Ambient Air Atmosphere Research Articles

Detonation Soot: A New Class of Ice Nucleating Particle

AbstractTemperatures and pressures from high explosive detonations far exceed atmospheric conditions in typical combustion reactions, and consequently, detonation soot forms with physiochemical properties distinct from soot formed by combustion. In this study, samples of detonation soot from two high explosives, PBX 9502 and Composition B‐3, were analyzed. Ice nucleation experiments on soot collected after controlled detonations were conducted in the laboratory to probe immersion and contact mode freezing. Samples nucleated ice at temperatures warmer than commercially available nanodiamonds, which has a mean nucleation temperature of −20.7°C. Ice nucleation rate coefficients increase rapidly by two to three orders of magnitude below −20°C for every sample. Size‐selected 137 μm diameter particles produced during detonation in an ambient air atmosphere yield bimodal distributions of freezing temperature with primary and secondary nucleation modes centered at −20°C and −13°C, respectively. The presence of a secondary mode allows for enhanced ice nucleation rate coefficients (one to two orders of magnitude greater than samples without a secondary mode) at temperatures outside the influence of the primary mode (>−17°C). Given the observed onset nucleation temperatures of −9.2°C, our results imply that detonation soot of the type studied here would only need to reach an altitude of approximately 4 km to facilitate ice formation.

Iterative synthesis of multi-grid topological nanostructures based on a stepwise friedel-crafts reaction

Covalent C–C bonded macrocycle topologies have been attracting increasing attention owing to their structural diversity and various applications. However, the methods for constructing such structures are limited, with most relying on transition metal-catalysis or requiring stringent reaction conditions, highlighting the urgent need to explore innovative synthetic approaches. Hence, we report a stepwise Friedel-Crafts gridization catalyzed by BF3·Et2O under ambient conditions and air atmosphere for the synthesis of the multi-grid topological nanostructures 2G-AG (30% yield) and 3G-AG (8% yield). Furthermore, the non-planar and structurally more complex multi-grid topologies, 2G-AG and 3G-AG, exhibit stronger excimer emission. This study provides a novel method for designing and synthesizing complex macrocyclic topological nanostructures connected by covalent bonds and with optoelectronic functionality.

Multi-step scheme and thermal effects of coal smouldering under various oxygen-limited conditions

Coal smouldering fires are global disasters and notoriously challenging to characterize. To better understand combustion and chemistry within these coal fires, TG-DSC experiments were carried out in two different coal samples in nitrogen and oxygen-limited (including ambient air) atmospheres. A mechanism with 8-step reactions simulating coal combustion was proposed, including one drying, two pyrolysis, two oxygen adsorption, and three high-temperature oxidations. The kinetic parameters were optimized via a Genetic Algorithm (GA). It was found that this 8-step mechanism created unnecessary overfitting to the TGA data. Therefore, two alternative schemes were developed with 5- and 4-step, which included and neglected oxygen adsorption, respectively. To compare the two schemes, GA and Gaussian multi-modal fitting were used to quantify the mass change rates in each step and their thermal effects as functions of oxygen concentrations. Moreover, the heat flow rates of coal samples were calculated and compared with measured DSC curves. The results indicated that oxygen adsorption could play a critical role in the transition from water evaporation to high-temperature combustion, and the 5-step scheme could reflect coal's intrinsic oxygen-limited combustion characteristics more accurately. Altogether, this study provides novel insight into coal smouldering under oxygen-limited conditions.

Decoding the oxidation mechanism of Zircaloy-4 via in situ synchrotron X-ray diffraction and computational elucidation

Comprehensive understanding of the oxidation behavior of Zr alloys, a vital cladding material in nuclear power plants, is essential for developing improved materials and enhancing the safety and performance of nuclear systems. Herein, the bulk oxidation behavior in ambient air atmosphere of Zircaloy-4 were revisited through in situ synchrotron X-ray diffraction and DFT computation. The results reveal the phase transition sequences at a representative 900 °C oxidation temperature: hcp Zr recrystallizes rapidly and then transforms into bcc Zr while reaching the α+β transus, followed by speedy appearance of textured tetragonal (t-)ZrO2, monoclinic (m-)ZrO2 and ZrN that consume oxygen and nitrogen. Continuous air ingress favors t-ZrO2 and m-ZrO2 dominance, accompanied by re-oxidation of ZrN into t-ZrO2 due to its low thermodynamic stability revealed by experiment-informed DFT calculation and low oxygen activity at the oxide-metal interface. Ensemble-averaged lattice volume expansions during phase transitions have been quantified. This expansion-induced compressive stress promotes the presence of a significant fraction of t-ZrO2 at elevated temperature that eventually transforms into m-ZrO2 during cooling.

