Use Of Argon Research Articles

Physically and chemically modified zeolite templated nitrogenous carbons for enhanced hydrogen adsorption

Carbon materials have great potential for hydrogen adsorption due to their remarkable specific surface area, unique pore size characteristics and ability to functionalize with metal or non-metal. In this work, zeolite templated carbons were physically and chemically modified by varying preparation conditions to study their impact on structure and hydrogen adsorption capacity. The resultant templated carbons showed surface area in the range of 608–1665 m2/g and pore volume between 0.63 to 1.00 cc/g, with 28–48 % microporosity depending on synthesis conditions. The surface area and pore volume increased with increasing carbon deposition temperature from 650 to 750 °C and both decreased at higher carbon deposition temperature of 850 °C. At heat treatment temperature of 900 °C, the surface area and pore volume of templated carbons were observed to be higher. Incorporation of nitrogen heteroatom in carbon matrix during carbon deposition might have facilitated porosity. Use of argon as carrier gas resulted in the highest surface area (1665 m2/g), micropore area (597 m2/g) and pore volume (1.0 cc/g). The same templated carbon showed maximum hydrogen adsorption capacity of 0.20 and 2.81 wt% at 25 and –196 °C, respectively at 15 bar. On addition of platinum to templated carbon, the hydrogen adsorption capacity was significantly improved from 0.20 to 0.28 wt% at 25 °C and from 2.81 to 3.24 wt% at –196 °C. The strong affinity of Pt for hydrogen might have enhanced hydrogen adsorption.

Complex Diagnostics of Silicon-on-Insulator Layers after Ion Implantation and Annealing

A technology was developed for activating ion-implanted dopants in silicon-on-insulator layers at a low annealing temperature (600°C) using the pre-amorphization technique of a silicon device layer. In the case of phosphorus implantation, silicon was amorphized directly by dopant ions. In the case of boron implantation for pre-amorphization, the layers were preliminary irradiated with argon or fluorine ions. Complex diagnostics of the implanted layers was carried out using secondary ion mass spectrometry, X-ray diffractometry and small-angle X-ray reflectometry. The combination of methods made it possible to characterize the impurity distribution, the degree of silicon crystallinity, the layer thicknesses, and the interface widths in structures. The results of diagnostics of the structure and composition correlate well with calculations in the SRIM software package and the electrophysical characteristics of the layers after annealing. It was shown that the use of argon for pre-amorphization of silicon interfered with the recrystallization process and did not make it possible to achieve acceptable electrical characteristics of the doped layer. Amorphization with phosphorus and pre-amorphization with fluorine during boron implantation allowed obtaining the required values of the resistance of the doped layers after annealing at a temperature of 600°C. The use of a complex approach made it possible to optimize the modes of amorphization, ion doping, and annealing of silicon-on-insulator structures at low temperatures, necessary for the creation of light-emitting device structures based on silicon-germanium nanoislands.

Impact of the atmosphere on the sintering capability and chemical durability of Nd-doped UO2+x mixed oxides

In this study, the influence of the working atmosphere on the sinterability and chemical durability of Nd-doped UO2 mixed oxides was investigated. To this end, the starting powder was first prepared by a hydroxide co-precipitation route, resulting in a nano-sized granulometry combined with a high specific surface area. The powders were then converted to oxides by heating and sintered in pellet form at 1600°C under an argon or reducing (Ar-4 %H2) atmosphere. The use of argon or reducing atmosphere resulted in very different densification pathways and final microstructures. The reducing sintering atmosphere hindered the uranium (IV) oxidation that could occur at high temperature, leading to the formation of U3O8, as was the case when working under argon atmosphere. Regarding the microstructure of the sintered pellets, the use of an argon sintering atmosphere resulted in an average grain size ten times larger than that of a reducing sintering atmosphere, while macroscopic properties such as relative density, porosity and homogeneity of cation distribution at the pellet scale remained the same. Nevertheless, a slight local enrichment of Nd at the grain boundaries was observed for the pellet sintered under Ar-4 %H2. In a second step, the study of the chemical durability of these sintered samples showed a significant influence of the sintering atmosphere on the dissolution kinetics and mechanism. These differences could be related to the microstructural properties of the pellets, i.e. the average grain size and the occurrence of grain boundaries. The cation distribution in the pellets could also influence their chemical durability, such as local Nd enrichment, the formation of defects in the oxygen sublattice and the presence of a different fraction of U(V) depending on the sintering atmosphere, as shown by HERFD-XANES measurements. The use of reducing or argon sintering atmospheres could even direct the charge compensation mechanisms that occur into the solid, thereby simultaneously affecting the sinterability and chemical durability of the samples.

