N2 Mixtures Research Articles

Assessment of ammonia as energy carrier in the use with reversible solid oxide cells

Ammonia represents one of the most promising potential solutions as energy vector and hydrogen carrier, having a higher potential to transport energy than hydrogen itself in a pressurized form. Furthermore, solid oxide fuel cells (SOFCs) can directly be fed with ammonia, thus allowing for immediate electrical power and heat generation. This paper deals with the analysis of the dynamic behavior of commercial SOFCs when fueled with ammonia. Several measurements at different temperatures have been performed and performances are compared with hydrogen and a stoichiometrically equivalent mixture of H2 and N2 (3:1 M ratio). Higher temperature led to smaller drops in voltage for both fuels, thus providing higher efficiencies. Ammonia resulted slightly more performant (48% at 760 °C) than hydrogen (45% at 760 °C), in short stack tests. Moreover, different ammonia-to-air ratios have been investigated and the stack area-specific resistance has been studied in detail by comparing numerical modeling predictions and experimental values.

Alkaline KMnO4 solution pretreat hydrochar to prepare high ultra-micropore volume carbon for CH4 enrichment from low-concentration coalbed methane

Rational design of the carbon adsorbent for recycling CH4 from low-concentration coalbed methane is impressive for sustainable development. However, facile approaches to prepare carbon materials with uniform pore size distribution and abundant ultra-micropore volume are still challenging. Herein, we designed a facile and effective strategy to produce ultra-microporous carbon material, which uses alkaline KMnO4 solution to pretreat carbon precursor, then activate at high temperature. The prepared carbon material has a microspherical morphology, uniform pore size distribution of mainly 0.4–0.7 nm and abundant ultra-micropore volume of 0.50 cm3/g. The excellent CH4 adsorption capacity was demonstrated by the adsorption data with 3.38 mmol/g, 1.87 mmol/g at 273 K, 298 K and 101.3 kPa. The IAST simulation suggested the CH4/N2 selectivity of sample AC-KP for a binary mixture of CH4 and N2 was 6.5 at 298 K and 101.3 kPa. Meanwhile, the adsorption capacity of the binary mixture of CH4 and N2 was also calculated. The fixed bed cycling breakthrough experiment showed good recycling performance with the regeneration rate maintained at about 95% in eight cycles. This work provides a promising avenue to carbon materials with abundant ultra-microporosity towards the superior performance of CH4 recycling from low-concentration coalbed methane.

Experimental determination of first Townsend ionization coefficient in mixtures of He and N2

First Townsend ionization coefficient α in gas mixture of He with N2 is relevant for modeling of the development and chemical activity of atmospheric pressure plasma jets. This study determined α from measurements of current versus electrode separation in a steady-state non-self-sustaining Townsend discharge set-up. The measurements were carried out in absolute pressure range of 10–800 Torr and reduced electric field E/N range of 20–1000 Td. The effect of the N2 concentration in the gas mixture on the density normalized ionization coefficient α/N depended on the reduced electric field strength E/N. At E/N values below 200 Td, increased N2 content reduced the α/N while at E/N values above 200 Td, increased N2 content increased the plateau value of α/N. Reasonably good coincidence was observed between calculation performed with Bolsig+ and measured α/N. The discrepancy between experimental results and calculations at N2 percentage in the mixture below 5% and E/N values below 200 Td can be attributed to the Penning effect.

Modelling the Atomic Layer Deposition of Cobalt and Ruthenium on NHx-Terminated Metal Surfaces

