O2 Mixture Research Articles

Statistical analysis on branching characteristics of positive streamer discharges in N2–O2 mixtures

Streamers are fast-propagating ionization channels that can usually branch and form complex tree-like structures in dielectric media. In this paper, we perform experiments on positive streamers in different N2–O2 mixtures under varying conditions including voltage, pressure, and electrode geometry, with at least 125 discharge images captured for each condition. We present a statistical analysis on streamer branching characteristics from 3D models that are reconstructed by stereoscopic stroboscopic images and our dedicated semi-automatic 3D reconstruction method.We found that by varying the concentration of O2, the morphology and branching characteristics are greatly changed. Specifically, the average branching angle decrease significantly from 90∘ in air to 66∘ in 1% O2, suggesting that photoionization plays an important role in streamer branching. The branching angles in our work are generally larger than previously reported results due to the resolved 3D structures of discharges by our method. A linear relation between the streamer diameter ratio and the branching direction difference of two daughter branches is found, which intersects the vertical axis almost at unity. It is also found that the average branching angles, streamer velocities and diameters increase as the voltage increases. This is again attributed to stronger photoionization effect under higher voltages. The velocities and diameters are similar at different pressures but at the same reduced electric field. The average branching angle decreases from 90∘ at 133 mbar to 79∘ at 200 mbar. This suggests that stochastic fluctuations become dominant over photoionization effect at higher pressures.

Robust approximation rules for critical electric field of dielectric gas mixtures

A semi-analytic method for quickly approximating the density-reduced critical electric field for arbitrary mixtures of gases is proposed and validated. Determination of this critical electric field is crucial for designing and testing alternatives to SF6 for insulating high voltage electrical equipment. We outline the theoretical basis of the approximation formula from electron fluid conservation equations, and demonstrate how for binary mixtures the critical electric field can be computed from the transport data of electrons in the pure gases. We demonstrate validity of the method in mixtures of N2 and O2, and SF6 and O2. We conclude with an application of the method to approximate the critical electric field for mixtures of SF6 and HFO1234ze(E), which is a high interest mixture being actively studied for high voltage insulation applications.

Differential responses to avian pathogenic E. coli and the regulatory role of splenic miRNAs in APEC infection in Silkie chickens.

Avian pathogenic Escherichia coli (APEC) is a bacterial disease that harms the poultry industry worldwide, but its effect on Chinese Silkie has not been reported. Studies on whether there are differences in Silkie individual resistance to APEC and the regulatory role of spleen miRNAs lay the foundation for strategies against APEC. Therefore, 270 Silkie chickens were infected with the median lethal dose of an E. coli O1, O2, and O78 mixture. These chickens were divided into a susceptible group (Group S) and a recovery group (Group R) according to whether they survived 15 days postinfection (dpi). Moreover, 90 uninfected APEC Silkie served as controls (Group C). The splenic miRNA expression profile was examined to evaluate the role of miRNAs in the APEC infection response. Of the 270 Silkies infected with APEC, 144 were alive at 15 dpi. Cluster analysis and principal component analysis (PCA) of splenic miRNAs revealed that the four Group R replicates were clustered with the three Group C replicates and were far from the three Group S replicates. Differentially expressed (DE) miRNAs, especially gga-miR-146b-5p, play essential roles in immune and inflammatory responses to APEC. Functional enrichment analyses of DEmiRNAs suggested that suppression of immune system processes (biological processes) might contribute to susceptibility to APEC and that FoxO signaling pathways might be closely associated with the APEC infection response and postinfection repair. This study paves the way for screening anti-APEC Silkies and provides novel insights into the regulatory role of miRNAs in APEC infection.

