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Even though catalyst loading is one of the first crucial steps in organic and inorganic catalytic reactions, it has not been frequently discussed or improved to date. In particular, when a solid catalyst is added to an oxygen- and moisture-sensitive reaction mixture, a carefully tuned process to ensure an inert atmosphere (under nitrogen or argon) is required. Although gloveboxes are nowadays considered to be a universal solution, it is still associated with unsolved problems, such as high cost, high space consumption, difficult temperature control, and handling difficulties on account of the gloves. Herein, we report a recently developed simple apparatus that enables the addition of a solid without opening the reaction vessel. This solid-addition funnel drastically improved the yield (from trace to 64%) and the reproducibility of our original glycosylation reaction.

The inductively-heated plasma generator IPG6-B at Baylor University has been established and characterized in previous years for use as a flexible experimental research facility across multiple applications. The system uses a similar plasma generator design to its twin-facilities at the University of Stuttgart (IPG6-S) and the University of Kentucky (IPG6-UKY). The similarity between these three devices offers the advantage to reproduce results and provides comparability to achieve cross-referencing and verification. Sub- and supersonic flow conditions for Mach numbers between M a = 0 . 3 − 1 . 4 have been characterized for air, argon, helium and nitrogen using a pitot probe. Overall power coupling efficiency as well as specific bulk enthalpy of the flow have been determined by calorimeter measurements to be between η = 0 . 05 − 0 . 45 and h s = 5 − 35 MJ kg−1 respectively depending on gas type and pressure. Electron temperatures of T e = 1 − 2 eV and densities n e = 1 0 1 8 − 1 0 2 0 m−3 have been measured using an electrostatic probe system. At Baylor University, laboratory experiments in the areas of astrophysics, geophysics as well as fundamental research on complex (dusty) plasmas are planned. The study of fundamental processes in low-temperature plasmas connects directly to electric propulsion systems. Most recent experiments include the study of dusty plasmas and astrophysical phenomena and the interaction of charged dust with electric and magnetic fields. In this case, dust can be used as a diagnostic for such fields and can reveal essential information of the magneto-hydrodynamics in low-temperature plasmas. Although some of these goals require further advancement of the facility, it is proposed that several phenomena relevant to electric propulsion as well as to other fields of plasma physics can be studied using the existing facility.

So far many attempts have been made to synthesize phase-pure Ti3AlC2 MAX-phase. But still the challenge posed by the presence of TiC and Ti-Al based intermetallic transient impurity phases in the final product is a persisting problem. Spark plasma sintering (SPS) technique has been the most successful method to decrease the impurity content of the final product. Even so, synthesis of phase-pure Ti3AlC2 MAX-phase, without any TiC and Ti-Al based intermetallic impurities, has not been achieved and reported in literature with substantial evidences. Further, high purity Ti3AlC2 MAX-phase synthesized using SPS technique has shown lack of phase and microstructural stability above 1350°C temperature. In this work, we have reported an optimized method for producing phase-pure Ti3AlC2 MAX-phase (having more than 99 % purity) using commercial grade Ti, Al and C elemental powders through SPS technique. The final product also showed very good high temperature stability up to 1500°C under flowing Argon inert atmosphere.

The effects of heat treatment on the mechanical properties of plain-woven SiC/SiC composites at 927 °C and 1200 °C in argon were evaluated through tensile tests at room temperature and at elevated temperature on the as-received and heat-treated plain-woven SiC/SiC composites, respectively. Heat treatment can improve the mechanical properties of composites at room temperature due to the release of thermal residual stress. Although heat treatment can damage the fiber, the effect of this damage on the mechanical properties of composites is generally less than the effect of thermal residual stress. Heat treatment will graphitize the pyrolytic carbon interface and reduce its shear strength. Testing temperature will affect the expansion or contraction of the components in the composites, thereby changing the stress state of the components. This study can provide guidance for the optimization of processing of ceramic matrix composites and the structural design in high-temperature environments.

In this work, we studied the change in the properties of powders with a core (magnesium) – shell structure (carbon and carbon/palladium) in the process of hydrogenation/dehydrogenation with hydrogen (99.995 wt%). Magnesium powders were obtained by plasma chemical synthesis in an atmosphere of argon containing a small amount of hydrogen (2–3 at.%) and nitrogen (8–9 at.%), when performing a low-frequency arc discharge between a tungsten electrode and a magnesium melt. The shell (carbon and carbon/palladium) was deposited in a plasma generator with vortex and magnetic stabilization. For all samples, a decrease in the sorption capacity of hydrogen was observed as a result of successive cycles of sorption and desorption reactions. It was found that the reason for this fall is associated with the formation of the MgO and Mg(OH)2 phase, which prevents the diffusion of hydrogen. The carbon shell provides a more complete hydrogenation of the magnesium particles, and an additional palladium shell increases the resistance to cyclic hydrogenation/dehydrogenation and reduces the temperature of these processes. According to the data obtained, powders with particles (Mg@C)@Pd can absorb the largest amount of hydrogen (6.9 wt%) for the duration of 5 cycles, after which the protective shell of the particles begins to collapse and a loss of sorption capacity is observed.

Direct reaction of precursors with the products of detonation remains an underexplored area in the ever-growing body of detonation synthesis literature. This study demonstrated the synthesis of silicon carbide during detonation by reaction of elemental silicon with carbon products formed from detonation of RDX/TNT mixtures. Continuum scale simulation of the detonation showed that energy transfer by the detonation wave was completed within 2–9 μs depending on location of measurement within the detonating explosive charge. The simulated environment in the detonation product flow beyond the Chapman-Jouguet condition where pressure approaches 27 GPa and temperatures reach 3300 K was thermodynamically suitable for cubic silicon carbide formation. Carbon and added elemental silicon in the detonation products remained chemically reactive up to 500 ns after the detonation wave passage, which indicated that the carbon-containing products of detonation could participate in silicon carbide synthesis provided sufficient carbon-silicon interaction. Controlled detonation of an RDX/TNT charge loaded with 3.2 wt% elemental silicon conducted in argon environment lead to formation of ∼3.1 wt% β-SiC in the condensed detonation products. Other condensed detonation products included primarily amorphous silica and carbon in addition to residual silicon. These results show that the energized detonation products of conventional high explosives can be used as precursors in detonation synthesis of ceramic nanomaterials.