Atomic layer deposition (ALD) is widely used in microelectronics and semiconductor industry to deposit very thin films as part of device fabrication in nano- or subnano-dimensions. The key advantages of ALD are the conformality and precise thickness control at the atomic scale, which are difficult for physical or traditional chemical vapor deposition methods. Cobalt (Co) and Ruthenium (Ru) are used as a seed layers for metallization of interconnects. They are also potential materials for the electrode in dynamic random-access memory (DRAM) capacitors and metal-oxide-semiconductor field-effect transistors (MOSFETs). Plasma-enhanced ALD (PE-ALD) is used for low-temperature thin film growth by alternating exposures of metal precursors and plasma reactants. During the PE-ALD growth of metals, N-plasma, for example, NH3 or a mixture of N2 and H2, has been applied to avoid surface metal oxidation. The PE-ALD of Ru and Co has been experimentally investigated using metal precursors such as RuCp2, Ru(EtCp)2, CoCp2, and CoCp(CO)2. However, the reaction mechanism is not clear and theoretical studies on the reaction mechanism is entirely lacking.In this presentation, we study the PE-ALD growth of Co and Ru by first principle calculations. The (001) surface of both metals, with a hexagonal structure, is the most stable and the (100) surface with a zigzag structure is less stable but has high reactivity. These two surfaces allow the study of the influence of the surface facet. The surface saturation coverage was studied by considering individual adsorption and co-adsorption of NH and NH2 to terminate both surfaces. On the (001) surface, the zero K saturation coverage for NH is 1ML on Ru and 6/9ML on Co. For NH2, the saturation coverages are 6/9ML on Co and Ru surfaces. On the (100) surface, the saturation coverages are 2ML for NH on Ru and Co surfaces, 1.33 ML for NH2 on Ru, and 1ML for NH2 on Co surface. The higher saturation coverage on (100) surface is attributed to the unique trench structure, which provides more available surface sites than that of (001) surface. We also consider co-adsorption of NH and NH2 on (001) and (100) surfaces. The results are then analyzed with ab initio thermodynamics by calculating the Gibbs free energy. Both the ultra-high vacuum (UHV) condition and standard ALD operating condition are used to elucidate the effect of pressure and temperature on the termination of metal surfaces.The adsorption and reactions of metal precursors (CoCp2 and RuCp2) on NHx terminated metal surfaces were investigated with the inclusion of van der Waals corrections. Two possible adsorption structures, namely the precursor lying parallel and perpendicular to the NHx-terminated surfaces, were considered at zero K and ALD conditions. Possible reactions include: precursor adsorption, first hydrogen transfer, first Cp ligand dissociation, first Cp ligand desorption, second hydrogen transfer, and second Cp ligand desorption. The barrier for proton transfer was calculated using climbing image nudged elastic band (CI-NEB) method. Our results show that (100) surface has higher activity than (001) surface. In addition, the Cp ligand elimination of CoCp2 has lower barrier than RuCp2, regardless of surface facet. After the metal precursor pulse, the surface is terminated with MCp fragment or M atom depending on surface facet, where M is Ru or Co. The surface N atom and H atom can be eliminated during the following plasma step by forming NH3, N2 or H2. After a full cycle, the surface is an NHx-terminated metal surface and ready for the next cycle. This work will be important to reveal the mechanism and feasibility of atomic layer deposition of metals using N-plasma.

Influence of Yttria Segregation and Platinum Nanoparticles on the Ionic Conductivity of Yttria-Stabilized Zirconia (YSZ) Films Under Hydrogen Exposure

