Increasing Oxygen Content Research Articles

Oxygen concentration modulates colibactin production

ABSTRACT Up to 25% of the E. coli strains isolated from the feces of healthy humans harbor the pks genomic island encoding the synthesis of colibactin, a genotoxic metabolite. Evidence is accumulating for an etiologic role of colibactin in colorectal cancer. Little is known about the conditions of expression of colibactin in the gut. The intestine is characterized by a unique oxygenation profile, with a steep gradient between the physiological hypoxic epithelial surface and the anaerobic lumen, which favors the dominance of obligate anaerobes. Here, we report that colibactin production is maximal under anoxic conditions and decreases with increased oxygen concentration. We show that the aerobic respiration control (ArcA) positively regulates colibactin production and genotoxicity of pks+ E. coli in response to oxygen availability. Thus, colibactin synthesis is inhibited by oxygen, indicating that the pks biosynthetic pathway is adapted to the anoxic intestinal lumen and to the hypoxic infected or tumor tissue.

Effects of oxygen contents on the physical properties of MgO films and carrier transport of Au/MgO/ZnO MIS diodes

MgO films with various oxygen contents were deposited on ZnO using radio-frequency magnetron sputtering, and Au/MgO/ZnO metal-insulator-semiconductor (MIS) diodes were fabricated. The effects of various oxygen contents on the physical properties of MgO and the carrier transport in MIS diodes were studied. The crystallinity of MgO films improved with increased oxygen content up to 66%; however, the crystallinity degraded upon further increase of oxygen content up to 100%. X-ray photoelectron spectroscopy showed that the oxygen vacancies were compensated by the introduced oxygen atoms; however, the excess oxygen atoms could not fill the lattice sites and were instead absorbed on the MgO surface. The optical bandgaps of MgO films increased from 5.16 to 5.22 eV for 0 and 100% oxygen content, respectively, resulted by the suppressed oxygen vacancies. The average roughness of MgO films increased from 4.02 to 6.86 nm for 0 and 100% oxygen content, respectively. As compared to MIS diodes without oxygen content, the leakage current was reduced by approximately 300 times in MIS diodes with 66% oxygen content. At a high bias voltage (V ≥ 0.4V), MIS diodes without oxygen exhibited ohmic conduction. In contrast, MIS diodes with oxygen exhibited Fowler-Nordheim tunnelling at high bias voltages. With increasing oxygen content, the tunnelling barrier height increased to its maximum of 0.46 eV in MIS diodes with 66% oxygen content. Nevertheless, the barrier height reduced to 0.29 eV for the excess oxygen content up to 100%. However, at low-bias voltages, all MIS diodes demonstrated a direct tunnelling mechanism owing to their rectangular barriers.

Effects of Local Mixing Ratios and Mass Flow Rates on Combustion Performance of the Fuel-Rich LOX (Liquid Oxygen)/kerosene Gas Generator in the ATR (Air Turbo Rocket) Engine

This paper presents a numerical simulation analysis of the flow and combustion characteristics of a fuel-rich LOX (liquid oxygen)/kerosene gas generator in an ATR (air turbo rocket) engine, examining the effects of local parameters on the combustion flow field and performance. The analysis considers variations in unit injector mixing ratios and unit mass flow rates. The results indicate that as the mixing ratio in the inner-ring injectors increases (while the mixing ratio in the middle-ring injectors decreases), the oxygen concentration area near the axis zone and the 50% radius zone of the gas generator expands. Conversely, the kerosene concentration area near the axis zone decreases while gradually increasing near the 50% radius zone. In the flow direction section, there is an inverse relationship between the variation trend of local temperature and the oxygen concentration in the local area. As the oxygen concentration increases, the temperature decreases. The temperature distribution across the cross-section of the gas generator exhibits a circular pattern. When the mixing ratio (or mass flow rates) of the unit injector are perfectly balanced, the temperature distribution becomes highly uniform. A larger disparity in flow rate between the inner ring injector and the middle ring injector leads to a lower combustion efficiency. This effect differs from the effect of the mixing ratio difference between the two injector rings. Increasing the mixing ratio in the inner-ring injectors (or decreasing the mixing ratio in the middle-ring injectors) initially leads to a rise in combustion efficiency, followed by a subsequent decline. The maximum combustion efficiency of 89.10% is achieved when the mixing ratio is set to Km-1 = 0.7 and Km-2 = 2.79, respectively. Increasing the flow rate in the inner-ring injectors (or decreasing the flow rate in the middle-ring injectors) initially leads to an improvement in combustion efficiency, followed by a subsequent reduction. The maximum combustion efficiency of 86.13% is achieved when the mass flow rate is set to m-1 = m-2 = 0.1 kg/s.

