Inert Gas Atmosphere Research Articles

Design and testing of an (inert) gas cell for in situ polarization modulation infrared reflection absorption spectroscopic (PM-IRRAS) measurements under specific atmospheres.

Infrared reflection absorption spectroscopy (IRRAS) is a powerful surface-sensitive analytical technique to characterize the adsorbed molecules on metal surfaces down to (sub)monolayer coverage. In this paper, a new (inert) gas cell is presented that expands the scope of the commercially available Bruker PMA50 module. The cell is designed as a sample holder to measure thin films of molecules adsorbed on a metal substrate under a specific gaseous atmosphere. The dimensions of the cell are chosen in such a way that it can be transferred into a glovebox via the standard entrance port (Ø150mm), allowing the investigation of air-sensitive molecules under an inert-gas atmosphere. The cell has two hose connections through which the gas atmosphere can be varied as desired. This also allows for studying the reactivity of the adsorbed structures toward the surrounding gas in situ and in a (potentially) time-dependent fashion. Furthermore, the metal substrate can be irradiated via an exposure window to investigate the influence of light on the adsorbed molecules and/or their reactivity. Using the polarization-modulation (PM-) IRRAS technique along with the described gas cell, an air-sensitive molybdenum(0) tricarbonyl complex adsorbed on an Au(111) surface is investigated. This complex reacts with molecular oxygen to the molybdenum(VI) trioxo analog, and this conversion is accelerated by irradiation with light of 365 and 440nm.

Sn-doped n-type GaN freestanding layer: Thermodynamic study and fabrication by halide vapor phase epitaxy

Results of a thermodynamic study of Sn doping and fabrication of a Sn-doped GaN freestanding layer with high structural quality by halide vapor phase epitaxy (HVPE) are described in this paper. Thermodynamic analysis revealed that SnCl2 and/or SnCl act as Sn precursors through the reaction between Sn metal and HCl gas. The equilibrium partial pressures of SnCl2 and SnCl increase with the input HCl partial pressure. To generate Sn precursors effectively, it is desirable that the reaction between Sn metal and HCl gas occurs in the inert gas ambient. On the basis of results of the thermodynamic study, the Sn-doped GaN freestanding layer with a Sn concentration of 5.7 × 1019 cm−3 is fabricated by removing the GaN seed substrate after HVPE growth. The Sn-doped GaN freestanding layer has high crystal quality, and the lattice constants along the c- and a-axes of the Sn-doped GaN freestanding layer are larger than those of the GaN seed substrate because of the high electron density and the size effect of Sn atoms.

Enhancing lubrication of electrified interfaces by inert gas atmosphere

Abstract Considering the growing interest in increasing performance and efficiency of driveline components of modern electric vehicles, this work aims to analyze and report the wear mechanisms and notable enhancement of the lubrication of electrified contact interfaces by inert gas atmospheres. Systematic tribological studies were conducted on AISI 52100 steel test pairs using driveline lubricants under unelectrified and electrified conditions in ambient air and dry N2. Test results showed that in ambient air and electrification, the formation of iron oxides (in particular hematite) was most dominant and gave rise to severe abrasive wear regardless of the lubricant type being used. In dry N2, however, the tribo-oxidation was suppressed but the formation of a carbon-rich tribofilm was favored (especially under electrified conditions). Such a shift from surface oxidation to carbonaceous film formation resulted in dramatic reductions (by factors of 8 to 10) in the wear of test pairs.

High-Temperature Reorganization Behavior of Single-Crystalline Porous 4H-SiC Thin Foils

This work reports on the high-temperature reorganization behavior of single-crystalline porous 4H-silicon carbide (4H-SiC) thin foils. Porous 4H-SiC thin foils are realized via state-of-the-art photoelectrochemical etching in hydrofluoric (HF) acid solution enabling for the first time a released foil with a diameter of 2 inches. Subsequent annealing under inert gas atmosphere and comparison between samples suggests that a temperature of 1500 °C allows for various degrees of compactification across the foil surface, whereas at 1600 °C single crystallinity can be preserved.