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 (NC@NiFe) via simply heating under ammonia and argon mixed gas atmosphere (Ar/NH3), aiming to further increase the nitrogen content. Compared to NC@NiFe, 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.

This work presents the results of study of combustion with carbon of transition metals of IV, V and VI groups of the periodic system in atmospheres of argon, hydrogen, nitrogen and nitrogen-hydrogen mixture. The significance of hydrogen in the formation of single-phase products in the self-propagating high-temperature synthesis (SHS) mode was underlined. The combustion of carbon containing systems in argon resulted in the synthesis of two-phase carbides with FCC lattice. In contrary, the combustion of the same systems in hydrogen atmosphere leaded to the synthesis of single-phase carbo-hydrides. The products of combustion of transition metals in nitrogen atmosphere were the multiphase nitrogen-containing compounds. Their following re-ignition in hydrogen leaded to the synthesis of single-phase nitrido-hydrides. It was demonstrated that in all the studied systems, the combustion in hydrogen atmosphere leaded to the homogenized final synthesis products. The results of these processes were the formation of single-phase carbo- and nitrido-hydrides based on the metals of IV, V and VI groups. The presence of hydrogen in the crystal lattice of synthesized refractory carbides and nitrides facilitated easy dispersion of the compound to submicron sizes. After removal of hydrogen, the single phase structure was not violated. The described results may be of commercial value in the industry of refractory materials.

The interfacial liquid layer formed by liquid atoms around the nanoparticle which is dispersed in a base fluid is considered among the mechanisms responsible for the thermal transport enhancement in nanofluid. The present work shows the effect of vibration of graphene nanosheets inside the argon liquid on the formation of a liquid layer at the liquid -solid interface near the graphene. This feature has been examined by using the (MDS) molecular dynamics simulation. The vibration of graphene nanosheet is surveyed by studying the behaviors of positions and velocities of carbon atoms that are recorded at each time step during molecular dynamics simulation. Similarly, the formation of the interfacial liquid layer near the graphene is examined by calculating the number density of liquid atoms in specified space near the graphene in the simulation domain. The numerical results show that the carbon atoms of graphene nanosheets vibrate around their local positions inside the liquid argon. Also, they show that no significant layering of liquid argon near the graphene nanosheet is observed, this last indicates that the interfacial liquid layer near the graphene nanosheet is not formed inside the liquid argon. Therefore, these results lead to the conclusion that the vibration of graphene is mechanism responsible for the lack of the layer liquid around the graphene nanosheet that is dispersed within liquid argon. Furthermore, the liquid layer at the liquid argon- graphene nanosheet interface in nanofluid (argon-graphene) is not a mechanism possible producing the enhanced thermal transport in nanofluid containing graphene nanosheets.

At present, the production of magnesium is mainly carried out semi-continuously with ferrosilicon as reducing agent under high temperature and high vacuum. In order to continuously produce magnesium, a new method of extracting magnesium from low-grade magnesite and calcium carbonate by silicothermal method in flowing inert gas was proposed. The effects of calcium fluoride (CaF2) on decomposition rate, decomposition kinetics, reduction rate of magnesia, and crystal type of dicalcium silicate in reduction slag were investigated in the paper. The experimental results showed that calcium fluoride could accelerate the decomposition of carbonate, and had no side effect on the calcined products. In addition, the analysis results of DTA curves showed that calcium fluoride could reduce the decomposition reaction activation energy and the reaction temperature of carbonate in the prefabricated pellets. The results of reduction experiments showed that proper calcium fluoride could promote the reduction rate of magnesia, and in the temperature range of 1250? ~ 1350?, with the same timeframe, the corresponding calcium fluoride contents were 5%, 3%, and 1% respectively when the reduction rate reached the maximum. Excessive calcium fluoride reduced the reduction rate of magnesia, but it promoted the transformation of dicalcium silicate to ? phase in the reduction slag.

Proportional gas counters are commonly used in the 57Fe Mossbauer spectroscopy for their good energy resolution and insensitivity to magnetic field. However, their counting rate is usually limited by relatively long dead time. This paper demonstrates a detection performance improving technique by registration Kα escape peaks coupled together with main full energy peaks. The validity of using both peaks was verified by transmission and conversion X-rays Mossbauer spectra recording, while using proportional gas counters filled with pure krypton and a mixture of argon and methane. The influence of this method on the resulted α-Fe Mossbauer spectra was studied in a view of resonance effect, energy resolution, spectra baseline, and statistical quality. The presented technique showed that the counting rate of Mossbauer spectra accumulation was increased by 95% while using pure krypton, whereas by using a mixture of argon and methane, the counting rate reached an increase of 27%.

In the present study, CuFeO vertical nanocolumnar structured arrays are deposited on fluorine-doped tin oxide substrates by reactive ballistic deposition technique in an oxygen atmosphere by fixing the deposition angle at 85°. Scanning electron microscopy images shows the presence of arrays of individual columns. The photocurrent density of the CuFeO2 annealed at 650 oC for 2 h in argon is determined to be -0.22 mA cm-2 at 0.4 V versus RHE in 1 M NaOH under AM 1.5 G illumination, while the same annealed in air exhibits a photocurrent density value of 0.12 mA cm-2 at 1.23 V versus RHE. Here, the film annealed in an argon atmosphere at 650 °C exhibits a p-type characteristic with cathodic photocurrent, while the same annealed in air depicts an n-type characteristic with anodic photocurrent. The p-type character was induced by the Cu vacancies and the shift in the conductivity from n-type to p-type is induced by phase transition formation of delafossite CuFeO2 from copper modfied FeO. The generation of photocurrent density from p-CuFeO2 is expected to be from the presence of Cu2+/Cu+ redox couple which is evidenced by X-ray photoelectron spectroscopy.

