Helium Atmosphere Research Articles

DETERMINATION OF FACTORS AFFECTING THE STABILITY OF WELDED TIPS OF OXYGEN LANCE

It has been established that the most likely cause of crack formation is differences in the chemical composition of the welding wire, the material of the Laval nozzle and the outer cage of the lance tip. For example, the difference in copper content is 6.79%. The microstructures of the weld, Laval nozzle metal, and outer lance tip rim were analyzed and compared along the cross section of the weld location. Microcracks located along the grain boundaries were detected, which is probably due to the appearance of weak compounds with low ductility and non-propagation at the grain boundaries. In the structure of welds, accumulations of oxygen inclusions along the boundaries of crystallites were found, which leads to copper embrittlement and can contribute to weld failure. Freezing a layer of converter slag with low thermal conductivity on the tip surface reduces the thermal conductivity of the formed slag metal layer and heat transfer to the cooling water. Even if there is a 1 mm layer of slag on the surface of the weld, thermal conductivity decreases by 79-95%, depending on the thickness of the slag and its properties, respectively. If there is a layer of slag on the surface of the weld, the heat transfer decreases by 51-56% (at 1 mm of slag) and by 72-88% at 20 mm, respectively.In order to prevent the formation of cracks between the Laval nozzle and the outer cage of thehandpiece, it is advisable to follow the following recommendations when performing welding operations. In the simplest case, the first welded layer should be performed using a non-consumable electrode (tungsten or graphite) in an argon or helium atmosphere, which will ensure the formation of a reliable, tight weld around the entire circumference of the nozzle. To reduce stresses in the weld, subsequent welded layers should be performed in alternating directions. A more effective option is the technology according to which, after the first weld is applied, the nozzle is connected to the tip from the inside with a partial (discrete) or continuous weld, which minimizes the likelihood of failures and can ensure the sealing of the tip when the initial cross-section of the Laval nozzles increases to the critical ignition diameter. The implementation of an internal weld will reduce mechanical loads on the external weld, especially when using metal hose expansion joints, and increase the strength of the welded joint as a whole.

JWST Resolves Collision-induced Absorption Features in White Dwarfs

Infrared-faint white dwarfs are cool white dwarfs exhibiting significant infrared flux deficits, most often attributed to collision-induced absorption (CIA) from H2–He in mixed hydrogen–helium atmospheres. We present James Webb Space Telescope (JWST) near- and mid-infrared spectra of three such objects using Near-Infrared Spectrograph (0.6–5.3 μm) and Mid-Infrared Instrument (5–14 μm): LHS 3250, WD J1922+0233, and LHS 1126. Surprisingly, for LHS 3250, we detect no H2–He CIA absorption at 2.4 μm, instead observing an unexpected small flux bump at this wavelength. WD J1922+0233 exhibits the anticipated strong absorption feature centered at 2.4 μm, but with an unexpected narrow emission-like feature inside this absorption band. LHS 1126 shows no CIA features and follows a λ −2 power law in the mid-infrared. LHS 1126's lack of CIA features suggests a very low hydrogen abundance, with its infrared flux depletion likely caused by He–He–He CIA. For LHS 3250 and WD J1922+0233, the absence of a 1.2 μm CIA feature in both stars argues against ultracool temperatures, supporting recent suggestions that infrared-faint (IR-faint) white dwarfs are warmer and more massive than previously thought. This conclusion is further solidified by Keck near-infrared spectroscopy of seven additional objects. We explore possible explanations for the unexpected emission-like features in both stars, and temperature inversions above the photosphere emerge as a promising hypothesis. Such inversions may be common among the IR-faint population, and since they significantly affect the infrared spectral energy distribution, this would impact their photometric fits. Further JWST observations are needed to confirm the prevalence of this phenomenon and guide the development of improved atmospheric models.

Finite-field Cholesky decomposed coupled-cluster techniques (ff-CD-CC): theory and application to pressure broadening of Mg by a He atmosphere and a strong magnetic field.

