Inert Gas Research Articles

Exceptional grain refinement induced by dispersed MgO particles in TIG-welded AZ31 alloy

Due to the low content of alloying elements and the lack of effective nucleation sites, the fusion zone (FZ) of tungsten inert gas (TIG) welded AZ31 alloy typically exhibits undesirable coarse columnar grains, which can result in solidification defects and reduced mechanical properties. In this work, a novel welding wire containing MgO particles has been developed to promote columnar-to-equiaxed transition (CET) in the FZ of TIG-welded AZ31 alloy. The results show the achievement of a fully equiaxed grain structure in the FZ, with a significant 71.9% reduction in grain size to 41 μm from the original coarse columnar dendrites. Furthermore, the combination of using MgO-containing welding wire and pulse current can further refine the grain size to 25.6 μm. Microstructural analyses reveal the homogeneous distribution of MgO particles in the FZ. The application of pulse current results in an increase in the number density of MgO (1-2 μm) from 5.16 × 104 m−3 to 6.18 × 104 m−3. The good crystallographic matching relationship between MgO and α-Mg matrix, characterized by the orientation relationship of [112‾0]α−Mg//[01‾1]MgO and (0002)α−Mg//(111)MgO, indicates that the MgO particles can act as effective nucleation sites for α-Mg to reduce nucleation undercooling. According to the Hunt criteria, the critical temperature gradient for CET is greatly enhanced due to the significantly increased number density of MgO nucleation sites. In addition, the correlation with the thermal simulation results reveals a transition in the solidification conditions within the welding pool from the columnar grain zone to the equiaxed grain zone in the CET map, leading to the realization of CET. The exceptional grain refinement has contributed to a simultaneous improvement in the strength and plasticity of welded joints. This study presents a novel strategy for controlling equiaxed microstructure and optimizing mechanical properties in fusion welding or wire and arc additive manufacturing of Mg alloy components.

Experimental investigation of the impact of GMAW welding parameters on the mechanical properties of AISI 316L/ER 316L using quaternary shielding gas

In this study, the parameters of Metal Inert Gas (MIG) and Metal Active Gas (MAG) were investigated of AISI 316L/ER 316L. A quaternary shielding gas mixture consisting of Argon (Ar), Helium (He), Carbon Dioxide (CO2), and Nitrogen (N2) was chosen. The Taguchi orthogonal array (OA-L9) methodology was employed to explore optimal welding settings, including arc current (120A, 160A, 200A), wire feed rate (3, 3.5, 4 m min−1), and shielding gas combination (G1, G2, G3). The findings highlighted the importance of shielding gas in influencing the ultimate tensile strength (UTS), elongation percentage (EL%), and material toughness of welding joints. Notably, the highest UTS (515.77 MPa), EL% (20.85%), and material toughness (133J) were achieved by the specific group gas combination shown as G1. It is recommended to configure welding parameters to an arc current of 160A, a wire feed rate of 4 m min−1, and the G1 gas combination. Welded specimens using a G1 gas mixture showcased the best UTS and EL%. Additionally, it was found that the fusion zone (FZ) and heat-affected zone (HAZ) hardness are most profoundly influenced by the choice of gas combination (G2), resulting in the best hardness values of 253.79 HV and 239.68 HV, respectively. The optimal parameters for achieving the desired material hardness were precisely identified as (120A, 3 m min−1, G2). These insights offer a pathway to enhance welding performance and, in turn, elevate the quality and efficiency of industrial applications.

Driver circuit with high-voltage pulse and high-frequency excitation for the cell of optically pumped sensors.

Helium optically pumped sensor is widely used in the application for the detection of weak magnetic fields, and the cell is the core component of that, which needs an external excitation signal to ignite and maintain its luminosity, and its luminosity affects the sensitivity performance of the sensor. To improve the performance of the cell and reduce the power consumption of the system, which is the largest power consumption component in the sensor, this study presents the design of a driver circuit for a helium cell based on a high-voltage pulse source and high-frequency excitation source and uses a T-type impedance matching circuit to realize the efficient transmission of energy. The experimental results demonstrate that the driver circuit can effectively light up the helium cell, in which the pulse voltage of the high-voltage excitation is more than 1.0kV, the output power of the high-frequency excitation signal is in the range of 0-6W, and it is easy to adjust the output power of the high-frequency excitation signal to optimize the sensitivity of the sensor with an the optimal power density of 1.1 W/cm2 and a sensitivity of 29.4 pT/Hz1/2 is obtained. The driver circuit method designed in this study is also suitable for other inert gases to generate metastable atoms.

