Air Atmosphere Research Articles

Pyrolysis mechanism of silicone rubber thermal protection system materials in service environment

The excellent oxidation and ablation resistance of silicone rubber thermal protection system (TPS) materials have made them extensively utilized in large-area thermal protection applications, such as ramjet engines and spacecraft reentry capsules, where air is present in the service environment. The ablation resistance is significantly influenced by the pyrolysis reactions, which serves as the foundation for subsequent ceramic transformation and the development of anti-erosion structures. The majority of previous research has been conducted in inert gas environments. To investigate the pyrolysis mechanism of silicone rubber TPS materials in realistic service environments, thermal analysis tests were performed using a range of analytical instruments including a thermal analyzer, mass spectrometer, infrared spectrometer, and X-ray photoelectron spectrometer from room temperature up to 1300 K in air atmosphere and compared with the results in argon atmosphere. The results demonstrate that silicone rubber TPS materials undergo both pyrolysis and oxidation reactions in air atmosphere. The primary pyrolysis of the matrix is attributed to cyclization reactions and side-chain cross-linking reactions. In comparison to argon atmosphere, the oxidation reaction produces a greater amount of organic gases, thereby diminishing the extent of cross-linking reaction and the thermal stability of the pyrolysis residue. The prolonged exposure to elevated temperatures allows for an extended duration of oxidation reactions, consequently diminishing the long-term thermal stability of TPS materials. The increase in mass of TPS materials at temperatures exceeding 1100 K can be attributed, in part, to the formation of new organic groups through oxidation reactions. The observed morphology of the residue, along with the weight gain from oxidation and SiO2 formation, promotes ceramic transformation of the materials at elevated temperatures.

Selective N=S Coupling Reactions of N-Methoxy Arylamides and Sulfoxides Catalyzed by Iron Salt.

An iron-catalyzed selective N=S coupling of N-methoxy amides and sulfoxides has been developed and was found to be a highly efficient method for the synthesis of N-acyl sulfoximines. Electron-donating as well as electron-withdrawing groups on the phenyl ring are tolerated, and even sensitive substituents are compatible. The current catalytic transformation was conducted under an air atmosphere and can be easily scaled up to a gram scale with a catalyst loading of only 1 mol %. In this case, both coupling partners are used in their native forms, thus obviating prior functionalization and activation.

Effects of adding Si3N4 whiskers to ZrB2–SiC ceramics on microstructure, mechanical properties and oxidation resistance

ZrB2–SiC–Si3N4w ceramics (ZSNw) were prepared via the hot-pressing sintering method. The bending strength and fracture toughness of ZSNw at room temperature reached to 520 ± 24 MPa and 5.2 ± 0.16 MPa m1/2, respectively. The enhancement in mechanical properties is attributed to the grain refinement and attenuation of grain boundary induced by the homogeneous distribution of Si3N4 whiskers. The oxidation resistance of ZSNw were conducted at 1500 °C in an air atmosphere. Remarkably, after 10 h of oxidation, ZSNw remained excellent strength and toughness reaching at 589 ± 26 MPa and 4.8 ± 0.12 MPa m1/2, respectively. This oxidation resistance of ZSNw was mainly attributed to the gain refinement induced by Si3N4 whiskers, which effectively reduced the voids within the ceramic matrix. Therefore, this process promoted the densification and homogenization of the SiO2 protective barriers, accompanied with hindering the inward permeation of oxygen and the outward release of oxides.

Corrosion studies of Inconel 617 in high temperature air and He-ppmO2 atmospheres

Air ingress accident is one of the typical accident conditions in Very High Temperature Reactors (VHTRs). This work investigates the oxidation kinetics, corrosion behavior and mechanism of Inconel 617 alloy in different oxygen concentration atmospheres under air ingress accident. The impact of O2 concentration and oxidation time of the alloy corrosion is investigated. A gas chromatograph was used to measure the impurity content in real time during the helium experiments. After the experiments, the alloys were characterized by electronic balance, were analyzed by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), X-ray diffraction (XRD) and carbon and sulfur analyzer. The results show that: the Inconel 617 alloy undergoes similar oxidation behavior and the degree of oxidation is very close in three groups of atmospheres with large differences in oxygen content; the alloy should show two oxidation mechanisms, linear oxidation and parabolic oxidation, during the oxidation process; the parabolic rate constant kp and kt of the alloy is a constant value and does not vary with large changes in oxygen concentration, but when the experimental temperature changes, the oxidation rate constants of the alloy change, and the lowering of the temperature leads to the lowering of the oxidation rate constants; When experimental temperature is at 950 °C, the alloy continues to undergo a “microclimatic reaction” in the atmosphere of He-ppmO2, and the microclimatic reaction disappears when the experimental temperature is lowered to 750 °C; In He-ppmO2 environment, gas chromatograph can be used instead of thermogravimetric analyzer for real-time monitoring.

