Argon Carrier Gas Research Articles

Employing Per-Component Time Step in DSMC Simulations of Disparate Mass and Cross-Section Gas Mixtures

AbstractA new approach to simulation of stationary flows by Direct Simulation Monte Carlo method is proposed. The idea is to specify an individual time step for each component of a gas mixture. The approach consists of modifications mainly to collision phase simulation and recommendations on choosing time step ratios. It allows lowering the demands on the computational resources for cases of disparate collision diameters of molecules and/or disparate molecular masses. These are cases important e.g., in vacuum deposition technologies. Few tests of the new approach are made. Finally, the usage of new approach is demonstrated on a problem of silver nanocluster diffusion in argon carrier gas under conditions of silver deposition experiments.

Liquid waste decomposition by long DC arc under atmospheric pressure

A model substance of biphenyl solution was used for the study of polychlorinated biphenyls (PCBs) decomposition. Biphenyl has the same chemical and molecular structure with the PCBs. Because of the severe toxicity of PCBs. the biphenyl was introduced instead of the PCBs. The biphenyl solution was directly injected to a long DC arc as a fine spray with argon carrier gas. The long DC arc system with a 350mm arc length was operated under atmospheric pressure at a 20kW DC power supply. The plasma gas of argon containing decomposition products was bubbled through ethanol to remove the decomposition products. The dissolved ingredients of decomposition products in ethanol were defined as liquid by-products, while the gas by-products are insoluble in ethanol as exhaust gas. The gas by-products of H2, CH4, and CO were identified with gas chromatography. The liquid by-products of benzene, toluene, phenylacetylene, styrene, indene, naphthalene, biphenyl, acenaphthylene, fluorine, phenanthrene and 4,5-methylenephenanthrene were qualitatively analyzed by a gas chromatography–mass spectrometry and were quantitatively measured by a high performance liquid chromatography. When introducing a sufficient oxygen into the arc, the high decomposition efficiencies of 99.83% biphenyl and 100% acetone were achieved and the by-products of gas and liquid are suppressed to convert to a desirable product of CO2. For the formation of liquid by-products, C6H5, CH3, and C2H2 are the important intermediates in low temperature region. Pyrolysis of biphenyl solution is initiated from the C6H5 to the polycyclic aromatic hydrocarbons (PAHs).

Microstructure characterization of TiO2 nanowires fabricated by thermal evaporation process

TiO2 nanowires (NWs) have been synthesized by thermal evaporation process, using the vapor–liquid–solid (VLS) growth mechanism and Au thin film as a catalyst which was deposited on titanium/quartz substrates. Optical and microstructure characteristics of TiO2 NWs have been studied under different argon carrier gas flows. The gas flow was varied from 60 to 170sccm. The results of X-ray diffraction show that TiO2 nanowires form in rutile phase and their preferred growth are in (110) direction. The field emission scanning electron microscope images indicate that with increasing gas flow, nanowires become thinner and longer. The absorbance spectrum has been obtained through using spectrophotometer and then band gap of TiO2 nanowires were calculated. According to results, the band gap has been increased due to the quantum confinement in comparison with bulk one. The band gap increased from 3.35eV to 3.45eV by increasing the argon flow, since the wires become thinner and longer. The Williamson–Hall method was used as the main tools for characterization of crystallite size and microstrain. Also the other microstructure characterizations have been determined by X-ray line profile analysis such as; dislocation density and texture coefficient. The crystallinity of TiO2 NWs has been improved by increasing Ar flow due to enhancement of VLS growth mechanism.

Photoelectron Spectroscopic and Theoretical Study of Aromatic–Bim Anionic Complexes (Aromatic = C6H5, C5H4N, C4H3O, and C4H4N; m = 1–3): A Comparative Study