Phase transformation and strengthening of the gas-atomized FeCoCrNiMo0.5Al1.3 high-entropy alloy powder during annealing

Phase evolution and strengthening of the FeNiCoCrMo0.5Al1.3 powder alloy produced via inert gas atomization and annealed in the temperature interval of 300–800 °C have been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and microhardness testing. It was found that annealing at 300–600 °C leads to an increase of the element segregations between the several solid solutions with a rise of the lattice misfit (ε) to 1.5 % and microhardness growth to 1070 HV. It was assumed that elastic stress caused by the element partitioning is the main strengthening mechanism: microhardness rises linearly with misfit rise with dHV/dε = 43400 MPa. Sigma arises after the maximum elastic deformation (in 1.5 %) was reached. Formation of the dispersed coherent sigma phase in the annealing interval 600–800 °C results in the microhardness rise. Oxidation that began at 800 °C in 27 h is accompanied with FCC formation due to a depletion of the B2 in Al caused by Al2O3 formation. Estimation of the activation energy of the initial stage of the solid solution decomposition gives a very low value in 0.65eV, apparently caused by the high concentration of quenched vacancies. The activation energy of sigma formation approximately coincides with the activation energy of self-diffusion in BCC metals (about 2.60 eV).

Extremely low coercivity of powder Co-rich amorphous alloy obtained by gas atomisation

A novel Co-base soft magnetic powder with ultra-low coercivity was produced by inert gas atomisation. The as-atomised powder is fully amorphous owing to its high glass forming ability and the proper selection of atomisation conditions; it exhibits a very low coercivity (0.130Oe) mainly due to the low magnetostriction coefficient of Co-based alloys. After production, the powder was annealed at different temperatures between 300 and 600 ºC for 30minutes. Crystallisation started at around 575 ºC, which is the temperature of the first exothermic peak detected by differential scanning calorimetry. Annealing the powder at temperatures below 550 ºC develops only structural relaxation of the amorphous structure. The smallest coercivity (0.056Oe) was found in the sample annealed at 400 ºC. On the other hand, an increment of the coercivity of four orders of magnitude occurred after full crystallisation at 600 ºC (394.320Oe). From the analysis of the curves of anisotropy field distribution, it can be concluded that this Co-base alloy shows lower average anisotropy field, a more gaussian shape and a wider distribution than Fe-base alloys. This is explained by a lower magnetoelastic anisotropy and a more homogeneous distribution of the magnetic anisotropy. The powder exhibits a spherical shape that makes it very suitable as ferromagnetic phase to manufacture powder cores with extremely low hysteresis loss for medium-high frequency applications.

Enhanced electrical performance of LiMnPO4 by carbon coating for solid-state battery applications

High-energy ball milling was employed to fabricate LiMnPO4 coated with varying carbon ratios (3%wt, 7%wt, and 10%wt), using glucose as a carbon source. The process involved pre-milling of LiMnPO4 precursors, followed by granulation through high-energy ball milling at 270 rpm for 2 h, and subsequent calcination at 700 °C without an inert gas flow. XRD analysis discerned the phases and structure of LiMnPO4, confirming the successful attainment of a single-phase LiMnPO4 without impurities. Rietveld refinement of the XRD data elucidated the crystallographic details, affirming the material's orthorhombic olivine structure with precise lattice parameters, thereby underpinning the structural integrity essential for electrochemical applications. FE-SEM analysis revealed uniformly distributed semi-sphere particles, with sizes ranging from 130 nm for LM to 183 nm for LM-10%C. FTIR analysis delineated the internal modes of vibration in the olivine structure and verified the presence of carbon on the powder surface. Electrical measurements conducted within the frequency range of 20 Hz–100 kHz demonstrated an increase in electrical conductivity with an escalation in carbon concentration, ranging from 31 μΩ−1m−1 to 75 μΩ−1m−1 for 0%C and 10%C, respectively. A temperature-dependent study spanning 30–160 °C revealed stable electrical conductivity behavior for the samples, with a marginal increase observed at elevated temperatures.

