylene blue by the plasma-treated Ce-doped ZnO in aqueous solution is higher than that of the untreated Ce-doped ZnO. The enhancement of the photocatalytic activity by the plasma-treated samples may come from the particle size reduction, enhancement in charge separation efficiency and increase of the surface area.
Keywords: Ce-doped ZnO; Non-thermal plasma; Morphology; Photocatalysis; Methylene blue

Cathodic Plasma Electrolysis Processing for Metal Coating Deposition by Xu Yang; Xianfei Ding; Guojian Hao; Yongfeng Liang; Junping Lin (177-187).
Cathodic plasma electrolysis (CPE) is used to deposit Zn coating on the surface of steel wire. The relationships between power parameters and coating characteristics were investigated in this study to determine the best way to control the coating process according to the CPE procedure and pulsed DC power cycle. We found that voltage should be greater than the critical voltage for the formation of plasma. Deposition coating is difficult to establish under DC supply, however, continuous coating is rather easily prepared under pulsed DC power of 120 V, 4000 Hz, and 80 % duty cycle. We adopted pulsed DC power to successfully facilitate Zn cations approaching the cathode surface as well as to prevent wire melting under high voltage by reducing the duty cycle. Decreases in voltage, frequency, or duty cycle did not contribute to plasma stability, but did increase the deposition rate and porosity. Our experimental plasma formation process showed that the role of plasma formation is to clean the cathode surface by melting and shocking, which produces deposition at the interval between two neighboring pulses.
Keywords: Cathodic plasma electrolysis; Deposition; Pulsed DC power; Parameters

Plasma Impedance Analysis: A Novel Approach for Investigating a Phase Transition from a-Si:H to nc-Si:H by Deepika Chaudhary; Mansi Sharma; S. Sudhakar; Sushil Kumar (189-205).
In the present article we report the transition regime of hydrogenated amorphous (a-Si:H) to nano-crystalline (nc-Si:H) silicon thin films in Silane (SiH4) plasma using 27.12 MHz assisted plasma enhanced chemical vapor deposition process with the approach of plasma diagnosis. The observed transitions occur within a narrow range of diverse deposition process window and hence plasma diagnosis was vital towards envisaging this variation. Impedance Analyser (V/I probe) was used to monitor plasma characteristics during growth at various process pressure (0.03–0.4 Torr) and applied power (4–20 W). Efforts were made to understand the radicals’ formation and plasma-substrate interaction by evaluating the discharge parameters such as electron density, bulk field, and sheath voltage. From the result of plasma characterizations, highest bulk field (5.7 V/cm) in combination to low sheath voltage (0.1 V) observed on 0.2 Torr pressure at 15 W power which thus provides a clear signature of transition from a-Si:H to nc-Si:H. The structural characterizations also validate the results of observed transition where in particular it was found that the mean crystallite size (4.2 nm) with high crystalline volume fraction (42%) and wider band gap (2.01 eV) with higher hydrogen content (35%) signifies the existing nano-crystalline phase. On account of these results, an empirical relation between plasma impedance and phase angle was established in terms of expansion and contraction of two distinct discharge zones (bulk and sheath) to diagnose the phase transition.
Keywords: Plasma impedance; 27.12 MHz assisted PECVD process; Transition zone; Nano-crystalline silicon thin films

The two key questions addressed in this paper were whether different cultivars of hemp (Cannabis sativa L.) have the same reactions to non-thermal plasma seed pre-treatments and whether different plasma sources have different effects on the seeds. Seed germination and early growth of hemp in design of hierarchical analysis of variance was conducted. Differences in response among seeds of three hemp cultivars (‘Finola’, ‘Bialobrzeskie’, ‘Carmagnola’) to the non-thermal plasma pre-treatment generated by two apparatuses (gliding arc and downstream microwave devices) in four time expositions (0, 180, 300, 600 s) were found. The high importance was found in type of apparatus and time exposition. A positive/neutral effect was observed in all measured characteristics after gliding arc plasma pre-treatment. Gliding arc pre-treatment increased the length of seedlings, seedling accretion and weight of seedling in both cv. ‘Finola’ and cv. ‘Bialobrzeskie’ hemp. On the other hand, the downstream microwave apparatus had an inhibiting effect on all tested hemp cultivars. It was the first time when significant differences in response to non-thermal pre-treatment were found in taxonomically close plants. The results obtained in this study describes different effect of various plasma treatment on germination and early growth of hemp seeds. The direct pre-treatment of non-thermal plasma discharge in condition of atmospheric pressure was better. Results of our experiment show that the use of non-thermal plasma pre-treatment may increase survival of some hemp cultivars during seedlings establishment in a drier period and may be used in new agro-technical measures in unconventional agriculture.
Keywords: Hemp cultivars; Nested ANOVA; Non-thermal plasma; Plasma device; Seed germination

