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  • 1
    Digitale Medien
    Digitale Medien
    Effect of a substrate on the temperature distribution in an argon-hydrogen thermal plasma jet (1994)
    Springer
    Plasma chemistry and plasma processing 14 (1994), S. 407-423 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Thermal plasma spraying ; Rayleigh scattering ; heat transfer coefficient ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Gas temperature profiles in the plume of an argon-hydrogen thermal plasma jet were determined /torn Rayleigh scattered laser light. Measured profiles were found to be well fitted by a Gaussian curve. Temperature data were compared with values obtained from thermocouples and showed an increasing discrepancy for temperatures higher than 800 K. The presence Q1 a cooled substrate in the flow was observed to increase the center-line temperature by about 22 at the substrate. By, combining the temperature results with calorimetric measurements of heal fox, a heat transfer coefficient to a copper substrate held at 300 K Iras determined to be in the range 400–1000 W/m2. K under typical plasma spraying conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01570204
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  • 2
    Digitale Medien
    Digitale Medien
    Unsteadiness and mixing in thermal plasma jets (1994)
    Springer
    Plasma chemistry and plasma processing 14 (1994), S. 425-436 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Thermal plasma jet ; turbulence ; unsteadiness ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract This study was undertaken to examine the mechanisms which produce the large entrainment measured at the exit of thermal plasma torches. The experiments studied a Metco 7MB plasma torch with a 706 (6.35 mm diameter) anode nozzle and swirled argon gas injection. The vortex structure produced in the shear layer of the plasma jet was visualized using a laser shadowgraph system with a short exposure lime (10−4 s). A high-speed video system provided information on the structure and unsteadiness of the hot potential core of the plume. Tile shear layer visualizations were compared to previous measurements of acoustical power spectra and indicate coherent vortex structure formation at low gas flowrates. At higher gas flowrates the shear layer rapidly broke down, producing relatively small scale turbulence. The visualizations of the hot potential core were compared to previous measurements of the torch voltage fluctuations caused by arc instabilities. At low flowrates the arc-produced voltage fluctuations were guile low card the phone was very steady. At higher flowrates the voltage fluctuations increased and produced “surging ” and “whipping” in the hot potential core.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01570205
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  • 3
    Digitale Medien
    Digitale Medien
    Light paraffin oxidative conversion in a silent electric discharge (1993)
    Springer
    Plasma chemistry and plasma processing 13 (1993), S. 479-488 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Silent discharge ; oxidation of light paraffins ; experimental ; methanol ; ethanol ; formaldehyde ; acetaldehyde
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Methane, ethane, and their mixtures with oxygen have been passed through the silent electric discharge at various operating conditions Beside.carbon oxides and water, formaldehyde and methane, and acetaldehyde and ethanol from ethane were the other major products. The effect of temperature, pressure, discharge voltage, contact time, and oxygen concentration have been examined. The rate of oxygen consumption is almost independent of oxygen concentration and depends mainly on the discharge voltage. The selectivities of methanol formation from methane and ethanol/formation from ethane were 20 and 15%, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01465877
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  • 4
    Digitale Medien
    Digitale Medien
    Process study of thermal plasma chemical vapor deposition of diamond, part I: Substrate material, temperature, and methane concentration (1992)
    Springer
