Atmospheric Pressure Research Articles

A novel device for conservation of supplemental oxygen: A randomized, crossover study of the efficiency and non-inferiority of the OXFO System

Background Oxygen is critical to the prevention of hypoxemia-induced morbidity and mortality; yet, access remains inadequate in most low- and middle-income countries despite billions of dollars spent over decades to increase supply. We present a new method for supplemental oxygen delivery whereby the OXFO System (OXFO Corporation, Boston, MA, USA) converts pressurized oxygen to ambient pressure for patient inhalation on demand at a fixed concentration across fluctuations in respiratory rate or tidal volume. This study’s primary aims were to examine the oxygen volume savings and test the non-inferiority of mean peripheral oxygen saturation (SpO2) with the OXFO System (OXFO Condition) compared to conventional continuous flow (Standard Condition) in a clinical population of oxygen-dependent hospitalized adults. Methods We conducted a non-inferiority, single-visit, randomized, crossover design. A total of 20 subjects were randomized to receive either OXFO Condition or Standard Condition first. Subjects were administered oxygen for 20 minutes during each condition after oxygen was titrated to target therapeutic SpO2. A one-sample t-test was performed to compare the mean ratio of oxygen volume dispensed (OXFO Condition/Standard Condition) with 100%. A paired t-test for non-inferiority was used to test the hypothesis that the mean SpO2 for OXFO Condition is no worse than 2.8% lower (absolute difference) than the mean SpO2 for Standard Condition. Results Nineteen subjects were included in the analyses. When considering the dispensing of oxygen as a ratio (OXFO Condition / Standard Condition) for each subject, the mean was 7.7% (standard deviation(SD)=5.4%; range=0-20%) and this was significantly different from 100% (P<0.001). The savings ratio was not significantly correlated with Standard Condition rate of flow (P=0.23). Mean SpO2 for OXFO Condition was 91.07% (SD=2.20%) and 91.35% (SD=1.62%) for Standard Condition and the difference was significantly above the non-inferiority margin of -2.80% (P<0.001). Conclusions The OXFO System saves a significant volume of oxygen while achieving non-inferior mean saturation for hospitalized oxygen-dependent patients. The OXFO System appears to maintain robust volume savings of nearly 13x across doses up to 6 liters per minute (L/min). This has significant implications for advancing equitable access to oxygen.

Enhancing Stability of Surface Au under Oxidizing Conditions through Reduced Bulk Au Content.

Contrary to the common assumption that a higher bulk content of precious metals facilitates the preservation of more surface noble metal by serving as a reservoir for surface enrichment, we demonstrate that a lower bulk content of Au results in a more stable arrangement of Au atoms at the surface of Cu-Au nanoparticles when exposed to an O2 atmosphere. Using ambient pressure X-ray photoelectron spectroscopy, we investigate the surface segregation and oxidation behavior of Cu-Au nanoparticles across various compositions. Our results reveal that in Au-rich nanoparticles exposed to an H2 atmosphere, surface segregation prompts the formation of a continuous Au-enriched shell, which subsequently oxidizes into a complete CuOx shell upon transitioning to an O2 atmosphere. Conversely, in Au-poor nanoparticles during H2 treatment, segregation results in the emergence of Au clusters embedded within the surface layer, persisting upon exposure to O2. This unexpected phenomenon shows that reducing the bulk content of precious metals can enhance the surface stability of noble atoms under oxidizing conditions, as further demonstrated by comparing the catalytic performance of Cu-Au nanoparticles with varying Au bulk contents in CO oxidation.