Experimental study on soot formation and primary particle size in oxy-combustion ethylene diffusion flames under CO2 substitution for N2

This paper reports an experimental study on the effects of O2 concentration and CO2 concentration on soot volume fraction and primary particle size of flame centre in ethylene laminar co-diffusion flame. The incandescent light was induced by a two-color band method and laser-excited by wavelength 1064 nm. Previous studies have shown that the oxygen concentration affects the soot volume fraction in the flame. However, the effects of O2 concentration on the primary particle size under CO2 atmosphere are unclear and need to be further discussed. Seven flames were optically detected, in which the oxygen concentration of the accompanying gas varied from 21% to 50% by volume. One primary flame was burned in co-flowing ethylene/air. Six ethylene flames were burned in an oxygen-rich O2/N2 or O2/CO2 atmosphere with an oxygen mole fraction from 30% to 50%. The C2H4 flow rate remained constant in all operating conditions. The results show that the SVF observed by the LII method and spectroscopy in the oxygen-enriched flame are in good agreement. Furthermore, the soot's primary particle diameter measured by the time-resolved LII method is in good agreement with the transmission electron microscope image analysis.With the increase of oxygen concentration, the flame height becomes shorter, the luminosity becomes brighter, and the soot yield increases. Compared with an N2 atmosphere with the same oxygen concentration, the soot yield in a CO2 atmosphere was significantly inhibited. In all the flames studied, the SVF along the flame axis showed a similar distribution: it first increased to the maximum value and then decreased rapidly until the flame tip. The maximum SVF on the axis appears between 0.64 and 0.78 based on the normalized height of the visible flame. In all ethylene/(O2/N2) flames, the maximum primary particle diameter and average primary particle diameter increase with oxygen content. For ethylene/(O2/CO2) flame, the maximum diameter of primary particles decreases with the increased oxygen content. The uncertainty of primary diameter is mainly caused by the thermal adaptation coefficient, the lower LII signal of smaller particles and the uncertainty of local flame temperature.

Pterostilbene mediates glial and immune responses to alleviate chronic intermittent hypoxia-induced oxidative stress in nerve cells.

Chronic intermittent hypoxia (CIH) induces oxidative stress in the brain, causing sleep disorders. Herein, we investigated the role of pterostilbene (Pte) in CIH-mediated oxidative stress in the brain tissue. A CIH mouse model was constructed by alternately reducing and increasing oxygen concentration in a sealed box containing the mouse; brain tissue and serum were then collected after intragastric administration of Pte. Neurological function was evaluated through field experiments. The trajectory of the CIH mice to the central region initially decreased and then increased after Pte intervention. Pte increased the number of neuronal Nissl bodies in the hippocampus of CIH mice, upregulated the protein levels of Bcl-2, occludin, and ZO-1 as well as the mRNA and protein levels of cAMP-response element binding protein (CREB) and p-BDNF, and reduced the number of neuronal apoptotic cells, Bax protein levels, IBA-1, and GFAP levels. Simultaneously, Pte reversed the decreased levels of superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), and BDNF and increased levels of malondialdehyde (MDA) in the serum of CIH mice. Pte increased Th2 cells, Treg cells, IL-4, IL-10, and TGF-β1 levels and decreased Th1 cells, Th17 cells, IFN-γ, IL-6, and IL- 17A levels in activated BV2 cells and hippocampus in CIH mice. The protein levels of p-ERK1/2, TLR4, p-p38, p-p65, and Bax, apoptosis rate, MDA concentration, Bcl-2 protein level, cell viability, and SOD and GSH-PX concentrations decreased after the activation of BV2 cells. Pte inhibited gliocytes from activating T-cell immune imbalance through p-ERK signaling to alleviate oxidative stress injury in nerve cells.

