Variation Of Oxygen Content Research Articles

Thermal treatment of H3PO4-impregnated hydrochar under controlled oxygen flows for producing materials with tunable properties and enhanced diclofenac adsorption

The chemical activation of biomass with phosphoric acid under an oxygenated atmosphere has been extensively studied in various papers. However, there is still uncertainty about how the oxygenated atmosphere affects the evolution of activated carbon properties, as the concentration of oxygen in the activation atmosphere has not been explored as an activation variable. Hence, this paper aims to fill the gap by exploring the effect of oxygen concentration on the activation process. The H3PO4-impregnated hydrochar was heated at 500 °C, under atmospheres containing various concentrations of oxygen. The evolution of activated carbons' properties was assessed by various techniques, including FTIR, SEM-EDS, N2-physisorption, CHNS/O elemental analysis, pHpzc, and Boehm titration. Additionally, the impact of oxygen concentration on the adsorption capacity was examined using diclofenac as a model pollutant. It was found that the activated carbons’ microporosity and surface functionality can be improved and controlled by changing the oxygen concentration in the activation atmosphere. This led to enhanced π-π and hydrogen bonding interactions between diclofenac molecules and activated carbons, resulting in increased adsorption capacities. This study emphasizes the importance of oxygen concentration as an activation variable, providing valuable insights for designing effective activated carbon adsorbents.

An investigation of the reaction of metallic uranium with oxygen/nitrogen gas mixtures

The effects of variations in oxygen content as a mixed oxygen/nitrogen gas on the exothermic reaction of uranium were investigated in this work. Samples of metallic uranium with various specific surface areas and masses were reacted in a thermogravimetric analysis system at temperatures ranging between 323 K and 1273 K using gas mixtures 10%, 5%, 1%, or 0.5% oxygen in nitrogen. From the results it was concluded that the minimum oxygen content necessary for the onset of ignition is correlated to the specific surface area of the metallic uranium. The higher the specific surface area, the lower the percentage of oxygen is needed to trigger an ignition event. Within the experimental parameters evaluated here, ignition does not appear to occur for any specific surface area investigated below 1% oxygen content.

Oxidative combustion law of water-soaked coal under oxygen-lean condition

ABSTRACT Residual coal is easily submerged and damaged by groundwater. In the course of mining underlying coal seam, coal belonging to the overlying gob area tends to spontaneously combust during draining water. To explore the effect of micro-functional group transformation in immersed coal on the coal spontaneous combustion (CSC) traits during the low-temperature oxidation process (LTO), the migrant law of special functional groups under varying oxygen concentration (Co) of immersed coal was discussed by infrared spectroscopy. The endothermal and exothermal properties of the function group inside of coal were studied via thermal analysis. It is shown that the higher Co, the more oxygenic function groups on the soaked, and by contrasted with the Co of 18% the 14% has a small increase and the chain length is shortened. The temperature increment together with the Co content determines the functional group content, the pyrolysis process produces some function group. The lower the Co, endothermic coefficient decreases and endothermic temperature increases, the higher the ignition temperature of coal oxy-combustion, the lower the total heat release. And the speed of the oxygen-absorbing weight gain and the conversion of the functional group would be improved followed by the burnout temperature rising. Below 14% Co, the oxidative combustion process will be greatly inhibited. Those findings complement a theoretical basis for preventing long-term water-soaked coal oxidative spontaneous combusting in shallow buried coal seams.

High-speed formaldehyde planar laser-induced fluorescence and schlieren to assess influences of injection pressure and oxygen concentration on Spray A flames

