Gas Atmosphere Research Articles

Collision of liquid drops: bounce or merge?

Whether colliding drops will merge with or bounce off each other is critical to numerous processes, and the physics involved is notoriously complex. In particular, experiments show that both sufficiently slow and fast head-on drop collisions lead to merging, but that there is often an intermediate regime in which bouncing is observed; these transitions in behaviour were recently discovered to be surprisingly sensitive to the radius of the drops and the ambient gas pressure. We show here that these transitions between bouncing and merging are governed by nanoscale phenomena; namely, gas-kinetic and disjoining pressure effects. To capture these crucial effects, a novel, open-source computational model is developed for the simulation of colliding drops. The model uses a hybrid approach, based on solving the Navier–Stokes equations in the drop with a lubrication approach for the unconventional physics of the gas film. Our simulations show remarkably good agreement with experiments of head-on collisions and also provide new experimentally verifiable predictions.

Development and morphological analysis of the zone refining process for high purity germanium

A highly efficient purification process has been developed to enhance the purity of germanium (Ge) up to 13 N from an initial 4N purity. Hall effect measurements demonstrated that part of the zone refined Ge (ZRGe) bars exhibited p-type conductivity and high purity with a net charge carrier concentration of around 4–9 × 1010 cm−3. Noteworthy observations include a rise in carrier concentration (1011 to 1012 cm−3) at a very low zone refining (ZR) velocity of 1 mm/min, which is attributed to the diffusion of impurities from the container into the Ge melt. The purification efficiency was enhanced by optimizing the ZR velocity to around 4–5 mm/min. Purification was carried out at different process steps using graphite and quartz containers. Subsequent microstructural examinations, conducted in conjunction with wet-chemical etching of the sample unveiled the presence of various grains, grain boundaries (GBs), and low & high-density of dislocation clusters: These observations were made in samples that had undergone zone refining under various gas atmospheres including argon, nitrogen and hydrogen. Electron back scattered diffraction (EBSD) analysis reveals the characteristics of multiple grains and grain boundaries (GBs) of Ge refined in argon and nitrogen atmosphere, including low-angle GBs, high-angle GBs with coincide site lattice (CSL) Σ3, Σ9, Σ27a, and random angle GBs. In contrast, the EBSD results of Ge refined in hydrogen atmosphere shows larger grains with only a few low-angle grain boundaries. The materials refined in argon and nitrogen show a lower carrier lifetime (10–30 μs) owing to the presence of various high angle grains boundaries as well as low purity. Conversely, zone refining in hydrogen resulted in the carrier lifetime of around 50 μs in polycrystalline Ge wafers with larger grains.

Activating colloidal synthesized Au catalyst by the electrochemical strategy: Gas atmosphere, electrolyte and electrochemical technique

Organic ligands are necessarily used to stabilize nanoparticles (NPs) in colloid synthesis, and the presence of these ligands in most cases can have adverse effects on heterogeneous nanocatalysis. Therefore, it is crucial to develop efficient methods to remove ligands and study the removal mechanism. In this article, we developed a combined electrochemical method (chronoamperometry (CA) + cyclic voltammetry (CV)), which can completely and efficiently remove thiol ligand from Au NPs to produce cleaned Au/C catalyst. Using the oxygen reduction reaction (ORR) activity as the evaluation criterion for ligand removal, we found that gas atmosphere (O2) plays an important role in the removal process, while the acidity and alkalinity of electrolyte have no effect on the removal efficiency. A proposed thiol ligand removal mechanism along with Au degradation is presented. The results of CA activation at an oxidation constant potential (1.7 V) indicate that oxidation of thiol alone cannot remove thiol ligand. Only if a reduction constant potential of 0.2 V is further applied, the ORR activity of Au/C catalyst will increase, indicating that both the oxidation and reduction processes of Au NPs are crucial for ligand removal. Although the CA method (with an upper potential of 1.7 V and a lower potential of 0.2 V) can efficiently remove the majority of thiol ligand, complete removal of thiol ligand requires further CV activation. Based on the relevant results, a combined electrochemical method (CA + CV) is established. Developing standardized methods for removing ligands on the surface of catalysts is important for obtaining efficient catalysts and is also important for the reproducibility of catalytic results.

