Influence Of Carrier Gas Research Articles

Homogeneous water nucleation in argon, nitrogen, and nitrous oxide as carrier gases.

Experimental results for homogeneous nucleation of water droplets in the presence of argon, nitrogen, and, for the first time, nitrous oxide as carrier gases are reported. The main objective of the study was to investigate the effects of different carrier gases on the nucleation rate. These gases differ in the number of atoms comprising the molecule, which affects the expansion ratio required to reach the target nucleation temperature. The experiments cover nucleation temperatures from 220 to 260K, nucleation pressures from 40 to 73kPa, supersaturations of 6.5-20, and nucleation rates ranging from about 4 × 105 to 4 × 109cm-3s-1. The new data obtained with a modernized expansion chamber utilizing the nucleation pulse method show good agreement with the available literature data. Another important point of our work is the application of real gas corrections to calculate the nucleation temperature and supersaturation. The results show that the influence of carrier gases on nucleation rate in the investigated pressure range is modest (less than a factor of 7), while without the real gas correction, the apparent effect of carrier gas is significant, with differences as high as a factor of 90.

Experimental investigation of homogeneous nucleation of water in various gases using an expansion chamber

Nucleation is an integral part of phase transitions and plays an important role in technology. The control of nucleation in devices such as turbines, rocket and jet engines, wind tunnels, and combustion processes is key to achieving efficient, ecologically sound operation. Our paper presents information about a modernized experimental setup used for homogeneous water nucleation research. The main goal of the study is an analysis of the influence of carrier gas on homogeneous nucleation. The experimental setup based on an expansion chamber has been used for research of homogeneous nucleation over several decades and has undergone various technical improvements. In the Institute of Thermomechanics, the setup was been completely disassembled and cleaned. Pressure transducers, laser, and the data acquisition system have been replaced with modern parts. After that, the chamber was assembled, and thoroughly tested and calibrated. Our investigations were carried with argon and nitrogen as carrier gases in a range of nucleation temperatures 220 – 260 K, pressure range 80-150 kPa, at several concentrations of water vapour. The results thus obtained are consistent with literature data. The findings suggest that this experimental approach is useful for homogeneous water nucleation research.

The influence of carrier gas on plasma properties and hydrogen peroxide production in a nanosecond pulsed plasma discharge generated in a water-film plasma reactor

The influence of carrier gas (argon and helium) on the properties of a nanosecond pulsed filamentary discharge propagating along the water surface in a water film plasma reactor, and the effects of plasma properties on the formation of hydrogen peroxide (H2O2) are investigated. The plasma properties, including electron density, gas temperature, and plasma volume, and the hydrogen peroxide production rate and energy yield were measured and compared in both argon and helium discharges. The results show that helium plasma is more diffusive compared with the argon plasma, and it has lower electron density and gas temperature but larger volume. The production rates and energy yields of hydrogen peroxide are only slightly higher in the helium plasma although the electron density is much lower. A simple mathematical model with time-dependent fast radical and electron quenching in a small film surrounding the plasma core and with lumped reaction kinetics for H2O2 formation and degradation suggests that the hydroxyl radical (·OH) concentration is approximately two times higher in the argon discharge, but the larger volume of the helium leads to about two times more total ·OH in the helium with correspondingly higher energy yields. The experimental data and model imply that the H2O2 energy yield may increase at lower power (or specific energy density) for both carrier gases.