Improving Electrical Conductivity of LiFePO4 through Advanced Synthesis and Multidoping Techniques

Extensive research has been conducted to enhance the electrical conductivity of LiFePO4. Several techniques, including doping with metal cations, synthesizing nanocrystalline grains, and carbon coating, have been employed [1]. Recent advances in material synthesis have revolutionized LiFePO4, such as depositing conductive carbon coatings on active material particles and exploring surface doping techniques. These advanced approaches have significantly improved the mass transfer rate [2]. High-capacity LiFePO4 materials close to the theoretical specific capacitance have been obtained.Efforts are currently underway to improve the electronic and ionic conductivity of LiFePO4 to enhance its efficiency. However, before it can be widely used, the material's low electronic conductivity and suboptimal performance in high-speed regimes must be overcome. Doping with supervalent cations is an effective method for narrowing the energy gap and increasing the electrical conductivity of LiFePO4 [3]. Additionally, the synthesis of nanocrystalline grains and the deposition of conductive carbon coatings on the particle surface contribute to an increase in mass transfer rate, removing critical performance limitations of LiFePO4. Reducing the size of LiFePO4 to the nanoscale has been identified as a strategic method to shorten the diffusion length of Li-ions and accelerate electron-conducting pathways during charging and discharging cycles, ultimately improving the overall performance of the material.This work compares the doping process of LiFePO4 cathode material using two methods: solid-phase synthesis in a planetary ball mill and spray pyrolysis in an inert gas atmosphere. The studies on the synthesis and modification of LiFePO4 have significant potential to overcome existing limitations and unlock its full potential for integration into high energy density batteries. The above multidoping methods enable the production of doped LiFePO4 materials with specific capacitance approaching theoretical values. Acknowledgments This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP19677233).

Hot deformation behavior of laser powder bed fusion newly developed MS400 grade maraging steel

AbstractIn this work, the hot deformation mechanism of as-printed laser powder bed fusion process (LPBF) newly developed MS400 grade maraging steel was investigated. The optimization processes allowed for obtaining samples with an average density of 8.200 ± 0.002 g cm−3 and hardness of 417 ± 5 HV. The hot compression procedure of maraging steel was carried out with the DIL 805 A/D dilatometer at different temperatures in the range of 1050 °C-1200 °C and strain rates of 0.01 s−1–1 s−1 in an inert gas atmosphere. The measured melt flow stress data were used to develop a constitutive model to determine the behavior of the alloy during hot deformation. The proposed equation can be used as an input to the finite element analysis to obtain the flow stress at a given strain, strain rate and temperature, useful for predicting flow localization or fracture during thermomechanical simulation. The activation energy for hot deformation was calculated to be 388.174 kJ mol−1, which corresponds to that of M350 grade. The proposed equation can be used during finite element analysis to calculate the flow stress at any strain, strain rate and temperature to determine the location of a flow or crack during a thermomechanical simulation.

A closer look at the effects of oxygen on the photoluminescence properties of CdSe/CdS quantum dots.

We present a detailed study on the effects of oxygen on the photoluminescence properties of CdSe/CdS quantum dots (QDs). We investigated the role of oxygen by performing confocal measurements on thin films as well as on single particles while rapidly exchanging the gaseous environment between oxygen and an inert gas atmosphere. We found that the deionization of negatively charged particles by oxygen depends on both the excitation power and the shell thickness of the QDs. For QDs with thin shells, which exhibit strong photoluminescence blinking, we observed that the presence of oxygen affects both band-edge carrier blinking and hot-carrier blinking.

