Dry Air Environment Research Articles

Bioinspired Underwater Adhesives.

Underwater adhesives are in high demand in both commercial and industrial sectors. Compared with adhesives used in dry (air) environments, adhesives used for wet or submerged surfaces in aqueous environments have specific challenges in development and performance. In this review, focus is on adhesives demonstrating macroscopic adhesion to wet/underwater substrates. The current strategies are first introduced for different types of underwater adhesives, and then an overview is provided of the development and performance of underwater adhesives based on different mechanisms and strategies. Finally, the possible research directions and prospects of underwater adhesives are discussed.

Novel Ultrabright and Air-Stable Photocathodes Discovered from Machine Learning and Density Functional Theory Driven Screening.

The high brightness, low emittance electron beams achieved in modern X-ray free-electron lasers (XFELs) have enabled powerful X-ray imaging tools, allowing molecular systems to be imaged at picosecond time scales and sub-nanometer length scales. One of the most promising directions for increasing the brightness of XFELs is through the development of novel photocathode materials. Whereas past efforts aimed at discovering photocathode materials have typically employed trial-and-error-based iterative approaches, this work represents the first data-driven screening for high brightness photocathode materials. Through screening over 74 000 semiconducting materials, a vast photocathode dataset is generated, resulting in statistically meaningful insights into the nature of high brightness photocathode materials. This screening results in a diverse list of photocathode materials that exhibit intrinsic emittances that are up to 4x lower than currently used photocathodes. In a second effort, multiobjective screening is employed to identify the family of M2 O (M = Na, K, Rb) that exhibits photoemission properties that are comparable to the current state-of-the-art photocathode materials, but with superior air stability. This family represents perhaps the first intrinsically bright, visible light photocathode materials that are resistant to reactions with oxygen, allowing for their transport and storage in dry air environments.

Variation characteristics of active groups and macroscopic gas products during low-temperature oxidation of coal under the action of inert gases N2 and CO2

This research is aimed at studying the different effects and mechanisms of CO2 and N2 on inhibiting coal spontaneous combustion (CSC) and providing theoretical guidance for the prevention and control of CSC in the goaf. The variations of free radicals and functional groups and the generation of indicator gas CO during low-temperature oxidation of coal under the conditions of dry air (DA), dry air-nitrogen mixture (DA + N2) and dry air-carbon dioxide mixture (DA + CO2) were investigated based on electron spin resonance spectrometer, Fourier transform infrared spectroscopy and gas chromatograph. The experimental results reveal that the reaction of free radicals and the transformation of functional groups occur in the low-temperature oxidation process. In the whole oxidation heating process (30–230 °C), the concentrations of free radicals (Ng) increase by 4.04 × 1017 spin/g, 2.24 × 1017 spin/g and 1.90 × 1017 spin/g under the conditions of DA, DA + N2 and DA + CO2, respectively. The variation ranges of peak areas of active functional groups (–C-O–, –CO, –CH2–, –CH3 and –OH) under the action of inert gases (CO2 and N2) are notably smaller than those in the DA environment. The time and amount of CO generation both exhibit an obvious “hysteresis effect”, indicating that the presence of N2 and CO2 inhibits coal oxidation and conduces to CSC prevention. A comparison between the values of inhibition effect parameters R (RCO, RNg, R-C-O- and R-CO) and P (P-CH2-, –CH3, P-OH) discloses that CO2 boasts a superior ability to inhibit CSC than N2. This study presents a comparison between N2 and CO2 in CSC prevention and control based on the variation characteristics of indicator gas and active groups. It provides an experimental and theoretical basis for developing and improving the technology of fire prevention and extinguishing by inert gases.

