Showing papers on "Argon published in 1999"
TL;DR: In this article, the authors present the data and models describing the secondary electrons that initiate the secondary and subsequent feedback avalanches required for the growth of current during breakdown and for the maintenance of low-current, cold-cathode discharges in argon.
Abstract: We review the data and models describing the production of the electrons, termed secondary electrons, that initiate the secondary and subsequent feedback avalanches required for the growth of current during breakdown and for the maintenance of low-current, cold-cathode discharges in argon First we correlate measurements of the production of secondary electrons at metallic cathodes, ie the yields of electrons induced by Ar+ ions, fast Ar atoms, metastable atoms and vuv photons The yields of electrons per ion, fast atom and photon vary greatly with particle energy and surface condition Then models of electron, ion, fast atom, excited atom and photon transport and kinetics are fitted to electrical-breakdown and low-current, discharge-maintenance data to determine the contributions of various cathode-directed species to the secondary electron production Our model explains measured breakdown and low-current discharge voltages for Ar over a very wide range of electric field to gas density ratios E/n, ie 15 Td to 100 kTd We review corrections for nonequilibrium electron motion near the cathode that apply to our local-field model of these discharges Analytic expressions for the cross sections and reaction coefficients used by this and related models are summarized
768 citations
TL;DR: In this paper, the effects of different ablation cell configurations and the use of helium, dry argon and argon moistened with water for the transport of aerosols into an ICP-MS, using a prototype 193 nm ArF excimer laser.
Abstract: Laser ablation-ICP-MS is a sensitive and accurate technique for major to trace multi-element analysis at high spatial resolution on the scale of 10 µm. A wide variety of samples can be studied quantitatively, including minerals and their solid, liquid or melt inclusions as required for geochemical studies. As the desired spatial resolution increases, however, detection limits become severely constrained by the total amount of sample material reaching the ICP. Detection limits are therefore determined by the ablation rate and by the efficiency of removal of ablated aerosol particles from the ablation spot and their transport into the plasma. Properties of the carrier gas are known to affect the ablation process and the efficiency of particle transportation. This study explores the effects of different ablation-cell configurations and the use of helium, dry argon and argon moistened with water for the transport of aerosols into an ICP-MS, using a prototype 193 nm ArF excimer laser. Deposition of visible particles deposited around the ablation pit is significantly reduced when helium is used instead of argon. A moderate flux of helium through the chamber, mixed with moistened argon immediately downstream from the ablation chamber, leads to at least a 2-3-fold increase in the signal intensities across the entire mass range when compared with argon gas only. Background intensities above mass 85 are significantly reduced, but polyatomic interferences in the low mass region increase by an order of magnitude, owing to oxide formation caused by the water load. A high flux of helium, mixed just behind the ablation cell with dry argon, yields a 2-3-fold sensitivity enhancement, in addition to greatly reduced background intensity across the entire mass range. This results in one order of magnitude improvement in detection limits for most elements. These modifications permit the routine determination of minor concentrations of chlorine in microscopic fluid inclusions or the analysis of minerals, such as trace element concentrations in quartz (e.g., Na and Li down to 500 ng g
–1
, using a 40 µ ablation pit). Furthermore, this improved sensitivity has recently yielded the first quantitative determination of gold concentrations (∼0.1 µg g
–1
) and full rare-earth element patterns in single 25 µm fluid inclusions.
375 citations
TL;DR: The Ailaoshan Gold Province, China is a series of gold deposits hosted on a 200-km segment of a major normal fault formed during Eocene extension as discussed by the authors, which is well characterised using conventional geochemical and microthermometric techniques, the results of which are consistent with a predominantly high temperature "magmatic" fluid present in the ore minerals.
219 citations
TL;DR: In this article, the authors compared the ablation characteristics of a 266 nm Nd:YAG laser and a 193 nm excimer laser using inductively coupled plasma mass spectrometry (ICP-MS).