Laser-induced controllable oxidation coupled with micro-milling (LOMM) provides a feasible way to machine difficult-to-machine materials such as TiB2–TiC ceramic composites. The oxidation mechanism of the material under laser irradiation represents the fundamental issue of LOMM. In this paper, laser-induced controllable oxidation of spark plasma sintered TiB2–TiC ceramic composites as the workpiece material was studied. A three-dimensional finite element model was established based on ABAQUS/CAE 6.14 software to simulate the effect of laser parameters on temperature field distribution and was verified by experiments. The influence of laser processing parameters and assisted gas atmospheres on the oxidation behavior of TiB2–TiC ceramic composites was investigated. Results revealed that the irradiated temperature which had a significant impact on oxidation behavior, increased with an increment of the laser fluence and decreased with an increment of scanning speed with other laser parameters fixed. In addition, based on experimental analysis, the thickness of the oxide-layer increased with an increase of laser fluence and reduced with increasing laser scanning speed. At a laser fluence of 10.78J/cm2 and scanning speed of 1 mm/s as well as in an oxygen-rich atmosphere, a loose and porous oxide-layer was produced on the irradiated surface. Cross-section thicknesses of the oxide-layer and sub-layer reached 63 μm and 22 μm, respectively. Moreover, the thickness of the oxide-layer was 22 μm in air surroundings and hardly be found in argon and nitrogen atmospheres under identical laser parameters, which indicated that oxygen content had a significant influence on the oxidation reaction of the material. The products of the oxide-layer were mainly composed of rutile- and anatase-TiO2. Furthermore, the hardness of the sub-layer was 9.6 ± 0.7 GPa at a laser fluence of 10.78J/cm2 and scanning speed of 1 mm/s, which was far lower than that of the substrate with a hardness of 20 ± 0.7 GPa. This study provides a theoretical basis for subsequent micro-milling.

Cryoablation is the most commonly used type of cryosurgery. Today, this treatment is insufficiently automated and therefore less accurate than alternative technologies that significantly limits and gradually reduces the scope of its application. However, from low temperature engineering point of view cryosurgery has the untapped potential of the improving its accuracy. In this paper three major methodological problems of cryosurgical equipment and procedure improving are considered: the impact on target isotherm location (1) of the soft biotissue moisture content solidification latent heat variation, (2) of the cryoprobe constructions and operating at maximum cooling power including the fluid cryogen features and the accuracy of boundary condition replacing a cryoprobe and (3) target isotherm fixation approach by modifying the cryoprobe operating mode. The numerical results showed that the target isotherm location depends insignificantly on different moisture content of soft biotissue, then it is not a limiting factor for cryoexposure prediction. Also numerical results showed that the theoretically minimum temperature of cryoprobe surface significantly overestimates their movement, this leads to a significant difference between the experimental and simulation results. The typical shape and movement of cryonecrosis isotherm at refined maximum cryoprobe cooling power for two typical constructions of cryoprobes and two cryogens are presented. The novel algorithm of modifying the cryoprobe operation mode for controlled precision cryosurgery is proposed and validated. All this complements the previously obtained data and shows the prospects for performing precision cryosurgery. The total average uncertainty of target isotherm location during the studied preliminary predicting stage of temperature field movement (virtual cryoablation) is estimated no more than ±0.41 mm. This information is expected to be useful for improving the quality of cryosurgery planning algorithms (e.g. for tumor treatment).

This work systematically examines the interactions of alkali metal cations and their isoelectronic halide counterparts with up to six solvating Ar atoms (M+Arn and X-Arn, where M = Li, Na, K, and Rb; X = H, F, Cl, and Br; and n = 1-6) via full geometry optimizations with the MP2 method and robust, correlation-consistent quadruple-ζ (QZ) basis sets. 116 unique M+Arn and X-Arn stationary points have been characterized on the MP2/QZ potential energy surface. To the best of our knowledge, approximately two dozen of these stationary points have been reported here for the first time. Some of these new structures are either the lowest-energy stationary point for a particular cluster or energetically competitive with it. The CCSD(T) method was employed to perform additional single-point energy computations upon all MP2/QZ-optimized structures using the same basis set. CCSD(T)/QZ results indicate that internally solvated structures with the ion at/near the geometric center of the cluster have appreciably higher energies than those placing the ion on the periphery. While this study extends the prior investigations of M+Arn clusters found within the literature, it notably provides one of the first thorough characterizations of and comparisons to the corresponding negatively charged X-Arn clusters.

HfxZr1-xO2 and lanthanum-doped HfxZr1-xO2:La thin films are candidates for applications in ferroelectric random-access memory. Here, we explore the atomic and electronic structure of Hf0.5Zr0.5O2 and Hf0.5Zr0.5O2:La thin films grown by atomic layer deposition. Using X-ray photoelectron spectroscopy, it was found that the oxides under study have an almost identical electronic structure and a bandgap of about 5.4 eV. The Hf0.5Zr0.5O2:La film was shown to consist of the mixture of Hf0.5Zr0.5O2 and La2O3 phases. The bombardment with argon ions of the studied films leads to oxygen vacancy generation in the near-surface layer. The oxygen vacancy concentrations in the bombarded films were evaluated from the comparison of experimental valence band photoelectron spectra with the theoretical ones calculated using the density functional theory.

The study was conducted in order to understand a mechanism of interphase mass transfer between liquid and vapor. The molecular dynamics (MD) simulation is used to examine details of condensation and evaporation from the viewpoint of molecular kinetics. First, molecular boundary conditions for condensing, reflecting, and evaporating molecules are presented for an argon molecule as a function of the surface-normal component of translation energy. The velocity distributions can be expressed by the modified Maxwellian and making use of the condensation coefficient. The condensation coefficient of water is also examined for two kinds of intermolecular potential, the Carravetta-Clementi (C-C) model and the extended simple point charge (SPC/E) model, in order to consider the effect of the surface structure of the liquid on the condensation coefficient. The results indicate that the condensation coefficient of water is close to unity for both models and its dependence on the translation energy is small compared w...