Accelerated High-Temperature Oxidation Behavior of Ferritic Stainless Steel under Air/H2+H2O Dual Atmosphere

Improvement in durability is one of the important subjects for utilizing solid oxide electrolyzer cell (SOEC) systems widely. In SOEC stacks, separators are exposed to complexed dual atmosphere (i.e. hydrogen - steam mixed gases and oxygen rich air are on each side). In this study, the degradation phenomena of separator materials (SUS430, ZMG232G10, Crofer22APU) in SOEC dual atmosphere were investigated. The samples were exposed in SOEC dual and simple atmospheres at 700 °C for 500 h. Then, their cross sections were analyzed by X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray analysis. The degradation mechanisms of the separator materials in the SOEC stack operating conditions were discussed. ZMG232G10 and Crofer22APU with high Cr content showed thin oxide layer under both the dual or single atmosphere, while SUS430 with low Cr content showed significant oxidation in the H2-steam atmosphere and on the air side under the dual atmosphere condition. The significant oxidation on the air side of the dual atmosphere of SUS430 observed in this study is a unique phenomenon under the dual atmosphere condition and not observed in a single air atmosphere.

Inkjet-Printed LSM-YSZ Thin Films for Enhanced Oxygen Electrodes in Solid Oxide Fuel Cells.

In the present work, symmetrical oxide ion conducting solid oxide single cells with inkjet-printed composite LSM-YSZ electrodes, onto commercially available YSZ dense substrates using GDC as buffer interlayer, were fabricated and characterized. Stable inkjet-printable LSM-YSZ nanoparticle inks were developed based on water solvent, after processing with high intensity ball milling. The deposition of LSM-YSZ electrodes was performed by inkjet printing, as well as a conventional additive manufacturing technique, screen printing, in order to compare the electrochemical performance of the produced cells for the reversible charge transfer reaction (O2 + 4 e- ↔ 2 O2-). The physicochemical properties of the LSM-YSZ nanoparticle ink was investigated to determine ink printability. The electrochemical performance of fabricated inkjet-printed and screen printed symmetrical cells (LSM-YSZ | GDC | YSZ | GDC | LSM-YSZ) exposed under a synthetic air atmosphere was evaluated in a single chamber cell reactor, employing the AC impedance spectroscopy and linear scan voltammetry techniques, at the temperature range of 700-850 °C. The inkjet-printed electrodes exhibited highly homogeneous and porous morphologies with the corresponding cell achieving current densities almost five times higher, up to 1 A/cm2 at 2 V cell potential and 850 °C, than those of the equivalent screen-printed one. To the best of our knowledge, this is the first successful implementation of water-based inks of LSM-YSZ electrodes in the fabrication of inkjet-printed solid oxide cells.

The Influence of Atmospheric Air Temperature on the Consumption of Natural Gas in Terms of Heating Costs of a Single-Family Building – A Case Study

The Influence of Atmospheric Air Temperature on the Consumption of Natural Gas in Terms of Heating Costs of a Single-Family Building – A Case Study

Assembling the 2D-3D-2D Heterostructure of Quasi-2D Perovskites for High-Performance Solar Cells.