Spatter-flow interaction behavior under protective gas flow parameters and scanning directions

Spattering is a common issue in selective laser melting (PBF-LB), causing contamination of the powder bed and negatively affecting product quality. One solution to this problem is introducing an inert gas flow that can remove spatter particles. The gas flow's characteristics and interaction with spatter particles depend on process parameters and involve a multi-physical field coupling process. However, current research mainly focuses on spattering behavior under single process conditions and lacks systematic exploration of gas flow characteristics and their interaction with spattering. This paper investigates the gas flow-spatter interaction process in PBF-LB, constructing a coupled model of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). The model investigates the effects of inlet height, inlet flow velocity and laser scanning direction on the deposition and removal of spattered particles. The study reveals that flow velocity and inlet height affect the dynamic behavior of spattering by altering the flow distribution, while the laser scanning direction influences spatter dynamics by changing the direction of spatter ejects. The rate of spatter removal increases as the angle between the scanning direction and flow direction, and the flow velocity, increase. Conversely, it decreases as the inlet height increases. This work provides theoretical understanding of the interaction between gas flow characteristics and spattering, which is significant for optimizing printing process parameters and improving printing quality.

Decompression illness: a comprehensive overview.

Decompression illness is a collective term for two maladies (decompression sickness [DCS] and arterial gas embolism [AGE]) that may arise during or after surfacing from compressed gas diving. Bubbles are the presumed primary vector of injury in both disorders, but the respective sources of bubbles are distinct. In DCS bubbles form primarily from inert gas that becomes dissolved in tissues over the course of a compressed gas dive. During and after ascent ('decompression'), if the pressure of this dissolved gas exceeds ambient pressure small bubbles may form in the extravascular space or in tissue blood vessels, thereafter passing into the venous circulation. In AGE, if compressed gas is trapped in the lungs during ascent, pulmonary barotrauma may introduce bubbles directly into the pulmonary veins and thence to the systemic arterial circulation. In both settings, bubbles may provoke ischaemic, inflammatory, and mechanical injury to tissues and their associated microcirculation. While AGE typically presents with stroke-like manifestations referrable to cerebral involvement, DCS can affect many organs including the brain, spinal cord, inner ear, musculoskeletal tissue, cardiopulmonary system and skin, and potential symptoms are protean in both nature and severity. This comprehensive overview addresses the pathophysiology, manifestations, prevention and treatment of both disorders.

Decompression illness: a comprehensive overview

Decompression illness is a collective term for two maladies (decompression sickness [DCS] and arterial gas embolism [AGE]) that may arise during or after surfacing from compressed gas diving. Bubbles are the presumed primary vector of injury in both disorders, but the respective sources of bubbles are distinct. In DCS bubbles form primarily from inert gas that becomes dissolved in tissues over the course of a compressed gas dive. During and after ascent (‘decompression’), if the pressure of this dissolved gas exceeds ambient pressure small bubbles may form in the extravascular space or in tissue blood vessels, thereafter passing into the venous circulation. In AGE, if compressed gas is trapped in the lungs during ascent, pulmonary barotrauma may introduce bubbles directly into the pulmonary veins and thence to the systemic arterial circulation. In both settings, bubbles may provoke ischaemic, inflammatory, and mechanical injury to tissues and their associated microcirculation. While AGE typically presents with stroke-like manifestations referrable to cerebral involvement, DCS can affect many organs including the brain, spinal cord, inner ear, musculoskeletal tissue, cardiopulmonary system and skin, and potential symptoms are protean in both nature and severity. This comprehensive overview addresses the pathophysiology, manifestations, prevention and treatment of both disorders.