The article reports the excitation of a helical argon atmospheric pressure plasma jet using a pulse modulated 13.56 MHz radiofrequency (RF) power source. This helical structure is observed in open ambient air which is far different from the conventional conical shape. This helical structure originates due to the periodic pressure variation in the discharge region caused by pulse modulated RF (2 kHz modulation frequency (fp)) and propagates downstream into the ambient air. The geometrical characteristics of the observed structure are explored using optical imaging. Moreover, the influence of various input parameters viz., duty cycle (D), gas flow rate (Q), and RF power (P) of the modulated pulse on the formation of helical structure are studied. These helical structures have an implication on the plasma jet chemical features (enhancement of reactive oxygen and nitrogen species (RONS)) as these are involved in increase in air entrainment into the ionization region desired for various plasma applications., 17 pages, 12 figures

Purpose This paper aims at examining the potentiality of using Hibiscus sabdariffa L. calyces’ (Hs) aqueous extract to remove soot stains from the surface of fire-damaged silver gelatin prints. It further studies the cleaning efficiency and impact of both a contact method and a noncontact method with argon dielectric barrier discharge plasma (DBD Ar. plasma) on the different properties of silver gelatin prints. Accordingly, it prompts using economic, eco-friendly materials and methods in the photograph conservation field. Design/methodology/approach To achieve the aims of this paper, four silver gelatin prints were stained with soot and treated with the Hs aqueous extract as a contact method and DBD Ar. plasma combined with the aqueous extract as a noncontact method. The assessment was carried out using digital microscopy, atomic force microscopy and spectrophotometer to study the efficiency of the tested treatments and their impact on the surface of the photographs. Fourier transform infrared was used to monitor the state of the binder after cleaning. Furthermore, the pH and the mechanical properties were measured. Findings The contact method resulted in lower concentrations of Hs extract that efficiently cleaned the surface without causing any stains or damage to the treated photographs. The noncontact method (plasma with an aqueous extract) proved to be less effective in cleaning and made the binder more susceptible to deterioration. Originality/value This paper reveals the success of Hs aqueous extract in cleaning soot on vulnerable photographs' surfaces.

In order to study the effect of gas atmosphere on forming performance of laser powder bed fusion (LPBF), AlSi10Mg alloy was prepared by direct forming and in situ laser remelting under the shielding gas of argon and nitrogen in this study, and its microstructure and properties were characterized and tested, respectively. The results show that the forming performance of AlSi10Mg under nitrogen atmosphere is better than that of argon. Moreover, in situ laser remelting method can effectively enhance the relative density and mechanical properties of AlSi10Mg, in which the densification is increased to 99.5%. In terms of mechanical properties, after in situ remelting, ultimate tensile strength under argon protection increased from 444.85 ± 8.73 to 489.45 ± 3.20 MPa, and that under nitrogen protection increased from 459.21 ± 13.77 to 500.14 ± 5.15 MPa. In addition, the elongation is nearly doubled and the micro-Vickers hardness is increased by 20%. The research results provide a new regulation control method for the customization of AlSi10Mg properties fabricated by LPBF.

Purpose: To consider new possibilities of refractive modeling of the cornea by the radiation of an argon-fluorine excimer laser in ablative and subablative modes after saturation of the stroma with riboflavin. Materials and Methods: Experimental (20 pork, 90 rabbit eyes) and clinical studies on photorefractive and phototherapeutic operations with saturation of the corneal stroma with riboflavin (610 operations) were analyzed. To activate riboflavin, secondary radiation induced by exposure to ablative and subablative energy densities was used. A quick transition to energy densities below the ablation threshold without additional calibrations was carried out using a “Microscan Visum-500” excimer laser (Optosystems, Russia). An objective assessment of the refractive keratomodelling effect and visual results was carried out according to the data of complex optometric studies. Results: Experimental and clinical studies have shown the advantages of refractive keratomodeling by theradiation of an argon-fluorine excimer laser in ablative and subablative modes after saturation of the stroma with riboflavin. Isotonic 0.25% riboflavin solution did not affect the accuracy of refractive ablation and blocked the negative effect of induced secondary radiation on keratocytes and corneal nerves. This reduced the aseptic inflammatory response and the risk of developing an irreversible form of fibroplasia. Ablation with riboflavin initiated a damped crosslinking effect, which increased the photoprotective and strength properties of the thinned cornea. A refractive keratomodelling effect was found when energy densities were applied below the stromal ablation threshold. The magnitude of this refractive effect depended on the total radiation dose and the topography of the affected area. This approach made it possible to implement laser-induced refractive keratomodeling without ablation of the corneal stroma. Conclusion: Refractive modeling of the cornea by the radiation of an argon-fluorine excimer laser in ablative and subablative modes after saturation of the stroma with riboflavin opens up new possibilities in laser correction of ametropia.

Background M.D. simulation is a kind of computational branch of physics. In this method, the interaction between particles at intervals of time according to physics laws is simulated by a computer. Methods In this computational study, metallic nanoparticles' effect in a phase transition of atomic fluid is described. In this research, the molecular dynamics (M.D.) method was used by Argon (Ar) atoms simulations as base fluid and copper (Cu) structure as nanoparticles between Platinum (Pt) walls. Further, the atomic barrier with cubic and rectangular shapes in simulated walls was intended for more atomic analysis of fluid/nanofluid. Some parameters such as potential energy, temperature, and thermal conductivity were reported for the atomic behavior description of defined structures. Also, in this study, change the number of roughness and changes in the radius of copper nanoparticles in the simulation structure were investigated. Significant findings The MD results show that simulated structures reach to equilibration phase after 2000000-time steps. Further, the heat flux increases by atomic barrier inserting into Pt walls. As a result, more fluid particles show the phase phenomenon in the M.D. box. Also, the addition of Cu nanoparticles to the Ar fluid shows a similar result in which these nanoparticles improve the base fluid's thermal behavior. Finally, the number of condensed argon fluid particles into the liquid phase increases from 3221 to 3347 particles.

Controlled ice nucleation offers several key benefits to the pharmaceutical lyophilization process, including reducing lyophilization cycle time, control of ice crystal morphology, and increased consistency of lyophilized product quality attributes. The rapid depressurization based controlled ice nucleation technique is one of the several demonstrated controlled ice nucleation technologies and relies on the rapid discharge of an inert pressurized gas to induce ice nucleation. In this work, a series of custom wireless gas pressure and temperature sensors were developed and applied to this process to better understand the mechanism of controlled ice nucleation by depressurization. The devices capture highly transient conditions both in the chamber near the vial and within the vial headspace throughout the entire process. The effects of ballast gas composition, initial charge pressure, and vial size on gas pressure and headspace/chamber temperature are explored individually. We model the depressurization as an isentropic process, allowing the influence of these parameters to be evaluated quantitatively. It is demonstrated that monatomic gases (e.g. argon) with low thermal conductivity produce the most favorable conditions for ice nucleation at the end of depressurization, based on temperature drop in the vial headspace. Experimental data also reveal a correlation between initial charge pressure and vial size with the temperature drop within the vial headspace, during depressurization. These findings ultimately provide deeper insight into the rapid depressurization based controlled ice nucleation process and help lay the foundation for a more robust process development and control.