The present study investigates the effect of injection pressure and ambient oxygen concentration variations on the Engine Combustion Network Spray A flame. The two-stage ignition and combustion processes for individual injections are characterized using a high-speed planar laser-induced fluorescence (PLIF) and schlieren imaging diagnostic at high pressure (near 6 MPa). For PLIF measurements, we use a pulse-burst-mode Nd:YAG laser capable of producing a 6 ms long 355-nm pulse-train with 300 pulses at 70 mJ/pulse, separated by 20 µs. The PLIF imaging at high-acquisition rate offers unique insights into understanding the spatiotemporal distribution of formaldehyde (CH2O) and polycyclic aromatic hydrocarbons (PAH). High-speed line-of-sight schlieren with a pulsed infrared light emitting diode (LED) is applied simultaneously with PLIF to visualize the spray penetration, low- and high-temperature ignition, and turbulent flame dynamics, while in-vessel pressure is used in concert with the optical diagnostics to assess the ignition delay time of the high-temperature ignition events. The PLIF and line-of-sight measurements, documenting the position and timing for formation and consumption of CH2O and the inception and distribution of PAH downstream with changes in ambient oxygen concentration and injection pressure, provide a unique database for detailed evaluation of single-event (e.g. LES) or ensemble-average CFD.

Tissue Oxygenation Around Capillaries: Effects of Hematocrit and Arteriole Oxygen Condition.

Oxygen transfer in the microvasculature is a complex phenomenon that involves multiple physical and chemical processes and multiple media. Hematocrit, the volume fraction of red blood cells (RBCs) in blood, has direct influences on the blood flow as well as the oxygen supply in the microcirculation. On the one hand, a higher hematocrit means that more RBCs present in capillaries, and thus, more oxygen is available at the source end. On the other hand, the flow resistance increases with hematocrit, and therefore, the RBC motion becomes slower, which in turn reduces the influx of oxygen-rich RBCs entering capillaries. Such double roles of hematocrit have not been investigated adequately. Moreover, the oxygen-hemoglobin dissociation rate depends on the oxygen tension and hemoglobin saturation of the cytoplasm inside RBCs, and the dissociation kinetics exhibits a nonlinear fashion at different oxygen tensions. To understand how these factors and mechanisms interplay in the oxygen transport process, computational modeling and simulations are favorite since we have a good control of the system parameters and also we can access to the detailed information during the transport process. In this study, we conduct numerical simulations for the blood flow and RBC deformation along a capillary and the oxygen transfer from RBCs to the surrounding tissue. Different values for the hematocrit, arteriole oxygen tension, tissue metabolism rate and hemoglobin concentration and affinity are considered, and the simulated spatial and temporal variations of oxygen concentration are analyzed in conjunction with the nonlinear oxygen-hemoglobin reaction kinetics. Our results show that there are two competing mechanisms for the tissue oxygenation response to a hematocrit increases: the favorite effect of the higher RBC density and the negative effect of the slower RBC motion. Moreover, in the low oxygen situations with RBC oxygen tension less than 50mmHg at capillary inlet, the reduced RBC velocity effect dominates, resulting in a decrease in tissue oxygenation at higher hematocrit. On the opposite, for RBC oxygen tension higher than 50mmHg when entering the capillary, a higher hematocrit is beneficial to the tissue oxygenation. More interestingly, the pivoting arteriole oxygen tension at which the two competing mechanisms switch dominance on tissue oxygenation becomes lower for higher oxygen-hemoglobin affinity and lower hemoglobin concentration. This observation has also been analyzed based on the oxygen supply from RBCs and the oxygen-hemoglobin reaction kinetics. The results and discussions presented in this article could be helpful for a better understanding of oxygen transport in microcirculation.

Investigation on nitrogen oxidation characteristics and volatile–char interaction during co‐combustion of semi‐coke and bituminous coal

AbstractBlending bituminous coal (BC) in semi‐coke (SC) is a promising approach to improve the combustion behaviors of SC, while the nitrogen conversion characteristics during the co‐combustion are still unclear. This paper deals with the oxidation characteristics of volatile‐N and char‐N and their contributions to total NO during the co‐combustion of SC and BC using a volatile–char separated combustion system. By comparing the volatile–char separated combustion with the entrained flow combustion, the interaction between volatile‐N and char‐N has also been elucidated. Results indicated volatile‐N was the main contribution to total NO formation for both SC and BC at temperatures above 1000°C. The volatile‐NO and char‐NO conversion ratios presented distinct variations along with the temperature, and the temperature had different impact on the two combustion modes. The char‐NO was more sensitive to the variation of oxygen concentration, and the nitrogen conversion of SC was more susceptible to oxygen compared with that of BC. The blending of BC inhibited the volatile‐NO and char‐NO formation of SC, and the inhibition effect enhanced in pace with the blending ratio of BC. The influence of volatile–char interaction on nitrogen conversion was temperature‐dependent and fuel‐varying: for SC, it was more significant in pyrolysis stage in the temperature range of 900°C to 1400°C, and sufficient pyrolysis measures can effectively reduce the NO formation; however, the identical result occurred when the temperature exceeded 1100°C for the blend.