Combustion behavior of single iron particles, Part II: A theoretical analysis based on a zero-dimensional model

Following the ignition and solid-to-liquid phase transition of a fine (on the order of 10–100µm in diameter) iron particle, the self-sustained combustion of a liquid-phase droplet of iron and its oxides takes place. The objective of the current work is to develop an interpretive and explanatory model for the liquid-phase combustion of a single fine iron particle. A zero-dimensional physicochemical model is developed assuming fast internal processes, such that the combustion rate is limited by the rate of external oxygen (O2) transport. The model considers a particle covered by a shell of liquid-phase FeO enclosing a core of liquid-phase Fe. Stefan flow and diffusion are considered for the gas-transport of O2, while the gas-transport of gas-phase Fe and FeO are calculated via diffusion only. The outward gas-phase Fe and FeO consume inward-transported O2 to stoichiometrically form hematite (Fe2O3), and the remaining oxygen that reaches the particle surface is entirely consumed to form liquid-phase FeO. The time history of simulated particle temperature shows consistent overprediction of the peak particle temperature when compared to experimental temperature measurements, indicating that the assumption of fast internal kinetics may be incorrect. The model is also unable to capture the apparent slow cooling rate observed in experiments. A further analysis is performed through a heuristic model with a calibrated reaction-rate law, where the internal diffusion of reactive Fe and O ions may become rate-limiting. The calibration of the pre-exponential factor in the Arrhenius term to match the experimental peak temperature yielded good agreement of time to peak temperature, as well as the slow cooling rate. The heuristic model considering internal diffusion predicts a plateau in peak temperature with increasing oxygen concentration. Possible uncertainties of the models, as well as future work, are discussed.

The Combustion of Forest Humus Blended with Low-Rank Coal: Effects of Oxygen Ratio and Blending Ratio

In this study, the combustion characteristics of pine needles, pine needle humus, and the co-combustion of these two types of biomass with coal were compared. In addition, the optimization of the combustion performance of coal/humus was assisted through the following studies: (i) the combustion performance of coal/pine needle humus was studied under four different oxygen concentrations (N2, 10%O2/90%N2, 20%O2/80%N2, and 40%O2/60%N2); (ii) the synergistic effect between the humus and coal during combustion was also investigated by adjusting the blending ratio and oxygen content; (iii) the mechanisms of the optimized combustion processes were expounded by kinetics and thermodynamics discussion. The results demonstrated that the combustion characteristics of the coal/humus blends were found to be higher than those of the coal/pine needle blends. The coupling interactions of the oxygen content and blending ratio contributed to the significant synergistic effect between the two fuels, and the synergistic effect showed a nonlinear variation with an increased oxygen concentration. The synergistic effect in a rich oxygen environment (O240%/N260%) is 5.1 times greater than that in the synthetic air (O220%/N280%) and 13.8 times greater than that in the oxygen-poor environment (O210%/N290%). Hence, the blending ratio could be adjusted to maintain the intensity of the synergistic effect in an oxygen-rich atmosphere.

Acute Toxicity of Chlorpyrifos on the Freshwater Bivalves (Unio Tigridis) and Effects on Bioindicators