In the present study, type 316L(N) bead-on-plates were welded using Activated-Tungsten Inert Gas (A-TIG) welding process with argon and helium gas at various ratios to evaluate the arc characteristics. The welding process parameters including shielding gas composition were optimized using the design of experiments to join 11 mm thick plate in a single pass. In addition, the A-TIG welding technique using optimized process parameters was developed to weld plates up to 20 mm thickness with significantly reduced heat input. High power density of helium arc shielding leads to constricted arc column that enhances arc efficiency and produces deeper penetration.

Sander Bekeschus and Sylvain Iséni equally contributed to this work as first authors.; International audience; Parameter studies of plasma treatment are informative about the optimal use of this technology in biomedical applications such as the argon radio-frequency plasma jet kINPen. However, the interdependence of the plasma-dissipated power in relation to input current and feed gas modulation on the resulting biological consequences has not been studied so far. To this end, a parameter study is presented, and the effect on human immune cell viability was investigated across different input current power and argon with oxygen/nitrogen feed gas admixture settings. It was found that with both nitrogen and oxygen admixtures, a concentration-dependent change in plasma-dissipated power emerged, which converged at 27.5 mA and 26.5 mA, respectively. The extent of cytotoxicity in immune cells confirmed the relevance of these findings, which were in congruency with the plasma dissipated powers identified. These findings underline the critical role and input parameter-dependent action of plasma sources for biomedical application.Dr Sander Bekeschus and Dr Sylvain Iséni equally contributed to this work as first authors.

When seeking for satisfactory metacomposites with negative permittivity behavior, an important factor which should be taken into consideration is how to realize a weakly negative permittivity (less than 100). A novel strategy has been proposed accordingly to prepare ternary multiwalled carbon nanotubes/titanium nitride/copper calcium titanate (MWCNT/TiN/CCTO) composites by a facile sintering method in an inert atmosphere. The negative permittivity was observed after the TiN-MWCNT network was constructed among the composites. TiN provided sufficient free electrons and MWCNT were regarded as transporter bridge. Under the synergistic effect of TiN and MWCNT, the negative permittivity decreased by several orders of magnitude owing to the dilution of overall electron density in the resulting composites. Exceptionally, when the permittivity switched from positive to negative along with a resonance, a Lorentz-like negative permittivity was observed in low frequency region. Meanwhile, the Drude-like negative permittivity derived from plasma oscillation was also observed in the higher frequency region. Further investigation confirmed that the permittivity was closely related to the reactance. The positive-negative reactance transition was consistent with the negative-positive permittivity transition, and the epsilon-near-zero was achieved near the zero-crossing point of permittivity. Moreover, the influence of different sintering atmospheres (nitrogen and argon) on the negative permittivity behavior was also explored. This work provides an effective approach for the realization of weakly negative permittivity, and presents, to our knowledge, the first investigation into the influence of sintering atmosphere on negative permittivity.

In plasma material processing, vacuum ultraviolet (VUV) emission is released from gas discharges, leading to undesirable results. Energetic VUV photons enable the creation of an electron-hole pair current when their energy is larger than the bandgap energy of the plasma-facing top layer during plasma material processing. For example, the high energy of VUV photons from helium (21.2 eV), argon (11.6 eV), and oxygen (13.6 eV) is sufficient to generate induced currents in SiO2 thin films. These feedstock gases are widely used in many procedures utilizing low-temperature industrial plasmas. Thus, the VUV emission evolution with both the power ratio between high (60 MHz) and low (2 MHz) frequencies and pulse duty ratio of the low-frequency radio frequency (rf) power in a dual-frequency capacitively coupled plasma, which is indispensable in modern plasma etching processes, was investigated. Both the power ratio between high and low frequencies and the pulse duty ratio changed the electron temperature, leading to evolution of the VUV emission intensity.

The effect of the process gas during laser powder bed fusion (L-PBF) was investigated using high-speed shadowgraphy while melting Ti-6Al-4V powder under high purity argon, helium, and a mixture of both, on a laboratory-scale machine. These recordings reveal that the generation of incandescent spatters can be reduced by at least 60% using pure helium and by ∼30% using addition of helium to argon in comparison to the use of traditional argon. The quantity of colder spatters appeared unaffected by the change of process gas. Different configurations of gas flow versus laser scanning direction were investigated and revealed that fumes and spatters are less accumulated at the laser spot with helium addition. Furthermore, the use of the argon–helium mixture proved to be as efficient as pure argon in the dragging and extraction of the fumes. Shadowgraphs revealed the more rapid expansion of fumes in helium-rich atmospheres, limiting the accumulation of scattering objects close to the laser spot and thus melt pool instability. These results were correlated to process snapshots on an industrial-scale system, confirming the reduction of hot spatter generation. Finally, the findings put in evidence the more rapid cooling of spatters with helium addition to the process gas – a promising aspect to limit powder bed degradation during L-PBF. In addition, the use of mixtures of helium and argon would be economically interesting compared to pure helium, typically more expensive than the traditionally used argon.