Evaluating steam oxidation kinetics of environmental barrier coatings

AbstractEnvironmental barrier coatings (EBCs) are a commercially proven means of protecting SiC‐based materials in gas turbine environments. However, there are little specific data in the literature on the impact of coatings like Yb2Si2O7 on preventing accelerated SiO2 growth in the presence of H2O. Quantification of reduced rates are necessary for evaluating and comparing EBC effectiveness and incorporation of silica growth rates into future EBC lifetime models. In this study, baseline kinetics of silica formation on bare Si and chemically vapor deposited (CVD) SiC in the 1250–1425℃ range were obtained via 100 h isothermal exposures in dry air and steam environments utilizing a SiC reaction tube to mitigate specimen volatility. An Arrhenius plot of the resulting rates was constructed, representing baseline minimum and maximum rates for Si and SiC oxidation at ambient pressure. Various EBC systems on CVD SiC substrates including air plasma sprayed (APS) EBCs with and without a Si bond coating and with surface roughening to enhance Yb2Si2O7 adhesion were subjected to 1‐h furnace cycle testing in air with 90vol%H2O at 1250–1350℃ for up to 500 cycles. After exposure, silica formation rates were measured and compared to the baseline rates to assess EBC effectiveness, where EBC effectiveness is gauged as the propensity to reduce underlying rates of silica formation. With a Si bond coating, a ~180 µm Yb2Si2O7 (YbDS) top coating reduced rates over the entire 1250°‐1350℃ range. Without a Si bond coating, ~60 µm (YbDS) coatings deposited directly onto CVD SiC exhibited poor adhesion, and had to be deposited onto substrates with enhanced roughness at 1350℃. While exhibiting good adhesion at 1350℃, overall the single layer YbDS coating exhibited a decreasing effectiveness from 1250° to 1350℃.

Environmentally-adaptive epoxy lubricating coating using self-assembled pMXene@polytetrafluoroethylene core-shell hybrid as novel additive

In this work, a novel lubricating additive was designed and synthesized via self-assembling of wrapped PTFE nanoparticles by exfoliated MXene nanosheets. Then the pMXene@polytetrafluoroethylene (pMXene@PTFE) hybrid was introduced into epoxy coating and painted to substrate. The composite with PTFE would effectively alleviate the oxidation of MXene sheets. The research results show that the epoxy-based composite coating has excellent friction-reduction and wear-resistance properties in dry air, humid air (RH = 80%), and vacuum (3 × 10−5 Mbar) environments, achieving multi-environmental stability binary composite coating. The performance improvement of composite coating mainly depends on the following points: (a) the lubricating synergistic effect of MXene sheets and PTFE hybrid additive with core-shell structure; (b) the good dispersibility and adhesion of composite additive in the epoxy matrix; (c) the formation of protective film on the upper counterpart. The obtained friction results demonstrate that self-assembled pMXene@PTFE epoxy coatings greatly enhance the lubricating and anti-wear properties in multiple environments, establishing a promising platform for the design and application of novel high-performance additive with environmental insensitivity.

Nickel-Decorated Black Phosphorus for Room Temperature NO2 Detection

Introduction In the rapidly emerging field of layered two-dimensional (2D) functional materials, bP, the all P-counterpart of graphene, is a potential candidate for various applications e.g., nanoscale optoelectronics, rechargeable ion batteries, electrocatalysts, thermoelectrics, solar cells, and sensors [1]. bP has been reported to exhibit superior chemical sensing performance. In particular, bP is selective for the detection of paramagnetic molecules, e.g., NO2, in addition to high sensitivity at a limit of detection (LOD) of ppb levels.[2] In this work, by applying a multiscale characterization approach we demonstrated a stability and functionality improvement of Nickel-decorated bP (Ni/bP) films for gas sensing prepared by a simple, reproducible and affordable deposition technique. Furthermore, we studied pos-sible electrical activity of these films for their employment as functional layers in gas sensors by exposing them to different gaseous compounds (NO2, CO2, H2, NH3, CO, Benzene, etha-nol, ethylene, Formaldehyde) in different relative humidity (RH%) conditions. Moreover, the influence in sensing perfor-mance of nickel nanoparticle (NP) dimensions in related to the decoration technique and the film thickness were investigated. Materials and Methods Black phosphorus microcrystals were suspended in dimethylsulfoxide and kept under ultrasonication for several hours. The exfoliated bP nanosheets were decorated with nickel nanoparticles following two different procedures: 1) preformed Ni NPs were immobilized on bP, 2) Ni NPs were grown directly on bP flakes. Electrical conductance measurements have been performed on Ni/bP flakes deposited via spin coating on Al2O3 substrates with built-in interdigitated gold electrodes, in order to better control the film thickness. Electrical conductance measurements have been performed at RT (25±2°C) by exposing the sensing film to certified mixtures of NO2 diluted in dry air (20% O2 and 80% N2) with different NO2 concentration ranging from 200 ppb to 1 ppm. Results and Conclusions Exfoliated black phosphorus nanoflakes decorated with nickel nanoparticles (Ni/bP) have been prepared and characterized with particular attention to the role of Ni nanoparticle dimension in the sensing mechanism. Electrical activity towards different concentrations of NO2 at room temperature in a dry air environment highlighted fast and stable response over the time. This latter characteristic is particularly relevant since environmental instability of exfoliated BP has been an issue so far, under ambient conditions few-layer bP degrades completely in less than a week, preventing its applications in several fields. In situ grown Ni/bP (2) shows stable response during all the four weeks measurements period with no dependence of the response on the film thickness. Ni decoration effectively suppress ambient degradation, for at least 1 week in Ni/bP (1) and over 4 weeks in Ni/bP (2) in ambient conditions. This result highlighted that Ni/bP (2) sensor can be practically used under ambient conditions for a reasonable period without performance degradation of the devices.The obtained results pave the way for the use of chemically exfoliated bP flakes for gas sensing applications, avoiding the use of a time-consuming technique for the exfoliation and for the fabrication of the metallic contacts, like electron beam lithography, focused ion beam lithography, etc.