Esterification and volatile compound manipulation using radiofrequency cold plasma

Esters are vital in many industries, including food; however, there are still significant opportunities to improve production efficiency, sustainability, and cost. Cold plasma was trialled as a novel tool to induce esterification. Cold plasma increased the esterification of hexanoic acid and methanol in gas and liquid phases. The use of argon significantly improved methanol-based esterification, when compared to air or nitrogen, of hexanoic acid in a mixed solution. This was attributed to interactions with the increased free hydroxyl radicals and hydrogen atoms produced by the argon-based plasma. However, air-based plasma significantly increased esterification when individually treating hexanoic acid in methanol, which indicates the potential use of different plasmas to induce esterification. Further evidence of this could be detected by analysing the intermediary compounds (from the proposed esterification pathway).

Sealing Wax and Bottles in Bags-A Paradigm Shift in Refined Olive Oil Packaging: Preliminary Results.

Generally, olive oil possesses natural protection against oxidation due to antioxidant compounds such as phenols and tocopherols. However, in the case of refined olive oil, the refining process unavoidably reduces the presence of these compounds. Considering these considerations, the objective of this study was to address the issues related to the "tightness" of the cap used for packaging oil in SALOV, aiming to extend the product's shelf life. The oil under investigation was packaged in 250 mL transparent glass bottles, each filled with either argon or air. Subsequently, the samples were divided into three groups: one group sealed with a conventional screw cap, another covered with a special protective bag, and a third one sealed with a wax cover directly on the cap. The storage period varied, during which the atmospheric conditions were monitored daily through both destructive and non-destructive analyses. The preliminary results indicate that alternative preservation techniques, such as the use of argon, sealing wax, and protective bags, can effectively enhance the shelf life of the oil and maintain its quality (reduce oxidation, preserve phenolic compounds, and reduce the degradation of pigments). Further research and development in this area could lead to the production of high-quality extra virgin olive oils with extended shelf life and improved sensory and nutritional properties.

Optimization of P25/PDMS supported catalysts preparation for the photocatalytic oxidation of parabens

Heterogenous photocatalysis is a suitable technology for the removal of contaminants of emerging concern (CEC), such as parabens, from wastewaters. However, typically the photocatalyst is applied as a powder, which requires time-consuming and expensive supplementary separation processes, for its separation and recovery. Therefore, supported-photocatalysis has gained interest in the scientific community. To develop a suitable supported photocatalyst, commercial TiO2 (P25) powder was immobilized in polydimethylsiloxane (PDMS) membranes, to promote the degradation of three parabens (methylparaben -MP, ethylparaben -EP, and propylparaben -PP), under UV irradiation. To enhance the photocatalytic activity of the membranes, a plasma process was applied during their preparation. The plasma process operating conditions were optimized, regarding the working gas, the power applied, the pressure used and the processing time selected. Thus, the best conditions, among those analyzed, were the use of argon as the working gas, a power of 100 W, a pressure of 0.6 mbar and an operating time of 4 min. To assess the photocatalytic activity, two protocols, which varied in the P25 immobilization methodology (surface or matrix), were developed. It was concluded that PDMS membranes with P25 on the surface achieved higher removals of parabens during the photocatalytic oxidation and, when the preparation parameters were optimized, these membranes achieved removals of 53 ± 2%, 53 ± 0%, 58 ± 2% for EP, MP and PP, respectively. As such, in this study, it was possible to develop a protocol to produce hydrophilic and photocatalytic P25/PDMS membranes efficient in the abatement of parabens under UV irradiation.