Made available in DSpace on 2022-05-01T08:44:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-11-15 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) In this research, the influence of synthesis process under Te4+ ion formation in lithium tellurite glass was investigated based in their optical and structural characteristics. The same 80TeO2 + 20Li2O nominal composition (in mol%) was used to prepare glasses with different synthesis temperatures (Ts = 600, 700, 750, 800 and 850 °C) and atmospheres (room, oxygen and argon). The study was based in the investigation of the UV–Vis absorption spectroscopy, Raman spectroscopy, photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. The linear refractive index was measured in function of the wavelength ranging all the visible region. The results indicate that Te4+ concentration into the glass is strongly dependent on both synthesis temperature and atmosphere. A more intense emission is observed in glasses prepared in oxygen atmosphere and in the 750–800 °C temperature range. Programa de Pós-Graduação em Recursos Naturais - PGRN Universidade Estadual de Mato Grosso do Sul - UEMS Grupo Vidros e Cerâmicas Universidade Estadual Paulista - UNESP Instituto de Física de São Carlos - IFSC Universidade de São Paulo - USP Grupo Vidros e Cerâmicas Universidade Estadual Paulista - UNESP CAPES: 00.889.834/0001-08

In this article, we studied the annealing process of AuCu layers deposited on TiO2 nanotubes (NTs) conducted in various atmospheres such as air, vacuum, argon, and hydrogen in order to obtain materials active in both visible and UV-vis ranges. The material fabrication route covers the electrochemical anodization of a Ti plate, followed by thin AuCu film magnetron sputtering and further thermal treatment. Scanning electron microscopy images confirmed the presence of spherical nanoparticles (NPs) formed on the external and internal walls of NTs. The optical and structural properties were characterized using UV-vis, X-ray diffraction, and X-ray photoelectron spectroscopies. It was proved that thermal processing under the argon atmosphere leads to the formation of a CuAuTi alloy in contrast to materials fabricated in air, vacuum, and hydrogen. The electrochemical measurements were carried out in NaOH using cyclic voltammetry, linear voltammetry, and chronoamperometry. The highest photoactivity was achieved for materials thermally treated in the argon atmosphere. In addition, the Mott-Schottky analysis was performed for bare TiO2 NTs and TiO2 NTs modified with gold copper NPs indicating a shift in the flatband potential. Overall, thermal processing resulted in changes in optical and structural properties as well as electrochemical and photoelectrochemical activities.

A miniaturized and improved method for Apparent Total Nitroso Compounds determination in liquid matrices was developed. The main improvement is based on a miniaturized and modified apparatus for chemical denitrosation of nitroso compounds by hydrogen bromide in a glacial acetic acid mixture. The reaction is carried out in a teflon reaction coil while the reaction product, gaseous nitric oxide, is drifted to a chemiluminescence detector by the flow of argon together with a vacuum obtained by the detector's oil pump. The apparatus significantly increased the efficiency of the Apparent Total N-Nitroso Compounds determination (compared to the previous method), specifically, the dead volume of the apparatus was significantly decreased, and the effect of the reverse reaction was eliminated as well. The apparatus shortens the analysis time (1.4 min/injection), further it provides a lower detection limit (3 μg(N-NO)/l), quantification limit (10 μg(N-NO)/l), and method uncertainty (15%), and is simpler for the operation.

Isotherms for nitrogen adsorption at 77 K and argon at 87 K in mesoporous adsorbents exhibit a hysteresis loop with a lower closure point (LCP) at a reduced pressure P/P0 of approximately 0.4. This observation has been attributed to the homogeneous nucleation of vapor bubbles in the condensate within a cavity when it has been stretched beyond its tensile strength limit; on this basis, it is argued that the LCP is a property of the adsorbate fluid. However, our extensive computer simulations of homogeneous cavitation invariably give an LCP of 0.25, rather than 0.4. In our quest for the microscopic origin of the observed LCP, we have explored the possible role of two properties of a solid adsorbent: surface heterogeneity and the nature of the conduits connecting a cavity to the surrounding gas. In the first case, cavitation originates from the birth of nanobubbles formed at weakly adsorbing patches on the pore walls, which we refer to as surface-induced cavitation; in the second case, referred to as window-induced evaporation, the condensate in the cavity evaporates because of the snapping of the adsorbate in the short conduits (or windows) connecting the cavity to the surrounding gas. Our simulations show that the evaporation of the condensate from a cavity occurs at a reduced pressure of around 0.4 only when the holding potential of the patches in the surface-induced model is so weak that an open adsorbent with a similar holding potential would be nonwetting. The hypothesis that weakly adsorbing patches are the reason for loop closure at a relative pressure of 0.4 must therefore be rejected because this condition is unlikely to be found in real adsorbent solids. On the other hand, window-induced evaporation of the condensate from a cavity at 0.4 occurs when the windows are of nanodimensions. We argue that windows of nanodimensions are very probable in adsorbents consisting of agglomerations of microparticles.

This review discusses the main methods for producing spherical powder particles of corrosion-resistant steels as a material widely used in all industries. Also the examples of products made by modern additive methods are described. Currently, spherical powder particles of corrosion-resistant steels are used in the following additive methods: selective laser melting, selective laser sintering, direct laser sintering, and electron beam melting. Each of these methods has its own requirements for the characteristics of spherical powder particles of corrosion-resistant steels. The review provides a brief description of the principles of operation of each method and the requirements for spherical powder particles of corrosion-resistant steels. It also considers a detailed description of each method of additive manufacturing with a description of the principle of operation and specific examples of obtaining spherical particles of corrosion-resistant steel powders with indication of their properties (morphology, structural features, chemical composition, fluidity, bulk density). A comparative analysis was carried out with a description of disadvantages and advantages of each method. Examples of the use of spherical particles of corrosion-resistant steel powders for the manufacture of products by various additive methods (including post-processing) are given with description of the final products characteristics. Based on the data presented, a conclusion was made about the preferred methods for obtaining spherical particles of corrosion-resistant steel powders for specific additive methods used in modern industry. The review considers the following methods for producing spherical powder particles: water atomization (atomization of liquid metal with a jet of water under pressure); gas atomization (atomization of the melt with a jet of inert gas (argon or nitrogen) under pressure); centrifugal atomization (atomization of molten metal with a high-speed rotating disc); ultrasonic atomization (atomization of liquid metal by ultrasound); non-contact atomization (atomization of liquid metal with a powerful pulse of electric current); plasma wire spraying; plasma spraying of a rotating electrode; plasma spheroidization.