High-Rate Long Cycle-Life Li-Air Battery Aided by Bifunctional InX3 (X = I and Br) Redox Mediators.

Redox mediators (RMs) are solution-based additives that have been extensively used to reduce the charge potential and increase the energy efficiency of Li-oxygen (Li-O2) batteries. However, in the presence of RMs, achieving a long cycle-life operation of Li-O2 batteries at a high current rate is still a major challenge. In this study, we discover a novel synergy among InX3 (X = I and Br) bifunctional RMs, molybdenum disulfide (MoS2) nanoflakes as the air electrode, dimethyl sulfoxide/ionic liquid hybrid electrolyte, and LiTFSI as a salt to achieve long cycle-life operations of Li-O2 batteries in a dry air environment at high charge-discharge rates. Our results indicate that batteries with InI3 operate up to 450 cycles with a current density of 0.5 A g-1 and 217 cycles with a current density of 1 A g-1 at a fixed capacity of 1 A h g-1. Batteries with InBr3 operate up to 600 cycles with a current density of 1 A g-1. These batteries can also operate at a higher charge rate of 2 A g-1 up to 200 cycles (for InBr3) and 160 cycles (for InI3). Our experimental and computational results reveal that while X3- is the source of the redox mediator, LiX at the MoS2 cathode, In3+ reacts on the lithium anode side to form a protective layer on the surface, thus acting as an effective bifunctional RM in a dry air environment. This evidence for a simultaneous improvement in the current rates and cycle life of a battery in a dry air atmosphere opens a new direction for research for advanced energy storage systems.

Oxidation of 3D‐printed SiC in air and steam environments

AbstractThe high‐temperature oxidation of additively manufactured and chemically vapor infiltrated (3D‐printed SiC) has been compared to chemical vapor deposited (CVD) SiC. 100‐h isothermal exposures were conducted at 1425° and 1300°C at 1 atm under both dry air and steam environments. A SiC reaction tube was utilized to reduce silica volatility. After steam oxidation at 1425° and 1300°C, on the 3D‐printed SiC surface, which was intrinsically rougher than the CVD surface, scales were 70%–90% thicker at the convex regions compared to concave/flat regions. In the convex regions, large cracks perpendicular to the oxidizing interface were observed. After dry air oxidation, scale thicknesses were comparable between 3D‐printed SiC and CVD SiC, regardless of geometry. Finite element modeling, conducted to elucidate the relationship between SiC geometry and ß‐ to α‐cristobalite transformation stress, determined cristobalite transformation tensile stresses to be on the order of 103 MPa during cool down, assuming a 6 vol% reduction. Compared to flat SiC substrates, tensile transformation stresses were elevated at concave regions and relaxed at convex regions. Combined with specimen mass gain (accounting for the rougher surface) of 3D‐printed SiC being 15%–32% higher for 3D‐printed SiC after 1300°C and 1425°C steam oxidation, the work presented concludes that the increased oxidation of 3D‐printed SiC is primarily caused by tensile hoop stresses driven by oxidation volume expansion. Lastly, the efficacy of the 3D‐printing method is demonstrated through the production of tristructural isotropic imbedded 3D‐printed SiC fuel forms.

