Inert Gas Flow Rate Research Articles

Atomic Layer Deposition of Al2O3 and ZnO at Atmospheric Pressure in a Flow Tube Reactor

Improving nanoscale thin film deposition techniques such as atomic layer deposition (ALD) to permit operation at ambient pressure is important for high-throughput roll-to-roll processing of emerging flexible substrates, including polymer sheets and textiles. We present and investigate a novel reactor design for inorganic materials growth by ALD at atmospheric pressure. The reactor uses a custom "pressure boost" approach for delivery of low vapor pressure ALD precursors that controls precursor dose independent of reactor pressure. Analysis of continuum gas flow in the reactor shows key relations among reactor pressure, inert gas flow rate, and species diffusion that define conditions needed to efficiently remove product and adsorbed reactive species from the substrate surface during the inert gas purge cycle. Experimental results, including in situ quartz crystal microbalance (QCM) characterization and film thickness measurements for deposition of ZnO and Al(2)O(3) are presented and analyzed as a function of pressure and gas flow rates at 100 °C. At atmospheric pressure and high gas flow, ZnO deposition can proceed at the same mass uptake and growth rate as observed during more typical low pressure ALD. However, under the same high pressure and flow conditions the mass uptake and growth rate for Al(2)O(3) is a factor of ∼1.5-2 larger than at low pressure. Under these conditions, Al(2)O(3) growth at atmospheric pressure in a "flow-through" geometry on complex high surface area textile materials is sufficiently uniform to yield functional uniform coatings.

Effect of Mixed Gas Top Blowing on Decarburization and Manganese Evaporation of Steel Melt in Low Carbon Content Range

Experimental and theoretical studies have been carried out to clarify the effects of mixed gas top blowing on decarburization and manganese evaporation of steel melt in low carbon content range.20 kg scale of induction furnace was used for decarburization experiment. Oxygen utilization efficiency for decarburization increased with an increase in inert gas flow rate and a decrease in oxygen flow rate of mixed gas top blowing. Decarburization rate below carbon content of 0.03 mass% depended on CO partial pressure caused by mixed gas of oxygen and inert gas. To explain these results, an index, IM for decarburization was introduced. The IM is found to be inversely proportional to the oxygen utilization efficiency for decarburization in the low carbon content range, and there is a good correlation between the IM and oxygen content in steel melt.Unexplained manganese content, which seems to depend on its evaporation, decreased with an increase in inert gas ratio of top blowing to oxygen. Manganese evaporation rate was introduced according to Hertz–Knudsen–Langmuir's equation which showed an increase with increasing temperature. Assuming that manganese evaporation occurs at the fire spot caused by top blowing during the final stage of refining, the temperature of the fire spot was estimated to reach 2890K for oxygen top blowing, and decrease to 2475K for mixed gas blowing of (Ar+N2)/O2=2/1.

Effects of Different Processing Parameters on Divinylbenzene (DVB)Production Rate

The effect of processing parameters such as temperature, steam injection rate, and inert carrier gas flow rate on DVB and ethyl vinyl benzene (EVB) production rate was investigated and discussed in isothermal condition and atmospheric pressure in an experimental scale packed bed reactor. The results show that the temperature increases the DVB production rate significantly

Effect of Inert Gas Flow Rate on Homogenization and Inclusion Removal in a Gas Stirred Ladle

AbstractIn the present study, the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was investigated. Both industrial trials and cold model experiments were conducted. CFD calculation was also carried out as an auxiliary tool. The mixing times predicted by CFD simulation agreed well with both the model experiments and industrial data. 99% mixing could be achieved in about 2–3 minutes. The increase of flow rate of inert gas would not improve the mixing substantially, while the mixing time decreased somewhat with the increase of gas flow rate. The water model study showed also that the gas flow rate had a negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that a low gas flow rate should be applied in the ladle treatment.