The reactions between Bi clusters generated by laser ablation and different aromatic molecules (C6H6, C5H5N, C4H4O, or C4H5N) seeded in argon carrier gas were studied by a reflectron time-of-flight mass spectrometer (RTOF-MS) with a photoelectron spectrometer. The photoelectron (PE) spectra of the dominant anionic products Bi(m)C6H5(-), Bi(m)C5H4N(-) (m = 1-4) and Bi(m)C4H3O(-), Bi(m)C4H4N(-) (m = 1-3) dehydrogenated complexes were obtained by 308 and 193 nm laser, respectively. It was found that the adiabatic electron affinities (EAs) of Bi(m)C4H4N are higher than those of Bi(m)C6H5, Bi(m)C5H4N, and Bi(m)C4H3O with the same metal number m. Theoretical calculations with density functional theory (DFT) were carried out to elucidate the possible structures for Bi(m)C4H4N(-) and Bi(m)C4H4N complexes. By comparison of the theoretical and experimental EAs, the most possible structures were the isomers in which the C4H4N group binds to metal clusters with the N-Bi bond, and their simulated spectra based on Koopmans' theorem were in correct agreement with the PES results. Furthermore, the analysis of the molecular orbital composition provided evidence that the C4H4N group contributes a single electron to bind to Bi(m) clusters with the Bi-N σ bond.

Modelling and Optimization of DLC Film Thickness Variation for PECVD Processes

This paper describes a modeling method for film thickness variation within plasma enhanced chemical vapour deposition (PECVD) processes. The model enables the identification and optimization of deposition process sensitivities to electrode configuration, deposition system design and gas flow distribution. An comparison between theory and experiment is provided for PECVD of diamond-like-carbon (DLC) deposition onto flat and curved substrate geometries. This process utilizes butane reactive feedstock with an argon carrier gas. Radio-frequency plasma is used. The PECVD deposition system is based on co-planar 300mm diameter electrodes with separate RF power matching to each electrode. The system has capability to adjust the electrode separation as a parameter to optimize uniformity. Vacuum is achieved using dry pumps with real time control of butterfly valve position for active pressure control. Deposited film thickness sensitivities to electrode geometry, plasma power density, and pressure and gas flow distribution are demonstrated. In addition to film thickness uniformity, optical, durability and environmental performance of resulting DLC on germanium substrate materialreported.

Optical Diagnostics of Electrical Discharge Water-Spray Reactors for Chemical Synthesis

Low-power (250–500 mW) pulsed gliding-arc discharge reactors that utilize water sprayed as a fine aerosol into an argon carrier gas have been previously shown to produce molecular hydrogen <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{H}_{2})$</tex></formula> and hydrogen peroxide <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{H}_{2}\hbox{O}_{2})$</tex></formula> with high energy yields. In this paper, optical emission spectroscopy in the range of 230–1000 nm is used to assess the formation of radicals in the plasma region of the reactor as functions of spatial position and liquid flow rate. Radical intensities of OH (309 nm) were the highest at 10 mm downstream from the point of discharge initiation, and the gradient of the OH radical intensities between 10 and 15 mm was higher for the higher liquid flow rates that correspond to the highest production rates and efficiencies of hydrogen peroxide. These results support the hypothesis that hydrogen peroxide production efficiency increases with rapid OH radical quenching.

Kinetics of the Decomposition of Hydrogen Sulfide in a Dielectric Barrier Discharge Reactor

AbstractKinetics of hydrogen sulfide (H2S) decomposition to hydrogen and sulfur was investigated in a nonthermal plasma dielectric barrier discharge (NTP‐DBD) reactor operated under ambient conditions. The reactions were carried out with a fixed flow rate and varying inlet concentration. The results indicated that the dissociation of H2S into H2 and S may be initiated by excitation of the carrier gas argon. A reaction rate model based on a Langmuir Hinshelwood/Michaelis‐Menten model was proposed. The formal reaction order approaches zero at high H2S concentrations. The parameters of the kinetic model were found to be dependent on the power input.

Half sandwich structures of [formula omitted] (M = Ag and Au): An experimental and theoretical study

The metal-hexafluorobenzene anionic complexes of [MC6F6]− (M=Ag and Au) were produced from the reactions between metal cluster generated by laser ablation and the hexafluorobenzene seeded in argon carrier gas, and were studied by photoelectron spectroscopy (PES) and density functional theory (DFT). The adiabatic electron affinities (EAs) of these corresponding complexes are measured from the experimental PE spectra at 193nm photon energy. Also, the calculated EAs and the calculated density of states (DOS) spectra of these complexes in the ground state are conducted, which are in good agreement with their experimental PE spectra. The most possible structures of the anions [AgC6F6]− and [AuC6F6]− are the half-sandwich structures with C6v symmetry, in which the metal atom is above the center of the C6F6 plane. Furthermore, the molecular orbital (MO) analysis of these species indicates that the additional electron of the anions binds on the metal.