Morphological and chemical characteristics of oxide scales formed on δ-Phase plutonium metal alloys I: 3.5 at% ga

Focused ion-beam scanning electron microscopy (FIB-SEM) and three-dimensional (3D) microscopy were applied to characterize the subsurface morphological features of oxide scales formed on an ~3.5 at.% Ga plutonium (Pu) metal alloy. Using the FIB-SEM technique, a number of morphological features formed in the interior of the oxide scale from Pu metal's environmental exposure were observed and identified. Auger electron spectroscopy (AES) was utilized to characterize the cross-sectional composition and chemistry of the oxide scale. The oxide scale formed during inert storage and operational environments has a characteristic internal scale structure that includes a relatively dense oxide layer with some lateral and transverse cracking. Generally, after subsequent exposure to dry air environment, the oxide scale retained most of the original structural and chemical characteristics. However, after aging in a moist air environment, while the oxide scale was found to maintain the chemical characteristics of the source oxide, the scale was found to be on average thinner and without the previously observed internal microcracking, likely the result of spallation of the source scale during exposure to the new environment.

Electrical properties of outer membrane extensions from Shewanella oneidensis MR-1.

Shewanella oneidensis MR-1 is a metal-reducing bacterium that is able to exchange electrons with solid-phase minerals outside the cell. These bacterial cells can produce outer membrane extensions (OMEs) that are tens of nanometers wide and several microns long. The capability of these OMEs to transport electrons is currently under investigation. Tubular chemically fixed OMEs from S. oneidensis have shown good dc conducting properties when measured in an air environment. However, no direct demonstration of the conductivity of the more common bubble-like OMEs has been provided yet, due to the inherent difficulties in measuring it. In the present work, we measured the electrical properties of bubble-like OMEs in a dry air environment by Scanning Dielectric Microscopy (SDM) in force detection mode. We found that at the frequency of the measurements (∼2 kHz), OMEs show an insulating behavior, with an equivalent homogeneous dielectric constant εOME = 3.7 ± 0.7 and no dephasing between the applied ac voltage and the measured ac electric force. The dielectric constant measured for the OMEs is comparable to that obtained for insulating supramolecular protein structures (εprotein = 3-4), pointing towards a rich protein composition of the OMEs, probably coming from the periplasm. Based on the detection sensitivity of the measuring instrument, the upper limit for the ac longitudinal conductivity of bubble-like OMEs in a dry air environment has been set to σOME,ac < 10-5 S m-1, a value several orders of magnitude smaller than the dc conductivity measured in tubular chemically fixed OMEs. The lack of conductivity of bubble-like OMEs can be attributed to the relatively large separation between cytochromes in these larger OMEs and to the suppression of cytochrome mobility due to the dry environmental conditions.

In Situ Oxidation Studies of High-Entropy Alloy Nanoparticles.

Although high-entropy alloys (HEAs) have shown tremendous potential for elevated temperature, anticorrosion, and catalysis applications, little is known on how HEA materials behave under complex service environments. Herein, we studied the high-temperature oxidation behavior of Fe0.28Co0.21Ni0.20Cu0.08Pt0.23HEA nanoparticles (NPs) in an atmospheric pressure dry air environment by in situ gas-cell transmission electron microscopy. It is found that the oxidation of HEA NPs is governed by Kirkendall effects with logarithmic oxidation rates rather than parabolic as predicted by Wagner's theory. Further, the HEA NPs are found to oxidize at a significantly slower rate compared to monometallic NPs. The outward diffusion of transition metals and formation of disordered oxide layer are observed in real time and confirmed through analytical energy dispersive spectroscopy, and electron energy loss spectroscopy characterizations. Localized ordered lattices are identified in the oxide, suggesting the formation of Fe2O3, CoO, NiO, and CuO crystallites in an overall disordered matrix. Hybrid Monte Carlo and molecular dynamics simulations based on first-principles energies and forces support these findings and show that the oxidation drives surface segregation of Fe, Co, Ni, and Cu, while Pt stays in the core region. The present work offers key insights into how HEA NPs behave under high-temperature oxidizing environment and sheds light on future design of highly stable alloys under complex service conditions.