Binder removal from ceramic stereolithography green bodies: A neutron imaging and thermal analysis study

AbstractStereolithography of ceramics remains one of the most powerful additive manufacturing routes for the creation of intricate ceramic parts. Despite its utility as a forming tool, ceramic stereolithography requires a challenging debinding stage due to the requisite high polymeric loading. Earlier research has identified both the polymeric resin composition and debinding atmosphere to be crucial factors in improving debinding performance. Here, we use a combination of thermogravimetric analysis and neutron imaging to examine samples of different compositions printed using the same processing and exposure parameters. We quantify the influence of both polyethylene glycol addition and the use of different debinding atmospheres (argon and vacuum) on the debinding behavior of ceramic pellets. Specifically, we demonstrate a method for examining the concentration gradients that develop during thermal debinding with the aid of neutron tomography. We find that at a constant heating rate of 1°C/min up to 500°C, vacuum atmosphere appears to result in a greater number of cracks as compared to the use of argon. The vacuum atmosphere led to the development of lower concentration gradients in the samples on average. The greatest improvement resulted with the addition of polyethylene glycol to the samples. This addition led to significantly less cracking and much lower concentration gradients in samples during debinding. These results prompt us to conclude that while keeping printing and exposure parameters constant, composition modification has a more significant effect on the debinding improvement than heating atmosphere.

Time-of-flight mass spectrometry with pulsed glow discharge for direct determination of volatile organic compounds in air, nitrogen and argon. Volatile organic compounds ionization processes

Determination of volatile organic compounds (VOCs) in various gases, including atmospheric and exhaled human air, is required to solve a wide range of environmental problems, control the composition of various gases and is increasingly used for diagnosis of various diseases. Lately, methods of soft ionization with minimal fragmentation of the components have been rapidly developed. In particular, our research group is developing an approach to direct analysis of mixtures of VOCs using time-of-flight pulsed glow discharge mass spectrometry. Previously, the effects of different gases and gas mixtures on ionization processes were not compared. Therefore, the ionization mechanisms of VOCs in argon, nitrogen, and air were investigated in the present work. Toluene, p-xylene, chlorobenzene and 1,2,4-trimethylbenzene were chosen as the model VOCs. Optimization of microsecond pulsed glow discharge parameters (period and duration of the discharge pulse, repelling pulse delay time and pressure in the discharge cell) for each compound and a gas mixture of several VOCs was carried out. The predominant ionization mechanisms are the formation of a VOC molecular ion by Penning ionization and the proton transfer reaction; their influence being different for various gases. It is shown that the use of argon even with a small addition of water leads to the predominance of the proton transfer reaction, whereas in nitrogen and air the Penning ionization predominates. The maximum VOC intensities were achieved in air, and the developed approach

Effect of Argon as Filling Gas of the Storage Atmosphere on the Shelf-Life of Sourdough Bread-Case Study on PDO Tuscan Bread.

The short shelf-life of PDO Tuscan bread limits its distribution to markets close to the production area, affecting its commercial success and the economic return by supply chain operators. While the application of MAP to store bread is widely accepted, the suitability of this technique to extend the shelf life of the PDO Tuscan bread is still to be explored. Furthermore, to the best of our knowledge no data are available in the literature about the use of argon as filling gas neither in pure atmosphere nor in combination with CO2. In this context, the aim of this study was to evaluate the effect of different modified packaging atmospheres on the shelf-life of sourdough bread. Slices of bread were stored individually in plastic bags at 23 °C in five different atmospheres (Ar (100%), N2 (100%), CO2 (100%), Mix CO2/N2 (70% CO2, 30% N2), Mix CO2/Ar (70% CO2, 30% Ar)), and Air was selected as a control. To select the best storage conditions, both chemical-physical, rheological, and organoleptic features were evaluated. Results showed that pure gases (CO2, N2, Ar) displayed good qualities as storage atmospheres compared to Air. In contrast, both Mix CO2/N2 and Mix CO2/Ar were the best in slowing down the staling process, thus doubling the shelf-life of bread, compared to other atmospheres. In conclusion, argon, as a preservation atmosphere, seems to be the best solution to extend the shelf-life of PDO Tuscan bread.