Abstract: The ablation characteristics of a 266 nm Nd:YAG laser and a 193 nm excimer laser were compared by successive experiments by inductively coupled plasma mass spectrometry (ICP-MS), using the same ablation cell without changing the carrier-gas flows within comparative experiments. Both laser-optical systems have a fairly flat-topped lateral energy distribution yielding pan-shaped ablation pits on the sample. Comparative experiments with the two optical systems were carried out with argon and with helium+argon as carrier gases. For both lasers and both gas set-ups, signals of 40 s duration were recorded with a pulse rate of 10 Hz, with similar fluence adjusted to give comparable rates of material ablation. ICP-MS signal intensities were normalised to the total ablated volume, to compare the effects of lasers and gases on transport efficiency, ionisation efficiency and response and time-dependent element fractionation. The accuracy of trace element results was tested using two materials that allow stable ablation with both lasers but have significantly different matrix compositions (SRM 612 silicate glass from NIST and AGV-1 geological reference material in lithium tetraborate fusion). The time-averaged rate of material ablation is similar for both lasers and independent of the carrier gas in the sample chamber, but decays more rapidly with the 266 nm system. In argon, the signal unit response per volume of ablated material is similar with both lasers. In helium, the signal intensity with the 266 nm laser is enhanced slightly (maximum two-fold) compared with argon, but with the 193 nm system a consistent 2-3-fold signal enhancement is achieved. The use of helium reduces the amount of visible (>1 µm size) particle deposition in the ablation cell, irrespective of laser wavelength, and tests with successive ablations of chemically contrasting samples indicate memory effects with the 266 nm system that are absent in the same experiment with the 193 nm system. The limits of detection for both lasers were further improved by the use of He owing to the decrease in background intensities. Time-dependent element fractionation during a 40 s single-spot ablation is almost eliminated with the 193 nm system (<10%), but with the 266 nm laser inter-element intensity ratios comparing the first and the second halves of the ablation period varied by up to 60% for some elements. Results for the cross-calibration between silicate (SRM 612) and borate glasses (AGV-1) obtained with both lasers indicate that the fractionation with the 266 nm system is similar for these two matrices, but this is not generally true for silicate minerals. The 193 nm system gives slightly better reproducibility between multiple analyses of one sample compared with the 266 nm system, yielding 2-5% RSDs for major and minor elements and 7-15% for concentrations below 10 ppm.
203 citations
TL;DR: In this paper, phase equilibria in helium-water, neon-water and hxdrogen-water SVstems were studied at pressures up to 15 kbar, and it was concluded that classical polyhedral clathrate hydrates are formed in all the systems, the stability of the hydates diminishing from xenon to neon.
Abstract: Phase equilibria in helium-water, neon-water, and hxdrogen-water svstems were studied at pressures up to 15 kbar. The results are compared with the data for the previously investigated water systems with argon, crypton, and xenon. It is concluded that classical polyhedral clathrate hydrates are formed in all the systems, the stability of the hydrates diminishing from xenon to neon. In all the systems, except the xenon system, the hydrates are based on the crystalline framework of ice II. Their formation demands high pressures; the larger the guest molecule, the higher the pressure required. The xenon molecule seems to be too large to fit the cage of the ice II framework; therefore, the xenon hydrate CS-I remains stable up to at least 15 kbar.
144 citations
TL;DR: In this paper, a pulsed dielectric barrier discharge (DBD) was used to measure the OH radical potential for pollutant oxidation in argon-water vapor gas mixtures.
Abstract: Good understanding of the different phases of the plasma-chemistry involved is essential for the development of nonthermal plasma technologies for pollution control. These techniques are often based on the dissociation of parent gases to produce radicals that, in turn, decompose the toxic compounds. Our research concerns OH radical production in a pulsed dielectric barrier discharge (DBD). OH[A 2Σ+–X 2Π(0,0)] emission in argon-water vapor gas mixtures has been studied. Particular attention has been paid to the influence of water vapor partial pressure on the lifetime and intensity of emitted fluorescence in order to develop a pulsed DBD ultraviolet light source for spectroscopic investigation. This source was used to perform OH(X 2Π) time-resolved average absolute density measurements in other DBD discharges based on resonant absorption spectroscopy. This diagnostic has been validated in argon and air-water vapor mixtures. The temporal behavior of the density OH(X 2Π) radicals after a pulse discharge has been studied in argon and air with and without 500 ppm of trichloroethylene. This simple and inexpensive tool, compared to more sophisticated laser absorption or laser-induced fluorescence measurements for plasma investigation, is very useful for characterizing the OH radical potential for pollutant oxidation.
134 citations
TL;DR: In this article, a numerical precision integration of the time-dependent Schrodinger equation in the single-electron approximation of the photoelectron spectrum of argon at 800 nm is studied.