Deposition rate and optical emissions in niobium oxide processes by reactive sputtering

Niobium oxide films find various applications, such as antireflective optical layers, gas sensors, and solar cells. They also show promise for emerging applications such as electrochromic and photocatalytic devices. In order to optimize the deposition of niobium oxide films by RF reactive sputtering, a detailed investigation of the plasma parameters was performed. A pure metallic target and a mixture of Ar and O2 in different proportions were used in the experiments. The deposition power was varied between 120 and 260 W, while the total pressure was kept at 0.67 Pa throughout. Deposition rates, discharge self-bias voltage, and plasma optical emissions were monitored and analyzed. Additionally, computer simulations of the process utilizing existing models were conducted and a comparative analysis with the experimental results was performed. The main findings include mapping the deposition conditions as functions of oxygen flow rate. The flow ranges in which the deposition regime changes from metallic to oxygen contaminated target conditions were identified. The narrow O2 flow range associated with the regime changes was characterized by significant changes in the self-bias voltages and plasma emissions from oxygen, argon, and niobium. The observations evidence the importance of the detailed analysis of the deposition process to get the desired stoichiometry and optimized film properties.

Thermogravimetric/Thermal-Mass Spectroscopy Insight into Oxidation Propensity of Various Mechanochemically Made Kesterite Cu2ZnSnS4 Nanopowders.

Thermogravimetry coupled with thermal analysis and quadrupole mass spectroscopy TGA/DTA-QMS were primarily used to assess the oxidation susceptibility of a pool of nanocrystalline powders of the semiconductor kesterite Cu2ZnSnS4 for prospective photovoltaic applications, which were prepared via the mechanochemically assisted synthesis route from two different precursor systems. Each system, as confirmed by XRD patterns, yielded first the cubic polytype of kesterite with defunct semiconductor properties, which, after thermal annealing at 500 °C under neutral gas atmosphere, was converted to the tetragonal semiconductor polytype. The TGA/DTA-QMS determinations up to 1000 °C were carried out under a neutral argon Ar atmosphere and under a dry, oxygen-containing gas mixture of O2:Ar = 1:4 (vol.). The mass spectroscopy data confirmed that under each of the gas atmospheres, a distinctly different, multistep evolution of such oxygen-bearing gaseous compounds as sulfur oxides SO2/SO3, carbon dioxide CO2, and water vapor H2O was taking place. The TGA/DTA changes in correlation with the nature of evolving gases helped in the elucidation of the plausible chemistry linked to kesterite oxidation, both in the stage of nanopowder synthesis/storage at ambient air conditions and during forced oxidation up to 1000 °C in the dry, oxygen-containing gas mixture.

A molecular simulation study on the adsorption and separation performance of carbon nanotubes for SO2 in flue gas

To control the emission of SO2 from flue gas into the atmosphere while considering the capture and collection of greenhouse gas CO2, the adsorption behavior of a binary mixture of SO2 and other gases in flue gas (O2/N2/H2O/CO[Formula: see text] in (10, 10) carbon nanotube (CNT) was simulated using grand canonical Monte Carlo (GCMC) simulation. The adsorption and separation performance of SO2 in CNTs with a diameter range of 0.81–1.63 nm for the five-component mixture gas was also analyzed. The findings suggest that the adsorption and separation of SO2 are primarily influenced by CO2 (reduction of adsorption capacity by about 50%, separation coefficient of SO2/CO2 is lowest) with this effect being more pronounced under high pressure. Meanwhile, it was observed that CNTs with larger pipe diameters exhibit higher SO2 adsorption capacity, but relatively lower SO2/CO2 selectivity and lower stability. On the other hand, CNTs with smaller diameters have relatively lower adsorption capacity for SO2, but exhibit good selectivity and stability (under different pressure) for SO2/CO2. Based on the statistical analysis of SO2 adsorption capacity and SO2/CO2 selectivity, it was determined that (6, 6) CNT with a diameter of 0.81[Formula: see text]nm can exhibit excellent SO2 adsorption and separation performance at atmospheric pressure, while appropriate large diameter CNTs should be selected for flue gas treatment under high pressure.