Vacuum sintering of the self-developed Chang’E-5 lunar regolith simulant

The utilization of in-situ lunar resources through the additive manufacturing of lunar regolith (LR) has attracted considerable interest. Sintering of LR is considered a promising method for lunar construction due to its high utilization rate and excellent service stability. However, numerous studies have been carried out on Apollo series LRs with similar chemical compositions in air or inert gas atmospheres. The effects of the lunar ultra-high vacuum conditions and the complex chemical composition of LRs on the sintering process require extensive investigation. In this study, a self-developed Chang’E-5 lunar regolith simulant (LRS) with a high-Fe content was used as the only raw material to investigate its potential applicability for future lunar construction in vacuum environment. The effects of sintering temperature on the microstructure, linear shrinkage, bulk density, weight loss ratio, and mechanical and thermal expansion properties were investigated. The results show that the linear shrinkage and weight loss ratio increase with increasing sintering temperature. However, the bulk density and unconfined compressive strength (USC) initially increase and then decrease, with the sample sintered at 1075℃ giving the highest bulk density of 2.10 ± 0.03 g/cm3 and a USC of 31.19 ± 1.96 MPa. This is attributed to the transformation of the sample sintered at 1090℃ into a semi-porous material with many cracks. Furthermore, the mechanism of pore and crack formation was revealed. The coefficient of thermal expansion (CET) of the sintered samples is approximately 7×10–6°C−1, which maintains a good service stability after cyclic temperature stress from room temperature up to 200°C. Both the USC and CET of the sample sintered at 1075℃ are superior to those of common terrestrial concrete materials. This indicates that the vacuum sintering process appears feasible for the production of building materials with sufficient mechanical strength and thermal durability for lunar base construction.

Characterization of atmospheric pressure plasma deposited (APPD) coatings to improve the friction behavior of thermoplastic surfaces

Achieving a significant friction reduction is crucial for using thermoplastic materials as substrates in tribological applications and presents an eligible alternative to the use of light metals. In this study, previously developed MoS2/graphite/zinc composite coatings, applied by an atmospheric pressure plasma deposition (APPD) process, were investigated to extend the understanding of their characteristics and the influence of the process and environmental parameters on friction behavior. Tribological tests were conducted in ambient conditions and at elevated temperatures (110 °C) to study the friction behavior under application-oriented conditions. The presence of atmospheric oxygen during the deposition process was shown to influence the durability of the coatings, which motivated the application of an inert gas atmosphere for the coating deposition. A novel shrouding plasma nozzle was introduced, which further lowered the friction coefficients. The oxidizing effect of the plasma spray deposition was studied with X-ray photoelectron spectroscopy to investigate the strong impact of the deposition current on the friction behavior and durability of the deposited coatings. Coating composition, morphology, and the effects of the tribological testing were evaluated using optical microscopy, 3D surface measurements, scanning electron microscopy, X-ray diffraction, and nanoindentation. The fabricated coatings with thicknesses in the 10 μm range and good adhesion on the polyamide substrate were stable under extended testing durations and at elevated temperatures and accomplished a significant friction reduction compared to the uncoated polyamide. Thus, APPD-fabricated MoS2/graphite/zinc coatings represent an excellent candidate for low-friction applications of thermoplastic substrates.

Flash sintering of silicon carbide at room temperature

Although flash sintering (FS) is an effective method for rapidly preparing ceramics, FS of non-oxide ceramics at room temperature (RT) has not yet been achieved. In this study, we developed a feasible method for FS of SiC at room temperature (RT). A dog-bone-shape SiC sample prepared without using any sintering aid achieved a relative density of 96.5 % after sintering in a low-pressure Ar atmosphere for 60 s. Arc heating, which was constrained by the height of an alumina plate fixed above the sample, increased the conductivity of the sample, which then reached the stable stage of FS. The sintered sample exhibited a typical 6H–SiC crystal structure, which was consistent with that of the raw powder. The proposed FS method, based on constraining the arc using an alumina plate under a low-pressure inert gas atmosphere, provides a reference for developing further advanced RT FS strategies for non-oxide ceramics with low conductivities at RT.

Linear dynamics of a thick liquid layer subjected to an oblique temperature gradient

The present study aims to demonstrate the application of the oblique temperature gradient (OTG) to manipulate the buoyancy instabilities and resulting mixing. To accomplish this, we consider a model consisting of a liquid layer supported by a perfectly conducting bottom wall from below and the upper surface is exposed to ambient inert gas in a shallow container. The stability analysis employs the pseudospectral method and perturbation energy budget approach. The imposed OTG consists of a negative vertical temperature gradient (VTG), which leads to unstable density stratification, and a negative horizontal temperature gradient (HTG) component responsible for the Hadley circulation, which can be utilised to control instabilities. Without the HTG, a Rayleigh–Bénard mode of instability exists due to the imposed VTG termed as a VTG mode. The imposed HTG induces a linear VTG term and a quintic polynomial VTG term in the bottom wall-normal coordinate $y$ . The induced linear VTG term reinforces the imposed VTG, while the induced quintic polynomial VTG term opposes the imposed VTG. For the vanishing Biot number ( $Bi$ ), the induced quintic VTG term stabilises the VTG mode for the Prandtl number, $Pr=7$ . However, for $Pr=0.01$ , the Reynolds stresses associated with the Hadley circulation destabilise the VTG mode. For non-zero $Bi$ , new streamwise and spanwise instability modes arise for $Pr=7$ due to the induced linear VTG term. Physical arguments show that the unstable density stratification near the gas–liquid interface caused by the synergistic effect of the imposed VTG and the induced linear VTG term lead to the existence of the predicted new modes. The present study thus shows that the strength of the HTG can be utilised to control the instability modes and critical parameters, thereby demonstrating the utility of the OTG in manipulating the buoyancy instabilities.