Friction coefficients for steel to steel contact surfaces in air and seawater

Through a series of laboratory friction tests on small scale specimens an understanding of the physical behaviour is gained. The test program of the friction tests contained 12 test specimen variants, with a combination of dry air and seawater environment and various surface conditions and contact pressures.

DEGRADATION OF MILD STEEL IN ETHANOL BURNING ENVIRONMENT: OXIDATION KINETICS AND MICROSTRUCTURAL ASPECT

: The isothermal oxidation of an AISI 1005 steel (mild steel) in water vapour and CO 2 mixtures containing environments resulted from ethanol combustion had been investigated for exposure times ranging from 1 hour to 49 hours at elevated temperatures (700 °C, 750 °C and 800 °C). The steel was also oxidized in dry air for comparison. In water vapour and CO2 environments, mild steel underwent a significant degradation in term of the oxidation kinetics compared with those of steel oxidized in dry air environment. This finding is supported by a lower activation energy for steel oxidized in ethanol combustion products (199 kJ/mol) than that of for steel oxidized in dry air (224 kJ/mol). In addition, the breakaway oxidation was found for the steel subjected to ethanol combustion products at 800 °C. The carbon deposited in the magnetite layer was believed to lead the breakaway oxidation after an exposure time for 4 hours. A typical iron oxide growing on steel oxidized in ethanol combustion product is a pyramidal grain structures with compact scale but in dry air environment the iron rich oxide growing on the steel surface is a wrinkle characteristic displaying hollow structures at 700 °C and rough-grained oxide structures at 750–800 °C.

An experimental and numerical study on the combustion of lignites from different geographic origins

Coal combustion involves multi-scale, multi-phase and multi-component aspects, in a process where both transport phenomena and reaction kinetics must be considered. The aim of the work is to investigate the differences between the combustion characteristics of Turkish (Soma lignite, Tunçbilek lignite, Afşin-Elbistan lignite) and German (Rhenish lignite) lignites. Combustion characteristics of these lignites were investigated experimentally and numerically. Experiments were conducted using a high temperature (1000 °C) and high heating rate (~104 °C/s) drop tube furnace (DTF), along with a thermogravimetric analyzer (TGA) at non-isothermal conditions (5, 10, 15, 20 °C/min). Both experimental trials were done in a dry air environment and atmospheric pressure. Additionally, DTF and TGA are the experimental setups used to validate the numerical model used in this work. The numerical part of the study includes the computational fluid dynamic analysis of DTF and the predictive multi-step kinetic model analysis of the fuel particle. TGA experiments showed that fuel ratio has an effect on the ignition times. Moreover, maximum reaction rates obtained by TGA experiments were inversely proportional to the ash contents of the fuels used. High heating rate DTF experiments showed similar combustion behaviours with TGA experiments. According to DTF experiments, RL has the highest reactivity (RL: 7.8 s−1) among all fuels (AEL: 5.3, SL: 4.7, TL: 2.9 s−1). In comparison to experimental data, PoliMi model predictions on high-temperature volatile yields are satisfactory with 5–7% errors. PoliMi model overpredicted the devolatilization rates whereas char oxidation rate predictions seem to be lower than the experimental results.