Oxidative coupling of methane using oxidant mixtures of CO2 and O2 over Sr/La2O3

Oxidative coupling of methane with CO2 (CO2-OCM) is beneficial because it avoids complete oxidation, an undesired reaction that occurs during O2-oxidative coupling of methane. Previous literature has sparsely considered the respective roles of CO2 and O2 as reactants at CO2-OCM reaction conditions. This work explores the roles of CO2 and O2 in OCM over Sr/La2O3 with different reactant oxidant mixtures. While CO2 alone did not significantly activate methane at 875 °C, a tenfold increase in C2 yield resulted from adding 2 % O2. The role of CO2 in heterogeneous reactions was supported by XPS and XRD, which showed presence of carbonate species on the catalyst surface while the bulk phase remained La2O3. The work shows that a small amount of gaseous oxygen in the reactants can greatly improve methane conversion, and while oxygen is crucial in converting methane, CO2 plays an important role during ethane dehydrogenation.

Proposition of a tool to calculate the oxygen and air flow for high-flow nasal oxygenation in obese patients

Blood desaturation after surgery in obese patients in not uncommon. Oxygen therapy is almost always necessary in these cases and we have to use low-flow catheters, Venturi masks or non-rebreathing systems, but maybe the most efficacious are the non-invasive ventilation (NIV), continuous positive pressure ventilation (CPAP) and the new high-flow oxygen therapy which offers a warm and humid high-flow mixture of O2 and air (up to 70l/min). We decided to use this device in a very obese patient scheduled for a gastroplasty but one question arose: how to calculate FiO2 without tables or mathematic calculations? We used a tool available in a website since 2020 to resolve this problem precisely. Patient’s SpO2 remained all the time between 99 and 100% and 4h after the surgery he was transferred to the ward.

Influence of SO2 on CO2 capture by adsorption on activated carbon: Individual pore performance via multiscale simulation

Carbon capture under post-combustion conditions has been the topic of numerous studies in the last decade. Although exhaust gases typically contain different components other than CO2, they are commonly neglected in these studies. The presence of sulfur dioxide, for example, tends to interfere in the carbon capture process through different mechanisms. The present work aimed to evaluate the effects of SO2 on the CO2 retention capacity through the integration of experimental evaluation, column dynamics modeling and molecular simulation (multiscale modeling) for an activated carbon sample under typical conditions found in the post-combustion environment. Results indicate that, under typical post-combustion flue gas conditions, SO2 has little influence on the CO2 retention capacity of the carbon in comparison to other adsorbent materials. The highest concentration of SO2 (5 000 ppmv) led to a decrease of approximately 10 % in the CO2 capture capacity. Significant deactivation (around 40 %) was observed experimentally and by molecular simulation only for very high concentrations of SO2 (50 000 ppmv). Additionally, no evidence of reactions with the material was found and both captured components could be completely desorbed by means of suitable regeneration methods. To access individual pore performance, molecular simulations were implemented for SO2 adsorption using, for the first time, a rigorous heterogeneous pore model (rMD). The results revealed a large deactivation for the 7.0 Å pore, a surprising cooperative effect for the 8.9 Å pore, and indifference for the larger 18.5 and 27.9 Å pores. For SO2 concentrations up to 5 000 ppmv, the use of carbon-based adsorbent could rule out the need of a pre-treatment operation to remove SO2 in carbon capture processes. For higher concentrations, molecular simulation showed that tailoring carbon porosity in the range of 7 Å to 8.9 Å considerably reduces the interference of SO2. Results also point out that the IAST and Langmuir models diverge from the molecular simulation results, particularly at low loadings (up to 5 000 ppmv SO2), indicating the need for caution when applying these models in systems where competitive interactions between molecules are relevant, as is the case with mixtures of CO2 and SO2.