Performance Analysis and Optimization of Fuel Tank Ground-Based Washing Inerting on Unmanned Aerial Vehicles

In this study, a ground-based washing inerting (GBWI) method was proposed, and the application of GBWI in the field of fire prevention and explosion suppression of unmanned aerial vehicle (UAV) fuel tanks was studied using a volume of fluid (VOF) two-phase flow model at a given typical flight envelope. The variation in oxygen concentration in tank ullage during flight was calculated considering the entrance of ambient air and the escape of dissolved oxygen from the fuel. The results indicate that the oxygen concentration in the ullage increases with increasing initial oxygen concentration in the ullage and the initial fuel load after GBWI. In the climb and cruise stages, the oxygen concentration in the ullage increases slowly, while in the tactical descent stage, the oxygen concentration in the ullage increases rapidly, easily exceeding the limiting oxygen concentration (LOC) of aviation fuel combustion. To expand the application range of GBWI, an optimization scheme of nitrogen filling protection was proposed so that the GBWI could meet the requirements of an inert tank at different fuel loads and initial oxygen concentrations in the ullage. Compared with a traditional on-board inert gas generation system (OBIGGS), the optimized GBWI method could greatly reduce the fuel compensation loss and improve the maneuverability of UAVs at the same time.

Metabolic Responses and Resilience to Environmental Challenges in the Sedentary Batrachoid Halobatrachus didactylus (Bloch & Schneider, 1801)

In the context of climate change, warming of the seas and expansion of hypoxic zones are challenges that most species of fish are, or will be subjected to. Understanding how different species cope with these changes in their environment at the individual level can shed light on how populations and ecosystems will be affected. We provide first-time estimates on the metabolic rates, thermal, and oxygen-related limits for Halobatrachus didactylus, a coastal sedentary fish that lives in intertidal environments of the Northeast Atlantic. Using respirometry in different experimental designs, we found that this species is highly resistant to acute thermal stress (CTmax: 34.82 ± 0.66 °C) and acute hypoxia (Pcrit: 0.59-1.97 mg O2 L-1). We found size-specific differences in this stress response, with smaller individuals being more sensitive. We also quantified its aerobic scope and daily activity patterns, finding this fish to be extremely sedentary, with one of the lowest standard metabolic rates found in temperate fish (SMR: 14.96 mg O2 kg-1h-1). H. didactylus activity increases at night, when its metabolic rate increases drastically (RMR: 36.01 mg O2 kg-1h-1). The maximum metabolic rate of H. didactylus was estimated to be 67.31 mg O2 kg-1h-1, producing an aerobic scope of 52.35 mg O2 kg-1h-1 (77.8% increase). The metrics obtained in this study prove that H. didactylus is remarkably resilient to acute environmental variations in temperature and oxygen content, which might enable it to adapt to the extreme abiotic conditions forecasted for the world's oceans in the near future.

Effect of rGO/GNP on the electrical conductivity and piezoresistance of cement-based composite subjected to dynamic loading