Investigations on the Heat Balance of the Melt Pool during PBF-LB/M under Various Process Gases

During the powder bed fusion of metals using a laser beam (PBF-LB/M), an inert atmosphere is maintained in the build chamber to avoid reactions of the liquid metal with ambient air leading to the creation of oxides or nitrides, which alter the mechanical properties of the processed part. A continuous gas flow is guided over the process zone to remove spatters and fumes. This flow induces a convective heat transfer from the molten metal to the gas, which, depending on the level of the heat flow, may alter the melt pool dimensions by influencing the cooling rate. The present work investigated these phenomena with single-line trials, both experimentally and numerically. For this reason, a smoothed-particle hydrodynamics model was utilized to investigate the temperatures of the melt pool, cooling rates, and the integral heat balance with various gas atmospheres. In parallel, an on-axis pyrometer was set up on an experimental PBF-LB/M machine to capture the surface emissions of the melt pool. The atmosphere in the simulations and experiments was varied between argon, helium, and two mixtures thereof. The results showed a slight increase in the cooling rates with an increasing fraction of helium in the process gas. Consistently, a slight decrease in the melt pool temperatures and dimensions was found.

Thermal Decomposition of Hematite Ore Fines in Air

Thermal decomposition of hematite plays an important role during pelletization and the iron fine‐based smelting processes such as HIsarna and flash shaft smelter. The temperature at which pure hematite decomposition occurs depends on the partial pressure of oxygen in the gaseous atmosphere. In the air, that is, at = 0.21, the hematite decomposes at 1386 °C. In the present work, for an ore of a given composition, the effect of gangue on the thermal decomposition of hematite is experimentally determined using thermogravimetric analysis (TGA). A decomposition temperature of 1320 °C is found in the platinum crucible after analyzing the TGA curve. Thermodynamic calculations have been carried out using FactSage8.1 to investigate the effect of gangue on the stability of hematite. Thermodynamics calculations confirm that the hematite present in the ore decomposes at a lower temperature with the increase in the gangue content. Additionally, if gangue content can affect the temperature at which dissociation of hematite occurs, it is expected that the crucible material can also affect the dissociation. Interestingly most of the reported TGA experiments are performed either in alumina crucibles or it was not reported in the literature. Therefore, the effect of crucible materials, namely alumina and platinum, is also investigated.

Temperature differentially regulates estuarine microbial N2O production along a salinity gradient

Nitrous oxide (N2O) is atmospheric trace gas that contributes to climate change and affects stratospheric and ground-level ozone concentrations. Ammonia oxidizers and denitrifiers contribute to N2O emissions in estuarine waters. However, as an important climate factor, how temperature regulates microbial N2O production in estuarine water remains unclear. Here, we have employed stable isotope labeling techniques to demonstrate that the N2O production in estuarine waters exhibited differential thermal response patterns between nearshore and offshore regions. The optimal temperatures (Topt) for N2O production rates (N2OR) were higher at nearshore than offshore sites. 15N-labeled nitrite (15NO2-) experiments revealed that at the nearshore sites dominated by ammonia-oxidizing bacteria (AOB), the thermal tolerance of 15N-N2OR increases with increasing salinity, suggesting that N2O production by AOB-driven nitrifier denitrification may be co-regulated by temperature and salinity. Metatranscriptomic and metagenomic analyses of enriched water samples revealed that the denitrification pathway of AOB is the primary source of N2O, while clade II N2O-reducers dominated N2O consumption. Temperature regulated the expression patterns of nitrite reductase (nirK) and nitrous oxide reductase (nosZ) genes from different sources, thereby influencing N2O emissions in the system. Our findings contribute to understanding the sources of N2O in estuarine waters and their response to global warming.