A freshwater bivalve plays a crucial function in aquatic habitats as the filtered water and burrowing mussels mix the sediment, thus increasing oxygen content and making the ecosystem healthier. The aim of the study is to see how chlorpyrifos affects biochemical markers in freshwater mussel Unio tigridis. About 180 individuals per taxon and water samples were collected from the Qandil water resource on the Greater Zab River, Erbil Province, Iraq. Once arrived at the lab, the individuals were kept in aquaria with river water and an air-conditioned room Temperature: 25±2 and Light: 12h/12h and acclimatized to laboratory conditions for seven days in aged tap water. The mussel's identification molecularly and the DNA sequence of the mussel includes U. tigridis supplied gene bank accession number ON872361, ON872362, ON872363, and ON872364 nucleotide sequencing. The 96-h toxicity of chlorpyrifos pesticide in the freshwater mussel U. tigridis was investigated using various nominal concentrations, including 50, 100, 200, 300 and 400 ppm. The water quality of the river and aquaria was tested for physicochemical parameters including water temperature, the potential of hydrogen ion pH, electrical conductivity EC, and total dissolved solids TDS, dissolved oxygen, total alkalinity, total hardness, calcium ion, magnesium ion. Water quality results of aquaria revealed that most tested variables were favorable for the breeding of mussels. The mortality of the mussels was observed daily and the 96 h LC50 value for mussels was 157.99 ppm. Within the tissue of the gills, Acetylcholinesterase (AChE), Glutathione S-transferase (GST), Catalase (CAT), and Malondialdehyde (MDA) were determined. The chlorpyrifos exposures caused significant increases in GST, CAT, and MDA. The elevation of oxidative stress biomarkers was inversely related to the AChE inhibition in the examined species. In conclusion water pollution by chlorpyrifos lead to unsafe condition for aquatic taxa.

Opto-electrical properties of amorphous silicon carbide thin films adjustably prepared by magnetron sputtering at room temperature

The application of silicon carbide (SiC) thin films is extensive, and they can be prepared at room temperature using magnetron sputtering. In this study, a wide range of deposition pressures (0.5–5.5 Pa) was utilized for the sputtering of amorphous SiC thin films. With an increase in deposition pressure, not only does the oxygen content increase, but also the carbon phase changes. The oxygen ratio increases from approximately 6.8% to 20.0% as the deposition pressure rises from 0.5 Pa to 1.5 Pa, and it gradually increases further to around 25.0% as the deposition pressure rises to 5.5 Pa. When the deposition pressure is>3.0 Pa, the amorphous carbon phase transforms into diamond-like and graphite-like carbons. As a result, the optical bandgap varies from about 1.7 eV to 3.6 eV with the change in deposition pressure, while the conductivity reduces from 2.5 × 10-4 S/cm to 1.3 × 10-8 S/cm. This study provides insights into the significant impact of high deposition pressure on the material properties of sputtered SiC thin films. It demonstrates that the chemical bonding, composition, and opto-electrical properties of SiC thin films can be effectively tailored for application in optoelectronic devices.

TGA Study of the Reaction Kinetics of a CuFeMnAlO4+δ Oxygen Carrier for Methane Chemical Looping Combustion under High Pressure and Atmospheric Pressure Conditions

Reduction and oxidation kinetics of a CuFeMnAlO4+δ oxygen carrier for methane were studied using an atmospheric thermogravimetric analyzer (TGA) and a pressurized TGA. Important parameters such as temperature (500–900 °C), particle size distribution (150–650 μm), and partial pressures of reactants (methane and oxygen) were evaluated. Results showed that the reduction of the oxygen carrier was not affected by particle size distribution studied in this work, and that above 750 °C, the effect of the temperature on oxygen carrier reduction started to diminish. The reaction time approaches an asymptotic limit as methane partial pressure increases. For oxygen carrier oxidation, it was found that the rate of oxidation increased with increasing oxygen concentration. The effect of the oxygen concentration was more noticeable when the oxygen concentration was below 7.5%. Because of the inherent feature of the oxygen carrier, its chemical looping with oxygen uncoupling property was also assessed. A phase boundary-controlled shrinking sphere model was used to model the test data from the TGAs. Modeling results showed that the oxygen carrier reduction had a reaction order of 1 with an activation energy of ∼46 kJ/mol. Oxygen carrier oxidation demonstrated a reaction order of 1.1 with an activation energy of ∼55 kJ/mol. Additionally, the differences of the experimental results between the atmospheric pressure TGA and the pressurized TGA were discussed in detail and the limitations of the pressurized TGA were highlighted.