For the interpretation of spectra of magnetic stellar objects such as magnetic white dwarfs (WDs), highly accurate quantum chemical predictions for atoms and molecules in finite magnetic field are required. Especially the accurate description of electronically excited states and their properties requires established methods such as those from coupled-cluster (CC) theory. However, respective calculations are computationally challenging even for medium-sized systems. Cholesky decomposition (CD) techniques may be used to alleviate memory bottlenecks. In finite magnetic field computations, the latter are increased due to the reduction of permutational symmetry within the electron-repulsion-integrals (ERIs) as well as the need for complex-valued data types. CD enables a memory-efficient, approximate description of the ERIs with rigorous error control and thus the treatment of larger systems at the CC level becomes feasible. In order to treat molecules in a finite magnetic field, we present in this work the working equations of the left and right-hand side equations for finite field (ff)-EOM-CD-CCSD for various EOM flavours as well as for the approximate ff-EOM-CD-CC2 method. The methods are applied to the study of the modification of the spectral lines of a magnesium transition by a helium atmosphere that can be found on magnetic WD stars.

Hot Uniaxial Pressing and Pressureless Sintering of AlCrCuFeMnNi Complex Concentrated Alloy-A Comparative Study.

External pressure is often applied during sintering to obtain materials with improved properties. For complex concentrated alloys (CCAs), this processing step is commonly performed in vacuum. However, this can promote the evaporation of elements and increase the oxide content, thereby degrading the properties of the alloy. In this study, we compared the microstructures and properties of AlCrCuFeMnNi CCA samples obtained by hot uniaxial pressing sintering (HPS) and pressureless sintering (PLS) using a helium atmosphere purified by an oxygen getter system. The powders were prepared from mixtures of CrFeMn, AlNi and Cu and sintered by HPS at 900 °C for 1 h with an applied pressure of 30 MPa and by PLS at 1050 °C for 1 h. The samples were characterised using X-ray diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattering diffraction, density measurements and hardness tests. It was found that the oxygen getter system promoted oxygen partial pressure values at sintering temperatures similar to those of a mixture of 90% helium and 10% hydrogen. The HPS allowed us to obtain almost fully dense samples with a smaller average grain size and finer distribution of aluminium oxides than PLS. These differences increased the hardness of the samples sintered under pressure.

Evaluating the Effect of Argon and Helium Atmospheric Cold Plasma Jets on Wound Healing in Rats: A Comparative Histopathological and Biochemical Analysis

Background: Cold atmospheric plasma (CAP) has emerged as a promising therapy for wound healing to deliver controlled doses of reactive species to tissues. Argon and helium, as gases used in CAP, are noted for their unique properties and therapeutic potential. Objectives: This study compared the effects of argon and helium atmospheric cold plasma jets on wound healing in a rat model, assessing histopathological changes and biochemical parameters. Methods: This randomized, controlled experimental study involved 18 male Wistar rats randomly assigned to control, helium-treated, and argon-treated groups. Wounds were created between the shoulders under anesthesia, treated with respective plasmas, and monitored for healing progress through macroscopic and microscopic evaluations. Results: Hemoglobin (HGB) and hematocrit (HCT) levels were significantly higher in experimental groups compared to controls (P < 0.05), while mean corpuscular volume (MCV) was lower (P < 0.05). Tumor necrosis factor alpha (TNF-α) levels were highest in helium-treated and lowest in argon-treated rats (P < 0.05). Argon-treated rats showed enhanced IL-6, hyperemia, angiogenesis, and re-epithelialization, with lower TNF-α and necrotic layer thickness than other groups (P < 0.05). Conclusions: Both argon and helium atmospheric cold plasma jets enhanced wound healing in rat models, demonstrating superior efficacy in promoting angiogenesis and re-epithelialization processes.