Graphene has good compatibility with cement-based materials. It can be introduced into cement to produce cement-based composite with electrical conductivity and loading sensitivity, and can effectively monitor the internal state of concrete components under stresses such as compression, bending, and tension. The electrical properties of such cement-based composites vary with the type and doping level of graphene. In this study, two types of reduced graphene oxide (rGO) with varying oxygen contents and two types of graphene nanoplates (GNPs) with varying sheet sizes were selected, and the conductivity and piezoresistive properties of the rGO/GNP cement-based composites subjected to cyclic compressive and tensile stress were investigated. Both tunnelling effect and percolation phenomena simultaneously played important roles in conductivity and electromechanical properties of graphene cement-based composite. The rGO/GNP cement-based composites exhibited excellent piezoresistive characteristics under compressive or tensile stress and stable repeatability. The cement-based composites filled with high oxygen content graphene (rGO-HO) or large sheet size graphene (GNP-L) has a larger stress sensitivity coefficient. This study reveals the great potential of graphene for real-time and in situ health monitoring of concrete structures. The excellent loading response ability of graphene has laid the foundation for the development of new smart materials based on graphene cement, which is of great significance for expanding the use of graphene and for the intelligent of traditional building materials.

Prediction modelling framework comparative analysis of dissolved oxygen concentration variations using support vector regression coupled with multiple feature engineering and optimization methods: A case study in China

Dissolved oxygen (DO) is an essential indicator for assessing water quality and managing aquatic environments, but it is still a challenging topic to accurately understand and predict the spatiotemporal variation of DO concentrations under the complex effects of different environmental factors. In this study, a practical prediction framework was proposed for DO concentrations based on the support vector regression (SVR) model coupling multiple intelligence techniques (i.e., four data denoising techniques, three feature selection rules, and four hyperparameter optimization methods). The holistic framework was tested using a data matrix (17,532 observation data in total) of 12 indicators from three vital water quality monitoring stations of the longest inter-basin water diversion project in the world (i.e., the Middle-Route of the South-to-North Water Diversion Project of China), during the year 2017 to 2020 period. The results showed that the framework we advocated for could successfully and accurately predict DO concentration variations in different geographical locations. The model used the “wavelet analysis–LASSO regression–random search–SVR” combination of the Waihuanhe station has the best prediction performance, with the Root Mean Square Error (RMSE), Mean Square Error (MSE), Mean Absolute Error (MAE), and coefficient of determination (R2) values of 0.251, 0.063, 0.190, and 0.911, respectively. The combined methods using feature selection and hyperparameter optimization techniques can significantly promote the robustness and accuracy of the prediction model and can provide a new universal and practical way of investigating and understanding the environmental drivers of DO concentration variations. For the water quality management department, this proposed comprehensive framework can also identify and reveal the key parameters that should be concerned and monitored under different environmental factors change. More studies in terms of assessing potential integrated water quality risk using multi-indicators in mega water diversion projects and/or similar water bodies are required in the future.

Analysis of Drain-Induced Barrier Lowering in InGaZnO Thin-Film Transistors

Characterization of short-channel amorphous indium gallium zinc oxide (InGaZnO) (a-IGZO) thin-film transistors (TFTs) has been a crucial issue to realize higher resolution display and heterogeneous integration with complementary metal–oxide–semiconductor (CMOS) technology. In this work, the drain-induced barrier lowering (DIBL) of the a-IGZO TFT was investigated with the variations in oxygen content in the IGZO layer. In order to accurately investigate the effect of the drain voltage on the channel potential, it is necessary to analyze the energy band diagram based on the dopant profile of the channel region. A new method for extracting the channel dopant profile through a simple <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> measurement of the a-TFT sample was proposed. We performed TCAD device simulation based on the extracted density of states and dopant profile of IGZO layer and confirm good agreement with the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> characteristics of a-IGZO TFTs with various oxygen contents. The effective channel length was found to be short with decreasing the oxygen content in the IGZO channel layer. The DIBL effect becomes more severe as the oxygen content decreases. Our methodology, which was successfully verified in this work, can be utilized for the analysis of short-channel effects including DIBL for the scaled a-IGZO TFTs.