Resistive switching memories with enhanced durability enabled by mixed-dimensional perfluoroarene perovskite heterostructures.

Hybrid halide perovskites are attractive candidates for resistive switching memories in neuromorphic computing applications due to their mixed ionic-electronic conductivity. Moreover, their exceptional optoelectronic characteristics make them effective as semiconductors in photovoltaics, opening perspectives for self-powered memory elements. These devices, however, remain unexploited, which is related to the variability in their switching characteristics, weak endurance, and retention, which limit their performance and practical use. To address this challenge, we applied low-dimensional perovskite capping layers onto 3D mixed halide perovskites using two perfluoroarene organic cations, namely (perfluorobenzyl)ammonium and (perfluoro-1,4-phenylene)dimethylammonium iodide, forming Ruddlesden-Popper and Dion-Jacobson 2D perovskite phases, respectively. The corresponding mixed-dimensional perovskite heterostructures were used to fabricate resistive switching memories based on perovskite solar cell architectures, showing that the devices based on perfluoroarene heterostructures exhibited enhanced performance and stability in inert and ambient air atmosphere. This opens perspectives for multidimensional perovskite materials in durable self-powered memory elements in the future.

Effects of Ambient Conditions on Helicopter Harmonic Noise Radiation: Theory and Experiment

The effects of ambient atmospheric conditions, air temperature, and density on rotor harmonic noise radiation are characterized using theoretical models and experimental measurements of helicopter noise collected at three different test sites at elevations ranging from sea level to 7000 ftabove sea level. Significant changes in the thickness, loading, and blade–vortex interaction noise levels and radiation directions are observed across the different test sites for an AS350 helicopter ying at the same indicated airspeed and gross weight. However, the radiated noise is shown to scale with ambient pressure when the flight condition of the helicopter is defined in nondimensional terms. Although the effective tip Mach number is identi ed as the primary governing parameter for thickness noise, the nondimensional weight coefficient also impacts lower harmonic loading noise levels, which contribute strongly to low-frequency harmonic noise radiation both in and out of the plane of the horizon. Strategies for maintaining the same nondimensional rotor operating condition under different ambient conditions are developed using an analytical model of single main rotor helicopter trim and confirmed using a CAMRAD II model of the AS350 helicopter. The ability of the Fundamental Rotorcraft Acoustics Modeling from Experiments (FRAME) technique to generalize noise measurements made under one set of ambient conditions to make accurate noise predictions under other ambient conditions is also validated.

Unveiling the temporal evolution of boron oxide exciplex species in laser-induced plasma: A detailed analysis of ro-vibrational spectra

The temporal evolution of boron oxide (BO) exciplex species in ambient air atmosphere was analyzed spectroscopically. The ro-vibrational bands (RVB) corresponding to BO:B2Σ+ → X2Σ+, BO:A2Πi → X2Σ+, and BO2: A2Πu → X 2Πg transitions were identified from experimentally recorded emission spectra of boric acid pellets. Temporal evolution and temporal intensity decay investigations were conducted on selected RVBs for each transition. The intensity decay rate of electronic transition was found to remain constant, regardless of the vibrational levels in the excited and ground electronic state. The type of the intensity decay profile and the decay rate contents were utilized to understand the extent of the spectral interference from BO: A2Πi - X2Σ+ transition by BO:B2Σ+- X2Σ+and BO2:A2Πu- X 2Πg transitions. By utilizing the Signal-to-envelope ratio, an optimum acquisition delay time was determined for the spectroscopic analysis of various transitions. This research study sheds light on the spectral interferences present in the optical emission spectra of RVBs and provides a comprehensive understanding of the spectral purity of these bands associated with BO exciplex species.