VOCs conversion in He/H2O plasma produced in a micro-capillary tube at atmospheric pressure

Abstract A non-equilibrium plasma is created in a micro-capillary quartz tube (800 µm of internal diameter), by a DC-pulsed micro-dielectric barrier discharge (micro-DBD) and the propagation of an ionisation wave, in mixtures of He/H2O/VOC at atmospheric pressure where the studied volatile organic compounds (VOCs) are representative of molecules belonging to different chemical families: alcohols (methanol, ethanol, isopropanol, tert-butanol), ketones (acetone), nitriles (acetonitrile), and aromatic hydrocarbons (toluene). The conversion efficiency of these VOCs is studied as a function of the applied voltage on the micro-DBD (or electrical energy deposited in the plasma) and of the initial concentration of the molecules in the range from 1 ppm up to 3000 ppm (depending on the molecule), with the help of high-resolution real-time mass spectrometry Fourier transform ion cyclotron resonance associated to chemical ionisation (CI-FTICR) using H3O+ as precursor ion. A variety of by-products resulting from the conversion of VOCs are identified and quantified, emphasising that the micro-capillary plasma is able to induce a complex chemical reactivity. A qualitative analysis of the involved kinetics, based on the existing literature, reveals that helium species (ions and metastable states) and radicals coming from the dissociation of the water molecules (O and OH) are the most probable candidates to explain the formation of all compounds detected by the CI-FTICR apparatus. Quenching processes of the metastable He(23S) by the VOCs, leading to the dissociation of the molecules, are suggested to explain some of the experimental results.

Predicting Leidenfrost Temperature and Effects of Impact Conditions on Droplet Size Distribution in Film-Boiling Regime

Abstract The interaction of a droplet with a solid wall is relevant in various engineering applications. The properties of the resulting secondary droplets are determined by the wall temperature, ambient pressure, impact momentum, and impact angle. This paper presents a comprehensive characterization of drop-wall interactions and the subsequent atomization as a function of the combined effects of such parameters. A drop-wall interaction model is derived for F-24 droplets using smoothed particle hydrodynamics (SPH). The model can predict different impact outcome regimes (deposition, rebound, contact-splash, and film-splash) for different ambient pressures, wall temperatures, and impact parameters. The model also addresses the effect of ambient pressure on the Leidenfrost behavior. Size distributions of secondary droplets are compared for vertical and nonvertical impacts of F-24 droplets on superheated surfaces in the film-boiling regime. The non-dimensional Sauter mean diameter (SMD) of the secondary droplets varies based on the position in the impact plane for all the nonvertical impacts but remains almost unchanged for vertical impacts. The leading arc for nonvertical impact consists of larger secondary droplets, and the size decreases toward the trailing arc. An empirical relation is proposed to represent this trend. This research sheds light on successive droplet impacts by studying the effects of impact frequency on SMD evolution. The results are compared to single droplet impact cases for different fuels and Weber numbers. The size of secondary droplets for successive impacts is observed to be nearly indistinguishable from that of single-droplet vertical impacts.

An evaluation of the combustion temperature profile of Ba(NO3)2-based composition

The study examined both theoretical and experimental combustion temperatures of Ba(NO3)2-based samples of composition with an oxidizer excess coefficient of α~0.72 under various pressures. The results indicate that at low pressures, the combustion temperature of the samples is significantly lower than the calculated value. The temperature profile in the combustion wave at atmospheric pressure was determined, revealing that the samples exhibit a high surface combustion temperature. The majority of the heat required for the propagation of the sample's combustion is released in the condensed phase. These findings underscore the influence of pressure on combustion characteristics and emphasize the importance of considering phase interactions in understanding combustion behaviors.

Methodology for Testing Selected Parameters of Low-Current Vacuum Electric Arc

This article presents the author’s methodology for testing selected parameters of a low-current vacuum arc, implemented using an innovative test stand based on a vacuum discharge chamber with a contact system mounted inside. In order to verify the validity of the adopted research methodology, as well as the correctness of the operation of the developed laboratory bench, measurements and calculations were made, among other things, of the energy and burning time of the vacuum arc, depending on selected factors, such as pressure and the delay time of the contact opening, calculated from the “passage through zero” of the sinusoid of the current flowing through the system. The tests were performed at 230 V and a current of 5 A for two pressure values: p1 = 1.00 × 105 Pa (atmospheric pressure) and p2 = 4.00 × 10−3 Pa (high vacuum environment). It was found that the vacuum insulation technique allows a significant reduction in the value of the arc energy and the burning time of the arc. It was also observed that in the case of a high vacuum environment, the ignition of the vacuum arc occurs after a time equal to about 3 ms from the “passage through zero” of the current flowing through the system. Below this value, the phenomenon did not occur. The results obtained provide an opportunity for the design and manufacturing of vacuum switchgear, where there is the prospect of reducing the negative effects associated with the arc burning process in the contact gap.