Abstract: Resonant enhancement of high-order peaks in the photoelectron spectrum of argon at 800 nm is studied by numerical precision integration of the time-dependent Schr\"odinger equation in the single-electron approximation. It is shown that electrons in the backscattering region of the spectrum are almost exclusively due to resonances. Wave-function analysis shows that there are two types of resonant states: high-angular-momentum states that stay away from the nucleus and mainly decay by emission of low-energy electrons, and states that are located near the polarization axis. These latter states predominantly decay through violent collision with the ionic core, and are responsible for the enhancement of high-energy photoelectrons.
132 citations
TL;DR: In this paper, time-resolved measurements of temperatures and electron densities of laser-produced plasmas generated in air, argon, and helium at atmospheric pressure are presented, showing that a faster decay of both magnitudes takes place in helium.
Abstract: Time-resolved measurements of temperatures and electron densities of laser-produced plasmas generated in air, argon, and helium at atmospheric pressure are presented. The plasmas are obtained by the focusing of a Nd:YAG laser on a low-alloyed steel sample. The relative experimental error for temperatures is in the range 0.6–3% and for electron densities, it is 4.5%. The higher temperatures and electron densities are obtained in argon, and the lower ones are found in helium. The temporal evolution of temperature and electron density in the three gases is compared, showing that a faster decay of both magnitudes takes place in helium.
130 citations
TL;DR: In this paper, a two-temperature, variable-density, arc model was developed for description of high-current free-burning arcs, including departures from thermodynamic and chemical equilibrium in the plasma.
Abstract: A two-temperature, variable-density, arc model has been developed for description of high-current free-burning arcs, including departures from thermodynamic and chemical equilibrium in the plasma. The treatment includes the arc, the anode and the cathode and considers the separate energy balance of the electrons and the heavy particles, together with the continuity equations for these species throughout the plasma. The output includes a two-dimensional distribution for the temperatures and densities both of the electrons and of the heavy particles, plasma velocity, current density and electrical potential throughout the arc. For a 200 A arc in pure argon at 1 atm, we calculate large differences between the temperatures of the electrons and the heavy particles in the plasma region near the cathode tip, together with large departures from local chemical plasma equilibrium. In the main body of the arc at high plasma temperatures, we predict minor differences between the temperatures of the electrons and the heavy particles, which are inconsistent with recent measurements using laser-scattering techniques showing differences of up to several thousand degrees. However, we find that, for the region in front of the cathode tip, the ground-state level of the neutral atoms is overpopulated relative to the corresponding populations under conditions of LTE, in agreement with experimental observations. These departures from LTE are caused by the injection of a large mass flow of cold gas into the arc core due to arc constriction at the tip of the cathode.
118 citations
TL;DR: In this article, the fluorescence and excitation spectra of selected Ag4 in an argon matrix were reported and the main fluorescence peak for Ag4 was observed at 458 nm, in good agreement with recent theoretical calculations and photodepletion experiments.
106 citations
TL;DR: In this paper, the single active electron model was conclusively shown to describe the physics of high-intensity photoionization to a high degree of accuracy, and while multiple electrons may be ionized, multielectron effects appear to be completely absent from above-threshold-ionization photoelectron spectra.
Abstract: Experimental photoelectron spectra, with high resolution in both kinetic energy and intensity, have been obtained and compared to a high-precision integration of the Schr\"odinger equation for photoelectron kinetic-energy yields in argon. We find exceptional quantitative agreement between data and calculation over a wide range of kinetic energies and peak laser intensities. In this paper we conclusively show that the single active electron model describes the physics of high-intensity photoionization to a high degree of accuracy. Furthermore, while multiple electrons may be ionized, multielectron effects appear to be completely absent from above-threshold-ionization photoelectron spectra.
TL;DR: In this paper, the effect of three surface electrochemical preparation techniques for single crystal surfaces on two platinum stepped surfaces [Pt(10,10,9) and Pt(11,10-10)] has been investigated by scanning tunneling microscopy and cyclic voltammetry.
TL;DR: In this paper, a system of equations based on the Rayleigh?Plesset dynamics of the bubble's radius, polytropic uniform heating of the gas inside the bubble during collapse, the dissociation of molecular gases, and thermal radiation of the remaining hot noble gas, where its finite opacity (transparency for its own radiation) is essential.