3D Effects of detonation re-initiation after diffraction at a back-facing step

Detonation diffraction at a backward facing step and subsequent re-initiation at the bottom wall at near critical detonation transmission conditions is studied in a square 7.6 cm channel. The experimental techniques used for this purpose include ultra high-speed schlieren video from the side and the top views. Direct photography is also performed in the top view configuration with a soot foil placed at the bottom wall after the step. The process of detonation re-initiation is studied for 2H2+O2+2Ar and CH4+2O2 mixtures that are characterized by a very regular and irregular detonation cellular structure, respectively. For both mixtures detonation re-initiation begins at discrete points where the descending transverse reflect from the bottom wall; the spacing of re-initiation points matches the wave number, suggesting the three-dimensional interaction of descending and lateral transverse waves on the reflecting wall trigger detonation re-initiation. The subsequent growth of these re-initiation kernels differs between mixtures. For regular cell mixtures, the detonation evolution is gradual and follows the lateral transverse wave along the bottom wall; whereas for irregular cell mixtures, explosive of hot spots grow independently of the lateral transverse waves. The observed initiation processes underscore the critical role of three-dimensional effects for both regular and irregular cell mixtures. The abrupt detonation initiation observed for methane-oxygen can be attributed to the high effective activation energy, i.e., high reaction rate temperature sensitivity.

Multi-speciation and ignition delay time measurements of ammonia oxidation behind reflected shock waves

Ammonia (NH3) oxidation was studied using emission and laser absorption diagnostics in a shock tube. Experiments were carried out using stoichiometric mixtures of NH3 and O2 highly dilute in Ar seeded with CO2 at post-reflected-shock conditions from 1700–2500K near 2atm. Five optical diagnostics in the infrared (IR), visible, and ultraviolet (UV) were implemented to measure NH3 (before and after shock-heating), NO, electronically excited amino radicals (NH2∗), electronically excited hydroxyl radicals (OH∗), and temperature during oxidation. To mitigate mixture uncertainty due to NH3 adsorption, a scanned-wavelength laser absorption diagnostic near 10.4μm was developed to measure initial NH3 concentration. A two-color, fixed-wavelength laser absorption diagnostic near 225 nm was developed to measure quantitative NO and NH3 time-histories. A detailed spectroscopic model of the NO A2Σ+←X2Π system was used to provide NO absorption cross-sections at both wavelengths, and NH3 absorption cross-sections were measured at the conditions of interest. Emission from NH2∗ near 600 nm was collected to provide qualitative insight into radical formation prior to ignition, and emission from OH∗ near 308 nm was used to determine ignition delay times (IDTs). A two-color, fixed-wavelength laser absorption diagnostic at 4.17μm and 4.19μm was developed to measure temperature using small quantities of seeded CO2. Measured time-histories are compared against predictions from two kinetic models. Experimental results and model predictions show several discrepancies, both in terms of timescales and absolute quantities. Sensitivity analysis shows that the reactions H + O2⇌ O + OH, NH3 + M ⇌ NH2 + H + M, and NH3 + H ⇌ NH2 + H2 are dominant across all conditions, and that NH3 pyrolysis reactions in general drive much of the chemistry. Direct, low-scatter rate constant measurements of the NH3 + M ⇌ NH2 + H + M reaction and additional multi-speciation measurements of NH3 pyrolysis and oxidation at combustion-relevant temperatures and pressures are recommended.Novelty and significance statementThe novelty of this work is exemplified most strongly by the use of UV laser absorption diagnostics to measure NH3 and NO during high-temperature oxidation of NH3. Simultaneous measurements of temperature via CO2 laser absorption at two wavelengths and light emission from NH2∗ and OH∗ are also novel. Simultaneous, time-resolved, quantitative measurements of NH3, NO, and temperature and qualitative measurements of NH2∗ and OH∗ light emission are of significant utility as a model validation-suited data set. Additionally, the data presented herein and the associated findings provide evidence of current chemical kinetic model deficiencies pertaining to NH3 chemistry and suggest avenues for model improvement.