Quasi-two-dimensional (quasi-2D) layered perovskites with mixed dimensions offer a promising avenue for stable and efficient solar cells. However, randomly distributed three-dimensional (3D) perovskites near the film surface limit the device performance of quasi-2D perovskites due to increased nonradiative recombination and ion migration. Herein, we construct a 2D (n = 4 top)-3D-2D (n = 2 bottom) heterostructure of quasi-2D perovskites by using 3-chlorobenzylamine iodine, which can effectively reduce defect density and restrain ion migration. A champion efficiency of 22.22% for quasi-2D perovskite solar cells is achieved due to remarkably reduced nonradiative voltage loss and increased electron extraction. Additionally, the 2D-3D-2D perovskite solar cells also exhibit excellent thermal and humidity stabilities, retaining over 90 and 85% of the initial efficiencies after 2000 h under a heat stress of 65 °C and at air ambient of ∼50% humidity, respectively. Our results provide a general approach to tune perovskite films for suppressing ion migration and achieving high-performance perovskite solar cells.

The effect of calcination gas atmosphere on the structural organization of Ru/Ce0.75Zr0.25O2 catalysts for CO2 methanation

In this study, supported 5 wt% Ru/Ce0.75Zr0.25O2 catalysts were prepared by sorption-hydrolytic deposition technique, followed by calcination under different conditions, namely in reductive H2/N2 (Ru/CeZr_red) and oxidative air (Ru/CeZr_ox) atmospheres. A thorough characterization of the catalysts was carried out by XRD, CO chemisorption, HRTEM, Raman spectroscopy, XPS, and in situ DRIFTS. The findings showed that the choice of the calcination atmosphere has a great impact on the structural organization of the catalyst. Calcination in air results in the formation of the larger crystalline RuO2 particles, which tend to enlarge upon reduction under CO2 methanation conditions. The reductive treatment results in a much higher dispersion of supported Ru species and a more pronounced metal-support interaction (MSI). In the Ru/CeZr_red catalyst, a large amount of atomic scale Ru species was detected along with metallic Ru nanoparticles and clusters. However, it was found that the superiority of the Ru/CeZr_red catalyst in the Ru dispersion did not result in the significant advantage in the CO2 methanation activity. In situ DRIFTS results suggested that the MSI affects the ability of Ru species to adsorb and activate reagent molecules, in particular, enhances the adsorption strength of the intermediate CO species.

Моделирование течения воздуха в упруго-деформируемой пористой среде, аппроксимирующей легкие человека: структура модели, ее основные уравнения и разрешающие соотношения

This paper is devoted to refining the mathematical model of the human respiratory system designed to predict the occurrence of respiratory pathologies caused by the negative effects of atmospheric air pollution. It is difficult to identify individual air channels in the human lungs, consisting of small respiratory tracts, called alveoli, through which oxygen from the air passes into blood. Therefore, the human lungs are modeled as a two-phase elastically deformable saturated porous medium, in which one phase is the deformable skeleton of the medium (lung tissue) described by the model of deformable solid body, and the other phase is gas filling the porous space. We construct the model of air flow in the human lungs, which consists of the sub-model of elastic deformation of the porous lung medium, experiencing large displacement gradients, and the sub-model of air filtration through the deformable porous medium. The model takes into account the relationships between sub-models of the respiratory system, i.e. we consider the coupled problems of deformation and filtration in differential form. Since at present the analytical solution of the stated essentially nonlinear problem is unfeasible, the problem is formulated in a generalized weak form to allow subsequent application of numerical methods using the Galerkin method. For the numerical solution of the nonlinear problem of deformation of the two-phase lung medium, it is suggested to use the finite element method, for the filtration problem - the finite volume method. The resolving relations needed to solve the formulated sub-problems are derived. To solve the nonlinear problem, we developed algorithms and a set of programs. The description of these computational tools, as well as analysis of the results obtained will be presented in our the next paper.

Photocatalyzed Selective Hydrocarbonation of Alkenes with Hantzsch Esters toward 4-Alkyl-Hantzsch Esters.

Here, we describe a mild photoredox-neutral reaction system that enables the selective hydrocarbonation of alkenes with Hantzsch esters, affording structurally diverse 4-alkyl-Hantzsch esters. This straightforward protocol can be performed under an air atmosphere without the need for any transition metals. The synthetic potential of this method is well exemplified by the late-stage structural modification of a series of pharmaceutically relevant complex molecules.