    Plasma chemistry and plasma processing 12 (1992), S. 35-53 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Diamond films ; thermal plasma synthesis ; chemical vapor deposition ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Effects of process parameters on diamond film synthesis in DC thermal plasma jet reactors are discussed including substrate material, methane concentration and substrate temperature. Diamond has been deposited on silicon, molybdenum, tungsten, tantalum, copper, nickel, titanium, and stainless steel. The adhesion of diamond film to the substrate is greatly affected by the type of substrate used. It has been found that the methane concentration strongly affects the grain size of the diamond films. Increased methane concentrations result in smaller grain sizes due to the increased number of secondary nucleations on the existing facets of diamond crystals. Substrate temperature has a strong effect on the morphology of diamond films. With increasing substrate temperature, the predominant orientation of the crystal growth planes changes from the (111) to the (100) planes. Studies of the variation of the film quality across the substrate due to the nonuniformity of thermal plasma jets indicate that microcrystalline graphite formation starts at the corners and edges of diamond crystals when the conditions become unfavorable for diamond deposition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447943
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  • 5
    Digitale Medien
    Digitale Medien
    Electrode erosion in plasma torches (1992)
    Springer
    Plasma chemistry and plasma processing 12 (1992), S. 327-343 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Plasma torches ; cold cathode erosion ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Cathode erosion rates are reported (or copper electrodes in a simulated plasma torch operating at atmospheric pressure. The are current was 100A (or most experiments; the magnetic field used to move the arc varied between 0.001 and 0.15 T. Different plasma gases were used (Ar, He, air, N2, CO, and mixtures of the noble gases with O2, N2, CO, CH4, Cl2, and H2S) at flow rates varying between 0.2 and 20 liters/min. Different criteria (arc velocity, arc attachment residence time, arc current density) were used to analyze the erosion results.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447029
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  • 6
    Digitale Medien
    Digitale Medien
    Formation of aluminum nitrides in thermal plasmas (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 41-56 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Thermal plasma synthesis ; aluminum nitride ; aluminum anode ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Aluminum nitride has been synthesized by evaporation of the aluminum anode of a free-burning atmospheric-pressure nitrogen arc. About 40% of the product was collected in the form of highly oriented polycrystalline aluminum nitride (from the gaseous phase) with a high deposition rate (≈ 1 μm/s) and very low oxygen content (0.34%). The rest was deposited on the reactor walls as an ultrafine powder with an average particle diameter of 300 Å. Destructive and nondestructive tests on the powder and crystals were carried out to determine the morphology and purity of the materials. The impact of other gases on the AlN formation has been studied. The probable mechanism in the AlN crystal growth is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447033
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  • 7
    Digitale Medien
    Digitale Medien
    Comparison of temperature and work function measurements obtained with different GTA electrodes (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 81-101 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Arc electrodes ; rare-earth additions ; thermionic emission ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract This work was carried out on one standard electrode (W-ThO2,) and other electrodes developed by additions of La2O3, CeO2, and Y2O3,. The effect of rare-earth metal oxides on GTAW electrode phenomena, concerning electrode temperature, emissivity, and work function, was analyzed and compared from the point of view of those oxides' behavior during arcing. The experimental results indicate that the electrode temperature, emissivity, and work (unction .strongly depend on the behavior of the rare-earth metal oxides during arcing. The investigation demonstrates good stability of La2O3 during arcing compared with the other oxides. The temperature distributions along the electrode axis of these electrodes were measured by using infrared pyrometer and grooved electrodes. The W-La2O3 electrode showed the lowest temperature values, followed by W-CeO2 and W-ThO2 electrodes in that order. Also W-La2O3 electrodes have a higher emissivity and lower work Junction, followed by W-CeO2 and W-ThO2 electrodes in that order.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447035
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  • 8
    Digitale Medien
    Digitale Medien