Effect of heat treatment on the thermal stability and properties evolution of TiAlPN thin film prepared by reactive HiPIMS

The influence of post-coating heat treatment on the thermal stability and evolving properties of TiAlPN thin film is investigated. Three different annealing temperatures of 350 °C, 550 °C, and 750 °C are used for 1 h in an ambient air and argon atmosphere to study the thermal stability, mechanical, structural, tribological and corrosion properties of the TiAlPN thin films prepared by High Impulse Magnetron Sputtering (HIPIMS). The X-ray diffraction analysis reveals the thermal decomposition and kinetic transformation of fcc-TiAlPN into mixed phases of fcc – TiN and fcc – AlN. Additional peaks of TiO2 and Al2O3 are identified in all the thin films. Broad bands assigned to acoustic, second-order acoustic and optical phonon range vibration modes were observed from the Raman spectroscopy of the as-deposited thin film. The Raman spectroscopy of annealed samples showed additional broad bands associated with the oxide layer. The increase of the annealing temperature from 350 °C to 550 °C enhances the mechanical properties of the TiAlPN thin films, resulting in a maximum hardness of 33.10 GPa, while enhanced adhesion strength is obtained for thin films annealed at 550 °C in an argon atmosphere. The optimal corrosion resistance with corrosion efficiency of 90.11 % and tribology properties are noticed after annealing in ambient air at an annealing temperature of 750 °C.

Preparation of Self-Coating Al2O3 Bonded SiAlON Porous Ceramics Using Aluminum Dross and Silicon Solid Waste under Ambient Air Atmosphere.

Al2O3-bonded SiAlON ceramic with self-coating was prepared using aluminum dross and silicon solid waste as starting materials under ambient air conditions. The changes in phase, microstructure, and physical properties of the ceramic with temperature were analyzed and the formation mechanism of the SiAlON phase was elucidated. The results showed that higher temperature was more suitable for the preparation of SiAlON ceramics. As the temperature increased from 1400 to 1600 °C, the main phases in the ceramic transformed from mullite, Al2O3, and SiAlON to Al2O3 and SiAlON. An Al2O3-rich layer spontaneously coated the surface of the porous ceramic as Al melted and oxidized at high temperature. The thickness of this layer decreased as the temperature increased. The presence of Al2O3-rich coating layer impeded air flow, allowing nitriding of Si and Al, and the formation of the SiAlON phase in ambient air conditions. This study not only presents a strategy to successfully recycle aluminum dross and silicon solid waste but also offers a straightforward approach to preparing SiAlON material in air atmosphere.

Effect of humid atmosphere on the microstructure and mechanical properties of a PM Ni-based superalloy: From powders to bulk alloys

Understanding the effects of powder storage condition is helpful to improve the mechanical properties of powder metallurgy (PM) and additive manufacturing (AM) superalloys. In this work, nickel-based FGH96 superalloy powders were stored under ambient air (relatively dry) and humid (25 °C/95%RH and 90 °C/95%RH) atmospheres and then consolidated by hot isostatic pressing (HIP). The powders and corresponding bulk alloys were characterized by XPS, OM, FESEM, EPMA, EBSD, and TEM. The results indicate that the humid atmosphere mainly affects the gas content, chemical state, and oxide/hydroxide layer thickness of powders, leading to highest values of oxygen content (~450 ppm), hydrogen content (~25 ppm), and NiO/Ni(OH)2 thickness (~13.9 nm) for 90 °C/95%RH powders, and further forms much severe prior particle boundaries (PPBs) defects in HIPed alloy. The detrimental PPBs are composed of large-sized γ', MC carbides-(Ti, Nb)C, Al2O3 and ZrO2 oxides. In comparison with ambient air powders compact, the strength of 90 °C/95%RH powders compact is unexpectedly increased, which is due to the internal grains pinned inside the original particle boundaries by higher severity degree of PPBs, and leads to the increase of grain boundary strength. Meanwhile, the ductility is significantly decreased, because the fracture mode transited from ductile transgranular fracture to brittle inter-particle debonding. The study reveals the relationship between humid atmosphere and properties of both powders and bulk alloys, and intends to obtain good combination of strength and ductility for PM Ni-based superalloys.