Numerical Simulation of Palm Biodiesel Droplet Evaporation at Various Temperatures and Pressures

This study uses numerical simulations to determine the evaporation characteristics of palm biodiesel droplets under normal gravity at temperatures ranging from 473 to 873 K and pressures ranging from 0.2 to 5 bar. A transient, two-phase, axisymmetric volume of fluid (VOF) model is employed to model transport processes across phases. The palm methyl ester is modelled as a single-component fuel with temperature- and pressure-dependent thermophysical properties. The study compares the obtained evaporation rates with those available in the literature and presents the effects of external parameters in experimental setups. Additionally, the study investigates the effects of changing the oxygen/nitrogen composition of the environment at elevated temperatures. The results show that elevated temperatures enhance the evaporation rate at all pressures and oxygen contents due to significantly enhanced thermal conductivity and droplet surface temperatures, while elevated pressures decrease the evaporation rates. Across the pressure range, evaporation rates decrease by 219%, 213%, and 196% for temperatures of 473, 673, and 873 K, respectively. Furthermore, increasing oxygen concentration in the environment can also increase the evaporation rate; however, the effect is less noticeable with a 6.4% increase at 473 K and more significant with a 27.8% increase at 873 K across the selected oxygen composition range.

White-light luminescence from Tm3+-doped borosilicate glass-ceramics synthesized by the sol-gel route

White-light luminescent Tm3+-doped borosilicate glass-ceramics were synthesized by the sol-gel method. The materials are predominantly amorphous with some embedded nanocrystals of H3BO3 and B2O3 with sizes ranging from 4 to 10 nm, which decrease as the Tm2O3 content is increased. Moreover, the glass transition and crystallization temperatures enhance with the Tm2O3, showing higher thermal stability in the glass-ceramic with 0.50 mol%. Also, the addition of Tm2O3 promotes an increase in the non-bridging oxygen concentration, the occurrence of the boric anomaly, and the incorporation of a higher amount of C species (CC and CO bonds) into the reticular structure of the glass ceramic. Therefore, the optical bandgap reduces (3.62–3.47 eV) while the photoluminescence intensity increases, being maximum at 0.75 mol% of Tm2O3. Interestingly, the luminescent glass-ceramics show a white-emission color, CIE coordinates are (0.31–0.33, 0.33–0.34) instead of those corresponding to blue, which is what usually occurs in other Tm3+-doped materials. This characteristic photoluminescence emission is due to the 1D2→3F4 electronic transitions of Tm3+ ions and the π– π* and n–π* transitions of CC and CO bonds originated by the carbon remnants inside the glass-ceramics. The released white emission has a correlated color temperature of 5600–6650 K, a color rendering index of ∼88, and a quantum yield of 12.3%. These materials are promising candidates for their use as phosphors in solid-state white-light-emitting devices.

SEM study of the microelement composition of the apical region of the tooth after the treatment of destructive periodontitis

Relevance. Trace elements play an important role in the life of the cell. Using a scanning electron microscope (SEM), the microelement composition of dentin and cement of the apical region of teeth previously treated for destructive chronic periodontitis in the acute stage was studied.Aim. Using a scanning electron microscope to study the microelement composition of the apical area of hard tissues of the tooth root after the treatment of destructive periodontitis.Materials and methods. To determine the presence of certain trace elements in the composition of solid tissues, we used spectral analysis performed on a JSM-6490LV scanning electron microscope (JEOL, Japan) and an INCA Penta FETx3 energy-dispersive spectrometer (Oxford, England).Results. After endodontic treatment, the content and ratio of Ca and P in the hard tissues of the resorbed apex of the tooth root changes. The presence of newly formed highly mineralized cement was found. The ratio of microelements Ca/P and Na/Mg in the cement before and after the treatment of destructive periodontitis changes. Conclusions. An increased oxygen content may indicate the presence of active forms of this element in the cells. An increased content of Na in hard tissues testifies in favor of triggered regenerative processes. Perhaps the use of Cacontaining drugs helps cells form the structure of the tissue.Conclusions. After a certain period of time, after the treatment of destructive periodontitis, calcification of the hard tissues of the apical region of the tooth root occurs. The changing ratio of trace elements indicates the predominance of regenerative processes in the tissues of the tooth.