Upgrading of derived pyrolysis vapors for the production of biofuels from corncobs

A bubbling fluidized bed pyrolyzer was integrated with an in-situ honeycomb as a catalytic upgrading zone for the conversion of biomass to liquid fuels. In the upgrading zone, zeolite coated ceramic honeycomb (ZCCH) catalysts consisting of ZSM-5 (Si/Al = 25) were stacked and N2 or recycled non-condensable gas was used as a carrier gas. Ground corncob particles were fast pyrolyzed in the bubbling bed using fine sand particles as a heat carrier and the resulting pyrolysis vapors were passed on-line over the catalytic upgrading zone. The influence of carrier gas, temperature, and weight hourly space velocity (WHSV) of catalyst on the oil product properties, distribution and mass balance were studied. Using ZCCH effectively increased the hydrocarbon yield and the heating value of the dry oil, especially in the presence of the recycled noncondensable gas. Even a low usage of zeolite catalyst at WSHVof 180 h‒1 was effective in upgrading the pyrolysis oil and other light olefins. The highest hydrocarbon (⩾C2) and liquid aromatics yields reached to 14.23 and 4.17 wt-%, respectively. The undesirable products including light oxygenates, furans dramatically decreased in the presence of the ZCCH catalyst.

Catalysts, Process Optimization, and Kinetics for the Production of Methyl Acrylate over Vanadium Phosphorus Oxide Catalysts

Vanadium phosphorus oxide (VPO) catalysts were developed for the aldol condensation of methyl acetate (MeOAC) with formaldehyde (HCHO) to methyl acrylate (MA). The influence of P/V ratio on catalytic activity and selectivity was revealed and optimized with a fixed bed reactor. The controllable preparation of VPO catalyst was reached, and the influence of carrier gas on the resistance of carbon deposition was also systematically investigated. Response surface methodology (RSM) with three independent variables of molar ratio of MeOAC to HCHO, space velocity, and reaction temperature was employed to optimize MA yield with VPO catalysts. The high value of “R-squared” presented a reasonable correlation of regression model to the experimental data. Lastly, the kinetics of aldol condensation to produce MA over VPO catalyst was studied.

Influence of carrier gas on microwave-induced pyrolysis

Interest in microwave-induced pyrolysis has increased in recent years due to its several advantages over conventional pyrolysis. Most of these advantages are related to the presence of microplasmas in microwave heating, since the pyrolysis reactions that take place in a plasma atmosphere generally produce light molecules, such as H2 and CO. Although the exact nature of these plasmas is as yet unknown, it is likely to be dependent on the ionization of the surrounding gases. For this reason, the influence of different carrier gases (N2, He or no carrier gas) on microwave-induced pyrolysis was chosen as the subject of this study. It was found that microwave-induced pyrolysis can be used to obtain equally good gas compositions and yields after the reactor has been inertized, without the need for a carrier gas.

Low temperature growth of catalyst-free carbon micro-trees

The growth of carbon micro-trees by classical isothermal-isobaric chemical vapor deposition technique at 900 °C without any catalyst has been explored using propylene and hydrogen as the carbon source and the carrier gas, respectively. The morphology and the microstructure of the as-prepared carbon micro-trees were characterized using scanning electron microscopy, polarized light microscopy, Raman spectroscopy, and transmission electron microscope. The obtained carbon micro-trees had diameters of hundreds of microns and lengths up to 1 mm. They were composed of a central filament and an outer disordered carbon sheath. From these observations, a growth mechanism is proposed for the carbon micro-trees growth, in which axial self-assembling of carbon onions and radical thickening of pyrolytic carbons are involved. The influence of carrier gases and propylene partial pressure on the formation of the carbon micro-trees was investigated. It was found that both the hydrogen and the high concentration of propylene were favorable for the growth of the carbon micro-trees.

Influence of carrier gas on the nucleation and growth of Nb nanoclusters formed through plasma gas condensation

Niobium nanoclusters with an average diameter from 2 nm to 10 nm were produced using a plasma gas condensation process. Cluster size and concentration can be tuned by controlling the sputter source current, aggregation length, and gas flow rate. In this paper, the effects of the addition of helium to the cluster growth process will be examined. Process parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. The results from the helium flow rate dependence study emphasize the competing mechanism present during these processes. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

Pilot-study on the influence of carrier gas and plasma application (open resp. delimited) modifications on physical plasma and its antimicrobial effect against Pseudomonas aeruginosa and Staphylococcus aureus.