Achievement of high electrochromic performance of TiO2 thin films prepared via spray pyrolysis method, influence of annealing process

In this study, an optimised TiO2 thin film was first prepared by the traditional spray pyrolysis method on SnO2:F (FTO) coated glass substrates, and then it was annealed at 450 °C in an ambient air atmosphere for different time durations of 1, 2, and 3 h. The FESEM images, XRD diffractograms, Raman and PL spectra indicate that compared to the pristine state, the annealing process has considerably affected the morphology and improved the crystallinity and stoichiometry of the layer. The electrochromic (EC) measurements revealed that the 3h annealed sample has the highest ever reported colouration efficiency of 91.54 cm2.C−1 (approximately 30 times bigger than the related reports) and low colouration and bleaching times of 0.2 and 1.1 s, respectively.

A fast, efficient, inexpensive and green way to outdoor photopolymerization

A series of environmentally friendly photoinitiating systems operating under mild conditions of visible light (Vis-PIs) were tested for vinyl polymerization using sunlight as a free of charge radiation source. These Vis-PIs based on water soluble xanthene dyes showed good performances after deaerating with an inert gas, obtaining colorless polymers with gravimetric yields up to 80–90% after short irradiation times (2–15 min). Aqueous solutions of the materials were highly viscous and viscosimetric measurements yielded molecular weights up to 106. Surprisingly, the evaluated Vis-PIs also worked successfully under ambient air atmosphere, obtaining similar polymer yields in the same irradiation times. Photolysis experiments and transient spectroscopy were used to shed light on the mechanism of the process, allowing both triplets and radicals formation of the dyes to be identified even in the presence of air. The kinetics of photopolymerization was studied following the monomer conversion at several irradiation times by FTIR. The results were interpreted based on kinetic data collected as competitive quenching mechanisms between the co-initiator and oxygen for the excited dyes. The present report represents a breakthrough in the search for fast, efficient and inexpensive Vis-PIs with low ecological impact, which can be very useful in outdoor coating applications among others.

Oxygen-permeable and moisture-proof membrane for stable Li-O2/air batteries in humid working environment

The deleterious shuttle of H2O in humid atmosphere causes fatal/irreversible Li-metal anode corrosion and continuous destruction of solid electrolyte interface (SEI) at the Li/electrolyte interface as well as cathode discharge product varies in Lithium-Oxygen/Air batteries (LOBs/LABs), which critically limits their electrochemical performance of LOBs/LABs. Herein, we employ a scalable/flexible polyetetrafluoroethylene@polystylene (PTFE@PS) membrane with excellent oxygen-permeability and moisture-proofing capability to effectively shield Li anode and entire battery systems from H2O corrosion. The stable dual phobicity of PTFE@PS membrane is evidenced by contact angle and penetration experiments, and its ability to block H2O crossover is demonstrated via spectroscopy characterizations of the SEI layer in cycled Li-metal surface. The success of the PTFE@PS membrane has been illustrated by the significantly enhanced cyclability of the Li-metal anodes, depth of full-discharge and cyclability of the LOBs/LABs operated in a humid O2 and practical ambient air atmosphere (RH: 70%). Cycled at limited capacity of 500 mAh/g, the cycle performance of LOBs assembled with PTFE@PS membranes is five times that of that without PTFE@PS membranes. This work reveals how the crossover of H2O damages the Li-metal anode (SEI structure/components) and entire LOBs/LABs, and offers a practically effective approach to improve battery operation stability in humid atmosphere.

Direct C−H Arylation of Quinoxalin‐2(H)‐ones with Arylhydrazine hydrochlorides

AbstractA convenient and base promoted methodology for the synthesis of 3‐arylquinoxalin‐2(1H)‐ones through direct C−H arylation of quinoxalin‐2(H)‐ones with arylhydrazine hydrochlorides was developed. Preliminary studies suggest that the reaction undergoes an aryl radical participation process generated via oxidative denitrogenation of arylhydrazine under ambient air atmosphere.

