Mixed Gas Atmosphere Research Articles

The effect of nitrogen on the tensile strength of Ti–22Al–25Nb alloy using laser beam powder bed fusion

Titanium-aluminum (TiAl) based alloys have a wide application prospect in aerospace and auto-industry fields due to low density, good physical and mechanical performances. However, the mechanical strength of TiAl-based alloys is also put forward more stringent requirements with the complexity of the application conditions. In this work, an argon-nitrogen (Ar–N2) reactive atmosphere was designed to achieve nitrogen interstitial solid-solution strengthening of Ti–22Al–25Nb alloy during the laser beam powder bed fusion (PBF-LB) process. An in-depth microstructure and mechanical performance analysis for the as-printed sample under various atmosphere conditions were performed via scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The nitrogen atoms can be dissolved in the octahedral gap of the β phase through the PBF-LB in the Ar–N2 atmosphere, and a small amount of nitride was detected when the volume ratio of Ar to N2 was 95:5. Compared with 100 vol% Ar atmosphere condition, finer grains of the β phase can be obtained after using the mixed gas atmosphere, and the ratio of the O phase was significantly reduced. The yield strength and ultimate tensile strength can be increased from 932 MPa to 947 MPa–1080 MPa and 1099 MPa at room temperature, respectively. At the same time, the elongation reaches ∼11 % while obtaining higher tensile strength. The strength of as-printed Ti–22Al–25Nb alloy was improved by adopting a practical methodology without sacrificing plasticity.

High-Performance Ni3(HHTP)2 Film-Based Flexible Field-Effect Transistor Gas Sensors.

Conductive metal-organic frameworks (MOFs) have received increasing attention in recent years and present high application potential as sensing elements in electronic sensors. In this study, flexible field-effect transistor (FET) sensors based on conductive MOF, i.e., Ni3(HHTP)2, have been constructed. This Ni3(HHTP)2 sensor has high sensitivity (detection limit of 56 ppb) as well as superior selectivity for NO2 detection at room temperature, which is demonstrated by accurate gas detection in a mixed gas atmosphere. Moreover, by employing six flexible substrates, i.e., polyimide (PI), tape (PET), facemask, paper cup, tablecloth, and take-out bag (textile), we successfully demonstrate the universality of the flexible sensor construction with conductive MOF as sensing film on various substrates. This study of conductive MOF-based flexible electronic sensors offers a new opportunity for a wide range of sensing applications with wearable and portable electronic devices.

Development of deoxidation process for off-grade titanium sponge using magnesium metal with wire mesh strainer type of crucible

In this study, the deoxidation process for off-grade titanium (Ti) sponge using magnesium (Mg) metal with a wire mesh strainer type of crucible was developed. Ti hydride (TiH2) feedstock, which was prepared by hydrogenating off-grade Ti sponge, was deoxidized using Mg in a molten magnesium chloride–potassium chloride salt at 933 K under an argon and 20% hydrogen (H2) mixed gas atmosphere. After deoxidation, the residual Mg-containing salt was separated in situ from the crucible to investigate the feasibility of minimizing salt loss during the leaching and production of pure TiH2. The results showed that the presence of residual Mg-containing salt inside the crucible strongly influenced whether a mixture of Ti and TiH2 or pure TiH2 was produced. When the salt was not sufficiently separated, a mixture of Ti and TiH2 was obtained and its oxygen (O) concentration was 0.121 mass% under certain conditions. Meanwhile, pure TiH2 was obtained by increasing the H2 gas flow rate during deoxidation. Therefore, these results demonstrate that the decrease of O concentration to below 0.180 mass% and the minimal loss of the salt are feasible.