Comparative Study of Microstructure and Phase Composition of Amorphous-Nanocrystalline Fe-Based Composite Material Produced by Laser Powder Bed Fusion in Argon and Helium Atmosphere.

Laser powder bed fusion (LPBF) is a prospective and promising technique of additive manufacturing of which there is a growing interest for the development and production of Fe-based bulk metallic glasses and amorphous-nanocrystalline composites. Many factors affect the quality and properties of the resulting material, and these factors are being actively investigated by many researchers, however, the factor of the inert gas atmosphere used in the process remains virtually unexplored for Fe-based metallic glasses and composites at this time. Here, we present the results of producing amorphous-nanocrystalline composites from amorphous Fe-based powder via LPBF using argon and helium atmospheres. The analysis of the microstructures and phase compositions demonstrated that using helium as an inert gas in the LPBF resulted in a nearly three-fold increase in the amorphization degree of the material. Additionally, it had a beneficial impact on phase composition and structure in a heat-affected zone. The received results may help to develop approaches to control and improve the structural-phase state of amorphous-nanocrystalline compositional materials obtained via LPBF.

Origin of extended visible light absorption in nitrogen-doped CuTa2O6 perovskites: the role of copper defects

Abstract The optical band gap of the semiconductor CuTa2O6, synthesised via solid-state reaction, can be greatly reduced by annealing in ammonia, which leads to a significant red-shift of the visible light absorption. Using X-ray photoelectron spectroscopy (XPS), we have shown that this absorption extension does not result from the incorporation of nitrogen, but can be attributed to copper defects formed under the reducing conditions of ammonia treatment. Photocatalytic hydrogen evolution experiments were used to investigate the influence of these defects on the photocatalytic performance. We have further shown that CuTa2O6 with similar increased visible light absorption can be prepared by annealing with an organic reducing agent – sodium citrate – in inert gas atmosphere.

Influence and inerting mechanism of inert gas atmospheres on the characteristics of oxidative spontaneous combustion in coal

To study the influence and inerting mechanism of inert gas atmospheres on the characteristics of oxidative spontaneous combustion in coal, a temperature-programmed experiment was conducted to quantitatively characterize the inhibition efficiency of N2, CO2, and mixed inert gas on the coal spontaneous combustion process. Quantum chemical methods were applied to disclose the weak interaction mechanism of CO2 and N2 with the active groups in SY bituminous coal. The results showed that during low-temperature oxidation of coal, the presence of both N2 and CO2 reduced the release of CO, increased the crossing point temperature of coal, and inhibited the oxidative coal spontaneous combustion process. The inerting effect of CO2 was always more significant than that of N2 on coal spontaneous combustion, and the mixed inert gas had an inerting effect between that of CO2 and that of N2. The differences in inerting of coal spontaneous combustion between CO2 and N2 were obvious in the low-temperature region, while differences were less notable in the high-temperature region. Moreover, the inerting effect of the mixed inert gas was consistent with that of CO2 on coal spontaneous combustion. In the absence of oxygen, the gas atmosphere had little influence on coal pyrolysis. However, the inerting effect of CO2 and N2 on coal oxidation gradually became noticeably different as the O2 concentration increased. Therefore, the selection of an inert gas atmosphere for fire prevention should be based on a comprehensive evaluation of the field temperature, O2 concentration, and type of inert gas. Both CO2 and N2 interacted with the six active groups of coal via VDW interactions. The interaction intensity, mutual penetration distance, and interaction energy produced by the interaction of CO2 with these active groups were always larger than those of N2. When O2 attacked dimers formed by these active groups and CO2, it was repulsed by oxygen atoms on both sides of the CO2 molecule and attracted to the central carbon atom of the CO2 molecule. This could prevent O2 from combining with the active groups in coal and effectively inhibit coal spontaneous combustion. These research results will lay a theoretical foundation for inert gas in underground coal mine fire prevention applications.