Size-controlled Pd nanocluster grown by plasma gas-condensation method

Syntheses of palladium (Pd) nanoclusters by sputtering gas-condensation technique are reported in this work. The Pd nanocluster size distribution and number of nanoclusters are found to depend on several factors which include the inert gas flow rate (f), sputtering discharge power, and growth region length. The discharge power and the length of the growth region are optimized to produce high nanocluster yield. It is found that low f produces small number of large nanoclusters which can be attributed to the formation of nanoclusters via the two-body collision mechanism. For high f, nanocluster size decreases and the number of nanocluster increases with f. This phenomenon can be assigned to nanocluster formation through three-body collision mechanism.

Experimental investigation on a membrane distillation based micro-separator

In this work a novel micro-separator combining the sweep gas membrane distillation principle with micro-fluidic channels was designed and tested for the separation of a mixture of methanol and water with a low to high methanol concentration. The performance of the new separation device was studied with different liquid–vapor/gas membrane contactors with respect to the separation factor and the distillate flux rate by varying the relevant operating parameters of the process like the methanol concentration in the feed (5–70 wt.%), the feed temperature (40–65 °C), the feed flow rate (up to 30 ml/min), and the flow rate of the inert carrier gas nitrogen (up to 600 ml/min at standard conditions). For all performed experiments, the feasibility of the separation has been proved and the possibility to separate mixtures with high methanol concentration by using a membrane distillation based micro-separator has been for the first time reported. The inert gas flow rate was identified as the crucial operating parameter influencing the separation performance of the micro-separator. In addition, the selection of an appropriate membrane liquid–vapor/gas contactor was found to be an important design parameter for the reduction of temperature polarization effects. Finally, the novel micro-separator offers the possibility for screening different polymeric hydrophobic/oleophobic micro-porous membranes, showing their potential and limitations as liquid–vapor/gas contactors for the separation of an aqueous mixture with a low to high methanol concentration.

Comparative Mass Transfer Performance Studies of CO2 Absorption into Aqueous Solutions of DEAB and MEA

The mass transfer performance of the absorption of CO2 in an aqueous solution of a new amino alcohol, 4-diethylamino-2-butanol (DEAB), which has been developed as an effective postcombustion CO2 capture solvent, was investigated and compared with the performance of CO2 absorption in a conventional amine, MEA. The absorption experiments were conducted in an absorption column containing structured packing, whereas the absorption performance was evaluated in terms of the overall mass transfer coefficient, KGav. In particular, the effects of parameters such as inert gas flow rate, liquid flow rate, and solution concentration were compared for both DEAB and MEA. The results show that KGav increases as both the liquid flow rate and concentration of solution increase whereas inert gas flow rate has little or no effect on KGav. An empirical correlation for the mass transfer coefficient for the CO2-DEAB system has been developed as a function of the process parameters. In terms of comparison, the results show that...

Fabrication of size-selected Pd nanoclusters using a magnetron plasma sputtering source

We report on the fabrication of palladium (Pd) nanoclusters using a dc magnetron sputtering source. Plasma sputtering vaporizes the target’s material forming nanoclusters by inert gas condensation. The sputtering source produces ionized nanoclusters that enable the study of the nanoclusters’ size distribution using a quadrupole mass filter. In this work, the dependence of Pd nanoclusters’ size distribution on various source parameters, such as the sputtering discharge power, inert gas flow rate, and aggregation length have been investigated. This work demonstrates the ability of tuning the palladium nanoclusters’ size by proper optimization of the source operation conditions. The experimental nanocluster sizes are compared with a theoretical model that reveals the growth of large nanoclusters from “embryos” by a two-body collision. The model is valid for a specific range of deposition parameters (low inert gas flow rates and aggregation lengths equal or below 70 mm).