Review of Methods for Converting Biomass into Biofuels

Thermochemical processes are among the most effective methods of obtaining hydrogen-rich gases from biomass. These technologies mainly include pyrolysis, gasification and hydrothermal liquefaction. Thermochemical conversion of dry biomass is similar to the conversion of fossil fuels using gasification and pyrolysis methods. Products obtained through thermochemical processes (CO and CH4) can be processed into other biofuels, e.g. syngas, a raw material for producing synthetic hydrocarbons, methanol and alcohols. In recent years, advanced research has been carried out using biomass to produce liquid fuels. The biomass pyrolysis process in the presence of a catalyst is based on the rapid heating of the biomass to a temperature of approximately 500°C in the so-called inert atmosphere in which there are no reactive gases. This process produces a liquid product: pyrolysis oil, gas and charcoal. The bio-oil produced in this process constitutes 60-75% of the mass of the biofuel and is thermally unstable because it contains up to 300 different chemical compounds. However, the bio-oil obtained in this way is incompatible with conventional liquid transport fuels (gasoline, diesel) due to its high oxygen content. Pyrolysis in the presence of a zeolite catalyst is a process that allows for the effective conversion of biomass in economic and ecological terms. A zeolite catalyst makes it possible to remove oxidized compounds in situ and modify the properties of the biofuel to ensure its compatibility with conventional transport fuels. The catalyst plays a crucial role in this process because it removes oxygen from oxygenates and, consequently, creates stable reaction products that can then be treated to obtain renewable transport fuels or other useful chemicals. The article presents methods of biomass conversion via pyrolisis, microorganisms usage, zeolite-based catalysis, biocatalysis and photo-fermentation, which poses a big possibility of diversification of renewable energy sources.

Metal saccharinate complexes with N,N-bis(2-hydroxyethyl)ethylendiamine: Synthesis, structural, thermal decomposition and DFT studies

New Co(III), Ni(II), Cu(II), and Zn(II) saccharinate (Sac) complexes bearing with N,N-bis(2-hydroxyethyl)ethylenediamine (N-bishydeten), namely [Co(2HN-bishydeten)2](Sac)⋅2H2O, [Ni(Sac)2(N-bishydeten)], [Cu(N-bishydeten)2](Sac)2 and [Zn(Sac)2(N-bishydeten)] were synthesized and characterized using UV–Vis, IR spectroscopy and magnetic susceptibility measurements. The crystal structures of the complexes were analysed by single crystal X-ray diffraction. Both N-bishydeten and Sac displayed coordination versality. The N-bishydeten ligands were octahedrally coordinated as two tridentate anionic ligands (2HN-bishydeten) (N, N, O-) to the Co(III) and two tridentate neutral ligands (N, N, O) to the Cu(II). The anionic Sac ligand was also located outside the coordination sphere in these complexes. However, the N-bishydeten ligand behaved as a tetradentate ligand (O, N, O, N) in the Ni(II) and Zn(II) complexes while two Sac ligands were coordinated the corresponding metals ions in a monodentate fashion, one through the N atom and the other via the carbonyl O atom. Thermal decomposition of the complexes was studied in inert atmosphere and thermal analysis data (TG and DTA) indicated multi-step decompositions of the metal complexes decomposed in a single stage. The thermal decomposition products were estimated as metal oxides. Finally, the structural properties of all complexes were investigated through quantum chemical computations.

Flash‐sintering behavior of the composites of 3YSZ and graphene oxide

AbstractFlash sintering is a novel technique that involves the sintering of green bodies in few seconds at relatively very low furnace temperature as compared to what is required to sinter them conventionally. In the present work, we flash‐sintered composites of 3 mol.% yttria‐stabilized zirconia (3YSZ) and graphene oxide (GO). The main aim of this work was to see if the decomposition or oxidation of carbonaceous materials can be prevented by the high heating rates during flash sintering and if composites of 3YSZ and GO can be processed in air. 3YSZ with 5, 10, and 20 wt.% of GO were prepared and subjected to constant heating rate flash‐sintering experiments where electric field was applied across the sample right from room temperature. A DC electric field of 100 V/cm was applied and the current density was set to 100 mA/mm2. It was observed that GO decomposed from the surface of the samples; however, in the core of samples, GO was retained but was reduced to graphite. Grain size of the 3YSZ phase increased with increase in the GO content, whereas the hardness decreased. It was observed that the composites containing carbonaceous reinforcements need to be flash sintered in inert atmosphere to realize their full potential.