Ceramic-to-metal bonding using rare-earth containing Sn–Bi solder

With the increasing miniaturization and power of optoelectronic devices, direct bonding of optical substrates like semiconductors and ceramics to metal heat sinks using low melting-point solder has gained significant interest. In this study, we demonstrated the bonding of glass to copper using Sn-58 wt% Bi solder (SB solder) doped with a small amount of rare earth (RE) elements. The RE elements act as active agents that facilitate the bonding to glasses without glass metallization. By optimizing the bonding parameters, such as reflow temperature and time, and employing an inert gas atmosphere to prevent solder or RE oxidation, we successfully achieved the highest shear strength in glass-copper solder joints using SB-RE solder, without the need for ultrasonic-assisted soldering (UAS). These results demonstrate the potential of using RE-containing solder for bonding unmetallized glass and ceramics in optoelectronic devices with metals at low soldering temperatures (< 200 °C). Furthermore, analysis of the shear strength and failure morphology of solder joints revealed only small degradation, primarily originating from the bulk solder region rather than the solder-glass interface, after both thermal aging (100 h) and cycling tests (100 cycles). The establishment of low-melting point RE-containing solders opens the possibility of direct jointing ceramic optoelectronic substrates to metal heat sinks for more efficient heat dissipation. In the meantime, our work also suggests that further optimization studies are necessary to explore its performance under more extreme working conditions.

Search for Novel Phases in Y-Ba-Cu-O Family

In order to search for possible residual minor phases in the Y-Ba-Cu-O family, powdered mixtures of Y2O3 + BaCO3 + CuO and, independently, superconducting compound YBa2Cu3O7−x have been treated in evacuated cells and elevated temperatures. YBa2Cu3O7−x was reduced to YBa2Cu3O5 by use of the special home-designed Taconis–Knudsen vacuum device. Subsequent doping by oxygen converts produced insulator YBa2Cu3O5 to semiconductor or metal YBa2Cu3O5+x (0 &lt; x &lt; 0.3). In addition to YBa2Cu3O5, 0.05 volume percent of the minor delafossite phase Y2Cu2O4 was spotted in the powder mixture 1/2 Y2O3 + 2BaCO3 + 6Cu2O, heated up to 818 °C in an inert gas atmosphere. An attempt to prepare the insulating bulk delafossite samples was successful, and subsequent doping by oxygen produced novel metallic phases.

Evaluation of Thermodynamic Model of Pd(II) Complex Formation with Isosaccharinic Acid

Palladium-107 is one of the selected radionuclides in the safety assessment of geological disposal of radioactive waste. Although isosaccharinic acid (ISA) forms strong complexes with many elements and enhances element solubility, the thermodynamic evaluation of the complex of Pd with ISA has not been conducted. In this study, the solubility of Pd(OH)2 at pH 8.5–12.5 in the presence of ISA was investigated under inert gas (N2) atmosphere. Furthermore, the coordination state of aqueous Pd and ISA was investigated by X-ray absorption and Fourier transform infrared spectroscopy, respectively. According to experimental results, the number of OH ligands in the mixed complex depends on pH. The thermodynamic model and conditional equilibrium constants of the Pd-ISA complex were estimated by slope analyses of solubility experiments at different pH levels and ionic strengths based on the specific ion interaction theory. Hence, the impact of complexation with ISA on Pd(II) solubility under disposal conditions could be quantified using the proposed thermodynamic models in this study.

Synthesis and Characterization of High-Energy Anti-Perovskite Compounds Cs3X[B12H12] Based on Cesium Dodecahydro-Closo-Borate with Molecular Oxoanions (X- = [NO3]-, [ClO3]- and [ClO4]-).