Carbothermic Reduction of Chromite Ore Under Different Flow Rates of Inert Gas

The reduction of chromite ore with carbon has been studied extensively in many laboratories. Inert gases have been used in these investigations to control the experimental conditions. However, little information is available in the literature on the influence of the gas flow rate on the rate of reduction. Experiments were carried out to study the influence of the flow rate of inert gas on the reducibility of chromite ore. The experiments showed that the rate of reduction increased with the increasing flow rate of argon up to an optimum flow rate. At higher flow rates, the rate of reduction decreased. The influence of the proportion of reductant on the extent of reduction depended on the rate of flow rate of inert gas. The experimental results are interpreted on the basis of a model that postulates that the mechanism of reduction changes with the flow rate of argon.

Study of Evaporative Convection in an Open Cavity under Shear Stress Flow

When a layer of volatile liquid is exposed to a shear flow of inert gas, thermal patterns, in the form of interfacial ripples and bulk plumes, are created by the combined action of evaporative, shear-driven and surface-tension-driven instabilities. The topology of the interfacial thermal patterns is mainly influenced by the geometry of the evaporating surface, the thickness of the evaporating layer, the intensity of the shear flow and by the physic-chemical properties of the working fluid. In this paper, by means of numerical simulations, we focused our attention on the dynamics of the interfacial thermal patterns for different working fluids and thicknesses of the volatile liquid layer. This study has been performed in the frame of the ESA sponsored Space Program on heat and mass transfer CIMEX-1. The choice of the fluids—ethyl alcohol and FC72 (n-perfluorohexane)—the reference values for the inert gas flow rate, the thickness of the liquid layer as well as the geometrical features of the computational domain correspond exactly to the ones foreseen for the CIMEX-1 experiment. However, the main conclusions can be considered of more general validity.

Dehydration of butanol to butene over solid acid catalysts in high water environments

The effects were studied of high water concentrations on the kinetics of alcohol dehydration, as encountered in aqueous-phase processing of biomass-derived oxygenated hydrocarbons. These studies were carried out for dehydration of an aqueous solution of 10 wt% 2-butanol at 513 K, and at a total pressure of 52 bar to maintain the water in the liquid state. Under these high pressures of water, silica-alumina, niobium phosphate and niobic acid are found to be stable and active for the dehydration of butanol. These three catalysts showed an increase in rate after contact with liquid water, caused by an increase in the concentration of Brønsted acid sites. Zeolite catalysts (Beta, USY, H-ZSM-5) and zirconia based catalysts (WO x /ZrO 2, MoO x /ZrO 2, and MgO/ZrO 2) were ineffective due to deactivation or low catalytic activity. The flow rate of inert gas at constant aqueous flow rate had a significant effect on the rate of butene production, due to vaporization of butanol and water. At low flow rates of gas, increasing the gas flow rate causes the preferential vaporization of butanol, leading to a decrease in the butanol pressure in the reactor and a corresponding decrease in the rate of dehydration. Above a critical gas flow rate, the liquid feed becomes completely vaporized in the reactor, and increasing the gas flow rate further leads to a decrease in the pressure of water and a corresponding increase in the rate of dehydration. In the vapor–liquid equilibrium regime, kinetic models predict that most of the catalyst is covered with multiple layers of water, and dehydration takes place by reaction of hydrated–adsorbed butanol with a hydrated surface site. In the vapor-only regime, kinetic models suggest that the fraction of vacant active sites increases with increasing gas flow rate, and dehydration takes place by reaction of adsorbed butanol with a vacant surface site.

Purge efficiency in the determination of trihalomethanes in water by purge-and-trap gas chromatography

Purge-and-trap gas chromatography–mass spectrometry (PT-GC–MS) has become an accepted method for the analysis of trihalomethanes (THMs) in water. The purge-and-trap technique is based on an efficient transfer of volatile organic compounds from the liquid (contained in the purge chamber) to the gaseous phase by bubbling with an inert gas. The aim of this work was to study the purge system's efficiency by means of several consecutive purge cycles lasting 11 min each of the same liquid sample. The concentration range chosen of THMs was very wide [5–200 μg L −1]. The inert gas flow rate was 40 mL min −1, and experiments were performed at temperatures of 25, 35 and 50 °C. Bromoform (CHBr 3), the least volatile compound, needed 19 cycles to be purged quantitatively at a concentration of 200 μg L −1 and only 7 cycles at 5 μg L −1 for a 25 mL sample at 25 °C. Chloroform (CHCl 3), the most volatile compound, required 4 cycles to be fully extracted at 200 μg L −1 and 2 at 5 μg L −1. Finally, Novak's theoretical model, based on the distribution constant between gas and liquid phases, was used to correlate the THMs purging extraction data.