Porous Copolymers of 3-(Trimethoxysilyl)propyl Methacrylate with Trimethylpropane Trimethacrylate Preparation: Structural Characterization and Thermal Degradation

Porous polymeric microspheres are among the most effective adsorbents. They can be synthesized from numerous monomers using different kinds of polymerization techniques with a broad selection of synthesis factors. The main goal of this study was to prepare copolymeric microspheres and establish the relationship between copolymerization parameters and the porosity and thermal stability of the newly synthesized materials. Porous microspheres were obtained via heterogenous radical copolymerization using 3-(trimethoxysilyl)propyl methacrylate (TMPSM) as functional monomers and trimethylolpropane trimethacrylate (TRIM) as the crosslinker. In the course of the copolymerization, toluene or chlorobenzene was used as the pore-forming diluent. Consequently, highly porous microspheres were produced. Their specific surface area was established by a nitrogen adsorption/desorption method and it was in the range of 382 m2/g to 457 m2/g for toluene and 357–500 m2/g in the case of chlorobenzene. The thermal degradation process was monitored by thermogravimetry and differential scanning calorimetry methods in inert and oxidative conditions. The copolymers were stable up to 269–283 °C in a helium atmosphere, whereas in synthetic air the range was 266–298 °C, as determined by the temperature of 5% mass loss. Thermal stability of the investigated copolymers increased along with an increasing TMPSM amount in the copolymerization mixture. In addition, the poly(TMSPM-co-TRIM) copolymers were effectively used as the stationary phase in GC analyses.

Resolving studies of Balmer alpha lines relevant to the LIBS analysis of hydrogen isotope retention

Utilizing Laser-Induced Breakdown Spectroscopy (LIBS) for detecting deuterium and tritium retention in fusion devices poses a significant challenge due to the experimental limitations in resolving hydrogen isotope Balmer alpha lines (Hα, Dα, and Tα). This study utilizes the Rayleigh criterion to distinguish Tα and Dα lines by determining the maximum line widths and corresponding plasma parameters. Experimental validation was performed through LIBS analysis of heavy water-doped graphite/silica gel targets in both argon and helium atmospheres to assess the predicted plasma parameters and line profile shapes. The optimization of laser pulse energy, gas pressure, delay, and gate times aimed at achieving fully resolved lines based on the intensity, width, and the dip between deuterium and hydrogen Balmer alpha lines. By fine-tuning these experimental parameters, the study successfully achieved a dip of less than 10 % between the Hα and Dα lines with a satisfactory signal-to-noise ratio, demonstrating the feasibility of fully resolving the Tα and Dα lines. These findings underscore the potential of LIBS in enhancing the detection of deuterium and tritium retention in fusion devices.

Formation conditions of the tungsten porous thin film with pulsed laser deposition under various gas atmosphere

Abstract Pulsed laser deposition (PLD) under gas atmospheres has been used to fabricate thin films for various applications. In this study, PLD was performed under various gas atmospheres (helium, oxygen, and argon) using tungsten (W) to investigate the morphology of thin films. Various types of structures were formed, including uniform, nanoparticles, and columnar structures. In particular, the substrate fabricated at an argon pressure of 100 Pa had a high porosity and a low light reflectance in the 200–1400 nm wavelength range. In addition, it was shown that the growth of the thin film thickness was non-linear with respect to time, and the formation of a fuzz-like structure may be influenced by particle diffusion in the gas phase and on the substrate.

Comparing Container Closure Integrity Test Methods - Performance of Headspace Carbon Dioxide Analysis versus Helium Leakage Using Positive Controls.