Long–Term Characteristics of Ambient Trace gases and Meteorology in Delhi, India

Long–Term Characteristics of Ambient Trace gases and Meteorology in Delhi, India

UV irradiation during fluorescence measurements affects the structures and fluorescence properties of isolated lignins in solution

There are no reports on the stability of autofluorescence, although lignins and their solutions are known to exhibit autofluorescence. An aim of this study is to investigate spectral change of lignin autofluorescence under prolonged excitation with ultraviolet (UV). Both fluorescence spectra of softwood milled wood lignin (MWL) and kraft lignin (SKL) in propylene glycol significantly changed upon an UV irradiation at 280 nm under O2 and Ar atmospheres even for 10 min. By the further irradiation, the autofluorescence intensities were remarkably changed together with the emission wavelengths. However, no tendency in the autofluorescence change was observed. The change varied between lignin preparations and gas atmosphere. These phenomena should be caused by autoxidation upon UV irradiation, and the reaction resulted in not only photodegradation but also photopolymerization.

Formation conditions of the tungsten porous thin film with pulsed laser deposition under various gas atmosphere

Abstract Pulsed laser deposition (PLD) under gas atmospheres has been used to fabricate thin films for various applications. In this study, PLD was performed under various gas atmospheres (helium, oxygen, and argon) using tungsten (W) to investigate the morphology of thin films. Various types of structures were formed, including uniform, nanoparticles, and columnar structures. In particular, the substrate fabricated at an argon pressure of 100 Pa had a high porosity and a low light reflectance in the 200–1400 nm wavelength range. In addition, it was shown that the growth of the thin film thickness was non-linear with respect to time, and the formation of a fuzz-like structure may be influenced by particle diffusion in the gas phase and on the substrate.

Study on the cracking process of epoxy resin under oxygen and water atmosphere based on ReaxFF force field

Amino-cured epoxy resins are widely used in the electrical and electronic industry for their excellent properties. To investigate the mechanism of the effect of O2 and H2O on the pyrolysis behavior of epoxy resin, in this paper, the cross-linked structure of bisphenol A type epoxy resin cured by adducts of diethylenetriamine and butyl glycidyl ether is modeled based on the ReaxFF force field, and the thermal decomposition processes at different temperatures and gas atmospheres were simulated and the pathways of the small molecule products were clarified. The results show that epoxy resin will produce small molecule gas products, such as H2, CO, H2O, OH, CH2O, and free radicals, in the process of pyrolysis; the presence of amino groups also generates nitrogen-containing radicals, such as CN, CH2N, and C2H4N; as the reaction temperature increases, the rate of pyrolysis reaction will be accelerated. The same temperature in oxygen and water atmospheres can accelerate the breakage of epoxy resin main chain by promoting the breakage of carbon and oxygen bonds and, at the same time, promote the generation of small molecule gases, such as H2 and CO.

Insight into high-temperature fast pyrolysis characterization, product distribution and interaction effect of municipal solid waste and its components under steam-containing hydrogen-rich syngas atmosphere

This research delves into the field of fast hydropyrolysis of mixed municipal solid waste (MSW), with the goal of understanding product distribution and interactions in a hydrogen-rich condition. Through experimental investigations on MSW and its components, this study thoroughly examines the impact of pyrolysis temperature and gasification atmosphere (30% H2+30% CO+20% CO2+20% H2O) on the yields and distribution of the three-phase products. As the temperature increases, the gas yield gradually increases, while the yields of tar and char gradually decrease. The introduction of a hydrogen source increases the methane content in the combustible gas, which generally reaches its maximum at 850 °C, and promotes aromatic formation in tar, making aromatics the main component of pyrolysis oil. Notably, aromatics have the highest-octane number in gasoline. This study highlights gasification as a promising technology for converting organic waste into valuable fuel, advancing waste management and energy recovery.

Non-thermal atmospheric pressure gas discharge plasma enhances tendon-to-bone junction repair in a rabbit model

Non-thermal atmospheric pressure gas discharge plasma enhances tendon-to-bone junction repair in a rabbit model

Numerical investigation on direct water injection characteristics under different injection and ambient conditions within oxygen/argon atmosphere