New experimental method for the simultaneous determination of concentration and size profiles of condensed combustion products around a burning aluminum droplet

When an aluminum particle burns in the diffusive regime, a cloud of nanometric particles of its primary oxide, alumina, is formed around the droplet. Characterizing this oxide smoke surrounding a burning aluminum droplet is essential. The original contribution of this paper is to introduce an experimental approach that allows for simultaneous size and concentration measurement of the particles composing the oxide smoke. This paper employs an electrodynamic levitator to facilitate the self-sustained combustion of an isolated aluminum particle, with a radius of 35μm, in atmospheric air. This levitation apparatus is paired with an optical setup that allows for a multi-spectral light extinction method. This technique is specifically designed to measure the size and concentration of alumina particles below the micrometric scale, which is scarcely documented in existing literature. Consequently, spatially resolved concentration and size profiles of the nanometric alumina particles are measured and compared to simulated data from the literature. The radii of alumina particles in the cloud are found to evolve closely around 80 nm. Volume fractions are evaluated from 2.8⋅10−4 near the particle surface to 3⋅10−5 further in the cloud. Therefore, significant concentrations of alumina particles are revealed during the short (15 to 20 ms) combustion process at distances of the order of magnitude of a few initial particle diameters. Such characterization could then lead to a better assessment of the interaction distance among aluminum particles as they burn collectively.Novelty and significance statementThis article introduces the first experimentally determined profiles of alumina concentration and size distribution surrounding a single burning aluminum droplet. The uniqueness of our experimental setup lies in its ability to study of the most fundamental case of the autonomous combustion of a single levitating particle, without any convective effects. A new non-intrusive method specifically designed provides unprecedented results in the field of metallic particle combustion. Data provided in the paper are crucial as they serve as the first reference case for future simulation and experiments. The results introduced in this paper highlight the inability of current simulation methods to accurately account for nucleation and condensation processes, and emphasize the need for a non-invasive characterization method.

Stability of Nitrogen-Doped Activated Carbon as an Electrocatalyst for the Oxygen Reduction Reaction in Various Storage Media.

Besides outstanding catalytic performance, the stability of nitrogen-doped carbon materials during storage is equally crucial for practical applications. Therefore, we conducted the first investigation into the stability of highly nitrogen-doped activated carbon (AC-NC-T) obtained by modifying activated carbon with CO2/NH3 in different storage media (air, vacuum and N2). The results of the catalysis of the oxygen reduction reaction and the activation of peroxymonosulfate for degrading bisphenol A by AC-NC-T show that the catalytic activity of AC-NC-T stored in air decays most prominently, while the performance attenuated only marginally when stored in vacuum and N2. The results from N2 adsorption isotherms, Raman spectroscopy, elemental and X-ray photoelectron spectroscopy indicate that the decline in catalytic activity is due to the presence of oxygen in the environment, causing a decrease in absolute contents of pyridinic N (N-6) and graphitic nitrogen (N-Q). After being stored in an air atmosphere for 28 days, the absolute contents of N-6 and N-Q in AC-NC-950 decreased by 19.3% and 12.1%, respectively. However, when stored in a vacuum or N2, the reduction in both was less than 7%. This study demonstrates that reducing oxygen concentration during storage is crucial for preserving high catalytic activity of nitrogen-containing carbon materials.

Adverse effects of sterilization processes on the fundamental topographic properties of modified dental implant surfaces

The employ of sterilization processes are essential to investigate biomaterials aiming for experimental, preclinical, or clinical applications with biological tissues. However, responsive surface properties of biomaterials may be susceptible to sterilization processes, compromising important physio-chemical characteristics. For that reason, this in vitro study aimed to investigate the effects of three different processes for sterilization (humid heat under pressure, UVC-light exposure, and Gamma irradiation) on the major topographical properties of implant surfaces applied to dental bone-anchored implants and/or implant-abutments. Three groups of implant surfaces were developed: a smooth machined surface, a micro-texturized surface, and a hydrophilic micro-texturized surface. The implants were sterilized with three methodologies and characterized regarding surface morphology, elemental surface composition, roughness parameters, wettability characteristics, and compared to the samples as-developed. Surface morphology and roughness parameters were not modified by any of the sterilization processes applied. On the other hand, hydrophilic implants were negatively affected by autoclaving. After package opening, hydrophilic features showed to be sensible to atmospheric air exposition independently of the sterilization process performed. Our findings revealed significant chemical changes on the implant surfaces caused by autoclaving and UVC exposure; additionally, the results showed the importance of selecting an appropriate sterilization method when investigating hydrophilic implants so as not to generate imprecise outcomes.Graphical