Evaluation of Selected Technological Parameters for Selective Laser Melting of AlSi10Mg Metal Powder

Reusing the powder across consecutive route cycles is typical in a Selective Laser Melting (SLM) process since it is more sustainable and cost-effective. The theoretical part of the paper is oriented on the explanation of the SLM method principle, construction, and parameters of the device Renishaw AM250 used for manufacturing samples made of AlSi10Mg aluminium alloy. The experimental part focuses on evaluating powders that had been used in the process for a long time with periodic ‘rejuvenation’. The main aim will be to monitor whether the samples will be affected and if they achieved the required quality of mechanical properties and compare results with virgin powder and manufacturer sheets for virgin powders. The experimental part further describes the procedures and analysis of the microstructure of the samples. AlSi10Mg aluminium alloy was chosen because of an assumption that it will be sensitive to increased oxygen content. A strong affinity for oxygen uptake exists in AlSi10Mg. Therefore, preventing the contamination, careful handling is required.

Response of microbial community to climate change in Liaohe Delta since the Last Glacial Maximum

Estuarine delta is a critical zone for a series of biogeochemical processes including greenhouse gas emissions, organic matter transport and burial. These processes are mainly mediated by microbial activities such as heterotroph, methanogenesis, and methanotroph. However, response of microbial activities in the delta to paleoenvironmental change is less constrained. In this study, we analyzed the concentrations and compositions of microbial ether lipids (branched GDGTs and isoprenoid GDGTs) in a core from the Liaohe Delta, the northeast China, to explore the response of bacteria and archaea communities to climate change since 32 ka BP. During the glacial periods, the concentrations of branched GDGTs and isoprenoid GDGTs were low possibly due to the low temperature inhibiting the growth of microorganisms. After the Last Glacial Maximum (LGM), the abundance of GDGT concentrations increased, and reached the maximum during the Bølling/Allerød (B/A) period, then decreased during the Younger Dryas (YD) and increased again during the early Holocene. This pattern indicated that the abundance of the microorganisms in the Liaohe Delta was mainly controlled by temperature since 32 ka BP. In addition to temperature, sea level fluctuation and local hydrological disturbance may also effect microbial growth in the Liaohe Delta. Significant increase in the ratio of GDGT-0 versus crenarchaeol (R0/5) indicates that the rise of lake level provided a favorable anaerobic environment for methanogen blooming during the B/A and the early Holocene. Low lake level and strong water mixing made oxygen content increase, thus inhibited methanogen growth and further led to the decrease of the R0/5 values in the YD, suggesting that methanogenesis in global estuaries may impact atmospheric methane content. Our results provide a means to interpret response of microbial abundance and biogeochemical processes to paleoclimate change since the Last Glacial Maximum in estuarine delta.

Stiffening of polydimethylsiloxane surface as result of exposure to low‐pressure argon discharge plasma

AbstractPolydimethylsiloxane (PDMS) surface has been exposed to negative glow discharge plasma of a low‐pressure discharge in pure argon for a duration varying from 10 s to 2 min. Shallow atomic force microscopy indentation experiments were performed to investigate the effect of plasma treatment on PDMS surface stiffness and adhesion energy to the silicon nitride indenter surface. The results showed an important increase in Young's modulus and a slight increase of work of adhesion. X‐ray photoelectron spectroscopy investigation of plasma‐treated PDMS surface showed a decrease of atomic content of carbon accompanied by an increase of oxygen content and suggests that the stiffening of PDMS surface can be attributed to generation of new cross‐linking Si–O–Si and Si–CH2–CH2–Si bonds between PDMS molecules.