Exploring the influence of pin geometry on metallurgical and mechanical characteristics of dissimilar aluminum TIG welds via friction stir processing

This study explored the effect of friction stir processing (FSP) on tungsten inert gas (TIG)-welded AA6061-T6 and AA7075-T6 joints by utilizing three different tool pin geometries, namely simple cylinder (SC), threaded cylinder with triflat faces (THF), and simple square (SS). The metallurgical aspects of unprocessed and processed weld regions were analyzed and correlated with the ultimate tensile strength, impact toughness, and microhardness properties. Results revealed that the post-FSP with a THF pin transformed the coarse dendritic structures (AGS of 34.55 µm) of the TIG weld into equiaxed fine structures (AGS of 3.51 µm) and increased the UTS, impact toughness, and microhardness by 71.51%, 95.40%, and 72.46%, respectively. The joint processed with the THF pin resulted in the highest ultimate tensile strength of 279 MPa, impact toughness of 15.02 J, and microhardness of 116.13 HV in the nugget region compared to the other two pin geometries. The highest joint properties of THF pin were attributed to the formation of fine grain structures in the nugget region, high effective strain and heat generation, improved material flow, and the decimation of intermetallic precipitates with their uniform dispersion in the nugget region. The tensile fractured surface of the TIG weldment had noticeable macro voids and coarse dimples with some rough cleavage facet in the fusion region, resulting in a brittle mode of failure. However, the tensile fractured surface of TIG + FSP weldments showed ductile failure due to the presence of fine and deep dimples with tear ridges without any void.

TECHNOLOGY FOR PRODUCTION AND QUALITY OF BREAD BAKED FROM WHOLE GRIND WHEAT FLOUR

This article examines the possibility of improving and expanding the range of functional breads. A number of laboratory bakings of bread were carried out from the whole-ground wheat flour of various sizes obtained by us; bread made from grade 1 wheat flour, baked in the laboratory of the Muhlenchemie Technology Center of Synar Group LLP (Almaty), was taken as control. The purpose of this work was to study the quality of bread made from whole-ground flour of various grindings. The flour used for baking bread was treated with an inert gas – nitrogen. Nitrogen treatment was used to increase the safety of flour during storage.Coarsely ground bread was characterized by a lower volume of 1670 cm3 and a low crumb porosity of 43.56%. which is significantly lower than the performance of bread made from medium and fine flour. The results of laboratory baking of bread from medium-ground whole-ground wheat flour, in comparison with other samples, showed better baking properties. Thus, with a crumb porosity of 63.87%, the volumetric yield of bread from medium-ground flour was 2180 cm3; from fineground flour, the volume of baked bread was 15% lower than from medium-ground flour and amounted to 1770 cm3.In terms of fat content, bread samples differ significantly, more than 2 times higher in comparison with bread made from 1st grade wheat flour. The mass fraction of carbohydrates in samples of bread made from whole-milled flour of various grindings is lower than in bread made from 1st grade wheat flour. Thus, in bread made from whole-ground coarse flour, the amount of carbohydrates was 45.96%; average 45.13%; small 43.37%.

Void nucleation and growth behavior of TIG welded AA2219 deformed at cryogenic temperatures

This work investigates the failure behaviour of tungsten inert gas (TIG) welded 2219 aluminum alloy butt welds deformed over a range of cryogenic temperatures relevant to liquid hydrogen/oxygen propellent storage tanks. A novel in situ tensile testing machine, able to deform samples at temperatures down to 83 K, was designed to be accommodated on synchrotron computed tomography beamlines. In this way we were able to observe the accumulation of damage from void nucleation through growth to coalescence and ultimate failure by time-lapse X-ray microtomography during tensile straining at 293 K and 123 K. The results reveal that micro-void nucleation is triggered by θ (Al2Cu) precipitates and α-Al + θ (Al2Cu) eutectics in the form of particle fracture and interface decohesion. After nucleation, these freshly nucleated voids, along with pre-existing welding defects, extend with straining along the loading direction. This leads to void linkage, a very short void coalescence stage and subsequent catastrophic failure. The probability distribution function that describes the rate at which voids nucleate by interface decohesion considering the particle orientation was determined through the Eshelby inclusion theory. The evolution of void aspect ratio and void growth were modelled using the Gurson-Tvergaard-Needleman model and Le Roy model, respectively. This suggests that pre-existing defects grow faster, but that the numerous closely spaced nucleated voids play a significant role in failure.