Combustion of bulk density powder mixtures in a coflow of inert gas: 1. The Ni-Al system

The burning velocity of bulk density Ti-C powder mixtures was found to increase with increasing flow rate of inert gas. In some cases, it was also accompanied by stabilization of planar combustion front. The obtained data were rationalized in terms of convention-conduction theory (CCT). The effect can be used as a simple and effective mean for controlling the combustion process and purification of products from impurity gases.

Experimental and Numerical Investigations of Residual Stress Distributions in the TIG Welding Process

Residual stresses are produced in weldments due to mismatching and non-uniform distributions of plastic and thermal strains. Attempts were made to analyze the residual stresses distributions produced in the TIG welding process using 2d and 3d finite element analyses. No attempts were made to find the optimum shape of grooves and gas flow rate to minimize the tensile residual stresses in the weldments, yet. In this paper, the effects of geometry configurations and inert gas flow rate on the residual stress distributions are presented using the thermo-elastoplastic constitutive equations and compared with the x-ray diffraction method. In this study, convection due to both air and inert gas flow rate along with conduction and radiation are considered.

Experimental and numerical analyses of residual stress distributions in TIG welding process for 304L stainless steel

Residual stresses are produced in weldments due to mismatching and non-uniform distributions of plastic and thermal strains. Attempts were made to analyze the residual stresses produced in the TIG welding process using 2D and 3D finite element analyses. No attempts were made to find the optimum shape of the grooves to minimize the tensile residual stresses in the weldments. In this paper, the effect of geometry configurations on the residual stress distributions are predicted from the 3D computer analysis using a thermo-elastoplastic constitutive equation and compared with the X-ray diffraction method. In this study, the effects of conduction, radiation and convection due to both air and inert gas flow rate are considered. Heat capacity, thermal conductivity, elastic modulus, yield stress and other material properties are assumed to be temperature dependent. The effects of the fluid flow, plasticity and external constraint on the residual stress distributions are also considered. Simulation results show that the peak of the tensile residual stress obtained for the u-grooved configuration is less than that predicted for the v-grooved configurations. The predicted residual stresses are in good agreements with those obtained by the X-ray diffraction experiments. It is also shown that the magnitude of the transverse residual stresses increases about threefold if mechanical constraints are applied. The constrained structure also produces less distortion than the un-constrained structure. The best agreement between the residual stress distributions and the X-ray experiments is obtained using the kinematic and isotropic hardening constitutive equations.

Thermal patterns in evaporating liquid

In this paper, some of the preparatory experiments of the ESA sponsored space program CIMEX-1 are presented. A liquid layer of variable thickness is subject to a flow of inert gas. The non-uniform evaporation induced by the gas flow creates a temperature gradient parallel to the interface triggering in that way thermocapillary convection. The combined action of evaporation, thermocapillarity and gravity has been not completely clarified both theoretically and experimentally. The experiment presented in this work concerns a liquid layer of ethanol of 2.2 mm thickness in presence of a mass flow of Nitrogen whose intensity varies in the range of hundreds of milliliter per minute. The experiments were performed at an initial liquid temperature of 21°C. The patterns observed are strongly dependent on the flow rate of inert gas. A change in the instability patterns has been observed for a gas flow of about 1.7 l/min.