High-Thermal-Conductivity AlN Ceramics Prepared from Octyltrichlorosilane-Modified AlN Powder

Aluminum nitride has been widely used as heat-management material for large-scale integrated circuits and semiconductor packages because of its excellent insulation, high thermal conductivity, low dielectric constant and loss, similar expansion coefficient to that of silicon, and non-toxicity. However, the increase of oxygen content caused by the hydration of aluminum nitride powder during storage often decreases the thermal conductivity of aluminum nitride ceramics. In this work, we propose an approach for preparing high-thermal-conductivity AlN ceramics via octyltrichlorosilane-modified AlN powder. The octyltrichlorosilane reacted with the hydroxyl group on the surface of the AlN powder forming a siloxane protective layer. The protective layer not only enhanced the water contact angle of AlN powder from 34.8° to 151°, but also ensured the phase of AlN powder did not change in the distilled water at 25 °C for 72 h. High-thermal-conductivity AlN ceramics up to 186 W·m−1·K−1 were successfully prepared based on the modified AlN powder which had been stored for one year. This work provides a simple, effective, and practical method for the stable preparation of high-thermal-conductivity AlN ceramics.

Super adiabatic flame temperature phenomenon for NH3/O2/N2 mixtures

The super adiabatic flame temperature (SAFT) phenomenon is important for understanding and controlling the flame stability, NO emission, reaction rate and other aspects of combustion. Therefore, a numerical study was conducted to study the SAFT phenomenon for NH3/O2/N2 mixtures under different initial conditions. It was found that the main characteristics of SAFT for NH3/O2/N2 mixture are the negative heat release in the post-flame zone and the overshoot of H2O. The chemical nature of SAFT was also analyzed and found that the reverse reaction of R4 (H2 + OH = H2O + H) in the post-flame zone, resulting in the overshoot of H2O concentration, is one of the reasons of SAFT. The study also found that H radical plays an important role in SAFT phenomenon, and the relative lack of H radical in the main reaction zone is another one of the important factors of SAFT phenomenon. In addition, the study found that the effects of initial temperatures, pressures and oxygen content on SAFT have opposite trends at different equivalence ratios. When the equivalence ratio is less than 1.6, the increase of initial temperatures and oxygen contents leads to the increase of SAFT; the increase of initial pressure leads to the decrease of SAFT. The opposite tendency occurs when the equivalence ratio exceeds 1.6. This is because the flame temperature and structure changes with the equivalence ratio increasing, and the chemical nature of SAFT changes accordingly.

Emission characteristics of benzene series in FCC flue gas

Benzene series are considered as air pollutants in refineries. However, the emissions of benzene series in fluid catalytic cracking (FCC) flue gas are poorly understand. In this work, we conduct stack tests on three typical FCC units. Benzene series, including benzene, toluene, xylene and ethyl benzene, are monitored in the flue gas. It shows that the coking degree of the spent catalysts affect the emissions of benzene series significantly, and there are four kinds of carbon-containing precursors in the spent catalyst. A fixed-bed reactor is used to conduct the regeneration simulation experiments, and the flue gas is monitored by TG-MS and FTIR. The emissions of toluene and ethyl benzene are mainly emitted in the early and middle stage of the reaction (250–650 °C), while the emission of benzene is mainly detected in the middle and late stage of the reaction (450–750 °C). Xylene group is not detected in the stack tests and regeneration experiments. Higher emissions of benzene series are released from the spent catalyst with lower C/H ratio during regeneration process. With the increase of oxygen content, the emissions of benzene series decrease, and the initial emission temperature is advanced. These insights can improve the refinery's awareness and control of benzene series in the future.

Surface hardening of TiZrNbHfTa high entropy alloy via oxidation

We investigate the oxidation of TiZrNbHfTa high entropy alloy between 550 °C and 650 °C as a surface hardening method. Coarse-grained specimens with grain boundaries perpendicular to the surface exhibit catastrophic oxidation, while ultrafine-grained, cold-rolled specimens show a continuous mass gain and the formation of an adherent, µm-sized, vitreous oxide layer. Underneath, TiZrNbHfTa decomposes into a bcc- and an hcp-phase, while selective internal oxidation of hafnium and zirconium occurs upon oxygen inward diffusion. Oxygen concentration- and microhardness-depth profiles confirm an increase in oxygen concentration and hardness at the surface, raising the initial hardness by four times to 1522 ± 64 HV0.5.