Hydrogen Exchange and Diffusion Kinetics at Elevated Temperatures in Proton-Conducting Solid Oxide Materials

Storage of purified hydrogen is one of the central challenges in addressing climate change and reducing our reliance on fossil fuels for energy conversion and storage, and therefore there is a global surge in research and development concerning hydrogen purification and storage. In this regard, we are studying proton conduction in solid oxide materials at elevated temperatures for applications in hydrogen separation and compression membranes. Hydrogen compression is the most recommended method to store hydrogen for automotive applications as it allows an increase in the hydrogen volumetric energy density.Traditionally the protonic conductivity in these materials is measured by indirect methods. For example, conductivity measurements in mixed gas atmospheres, comparing for example dry N2 with humidified N2, thereby allowing the contribution of protons to be evaluated. In this study, we for the first time report the evaluation of protonic conductivity in BaZr1-xCexY0.2O3−δ, BaZr0.1Ce0.7Y0.2–xYbxO3–δ and Ba7Nb4MoO20 by direct measurements afforded by the Isotope Exchange Depth Profiling technique with deuterium labelling. We also report the kinetics of H/D transport through the bulk materials and across metal-ceramic interfaces with a particular interest in the behaviour of the interface between the key Pd/Pd alloy catalyst component and the hydrogen-transporting oxide ceramic material. The transport and interface behaviour information will be of significance in designing hydrogen separation and compression membranes. Figure 1

Optimization and analysis of biomass carbon loaded metal catalyst for catalytic cracking of toluene

The technology of hydrogen production from biomass pyrolysis is on the way, but the biomass tar produced in the process of pyrolysis seriously affects its practical application. The key to catalytic cracking technology was to develop highly low-temperature active and stable catalysts. In view of that, a new anti-sintering carbon-based nanocatalyst with distinct micro-mesoporous structure was synthesized by carbothermic reduction of the catalyst under mixed gas (H2/N2) atmosphere using cigarette stalks as raw material. The results showed that at a relatively low temperature of 700 °C, the catalyst had a high toluene conversion of 100 %, a stable lifetime of 250 min, a maximum hydrogen yield of 12,250 ppm and a desirable hydrogen selectivity of 77 %. The addition of hydrogen during the catalyst synthesis enabled a stronger interaction between the metal and the carbon support, which maintained a high metal distribution, resulting in a more interesting anti-sintering phenomenon of nickel nanoparticles at high temperatures. In particular, hydrogen etching of the support avoided collapse of the pores at high temperatures. At the same time, the etching enriched the pore structure of the support, thus increasing the specific surface area and pore volume of the support. This study provided a simple treatment of a carbon loaded nickel catalyst in the synthesis process and reported a novel low-temperature catalytic cracking catalyst with good toluene cracking activity and hydrogen generation.

Reactive sputter deposition of β-Ni(OH)2 thin films in Ar + H2O mixed gas atmosphere at a substrate temperature of −80 °C

Nickel hydroxide [Ni(OH)2] is an electrochemically-active material used for rechargeable batteries, electrochemical capacitors, and electrochromic devices. Although there have been some studies on Ni(OH)2 thin films deposited by sputtering, the Ni(OH)2 formation has not been fully confirmed. In this study, a Ni metal target was reactively sputtered in atmospheres of O2 and Ar + H2O at substrate temperatures of RT (RT, around 20 °C), −80 °C, and −170 °C, and the aging treatment effects in the air at RT were studied. From optical, X-ray diffraction, and IR absorption measurements, β-Ni(OH)2 thin films were found to be formed after aging the films deposited at −80 °C in Ar + H2O, however, NiO thin films were formed at RT. These results corresponded well with a thermodynamic consideration of Ni(OH)2. At −170 °C, mixed metal and oxide films were formed, presumably because of insufficient Ni oxidation.

Microstructural analysis of tristructural isotropic particles in high-temperature steam mixed gas atmospheres

High-temperature gas-cooled reactors (HTGRs) use tristructural isotropic (TRISO) particles embedded in a graphitic matrix material to form the integral fuel element. Potential off-normal reactor conditions for HTGRs include steam ingress with temperatures above 1,000 °C. Fuel element exposure to steam can cause the graphitic matrix material to evolve, forming an atmosphere composed of oxidants and oxidation products and potentially exposing the TRISO particles to these conditions. Investigating the oxidation response of TRISO particles exposed to a mixed gas atmosphere will provide insight into the stability under off-normal conditions. In this study, surrogate TRISO particles were exposed to high temperatures (T = 1,200 °C) in flowing steam (3% < pH2O < 21%) and CO (pCO < 1%) to determine the oxidation behavior of the SiC layer when exposed to various mixed gas atmospheres. Scanning electron microscopy, x-ray diffraction, and focused ion beam milling was used to determine the impact of CO and steam on the oxidation behavior of the SiC layer. The data presented demonstrates how the SiC layer showed strong oxidation resistance due to limited SiO2 growth and maintained its structural integrity under these off-normal conditions.