Improving efficiency and reducing emissions are essential to achieve carbon neutrality in transportation sector. The hydrogen-fueled argon power cycle (H2-APC) is a novel power system with high efficiency and zero emission by utilizing argon-oxygen mixture as working fluids. However, knock suppression is a problem within H2-APC engines. Direct water injection (DWI) is an effective method to inhibit detonation. Spray morphology greatly influences the effectiveness of DWI, the investigation of spray characteristics in oxygen/argon atmosphere is critical. This paper established a computational model based on experimental data to investigate DWI characteristics under different injection and ambient conditions within oxygen/argon atmosphere. The results reveal increased jet temperature leads to stronger superheated jet spray collapse, while Sauter mean diameter (SMD) decreases and atomization improves. Increasing jet pressure effectively reduces spray SMD and improves atomization effect and evaporation rate. Higher ambient temperature reduces ambient gas density, spray SMD and penetration are decreased and increased, respectively. Moreover, spray evaporation rate and evaporated mass are dropped with higher ambient pressure for both superheated and subcooled sprays. As ambient density rises, the capacity for jet perturbation and fragmentation is enhanced, and spray SMD decreases. The research results can provide an effective guide for the DWI strategy of H2-APC engines.

Electro-Mechanical Behavior of Copper-Based Electrical Motor Brushes

This study was mainly performed in order to examine the properties of electric motor brushes (EMB). EMBs are electrically conductive and work under wear conditions due to direct contact with the moving part (rotor) of electric motors. In accordance with the scope of the study, EMB characteristics were investigated in two different groups and reproduced with a new technique at the end of this phase. New EMBs were produced via varying proportions of copper matrix, graphene, and silicon carbide reinforcements. The composite-alloy powder elements were carefully squeezed by a cold and single-axis hydraulic press under a pressure of 500 MPa (±5 MPa) following 8 hours of mechanical alloying (MA). The molded composite product (sample) was sintered at 900° C for 1 hour in a reducing gas atmosphere. 100 kPa spring pressure was tested on each sample thrice with 8, 16, 24, and 32 m/s rotational speeds and densities of 4, 8, 12, and 16 A/cm2. Following this process, the electrical conductivity, porosity, hardness, wear loss, surface roughness, and temperature changes were investigated for each sample. It was determined that the electrical conductivity decreased with increasing reinforcement ratio and, in terms of electrical conductivity, affected the brushes’ properties negatively.

Torrefaction performance of Macadamia husk under a flue gas atmosphere for solid biofuel applications

Torrefaction performance of Macadamia husk under a flue gas atmosphere for solid biofuel applications

Evaluation of a Commercial MoS2 Dry Film Lubricant for Space Applications

Molybdenum disulfide coatings, particularly Microseal 200-1, have been extensively used as dry film lubricants for actuating mechanisms in space applications. Although Microseal 200-1 has historically been a popular choice for space missions, recent assessments indicate a need for reexamination. This study evaluates sliding friction in air and dry gaseous nitrogen atmospheres at ambient temperatures with both linear reciprocating and rotary unidirectional tribo-tests. Measurements are performed for Microseal 200-1 applied on substrates and surface treatments commonly used in aerospace components, particularly stainless steel and a titanium alloy. Our findings indicate that the friction of stainless steel balls sliding on Microseal 200-1-coated disks is significantly influenced by the environment as well as the disk substrate material. The average friction coefficient ranges from 0.12 to 0.48 in air and from 0.04 to 0.41 in dry gaseous nitrogen, and the amount of friction is consistently much higher for the Microseal 200-1 on the stainless steel than on the titanium alloy. Microscopy and surface analyses, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence, of the coatings on stainless steel substrates reveals that the coatings are sparse and relatively thin, likely a key factor contributing to their high friction. This insight underscores the substrate dependence of this widely used coating and highlights the importance of detailed tribological testing in accurately assessing the tribological performance of commercial dry film lubricants, a key step towards improving the reliability and effectiveness of actuating mechanisms for space applications.