Emergence of topological phase and non-trivial surface states in rare-earth semimetal GdSb with pressure

Abstract We study the evolution of band topology under external pressure in rare-earth gadolinium mono-antimonide (GdSb) using first-principles calculations. This material crystallizes in a rocksalt-type structure and shows a structural phase transition (SPT) to a CsCl-type structure at 26.1 GPa. The phonon dispersions are analyzed to ascertain the dynamical stability of this material. We use hybrid density functional theory with the inclusion of spin–orbit coupling to investigate the structural, electronic, and topological phase transitions (TPTs). At ambient pressure, GdSb shows a topologically trivial state which is in agreement with existing experimental reports. The first TPT is observed at 6 GPa of hydrostatic pressure (at the high symmetry X-point) which is verified with the help of single-band inversion and surface state analysis along the (001) plane. The non-zero value of the first Z2 topological invariant and the presence of the Dirac cone also confirm the topological phase of this material. A further increase in pressure to 12 GPa results in two band inversions at Γ- as well as X-points, which corresponds to the trivial nature of GdSb. The same is also verified with (0; 000) values of Z2 topological invariants and a pair of Dirac cones in surface states. It is noted that the crystal symmetries are preserved throughout the study and the TPT values are much lower than the SPT pressure, i.e. 26.1 GPa.

Selective hydrogenation of 5‐hydroxymethylfurfural to 5‐hydroxymethyltetrahydrofurfural over heterogeneous Pd catalyst under mild conditions

5‐Hydroxymethylfurfural (5‐HMF) derived from lignocellulose represents an important platform molecule that could be employed in the selective hydrogenation of the furan ring to prepare 5‑hydroxymethyltetrahydrofurfural (HMTHF). However, the reported catalytic systems for the synthesis of HMTHF using 5‐HMF still require additional hydrogen pressure. In this study, the Pd/ZrO2 catalyst with uniformly dispersed Pd nanoparticles was prepared via a simple impregnation reduction process. This catalyst exhibited excellent catalytic activity and selectivity for the hydrogenation of 5‐HMF to HMTHF. High HMTHF yield up to 92.3% was produced under mild reaction conditions of ambient hydrogen pressure and room temperature in methanol solvent. This result was superior to the most catalytic systems that had been reported so far. The mechanism study revealed that the active hydrogen species on the surface of the Pd nanoparticles and the reaction solvent in this study were the pivotal factors influencing the hydrogenation of furan rings in 5‐HMF.

Optimizing the Pore Structure of Lotus-Type Porous Copper Fabricated by Continuous Casting.

Lotus-type porous copper was fabricated using a continuous casting method in pressurized hydrogen and nitrogen gas atmospheres. This study evaluates the effects of process parameters, such as the hydrogen ratio, total pressure, and transference velocity, on the resulting pore structure. A continuous casting process was developed to facilitate the mass production of lotus-type porous copper. To achieve the desired porosity and pore diameter for large-scale manufacturing, a systematic evaluation of the influence of each process parameter was conducted. Lotus-type porous copper was produced within a hydrogen ratio range of 25-50%, a transference velocity range of 30-90 mm∙min-1, and a total pressure range of 0.2-0.4 MPa. As a result, the porosity ranged from 36% to 55% and the pore size varied from 300 to 1500 µm, demonstrating a wide range of porosities and pore sizes. Through process optimization, it is possible to control the porosity and pore size. The hydrogen ratio and total pressure were found to primarily affect porosity, whereas the hydrogen ratio, transference velocity, and total pressure significantly influenced pore diameter. When considering these parameters together, porosity was most influenced by the hydrogen ratio, whereas the total pressure and transference velocity had a greater influence on pore diameter. Reducing the hydrogen ratio and increasing the transference velocity and total pressure reduced the pore diameter and porosity. This optimization of the continuous casting process enables the control of porosity and pore diameter, facilitating the production of lotus-type porous copper with the desired pore structures.