Effects of Oxygen-Containing Functional Groups on the Electrochemical Performance of Activated Carbon for EDLCs

Activated carbon (AC) is used in commercial electric double-layer capacitors (EDLC) as electrode active material owing to its favorable properties. However, oxygen functional groups (OFGs) present in AC reduce the lifespan of EDLCs. Thus, we investigated the correlation between the OFGs in AC and their electrochemical characteristics. Samples were prepared by heat-treating commercial AC at 300 °C-900 °C for 1 h under two gas atmospheres (N2 and 4% H2/N2 mixed gas). The textural properties were studied, and the reduction characteristics of AC under Ar and H2/Ar mixed gas atmospheres were investigated. Additionally, changes in the OFGs with respect to the heat-treatment conditions were examined via X-ray photoelectron spectroscopy. The specific surface areas of AC-N and AC-H were 2220-2040 and 2220-2090 m2/g, respectively. Importantly, the samples treated in hydrogen gas exhibited a higher yield than those treated in nitrogen while maintaining their pore characteristics. Additionally, the electrochemical performance of the AC was significantly enhanced after the reduction process; the specific capacitance increased from 62.1 F/g to 81.6 F/g (at 0.1 A/g). Thus, heat treatment in hydrogen gas improves the electrochemical performance of EDLCs without destroying the pore characteristics of AC.

The effects of hot rolling process on mechanical properties, corrosion resistance, and microstructures of Mo-Ni alloyed steels produced by powder metallurgy

This study examined the effects of hot rolling on the microstructure, tensile strength, and corrosion behaviors of three different alloy steels made by powder metallurgy: Fe-0.55C, Fe-0.55C-3Mo, and Fe-0.55C-3Mo-10Ni. 700 MPa pressure was applied to press the particles. The cold pressed samples were sintered in a mixed-gas atmosphere (90% nitrogen, 10% hydrogen) at 5?C/min up to 1400?C for 2 hours. Then, the produced steels were hot rolled with a deformation rate of 80%. The microstructures show that deformed Mo and Mo-Ni steels have finer microstructures, better mechanical properties than undeformed Mo and Mo-Ni steels, and MoC, MoN, or MoC(N) was formed in the Mo-Ni steels. The highest mechanical properties were obtained in rolled steel samples containing Mo-Ni, followed by rolled Mo steel and rolled carbon steel samples, and then unrolled samples. Additionally, Tafel curve analysis demonstrated that alloy corrosion resistance rose as Ni concentration increased. It has also been observed that the hot rolling process improves corrosion resistance. The increase in the density value with the rolling process emerged as the best supporter of corrosion resistance.

Interactions of H2O and O2 with char during gasification in mixed atmosphere analyzed by isotope tracer method and in-situ DRIFTS

The interactions of char with H2O and O2 were important for describing the synergistic mechanism of char gasification in H2O/O2 atmosphere. The gases produced during gasification in specific atmospheres were tracked by isotope-labeled oxygen tracing experiment. The interactions of H2O with char and O2 with char during gasification in H2O and O2 atmospheres were separately studied. This helped to explore the interactions between H2O and char and O2 and char during the gasification in mixed-gas atmosphere. It was found that H2O inhibited oxidation of char during gasification, whereas O2 promoted the char-H2O reaction in mixed atmosphere. The overall gasification reactivity in mixed-gas atmosphere was determined by superimposing the effects of O2 on char-H2O reactions and the effects of H2O on O2-char reactions. This could also explain the reason for the influence of H2O on the overall changes in reactivity, based on O2 concentration. The interactive mechanisms during char gasification with H2O and O2 atmospheres were investigated by in-situ DRIFTS experiment and molecular dynamics simulation. In the H2O/O2 atmosphere, H2O was more likely to promote the curling of char structure. The free H radicals obtained in the decomposition of H2O molecules consumed the active sites of reaction between char and O2 and decreased its reactivity. Oxygen could inhibit the curling of the char structure caused due to water and promote the formation of OH radicals. This in turn, promoted the cracking of aromatic rings, increased the number of sites for reaction between char and H2O, and improved the gasification of char in H2O. In case of mixed-gas atmosphere, the interactions between isotope decoupled single reactions could provide new understanding.