Yttria-stabilized zirconia (YSZ) films have high ionic conductivities over the range 400-800oC which make them useful for solid oxide fuels cells, oxygen sensors, and other sensing applications. Adding catalytic particles to the YSZ surface can induce reactivities and associated conductivity changes for gases other than oxygen. In this work, the surface reactivity towards hydrogen was investigated on thin films with a 8-YSZ composition (8at.% Y2O3 - 92at.% ZrO2) that were deposited onto Langasite (La3Ga5SiO14) substrates using RF-magnetron sputtering in a 5% O2 - 95% Ar gas mixture. Films were grown to thicknesses up to 200 nm using different growth temperatures (30 - 7000C), deposition rates (0.03 - 0.07 nm/s), and substrate bias (-300 - +300 V). To create Pt nanoparticles on the YSZ film surface, Pt was deposited in-situ via e-beam evaporation to equivalent Pt thicknesses of 1 - 10 nm with the YSZ film held at either 25oC or 400oC and then subsequently annealed in an air furnace up to 1000oC to cause Pt agglomeration and nanoparticle formation. To assess steady-state surface reactivity to hydrogen in the range 400 - 600oC after the 1000oC treatments, film ionic conductivities were measured with electrochemical impedance spectroscopy (EIS) using an impedance/gain-phase analyzer after long annealing times in air, in pure N2, or in a 4% H2 - 96% N2 mixture within the furnace tube. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also used to analyze the characteristics of the as-deposited and annealed YSZ and Pt/YSZ films.YSZ films were synthesized with a variety of crystallographic textures, nanomorphology, and composition using the deposition parameters discussed above. Films deposited at 25, 400, or 700oC all have (111) cubic YSZ preferred texture with random in-plane orientation on the Langasite substrate. The smoothest films were produced using a rate of 0.07 nm/s at 400oC. However, films deposited using the other growth conditions contain significant nano-roughness and hillocks generated by film stress as evidenced by Williamson Hall XRD measurements. In films deposited at 25oC there is also a minor (200) grain population in addition to (111). To create Pt nanoparticles on these various film surfaces, Pt was evaporated with the YSZ film surface being held at either 25oC or 400oC. Pt layers (1 - 10 nm) were uniform at 25oC whereas the Pt started to agglomerate during deposition at 4000C.Following deposition, all the YSZ and Pt/YSZ films were annealed in air up to 1000oC and held for 1 hour prior to measuring conductivity and hydrogen reactivity over the range 400-600oC. This 1000oC annealing treatment was performed to (i) promote Pt agglomeration at high temperature to form individual Pt islands, (ii) stabilize the YSZ nanostructure in terms of film stress and grain size, and (iii) obtain high temperature ionic conductivity measurements over a range of temperatures. XPS indicates that post-deposition air annealing causes significant yttria segregation to the YSZ surface region as evidenced by increases in the Y3d/Zr3d photoelectron peak area ratio upon annealing up to 1000oC. This yttria enrichment decreases the film ionic conductivity and decreases the activation energy for ion transport compared to the as-deposited films. EIS experiments performed in air, N2 or 4%H2-N2 between 400-600oC indicate that the YSZ films without Pt that are most sensitive to hydrogen are those deposited at 400-700oC using a rate of 0.03 nm/s which contain rough surfaces, a population of (200) grains, and minimal yttria surface enrichment. The EIS results also show that YSZ films decorated with Pt nanoparticles all exhibit varying baseline conductivities and sensitivities to hydrogen with a magnitude dependent on the Pt nanoparticle distribution as well as film nanostructure. These YSZ and Pt/YSZ films hold promise as hydrogen sensing films that can be incorporated onto a variety of sensing platforms for H2 gas detection and management. Figure 1

Discrimination of Binary Gas Mixture Using CMUT Based Sound Attenuation Spectrum Gas Sensor

Introduction In order to overcome the long term stability issues caused by functionalized films in gas sensing [1], uncoated sensors have become increasingly attractive for applications where the selectivity is not a major concern such as industrial gas monitoring. Despite their poor selectivity, discrimination can be achieved by measuring different properties of the gas mixture [2]. The sound attenuation of a gas depends on several of its physical properties such as mass density, viscosity and sound velocity among several others [3]. Its value depends on the frequency in a non-linear manner which makes measuring large parts of its spectrum interesting for gas discrimination.In this abstract, an uncoated sensor capable of measuring the attenuation spectrum continuously over a frequency range is presented. Measurements on binary mixtures such as nitrogen (N2) with either hydrogen (H2), carbon dioxide (CO2) or methane (CH4) are presented. Then, a simple method based on the construction of a preliminary mixture signature allowing to distinguish each type of mixture demonstrates the potential of this sensor to be used in smart gas sensors as a perspective to future work. Although attenuation sensors can be found in the literature [3], to the best of our knowledge, it is the first of this kind with easy integration thanks to the use of capacitive micromachined ultrasonic transducers (CMUTs) and allowing discrimination of binary mixtures. Setup The manufacturing process of the CMUT arrays is similar to the one used in reference [4] and their characteristics are reported in Table 1. Schematics of the experimental setup are shown in Figure 1. An electrical signal (1) is sent to an emitter CMUT array (2) which generates a continuous ultrasonic wave at a given frequency f. The wave travels a distance d through the gas and is attenuated by an amount that depends on the gas composition, through the attenuation coefficient α, before reaching the receiver (3) which is connected to a charge amplifier (4). Both the emitter and receiver signals are fed to a network analyzer (5) in order to measure the total transfer function of the setup |H| as a function of frequency. Far from the resonant frequency of the CMUT array (fr = 9.6MHz), |H| is given by Equation 1, where |He | is the transfer function of the setup which is independent of the gas. Thus, by measuring first |H| under pure N2, |HN2 |, it is possible to know the shift in attenuation Δαaccording to Equation 2. Results Tests under H2, CO2 and CH4 in N2 at different concentrations were performed at 20°C and 1atm for f ranging from 2MHz to 4.5MHz. The normalized measurements are shown in Figures 2, 3 and 4, respectively. The normalization consists in multiplying Δα by the wavelength in N2, λN2 , at the optimal frequency, fopt , for each mixture. Theses frequencies correspond to the best theoretical limit of detection LOD (Equation 3). The noise standard deviation σ increases with the frequency from 1.7x10-5 at 2MHz to 6.1x10-5 at 4.5MHz. For each mixture, the optimal frequency, fopt , sensitivity, S, and theoretical limit of detection, LOD, are reported in Table 2. The calculated values of the LOD were then verified for the three binary mixtures at lower concentrations. The results are shown in Figures 5, 6 and 7 and are consistent with the calculations and even better in the case of CH4 where the step at 0.25% is still visible. These values of LOD correspond approximately to an attenuation of 1m-1,which corresponds to the state of the art on attenuation sensors [3]. Finally the normalized attenuation spectra for the three mixtures, shown in Figure 8, makes the discrimination of the three mixtures possible. In this study, it is done by simply considering both the sign of λN2 Δα and the one of the mean slope Σ in the region between 2MHz and 3.6MHz defined by Equation 4 (both signs are reported in Table 2 for each mixture). Conclusion A CMUTs based device is used to measure the attenuation spectrum of a gas. Its characterization shows performances comparable to the state of the art of attenuation sensors. Such measurements allow to determine the concentration of binary mixtures of N2 with either H2, CO2 or CH4. Finally, a signature of each of the three binary mixture is introduced to show the potential of this sensor as part of a smart sensor network. Possible perspectives include increasing the frequency range and testing in other gases.