Effects of atmospheric pressure plasma treatment and its aging behaviors on interfacial strength of PI/PEEK composite film

AbstractSince the properties of surface roughness with time and the wettability pattern of polymer surfaces transformed by plasma remain unclear. In order to understand the mechanism of aging effect on film properties, this paper analyzes the aging of plasma‐treated PI films. The optimal treatment conditions were first explored by adjusting the plasma treatment power. Based on the effect of plasma treatment power on the surface physicochemical properties and mechanical properties of PI films. It was found that the content of oxygen‐containing functional groups on the surface of the film was highest at a plasma treatment power of 800 W, and the surface energy reached a maximum value of 67.71 mJ/m2. As the treatment power increases, the surface etching of the PI film increases significantly, as does the roughness. However, if the power is too high, it can cause excessive etching, resulting in peeling of the film surface. In addition, the mechanical properties of the films decreased with increasing plasma treatment power. Based on the effect of plasma treatment power on the surface physicochemical and mechanical properties of PI films, the best overall modification effect of PI films was determined when the treatment power was 800 W and the speed was 6 mm/s. And at 800 W, the peel strength of the PI/PEEK composite film reached a maximum value of 9.55 N/cm, which was 77.84% higher than that of the untreated composite film. However, plasma‐treated PI films can experience surface remodeling after being exposed to air for a period of time. In this paper, the wettability as well as the mechanical properties of the films are analyzed for different aging times. The results showed that after 30 days of plasma treatment, the O/C and N/C contents on the surface of the PI film decreased, and the wettability performance decreased by 19.45% compared with that of the recently treated film.

Sensitive determination of volatile nitrosamines with ambient pressure ammonium-adduct ionization mass spectrometry.

In recent years, the control of volatile N-nitrosamines (NAs) has been of interest in the pharmaceutical and food industries, as many of these compounds are probable human carcinogens. Thus, rapid and trace-level quantitative determination methods are in urgent demand. In this work, ambient pressure ammonium-adduct ionization mass spectrometry was proposed for the sensitive detection of volatile nitrosamines in various pharmaceutical headspaces. The ammonium ions produced through electrospray ionization acted as reactant ions for NAs to generate ammonium-NA adduct ions and underwent in-source collision-induced dissociation to produce protonated NAs, which were detected by mass spectrometry. The ionization selectivity and sensitivity for various volatile NAs were improved significantly using the developed method, which was demonstrated by the limit of quantification (LOQ) below 52ng L-1 for all NAs, and the quantitative performance was consequently improved. Different NAs exhibited almost equimolar response using NH4+ as the reactant ion, with at least a twofold enhancement in intensity for the individual compounds relative to when using H+ as the reactant ion. The proposed method is a rapid, sensitive, and environmentally economical approach that uses few reagents.

Ion Source Complementarity for Characterization of Complex Organic Mixtures Using Fourier Transform Mass Spectrometry: A Review.

Complex organic mixtures are found in many areas of research, such as energy, environment, health, planetology, and cultural heritage, to name but a few. However, due to their complex chemical composition, which holds an extensive potential of information at the molecular level, their molecular characterization is challenging. In mass spectrometry, the ionization step is the key step, as it determines which species will be detected. This review presents an overview of the main ionization sources employed to characterize these kinds of samples in Fourier transform mass spectrometry (FT-MS), namely electrospray (ESI), atmospheric pressure photoionization (APPI), atmospheric pressure chemical ionization (APCI), atmospheric pressure laser ionization (APLI), and (matrix-assisted) laser desorption ionization ((MA)LDI), and their complementarity in the characterization of complex organic mixtures. First, the ionization techniques are examined in the common direct introduction (DI) usage. Second, these approaches are discussed in the context of coupling chromatographic techniques such as gas chromatography, liquid chromatography, and supercritical fluid chromatography.