Abstract: Single bubble sonoluminescence is not an exotic phenomenon but can quantitatively be accounted for by applying a few well-known, simple concepts: the Rayleigh?Plesset dynamics of the bubble's radius, polytropic uniform heating of the gas inside the bubble during collapse, the dissociation of molecular gases, and thermal radiation of the remaining hot noble gas, where its finite opacity (transparency for its own radiation) is essential. A system of equations based on these ingredients correctly describes the widths, shapes, intensities, and spectra of the emitted light pulses, all as a function of the experimentally adjustable parameters, namely, driving pressure, driving frequency, water temperature, and the concentration and type of the dissolved gas. The theory predicts that the pulse width of strongly forced xenon bubbles should show a wavelength dependence, in contrast to argon bubbles
TL;DR: In this paper, the laser nitriding of a commercial purity (CP) Ti and a near gamma TiAl based alloy in Ar-N 2 gas mixtures has been investigated both experimentally and theoretically.
TL;DR: In this paper, the 3p 6 -3p 5 4s 0 1 1 (1s2 in Paschen notation) transition in argon by resonance-enhanced 1 VUV + 1 UV photo-ionization spectroscopy at 105 nm is presented.
Abstract: The results of a precision measurement of the 3p 6 -3p 5 4s 0 1 1 (1s2 in Paschen notation) transition in argon by resonance-enhanced 1 VUV + 1 UV photo-ionization spectroscopy at 105 nm are presented. Tunable narrow-band VUV radiation is generated by frequency up- conversion of the powerful output of a pulsed dye amplifier system. A transition frequency of 95 399:833.3/ cm 1 in 40 Ar is measured, in agreement with (but an order of magnitude more accurate than) the existing value for this transition. Transition isotope shifts 40 38 D 550.10/ MHz and 40 36 D 1036.7/ MHz are obtained, from which specific mass shifts are deduced. An improved value for the ionization potential in argon (IPD 127 109:842.4/ cm 1 )i s also given. Over the past decade, with the development of powerful dye amplifiers and harmonic- generation techniques, the vacuum ultraviolet (VUV) spectral region became accessible with narrow-band tunable laser sources, thus making possible spectroscopic studies of transitions involving ground states of noble gas atoms with unsurpassed accuracy. The energy level structure of the noble gases is such that the entire manifold of electronically excited states is separated from the electronic ground state by a large energy gap. A laser at 58 nm was used (1) to bridge this gap in helium, resulting in accurate values for the ionization potential (IP), the ground state Lamb shift and the 3 He- 4 He isotope shift. Similar studies of heavier rare gases such as Ne and Kr in the VUV (2, 3) gave valuable information on the level structure of these more complex systems and at present an accuracy of 0:005 cm 1 has been reached for some VUV transitions. However, in Ar accurate values for the VUV transition frequencies are missing; hence the ionization potential is not known accurately for this atom. Recently (4), a multichannel quantum defect analysis of the Rydberg series of 40 Ar was reported, determining accurate values (0:003 cm 1 ) for the two ionization potentials jcD 1 ; 3 with respect to the metastable 3 P2 level (1s5 in Paschen notation), populated in a discharge. In this letter we report on a precise calibration of the 3p 6 . 1 S0/-3p 5 4s 0 1 1 .1s2/ transition in argon by 1VUV+1UV photo-ionization using a narrow-band laser source at 105 nm. The accuracy of 0:003 cm 1 is a factor of 15 better than the best known value of 0:05 cm 1 (5) dating from the early 1970s. Furthermore, an analysis of the isotope shifts in the 1 S0-1s2 transition for the three stable argon isotopes (36, 38, 40) is made. In general, these shifts are due to differences in the nuclear mass (mass shifts) and nuclear charge distribution (field shifts). To a good approximation (6) the isotope shift can be presented as a sum of the mass and field shift. The latter is negligible for light elements such as argon, but it can dominate the isotope shift in heavy elements. The mass shift can be described as consisting of two parts:
TL;DR: In this article, an Al-1Li alloy along with tin (under argon and helium) and pure copper powders (under helium) were produced in a pilot plant gas atomiser, and the pressure of the atomising gases used was 1·85 MPa, except that of argon gas in Sn powder production (1·56 MPa).