Introduction: Physical plasma is a promising new technology regarding its antimicrobial effects. This is especially accounting for treatment of bacterial infection of chronic wounds. Plasma can be generated with different carrier gases causing various biological effects. Screening of different carrier gases and plasma generation setups is therefore needed to find suitable compositions for highly effective antimicrobial plasma treatments and other applications. Method: The plasma source used was a radio-frequency plasma jet which generates tissue tolerable plasma (TTP). The study compared the antimicrobial efficacy of air, argon, or helium plasma alone or admixed with 0.1%, 0.5%, and 1% oxygen against Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus). Treatment took place in an environmentally open and delimited system. Therefore, bacteria were plated on agar and treated with plasma in a punctiform manner. The resulting inhibition zones were measured and the reduction factors were calculated by colony counting, respectively. Results: For S. aureus and P. aeruginosa, inhibition zones and overall reduction of colony forming units (CFU) on the agar plate were observed while an accumulative reduction of CFU dominated for S. aureus. The highest antimicrobial effect was shown in form of an inhibition zone for argon plasma with 0.1% oxygen admixture for both species. S. aureus was more sensitive for helium plasma with >0.1% oxygen admixture compared to P. aeruginosa which in turn was more sensitive for argon plasma with and without oxygen. The efficacy of air plasma was very low in comparison to the other gases. The treatment in a closed system predominantly enhanced the antimicrobial effect. The effect intensity varied for each treatment time and gas mixtures. Discussion: As expected, the antimicrobial effect mostly increased when increasing oxygen admixture to the carrier gases. The variation in bacterial growth and inhibition after exposure to different plasma gas compositions could be due to a varying generation of reactive oxygen species or radiation. Conclusion: The applied plasma in a “closed system” accumulates bactericidal plasma species and might increase antimicrobial efficacy in clinical settings as in wound management involving multi-drug resistant bacteria.

Influence of carrier gas on the prediction of gas chromatographic retention times based on thermodynamic parameters

We present an investigation into the influence of carrier gas on the thermodynamics governing a capillary gas chromatographic separation. Thermodynamic parameters are estimated for a series of alkanes and alcohols on three common stationary phases using helium, hydrogen, and nitrogen carrier gases. It is shown that the substitution of carrier gases for one another results in a change in the thermodynamic parameters governing the separation. The effect of the carrier gas on the thermodynamic parameters is large enough to compromise the accuracy of the retention time calculations based on thermodynamic parameters collected in a carrier gas other than the one actually in use in a specific gas chromatographic system. A possible kinetic explanation for these observations is also investigated.

The influence of carrier gas in the analysis of alumina by laser ablation inductively coupled plasma mass spectrometry

The influence of carrier gases, Ar and He, on the signal intensities, relative standard deviation of signal intensities and ablated particle size was investigated using 213 nm wavelengths for ablation. Fe, Ti, Mn, Mg, Na, and K in the alumina certified reference material were analyzed with LA–ICP-MS. The results illustrate that the ablation carrier gas strongly influences the sampling efficiency and particle size. In He atmosphere the signals were more stable than in Ar atmosphere for both pressed powders and sintered pellets. Examination of ablated particles and sample surface reveals that more wide surfaces were ablated in Ar, while the particle size was big and irregular in comparison to He.

Catalytic deoxygenation of unsaturated renewable feedstocks for production of diesel fuel hydrocarbons

The liquid-phase deoxygenation reaction of unsaturated renewables has been investigated in a semi-batch reactor. The reactants examined were the monounsaturated fatty acid, oleic acid, the diunsaturated fatty acid, linoleic acid and the monounsaturated fatty acid ester, methyl oleate. The reactions were carried out over a Pd/C catalyst under constant pressure and temperature in the following domain, 15–27 bar and 300–360 °C, respectively. The influence of carrier gas was additionally investigated. The impact as solvent (mesitylene) was studied as well and reaction pathways were proposed. Furthermore, continuous deoxygenation experiments were conducted, facilitating understanding of the catalyst stability and catalyst deactivation. The deoxygenation catalyst was characterized by physisorption, temperature programmed desorption (TPD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).