Nickel-Decorated Black Phosphorus for Room Temperature NO2 detection

We study the electrical characterization at room temperature (RT) of black phosphorus nanoflakes decorated with nickel nanoparticles (Ni/bP). The latter has been exposed to different concentrations of NO2 at RT in a dry air environment highlighting fast and stable response over the time. This latter characteristic is particularly relevant since environmental instability of exfoliated BP has been an issue so far, under ambient conditions few-layer BP degrades completely in less than a week, preventing its applications in several fields. Introduction In the rapidly emerging field of layered two-dimensional (2D) functional materials, bP, the all P-counterpart of graphene, is a potential candidate for various applications e.g., nanoscale optoelectronics, rechargeable ion batteries, electrocatalysts, thermoelectrics, solar cells, and sensors [1]. bP has been reported to exhibit superior chemical sensing performance. In particular, bP is selective for the detection of paramagnetic molecules, e.g., NO2, in addition to high sensitivity at a limit of detection (LOD) of ppb levels.[2] In this work, by applying a multiscale characterization approach we demonstrated a stability and functionality improvement of Nickel-decorated bP (Ni/bP) films for gas sensing prepared by a simple, reproducible and affordable deposition technique. Furthermore, we studied possible electrical activity of these films for their employment as functional layers in gas sensors by exposing them to different gaseous compounds (NO2, CO2, H2, NH3, CO, Benzene, etha-nol, ethylene, Formaldehyde) in different relative humidity (RH%) conditions. Moreover, the influence in sensing perfor-mance of nickel nanoparticle (NP) dimensions in related to the decoration technique and the film thickness were investigated. Materials and Methods Black phosphorus microcrystals were suspended in dimethylsulfoxide and kept under ultrasonication for several hours. The exfoliated bP nanosheets were decorated with nickel nanoparticles following two different procedures: 1) preformed Ni NPs were immobilized on bP, 2) Ni NPs were grown directly on bP flakes. Electrical conductance measurements have been performed on Ni/bP flakes deposited via spin coating on Al2O3 substrates with built-in interdigitated gold electrodes, in order to better control the film thickness. Electrical conductance measurements have been performed at RT (25±2°C) by exposing the sensing film to certified mixtures of NO2 diluted in dry air (20% O2 and 80% N2) with different NO2 concentration ranging from 200 ppb to 1 ppm. Results and Conclusions Exfoliated black phosphorus nanoflakes decorated with nickel nanoparticles (Ni/bP) have been prepared and characterized with particular attention to the role of Ni nanoparticle dimension in the sensing mechanism. Electrical activity towards different concentrations of NO2 at room temperature in a dry air environment highlighted fast and stable response over the time. This latter characteristic is particularly relevant since environmental instability of exfoliated BP has been an issue so far, under ambient conditions few-layer bP degrades completely in less than a week, preventing its applications in several fields. In situ grown Ni/bP (2) shows stable response during all the four weeks measurements period with no dependence of the response on the film thickness. Ni decoration effectively suppress ambient degradation, for at least 1 week in Ni/bP (1) and over 4 weeks in Ni/bP (2) in ambient conditions. This result highlighted that Ni/bP (2) sensor can be practically used under ambient conditions for a reasonable period without performance degradation of the devices.The obtained results pave the way for the use of chemically exfoliated bP flakes for gas sensing applications, avoiding the use of a time-consuming technique for the exfoliation and for the fabrication of the metallic contacts, like electron beam lithography, focused ion beam lithography, etc.

Strongly adherent Al2O3 coating on SS 316L: Optimization of plasma spray parameters and investigation of unique wear resistance behaviour under air and nitrogen environment

Plasma spray deposition of Al2O3 is a well-established technique for thick ceramic coatings on various substrates to shield them from corrosion and wear. Owing to its high hardness, aluminum oxide is known to protect stainless steel substrates from wear. However, the plasma process requires optimization for desired coating thickness and adhesion strength. It is also necessary to understand the sensitivity of friction and wear resistance of the deposited coating on exposed environment for evaluation of service life. The study offers comprehensive investigation on plasma process parameters for the development of strongly adherent aluminium oxide coatings on SS 316L substrate. Impact of environment like dry air and dry nitrogen on tribological properties of the coatings was also investigated. Dense adherent coatings of alumina could be deposited on SS 316L at a plasma power of 20 kW with an intermediate bond coat of NiCrAlY to enhance the adhesion properties. The effects of stand-off distance and bond coat thickness on adhesion strength were additionally examined. Further, the coatings were characterised for phase composition, microstructure, microhardness and wear resistance potential. Reciprocating wear tests of the coatings were carried out using ball on disc reciprocating tribometer at different loading conditions (5, 10 and 15 N) at constant (5 Hz) sliding frequency. Unlike the coefficient of friction (COF), wear volume was found to increase with an increase in normal load. These adherent coatings revealed promising properties for the applications where the tribological failure of SS 316L in dry air or dry nitrogen environment is to be controlled.

Paralinear Oxidation of Cr-Si-C-Coated C/SiC at 1300°C in Wet and Dry Air Environments

The oxidation kinetics of a Cr3Si-Cr7C3/SiC/SiC-coated C/SiC were comparatively investigated in dry and wet air at 1300°C under 1 atm. After oxidation for 10 h, Cr2O3 and SiO2 were produced in both oxidations. However, a larger amount of SiO2 formed during the wet air oxidation. After the dry air oxidation, the surface of Cr3Si-Cr7C3/SiC/SiC coating became relatively loose with many pores. After the wet air oxidation, the surface of Cr3Si-Cr7C3/SiC/SiC coating became undulating and loose with notable damage at the position of bulges. The Cr3Si-Cr7C3/SiC/SiC-coated C/SiC showed paralinear weight gains in both oxidation environments. Although the initial weight gains within the first 1 h in the wet air oxidation condition were higher, the gradual weight gains thereafter were lower. The parabolic rate constant for oxide formation and the linear rate constant for oxide volatilization in the wet air oxidation condition were higher than those in the dry air oxidation condition.