Closed-loop control of laser assisted chemical vapor deposition growth of carbon nanotubes

Laser-assisted chemical vapor deposition growth is an attractive mask-less process for growing locally aligned nanotubes in selected places on temperature sensitive substrates. An essential parameter for a successful and reproducible synthesis of nanotubes is the temperature during growth. Here, we demonstrate a temperature feedback control mechanism based on the dynamic, in situ monitoring of the infrared radiation coupled with reflectivity information. With the information provided by these sensors, an infrared laser, focused on a silicon substrate covered with aluminum-oxide and iron catalyst layers, can be controlled. The growth takes place in a gaseous mixture of argon (carrier gas), hydrogen (process gas), and ethylene (carbon-containing gas). Scanning electron microscopy and Raman spectroscopy analysis demonstrate the excellent reproducibility of the closed-loop control process over multiple experiments. Furthermore, we developed a unique method to identify the onset for catalyst formation and activation by monitoring the fluctuation of the reflected laser beam.

Preparation of γ-Gd2S3 via thermolysis of Gd[S2CN(C4H8)]3·phen coordination

Pure γ-Gd2S3 was synthesized by the thermolysis of a single Gd[S2CN(C4H8)]3phen complex precursor in a flow of argon carrier gas containing sulfur vapor. The complex precursor was decomposed into amorphous Gd2S3 and carbon at about 350 C. Crystalline γ-Gd2S3 could be achieved at temperature exceeding 600 C, and the obtained γ-Gd2S3 presented a very high degree of crystallinity at 800 C. Carbon prevented the formation of Gd2O2S impurity in the preparation of γ-Gd2S3. However, the carbon blackened the product. At temperature ≥1000 C, the residual carbon impurity could be efficiently removed by introducing sulfur into the system for the volatile CS2 could be formed in situ via the reaction of sulfur with the deposited carbon. In the meantime, S also promoted the crystallization of γ-Gd2S3 remarkablely.

The chemical generation of NO for the determination of nitrite by high-resolution continuum source molecular absorption spectrometry

In the present work, we propose a method for the determination of nitrite based on the chemical generation of nitric oxide (NO) and its detection by high-resolution continuum source molecular absorption spectrometry. NO is generated by the reduction of nitrite in acidic media with ascorbic acid as the reducing agent and then transferred into a quartz cell by a stream of argon carrier gas. The conditions under which the NO is generated are as follows: 0.4molL−1 hydrochloric acid, 1.5%(w/v) ascorbic acid, an argon gas pressure of 0.03MPa and an injection time of the reducing agent of 4s. All measurements of molecular absorption were performed using the NO line at 215.360nm, and the signal was measured by peak height. Under these conditions, the method described has limits of detection and quantification of 0.045 and 0.150μgmL−1 of nitrite, respectively. The calibration curve is linear for nitrite concentrations in the range 0.15–15μgmL−1. The precision, estimated as the relative standard deviation (RSD), was 3.5% and 4.4% for solutions with nitrite concentrations of 0.5 and 5.0μgmL−1, respectively. This method was applied to the analysis of different water samples (well water, drinking water and river water) collected in Cachoeira City, Bahia State, Brazil. The results were in agreement with those obtained by a spectrophotometric method using the Griess reaction. Addition/recovery tests were also performed to check the validity of the proposed method. Recoveries of 93–106% were achieved.

Characterization of Palladium-based Thin Films Prepared by Plasma-enhanced Metalorganic Chemical Vapor Deposition

The plasma-enhanced metalorganic chemical vapor deposition (PEMOCVD) was used to prepare palladium–based thin films starting with palladium (II) acetylacetonate precursor (Pd(acac)2) mixed with argon (carrier gas). To characterize chemical structure and morphology of deposited films Raman spectroscopy and electron diffraction techniques were used. The energy dispersive X-ray microanalysis (EDX) was applied to specify composition of films. The film thickness was estimated by ellipsometric measurements. The obtained results show that the films have various composition depending on deposition parameters. It has been found that the thermal decomposition at 623 K of the films leads to the formation of fine 5 nm – 10 nm size palladium nanoparticles, to which the catalytic activity is attributed.DOI: http://dx.doi.org/10.5755/j01.ms.18.2.1913