Influence of carrier gas pressure and flow rate on atomic layer deposition of HfO 2 and ZrO 2 thin films

Influence of the carrier gas on HfCl 4–H 2O and ZrCl 4–H 2O atomic layer processes was investigated. The growth rates of HfO 2 and ZrO 2 decreased with increasing flow rate and pressure of the N 2 carrier gas. Data of real-time quartz crystal microbalance measurements demonstrated that the effect observed was mainly due to influence of carrier gas on surface reactions and the role of overlapping the precursor pulses was negligible. At the same increase of the carrier gas mass flow, the increase of the linear flow rate led to more significant changes of thin-film properties than the increase of the carrier gas pressure did. Thin films with higher density, higher refractive index and, particularly, lower concentration of residual chlorine were obtained at higher carrier gas flow rates. Increase of the carrier gas flow rate also resulted in a higher concentration of a metastable phase in HfO 2 thin films deposited at 300 °C.

화학기상응축공정(Chemical Vapor Condensation)으로 제조된 Co 나노분말의 미세구조 및 자기적 성질에 미치는 운송기체의 영향

The nano-sized Co particles were successfully synthesized by chemical vapor condensation (CVC) process using the precursor of cobalt carbonyl (). The influence of carrier gases on the microstructure and magnetic properties of nanoparticles was investigated by means of XRD, TEM, XPS and VSM. The Co nano-particles with different phases and shapes were synthesized with a change of carrier gas : long string morphologies with coexistence of fcc and hcp structure in Ar carrier gas condition; finer Co core in a mass of cobalt oxide with only fcc structure in He; rod type cobalt oxide phase in Ar＋6vol％. The saturation magnetization and coercivity was lower in Co nanoparticles synthesized in He carrier gas, due to their finer size.

Carrier gas as a new factor influencing the selectivity of the gas–stationary liquid phase chromatographic system

This paper generalizes studies on the influence of carrier gas on relative and absolute retention values. This line of research is also of importance due to the fact that, in the opinion of many chromatographers, the role of the carrier gas is limited only to transporting analyzed compounds along the column. However, even under conditions of the conventional capillary gas–liquid chromatography (i.e. at column pressures under 5 atm) carrier gas (its nature and pressure) significantly influences retention and separation of the analyzed compounds. First, carrier gas (N 2 and CO 2, for example) dramatically affects relative retention values. For this reason, one should use limit values of α ij(0)= lim α ij(P av ) and I i(0)= lim I i(P av ) I i(0)= limI i(P av ) with P av→0 as chromatographic constants, rather than traditional relative retention values α ij ( P av) and I i ( P av). Second, the average pressure P av of the carrier gas in a column and the nature of the carrier gas influence the selectivity of the gas–stationary liquid phase chromatographic system. Third, wishing to maximize the role of the carrier gas as a factor that improves separation of analyzed compounds, we should design a special gas chromatograph that would allow work with pressures in the column up to 30–50 atm.

Influence of carrier gas on the morphology and structure of GaN layers grown on sapphire substrate by six-wafer metal organic chemical vapor deposition system

The influence of hydrogen and nitrogen III-carrier gas mixture on the GaN layers grown at a high temperature of 1100°C by a novel six-wafer metal-organic chemical vapor deposition (MOCVD) were studied using optical microscopy, X-ray diffraction (XRD), and photoluminescence (PL). The different ratio of nitrogen and hydrogen of III-carrier gas strongly affect the growth mechanism of GaN layers. In the case of higher ratio of N 2/(N 2+H 2), the surface shows a hillock morphology. On the other hand, with decreasing the flow rate of N 2 to a smaller ratio of N 2/(N 2+H 2), the surface shows a mirror like morphology. In this case, the growth rate was also decreased. The measurement of X-ray diffraction (XRD) shows that the FWHM of XRD rocking curve of sample grown with smaller flow rate of N 2 becomes wider.