DEPENDENCE OF THE PAIN SYNDROME INTENSITY AFTER LAPAROSCOPIC SURGERY ON THE RESIDUAL VOLUME OF WORKING GAS IN THE ABDOMINAL CAVITY

Induction of pneumoperitoneum is a mandatory step in laparoscopic surgery in order to create a workspace for the surgeon. The cause of omalgia (pain in shoulder area) after such interventions is the accumulation of residual gas in the abdominal cavity.There are still no proven methods of quantitative assessment of the residual pneumoperitoneum. Thus, the patterns of relationship between the amount of residual gas and the intensity of pain syndrome have not been studied yet. Considering the fact that the residual gas exerts mechanical distention of anatomical structures and apparently causes local irritation in the peritoneum, it is necessary to develop preventive measures for omalgia which may involve not only the approaches to reduce the amount of residual gas but also the use of alternative gas sources, particularly argon. As inert gas argon possesses many positive qualities, it does not affect the peritoneum, and has no resorptive metabolic effects.
 The goal of our research is to work out an X-ray planimetric method for determining the amount of residual gas after laparoscopic surgery and to assess the dependence of the pain intensity on both, the amount of residual gas and the type of working gas used.
 Material and methods of research. Two experimental groups of patients with uncomplicated cholelithiasis were formed, and carboxyperitoneum and argonperitoneum were used to create the space during laparoscopic cholecystectomy. The groups of examined patients are equivalent by age and sex and are randomized for consecutive admission to the hospital. Both groups include patients who underwent surgery without the use of any drainage means. 24 hours after the operation, a chest plain radiography was performed in order to identify the area of gas crescent sign under the right hemidiaphragm using personally-developed original approach. The technique is based on the use of a mobile application to measure the area of complex geometric shapes. At the same time, the intensity of pain syndrome in the shoulder area was assessed in all the patients by means of NRS (Numeric Rating Scale) in combination with Rotterdam Elderly Pain Observation Scale (REPOS). The technique is aimed to objectify the subjective assessment of pain. Statistical software for Microsoft Excel 2010 was used for processing the study results and calculating Pearson’s correlation coefficient.
 Results of research and their discussion. The obtained results revealed moderate correlation relationship between the area of gas crescent sign under the right hemidiaphragm and pain syndrome intensity. This relationship was confirmed both in the group with carboxyperitoneum and in the group with argon as the working gas. However, it was observed that the proportion of patients with postoperative omalgia in the group with argonoperitoneum is significantly lower. Thus, both hypotheses, concerning the role of mechanical factors in the development of omalgic syndrome and the significance of chemical local peritoneal irritation have been confirmed.
 Conclusions:
 
 The suggested method of radiological planimetry allows to obtaine the digital indicators suitable for statistical analysis which characterize the amount of residual gas after laparoscopic surgery.
 The intensity of pain syndrome exhibits correlation with the amount of residual gas after the surgery.
 The severity of omalgia depends primarily on the amount of residual gas. However, the incidence of omalgic syndrome with the use of carbon dioxide is higher than with argon use.

COMPARATIVE CHARACTERISTICS OF THE DYNAMICS OF CARDIOVASCULAR AND RESPIRATORY EFFECTS OF PNEUMOPERITONEUM BASED ON CARBON DIOXIDE AND ARGON IN LAPAROSCOPIC CHOLECYSTECTOMY