Electron Impact Cross Sections and Transport Studies of C3F6O

Electron impact scattering from C3F6O is studied in this work. The R-matrix method was used for the calculations of elastic, momentum transfer, and excitation cross sections. The attachment cross section was obtained through a parametric estimator based on the R-matrix outputs. The Binary-Encounter-Bethe (BEB) method was used for computing the ionization cross section. The obtained cross section set was used for the transport studies using the BOLSIG+ code, which is a two-term Boltzmann equation solver. The present calculation was performed for steady-state Townsend experimental conditions for E/N, covering a range of 100–1000 Td. The critical dielectric strength of pure C3F6O was found to be 475 Td, which is much greater than that of SF6 (355 Td). The effect of the addition of different buffer gases, such as CO2, N2, and O2, was also examined. For the C3F6O–CO2, C3F6O–N2, and C3F6O–O2 mixtures with 65%, 55%, and 60% C3F6O, respectively, the critical dielectric strength was determined to be essentially the same as that of pure SF6. The presence of synergism was confirmed for these gas mixtures. We further derived the Paschen curve using a fitting method with the transport parameters as the basic inputs. The minimum breakdown voltage of C3F6O accounted for only 55% of that of SF6. The buffer gas mixture improved the condition; however, the performance of CO2 and O2 mixtures was not satisfactory. The addition of N2 as the buffer gas significantly improved the breakdown property of the gas. The mixture of ≥99% of N2 or ≤1% of C3F6O gave a better breakdown characteristic than SF6. Any proportion ≥90% of N2 or ≤10% of C3F6O was suitable in the higher pressure ranges. The present work demonstrates the potential of C3F6O as a substitute gas for SF6 with a negligible environmental threat.

Synergistic Nitrogen Binding Sites in a Metal-Organic Framework for Efficient N2 /O2 Separation.

Porous materials with d3 electronic configuration open metal sites have been proved to be effective adsorbents for N2 capture and N2 /O2 separation. However, the reported materials remain challenging to address the trade-off between adsorption capacity and selectivity. Herein, we report a robust MOF, MIL-102Cr, that features two binding sites, can synergistically afford strong interactions for N2 capture. The synergistic adsorption site exhibits a benchmark Qst of 45.0 kJ mol-1 for N2 among the Cr-based MOFs, a record-high volumetric N2 uptake (31.38 cm3 cm-3 ), and highest N2 /O2 selectivity (13.11) at 298 K and 1.0 bar. Breakthrough experiments reveal that MIL-102Cr can efficiently capture N2 from a 79/21 N2 /O2 mixture, providing a record 99.99 % pure O2 productivity of 0.75 mmol g-1 . In situ infrared spectroscopy and computational modelling studies revealed that a synergistic adsorption effect by open Cr(III) and fluorine sites was accountable for the strong interactions between the MOF and N2 .

Experimentally-measured rate parameters for vibrational quenching of CO by N2

Carbon monoxide is a trace species in Titan's atmosphere that is not consistently found in local thermodynamic equilibrium at all altitudes. Understanding how CO exchanges energy with atmospheric collision partners is therefore crucial for accurate atmospheric modelling. Particularly significant could be vibrational relaxation of CO by nitrogen due to the high collision frequency in Titan's N2-based atmosphere. Some CO(v)-N2 rate coefficients have never been experimentally measured while others were measured decades ago in low-precision experiments. In this work, we present precise experimental measurements of the rate coefficients for the quenching of CO(v = 1,2) by N2. To perform the experiment, an equilibrium mixture of CO, N2, O3, and bath gases was subjected to a temperature-jump, creating a small amount of vibrationally-excited CO. Transient diode laser absorption spectroscopy was then used to observe the evolving vibrational state populations as a function of time. The rate coefficients of interest were found by measuring quenching rate as a function of quencher concentrations. The rate coefficient for quenching of CO(v = 1) by N2 was measured to be k = (1.3 ± 0.2) x 10−14 cm3 molecule−1 s−1 and the rate coefficient for quenching of CO(v = 2) by N2 was measured to be k = (2.1 ± 0.5) x 10−13 cm3 molecule−1 s−1 at 315 K.