Deep-level states in MOVPE AlGaAs:: the influence of carrier gas

We have studied the deep-level state content in AlGaAs grown by low-pressure metalorganic vapour-phase epitaxy with nitrogen and hydrogen as the carrier gases at various growth temperatures. Layers grown in the N 2 and H 2 ambients contain the same type of donor-like traps with apparent activation energies 0.34, 0.56 and 0.89 eV, besides the 1.03 eV trap unique for the former layer. Moreover, the layers grown in N 2 exhibit a lower total concentration of deep-level states as well as net residual doping concentration N D− N A. These results favour nitrogen as the carrier gas over hydrogen in the MOVPE process. Finally, we found out that increasing the temperature of epitaxial growth gradually reduces the gain observed for the carrier gas N 2.

Influence of carrier gas on Cu nucleation, film properties and MOCVD reaction kinetics

To improve the deposition process parameters like deposition rate and incubation time and also the properties of MOCVD deposited copper films the influence of chemical active carrier gas and precursor additives were investigated. The blanket copper films were deposited in presence of water generating additives in inert or reducing ambient. A significant reduction in incubation time and an improvement of film properties like resitivity was found. Symptoms for a deviating reaction pathway in presence of a reducing agent could not be confirmed. Film properties were determined by four-point probe, surface profilometer and scanning electron microscope (SEM). Deposition rates of up to 140 nm/min at precursor flow rates as low as 200 mg/min and film resistivities down to 1.8–2 μΩcm were obtained depending on the process conditions.

Zirconia coatings by spray pyrolysis

Zirconia coatings were obtained with the spray pyrolysis process, using a precursor solution of zirconium n-propoxide in 1-propanol. An investigation was undertaken into the influence of carrier gas (air, He, N 2 and Ar), temperature (450 and 600 °C), time (1 and 2 h) and substrate composition (borosilicate glass, alumina, stainless steel and carbon steel) on coating characteristics. The most important deposition parameters were found to be the atomic or molecular weight of the carrier gas and the pyrolysis temperature. Cubic ZrO 2 thin films, with dense and homogeneous nanostructrure were obtained using He and N 2 as carrier gas, at 600 °C, on ceramic substrates.

Roles of Carrier Gases on Deactivation and Coking in Zeolite Beta during Cumene Disproportionation

The influence of carrier gases (N2, H2, He, and CO2) on the catalytic activity, stability, and coke formation in zeolite beta during cumene disproportionation reaction is discussed. The reaction intermediates as well as the carbonaceous residues were characterized by13C NMR spectroscopy under proton cross-polarization and magic-angle spinning and by thermogravimetric method. The effects of carrier gas dilution on coke formation, catalyst deactivation, and product shape selectivity have also been examined by varying carrier gas (N2) to reactant molar ratios (0.2–20). The amount of total coke decreases linearly with increasing N2/cumene ratios above a value near 2. It is also found that the coke induced shape selectivity is notable only at extreme dilution. In the presence of various carrier gases, a notable decrease in catalytic activity has been found to obey the order N2>H2>He>CO2, whereas a reverse order was observed for the catalytic stability. Moreover, the amount of coke deposit is found to decrease linearly with the kinetic diameter of the carrier gases. Hence, the incorporation of carrier gases resulted in a decrease in the amount of coke deposition which is mainly due to the transport of coke precursors and less bulky carbonaceous compounds (soft coke). Similarly, as proposed by the transition complex solvation model, the carrier gas molecules stabilize the biphenyl alkane reaction intermediates by van der Walls interactions and prevent them from further dissociation into product molecules. With the exception of H2, the combination of the carrier gas transport effect and transition complex solvation model is used to describe the observed trends in the activity and stability of the catalyst.