Pneumoperitoneum is one of the most critical components of laparoscopic surgery, which has a negative effect on gas exchange and stress to circulatory buffering system. One of the top priorities of laparoscopic technologies is to minimize the impact on the respiratory and cardiovascular systems, metabolic dynamics and compensatory abilities of homeostasis.
 The main goal of this research work is to compare the effects of carboxyperitoneum and argonoperitoneum on the intraoperative dynamics of CO2 concentration as well as cardiovascular and respiratory characteristics in patients undergoing laparoscopic cholecystectomy for various forms of cholelithiasis.
 Materials and methods. Four experimental groups involved patients based on their nosological form of cholelithiasis and the gas used to induce pneumoperitoneum. All patients underwent laparoscopic cholecystectomy by means of standard procedure. Either medical carbon dioxide or medical argon was used to induce pneumoperitoneum. Intraoperative monitoring of blood carbon dioxide levels PaCO2 was performed by taking venous blood every 15 minutes. Capnometry was performed by means of mainstream analysis using “BIOMED” BM1000C modular patient monitor by recording the discrete values of PetCO2 every 15 minutes, as well as by analyzing photocopies of capnography curves every 15 minutes.
 Intraoperative echocardiography was performed to identify the mean arterial pressure (MAP), heart rate (HR) and cardiac output (CO) in order to assess the effects of different types of pneumoperitoneum on the cardiovascular system.
 Results. The obtained data confirm the expected difference in the indices of cardiorespiratory functions between patients with acute cholecystitis and cholelithiasis without signs of inflammation. The investigation revealed that under the influence of pneumoperitoneum, heart rate and mean arterial pressure increase, while the cardiac output decreases. The respiratory pressure marker depends more on the intra-abdominal pressure and presumably the patient’s body type than on the presence of inflammatory syndrome. Argon insufflation has a slight negative impact on the cardiovascular system. Particularly, the mean arterial pressure and heart rate increase, while the cardiac output marker is less decreased as compared to the use of carbon dioxide. Abdominal pressure has a significant effect on the cardiovascular and respiratory systems regardless of the used type of gas. The combination of high intra-abdominal pressure with the elevated head end of the operating table, which is a common practise during cholecystectomy, has especially great influence on cardiovascular and respiratory functions. Operation which is carried out at decreased pressure allows reducing the deviations of practically all indices.
 Conclusions. Thus, the cardiovascular and respiratory systems adapt under the influence of pneumoperitoneum, providing compensation for the negative effects of mechanical and resorptive-metabolic character. Compensatory-adaptive abilities of the cardiovascular and respiratory systems increase with the decrease of intra-abdominal pressure. The use of argon as a working gas for insufflation into the abdominal cavity during laparoscopy reduces the negative impact of pneumoperitoneum on the cardiovascular and respiratory systems, providing a greater reserve of homeostatic and buffer systems of the body.

Reduction of incandescent spatter with helium addition to the process gas during laser powder bed fusion of Ti-6Al-4V

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.

Development of an inverse low-temperature plasma ionization source for liquid chromatography/mass spectrometry.

An argon inverse low-temperature plasma (iLTP) ionization source for liquid chromatography/tandem mass spectrometry was developed. The iLTP is constructed from simple chromatographic supply materials and is implemented into an atmospheric pressure chemical ionization (APCI) source replacing the APCI discharge needle electrode. The newly developed ion source was coupled to an ultra-high-performance liquid chromatography (UHPLC) system. The argon iLTP was characterized by optical emission spectroscopy. The soft ionization of selected standards was also demonstrated by direct infusion experiments. In addition to the use of argon as the discharge gas, helium, synthetic air, and oxygen were used, which were tested for their performance using testosterone and vitamin D3 . Spectroscopic measurements of the argon plasma were conducted, demonstrating the main emission band of argon metastables with corresponding energies of 11.53 eV and 11.72 eV. Infusion experiments indicate a gentle ionization by iLTP, e.g. caffeine, testosterone, reserpine, vitamin D3 , and 25-hydroxyvitamin D3 , which resulted in the corresponding protonated molecules. The splitless coupling with UHPLC (possible flow rates >1000 μL min-1 ) shows promising results in interday repeatability (n = 10) for the substances with a relative standard deviation of less than 5% and limits of detection for caffeine, testosterone, reserpine, vitamin D3 , and 25-hydroxyvitamin D3 of 10 ng L-1 , 50 ng L-1 , 500 ng L-1 , 5 μg L-1 , and 5 μg L-1 , respectively. The argon iLTP ion source presented in this work shows promising approaches in the field of ionization of small organic molecules. The mechanism related to the discharge gas argon has not been elucidated so far and further investigations are needed. The iLTP ion source shows a very good performance with UHPLC coupling, even at increased flow rates. It could be shown that an argon iLTP can compete with the helium dielectric barrier discharge (DBD) preferred in the literature, making it a more economical choice.