Apparent molar volume at infinite dilution, expansivities and electrochemical behaviours of binary system (tetramethylpiperidine 1-oxyl-based ionic liquids + water)

ABSTRACT At T = (278.15–318.15) K and atmospheric pressure, Hepler’s constant values, (∂2 V B/∂ T 2) P , and apparent molar expansivities (E φ) were calculated using the temperature dependence of apparent molar volumes (V B). Because of the increase in hydrophobic hydration of tetramethylpiperidine 1-oxyl-based ionic liquids (TILs), the Hepler’s constant values were found to change from positive to negative, indicating that the TILs under consideration changed primarily from structure-promoting to structure-breaking. The critical micelle concentration of conductivity (CMC) was calculated based on experimental conductivity, which reflects the dissociation and the interaction and aggregation behaviour of TILs.

Synergetic effect of iron and tungsten on molybdenum‐doped HZSM‐5 zeolite in catalytic methane dehydroaromatization

AbstractMethane dehydroaromatization is a viable route for production of carbon and valuable petrochemicals. Unlike Fischer–Tropsch and methanol synthesis processes which have been scaled up to commercial level, development of methane dehydroaromatization to commercial level has been hampered by various challenges. In this work, a 5.4 wt. % trimetallic (Fe‐W‐Mo/HZSM‐5) catalyst has been synthesized, characterized, and applied in catalytic methane dehydroaromatization reaction. A gas chromatograph was used to analyze both liquid and gaseous products from the reactor. Based on 0.0013 moles of reacted methane after 240 min time on stream at 750, GHSV 960 mlg‐1cath‐1, and atmospheric pressure, a 5.4% Mo/HZSM‐5 catalyst recorded 7.9% methane conversion, 10.6% C2 hydrocarbon selectivity, 51.8% benzene selectivity, 9.8% toluene selectivity and 27.8% coke selectivity. Doping Mo/HZSM‐5 with Fe reduced methane conversion by 4.0%, increased C2 hydrocarbon selectivity by 1.7%, reduced benzene selectivity by 6.2% and increased toluene and coke selectivity by 1.8% and 2.8% respectively. Doping Mo/HZSM‐5 with W increased methane conversion by 7.3%, reduced C2 hydrocarbon selectivity by 2.1%, reduced benzene selectivity by 7.6% and increased toluene and coke selectivity by 0.3% and 9.4% respectively. When iron and tungsten were loaded onto Mo/HZSM‐5, catalytic activity of the tri‐metallic catalyst in methane conversion reduced by 2.0%, C2 hydrocarbon selectivity increased by 2.7%, benzene selectivity reduced by 3.1%, toluene selectivity reduced by 3.7%, and coke selectivity increased by 4.1%. Therefore, this present work demonstrates that metal synergy in a tri‐metallic catalyst plays a role in methane conversion and selectivity towards useful hydrocarbons.

Development of a novel bio char for CO2 capture and biogas upgrade: Static and dynamic testing