Polytetrafluoroethylene Sputtered PES Membranes for Membrane Distillation: Influence of RF Magnetron Sputtering Conditions by Sara Pedram; Hamid R. Mortaheb; Houssam Fakhouri; Farzaneh Arefi-Khonsari (223-241).
Thin films of fluorocarbon were deposited on polyethersulfone membranes via argon plasma sputtering of a poly(tetrafluoroethylene) (PTFE) target in an RF magnetron plasma reactor. The obtained deposited ultrathin coatings had nanoscale roughnesses and high degrees of fluorination. The intensity of fluorine atom in plasma environment during fluorocarbon deposition was investigated. Depending on the deposition conditions comprising working gas pressure, applied RF power, and distance between the target and the substrate, polymeric films with different chemical compositions and/or morphologies were obtained. The morphologies of the films were analyzed by means of SEM, XPS, and AFM. The results suggested that the sputtered film deposited at a higher pressure and longer target–substrate distance and moderate RF power had a surface composition and chemical structure closer to those of the PTFE film. The treated hydrophobic PES membranes with water contact angles as high as 115° were applied for the first time in an air gap membrane distillation setup for removal of benzene as a volatile organic compound from water. The results showed that the plasma-treated membranes have a comparable or superior performance to that of commercial PTFE used in membrane distillation with similar permeate flux and separation factor after 20 h long term performance.
Keywords: PVD; Polytetrafluoroethylene (PTFE); RF magnetron sputtering; Thin film; Air gap membrane distillation; VOC removal

The expansion of an oxygen low-pressure microwave plasma was investigated in order to determine the optimal plasma parameters for the growth of functional oxide semiconductors. Langmuir probe measurements show that the electron density (n e ) increases with the injected power up to a saturation value of 3.0 × 109 cm−3 determined at 10 mTorr while electron temperature (T e ) remains constant at a value of 1.5 eV. When pressure is varied, n e shows a maximum value at a range from 12 to 20 mTorr while T e decreases monotonously with increasing pressure. In addition, both n e and T e decrease with the axial distance from the plasma source. These effects were discussed through the loss mechanisms in the remote plasma. For a pressure of 13 mTorr and at a substrate temperature of 500 °C, plasma enhanced oxidation of pure metallic Ti thin films lead to the formation of a pure TiO2 anatase phase compared to a mixed phase of TiO2 and TiO in the absence of plasma activation. For Mn thin films, the exposure to oxygen remote plasma led to the formation of MnO2 as opposed to obtaining Mn3O4 when oxidation is performed in the oxygen gas ambient. Remote plasma processing was thus found to provide selective pathways to control oxidation states, stoichiometry and phase composition of technologically attractive oxide thin films.
Keywords: Langmuir probe; Plasma expansion; Remote plasma oxidation; Titanium oxide; Manganese oxide

Energy Conversion Efficiency in Low- and Atmospheric-Pressure Plasma Polymerization Processes, Part II: HMDSO by Dirk Hegemann; Bernard Nisol; Sean Watson; Michael R. Wertheimer (257-271).
For at least forty years, there has been an interest to correlate the structure of plasma polymer coatings with fabrication parameters during deposition, most particularly with the energy input per monomer molecule, $$ E_{ ext{m}} $$ E m . In our two laboratories, we have developed methods for measuring $$ E_{ ext{m}} $$ E m (or somewhat equivalent activation energy, $$ E_{ ext{a}} $$ E a ) in low- (LP) and atmospheric-pressure (AP) discharge plasmas. We earlier proposed energy conversion efficiency, ECE, as a new parameter which permits direct comparison of LP and AP experiments. This is done here for the case of a much-studied organosilicon precursor (monomer), hexamethyl-disiloxane. “Critical” $$ E_{ ext{m}} $$ E m (or $$ E_{ ext{a}} $$ E a ) values that demarcate ECE regimes separating different fragmentation/reaction mechanisms are found to agree remarkably well, and to correlate with specific mechanisms. Furthermore, deposition rates, and structural (for example, “organic/inorganic” content ratio) characteristics are seen to display very similar behaviors, despite additional drastically differing fabrication conditions like pure or highly diluted (in Ar carrier gas) monomer feed in the LP and AP cases, respectively.
Keywords: Plasma polymerization; Low- and atmospheric-pressure; Energy per monomer; Energy conversion efficiency; Hexamethyl-disiloxane