As described in USP Chapter <1207>, the deterministic leak test methods using laser-based gas headspace analysis and helium leakage are those with the highest sensitivities. As stated in the chapter, ″no single package leak test or package seal quality test method is applicable to all product-package systems″; therefore, knowing the advantages and disadvantages of both of these techniques, and the extent to which they can be substituted for each other, is valuable. In an effort to begin addressing this issue, a systematic study using these two techniques has been performed. This study used the same well-defined positive controls prepared with microcapillaries for both measurement techniques. For the headspace gas analysis technique, the headspace carbon dioxide content was measured at multiple timepoints during three separate conditioning cycles using either a 0.5, 1.0, or 2.0 bar CO2 overpressure; the observed change in headspace carbon dioxide was then used to determine an ingress rate for each positive control. For the helium leakage technique, the positive controls were measured with a standard helium leak detector with 100% helium atmosphere on the atmospheric pressure side of the artificial defects. The resulting leakage rates from both techniques were compared for ingress into both ISO 2R and ISO 10R vials. The obtained correlation between helium and carbon dioxide leakage rates resulted in a minimum R2 coefficient of 0.98 across all 12 runs. Additionally, both setups met the acceptance criteria for accuracy with their respective calibrated standards.

Effective thermal conductivity of LaNi5 powder beds for hydrogen storage: Measurement and theoretical analysis

Accurately measuring and analyzing the effective thermal conductivity of metal hydride beds is critical to design the structure of solid-state hydrogen storage tanks. On the basis of the steady-state radial heat flow method, a measurement cell of effective thermal conductivity was manufactured. The effective thermal conductivities of nonactivated and activated LaNi5 powder beds were measured in helium, nitrogen, and argon atmospheres with the temperature changing from 20 to 60 °C and pressure from 0.1 to 4.0 MPa. Then, the effective thermal conductivities were further analyzed using the Zehner–Schlünder–Damköhler model. Results show that the effective thermal conductivities can be enhanced by increasing gas thermal conductivity, gas pressure, and bed temperature. In addition, the effective thermal conductivities can be accurately predicted using the modified Zehner–Schlünder–Damköhler model considering the Smoluchowski effect (error < ± 5 %). With the use of the modified Zehner–Schlünder–Damköhler model, the contributions of different heat transfer pathways to the entire heat transfer of LaNi5 powder beds were analyzed. Approximately 70 %–91 % of the effective thermal conductivity of LaNi5 powder beds is contributed by the conduction of the particle–gas–particle pathway.

Cosolvent-free sol–gel synthesis of macroporous silica gels from tetramethoxysilane–tetraethoxysilane mixtures

Abstract Tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), and their mixtures were used for the cosolvent-free synthesis of macroporous silica gels as precursors for monolithic silica glasses. The liquid-state 29Si nuclear magnetic resonance (NMR) spectroscopy of precursor solutions indicated that cross-transesterification between TMOS and TEOS was completed in a few hours at 20 °C in the presence of an acid catalyst, whereas it was negligible when the catalyst was absent. In the precursor solutions prepared from TMOS, phase separation occurred after gelation, resulting in translucent gels. In contrast, in the solutions prepared from TEOS or a mixture of TMOS and TEOS at a TMOS mole fraction of 0.8, the phase separation can be induced before gelation, and opaque xerogels were easily obtained without fracture. The average size of macroscopic particles and macroporous structures were uniform over opaque xerogels prepared from TEOS. In contrast, in opaque xerogels prepared from the TMOS-rich mixture of TMOS and TEOS, the average particle size and macroscopic porosity inside them were notably smaller than those of the subsurface, probably because of a large exotherm upon gelation and the resulting temperature gradient in the gelling solutions. Such spatial morphology distribution made the sintering of the opaque gels into clear silica glasses difficult. Opaque gels prepared from TEOS and translucent gels prepared from solutions containing TMOS were transformed to clear silica glasses in high yields of ~99% by sintering in a helium atmosphere at 1050–1350 °C. Graphical abstract

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.