Droplet-Dispensed Ultraviolet Nanoimprint Lithography in Mixed Condensable Gas of Trans-1,3,3,3-Tetrafluoropropene and Trans-1-Chloro-3,3,3-Trifluoropropene

Droplet-dispensed ultraviolet nanoimprint lithography (UV-NIL) in helium enables adaptive material deposition to match pattern variations in a mold. It is a potential lithographic technology for semiconductor devices, but process throughput is an issue. UV-NIL in trans-1,3,3,3-tetrafluoro-propene (TFP) and 1-chloro-3,3,3-trifluoropropene (CTFP) gases has enabled bubble-free and high-throughput processes for spin-coated films. This study investigated the applicability of a mixed condensable TFP/CTFP gas to droplet-dispensed UV-NIL. The filling time in a local area of the mold in a mixed condensable gas atmosphere was as low as 1/30th that in helium. Similarly, the filling in the entire mold was faster in a mixed condensable gas atmosphere than in helium, and micropatterns could be filled within 1.6 s. When the droplets were exposed to the mixed TFP/CTFP gas, the droplet diameter of 108 µm increased to 127 µm owing to gas absorption. The quality obtained for an L/S 90-nm pattern was the same as for the pattern of a spin-coated film, but the line width of patterns fabricated by UV-NIL in ambient TFP/CTFP was 6 nm narrower than that for UV-NIL in He.

Highly Sensitive Oxygen Sensing Characteristics Observed in IGZO Based Gasistor in a Mixed Gas Ambient at Room Temperature.

Oxygen (O2) sensing in trace amounts and mixed gas is essential in many types of industries. Semiconductor sensors have proven to be invaluable tools for the O2 measurements in a wide concentration range, but the sensors are only able to quantify O2 in a concentration range of subppm, thus far, especially in mixed gas. We present in this paper a new concept for O2 sensing with incomparable sensitivity using IGZO-films with oxygen vacancy-based conducting filaments (CFs). O2 sensing relies on rupturing of the CFs, and the proposed device quickly recovers to the initial state using a pulse of 0.6 V/90 μs after the sensing. The proposed device has a high sensitivity of 14 even at an O2 concentration of 500 ppb, a detection limit of 150 ppb for O2 at RT, and excellent selectivity for O2 in mixed gas, which is remarkable compared to other gas sensors. The proposed device can be widely used in gas sensors especially for detecting O2 at a low ppb level, which is due to excellent sensing characteristics.

High temperature corrosion behavior of alloys in reducing HCl and H2S containing environments: Thermodynamical and experimental assessment

AbstractHigh‐temperature corrosion mechanisms in reducing atmospheres containing HCl (3.8 vol%) and a varying amount of H2S (0.02 –2 vol%) were developed for several alloys between 420°C and 680°C. These mechanisms are mainly based on practical observations and kinetic considerations—and less on thermodynamic data. This is due to the complexity of these mixed gas atmospheres, volatile corrosion products, and the ever‐changing conditions within the corrosion layer, which made it not possible to predict and calculate the actual conditions in the corrosion zone. In this article, a detailed thermodynamic analysis of previously achieved corrosion mechanisms and experimental observations is presented. Correlations and deviations between thermodynamic calculations and practical findings are stated and discussed. The corrosion behavior of ferritic K90941, which performs worse than corrosion‐resistant austenitic alloys, except for one test condition at 580°C in the atmosphere with 0.2 vol% H2S, is explained and supported by thermodynamic data. By combining experiments with thermodynamics, corrosion mechanisms in reducing HCl and H2S‐containing atmospheres are explained.