ИНФРАКРАСНАЯ СПЕКТРОСКОПИЯ КАК МЕТОД ОПРЕДЕЛЕНИЯ СТРУКТУРНЫХ ОТКЛИКОВ ПРИРОДНЫХ ГЛИН НА СВЧ-ВОЗДЕЙСТВИЕ

Методом ИК-спектроскопии изучены структурные отклики частиц монтмориллонитовой и каолинитовой глин месторождений Оренбургской области на СВЧ-воздействие. Обработку проб в течение 10 минут проводили в поле магнетрона мощностью 750 Вт в воздушной и влажной средах. Спектры получены с помощью ИК-Фурье спектрометра в диапазоне длин волн 4000–400 cм-1. Установлено, что в монтмориллонитовой глине количество доминирующих связей в тетраэдре SiO4 снижается в 1.5 раза при обработке в сухом воздухе и в 1.8 раза – во влажном. В глине, содержащей каолинит, все типы связей активно разрушаются под воздействием СВЧ-поля.&#x0D; &#x0D; &#x0D; ИСТОЧНИК ФИНАНСИРОВАНИЯРабота выполнена при финансовой поддержке РФФИ и правительства Оренбургской области в рамках научного проекта № 19-43-560001 р_а «Физико-химические принципы процессов СВЧ-консолидации каолинитов».&#x0D; &#x0D; &#x0D; &#x0D; REFERENCES&#x0D; &#x0D; Domashevskaya, E. P., Builov, N. S., Lukin, A. N. Sitnikov A. V. 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Fatigue behavior investigation on dissimilar aluminum alloy ring welded joints in a new type sandwich high-pressure shell

Fatigue tests subjected to constant amplitude under the environments of dry air were performed on 5A06-O aluminum alloy, 7A05-T6 aluminum alloy and 5A06-O/7A05-T6 dissimilar aluminum alloy ring welded joints in a new type sandwich high-pressure shell. The fatigue behaviors were analyzed and compared based on the experimental data, and the mechanisms of welding defect impacts on fatigue properties of the welded joints were deduced from fractographic analysis. It is showed that welding defect has a detrimental influence on fatigue properties of the welded joints. The lower stress level can cause the more obvious decrease of fatigue life of the welded joints. Fatigue cracks of aluminum alloys base metal usually initiated at the surface defects such as two-phase particles and inclusions, and however, welding defect of welded joints are more likely to cause stress concentration and lead to the early initiation of fatigue cracks, which is dominated in decreasing of fatigue life of the welded joints.

Activation of buried p-GaN in MOCVD-regrown vertical structures

Thermal activation of buried p-type GaN is investigated in metal-organic chemical vapor deposition-regrown vertical structures, where the buried p-GaN is re-passivated by hydrogen during regrowth. The activation is performed by exposing the buried p-GaN through etched sidewalls and characterized by reverse breakdown measurements on vertical diodes. The effect of the n-type doping level on the activation has been observed. After 725 °C/30 min annealing in a dry air environment, the buried p-GaN with a regrown unintentionally-doped (UID) capping layer is sufficiently activated due to significant Mg-incorporation in the UID layer, allowing for hydrogen up-diffusion. With an additional regrown n+-GaN capping layer (i.e., in n+/i/p-n diodes), only lateral diffusion of H out of the exposed mesa sidewall is permitted. A critical lateral dimension between 10 and 20 μm is found for the n+/i/p-n diodes, under which the buried p-GaN is sufficiently activated. The diodes with activated buried p-GaN achieved up to 1200 V breakdown voltage, indicating that over 28% of the Mg dopants is activated. The study demonstrates the effectiveness of sidewall p-GaN activation in achieving high breakdown voltage pertinent to GaN vertical power devices, while providing guidelines on the required device geometry.