Effects of surface oxide layer on the impact dynamic behavior of molten aluminum droplets

Oxide layer is easily formed on the surface of some metal droplets, which affects the dynamic behavior of droplet impact. In this paper, experiments were conducted for the impacting process of a molten aluminum droplet on a Teflon substrate. The thickness of surface oxide layer of aluminum droplets was controlled by varying oxygen concentrations in the gas atmosphere. The effects of oxygen concentration and Weber number on droplet spread, rebound, and splash behavior were investigated. The results show that the oxygen concentration in the environment directly affects the droplet impact behavior. The differences in the droplet retraction process at different oxygen concentrations are more significant than the spread process. Strong retraction causes droplet rebound (We = 17.11) and splash (We = 102.3) in hypoxic environments, whereas only weak retraction in air. The viscous dissipation of the droplet impact in different oxygen concentration environment is estimated by counting the droplet bounce height, and the dissipation increases with the increase in the oxygen concentration. The thickness of the oxide layer measured by scanning electron microscope became thinner as the oxygen concentration decreases and, accordingly, the aluminum droplet collisions show different dynamic behavior. The experimental results are analyzed and explained regarding the reduction in surface tension, the increase in viscous forces, and the shear-thinning properties which increase the viscous dissipation during retraction. Ryan model was used to predict the droplet maximum spreading factor ξmax with the Weber number to the power of 0.5, better than the energy conservation-based Pasandideh-Fard model.

LOW-TEMPERATURE CATALYZED GROWTH AND PLASMONIC PROPERTIES OF COLUMNAR Au-SiOx NANOCOMPOSITE THIN FILMS

The optical properties of noble metal nanoparticles (NPs) can be efficiently controlled by their incorporation into host matrix films. Here, we report on the fabrication of composite films of gold NPs in a silicon suboxide matrix by a novel approach using a combination of pulsed laser deposition for NP production and gas-jet, electron-beam plasma chemical vapor deposition for low-temperature (300&amp;deg;C) synthesis of a SiO&lt;sub&gt;x&lt;/sub&gt; (x &amp;#61; 0.38-1.55) thin film as a matrix for the NPs. The produced nanocomposite exhibits unexpected plasmonic properties, non-monotonically dependent on the matrix thickness, due to a porous columnar matrix structure grown from the NPs with variable oxygen content along the columns. This implies that low-temperature, gold-catalyzed oxidation of silicon occurs during the structure growth. Calculations based on Mie theory show that the refractive index of the obtained SiO&lt;sub&gt;x&lt;/sub&gt; matrix can be as low as 1.2 at certain film thicknesses. Mechanisms of the columnar structure formation at different deposition stages are discussed. The synthesis approach can be used for the fabrication of optical thin-film materials with controllable low refractive index.

Opposed-flow flame spread over carbon fiber reinforced plastic with different carbon fiber orientations

Herein, carbon fiber reinforced plastic (CFRP) sheets with different carbon fiber (CF) orientations were combusted in an environment of variable opposed-flow velocity (Vg) and oxygen concentration, and the effects of the CF orientation angle (θ) on the flame spread characteristics were studied. The limiting oxygen concentration increased with θ and linearly decreased with increasing Vg. The flame spread rate (Vf) was the highest when the CF orientation corresponded to the flame spread direction (i.e., θ = 0 deg.) and increased with Vg. Conductive heat transfer sideways became more significant as θ increased, which signifies increased heat loss. Thus, the net heat transfer rates that directly contributed to the flame spread decreased, leading to low flammability and weak flame spread. Vf was calculated using our previous CFRP flame spread model. The calculated Vf was higher than the measured Vf, and the difference between them increased as Vg increased. This is because the flame height (Hf) decreased considerably with increasing Vg, resulting in high heat transfer rate from the flame and high Vf. The Hf model was thus revised based on the dataset of the opposed-flow flame spread tests; then, the calculated Vf agreed well with the measured Vf. The Vf for the buoyant-flow flame spread assuming Vg = 35 cm/s was also calculated using the flame spread model with the original and revised Hf models, and no significant difference was noted between the calculated and measured Vf. Thus, this study succeeded in improving the CFRP flame spread model to deal with both the opposed-flow flame spread and the buoyant-flow flame spread. This revised model will help understand the physics of the flame spread over CFRP sheets and assess the fire risk of CFRP products for fire safety.