We report the spectroscopic observation of the jet-cooled para-ethynylbenzyl (PEB) radical, a resonance-stabilized isomer of C9H7. The radical was produced in a discharge of p-ethynyltoluene diluted in argon and probed by resonant two-color two-photon ionization (R2C2PI) spectroscopy. The origin of the D0(2B1)-D1(2B1) transition of PEB appears at 19,506 cm-1. A resonant two-color ion-yield scan reveals an adiabatic ionization energy (AIE) of 7.177(1) eV, which is almost symmetrically bracketed by CBS-QB3 and B3LYP/6-311G++(d,p) calculations. The electronic spectrum exhibits pervasive Fermi resonances, in that most a1 fundamentals are accompanied by similarly intense overtones or combination bands of non-totally symmetric modes that would carry little intensity in the harmonic approximation. Under the same experimental conditions, the m/z = 115 R2C2PI spectrum of the p-ethynyltoluene discharge also exhibits contributions from the m-ethynylbenzyl and 1-phenylpropargyl radicals. The former, like PEB, is observed herein for the first time, and its identity is confirmed by measurement and calculation of its AIE and D0-D1 origin transition energy; the latter is identified by comparison with its known electronic spectrum (J. Am. Chem. Soc.,2008,130, 3137-3142). Both species are found to co-exist with PEB at levels vastly greater than might be explained by any precursor sample impurity, implying that interconversion of ethynylbenzyl motifs is feasible in energetic environments such as plasmas and flames, wherein resonance-stabilized radicals are persistent.

The structure characteristics of Ar−Kr mixtures deposited under special conditions have been investigated in the whole interval of concentrations applying the transmission electron diffraction technique (THEED). The samples were prepared in situ by condensing a gas mixture preliminary cooled down to the sub-liquid-nitrogen level onto substrates at T = 6 K and 20 K. The experimental results show that the structure and morphology of the Ar−Kr condensates are dependent on the nucleation dynamics prevailing in the course of the sample formation. It is shown that cooling a gas mixture is favorable to the clusterization of solute atoms in the gas flow. The krypton small clusters can serve as condensation clusters. The phase boundaries of the condensates have been determined. Regular Ar−Kr solutions are formed when the contents of one of the components are low (0−10 mol % Ar), (0−5 mol % Kr). The diffraction patterns of the condensates with prevailing Kr contents corresponded to a mixture of Kr-enriched fcc solutions and a dispersed phase of argon. The excess Kr contents are due to the specific morphology of the solutions dictated by condensation conditions. The Ar-based samples contained a mixture of two crystalline phases (an fcc solution and the hcp phase of nearly pure argon) and a glass phase of nearly pure krypton. In the concentration range 58−78 mol % Ar the new morphological form of the Ar−Kr condensates resembles the gel. The phase state diagram of the Ar−Kr condensates has been obtained.

Any biological material contains dissolved gases that affect physical and biological processes associated with cooling and freezing. However, in the cryobiology literature, little attention has been paid to the effect of gasses on cryopreservation. We studied the influence of helium, neon, krypton, xenon, argon, nitrogen, and sulfur hexafluoride on the survivability of HeLa and L929 cell lines during cryopreservation. Saturation of a cell suspension with helium, neon, and sulfur hexafluoride enhanced survival of HeLa and L929 cells after cryopreservation. Helium exerted the most significant effect. For a range of noble gases, the efficiency of the positive effect decreased as the molecular mass of the gas increased. This paper discusses possible mechanisms for the influence of gases on the cryopreservation of biological material. The most probable mechanism is the disruption of the frozen solution structure with gas-filled microbubbles produced during water crystallization. Ultimately, it was concluded that helium and neon can be used to improve methods for cryopreservation of cell suspensions with a low concentration of conventional penetrating cryoprotectants or even without them.

In this paper, the flow field characteristics of Oblique Detonation Waves (ODWs) induced by a finite wedge under argon dilution are studied by solving the Euler equations with a detailed chemical model of hydrogen and air. First, the effects of the expansion waves, argon concentration, geometric parameters, and Mach number on the ODW are discussed. The results show that the changes of these parameters may make the oblique detonation not be initiated. Then, the ODW initiation criterion of the finite wedge is summarized, as the characteristic length of the induction zone LC and the characteristic length of the oblique wedge LW meet the condition LC/LW

This work encompasses identification of the crystal structure and analysis of the TiC precipitates in 18Cr-10Ni-Ti austenitic stainless steel under Ar-ions irradiation. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) are used. Orientation relationship of TiC particles in surrounding matrix are indicated by HRTEM and diffraction patterns. The size of the precipitates is found to be critical: the coherency of TiC is kept at the interfaces when the precipitate is in the stage of nucleation, whereas the growth of precipitate up to 10 nm can lead to the loss of coherency in the austenitic steel. The findings suggest that the incoherent precipitate-matrix interface is an important point defect sink and contributes to inert gas bubble formation at elevated irradiation temperatures.

To modify easily chemical consistence of molten steel metallurgical plants usually add alloys in a form of lumps through a hopper at ladle`s top. The problem is a large variety of adjusted technological conditions for this process, which leads to iterative discovery of rational ones. The article presents synthesis of a mathematical model for the mentioned process using Navier-Stokes and Euler-Lagrange equations. It is designed for researching of process modes depending on: a horizontal position of addition hopper relatively to argon plug at ladle bottom, an average diameter of spherical addition lumps, a total mass of addition heap, a necessity of the second hopper, a temperature of the melt. It takes into account interconnected three-dimensional fluid and solids dynamics, temperature exchange between melt and lump, also it computes level of concentration homogenization. A numerical experiment shows a significantly better addition homogenization when two hoppers are simultaneously used for a feeding. Adequacy checks are performed using ice balls in air-stirred water.

We report electron diffraction of cationic argon nanoclusters embedded in superfluid helium droplets. Superfluid helium droplets are first doped with neutral argon atoms to form nanoclusters, and then the doped droplets are ionized by electrons. The much lower ionization energy of argon ensures that the positive charge resides on the Ar nanocluster. Using different stagnation temperatures therefore droplets with different sizes, we have been able to preferentially form a small ionic cluster containing 2 – 4 Ar atoms and a larger cluster containing 7 – 11 atoms. The fitting results of the diffraction profiles agree with structures reported from theoretical calculations, containing a cationic trimer core with the remaining atoms largely neutral. This work testifies to the feasibility of performing electron diffraction from ionic species embedded in superfluid helium droplets, dispelling the concern over the particle density in the diffraction region. However, the large number of neutral helium atoms surrounding the cationic nanoclusters poses a challenge for the detection of the helium solvation layer, and the detection of which awaits further technological improvements.