Effects of Straw Amendment in Combination with Synthetic N Fertilizer Addition on N2O, N2, and Their Stoichiometric Ratios in Three Different Agro-Ecosystems

Nitrogen (N) fertilizer and crop residue amendments are important agricultural practices that could increase soil health, fertility, and crop yield. Such practices may also change soil denitrification processes where contradictory observations have been reported on soil N2O emissions with fewer studies on N2 emissions due to its large atmospheric background concentrations limiting its soil-borne measurement. This study aims to investigate N2O production and reduction of N2 emissions under a conducive denitrifying environment (like anaerobic microsites, 80% WFPS, available N and C) after rice straw amendment and KNO3 application to three different soil types (fluvo-aquic, black, and paddy soils). In this regard, three treatments for three different soil types were set consisting of (a) a non-amended treatment (control), (b) a KNO3 treatment (KNO3, 20 mM KNO3), and (c) a straw plus KNO3 treatment (2.5 g rice straw kg−1 dry soil and 20 mM KNO3), which were incubated under 80% WFPS. Moreover, direct N2O and N2 fluxes were measured over 17 days in the current incubation experiment with a robotized incubation system using a helium atmosphere. Results showed that rice straw amendment combined with N fertilizer increased both N2O and N2 fluxes compared with control or KNO3 treatments in all three soil types. Overall, compared with the black and paddy soils, the N2O and N2 fluxes were higher in the fluvo-aquic soil, with a maximum of 234.2 ± 6.3 and 590.1 ± 27.3 g N ha−1 from F_SK treatment, respectively, during the incubation period. The general trends in three soil types of both N2O and N2 emissions were control &lt; KNO3 &lt; rice straw plus KNO3 treatments. Straw amendment in combination with KNO3 can stimulate a high denitrification rate (less N2O and higher N2), whereas their effect on stoichiometric ratios of N2O/(N2O + N2) highly depends on soil nitrate concentration, oxygen level, soil moisture content, and labile C. The current study underscores that the rice straw amendment in combination with N fertilizer can trigger denitrification with less increment on soil N2O but higher N2 emissions under conditions favoring denitrification.

Experimental study of friction coefficient of graphite for high-temperature gas-cooled reactors

High-temperature gas-cooled reactors, as highly regarded fourth-generation reactors, extensively utilize graphite materials. It is necessary to perform a study of the characteristics of the graphite materials aiming at optimizing the structural design and neutron physics calculation for the reactor. Thus, the investigation of the graphite friction coefficient is a crucial aspect of the research. This paper presents experiments on the graphite friction coefficient conducted using a specially designed experimental device that closely replicates the operational conditions of high-temperature gas-cooled reactors. The experimental data on the graphite friction coefficients under various atmospheric and temperature conditions are obtained. The graphite friction coefficient under a helium atmosphere demonstrates an initial increase followed by a decrease with rising temperature, reaching a maximum value of 0.17 at 200 °C. However, beyond 400 °C, the friction coefficient stabilizes gradually and fluctuates within the range of 0.03 to 0.06. Under a nitrogen atmosphere, the graphite friction coefficient exhibits the same temperature-dependent pattern as observed in helium. The peak value likewise occurs at 200 °C, measuring 0.23. At temperatures below 400 °C, the graphite friction coefficients in a nitrogen atmosphere surpass those in helium. While beyond 400 °C, the friction coefficients in a nitrogen atmosphere likewise fluctuate within the range of 0.03 to 0.06.

Effect of long-term high-temperature exposure in a controlled atmosphere on mullite-corundum ceramics for advanced applications in nuclear power technology

This work investigates the behavior and properties of corundum and mullite ceramics at high temperatures and during very long exposures in a controlled atmosphere. The motivation of the work lies primarily in advanced applications in nuclear energy technology, specifically in the search for materials for helium-cooled reactors of the 4th generation. The studied ceramic samples Al63, Al70, Al76, Al96, Al100, where the number indicates the mass percentage of Al2O3, were exposed for 1000 h at a temperature of 900 °C in gaseous atmospheres of helium, nitrogen and air. The properties of the exposed and unexposed samples were evaluated by measuring the bending strength at room temperature (CMOR), hot modulus of rupture at high temperature (HMOR), and isothermal creep, BET method, and using electron microscopy. The color changes induced by the reducing atmosphere and temperature were also interpreted using a simple thermochemical model. The CMOR measurement results show that all ceramic samples do not significantly change their properties due to long-term exposure. The detected deviations in the exposed samples from the unexposed ones can be considered random caused by the inherent heterogeneous structure. A similar conclusion also applies in the case of the HMOR measurement results, except for the results for the Al63 sample, where the drop in the strength of the exposed samples by approx. 37 MPa (20 %) may be related with the highest proportion of polyvalent oxide admixtures of all studied ceramics, i.e. 1.01 wt % Fe2O3 and 0.52 wt % TiO2. The change in color indicates that the iron and titanium present are being reduced. However, none of the conducted experiments indicate that changes in the redox state associated with the formation of oxygen vacancies would significantly reduce strength at high temperatures or increase creep in mullite ceramics.