Highly efficient and air-tolerant calcium-based Birch reduction using mechanochemistry

Abstract In this study, we report a mechanochemical protocol for highly efficient and air-tolerant calcium-based Birch reduction. The developed mechanochemical approach allows the use of readily available calcium metal as a safer-to-handle reductant for Birch reduction of various aromatic compounds. The reaction was rapid and the desired dearomatization products were obtained in good yields within 15 min at ambient temperature. Notably, all synthetic operations can be performed under ambient conditions without a complicated reaction setup involving inert gases. The feasibility of the gram-scale synthesis was demonstrated, further highlighting the practical utility of this protocol.

Effects of H2O on Improving the Performance of a Solid Composite Electrolyte Fabricated via an Air-Processable Technique.

Inert atmosphere is normally necessary for fabrication of solid composite electrolytes (SCEs) as a crucial part of solid-state Li-metal batteries in order to avoid undesirable reactions induced by ambient moisture. Herein, we developed an air-processable technique to fabricate SCEs by employing LiCF3SO3 (LiOTf) as the Li salt, which was combined with Li6.4La3Zr1.4Ta0.6O12 (LLZTO) as the fast Li-conductor and polyvinylidene difluoroethylene/polyvinyl acetate (PVDF/PVAC) as the polymer matrix. With the assistance of trace H2O dissolved in electrolyte solution, the room-temperature Li+ conductivity of the obtained aSCE reached as high as 5.09 × 10-4 S cm-1, which was over 3 orders of magnitude higher than that of the one (iSCE, 1.93 × 10-7 S cm-1) cast by the electrolyte solution prepared in an inert atmosphere. The theoretical calculation results reveal that the oxygen atom of H2O exhibits a high propensity to interact with the Li atom in LiOTf (Li···O), thereby establishing a hydrogen bond with the oxygen atom (H···O) in N,N-dimethylformamide (solvent). Such interactions promoted the dissociation of LiOTf and led to the formation of uniform Li+ transportation channels. Simultaneously, the composition distribution was also altered, resulting in a smoother surface of aSCE and lowered crystallinity of PVDF. On this basis, the LiOTf/LLZTO/PVDF/PVAC solution at 60 °C was directly coated onto the surface of the LiFePO4 (LFP) cathode to fabricate the LFP-aSCE film after drying in an oven. The assembled LFP-aSCE/Li battery wetted by trace sulfolane exhibited an initial Coulombic efficiency of 94.7% and a capacity retention rate of up to 96% at 0.2 C (137 mAh g-1) after 180 cycles and a high capacity of 143.7 mAh g-1 at 0.5 C (150 cycles). Overall, this work could pave the way for the facile fabrication of solid electrolytes.

Investigating the impact of Trombe wall parameters on thermal performance and room temperature in the Iraqi climate

AbstractTrombe wall serves as an effective passive heating element, and its performance is heavily reliant on local climate conditions. This study involved both experimental and numerical analyses of a full‐scale test room equipped with a Trombe wall under Iraqi climate conditions. To facilitate this investigation, an experimental test room was constructed in Kirkuk city with dimensions of 4.0 m × 3.0 m × 2.75 m. In addition, a numerical simulation method based on computational fluid dynamics was developed and a computer code was created to investigate the performance of the system. The accuracy of the developed numerical approach was validated against experimental data collected from the test room. This analysis was conducted specifically for the period of February 17–18, which represents the coldest month of winter in the study area. The performance of the system was assessed with respect to various parameters; air gap width variations (2, 4, 6, and 10 cm), massive wall thickness ranging from 15 to 35 cm with 5 cm increments, channel width options (3, 5, 10, 15, and 20 cm), and vent heights ranging from 5 to 20 cm in 5 cm increments. Furthermore, an investigation of the impact of replacing the air in the air gap with inert gases, specifically argon, krypton, and a mixture of these gases with air was conducted, as well. The outcomes indicate that both the channel width and vent height do not have a significant impact on the system's performance. However, the width of the air gap has a modest effect on system performance, and the best performance was observed with a smaller gap width, specifically 2 cm. The most significant impact on room temperature is observed when the storage wall thickness is varied. In the case of wall thickness of 15 cm, there is a notably higher fluctuation in room temperature between the maximum and minimum values, reaching approximately 16°C. For a wall thickness of 35 cm, however, this fluctuation is significantly reduced to about 3°C. The system efficiency as determined after 24 h of operation period improved significantly when the air was replaced by an inert gases or a mixture of gases in the air gap. Compared to air, the increase in efficiency is about 14.8% for argon, 17.7% for krypton, and 20.6% for the mixture of gases.