Rb-Ni/Al2O3 as dual functional material for continuous CO2 capture and selective hydrogenation to CO

Ni-based dual-functional materials (DFMs) have been widely investigated for CO2 capture and reduction with H2 (CCR). However, controlling the selectivity of CO2 hydrogenation to CH4 or CO is a fundamental challenge. Most Ni-based DFMs favor the selectivity of CH4 over CO, although CO is more desirable than CH4 from a chemical-synthesis perspective. In this study, Rb-promoted Ni nanoparticles on Al2O3, Rb-Ni/Al2O3, are developed as an effective DFM for selective CO production through CCR with a CO2 conversion of 68% and a CO selectivity of 97% under isothermal conditions at 450 °C in the mixture of O2 during CO2 capture process. The developed Rb-Ni/Al2O3 is applicable to continuous CCR using double reactor system. The roles of Rb and Ni in CCR over Rb-Ni/Al2O3 for CO formation are also discussed based on temperature-programmed surface reactions and in situ spectroscopic studies.

Study of apparent effective ionization coefficient in CO2 and Ar gas mixtures

Ar:CO2 gas mixtures have recently received research interest due to the possibly beneficial effects of Ar addition to CO2 for CO2 conversion using electrical discharges. For any gas discharge, knowledge of fundamental parameters, such as the effective ionization coefficient, is necessary to optimize the efficiency of the discharge for a particular application. The reduced apparent effective ionization coefficient αea/N is a measure of total ionization. αea/N is influenced by electron impact ionization, electron attachment and also by charge transfer reaction, Penning ionization, and photoionization. This study determined the αea/N of Ar:CO2 gas mixtures in the pressure range of 10–800 Torr and reduced electric field strength E/N range of 40–1200 Td utilizing a steady-state non-self-sustaining Townsend discharge. Experimental results were compared with calculations of Boltzmann equation solver BOLSIG+. Differences between measurements and calculations increased with decreasing CO2 content in the mixture down to 20%, and the differences were highest at low E/N values (below 150 Td). As the simple modification of the model, contribution of ionization of CO2 by Penning transfer from Ar* 3p53d excited states (13.86 eV) was added to the BOLSIG+ calculations, which resulted in good fit of the experimental measurements. Comparison of CO2 addition to Ar with the addition of O2 or N2 revealed that ionization of CO2 or O2 from Ar* 3p53d excited states influences ionization in Ar:CO2 and Ar:O2 mixtures but not in Ar:N2 mixtures, due to the different ionization energies of CO2, O2, and N2.

Pore-scale resolved simulation of quenching, acceleration, and transition to detonation of hydrogen explosions by metal foams

Pore-scale simulations of quenching, acceleration, and transition to detonation of gaseous hydrogen explosions by metal foams were performed. The model solves the three dimensional compressible reactive Navier-Stokes equations with detailed chemistry in a closed square channel with a metal foam placed inside. The structures of the foam were fully resolved using an immersed boundary method. Stoichiometric mixtures of hydrogen-oxygen and hydrogen-air were considered. An explosion in the channel was initiated with a high-pressure and high-temperature spark. The simulation results show that the explosion can be quenched, accelerate, or transition to detonation depending on the foam pores-per-inch (PPI). Hydrogen-air explosions were quenched with foams of ∼39 PPI or higher due to heat losses from the flame, which is consistent with experimental observations. The explosion was not quenched by foams with low PPI. Instead the low PPI foams exacerbated the explosion by causing flame acceleration. Worse, a 78 PPI foam caused a stoichiometric H2 and O2 mixture to transition to detonation. Hydraulic resistance due to products venting away from the flame surface was found to produce strong pressure gradients within the foam. This causes a self-pressurizing effect that grows as the flame propagates further into the foam. The pressure within the foam grows and steepens into a shock. The shock initiated the detonation by a Mach reflection, which is similar to deflagration-to-detonation transition mechanisms in traditional obstacle-laden channels. Statement of SignificanceMetal foam structures are often used as devices to inhibit flames in scenarios where explosion hazards are a concern. Direct numerical simulations were performed to increase understanding of how flames and explosions interact with metal foams. The simulation results show that high pores-per-inch (PPI) foams quench the explosion by removing heat from the flame. Lower PPI foams can have the opposite effect and exacerbate the explosion by promoting flame acceleration or even transition to detonation. Flames self-pressurize as they propagate through low PPI foams due to hydrodynamic friction and gas-dynamic effects from flowing product gases. In extreme cases, the pressure waves near the flame can steepen into a shock and initiate a detonation. These results indicate that improperly selected metal foam flame arresters can exacerbate the explosion.