Plasma-Chemical Treatment of Process Gases with Low-Concentration Fluorine-Containing Components by H. S. Park; S. P. Vaschenko; E. V. Kartaev; D. Yu. Batomunkuev (273-286).
The problems of recycling of the gases with low concentration of fluorine-containing components have been considered. The model of their plasma-chemical treatment with the heat recovery of effluent gases is proposed. The process thermodynamics for various compounds of reacting gases is considered. The heat- and mass transfer processes are simulated in the plasma-chemical reactor. Temperature and velocity profiles of treated gas flows have been obtained within the recovery zone, mixing area with the plasma jet as well as in the reactor working zone. The compliance of the resulting distributions and the temperature range needed for the full conversion is demonstrated. The experiments on the plasma-chemical treatment of carbon tetrafluoride and nitrogen trifluoride have been conducted. The resulting degrees of CF4 and NF3 decomposition turned out to be above 90% providing more than double reduction of specific energy cost as compared with the available facilities of similar purposes. An approach is proposed to reduce nitrogen oxide content in effluent gases at reactor outlet and to decrease in future the specific energy cost of conversion of halogen-containing gases.
Keywords: Plasma-chemical reactor; Fluorine-containing compounds decomposition; Gas dynamics simulation; Recuperative heat exchange

Laser Induced Surface Morphology of Molybdenum Correlated with Breakdown Spectroscopy by Mahreen Akram; Shazia Bashir; Muhammad Shahid Rafique; Asma Hayat; Khaliq Mahmood (287-304).
Surface modifications of laser irradiated molybdenum have been correlated with plasma parameters. Nd:YAG laser (1064 nm, 10 ns) was employed at various laser irradiances ranging from 6 to 50 GW/cm2 under argon environment. The ablation efficiency has been investigated by measuring the crater depth using surface profilometry analysis. Scanning electron microscope (SEM) analysis reveals the formation of coarse grains along with cracked boundaries, cavities and cones at the central ablated areas. Whereas, uplifted re-solidified material, cavities, ridges, droplets and cones were observed at boundary regions. Laser Induced Breakdown Spectroscopy (LIBS) analysis has been performed to evaluate electron temperature and number density of molybdenum plasma. Electron temperature and electron density varies from 6670 to 9305 K and 0.62 × 1018 to 0.72 × 1018 cm−3 respectively. Both the parameters showed similar trend in variation with laser irradiance i.e. an initial increase from 13 to 19 GW/cm2 followed by a decrease from 19 to 25 GW/cm2 and then a saturation from 25 to 50 GW/cm2. The initial increasing trend is attributed to the enhanced excited vapor content of the ablated material, confinement effects of the surrounding argon and absorption of laser energy into the molybdenum vapor plasma during the trailing part of laser pulse leading to ignition of laser supported combustion (LSW) waves. The decreasing trend is attributed to the shielding effect and saturation is explainable on the basis of the formation of a self-regulating regime. Surface modifications of laser irradiated molybdenum were correlated with the plasma parameters.
Keywords: Laser ablation; Micro structuring; Crater depth; Molybdenum; LIBS; Electron temperature and number density

A study is made on optical emission spectrum modification during X-ray exposure, in the case of a high-pressure mercury discharge lamp operated at several powers. A strong dependence on the lamp operating power for all the spectral lines intensities is observed. Erosion of the emissive mixture based on barium, calcium and yttrium compounds is evidenced by higher values recorded for spectral line intensities in all cases of X-ray exposure compared with those corresponding to non-irradiated lamps. Boltzmann type functions fitted the experimental data of measured optical emission intensities versus time for Ba+, Ca+ and Y+ lines. However, X-ray influence on plasma electron temperature is not significant. The spectroscopic data are correlated with the results of electrical measurements and of thermal analysis performed for the electrode having the emissive mixture based on barium, calcium and yttrium compounds. A qualitative explanation of the results is also given.
Keywords: High pressure mercury lamp with tungsten electrode having emissive mixture based on barium, calcium and yttrium compounds; Optical emission spectrum; Electrical measurements; Thermal analysis; X-ray adsorption

Influence Mechanisms of Trace H2O on the Generating Process of SF6 Spark Discharge Decomposition Components by Ju Tang; Xiajin Rao; Fuping Zeng; Wei Cai; Lin Cheng; Chaohai Zhang (325-340).
Trace H2O directly participates in the SF6 decomposition generating process under spark discharge, but its mechanism remains ambiguous. Thus , determining the influence rules of trace H2O on the decomposition characteristics of SF6 spark discharge is necessary . Moreover, the foundation of the effective spark discharge fault diagnosis methods should be established for SF6 gas-insulated apparatus. In this paper, a series of spark decomposition experiments of different proportions of SF6/H2O mixtures were conducted with a trace H2O injector accurately controlling H2O content. Influence mechanisms of trace H2O on the effective generation rates and the characteristic ratio of spark decomposition components were determined. Results show that trace H2O remarkably influences the effective generation rates of SF6 spark decomposition components, including SOF2, SOF4, SO2F2, SO2 and CF4. The characteristic ratio varies because of the distinct mechanisms of H2O on the components. Mathematical expression between the ratio and H2O contents was also derived. In addition, the X-ray photoelectron spectra show that the solid materials contain Al2O3 and AlF3, and the existing forms of S are sulfite and sulfate.
Keywords: SF6 ; Spark discharge decomposition; Trace H2O; Effective generation rate; Characteristic ratio; X-ray photoelectron spectra