Effect of Oxygen on the Gas-Sensitive Properties of α-Ga2O3/ε-Ga2O3 Structures

Miniature O2 sensors with low energy consumption are of practical interest for the chemical and metallurgical industries, development of systems for analyzing the performance of internal combustion engines and as functional elements of artificial lung ventilation devices. The requirements for miniaturization, high sensitivity, speed and relative cheapness are satisfied by O2 sensors based on β-Ga2O3. The chemical and thermal stability of β-Ga2O3 allows developing gas sensors with extremely high operating temperatures of 400-1100 °C ensuring high reproducibility of their characteristics and high speed of operation. In turn, the high operating temperatures of O2 β-Ga2O3 sensors are their drawback causing high energy consumption.Previously, we studied the effect of H2 on the gas-sensitive properties of the α-Ga2O3/ε-Ga2O3 structure with Pt contacts grown by the halide vapor phase epitaxy (HVPE) on the patterned sapphire substrates (PSS) [1]. Low operating temperatures, weak dependence of properties on the humidity and control of selectivity by means of voltage changes indicate that the research of α-Ga2O3/ε-Ga2O3 structures as sensitive elements of gas sensors is promising. We presume that in addition to increasing the applied voltage to the structures, the sensitivity of α-Ga2O3/ε-Ga2O3 to certain gases, in particular O2 can be increased by reducing the level of doping with a donor impurity. Thus this work is devoted to research the effect of O2 on gas-sensitive properties of α-Ga2O3/ε-Ga2O3 structures doped with Sn.Ga2O3 films were grown by the HVPE in Perfect Crystals LLC. PSS of (0001) orientation and 430 microns in thickness were used as substrates. During the synthesis, the films were doped with Sn. To measure the gas-sensitive properties of the α-Ga2O3/ε-Ga2O3 structures Pt contacts were formed on their surface.The samples consisted of a mixture of α and ε phases with the orientation (0001). Using scanning and transmission electron microscopy, it was found that the α-phase forms columnar structures at the top of the sapphire cone, and the ε-phase fills the gaps between the columns. The characteristic triangular shape of columnar structures indicates that they consist of α-Ga2O3 with trigonal symmetry. ɛ-Ga2O3 has a grain but not polycrystalline structure taking into account the XRD results.Figure 1 shows the I-U characteristics of α-Ga2O3/ε-Ga2O3 structures at the exposure of O2 in a wide range of concentrations C O2 from 2 to 100 % at temperature T = 200 °C. The current through the samples decreases with C O2 increasing. In the range of the T = 180 - 200 °C, at T = 200 °C, the highest response to O2 are observed. It is worth noting that the operating temperatures of the α-Ga2O3/ε-Ga2O3 structures in the reaction to O2 are significantly lower than the operating temperatures of O2 β-Ga2O3 sensors. These low values of T are an advantage in developing gas-analytical systems with low energy consumption. The concentration dependences of the response at the T = 180 - 200 °C are approximated fairly accurately by a power function: response ~ C O2 b , where b is the exponent that depends on the temperature.Figure 1-Effect of O2 on I-U characteristics of α-Ga2O3/ε-Ga2O3.A decrease in the Sn impurity concentration in α-Ga2O3/ε-Ga2O3 from ~4×1018 cm-3 to ~1.5×1017 cm-3 leads to a significant sensitivity to O2 in the temperature range from 180 to 220 °C at low values of the applied voltage U ≤ 7.5 V. The I-U characteristics of α-Ga2O3/ε-Ga2O3 structures in a dry gas mixture N2 + O2 are described by the model of MSM structures based on the theory of thermoelectronic emission in diode approximation with the resistance of the semiconductor layer exceeding the resistance of the space charge regions at the metal/semiconductor interface. The sensory effect consists in the chemisorption of oxygen molecules on the surface of ε-Ga2O3 that according to SEM has a grain structure. As a result, the energy barrier at the grain boundaries of ε-Ga2O3 increases leading to a decrease in the current. The studied structures showed high sensitivity to relatively low concentrations (0.745 %) of H2 and CO at the T = 180-220 °C and practically did not react to the effects of NO2 and CH4.This research was financially supported by the Russian Scientific Foundation, grant No 20-79-10043.[1] A V Almaev, V I Nikolaev, S I Stepanov, A I Pechnikov, A V Chikiryaka, N N Yakovlev, V M Kalygina, V V Kopyev and E V Chernikov. J. Phys. D: Appl. Phys. 53 (2020) 414004 (9pp) https://doi.org/10.1088/1361-6463/ab9c69 Figure 1