Organic-vapor-liquid-solid deposition with an impinging gas jet

A method for rapid, mass-efficient deposition of highly crystalline organic films under near ambient conditions of pressure and temperature is reported based on delivery of an organic precursor via an impinging gas jet to a substrate coated by a thin liquid solvent layer. Films of the organic semiconductor tetracene were deposited by sublimation into a flow of argon carrier gas directed at an indium-tin-oxide/glass substrate coated by a thin layer of bis(2-ethylhexyl)sebecate, and growth was followed in situ with optical microscopy. A fluid dynamics model is applied to account for the gas phase transport and aggregation, and the results compared to experiment. The combination of gas jet delivery with an organic-vapor-liquid-solid growth mechanism leads to larger crystals and lower nucleation densities than on bare surfaces, with markedly different nucleation and growth kinetics. An explanation based on enhanced solution-phase diffusivity and a larger critical nucleus size in the liquid layer is proposed to account for the differences.

Non‐stick Polymer Coatings for Energy‐based Surgical Devices Employed in Vessel Sealing

AbstractEnergy‐based surgical devices are widely used to fuse tissues and seal vessels, but tissue adhesion to the instrument complicates the procedure. We deposit a robust non‐stick coating on the jaws of LigaSureTM tissue fusion devices by employing an atmospheric pressure RF‐driven plasma with hexamethyldisiloxane (HMDSO) entrained in argon carrier gas. The hydrophobicity, surface energy, surface topography, and chemical characteristics of deposited films are characterized by water contact angle measurements, surface energy test pens, atomic force microscopy, and Fourier transform infrared spectroscopy, respectively. We demonstrate significantly reduced tissue adhesion to HMDSO polymer film‐coated instruments during the tissue fusion procedure in comparison with uncoated and chromium nitride‐coated instruments.magnified image

Femtosecond laser ablation particle introduction to a liquid sampling-atmospheric pressure glow discharge ionization source

This work describes the use of a compact, liquid sampling–atmospheric pressure glow discharge (LS-APGD) ionization source to ionize metal particles within a laser ablation aerosol. Mass analysis was performed with a Thermo Scientific Exactive Mass Spectrometer which utilizes an orbitrap mass analyzer capable of producing mass resolution exceeding m/Δm > 160,000. The LS-APGD source generates a low-power plasma between the surface of an electrolytic solution flowing at several μl min−1 through a fused silica capillary and a counter electrode consisting of a stainless steel capillary employed to deliver the laser ablation particles into the plasma. Sample particles of approximately 100 nm were generated with an Applied Spectra femtosecond laser located remotely and transported through 25 meters of polyurethane tubing by means of argon carrier gas. Samples consisted of an oxygen free copper shard, a disk of solder, and a one-cent U.S. coin. Analyte signal onset was readily detectable relative to the background signal produced by the carrier gas alone. The high mass resolution capability of the orbitrap mass spectrometer was demonstrated on the solder sample with resolution exceeding 90,000 for Pb and 160,000 for Cu. In addition, results from a laser ablation depth-profiling experiment of a one cent coin revealed retention of the relative locations of the ∼10 μm copper cladding and zinc rich bulk layers.

Modeling of Chemical Vapor Deposition of Pyrolytic Carbon in a Gas-Spouted Bed Reactor

Spouted beds are used in chemical vapor deposition as they provide good solid mixing, thereby enhancing high mass and heat transfer rates. In the present study, investigations on the kinetics of a coating process by chemical vapor deposition were carried out in a spouted-bed reactor. Pyrolytic carbon coatings were studied by thermal cracking of acetylene mixed with carrier gas argon at 1350 °C. A theoretical model was proposed based on the mass balance of the precursor in the spout and annulus zones at isothermal condition, and the model equations were solved using MATLAB (version 7.1) software. The effect of the operating gas velocity, initial static bed height, and acetylene concentration on the coating rate was examined experimentally and also by simulation results. The simulated results agreed well with the experimental results. Model equations used for simulation were utilized to evaluate the reaction rate constant and radial gas diffusion coefficient and then to study the effect of spout diameter, operating gas velocity, and precursor concentration on the overall conversion of the precursor.