Asymetrical shape of C–He lines in the ultraviolet

ABSTRACT We present the first theoretical line profile calculations of the ultraviolet spectral lines of carbon perturbed by helium using a semiclassical collision approach and high-quality ab initio potentials and electronic transition dipole moments. The temperature range is from 5000 to 8000 K. These results are important for astrophysical modelling of spectra in atmospheres of white dwarf stars showing atomic carbon in an helium atmosphere. Beyond the conventional symmetrical Lorentzian core at low He density, these lines exhibit a blue asymmetric behaviour. This blue asymmetry is a consequence of low maxima in the corresponding C–He potential energy difference curves at short internuclear distances. The collisional profiles are carefully examined and their perturber density dependence allow to understand the various line shapes of the observed carbon spectral lines in helium-rich white dwarf photosphere where the He perturber densities reach several 1021 cm−3.

Thermal-assisted resistive sensor based on the PdCr alloy thin film for sensitive detection of hydrogen isotopes in helium atmosphere

The detection of hydrogen isotopes is not only the premise of ensuring safety of hydrogen energy, but also has very important application value and scientific significance in the field of fusion energy. Therefore, it is imperative to develop efficient and reliable hydrogen isotope sensors. Herein, a thermal-assisted resistive sensor is constructed based on the hydrogen isotope effect of PdCr alloy thin film for sensitive detection of hydrogen isotopes in helium atmosphere. The permeation of hydrogen isotopes in palladium lattice is facilitated through thermal effect to improve the dynamic response capability of sensor. The research results show that the response time of sensor to hydrogen and deuterium is reduced from 192 s to 113 s–17 s and 10 s respectively. However, the sensitivity deteriorated by about 40% at 110 °C compared with room temperature. Meanwhile, the PdCr alloy thin film resistive sensor represents a remarkable linear response in a range of 0.1%–4% hydrogen and deuterium, with correlation coefficients of 0.9971 and 0.9998 respectively. And the response difference of hydrogen and deuterium may be utilized to discriminate hydrogen isotopes. Furthermore, the sensor exhibits prominent selectivity, extraordinary working stability and a wide range of 100ppm-100%. Therefore, this work presents a feasible approach to design high-performance resistive hydrogen isotope sensors for the development of hydrogen energy and fusion energy.