SiC3 as a Charge-Regulated Material for CO2 Capture

The increasing CO2 emission rate is deteriorating the atmospheric environment, leading to global warming and climate change. The potential of the SiC3 nanosheet as a functioning material for the separation of CO2 from the mixture of CO2, H2, N2 and CH4 by injecting negative charges is studied by DFT calculations in this paper. The results show that in the absence of injecting negative charges, CO2 interacts weakly with the SiC3 nanosheet. While the interaction between CO2 and the SiC3 nanosheet can be strengthened by the injection of negative charges, the absorption mechanism of CO2 changes from physisorption to chemisorption when the injection of negative charges is switched on. H2/N2/CH4 are all physiosorbed on the SiC3 nanosheet with/without the injection of negative charges. The mechanism of CO2 adsorption/desorption on the SiC3 nanosheet could be tuned by switching on/off the injection of negative charges. Our results indicate that the SiC3 nanosheet can be regarded as a charge-regulated material for the separation of CO2 from the CO2/H2/N2/CH4 mixture.

Development of Ammonia Selectively Permeable Zeolite Membrane for Sensor in Sewer System.

Ammonia (NH3) and hydrogen sulfide (H2S) are hazardous and odorous gases. A special device that is not affected by other gases is necessary so that it can detect such gases. Zeolite membranes can separate the desired component selectively by molecular sieving and selective adsorption. LTA-, MFI-, and FAU-type zeolite membranes were prepared in this study, and the permeation and separation performances were determined for the ternary mixture of NH3, H2S, and N2 to develop an NH3 selectively permeable membrane. Although the separation factors of NH3 were high enough for the LTA-type zeolite membrane, the NH3 permeance was the lowest among the three membranes. In contrast, the FAU-type zeolite membrane with Si/Al = 1.35 showed a high enough NH3 permeance and a NH3/N2 separation factor. The membrane modification and varying the membrane composition were carried out to reduce the H2S permeance. As a result, the H2S permeance could be decreased by modification with silane coupling agents, and a separation factor of NH3 toward H2S of over 3000 was achieved.