The optimization of the pyrolysis of the spruce sawdust was conducted based on the yield, textural properties, and static capture capacity of the chars to generate a new micro porous char for biogas upgrade. The nature of the precursor (C: 45.68 %, H: 6.08 %, N: 0.15 %, and 0.34 % ash content) helped to tune the porosity of the char for capturing CO2 from gas streams and biogas. The optimization of the pyrolysis at 700 °C, a heating rate of 10 °C / min and holding time of 1 hour, produced a microporous char with high yield, CO2 capture capacity and CO2/CH4 selectivity. The presence of the oxygen and nitrogen-containing functional groups in the optimum char help in the selective capture of CO2. The static CO2 capture capacity of the optimum char was 1.98 mmol/g at atmospheric pressure and 25 °C (90 % CO2 stream). The CSD (700−10−60) have capture capacity of 1.50 mmol/g (at a feed gas stream of 50 % CO2 and adsorption temperature of 25 °C and 120 kPa) which is equivalent to Norit C and Calgon BPL. Hence, spruce sawdust can be used to produce efficient biochar for biogas upgrade (CO2 capture) owing to high capture capacity and CO2/CH4 selectivity (around 3) and easy regeneration of the biochar for 10 consecutive cycles.

Investigation of heat leakage calculations and experiments for a wide-mouth liquid nitrogen tank

ABSTRACT With the continuous development of biomedicine, the long-term low-temperature storage of biological samples has become essential. In order to meet the demand for long-term storage of liquid nitrogen to keep samples safe, a study on the evaporated gas recycling storage of liquid nitrogen tanks will be carried out. This research utilizes new approach to accurately calculate the heat leakage of the liquid nitrogen tank. The experimental results show that the theoretical heat leakage is 6.16 W, and the actual heat leakage is 7.07 W. By incorporating the insulating plug, the actual heat leakage was reduced by 61.2%, decreasing to 2.74 W, and the calculated heat leakage is 2.47 W. The error margin in both cases was approximately 10%. Furthermore, in contrast to existing investigations, this experiment with the 8W@77K pulse tube cryocooler for recovering nitrogen is conducted under environmental pressure rather than overpressure, and it also takes into account the sensible heat issues caused by ambient pressure. The ratio of 1.81 W of sensible heat to 2.74 W of latent heat is 2:3, indicating that under ambient pressure conditions, the impact of sensible heat cannot be ignored. The key improvement methods are given to improve the success rate of the experiment. The research results provide a useful reference for the re-cycling and storage of liquid nitrogen.

Chromium Immobilization as Cr-Spinel by Regulation of Fe(II) and Fe(III) Concentrations

The complex environmental conditions at Cr-contaminated sites, characterized by uneven ion distribution, oxidants competition, and limited solid-phase mobility, lead to inadequate mixing of Fe-based reducing agents with Cr, posing significant challenges to the effectiveness of Cr remediation through Cr-spinel precipitation. This study investigates the distinct roles of Fe(II), Fe(III), and Cr(III) in Cr-spinel crystallization under ambient temperature and pressure. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray absorption near-edge structure spectroscopy, and Mössbauer spectroscopy were employed to elucidate the phase composition, microstructure, and ion coordination within the precipitates. Our findings indicate that Fe(II) acts as a catalyst in the formation of the spinel phase, occupying octahedral sites within the spinel structure. Under the catalytic influence of Fe(II), Fe(III) transitions into the spinel phase, occupying both the tetrahedral and the remaining octahedral sites. Meanwhile, Cr(III), due to its high octahedral site preference energy, preferentially occupies the octahedral sites. When Fe(II) or Fe(III) is present but does not meet the ideal stoichiometric ratio, a deficiency in Fe(II) leads to low yield and poor crystallinity of Cr-spinel, whereas a deficiency in Fe(III) can completely inhibit its formation. Conversely, when either Fe(II) or Fe(III) is in excess, the formation of Cr-spinel remains feasible. Furthermore, metastable Cr phases can be transformed into stable Cr-spinel by adjusting the Fe(II)/Fe(III)/Cr(III) ratio. These results highlight the broad range of conditions under which Cr-spinel mineralization can occur in environmental settings, enhancing our understanding of the mechanisms driving Cr-spinel formation in Cr-contaminated sites treated with Fe-based reducing agents. This research provides critical insights for optimizing Cr remediation strategies.