Detection of a C4 Criegee Intermediate: Fourier-Transform Microwave Spectroscopy of Methacrolein Oxide.

Pure rotational transitions of methacrolein oxide (MACRO) were observed by Fourier-transform microwave spectroscopy. Among the four low-lying conformers existing within an energy window of 3 kcal/mol, only the lowest-energy conformer, the anti-trans conformer, was detected in a discharged jet of a 1,3-diiode-2-methylprop-1-ene and O2 mixture diluted in Ar. Nineteen pure rotational transitions, in the frequency range from 10 to 25 GHz, most of them showing A/E splitting due to the methyl-top internal rotation, were observed and analyzed by the XIAM program, yielding the internal rotation barrier of 559 cm-1, which very well agrees with a theoretically calculated value, 558 cm-1, at the CCSD(T)/cc-pVTZ level of theory.

Hierarchical Computational Screening of Quantum Metal-Organic Framework Database to Identify Metal-Organic Frameworks for Volatile Organic-Compound Capture from Air.

The design and discovery of novel porous materials that can efficiently capture volatile organic compounds (VOCs) from air are critical to address one of the most important challenges of our world, air pollution. In this work, we studied a recently introduced metal-organic framework (MOF) database, namely, quantum MOF (QMOF) database, to unlock the potential of both experimentally synthesized and hypothetically generated structures for adsorption-based n-butane (C4H10) capture from air. Configurational Bias Monte Carlo (CBMC) simulations were used to study the adsorption of a quaternary gas mixture of N2, O2, Ar, and C4H10 in QMOFs for two different processes, pressure swing adsorption (PSA) and vacuum-swing adsorption (VSA). Several adsorbent performance evaluation metrics, such as C4H10 selectivity, working capacity, the adsorbent performance score, and percent regenerability, were used to identify the best adsorbent candidates, which were then further studied by molecular simulations for C4H10 capture from a more realistic seven-component air mixture consisting of N2, O2, Ar, C4H10, C3H8, C3H6, and C2H6. Results showed that the top five QMOFs have C4H10 selectivities between 6.3 × 103 and 9 × 103 (3.8 × 103 and 5 × 103) at 1 bar (10 bar). Detailed analysis of the structure-performance relations showed that low/mediocre porosity (0.4-0.6) and narrow pore sizes (6-9 Å) of QMOFs lead to high C4H10 selectivities. Radial distribution function analyses of the top materials revealed that C4H10 molecules tend to confine close to the organic parts of MOFs. Our results provided the first information in the literature about the VOC capture potential of a large variety and number of MOFs, which will be useful to direct the experimental efforts to the most promising adsorbent materials for C4H10 capture from air.

Palladium-Based Contacts on p-GaN and Their Application in Laser Diodes.

In this paper, we investigate the effect of Pd thickness and heat treatment on Pd/Ni/Au/p-GaN metal contacts. The as-deposited samples exhibit a smooth morphology and non-linear I-V characteristics. Heat treatment in a N2 atmosphere leads to degradation of the contact microstructure, resulting in diffusion of Ga, void formation on the interface and mixing of metals. Annealing in a mixture of N2 and O2 improves adhesion and reduces contact resistance. However, this process also induces GaN decomposition and species mixing. The mixing of metal-Ga and metal-metal remains unaffected by the method of thermal treatment but depends on gas composition for thin Pd contacts. To achieve low-resistance contacts (≈1 × 10-4 Ω cm2), we found that increasing the Pd thickness and using N2 + O2 as the annealing environment are effective measures. Nevertheless, the degradation effect of the annealed contact microstructure in the form of the void generation becomes evident as the thickness of Pd increases. Laser diodes (LDs) with optimized palladium-based contacts operate at a voltage of 4.1 V and a current density of 3.3 kA/cm².