Carbon nanowalls deposited by inductively coupled plasma enhanced chemical vapor deposition using aluminum acetylacetonate as precursor

Well aligned carbon nanowalls, a few nanometers thick, were fabricated by continuous flow of aluminum acetylacetonate (Al(acac) 3) without a catalyst, and independent of substrate material. The nanowalls were grown on Si, and steel substrates using inductively coupled plasma-enhanced chemical vapor deposition. Deposition parameters like flow of argon gas and substrate temperature were correlated with the growth of carbon nanowalls. For a high flow of argon carrier gas, an increased amount of aluminum in the film and a reduced lateral size of the carbon walls were found. The aluminum is present inside the carbon nanowall matrix in the form of well crystallized nanosized Al 4C 3 precipitates.

Novel low temperature atmospheric pressure plasma jet systems for silicon dioxide and poly-ethylene thin film deposition

In this study, both low-density plasma quartz tube (QT) and high-density plasma metallic tube (MT) jet-electrodes with pulsed-type alternating-voltage (AC) generator were used to investigate the influences of the process parameters and electrode types on the microstructures and the corrosion behaviors of silicon dioxide (SiO 2) or poly-ethylene (PE, (CH 2CH 2)n ) thin films. Tetraethoxysilane (TEOS) and ethylene (C 2H 4) were used as precursors for SiO 2 and PE thin film deposition. The TEOS precursor was vaporized by an ultrasonic oscillator and introduced into the AP plasma systems by argon (Ar) carrier gas. The main plasma working gas was Ar gas mixed with or without oxygen gas. The pulsed-type AC generator, with a frequency of 30 kHz, a voltage of 10 kV and a wattage of 300 W, was used to deposit SiO 2 and PE thin films on the silicon and AISI 1005 low carbon steel substrates at the room temperature, respectively. The high-density plasma MT jet-electrode with an Ar gas flow rate of 6 slm, a precursor flow rate of 40 sccm and an oxygen flow rate of 40 sccm revealed optimal plasma dissociation and chemical reaction efficiencies to synthesize effective atomic stoichiometry of SiO 2 (in-organic films) thin films. However, the low-density plasma QT jet-electrode with an Ar gas flow rate of 6 slm and an ethylene flow rate of 15 sccm appeared optimal plasma-induced polymerization efficiency to exhibit reasonable atomic stoichiometry of PE (organic films) thin films. Moreover, the optimal SiO 2 thin films deposited by MT jet-electrode possessed better corrosion resistant integrity than the optimal PE thin films synthesized by QT jet-electrode. It was also found that SiO 2 and PE thin films synthesized by the AP plasma method possess effective corrosion barrier characteristics like other deposition techniques.

Investigation of novel low temperature atmospheric pressure plasma system for deposition photo-catalytic TiO 2 thin film

The purpose of this study was to develop a novel low-temperature atmospheric pressure (AP) plasma system and to use the system to deposit photo-catalytic titanium dioxide (TiO 2) thin film. In this study, titanium tetraisopropoxide (TTIP) was used as a precursor for TiO 2 thin film deposition. The precursor was vaporized by ultrasonic oscillator and introduced into an atmospheric plasma system by argon (Ar) carrier gas. The main plasma working gas was Ar mixed with O 2. Microstructure evolutions of TiO 2 thin film were investigated by low-angle grazing-incidence x-ray diffraction (GID), x-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM). The photo-catalytic properties were determined by contact angle and methylene orange de-coloration testing. In this study, the substrate temperature, the precursor flow rate and the O 2 flow rate were varied. TiO 2 thin film grown at a temperature of 350 °C, with precursor and O 2 flow rates of 20 sccm and 200 sccm, respectively, revealed the optimum photo-catalytic properties. It was also found that titanium dioxide thin films synthesized by the AP plasma method possess reasonable photo-catalytic characteristics like other deposition techniques.

Modification of optical and electrical properties of chemical bath deposited CdS using plasma treatments

Cadmium sulphide (CdS) is a well known n-type semiconductor that is widely used in solar cells. Here we report preparation and characterization of chemical bath deposited CdS thin films and modification of their optical and electrical properties using plasma treatments. CdS thin films were prepared from a chemical bath containing Cadmium chloride, Triethanolamine and Thiourea under various deposition conditions. Good quality thin films were obtained during deposition times of 5, 10 and 15 min. CdS thin films prepared for 10 min. were treated using a glow discharge plasma having nitrogen and argon carrier gases. The changes in morphology, optical and electrical properties of these plasma treated CdS thin films were analyzed in detail. The results obtained show that plasma treatment is an effective technique in modification of the optical and electrical properties of chemical bath deposited CdS thin films.