Decadal Time‐Series Depletion of Dissolved Oxygen at Abyssal Depths in the Northeast Pacific

AbstractDissolved oxygen depletion in the global ocean is well documented over several decades from the surface ocean to abyssal depths. This decline is especially prevalent in the Northeast Pacific. A significant decline in dissolved oxygen has been measured over 30 years at 4,000–4,100 m depth (Station M) beneath the California Current off central California. Three principal hypotheses examined the relationship of declining oxygen with biological and physical factors over the 30‐year time series. Annual resolution revealed Ekman pumping, coastal upwelling, particulate matter flux, and sediment community oxygen consumption having significant correlations with bottom water dissolved oxygen concentration. Coastal upwelling accounted for 65% of the annual variation in bottom water oxygen concentration. Stepwise regression yielded descriptive models of bottom water dissolved oxygen using coastal upwelling, wind stress and primary production variables. Is continued oxygen depletion in the Northeast Pacific indicative of abyssal regions in the world ocean?

Unilateral Blow-Off and Periodic Smoldering Holes in Upward Flame Spread Over Thin Charring Material

ABSTRACT In this study, upward flame spread over thin charring material under varied ambient pressures and oxygen concentrations diluted with different inert gases was investigated. After symmetric ignition, a small systematic disturbance at the flame base region triggers asymmetric two-sided flames, while the flame tips remain aligned. Afterward, one branch of flame dwells and speeds up in a cycle, associated with periodic smoldering holes, mainly ascribed to the secondary pyrolysis and surface oxidative degradation (smoldering) of the remaining char, while the other branch of flame extinguishes eventually, primarily attributed to the self-induced buoyant blow-off at a low critical Damköhler number associated with finite-rate kinetics. The temperature distribution over the sample surface is obtained by infrared thermal imagers, and six stages of the whole pyrolysis process are roughly divided, which gives a better perspective on the underlying mechanism of these unique combustion behaviors. With the burnout (end) of the primary or secondary pyrolysis processes, the local fuel/oxidant mixture ratio at the flame base region approaches that of the inflammability limit (neutral stable point) where the near-limit flames are extremely sensitive to the environmental disturbances, and thus the flame base instability appears. With the increase of the oxygen concentration, the pressure range of the existence of the unique combustion behaviors narrows down due to intensified chemical reactions and thus the stability of the flame base. Furthermore, compared with the environments diluted in N2, the unique combustion behaviors are more conspicuous in that of CO2 (radiative intervening medium) due to larger molecular weight and lower Lewis number. This investigation into the upward flame propagation will enrich the combustion science at transition regimes such as the fire scenarios after the application of the carbon dioxide fire extinguisher.

Role of oxygen vacancy ordering on structure and reactivity of iron-doped Sr-based perovskites: A computational study

Density functional theory (DFT) methods were used to investigate the structure and reactivity of pure SrCoO3, SrFeO3, and iron-doped SrCo0.8Fe0.2O3 and SrCoxFe1-xO3 (x ​= ​0.25, 0.50, 0.75) perovskites. The electronic properties of bulk perovskites were compared to the electronic properties of iron-doped perovskites of various iron compositions within the bulk material. The effect of iron position on SrCo0.8Fe0.2O3 was investigated for various configurations, and it was found that the structure with two FeO6 polyhedra intercalated in between CoO6 polyhedra was relatively more stable than others. The presence of Fe polyhedra adjacent to each other enhances the Jahn-Teller distortion resulting in a lowered symmetry. The structure and reactivity of oxygen vacancy ordered SrCoO2.5, SrFeO2.5, and iron-doped SrCo0.8Fe0.2O2.5, SrCoxFe1-xO2.5, and SrCoxFe1-xO2.75 (x ​= ​0.25, 0.50, 0.75) corresponding to varying oxygen content was also investigated. Electron density distribution plots and Bader charges were examined to understand the bonding interactions. The work functions of perovskites with and without oxygen vacancies were calculated to predict the conductive behavior. Furthermore, hydrogen atom and hydrogen molecule was incorporated into the oxygen vacant site of perovskites to understand the structural transformation in hydrogenated perovskites and predict the plausible use of these materials in hydrogen storage. The adsorption of water on the SrFeO3 slab was also studied by molecular dynamics simulations. The water molecule is split into hydroxyl and proton, where the proton associates with the surface oxygen at a distance of 0.91 ​Å, and the hydroxyl ion occupies an oxygen vacant site on the surface coordinating with Fe at a distance of 2.73 ​Å.