    Experimental investigation of powder vaporization in thermal plasma jets (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 185-201 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Thermal plasma jet ; metallic and ceramic particles ; evaporation ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract An experimental study of the vaporization of metallic and ceramic particles in a thermal do plasma jet has been initiated and two series of experiments have been performed: (1) measurement of the vapor concentration within the plasma jet by absorption spectroscopy. (2) Investigation of the vapor cloud surrounding a single particle in flight by emission spectroscopy. The temperature within this cloud is determined by the intensity ratio of two lines which are simultaneously measured. The cloud radius is deduced /torn measurement of the particle velocity by laser doppler anemometry, and the vapor concentration is calculated from the line intensity profile, once the temperature is known. Results on iron and alumina particles injected in argon or argon-hydrogen plasma jets are given and discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447242
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  • 9
    Digitale Medien
    Digitale Medien
    Rate constants for the etching of gallium arsenide by atomic chlorine (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 311-321 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Plasma etching ; rate constants ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Known chlorine atom concentrations were prepared in a discharge flow system and used to etch the (100) face of a gallium arsenide single crystal. The etch rate was monitored by mass spectrometry, laser interferometry, and surface proftlometry. In the temperature range from 90 to 160°C the reaction can be described by the rate law $$Etch rate = kP_{Cl} $$ where $$k = 9 \times 10^{(6 \pm 0.5)} \mu m min^{ - 1} Torr^{ - 1} e^{ - 9 \pm 1)kcal/RT} $$
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447249
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  • 10
    Digitale Medien
    Digitale Medien
    Use of CF3,Br/Al, discharges for reactive ion etching of III-V semiconductors (1991)
    Springer
    Plasma chemistry and plasma processing 11 (1991), S. 295-310 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Plasma etching ; semiconductors ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The reactive ion etching of GaAs, InP, InGaAs, and InAlAs in CF3Br/Ar discharges was investigated as a function of both plasma power density (0.56-1.3 W - cm−2) and total pressure (10-40 mTorr) The etch rate of GaAs in 19CF3Br:1Ar discharges at 10 m Torr increases linearly with power density, from 600 Å min−1 at 0.56 W · cm−2, to 1550 Å · min at 1.3 W · cm−2. The in-based materials show linear increases in etch rates only for power densities above − 1.0 W · cm−2. These etch rates are comparable to those obtained with CCI2F2:O2 mixtures under the same conditions. Smooth surface morphologies and vertical sidewalls are obtained over a wide range of plasma parameters. Reductions in the near-surface carrier concentration in n-type GaAs are evident for etching with power densities of 〉0.8 W cm−2, due to the introduction of deep level trapping centers. At 1.3 W· cm−2, the Schottky barrier height of TiPtAu contacts on GaAs is reduced from 0.74 to 0.53 eV as a result of this damage, and the photoluminescent intensity from the material is degraded. Alter RIE, we detect the presence of both F and Br on the surface of all of the semiconductors. This contamination is worse than with CCl2F2-based mixtures. High-power etching with CF3Br/Ar together with Al-containing electrodes can lead to the presence of a substantial layer of aluminum oxide on the samples if the moisture content in the reactor is appreciable.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447248
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  • 11
    Digitale Medien
    Digitale Medien
    Plasma polymerization anda-C:H film ablation in microwave discharges in methane diluted with argon and hydrogen (1990)
    Springer
    Plasma chemistry and plasma processing 10 (1990), S. 451-471 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Gas-phase polymerization ; microwave discharge ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract Neutral hydrocarbons are observed from a microwave discharge in a fast flow of (A) 0.5–6% methane in argon, (B) 0.5–6% methane in hydrogen, and (C) hydrogen over a previously depositeda-C:H film. System (A) produces polyacetylenic and other hydrocarbons through C8 by predominantly gas-phase reactions and deposits ana-C: H film. Reactions under conditions (B) and (C) produce hydrocarbon radicals and molecules with masses through 300 that in case (B) arise from both gas-phase reactions and film ablation, and in case (C) from film ablation alone. Proposals are made for the mechanisms of gas-phase polymerization, film deposition, and ablation. Hydrocarbon ions observed downstream from these discharges appear to arise from ionization of neutral species with a distribution determined by subsequent ion-molecule reactions and selective diffusion losses.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01447203
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  • 12
    Digitale Medien
    Digitale Medien
    Gas-phase reactions in plasmas of SF6 with O2: Reactions of F with SOF2 and SO2 and reactions of O with SOF2 (1989)