Edge Bonding Voids Management Using Humid Helium Bonding Atmosphere

As far as hydrophilic direct wafer bonding is concerned, there are, beside classical bonding voids induced by particle contamination or surface topography, edge bonding voids due to the bonding wave dynamic itself. Indeed, as shown by Castex et al. [1], during the adiabatic expansion of the bonding wave at the wafer edge, humidity inside the bonding wave gas can liquefy and small water droplets nucleate. This is shown in Figure 1a, with the bonding of a 300mm silicon wafer on another one having a 145 nm thermal oxide on top and after a post bonding thermal annealing at 300°C. These wafer edge droplets result in bonding defects without the presence of particle contamination or surface topography. Even if bonding is performed under a dry gas like Nitrogen or Argon, these defects remain at the hydrophilic direct bonding interface. Indeed, there is always a small amount of water on a hydrophilic surface. During the first bonding wave propagation stage, gas compression increases the temperature and enables the gas to take water from the surfaces, as explained V. Larrey et al. [2]. The humid gas will result in edge bonding voids at the end of the propagation. There are only two methods to get rid of this phenomenon. The first one is to perform bonding under vacuum (<0.1 mbar). The second is to use a gas with a negative Joule-Thomson coefficient.Such gases will be heated during the adiabatic expansion when the bonding wave will go out of the bonding interface. Three gases have such a negative coefficient: Helium, Hydrogen and Neon. Helium has the lowest joule-Thomson coefficient at ambient condition and is the saver and cheapest one. Bonding under Helium atmosphere will then prevent water nucleation, as shown in Figure 1b. Usually, pure Helium is used which is then a dry gas. Some water will then be removed from the surface. As shown by Radisson [3], the adhesion will then be less important as well as the adherence as shown by Fournel et al. [4]. Adding water vapor to increase the relative humidity (RH) of helium could then enable us to recover standard bonding conditions regarding the amount of trapped water.In our EVG850LT bonding tool, a humidifier has thus been installed on the Helium gas line in order to purge the bonding chamber with a varying RH gas mixture (from 0 to 80%). As shown in Figure 1c, even with 68% of RH, no bonding voids are detected by scanning acoustic microscopy. It will be shown also that the bonding wave speed increases with the RH value, highlighting an adhesion energy recovery. The evolution of the adherence with the RH bonding conditions and after the post bonding annealing will be also presented. REFERENCES [1] A. Castex, M. Broekaart, F. Rieutord, K. Landry, and C. Lagahe-Blanchard, ECS Solid State Lett. 2, p. 47 (2013).[2] V. Larrey, G. Eleouet, C. Bridoux, C. Morales, F. Fournel, F. Rieutord, D. Landru, Proceeding of The International Conference on Wafer Bonding 2019-WaferBond'19, p.91 (2019).[3] D. Radisson, Direct Bonding of Patterned Surfaces, PhD thesis, Université Grenoble Alpes, (2014).[4] F. Fournel, C. Martin-Cocher, D. Radisson, V. Larrey, E. Beche, C. Morales, P.A. Delean, F. Rieutord, and H. Moriceau, ECS J. Solid State Sci. Technol. 4, P124 (2015). Figure 1

Experimental measurement of stiffness coefficient of high-temperature graphite pebble fuel elements in helium at high temperatures

Graphite material plays an important role in nuclear reactors especially the high-temperature gas-cooled reactors (HTGRs) by its outstanding comprehensive nuclear properties. The structural integrity of graphite pebble fuel elements is the first barrier to core safety under any circumstances. The correct knowledge of the stiffness coefficient of the graphite pebble fuel element inside the reactor's core is significant to ensure the valid design and inherent safety. In this research, a vertical extrusion device was set up to measure the stiffness coefficient of the graphite pebble fuel element by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University in China. The stiffness coefficient equations of graphite pebble fuel elements at different temperatures are given (in a helium atmosphere). The result first provides the data on the high-temperature stiffness coefficient of pebbles in helium gas. The result will be helpful for the engineering safety analysis of pebble-bed nuclear reactors.

Measurements of electrical resistivity and Seebeck coefficient for disc-shaped samples

Herein we develop a methodology to measure the resistivity of discs by deriving a mathematic formula between resistivity and resistance from solving the electrostatic Laplace equation in polar coordinates. Then the resistivity and Seebeck coefficient of disc samples of p- and n-type bismuth telluride are measured experimentally either in nitrogen or helium atmosphere. The validity of Seebeck coefficient is demonstrated by the excellent linearity between Seebeck voltages and temperature differences. The bar samples are also measured for comparison. Finite element simulation is utilized to display the two-dimensional potentials and currents and have an error analysis. Furthermore, the resistivity error due to the probe distance error is discussed analytically based on the mathematic formula, and the probe distance can be optimized to minimize the resistivity error. The disclosed approach would extend the applicability of the present instruments to the disc-shaped samples and be useful in the emerging transverse thermoelectricity.