Structure and properties of samples made from XH50BMTJuB-VI (EP648-VI) alloy produced by using selective laser melting process

The paper presented examines the composition, the structure and properties of samples made from the XH50VMTJuB-VI (hereinafter EP648-VI) alloy obtained by using the selective laser melting process (the SLM-process) in relation to manufacturing parts for aviation purposes. The authors carried out a comparative study of the samples’ structure and properties upon conducting such operations as depositing in two directions (horizontal and vertical), separate heat treatment and after hot isostatic pressing (HIP) followed by a standard heat treatment process applied for deformable semi-finished products made from the XH50VMTJuB-VI(EP648-VI) alloy. The authors inform that the manufacturing of samples by means of the SLM-process involved powders obtained through the technology of the vacuum-induction spraying of the molten metal jet with an inert gas (argon). The paper has established that samples obtained by using the HIP process with the application of the heat treatment (a vacuum high-temperature homogenization followed by a long-term aging) demonstrated the best set of mechanical properties, since the implemented complex process ensured the “healing” of pores and discontinuities in the structure, and strengthening by means of the intermetallic g¢-phase, while separations of the excess, needle-shaped a -Cr phase are fine and evenly distributed in the material structure. The authors noted that mechanical properties of samples under analysis were generally in compliance with the requirements set forth in the regulatory documentation for deformable semi-finished products made from the XH50VMTJuB-VI (EP648-VI) alloy, while underlining the increase in the level of impact strength of samples that underwent the HIP process, and the long-term strength of samples manufactured in the vertical direction compared to other options studied. Following the results of the analysis, the authors established that the SLM-process made it possible to manufacture products whose level of mechanical properties was close to the level of the deformable material, and even exceeded it in some cases.

Experience from radon in soil gas comparison measurements held in Czech Republic and in other countries, 1992–2022

Radon 222Rn, an inert natural radioactive gas, a daughter product in the 238U natural decay series, a source of alpha radiation, together with its short-lived decay products is a dominant source of absorbed radiation doses in the population. Rocks and building materials are fundamental sources of radon in dwellings. Elevated indoor radon activity concentration in houses and workplaces, surpassing recommended reference levels, is not desirable. Since radon penetrates into the houses from the geological basement, various technical aids for protection of houses have been developed. Their individual application derives from the radon potential of a building site. Radon risk mapping of building sites became a standard procedure for gauging the local radon potential. Various instruments and techniques of measurements of radon activity concentration in soil gas (Bq/m3) at building sites are available. Since radon in soil gas and radon measurement techniques are affected by several natural and technical conditions, resultant values of radon risk mapping by individual organizations vary, sometimes fundamentally. Radon comparison measurements at selected reference sites are an important tool for single organizations to verify their radon measuring procedures and reliability of their reported results. Based on legislative regulations, comparison measurements at established radon reference sites are a part of the obligatory activities for radon risk mapping at building sites in the Czech Republic. Experience and analyses of 30-year radon in soil gas comparison measurements in the Czech Republic show the dispersion of values reported by participating organizations and indicate that more than 10% of participants do not fulfill the established local criteria. This paper introduces requirements for the establishment of radon reference sites, documents their natural variability, recommends the procedure of radon comparison measurement, and analyses its results. A long-term experience was gained by testing organizations from the Czech Republic (1992–2022) as well as from the international comparison measurements organized in the Czech Republic and in several other countries (2010–2021).