Effects of relative humidities on the superlubricity of GO/MoS2/H-DLC triple composite

The application of superlubricity will largely decrease the dissipation of energy. The MoS2/H-DLC composite can achieve superlubricity in active atmospheres. Unfortunately, in dry air atmosphere, the composite can establish superlow friction with an extremely short life, hindering the application of the MoS2/H-DLC composite with superlow friction in engineering. To establish superlubricity in dry and moist air, we adopted GO with O-containing groups to prepare a GO/MoS2/H-DLC composite to endow the triple composite with superlubricity in dry and moist air. The friction and wear performance of the triple composite were studied comprehensively in this work. The composition and structures of transfer films and wear tracks were also investigated here. This work would provide some helpful advice for application of H-DLC composite with superlubricity in air.

Enhancement of aluminum powder reaction behavior at high temperatures—Aluminum powders with “sea urchin structure” coated by AP

To solve the problem of high ignition temperature of aluminum powder and easy to burn into blocks at high temperatures, “sea-urchin-structured” aluminum powders (μAl@nAl) obtained by electro-explosion were coated by ammonium perchlorate (AP) on its surface. AP in a high-temperature environment has a rapid decomposition, then the gas production will promote the dispersion of aluminum powder into micro-clusters, thus preventing the aluminum powder agglomeration during the combustion process. The micro-nano composite aluminum powder (μAl@8 %nAl) and physical mixed aluminum powder (μAl + 8 %nAl) coated by AP were completed by solvent volatilization method. The coating surface was observed by scanning electron microscopy. The heat of combustion and pressure curves for different AP contents were tested using a chamber with a constant volume, and the ignition and combustion performance of the AP samples were investigated using a carbon dioxide (CO2) laser ignition device. The AP samples shortened the ignition delay time and improved the combustion performance in the fixed-volume combustion and laser ignition tests. Under atmospheric air, taking into account the theoretical calorific value, pressure curve, and combustion performance, the optimal AP content is 10 %. The thermal decomposition process of two samples was further analyzed using the thermogravimetric and differential scanning calorimetry (TG-DSC) method. The decomposition of AP advanced the first oxidation peak of aluminum powder; however, in the second step oxidation peak, the peak temperature of μAl@8 %nAl@10 %AP sample was delayed compared to μAl + 8 %nAl@10 %AP sample. High-voltage electrical explosions and high-energy laser-induced air shock waves were created to simulate the high-temperature environment of the detonation reaction zone, and pictures of the reaction process and pressure change curves of the “sea urchin structure” aluminum powder coated by AP at high temperatures were recorded. The results showed that the “sea urchin structure” aluminum powder coated by AP exhibited better combustion performance, and the reaction degree of the aluminum powder had been deepened.

Studies of the Morphology of Hematite Synthesized from Waste Iron Sulfate.

Microwave-based reactions have gained traction in recent years due to their ability to enhance reaction rates and yield while reducing energy consumption. Also, according to the conception of 'waste to materials', various waste feeds are intensively sought to be tested. The experimental setup of this study involved varying pH levels, oxidation agents, and precipitation agents to optimize the synthesis process of iron red based on waste iron sulfate. The selection of oxidation and precipitation agents was found to significantly influence the pigment synthesis process. Various oxidizing agents, including hydrogen peroxide and atmospheric air, were evaluated for their effectiveness in promoting the oxidation of ferrous ions to ferric ions, essential for pigment formation. Additionally, different precipitation agents such as sodium hydroxide and ammonia solution were assessed for their ability to precipitate iron hydroxides and facilitate pigment particle formation. The characterization of synthesized pigments revealed promising results in terms of quality and color properties. Helium Ion Microscopy (HIM) analysis confirmed the formation of well-defined pigment particles with controlled morphology. X-ray diffraction (XRD) studies provided insights into the crystalline structure of the pigments, indicating the presence of characteristic iron oxide phases. By improving this technology, waste iron sulfate can be efficiently transformed into valuable iron pigments, offering a sustainable solution for waste management while meeting the growing demand for high-quality pigments.