Experimental study on the conductance of pure and binary gas mixtures

A binary gas mixture conductance measurement apparatus with an independent gas distribution system was established, the constant volume method to measure the conductance of the mixed gas was used. Also, the conductance of pure gas Ar, He, N2 and binary gas mixtures Ar–He, N2–He, Ar–N2 through a short tube under different gas distribution chamber pressures and different molar fractions were measured. Meanwhile, the equivalent single gas method was used to calculate the conductance of binary gas mixtures. To verify the accuracy of this method, the relative error between the calculated and the measurement was carried out. The result shows that the equivalent single gas method is suitable for a small Knudsen number (1/Kn≥10), the molar fraction of lighter species is low and a small difference in the molecular mass of the components in the mixed gas. The uncertainty of conductance measurement is better than 3.1%.

Preliminary research: Gas mixture flowrate detector based on acoustic measurement

In preliminary research, a system for detecting the flow rate of the gas mixture (N2 and CO2) has been successfully built using acoustic measurements. This detector consists of a speaker as a transmitter of ultrasonic waves, and 3 microphones as a receiver of the ultrasonic waves. The quantity measured in this detection system test is the phase difference of the ultrasonic waves captured by the left and right microphones. The flow rate of the gas mixture will affect the phase difference value between the left and right microphones. With the increase of the flow rate of the gas mixture, the phase difference between the two microphones will increase. The flowrate range tested was between 0 and 0.8 l/min, with a concentration of 20% CO2 in the gas mixture of N2 and CO2. In testing this detection system, the absolute error is 2,4 10-2 l/min.

Experimental investigation of combustion modes and transition mechanism in confined combustion chamber

In the present work, different combustion modes and the transition mechanism were experimentally investigated in a confined combustion chamber. A H2–O2–N2 mixture with variable oxygen concentration was used as test fuel. Different numbers of perforated plates with varying porosities were employed to change the flame propagation velocity. Depending on the initial thermodynamic conditions, four types of combustion modes were observed: normal combustion (mode 1), end-gas autoignition without detonation (mode 2), end-wall detonation (mode 3), and side-wall detonation (mode 4). It was found that with the transition of the combustion mode from mode 1 to mode 4, the overall level of pressure and pressure oscillation increased due to autoignition and detonation. Moreover, the effects of ignition delay time and flame propagation velocity on the combustion mode transition were studied. With increasing oxygen concentration, the ignition delay time was shortened, and the flame propagation was accelerated, which consequently caused the combustion mode to evolve from mode 1 to mode 4. In addition, different perforated plate configurations were employed to separately investigate the effects of the flame propagation velocity on the combustion mode transition. In summary, the combustion mode was jointly affected by the ignition delay time and flame propagation velocity. Both a shorter ignition delay time and a higher flame propagation velocity were favorable for the occurrence of autoignition and detonation.

Plasma-Assisted Catalysis of Ammonia Using Tungsten at Low Pressures: A Parametric Study

The production of ammonia (NH3) with low-pressure, radiofrequency plasmas is studied in this paper in a wide range of experimental conditions using tungsten as a catalyst. The relative position of the tungsten foil in the pyrex tube was observed to dramatically impact ammonia formation. By positioning the catalyst in the middle of the tube, the concentration of NH3 peaked at 120 W with ≈20 mol %, while it decreased by more than a factor of 2 at 300 W. When the foil was placed close to the end of the tube, the production of NH3 was rather stable beyond 120 W. These results provide clear evidence of the surface’s role in the local enhancement of the NH3 formation rates. In the plasma volume, at some distance from the foil, the decomposition of NH3 is the major occurring process and the decomposition rate increases with the power primarily due to a higher electron density. The optimum production of NH3 was found to be at 45 mol % N2 and 120 W, and the position of the maximum was observed to slightly decrease to <40 mol % N2 with an RF power of 60 W, highlighting that not only the material characteristics play a role but also the discharge conditions. The measured NH3 decreased by increasing the pressure from 3 to 5 Pa, which is associated with a decrease in the electron temperature. The temperature of the discharge was found to have a negligible effect on NH3 formation up to 673 K, demonstrating one of the key features of plasma catalysis in respect to thermal catalysis. The largest energy yield of 0.075 g-NH3 kW h–1 was obtained with an equimolar mixture of N2–H2 at 30 W and 3 Pa. Overall, our results show that the changes in the electron density, electron temperature, and gas composition allow a more effective tuning of the catalytic properties of tungsten than varying the bulk gas temperature.