An Assessment of Hydrogen Addition to Methane Combustion with Argon as a Working Fluid in a Constant Volume Combustion Chamber

ABSTRACT Combustion of natural gas in combination with hydrogen, coupled with argon as a working fluid, is a promising approach to increasing the efficiency of internal combustion engines while decreasing emissions. The use of argon as a working fluid effectively eradicates NOx, extends the flammability limits, and increases the thermal efficiency due to its high specific heat ratio. Additionally, the hydrogen addition aids in emissions reduction and enhances the flammability range. In this study, premixed CH4-H2-O2-Ar combustion is experimentally investigated in an optically accessible constant volume combustion chamber to determine the effect of hydrogen addition on laminar burning velocity, flame morphological structure, and instabilities when argon replaces nitrogen as the working fluid. A numerical thermodynamic model is applied to calculate the laminar burning velocity and an image processing technique is used to quantify the flame speed. The experiments show that, in comparison to methane alone, the addition of hydrogen (40%) to the mixture at atmospheric pressure (1 bar) and room temperature (298 K) increases the maximum laminar burning velocity by 37%, increases the maximum flame speed by 35%, and extends the lower and upper flammability limits from equivalence ratio of 0.4 to 0.3 and 1.6 to 1.7, respectively.

Effect of Argon Concentration on Laminar Burning Velocity and Flame Speed of Hydrogen Mixtures in a Constant Volume Combustion Chamber

Abstract Hydrogen combustion, coupled with the use of argon as a working fluid, is a promising approach to delivering clean and efficient energy from internal combustion (IC) engines. The use of hydrogen-oxygen-argon (H2/O2/Ar) mixtures in combustion aids in mitigating harmful environmental pollutants and enables a highly efficient energy conversion process. The use of argon as a working fluid decreases the NOx emissions and increases the thermal efficiency of internal combustion engines due to the high specific heat ratio of noble gases. In this study, premixed hydrogen combustion was investigated with the purpose of examining the effect of the full or partial substitution of argon for nitrogen in air on laminar burning velocity (LBV), flame speed, flame morphology, and instability. The experimental approach uses an optically accessible constant volume combustion chamber (CVCC) with central ignition; the spherical flame development was studied using a high-speed Z-type Schlieren visualization system. Moreover, a numerical model was developed to convert the experimental dynamic pressure rise data to laminar burning velocity. Coupling the model to a chemical equilibrium code aids in determining the burned gas properties. Additionally, an image processing technique has been suggested to compute the flame propagation speed. The experimental and numerical investigations indicate that increasing the concentration of argon as the working fluid in the mixture increases the laminar burning velocity and flame speed while extending the lean flammability limit.

Evaluation of Argon as a Carrier Gas of Liquid Material Vaporization During the Plasma-Enhanced Chemical Vapor Deposition (PECVD) Silicon Oxide Process

This paper investigated the potential use of argon (Ar) as an alternative carrier gas to helium (He) during the tetraethyl orthosilicate–silicon dioxide (TEOS–SiO2) process using a plasma-enhanced chemical vapor deposition (PECVD) system. Due to the shortage or depletion of conventional He gas, it is important to find alternative gases. This study investigated the effects of the Ar carrier gas on the vaporization efficiency and properties of SiO2 film in the PECVD TEOS–SiO2 process for different process conditions, such as flow rate and plasma power. Ar showed a much higher vaporization efficiency and faster deposition rate than He due to its higher molecular weight and plasma density, indicating that SiO2 film can be deposited considerably faster with less Ar gas. While changes in the film density and residual film stress were also noted depending on the types of carrier gas and amounts or types of plasma power, these changes were insignificant and within the controllable process range during the PECVD process. Therefore, the use of Ar gas can reduce costs and contribute to improvements in productivity without affecting the quality of SiO2 film.