Abstract: An Al–1Li alloy along with tin (under argon and helium) and pure copper powders (under helium) were produced in a pilot plant gas atomiser. The pressure of the atomising gases used was 1·85 MPa, except that of argon gas in Sn powder production (1·56 MPa). The atomising agents were used in a confined design nozzle operating vertically upwards. The morphology, size, size distribution, and surface features of the powder particles used in the present study (i.e. Al, Al–Li, Cu, Mg, and Sn powders) were examined by scanning electron microscopy and by dry sieving in order to size the powders. It was observed that for satellite formation in gas atomised powders there is a need for both coarse and fine particles. Under turbulent atomisation conditions these two families of particles of different size and mass must interact with each other. The probability of this interaction increases not only when the amount of fine particles is high, arising from efficient secondary breakup depending on the type of atomi...
TL;DR: The Hi-NicalonTM fiber as mentioned in this paper is a low-oxygen SiC fiber, which was prepared by pyrolysis of polycarbosilane fibers cured with electron-beam irradiation.
TL;DR: In this article, a two-dimensional model was developed for calculating the behavior of Ar2 and Ar2+ ions in a direct current argon glow discharge, by the use of balance equations describing the various production and loss processes for these species, as well as their transport by diffusion and migration.
Abstract: A two-dimensional model has been developed for calculating the behavior of Ar2+ and Ar2+ ions in a direct current argon glow discharge, by the use of balance equations describing the various production and loss processes for these species, as well as their transport by diffusion and migration. These balance equations are coupled to the equations for the Ar+ ions and electrons and solved simultaneously with Poisson’s equation, to obtain a self-consistent description of the charged particles behavior and the electrical characteristics in the glow discharge. Moreover, this model is combined with the other models that we have developed previously for the Ar atoms in various excited levels and the Cu atomic and ionic species, to obtain an overall description of the direct current argon glow discharge. The model is applied to typical conditions used for glow discharge mass spectrometry (pressure of 50–100 Pa, voltage of 600–1400 V, and current of 0.4–15 mA). Typical calculation results include the densities and...
TL;DR: In this article, a plasma-enhanced deposition of fluorocarbon films was performed at 120°C from a mixture of pentafluoroethane (CF3CHF2) and argon in a parallel plate plasma reactor.
Abstract: Plasma-enhanced deposition of fluorocarbon films was performed at 120 °C from a mixture of pentafluoroethane (CF3CHF2) and argon in a parallel plate plasma reactor. Mass spectrometry of the reactor effluent was used to gain an understanding of the plasma chemistry of this monomer. The monomer primarily dissociated into CF3• and CHF2• in the plasma. The results from mass spectrometry indicated that CHF2* was the primary precursor for deposition and that the fluorine radicals in the plasma were primarily scavenged as CF4 and HF. Monomer conversion (fraction of monomer fragmented) in the plasma was determined based on mass spectrometer partial pressure analysis of CH3CHF+ fragments (parent molecule: CF3CHF2) before and after plasma ignition. The conversion correlated directly with both the applied power and the deposition rate. The overall gas phase reactions did not change significantly with rf power within our range of operation, indicating a common reaction mechanism at all powers. No significant change i...
TL;DR: In this article, the rotational energy transfer (RET) in collisions of OH with the bath gases Ar, N2, O2, and H2O at 293 K was studied, and the data were remarkably well described by an exponential gap model for the matrix of state-to-state RET rate constants.
Abstract: We have studied rotational energy transfer (RET) in collisions of OH with the bath gases Ar, N2, O2, and H2O at 293 K. Rotationally hot OH(X 2Π3/2, v″=0, N″=1–12) was generated by photolysis of H2O2 at 266 nm, and collisional relaxation of the nascent rotational distribution was monitored by laser-induced fluorescence. The data are remarkably well described by an exponential-gap model for the matrix of state-to-state RET rate constants. For Ar, N2, and O2, RET rates are significantly faster at low N″ than high N″; for H2O, RET is approximately an order of magnitude faster than for the other bath gases, and the rate is not as strongly dependent on N″. The rates of rotationally inelastic energy transfer are similar in the X and A states, but the X-state depopulation rate constants (including nearly elastic, Λ-doublet-changing collisions) are faster than the A-state values. By comparing the depopulation rates derived from the present experiment with previous linewidth measurements, we conclude that RET is th...
TL;DR: In this paper, the authors report ion energy distributions, relative ion intensities, and absolute total ion current densities at the grounded electrode of an inductively coupled Gaseous Electronics Conference radio-frequency reference cell for discharges generated in pure argon, nitrogen, oxygen, and chlorine, and in mixtures of argon with N2, O2, and Cl2.