Investigation of CO2 and CH4 competitive adsorption during enhanced shale gas production

CO2–CH4 competitive adsorption during shale gas production is investigated through a replacement dynamics method at an isotherm temperature of 30 °C from 14.12 to 7.46 MP CH4 production experiments from pure CH4 (with no other gas injection), a mixture of CO2–CH4, and a mixture of N2–CH4 tests were conducted on a Silurian age Lower Jurassic whole shale sample. Gas production performances, pore size distribution, pressure, CO2/CH4 concentration ratio, and gas flow, are discussed to assess their impacts on CO2–CH4 competitive adsorption. Experimental results are validated by the Langmuir model of adsorption and model for multicomponent gas flow dynamics. At the initial stage of production when pressure is high, gas recovery is largely dependent on depressurization, while in the later stage as pressure decreases, competitive adsorption becomes significant. Observed dominances of bulk flow in larger pores (>10 nm) and surface diffusion in smaller pores (<10 nm), show gas recovering mechanism transforms from being largely dependent on reservoir depressurization to competitive adsorption as pressure decreases. Results from this study suggest that CO2–CH4 competitive adsorption is a dynamic process that changes with production conditions.

Steel Corrosion in Aqueous Piperazine at Water Wash Conditions

Corrosion of a carbon steel (C1010) and three stainless steels (430, 304L, and 316L) was measured at water wash conditions in the low-gas flow reactor. Due to the low piperazine (PZ) concentration in the water wash (WW), dissolved CO2 in the WW solution can be acidic and cause C1010 corrosion. The presence of PZ increases the solution pH and reduces the corrosion rate, and the correlation between C1010 corrosion rate and PZ concentration is presented. Solutions saturated with CO2 in N2 mixtures showed lower carbon steel corrosion than those with a CO2 in air mixture. Higher CO2 partial pressure in the gas phase results in a more acidic solution, which requires more PZ to lower the corrosivity. Stainless steels have great resistance to corrosion in the WW.

Combination of nitrous oxide and the modified inflation-deflation method for identifying the intersegmental plane in segmentectomy: A randomized controlled trial.

BackgroundDuring thoracoscopic segmentectomy, accurately and rapidly identifying the intersegmental plane (ISP) is of great importance. This study aimed to investigate the effect and safety of a nitrous oxide (N2O)/oxygen (O2) inspired mixture on the appearance time of the ISP (TISP) via the modified inflation‐deflation method.MethodsA total of 65 participants who underwent segmentectomy were randomized into three groups: 75% N2O (n = 24), 50% N2O (n = 23) or 0% N2O (n = 18). The 75% N2O group received a gas mixture of N2O/O2 (Fio2 = 0.25), the 50% N2O group received N2O/O2 (Fio2 = 0.5), and the 0% N2O group received 100% oxygen during lung expansion. The appearance time of satisfactory and ideal planes was recorded. Furthermore, arterial blood gas at breathing room air, one‐lung ventilation (OLV) before lung expansion, 5 and 15 min after lung expansion were also recorded.ResultsTISP was significantly shorter in the 75% N2O group (320.2 ± 65.9 s) compared with that of the 50% N2O group (552.4 ± 88.9 s, p < 0.001) and the 0% N2O group (968.3 ± 85.5 s, p < 0.001), while the 50% N2O group was shorter than that of the 0% N2O group (p < 0.001). Arterial oxygenation was significantly improved in the 0% N2O group only after lung expansion, before which there were no differences in mean PaO2 values among groups.ConclusionsThe use of N2O in the inspired gas mixture during lung expansion is an applicable strategy to rapidly identify the ISP via the modified inflation‐deflation method without any adverse effect on OLV related arterial oxygenation during segmentectomy.

Laminar Flame Characteristics of Sequential Two-Stage Combustion of Premixed Methane/Air Flames