Welding Defect and Mechanical Properties of Nanosecond Laser Cleaning 6005A Aluminum Alloy.

Nanosecond laser cleaning effectively removes oxide film and dirt from the surface of aluminum body parts for rail transit, as well as improving surface properties. The effect of laser cleaning on the quality of weld was studied in detail for different scanning frequencies and cleaning speeds. The effect of post-weld laser cleaning on weld quality was investigated. After laser cleaning at different parameters, the surface oxygen content was decreased and the surface roughness and surface hardness were increased. Variation of surface oxygen content was related to energy density and spot density. The lowest oxygen content was obtained at 150 W, 100 Hz and 0.8 m/min. Laser-generated craters changed surface morphology and improved surface roughness. The mechanical properties of the welded joints were slightly improved, which relates to a decrease in porosity. The minimum porosity of the laser-cleaned weld was 0.021%. This work provides new ideas for the nanosecond laser cleaning of aluminum alloy and its welding properties.

Influence of Oxygen Concentration on Combustion Kinetics and Gas Products of a Polyurethane–Coal Mixture

Polyurethane materials are often used in mines to fill the geological structural areas for pretreatment and plugging. These areas are primarily high-incidence areas of coal spontaneous combustion (CSC). Polyurethane will promote the spontaneous combustion of the remaining coal because of its superior thermal insulation performance. Previous studies have focused on the effect of polyurethane on the spontaneous combustion of coal in air atmosphere, without considering the variation of oxygen concentration in the mining area. The paper investigates the effect of polyurethane on the spontaneous combustion of coal in the mining area under different oxygen concentration conditions according to the variation law of oxygen concentration in the mining area. Herein, thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) coupled methods were used to study the kinetics and gas release laws of a polyurethane–coal mixture. The critical temperature of coal increases with the decrease of oxygen concentration. When the oxygen concentration exceeds 10%, the shift of the thermogravimetric curve to the right is smaller, indicating that the oxygen concentration has less influence on the combustion of a polyurethane–coal mixture. When the oxygen concentration is less than 10%, the shift of the thermogravimetric curve toward a higher temperature is more prominent, indicating that the oxygen concentration has a greater influence on the thermogravimetric curve. Simultaneously, the maximum value of DTG increases with the increasing oxygen concentration. The main gas products of coal pyrolysis are CO2, CH4, and H2O, while those of polyurethane pyrolysis are mainly CO2, CO, CH4, and H2O during the pyrolysis process. The amount of CO2 during the pyrolysis of various proportions of coal and polyurethane is the main difference in the gas products. Coal can promote the pyrolysis of polyurethane to some extent. The characteristic temperature rises and falls as the proportion of polyurethane in the polyurethane–coal mixture changes. In the actual monitoring, small amounts of H2O, CO2, and CO gases appear in the starting phase, then a large increase in the amount of gases can be considered that polyurethane is involved in the relevant combustion reactions, which can avoid misjudgment of the spontaneous combustion of coal in the mining area.

Lowering the Operating Temperature of Gold Acetylene Hydrochlorination Catalysts Using Oxidized Carbon Supports

The commercialization of gold for acetylene hydrochlorination represents a major scientific landmark. The development of second-generation gold catalysts continues with a focus on derivatives and drop-in replacements with higher activity and stability. Here, we show the influence that the support surface oxygen has on the activity of carbon supported gold catalysts. Variation in the surface oxygen content of carbon is achieved through careful modification of the Hummers chemical oxidation method prior to the deposition of gold. All oxidized carbon-based catalysts resulted in a marked increase in activity at 200 °C when compared to the standard nontreated carbon, with an optimum oxygen content of ca. 18 at % being observed. Increasing oxygen and relative concentration of C–O functionality yields catalysts with light-off temperatures 30–50 °C below the standard catalyst. This understanding opens a promising avenue to produce high activity acetylene hydrochlorination catalysts that can operate at lower temperatures.