Abstract: We report ion energy distributions, relative ion intensities, and absolute total ion current densities at the grounded electrode of an inductively coupled Gaseous Electronics Conference radio-frequency reference cell for discharges generated in pure argon, nitrogen, oxygen, and chlorine, and in mixtures of argon with N2, O2, and Cl2. Measured current densities are significantly greater for pure argon and for mixtures containing argon than for pure N2, O2, and Cl2. For all three molecular gases, the ratio of molecular ions to the fragment ions decreases when argon is added to the molecular gas discharges. A possible destruction mechanism for the molecular ions involving metastable argon is discussed.
TL;DR: In this paper, the authors analyzed the positive column of a dc glow discharge in argon at high pressures using the continuity equations for the charged particles and the gas thermal balance equation coupled with the local electron Boltzmann equation and a detailed collisional-radiative model for the atomic and ionic species.
Abstract: The constriction of the positive column of a dc glow discharge in argon at high pressures is analyzed using the continuity equations for the charged particles and the gas thermal balance equation coupled with the local electron Boltzmann equation and a detailed collisional-radiative model for the atomic and ionic species. Contrary to the other existing models of the constriction in inert gas, the present model is self-consistent and fully detailed, and provides a quantitative description of all the discharge properties. The numerical techniques used to solve the boundary value problem corresponding to our set of equations are discussed in detail. The transition from the diffuse to the constricted state and the properties of this latter state are investigated. The model predicts the existence of multimodal solutions for the discharge parameters as a function of the discharge specific power, within a limited range of values of the latter above a critical value, which explains the observed abrupt changes in the discharge parameters and the hysteresis associated with constriction. The radial distributions of the gas temperature and of the densities of all neutral and charged species considered are determined along with various other discharge characteristics, such as the steady-state discharge maintenance electric field, as a function of the discharge operating parameters. The results for argon show satisfactory agreement with data from experiments. A few model simulations are further presented that enable one to gain physical insight on the relevant kinetic processes of constriction in argon. Such simulations are instrumental to understanding also the mechanisms of constriction in the other inert gases.
TL;DR: In this article, an in-situ set-up which combines IR-spectroscopy under grazing incidence and quartz crystal micro weighing was used to measure the influence of the glow discharge on the electronic properties of the iron oxide surface.
TL;DR: In this article, the power density at the substrate during sputter deposition was measured by a calorimetric method in combination with measurements of the atomic deposition rate, and the total amount of the energy input per incorporated atom was determined.
Abstract: The power density at the substrate during sputter deposition was measured by a calorimetric method In combination with measurements of the atomic deposition rate, the total amount of the energy input per incorporated atom was determined The measured values range from 18 eV for aluminum to about 1000 eV maximum per atom for carbon There is, for all elements investigated, a general trend for a linear increase of the energy per atom with increasing sputtering argon pressure over the range from 02 to 7 Pa The energy per atom decreases with increasing power of the sputtering discharge The application of a negative bias to the substrate reduces the total energy per atom to the values measured at low pressure of 04 Pa or below The total energy flux in the low pressure range (04 Pa or less) can be well described by contributions due to plasma irradiation, the heat of condensation of the deposited atoms, their kinetic energy, and the kinetic energy of the reflected argon neutrals The latter two components are a priori calculated by TRIMSP Monte Carlo simulations There is good agreement between the a priori calculated and the measured values The combination of experimental and theoretical data result in empirical rules for the energies of the sputtered and reflected species, which allow an estimate of the energy input during sputter deposition for every elemental target material in the low pressure range In a first approximation, the energy per incorporated atom is proportional to the ratio between target atomic mass and sputtering yield
TL;DR: In this article, a microprobe/triple quadrupole mass spectrometer system was used to analyze species products, and thermocouples were used to measure temperature.
01 Jun 1999-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the spout eyes developed at the surface of a metal melt in the ladle during argon stirring were measured with a video technique and the time average of the free surface area and time fraction of complete coverage have been determined.
Abstract: This article deals with the spout eyes developing, at the surface of a metal melt, in the ladle during argon stirring. Cold model experiments involving a mercury bath with an oil layer as slag and industrial experiments on a 350 t steel ladle have been carried out. The eye geometry as measured with a video technique is highly dynamic. The time average of the free surface area and the time fraction of complete coverage have been determined and are represented with dimensionless correlations.