Effects of heavy-ion irradiation on the structure and anti-wear properties of polycrystalline diamond compacts for nuclear applications

The structural transitions and resultant changes in the tribological properties of HT/HP-sintered polycrystalline diamond compacts (PDCs) irradiated by 3.25 MeV Xe15+ ions with ion fluence of 4.3 × 1014−4.3 × 1015 ions/cm2 have been examined using various characterization techniques. A significant destruction of sp3 bonds was observed when the damage increased to 0.5 dpa. Thereafter, with a further increase in the irradiation damage, the samples stepped into a quasi-saturation amorphous state at a threshold value of damage, critically depending on the size of diamond grains. Thereafter, no other difference could be found between the samples composed of diamond grains in different sizes, especially in terms of the chemical structure and lubrication performance in an ambient air atmosphere. Thanks to the irradiation-induced transitions of the morphology and chemical structures, the anti-wear property of the PDCs degraded significantly in a damage range of 0–3.5 dpa, and then kept stable in a quasi-saturation state. But overall, owing to the formation of lubricious tribofilms with a rich presence of multilayer graphene on sliding interfaces, the wear rates of all the quasi-saturation samples were below the value of 3.0 × 10−7 mm3/N‧m, which suggests that the PDCs can be applied as one of the potential materials for solid lubrication in nuclear applications.

Metal-free photocatalysis at charged aqueous interfaces: boosting the photocatalytic oxidative coupling of arylamines to azoaromatics under ambient conditions

We have developed a sustainable metal-free photocatalytic oxidative coupling approach for the conversion of arylamines to azoaromatics at the charged aqueous interfaces of micelles under ambient air atmosphere in aqueous media.

Bifunctional role of PDMS membrane in designing humidity-tolerant H2S chemiresistors with high selectivity.

A thermally evaporated hydrophobic PDMS membrane could significantly mitigate humidity interference/poisoning (without a decline in response at 50% RH for nearly 3 months) and enhance the selectivity of a CuCrO2 chemiresistor toward erosive H2S, offering an avenue for the practical applications of (H2S) chemiresistors in an ambient humid air atmosphere.

Disentangling X‐Ray and Sunlight Irradiation Effects Under a Controllable Atmosphere in Metal Halide Perovskites

Metal halide perovskites are versatile materials for photovoltaic and optoelectronic applications owing to their adjustable bandgap and emission properties. Nevertheless, a drawback is their photo‐structural–chemical instability. Herein, structural and optical responses of metal halide perovskite films, exploiting in situ X‐ray and visible light stimuli under dry and humid atmospheres, are correlated. It shows that the interplay of the physical parameters responsible for sample evolution depends in a nontrivial way on the nature of the excitation, radiation power density, and moisture conditions. Two perovskite samples demonstrate the relevance of each composition. They are resilient under a dry atmosphere, but the presence of water or oxygen molecules in the ambient air leads to structural and optical changes under irradiation. However, the sample reaction depends on the photons’ excitation energy and power density to be effective. Under a dry atmosphere, the halide segregation involving Br and I atoms does not occur for the low‐power density of X‐ray and sunlight excitations. On the contrary, under the ambient air atmosphere, compound stability depends on sample composition, which relates to defects and traps, and the excitation source. Herein, the probe's relevance to perovskites’ photoinduced structural and optical responses is highlighted.

Sensitive and selective ozone sensor based on CuCo2O4 synthesized by a facile solution combustion method

In this study, p-type spinel CuCo2O4 nanomaterials with abundant oxygen vacancies were synthesized by a facile one-step solution combustion method, and their sensing characteristics have been investigated. The p-type CuCo2O4 sensor shows a high response of 11 to 1 ppm O3 and low responses (< 2) to various interference gases (100 ppm NH3, NO2, SO2, and 500 ppm ethanol, methanol and acetone) at 90 °C in dry air, indicating a superior selectivity. The sensor also possesses a wide O3 detection range from 10 to 3000 ppb and good repeatability. More importantly, the relative humidity (RH) could promote the electrical response to O3, and the response to 1 ppm O3 only deviates from 24 to 27 as the RH increases from 50% to 90%, benefitting for practical applications in ambient humid air atmospheres. The humidity enhanced response for p-type CuCo2O4 could be ascribed to the competition of hole carrier reduction, O2− active sites reduction and O3 decomposition promotion induced by the hydroxyl groups.

Visible-Light-Induced Recyclable g-C3N4 Catalyzed C–H Hydroxylation of Quinoxalin-2(1H)-ones

AbstractA visible-light-promoted hydroxylation of quinoxalin-2(1H)-ones using recyclable graphitic carbon nitride (g-C3N4) as a heterogeneous photocatalyst has been developed. This protocol enables the selective synthesis of various hydroxyl-containing quinoxalin-2(1H)-ones in good to excellent yields under an ambient air atmosphere. Importantly, this heterogeneous catalyst can be used at least six times without significant loss of activity.