AbstractDue to their high load flexibility and air-quality benefits, axial (sequential) stage combustion systems have become more popular among ground-based power gas turbine combustors. However, inert combustion residuals passing from the initial stage onto the secondary stage affects the reactivity and stability of the flame in the second stage of the combustor. The present study investigates laminar flame characteristics of the combustion within the second stage of a sequential combustor. The method of constant pressure for spherically expanding flames was employed to obtain laminar burning velocities (LBV) and burned gas Markstein lengths (Lb) of premixed methane/air mixtures diluted using flue gas at 3 bar and 423 K. Combustion residuals were imitated using a 19.01% H2O + 9.50% CO2 +71.49% N2 mixture by volume, while tested dilution ratios were 0%, 5%, 10%, and 15%. Experimental results showed that the LBV was decreased by 18–23%, 36–42%, and 50–52% with additions of 5%, 10%, and 15% combustion products, respectively. As the dilution and equivalence ratios increased, the Lb values increased slightly, suggesting that the stability and stretch of the CH4/air flames increased at these conditions. Numerical results were obtained from CHEMKIN using the GRI-Mech 3.0, USC Mech II, San Diego, HP-Mech, NUI Galway, and AramcoMech 1.3 mechanisms. The GRI-Mech 3.0 and HP-Mech performed best, with an average of 2% and 3% difference between numerical and experimental LBVs, respectively. The thermal-diffusion, dilution, and chemical effects of inert postcombustion gases on the LBV were found using numerical results. The dilution effect was primarily responsible, accounting for 79–84% of the LBV reduction.

An Experimental Study of the Leakage Flow Effect on the Film Cooling Effectiveness of a Gas Turbine Shroud

Abstract In the vicinity of gas turbine blades, a complex flow field is formed due to the flow separation, reattachment, and secondary flows, and this results in a locally non-uniform and high heat transfer on the surfaces. The present study experimentally investigates the effects of leakage flow through the slot between the gas turbine vane and blade rows on the film cooling effectiveness of the forward region of the shroud ring segment. The experiment is carried out in a linear cascade with five blades. Instead of the vane, a row of rods at the location of the vane trailing edge is installed to consider the wake effect. The leakage flow is introduced through the slot between the vane and blade rows, and additional coolant air is injected from the cooling holes installed at the vane’s outer zone. The effects of the slot geometry, cooling hole configuration, and blowing ratio on the film cooling effectiveness are experimentally investigated using the pressure-sensitive paint (PSP) technique. CO2 gas and a mixture of SF6 and N2 (25% + 75%) are used to simulate the leakage flow to the mainstream density ratios of 1.5 and 2.0, respectively. The results indicate that the area-averaged film cooling effectiveness is affected more by the slot width than by the cooling hole configuration at the same injection conditions, and the lower density ratio cases show higher film cooling effectiveness than the higher density ratio case at the same cooling configuration.

Gas Permeation Properties of High-Silica CHA-Type Zeolite Membrane.

The polycrystalline CHA-type zeolite layer with Si/Al = 18 was formed on the porous α-Al2O3 tube in this study, and the gas permeation properties were determined using single-component H2, CO2, N2, CH4, n-C4H10, and SF6 at 303–473 K. The membrane showed permeation behavior, wherein the permeance reduced with the molecular size, attributed to the effect of molecular sieving. The separation performances were also determined using the equimolar mixtures of N2–SF6, CO2–N2, and CO2–CH4. As a result, the N2/SF6 and CO2/CH4 selectivities were as high as 710 and 240, respectively. However, the CO2/N2 selectivity was only 25. These results propose that the high-silica CHA-type zeolite membrane is suitable for the separation of CO2 from CH4 by the effect of molecular sieving.

Composition, dielectric breakdown, and bandgap of ultra-thin amorphous boron oxynitride produced by magnetron sputtering

Ultra-thin amorphous boron oxynitride films were deposited at room temperature on silicon and polymer substrates using radio frequency magnetron sputtering of a hexagonal boron nitride target in varied argon-nitrogen background gas ratios. The effects of nitrogen content in the sputtering gas, changes in target-to-substrate distance, and magnetron power density on the film composition were investigated with X-ray photoelectron spectroscopy and correlated to the dielectric breakdown strength and bandgap obtained from current-voltage measurements and Tauc plots. Films grown in pure Ar atmosphere at a large target-to-substrate distance displayed compositions containing metallic boron, which led to a decrease in the dielectric breakdown strength. The use of Ar:N2 mixtures and pure N2 eliminated metallic boron bonding. Decreasing the target-to-substrate distance and target power density during reactive sputtering resulted in B:N stoichiometry ratio closer to one and about 25–30 at.% oxygen. Smooth surface morphology films grown in pure N2 at a small target-to-substrate distance exhibited dielectric breakdown strength of 2.1–2.4 MV cm−1at 30 nm film thickness and bandgap of 5.4 eV. The results show the suitability of amorphous boron oxynitride for application as an insulator or gate dielectric in thin-films flexible transistors and other electronics when a low processing temperature is required.