Three novel anti-perovskite compounds, formulated as Cs3X[B12H12] (X- = [NO3]-, [ClO3]-, and [ClO4]-), were successfully synthesized through the direct mixing of aqueous solutions containing Cs2[B12H12] and CsX (X-: [NO3]-, [ClO3]-, [ClO4]-), followed by isothermal evaporation. All three compounds crystallize in the orthorhombic space group Pnma, exhibiting relatively similar unit-cell parameters (e.g., Cs3[ClO3][B12H12]: a = 841.25(5) pm, b = 1070.31(6) pm, c = 1776.84(9) pm). The crystal structures were determined using single-crystal X-ray diffraction, revealing a distorted hexagonal anti-perovskite order for each. Thermal analysis indicated that the placing oxidizing anions X- into the 3 Cs+ + [B12H12]2- blend leads to a reduction in the thermal stability of the resulting anti-perovskites Cs3X[B12H12] as compared to pure Cs2[B12H12], so thermal decomposition commences at lower temperatures, ranging from 320 to 440 °C. Remarkably, the examination of the energy release through DSC studies revealed that these compounds are capable of setting free a substantial amount of energy, up to 2000 J/g, upon their structural collapse under an inert-gas atmosphere (N2). These three compounds represent pioneering members of the first ever anti-perovskite high-energy compounds based on hydro-closo-borates.

Effect of irradiation modification above melting point on the wear resistance of polytetrafluoroethylene

AbstractThe cross‐linked polytetrafluoroethylene (PTFE) and PTFE/carbon fiber (CF) composites were synthesized through electron beam irradiation in the molten state of PTFE at a controlled temperature of 340 ± 3°C under an inert gas atmosphere for this study. The wear resistance of raw (raw‐PTFE), irradiated modified PTFE (RM‐PTFE), and CF‐reinforced PTFE composites were evaluated using a friction and wear testing machine. The testing was conducted under varying ambient temperatures and dynamic loads. After irradiation, the samples were sectioned into specific sizes for subsequent testing purposes. Under the test conditions of 4.64 MPa positive pressure, 800 rpm speed, and a duration of 300 s at 20°C, the wear amount of PTFE after irradiation modification is significantly reduced from 1.4103 mm to only 0.0233 mm, representing a remarkable reduction by a factor of 60. Similarly, under the test conditions of 4.64 MPa positive pressure, 200 rpm speed, and a duration of 300 s at 20°C, the friction coefficient of PTFE after irradiation modification is substantially decreased from an initial value of 0.13 to just 0.03. The observed improvement can be attributed to the transformation of PTFE's crystalline form into spherulite, accompanied by a significant enhancement in the degree of cross‐linking within its molecular chain. The PTFE was supplemented with 10% CF prior to irradiation. Under the test conditions of a positive pressure of 4.64 MPa, rotation speed of 800 rpm, and a duration time of 300 s at 20°C, the wear amount of the composite material measured only 0.0007 mm, representing a reduction by a factor of 2000 compared to that observed for pure PTFE. This improvement can be attributed to the CF filler's high wear resistance properties and the composite's enhanced thermal conductivity.

Glovebox-assisted magnetic force microscope for studying air-sensitive samples in a cryogen-free magnet.

Most known two-dimensional magnets exhibit a high sensitivity to air, making direct characterization of their domain textures technically challenging. Herein, we report on the construction and performance of a glovebox-assisted magnetic force microscope (MFM) operating in a cryogen-free magnet, realizing imaging of the intrinsic magnetic structure of water and oxygen-sensitive materials. It features a compact tubular probe for a 50 mm-diameter variable temperature insert installed in a 12T cryogen-free magnet. A detachable sealing chamber can be electrically connected to the tail of the probe, and its pump port can be opened and closed by a vacuum manipulator located on the top of the probe. This sealing chamber enables sample loading and positioning in the glove box and MFM transfer to the magnet maintained in an inert gas atmosphere (in this case, argon and helium gas). The performance of the MFM is demonstrated by directly imaging the surface (using no buffer layer, such as h-BN) of very air-sensitive van der Waals magnetic material chromium triiodide (CrI3) samples at low temperatures as low as 5K and high magnetic fields up to 11.9T. The system's adaptability permits replacing the MFM unit with a scanning tunneling microscope unit, enabling high-resolution atomic imaging of air-sensitive surface samples.