    Springer
    Plasma chemistry and plasma processing 9 (1989), S. 409-420 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Gas flow reactor ; plasma chemistry of SF6/O2 ; rate coefficients ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The plasma chemistry of SF6/O2 mixtures is particularly complicated because of the large number of possible reactions. Over a wide range of conditions, products including SF4, SOF4, SOF2, and SO2F2 can be formed but thre is considerable uncertainty about the major reactions which contribute to the formation of these species. In this work reactions of oxygen atoms with SOF2 and fluorine atoms with SOF2 and SO2 have been studied in order to determine the principal sources of SO2F2 in these plasmas. Reactions were studied at 295 K in a gas flow reactor sampled by a mass spectrometer. No reaction could be detected between oxygen atoms and SOF2, which for the conditions employed, means that the upper limit for the reaction rate coefficient is 1×10−14 cm3 sec−1. The reaction of fluorine atoms with SOF2 was studied with the helium bath gas number density ranging from 3.1×1016 to 2.0×1017 cm−3. Within this range the rate coefficient increased with increasing [He] from (4.1 to 10.8)×10−14 cm3 sec−1. SO2 was found to react with fluorine atoms with a rate coefficient which appeared to be independent of the helium bath gas number density over the range given above. The possibility that this reaction occurred entirely on the walls of the reactor is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01083675
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  • 13
    Digitale Medien
    Digitale Medien
    Transfer of F− in the reaction of SF 6 − with SOF4: Implications for SOF4 production in corona discharges (1988)
    Springer
    Plasma chemistry and plasma processing 8 (1988), S. 225-246 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Corona discharges ; chemical reactions ; rate coefficients ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The temperature (T) and electric field-to-gas pressure (E/P) dependences of the rate coefficientk for the reaction SF 6 − +SOF4→SOF 5 − +SF5 have been measured. ForT〈270 K,k approaches a constant of 2.1×10−9 cm3/s, and for 433〉T〉270 K,k decreases withT according tok (cm3/s)=0.124 exp [−3.3 lnT(K)]. ForE/P〈V/cm·torr,k has a constant value of about 2.5×10−10 cm3/s, and for 130 V/cm·torr〉E/P〉60 V/cm·torr, the rate is approximately given byk (cm3/s)∼7.0×10−10 exp (−0.022E/P). The measured rate coefficient is used to estimate the influence of this reaction on SOF4 production from negative, point-plane, glow-type corona discharges in gas mixtures containing SF6 and at least trace amounts of O2 and H2O. A chemical kinetics model of the ion-drift region in the discharge gap is used to fit experimental data on SOF4 yields assuming that the SF 6 − +SOF4 reaction is the predominant SOF4 loss mechanism. It is found that the contribution of this reaction to SOF4 destruction falls considerably below the estimated maximum effect assuming that SF 6 − is the predominant charge carrier which reacts only with SOF4. The results of this analysis suggest that SF 6 − is efficiently deactivated by other reactions, and the influence of SF 6 − +SOF4 on SOF4 production is not necessarily more significant than that of other slower secondary processes such as gas-phase hydrolysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01016159
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  • 14
    Digitale Medien
    Digitale Medien
    Identification of corona discharge-induced SF6 oxidation mechanisms using SF6/18O2/H2 16O and SF6/16O2/H2 18O gas mixtures (1988)
    Springer
    Plasma chemistry and plasma processing 8 (1988), S. 207-223 
    Details
    ISSN: 1572-8986
    Schlagwort(e): Corona discharge ; SF6 oxidation mechanisms ; experimental
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Technik allgemein
    Notizen: Abstract The absolute yields of gaseous oxyfluorides SOF2, SO2F2, and SOF4 from negative, point-plane corona discharges in pressurized gas mixtures of SF6 with O2 and H2O enriched with18O2 and H2 18O have been measured using a gas chromatograph-mass spectrometer. The predominant SF6 oxidation mechanisms have been revealed from a determination of the relative18O and16O isotope content of the observed oxyfluoride by-product. The results are consistent with previously proposed production mechanisms and indicate that SOF2 and SO2F2 derive oxygen predominantly from H2O and O2, respectively, in slow, gas-phase reactions involving SF4, SF3, and SF2 that occur outside of the discharge region. The species SOF4 derives oxygen from both H2O and O2 through fast reactions in the active discharge region involving free radicals or ions such as OH and O, with SF5 and SF4.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01016158
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