Direct Measurements of Hydrogen Exchange and Diffusion Kinetics at Elevated Temperatures in Proton-Conducting Solid Oxide Materials

Storage of purified hydrogen is one of the central challenges in addressing climate change and reducing our reliance on fossil fuels for energy conversion and storage, and therefore there is a global surge in research and development concerning hydrogen purification and storage. In this regard, we are studying proton conduction in solid oxide materials at elevated temperatures for applications in hydrogen separation and compression membranes. Hydrogen compression is the most recommended method to store hydrogen for automotive applications as it allows an increase in the hydrogen volumetric energy density.Traditionally the protonic conductivity in these materials is measured by indirect methods. For example, conductivity measurements in mixed gas atmospheres, comparing for example dry N2 with humidified N2, thereby allowing the contribution of protons to be evaluated. In this study, we for the first time report the evaluation of protonic conductivity in BaZr1-xCexY0.2O3−δ (BZCY) and BaZr0.1Ce0.7Y0.2–xYbxO3–δ (BZCYYb) by direct measurements afforded by the Isotope Exchange Depth Profiling (IEDP) technique with deuterium labelling. We also report the kinetics of H/D transport through the bulk materials and across metal-ceramic interfaces with particular interest in the behaviour of the interface between the key Pd/Pd alloy catalyst component and the hydrogen transporting oxide ceramic material. The transport and interface behaviour information will be of significance in designing hydrogen separation and compression membranes. Figure 1

Stable Ni-rich layered oxide cathode for sulfide-based all-solid-state lithium battery

Sulfide-based all-solid-state lithium-ion batteries (ASSLIBs) are one of the most promising energy storage technologies due to their high safety and ionic conductivity. To achieve greater energy density, a Ni-rich layered oxide LiNixCoyM1-x-yO2 (NCM, M ​= ​Mn/Al, x ​≥ ​0.6) is desirable due to its relatively high voltage and large capacity. However, interfacial side reactions between the NCM and sulfide solid electrolytes lead to undesirable interfacial passivation layers and low ionic conductivity, thereby degrading the electrochemical performance of NCM sulfide all-solid-state batteries. Herein, a time-/cost-effective sulfidation strategy is exploited to sulfidize a Ni-rich NCM88 cathode in a mixed gas atmosphere of N2 and CS2. A new type of cathode (NCM88-S) with an ultrathin (∼2 ​nm) surface layer is obtained, which significantly reduces the interfacial side reactions/resistance and improves the interfacial stability. The resulting NCM88-S/Li6PS5Cl/Li4Ti5O12 ASSLIB exhibits superior performance, including a high discharge specific capacity (200.7 mAh g−1) close to that of liquid batteries, excellent cycling performance (a capacity retention of 87% after 500 cycles), and satisfactory rate performance (158.3 mAh g−1 at 1C).

Large coercivity of 13 kOe in L10-ordered CoPt on Si/SiO2 substrates by hydrogen annealing

L10-ordered CoPt with a large coercivity (H c) of 13 kOe was demonstrated on Si/SiO2 substrates by hydrogen annealing. Equiatomic 11.2 nm thick (Co/Pt)4 multilayer thin films were fabricated by electron-beam evaporation and were annealed at 500 °C–900 °C for 10–90 min under an Ar/H2 mixed gas atmosphere. The annealing temperature and time dependences of the crystal structures, magnetic properties, and surface morphologies of the films were systematically analyzed based on the experimental results obtained from grazing incidence X-ray diffraction (GI-XRD), vibrating sample magnetometer, and scanning electron microscope, respectively. Hydrogen annealing effectively promoted the out-of-plane c-axis orientation of L10-ordered CoPt compared to the vacuum annealing according to the GI-XRD patterns. A maximum H c of 13.3 kOe was obtained in L10-ordered CoPt with angular-outlined isolated grains by hydrogen annealing at 800 °C for 60 min, where the c-axis of L10-ordered CoPt was randomly distributed.