The oxidative stress mechanism of Bacillus cereus spores induced by atmospheric pressure plasma jet

Emerging plasma technology has demonstrated its effectiveness in inactivating bacteria and spores, showing wide applicability in environment cleaning and in the food supply chain. Studies have revealed that the main reason of plasma-mediated bacterial inactivation were contributed to the oxidative damage on inner membranes (IMs) of cell, while few research paid attention to the oxidation stress process of lipid in spores’ IMs. This study investigated the impact of atmospheric pressure plasma jet (APPJ) treatment on spore inactivation, focusing on oxidative stress mechanisms and changes in membrane lipid composition. Results demonstrated that APPJ treatment induced significant oxidative stress within spores, characterized by elevated levels of reactive oxygen and nitrogen species (RONS). This oxidative stress led to the peroxidation of glycerophospholipids, particularly phosphatidylglycerol, phosphatidylcholine, and cardiolipin, major components of spore membranes. Subsequently, the rearrangement of membrane lipid and the formation of lipid hydroperoxide, caused by the released cations and RONS, accelerated membrane instability. These changes correlated with increased membrane permeability and structural damage observed via flow cytometry, indicating the critical role of membrane lipid peroxidation in spore inactivation. Furthermore, the study highlighted the potential of APPJ as a robust technology for enhancing food safety by targeting spore-forming pathogens throughout the food supply chain.

PNIPAM Mesoglobules in Dependence on Pressure.

Poly(N-isopropylacrylamide) (PNIPAM) in aqueous solution forms mesoglobules above its cloud point temperature Tcp. While these are small and compact at atmospheric pressure, they are large and water-rich at high pressure. To identify the transition between these states, we employed optical microscopy and carried out isothermal pressure scans. Using very small angle neutron scattering, we determined the size and water content of the mesoglobules in pressure scans at different temperatures above Tcp. We observe a distinct transition at pressures of 35-55 MPa with the transition pressure depending on temperature. While the transition is smooth at high temperatures, i.e., far away from the coexistence line, it is abrupt at low temperatures, i.e., close to the coexistence line. Hence, at high temperatures, the swelling of the mesoglobules dominates, whereas at low temperatures, the coalescence of mesoglobules prevails. Subsequently decreasing the pressure results in a gradual deswelling of the mesoglobules at high temperature. In contrast, at low temperatures, small and compact mesoglobules form, but the large aggregates persist. We conclude that, on the time scale of the experiment, the disintegration of the large swollen aggregates into small and compact mesoglobules is only partially possible. Erasing the history by cooling the sample at the maximum pressure into the one-phase state does not result in qualitative changes for the behavior with the only difference that Fewer mesoglobules are formed when the pressure is decreased again. The newly identified transition line separates the low-pressure from the high-pressure regime.

Microscopic probing of the superconducting and normal state properties of Ta2V3.1Si0.9 by muon spin rotation

The two-dimensional kagome lattice is an experimental playground for novel physical phenomena, from frustrated magnetism and topological matter to chiral charge order and unconventional superconductivity. A newly identified kagome superconductor, Ta2V3.1Si0.9 has recently gained attention for possessing a record high critical temperature, TC = 7.5 K for kagome metals at ambient pressure. In this study we conducted a series of muon spin rotation measurements to delve deeper into understanding the superconducting and normal state properties of Ta2V3.1Si0.9. We demonstrate that Ta2V3.1Si0.9 is a bulk superconductor with either a s+s-wave or anisotropic s-wave gap symmetry, and has an unusual paramagnetic shift in response to external magnetic fields in the superconducting state. Additionally, we observe an exceptionally low superfluid density − a distinctive characteristic of unconventional superconductivity − which remarkably is comparable to the superfluid density found in hole-doped cuprates. In its normal state, Ta2V3.1Si0.9 exhibits a significant increase in the zero-field muon spin depolarisation rate, starting at approximately 150 K, which has been observed in other kagome-lattice superconductors, and therefore hints at possible hidden magnetism. These findings characterise Ta2V3.1Si0.9 as an unconventional superconductor and a noteworthy new member of the vanadium-based kagome material family.