A certified reference material (CRM) of sulfur dioxide (SO2) gas, with a certified value of purity, was developed for the preparation of primary reference gas mixtures of SO2 in nitrogen (N2) gas. Impurity analyses by “subtraction method” were performed using a gas chromatograph (GC) with a thermal conductivity detector (TCD), a GC with a flame ionization detector (FID), and a Fourier transform infrared spectrometer (FT-IR), all calibrated with gas mixtures traceable to the Internal System of Units (SI). First, qualitative analysis using the FT-IR was performed on two samples of liquefied SO2 of different quality grades, contained in gas cylinders. Using the FT-IR and the GC-TCD, carbon dioxide (CO2) was detected in the lower- and higher-grade cylinders at approximately 0.5 cmol/mol and 5 µmol/mol, respectively. The FT-IR did not detect any sulfur compound peaks, other than SO2, in the higher-grade sample. Other atmospheric constituents such as N2, oxygen (O2), water (H2O), argon (Ar), and methane (CH4) were also tested for in this sample. The detection limit of H2O in the FT-IR was 49 µmol/mol, while those of N2, O2, Ar, by the GC-TCD were a few µmol/mol, and CH4, using the GC-FID, were better than 1 µmol/mol. The high detection limit of H2O was due to large baseline fluctuations when measuring the FT-IR spectrum of the SO2 gas. Responses corresponding to these analytes were not detected or were detected below the detection limits. For an estimation of purity by the subtraction method, each reported mol fraction was regarded as half the value of each detection limit, except for the CO2. The purity and its expanded uncertainty [k = 2] of the high-purity SO2 gas by the subtraction method were 99.9964% and 0.0028%, respectively.

Optimization of mathematical model of flow field in slab continuous casting mold was performed by means of industrial measurement and mathematical modeling. The rod deflection method was used to quantitatively measure the velocities near the mold surface at high temperature. The measurement results were compared with the simulation results of three mathematical models at different argon gas flow rates of 6, 10 and 14 L min−1. The model 1 neglects the mold powder layer, thermal effect and solidified shell. The model 2 only considers the influence of mold powder layer. The model 3 considers the influence of mold powder layer, thermal effect and solidified shell on the flow field. In all three models, the diameter of argon bubbles obeys Rosin–Rammler distribution fitted according to the experimental data of others’ previous work. With increasing the argon gas flow rate, the velocity of liquid steel near the mold surface decreases. The model 1 seriously underestimates the shear stress of liquid steel near the mold surface, and its calculation results show higher velocity near the mold surface, lower turbulent kinetic energy and wider distribution of argon gas bubbles in the mold. The simulation results of model 2 only considering the viscous resistance of the mold powder layer to liquid steel makes the velocity near the surface lower than the measurement results obviously. The calculated velocities near the mold surface with model 3 are in best agreement with the measured results, showing the reasonable spatial distribution range of argon bubbles in the mold and the moderate turbulent kinetic energy. In the present conditions, the best argon gas flow rate is 10 L min−1 due to the moderate velocity near the mold surface, the appropriate distribution of argon gas bubbles in the mold and the smallest fluctuation amplitude on the mold surface.

Two variants of the self-propagating high-temperature synthesis process, namely SHS from elements and SHS metallurgy, were combined to obtain cast materials based on the MAX phases of Cr2AlC and (Cr0,7Ti0,3)2AlC. Experiments involved mixtures with compositions calculated according to the chemical scheme 70%(Cr2O3 + 3Al + C)/(2Ti + Al + C) + + 30%(3CaO2 + 2Al). Synthesis was carried out in a 3 l reactor at an argon pressure of 5 MPa. The structure and phase composition of the reaction product were studied by X-ray diffraction and scanning electron microscopy. It was found during the research that the ratio of original reagents has a significant effect on the synthesis parameters and phase composition of desired products. The possibility of obtaining a cast material based on the titanium-doped Cr2AlC phase was shown. It was found that the resulting product is a composite material based on the (Cr1–хTiх)2AlC (х = 0,18÷0,28) phase, and the content of this phase is 43–62 wt.% depending on the original ratio of reagents. The material microstructure features by the presence of laminate layers with carbide grain inclusions. The end product contains carbide (Ti0,9Cr0,1C, Cr7C3, Cr3С2)and intermetallic (Al8Cr5, AlTi3) impurities due to the insufficient life time of a melt formed in the combustion wave.

We report a viable method to produce nanocrystalline graphene films on polycrystalline nickel (Ni) with enhanced N doping at low temperatures by a cold-wall plasma-assisted chemical vapor deposition (CVD) method. The growth of nanocrystalline graphene films was carried out in a benzene/ammonia/argon (C6H6/NH3/Ar) system, in which the temperature of the substrate heated by Joule heating can be further lowered to 100 °C to achieve a low sheet resistance of 3.3 kΩ sq-1 at a high optical transmittance of 97.2%. The morphological, structural, and electrical properties and the chemical compositions of the obtained N-doped nanocrystalline graphene films can be tailored by controlling the growth parameters. An increase in the concentration of atomic N from 1.42 to 11.28 atomic percent (at.%) is expected due to the synergetic effects of a high NH3/Ar ratio and plasma power. The possible growth mechanism of nanocrystalline graphene films is also discussed to understand the basic chemical reactions that occur at such low temperatures with the presence of plasma as well as the formation of pyridinic-N- and pyrrolic-N-dominated nanocrystalline graphene. The realization of nanocrystalline graphene films with enhanced N doping at 100 °C may open great potential in developing future transparent nanodevices.

This study investigated the microstructures and properties of deposits protected by seven different proportions of N2 and Ar by performing wire-arc additive manufacturing of the 5356 aluminium alloy. The results show that when the proportion of N2 in the shielding gas was larger than and equal to 50%, flaky nitrides were generated in the deposits. With an increase in the proportion of N2 in the shielding gas, the number and size of nitrides in the deposits as well as the fluctuation frequency and amplitude of the microhardness of the deposits all increase. The existence of flaky nitrides incurs a low ultimate tensile strength of additively manufactured parts protected by a mixed gas containing N2. The presence of large-size flaky nitrides between layers in the deposits leads to a large difference in tensile properties in the horizontal and vertical directions of the deposit. Tensile fracture shows that the deposits were fractured in the mixed mode of ductile and brittle fracture.