21 Feb 1999-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the operation of the Gas Electron Multiplier (GEM) in pure Ar, in comparison to that in Ar-CO2 mixture, has been studied, and high GEM gains, of above 700 and 3000 for single and double GEM structures, respectively, have been obtained.
Abstract: We study the operation of the Gas Electron Multiplier (GEM) in pure Ar, in comparison to that in Ar–CO2 mixture. In pure Ar, high GEM gains, of above 700 and 3000 for single and double GEM structures, respectively, have been obtained. It is observed that the GEM effective gain and its charging-up are strongly affected by electric field values above and below the GEM. Applications to the development of non-ageing gas photomultiplier are discussed.
TL;DR: In this paper, the authors studied the IR spectra of hydrogen sulfide (H2S), some of its complexes, and their photolysis products in rare-gas matrixes at 7.5 K. In all of these matrixes, H2S is found to undergo hindered rotation.
Abstract: Infrared (IR) spectra of hydrogen sulfide (H2S), some of its complexes, and their photolysis products are studied in rare-gas matrixes (Ar, Kr and Xe) at 7.5 K. In all of these matrixes, H2S is found to undergo hindered rotation. The vibration−rotation structures of monomeric H2S are observed at 2651−2615, 2640−2600, and 2625−2580 cm-1 in Ar, Kr, and Xe matrixes, respectively. Furthermore, the H2S dimer and the H2S···H2O complex are observed in various matrixes. Upon UV-induced decomposition of H2S, IR absorptions of SH radical appear at 2607 cm-1 (Ar) and 2594 cm-1 (Kr). The SH radical is also observed to be complexed with H2S (2563, 2553, and 2550 cm-1 in Ar, Kr, and Xe, respectively) and water (2556 cm-1 in Kr).
TL;DR: In this paper, a system designed for magnetic as well as non-magnetic nanoparticle production for ferrofluids and magneto-rheological fluids was described. But this system was not suitable for magnetic materials.
Abstract: The paper describes a system designed for magnetic as well as nonmagnetic nanoparticle production for ferrofluids and magneto-rheological fluids. Particles of Fe 3 O 4 with a mean diameter of 11.65 nm were obtained by melting the steel and sputtering the molten metal in the argon plasma jet. The thermal decomposition of Fe(Co) 5 in plasma led to the obtaining of magnetic particles with a mean diameter of 12.2 nm. Through thermal decomposition in plasma of Fe 2-etilhexamaleath, amorphous and crystalline graphite particles were obtained with a mean diameter of 6.4 nm, useful for producing conductive magnetic liquids. The vaporization of the steel in argon plasma and in helium plasma respectively, led to obtaining of particles of α-Fe and Fe 3 O 4 with diameters in the range 3–90 nm.
TL;DR: In this paper, the influence of nitrogen in shielding gas on the corrosion resistance of welds of a duplex stainless steel (grade U-50), obtained by gas tungsten arc (GTA) with filler wire, autogenous GTA (bead-on-plate), electron beam welding (EBW), and microplasma techniques, has been evaluated in chloride solutions at 30 °C.
Abstract: The influence of nitrogen in shielding gas on the corrosion resistance of welds of a duplex stainless steel (grade U-50), obtained by gas tungsten arc (GTA) with filler wire, autogenous GTA (bead-on-plate), electron beam welding (EBW), and microplasma techniques, has been evaluated in chloride solutions at 30 °C. Pitting attack has been observed in GTA, electron beam welding, and microplasma welds when welding has been carried out using pure argon as the shielding gas. Gas tungsten arc welding with 5 to 10% nitrogen and 90 to 95% argon, as the shielding gas, has been found to result in an improved pitting corrosion resistance of the weldments of this steel. However, the resistance to pitting of autogenous welds (bead-on-plate) obtained in pure argon as the shielding gas has been observed to remain unaffected. Microscopic examination, electron probe microanalysis (EPMA), and x-ray diffraction studies have revealed that the presence of nitrogen in the shielding gas in the GTA welds not only modifies the microstructure and the austenite to ferrite ratio but also results in a nearly uniform distribution of the various alloying elements, for example, chromium, nickel, and molybdenum among the constitutent phases, which are responsible for improved resistance to pitting corrosion.