Transceiving telescope for a mobile TDLAS system for remote sounding of anthropogenic methane

In this paper, we report on stages of the development of a transceiving telescope for atmospheric gas analysis TDLAS systems. Design of transmitters and receivers for active remote sounding systems is an important problem when creating instruments for studying atmospheric parameters. Transmitter and receiver aperture size directly influences the minimum permissible and maximum practicable sounding ranges. The work describes the stages of designing the receiving and transmitting parts of an atmospheric gas analysis tunable diode laser absorption spectroscopy (TDLAS) system (with anthropogenic methane as a target gas). Calculations show that a backscattered signal is reliably detected over an optical path 0–1000 m long with the use of a transceiving telescope with aperture 50–80 mm diameter and magnification of no less than 5. This design enables minimizing the dead zone of the coaxial TDLAS system within the 1645–1655 nm spectral range, which is informative for anthropogenic methane sounding. The use of a transceiving telescope will ensure resistance to misalignment, namely, resistance to mismatch between the mutual overlap of the device field of view and the laser radiation spot on the topographic target. Results of this work can be useful when designing and manufacturing telescopes for TDLAS systems methane (CH4) and also other atmospheric gas analysis.

Thermodynamic properties of MnV2O6 and Mn2V2O7 at high temperatures

MnV2O6 and Mn2V2O7 are the key compounds during the manganese salt roasting for extracting vanadium from vanadium bearing slag. Thermodynamic properties of MnV2O6 and Mn2V2O7 are dispensable to get insight into the multi-phase reaction mechanism and clarify the phase evolution. In this study, the MnV2O6 and Mn2V2O7 compounds were synthesized through solid-state roasting routes under a nitrogen gas atmosphere, and their crystal structure and thermodynamic properties were determined using X-ray powder diffraction, differential scanning calorimetry, and drop calorimetry. The enthalpy increments of MnV2O6 and Mn2V2O7 were experimentally measured for temperatures ranging from 573 K to 1023 K and 573 K to 1173 K, respectively, using drop calorimetry for the first time. Based on the experimentally measured enthalpy increments, the temperature dependence of the molar heat capacity of MnV2O6 and Mn2V2O7 was then derived. Furthermore, thermodynamic properties such as enthalpy, entropy, and Gibbs free energy were also calculated. Finally, the Gibbs free energy of the chemical reactions during the roasting of vanadium slag was evaluated, and compared with other roasting techniques.

Improved accuracy of continuum surface flux models for metal additive manufacturing melt pool simulations

Computational modeling of the melt pool dynamics in laser-based powder bed fusion metal additive manufacturing (PBF-LB/M) promises to shed light on fundamental mechanisms of defect generation. These processes are accompanied by rapid evaporation so that the evaporation-induced recoil pressure and cooling arise as major driving forces for fluid dynamics and temperature evolution. The magnitude of these interface fluxes depends exponentially on the melt pool surface temperature, which, therefore, has to be predicted with high accuracy. The present work utilizes a diffuse interface finite element model based on a continuum surface flux (CSF) description of interface fluxes to study dimensionally reduced thermal two-phase problems representative for PBF-LB/M in a finite element framework. It is demonstrated that the extreme temperature gradients combined with the high ratios of material properties between metal and ambient gas lead to significant errors in the interface temperatures and fluxes when classical CSF approaches, along with typical interface thicknesses and discretizations, are applied. It is expected that this finding is also relevant for other types of diffuse interface PBF-LB/M melt pool models. A novel parameter-scaled CSF approach is proposed, which is constructed to yield a smoother temperature field in the diffuse interface region, significantly increasing the solution accuracy. The interface thickness required to predict the temperature field with a given level of accuracy is less restrictive by at least one order of magnitude for the proposed parameter-scaled approach compared to classical CSF, drastically reducing computational costs. Finally, we showcase the general applicability of the parameter-scaled CSF to a 3D simulation of stationary laser melting of PBF-LB/M considering the fully coupled thermo-hydrodynamic multi-phase problem, including phase change.

High-Temperature Reorganization Behavior of Single-Crystalline Porous 4H-SiC Thin Foils

This work reports on the high-temperature reorganization behavior of single-crystalline porous 4H-silicon carbide (4H-SiC) thin foils. Porous 4H-SiC thin foils are realized via state-of-the-art photoelectrochemical etching in hydrofluoric (HF) acid solution enabling for the first time a released foil with a diameter of 2 inches. Subsequent annealing under inert gas atmosphere and comparison between samples suggests that a temperature of 1500 °C allows for various degrees of compactification across the foil surface, whereas at 1600 °C single crystallinity can be preserved.