Single step grown porous polycrystalline nickel microstructures with ultra-thin defect rich surface oxide for alkaline water oxidation

Investigation on the intrinsic catalytic activity of structurally diverse polycrystalline nickel microstructures such as porous nickel sheets (PNS), porous folded/curled nickel structures (PFNS) and porous nickel balls (PNB) revealed the surface bounded electrocatalytic activities within an alkaline reaction environment for water oxidation. Nickel microstructures were grown via template/surfactant-free, single step solution combustion technique in air atmosphere. The distinct morphologies (porous nickel sheets, porous folded/curled nickel structures and porous nickel balls) were achieved through changing the quantity of HNO3 in the reaction mixture. The physicochemical characterisations were done with XRD, FESEM, EDS and XPS. Microscopic studies revealed the growth of nickel grains with numerous macro pores forming microstructures in distinct morphologies. The O ls spectra of XPS studies revealed the presence of O−/O2− sites and Ni 2p spectra were distinguished between the formation of Ni0/Ni2+/Ni3+ states, implied the existence of surface oxide with plenty of defects. The synergistic effect results from the formation of microscopic porous architectures with defect rich surface oxide on the electrochemical behaviour and OER activity of PNS, PFNS and PNB were discussed with electrochemical techniques such as CV, LSV, EIS and CP. The OER kinetics in terms of relatively low value of overpotential at 10 mA cm−2 and Tafel slope along with high specific activity of PNS/GCE with respect to PFNS/GCE and PNB/GCE were attributed to the combined effect of increase in electrochemical surface area, high roughness factor and fast charge transfer kinetics. The better electrochemical performance and OER activities of porous nickel sheets in comparison with folded/curled nickel structures and nickel balls is contributed to the unique 2D porous architecture with plenty of oxygen vacancies. This structure not only expose more surface for the formation of passive oxide layer in an alkaline reaction environment but also exhibit facile charge transport properties, causes the generation of numerous surface-active sites for electrocatalytic water oxidation. The outcome of our work gives new insights on the surface electrochemistry of polycrystalline nickel, enables micro-structuring as a prospective strategy towards the optimization of electrocatalysts as anode material for alkaline water oxidation.

Accounting for climate changes when constructing the Rossander graph

The temperature of the atmospheric air affects the design and indicators of energy efficiency of all elements of heat supply systems. An extremely important tool to develop heat sources that allows us to assess changes in consumer heat loads and model algorithms for heat source operation, taking into account the variability of outdoor air temperature in the geographical conditions of the design objects, is a graph of the duration of heat loads during the heating period (Rossander’s graph). It is impossible to construct the Rossander’s graph without data on the duration of the outdoor temperature standing during the heating period. In this paper, the problem of the lack of temperature data necessary for the construction of the Rossander’s graph in the current regulatory documents is revealed. The analysis of previous studies that produced temperature data with the duration of temperature standing is carried out, and the need for their refinement is substantiated. The arrays of hourly outdoor air temperatures were processed according to two weather models, as well as the array of average daily temperatures obtained as a result of measurements from the weather station for the geographical location of the main building of KNUCA. As a result of the comparative analysis, a model closer to reality was identified and, on its basis, actual data on the duration of outdoor temperatures standing for the city of Kyiv with a temperature step of 1℃ were developed. The obtained temperature data were compared with those that were developed in previous studies, as well as with the temperature data that are contained in the cancelled standard. The curve of the long-term run of the moving average outdoor air temperatures for the winter periods of 1973-2023 and its polynomial trend are constructed and compared with the curve that characterizes the run of the moving average five-year temperatures for the winter periods of 1861-1970 and its polynomial trend.

Copper‐Catalyzed Synthesis of Sulfinic Esters via Oxidative Coupling of Thiols or Disulfides with Alcohols

AbstractThe copper‐catalyzed coupling of thiols with alcohols was achieved under air atmosphere. The reaction proceeded smoothly in the presence of a base such as Cs2CO3 or Rb2CO3 affording sulfinic esters in good yields. Furthermore, disulfides were also available in the procedure. Both sulfide‐groups on disulfide were efficiently consumed.