DArT, a detector for measuring the 39Ar depletion factor

One of the most powerful techniques for direct detection of dark matter via elastic scattering of galactic WIMPs is the use of liquid argon time projection chambers. Atmospheric argon (AAr) has a naturally occurring radioactive isotope, 39Ar, of cosmogenic origin. The use of argon extracted from underground wells, deprived of 39Ar, is key to the physics potential of these experiments. The DarkSide-20k (DS-20k) dark matter search experiment will operate with 50 tonnes of radio-pure underground argon (UAr), extracted from the Urania plant in Cortez (U.S.A.) and purified in the Aria distillation plant (Sardinia, Italy). Assessing the radio-purity of UAr in terms of 39Ar is crucial for the success of DS-20k, as well as for future experiments of the Global Argon Dark Matter Collaboration (GADMC), and will be done with the experiment named DArT in ArDM. DArT is a small chamber that will contain the argon under test. The detector will be immersed in the LAr active volume of the ArDM detector, located at the Canfranc Underground Laboratory (LSC) in Spain, which will act as active veto for background events coming from photons from detector materials and surrounding rock radioactivity.

Design and construction of a new detector to measure ultra-low radioactive-isotope contamination of argon

Large liquid argon detectors offer one of the best avenues for the detection of galactic weakly interacting massive particles (WIMPs) via their scattering on atomic nuclei. The liquid argon target allows exquisite discrimination between nuclear and electron recoil signals via pulse-shape discrimination of the scintillation signals. Atmospheric argon (AAr), however, has a naturally occurring radioactive isotope, 39Ar, a β emitter of cosmogenic origin. For large detectors, the atmospheric 39Ar activity poses pile-up concerns. The use of argon extracted from underground wells, deprived of 39Ar, is key to the physics potential of these experiments. The DarkSide-20k dark matter search experiment will operate a dual-phase time projection chamber with 50 tonnes of radio-pure underground argon (UAr), that was shown to be depleted of 39Ar with respect to AAr by a factor larger than 1400. Assessing the 39Ar content of the UAr during extraction is crucial for the success of DarkSide-20k, as well as for future experiments of the Global Argon Dark Matter Collaboration (GADMC). This will be carried out by the DArT in ArDM experiment, a small chamber made with extremely radio-pure materials that will be placed at the centre of the ArDM detector, in the Canfranc Underground Laboratory (LSC) in Spain. The ArDM LAr volume acts as an active veto for background radioactivity, mostly γ-rays from the ArDM detector materials and the surrounding rock. This article describes the DArT in ArDM project, including the chamber design and construction, and reviews the background required to achieve the expected performance of the detector.

Plasma nitriding Ti-6Al-4V with the aid non-transmitted plasma-arc using different protection atmosphere

Investigations on the atmospheric plasma nitriding of Ti-6Al-4V are presented. Different operating parameters were varied, e.g. nitriding time, sample temperature and plasma gas composition. The plasma process was realized by a protective argon gas flow as well as by the operation in an argon glove box to investigate the influence of the residual oxygen on the sample surface. The nitride layers were characterized by X-ray diffraction and scanning electron microscopy. Also microhardness measurements were performed on cross sections. The results show that the nitriding success strongly depends on the residual oxygen concentration in the process environment. The use of argon as a local protective gas in the process leads to a reduction of this involuntary oxidation, whereby the quality of the protective gas coverage correlates directly with the quality of the nitride layer formation. A surface hardening of more than 400% compared to the base material could be achieved.

Intensification of the Removal of Iron Impurities from Microporous Aluminum Oxide via Argon Blowing

A model is proposed for intensification of the process of high-temperature vacuum removal of iron impurities from microporous aluminum oxide via purging of the particle layer with argon. In the temperature range characteristic of this process, the pressure of saturating vapors above pure iron is on the order of 0.1 mm Hg. For an impurity with a concentration of several particles per million, the figure is proportionally smaller, and this creates problems with evacuation of the chamber. The use of argon as a carrier gas destroys the rigid connection between the partial vapor pressure of the impurity and the pressure in the vacuum chamber. Calculations show that the argon flow under moderate vacuum 10–5 mm Hg with a mass flow rate on the order of 10–7 kg/(m2 s) provides a very deep purification.