Comprehensive insights into competitive oxidation/sulfidation reactions on binary ferritic alloys at high temperatures

Interpreting high-temperature corrosion induced by mixed-gas atmospheres is challenging due to the different contributions of oxidizing gases. Here, a comprehensive study on the combined oxidation/sulfidation using label molecules is presented. Fe-Cr model alloys with 2 wt% and 9 wt% Cr were isothermally exposed using a volumetric mixture of 0.5%S16O2/27%H218O and 0.5%S16O2/7%H218O at 650 °C for 5 h and then characterized by secondary ion mass spectroscopy (SIMS). Additionally, the reactions were followed in-situ utilizing energy dispersive X-ray diffraction. The study showed that both S16O2 and H218O contribute to the oxidation of the alloys but to different extents depending on the Cr-content.

Effect of Surface-Active Element Oxygen on Heat and Mass Transfer in Laser Welding of Dissimilar Metals: Numerical and Experimental Study

The effects of the surface-active element oxygen on the laser welding of 304 stainless steel (304SS) and nickel were numerically and experimentally studied in pure argon and argon–oxygen mixed gas atmospheres containing 21% oxygen (AMO). In this study, the molten pool morphology, thermal behavior, solidification phenomenon, correlation between dilution and convection flow, and microhardness of welding joints were analyzed. As a result of oxygen effects, the molten pool was deeper, the maximum temperature was higher, and the maximum flow velocity was lower in the AMO. The cooling rate (GR) and combination parameter (G/R) were studied by the direct simulation of temperature gradient (G) and solidification growth rate (R). Combined with the solidification microstructure, it was found that oxygen had little effect on grain size. The major elements Fe, Cr, and Ni within the solidified molten pool in the AMO were uniformly diluted, while the distribution of the above elements was non-homogenous in pure argon. Stronger flow and multiple directions of convection inside the molten pool contributed to uniform dilution in the AMO. The distribution of microhardness was similar to the content of Cr, and the microhardness at the substrate interface of the joint was higher in the AMO than in pure argon. The preliminary conclusions of this study provide in-depth insights into the effects of surface-active element oxygen on heat and mass transfer in laser dissimilar welding.

Correlated Electrical Conductivities to Chemical Configurations of Nitrogenated Nanocrystalline Diamond Films.

Diamond is one of the fascinating films appropriate for optoelectronic applications due to its wide bandgap (5.45 eV), high thermal conductivity (3320 W m−1·K−1), and strong chemical stability. In this report, we synthesized a type of diamond film called nanocrystalline diamond (NCD) by employing a physical vapor deposition method. The synthesis process was performed in different ratios of nitrogen and hydrogen mixed gas atmospheres to form nitrogen-doped (n-type) NCD films. A high-resolution scanning electron microscope confirmed the nature of the deposited films to contain diamond nanograins embedded into the amorphous carbon matrix. Sensitive spectroscopic investigations, including X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS), were performed using a synchrotron beam. XPS spectra indicated that the nitrogen content in the film increased with the inflow ratio of nitrogen and hydrogen gas (IN/H). NEXAFS spectra revealed that the σ*C–C peak weakened, accompanied by a π*C=N peak strengthened with nitrogen doping. This structural modification after nitrogen doping was found to generate unpaired electrons with the formation of C–N and C=N bonding in grain boundaries (GBs). The measured electrical conductivity increased with nitrogen content, which confirms the suggestion of structural investigations that nitrogen-doping generated free electrons at the GBs of the NCD films.

A composite consisting of intermetallic Ni3Fe and nitrogen-doped carbon for electrocatalytic water oxidation: The effect of increased pyridinic nitrogen dopant

Nitrogen-doped carbon (NC) has been studied as electrocatalysts or electrocatalyst support and the nitrogen content in carbon matrix is mainly dependent on the nitrogen-rich precursors. In this study, we prepare a composite consisting of intermetallic Ni3Fe and NC ([email protected]) via simply heating under ammonia and argon mixed gas atmosphere (Ar/NH3), aiming to further increase the nitrogen content. Compared to [email protected], the NH3-derived electrocatalyst has more N atoms which are in the form of pyridinic N in carbon structure, significantly improving the electron transport efficiency and reaction kinetics, and thereby further boosting the electrocatalytic activity. This work demonstrates that the introduction of ammonia gas flow during calcination is a simple and effective strategy to increase the nitrogen content for engineering NC-based electrocatalysts toward high-performance water splitting.