Solid state post-polymerization of PA 6,6: The effect of sodium 5-sulfoisophthalic acid

Solid state polymerization (SSP) starting from polyhexamethyleneadipamide (PA 6,6) precursors was studied in the temperature range of 160–200°C in a solid bed reactor. Process parameters, such as temperature, time and inert gas flow rate were investigated, meanwhile emphasis was given on the effect of a dyeability modifier (sodium 5-sulfoisophthalic acid, NaSIPA) on the SSP rate, due to the importance of the pertinent sulfonated ionomers in the polyamide industry. Under the specific experimental conditions, the copolyamides with NaSIPA exhibited lower SSP rates than PA 6,6 homopolymer and their retarding behavior was found proportional to the comonomer content. A possible retardation mechanism related to the NaSIPA ionic species has been suggested and verified through modifying the kinetics so as to describe and predict the copolyamide SSP performance.

Effect of inert gas flow on hydrogen underpotential deposition measurements in polymer electrolyte fuel cells

The effect of inert gas flow rate on hydrogen underpotential deposition ( H upd) measurements in polymer electrolyte fuel cells (PEFCs) was investigated using a novel experimental technique. The method combines local voltammetric measurements in PEFCs with the use of sectioned electrodes. The results give experimental proof that the high inert gas flow rate usually employed in voltammetric measurements in PEFCs at the working electrode results in high hydrogen reduction currents in both the cathodic and the anodic sweep, which hampers an accurate determination of the electrochemically active surface area (ECA). Strong spatial inhomogeneities occur at low potentials as a consequence of formation and accumulation of molecular hydrogen along the flow field. The results show that the flow of inert gas should be minimized or even stopped during a measurement to allow molecular hydrogen to accumulate at the working electrode and to provide uniform conditions along the flow field.

Organic layer-coated metal nanoparticles prepared by a combined arc evaporation/condensation and plasma polymerization process

A process for the synthesis of organic layer-coated metal nanoparticles is presented. Metal nanoparticles are synthesized by the low-pressure pulsed arc evaporation of a metal cathode surface, followed by the in-flight deposition of a thin organic layer by capacitively coupled radio-frequency plasma polymerization from a gaseous hydrocarbon monomer. The stability of the pulsed arc system and the cathode erosion rate are discussed. The effects of operating conditions such as power, reactor pressure and inert gas flow rate on the average size of produced bare copper nanoparticles and the properties of the organic coating are studied. A ‘characteristic map’ for the in-flight plasma polymerization from the C2H6 monomer of the organic layer onto the Cu nanoparticles is developed. The produced copper nanoparticles are characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The FE-SEM and TEM images reveal coated copper nanoparticles with the diameter of the metal core ranging from a few to 50 nm and the thickness of the organic layer ranging from 3 to 10 nm. The XPS results show that the plasma polymer film is chemically adsorbed onto the surface of the copper nanoparticle.

Hydrogen production from solar thermal dissociation of methane in a high-temperature fluid-wall chemical reactor

This study addresses the exploration of an unconventional route for potentially cost effective hydrogen production with solar thermal energy. The process co-produces hydrogen-rich gas and high-grade Carbon Black (CB) from concentrated solar energy and methane. The approach is based on a single-step thermal decomposition (pyrolysis) of methane to hydrogen and CB, without catalysts and without emitting carbon dioxide since solid carbon is sequestered as carbon black. A high temperature nozzle-type solar chemical reactor has been developed in which the solar radiation absorbed by a graphite nozzle is transferred to the flow of reactant (fluid-wall reactor). The conversion of methane dissociation depends strongly on the solar power input, on the geometry of the graphite nozzle, and on the inert and reactive gas flow rates, which determine both the residence time and the inlet CH 4 mole fraction. Maximum chemical conversion of methane was up to 99% (yield of hydrogen up to 90%). It was obtained with a vertical-axis solar furnace (2 m-diameter concentrator), with a given geometry of the nozzle determining the fluid-wall reaction surface area, and with the lowest flow rate of methane investigated (0.1 L n /min). For each target tested, the higher the inlet flow rate of methane or argon, the lower the gas residence time, thus the lower the chemical conversion.