Application Of External Pressure Research Articles

Does gas supersaturation by a chemical reaction produce bulk nanobubbles?

HypothesisSupersaturation of dissolved gas is the most commonly reported method for generating long-lived bulk nanobubbles. However, these reports are treated with skepticism because of the lack of techniques that directly show that these particles are gas filled bubbles. Therefore, this work has tested the hypothesis that supersaturation obtained by a chemical reaction produces long-lived nanosized bubbles in bulk using an established protocol that relies on evaluating the density of nanoparticles and measuring their response to external pressure. ExperimentsNanoparticles were generated using a chemical reaction between aqueous solutions of ammonium chloride and sodium nitrite. Standard nanoparticle sizing techniques, such as nanoparticle tracking analysis and dynamic light scattering, were utilized to determine the size and stability of the nanoparticles. Resonant mass measurement was used to measure the buoyant mass of the nanoparticles, and their compressibility was investigated by measuring their size under the application of external pressure. FindingsThe formation of nanoparticles was consistent with the kinetics of nitrogen gas evolution produced in the reaction, where the nanoparticle size was shown to be dependent on the pH and concentration of the reactants. However, the chemical reaction was found to generate incompressible nanoparticles with a density larger than that of the solvent, confirming that these particles were not gas-filled bubbles.

Permanent disposal of Cs ions in the form of dense pollucite ceramics having low thermal expansion coefficient

Abstract A promising method for removal of Cs ions from water and their incorporation into stable crystal structure ready for safe and permanent disposal was described. Cs-exchanged X zeolite was hot-pressed at temperature ranging from 800 to 950 °C to fabricate dense pollucite ceramics. It was found that the application of external pressure reduced the pollucite formation temperature. The effect of sintering temperature on density, phase composition and mechanical properties was investigated. The highest density of 92.5 %TD and the highest compressive strength of 79 MPa were measured in pollucite hot-pressed at 950 °C for 3 h. Heterogeneity of samples obtained at 950 °C was determined using scanning electron microscopy. The pollucite hot-pressed at 950 °C had low linear thermal expansion coefficient of ∼4.67 × 10−6 K−1 in the temperature range from 100 to 1000 °C.

Red Shift in Optical Properties of Type-I Al0.45Ga0.55As/GaAs0.84P0.16/Al0.45Ga0.55As Nano-heterostructure under External Strain

The application of external pressure on a heterostructure produces changes in the lattice parameter and symmetry of the material. These in turn produce significant changes in the electronic bandstructure. Due to the application of external pressure energy gaps are altered. This paper reports the energy bandstructure, wavefunctions and optical gain in type-In-Al0.45 Ga0.55 As/GaAs0.84P0.16 / p-Al0.45 Ga0.55 As nano-heterostructures under uniaxial strain (-1 to +1 GPa) along [110] directions in the red visible region. Numerical calculations of the photonic energy and optical gain of TE and TM modes in GaAsP/AlGaAs laser diode structure have been carried out for various uniaxial strain at temperature 300 K. The band structure was calculated using 6×6 Luttinger-Kohn Hamiltonian to determine sub-band dispersion and corresponding wavefunctions. The Heterostructure is observed to operate in the energy range 1.62 to 1.78 eV (696 to 765 nm).

Structure/function correlation of thixotropic additives based on three leaf-like triamide derivatives containing three alkyl-chains

The effect of the solvent gelation ability of three leaf-like triamide derivatives, having three 12-hydroxystearyl or octadecyl chains, as thixotropic-induced additives was investigated. Furthermore, the clarification of origin of the physical properties of these compounds was carried out by monolayer investigation on the water surface. The solvent gels formed by the addition of these triamide compounds reflowed on application of external pressure. Two kinds of three leaf-like triamide derivatives achieved nanofiber formation by intermolecular hydrogen bonding in an organic solvent. The nanofiber film of the three leaf-like triamide derivative with an asymmetric carbon (owing to the introduction of a hydroxyl group at the 12th position of the stearyl chain) exhibited chirality because of its structural configuration. The nanofibers of the triamide derivative that exhibited chirality did not grow linearly, and the solvent containing these fibers gelled more efficiently. It was predicted that a more entangled nanofiber aggregate forms a sponge-like structure, which abundantly incorporates the solvent molecules. The influence of the hydrogen bond between the hydroxyl groups at the 12th position of the stearyl chain was evaluated by experiments on the monolayers of the triamides. As a result, only the triamide derivative containing an asymmetric carbon was able to form a nanofiber in the monomolecular layer.

(Invited) Electronic Properties of ABO4 Photo-Catalysts Under Nb-Substitution and Phase/Pressure-Related Distortions

Both SbTaO4 and SbNbO4 in the orthorhombic α-Sb2O4 phase have demonstrated pure water splitting as photo-catalysts. Previous experimental studies have shown a significant difference in reported bandgap values for SbTaO4 such as 3.71 eV and 2.28 eV. We have studied SbTa1-xNbxO4 (x = 0, 0.25, 0.5, 0.75, 1) in the tetragonal, orthorhombic, and monoclinic phases. The resulting Sb3+ M 5+O-2 4 material can be classified as a ns2 md0 ternary metal oxide. We have studied the effects of structural symmetry related distortions on the band gaps and overall energetics of SbMO4 compounds (M = Ta, Nb). Evolution of the electronic structures was studied as one transitions from a system of 4d bands to 5d bands, and whether this has any effect on the Sb oxidation state or its lone pair s electrons. From the atomic point of view, electronic correlation energy is higher in Ta 5d than in Nb 4d, and Nb 4d band is higher in energy than Ta 5d. These were examined in terms of oxidation states in their respective solids. We look at the effects of increasing Nb concentration on the electronic structure of SbTa1-xNbxO4 alloy with emphasis on polyhedral and overall cell distortions. We decouple the effects caused by the presence of different nd cations from those caused by distortions and reorientation of various polyhedra. BiVO4 Belongs to the same group of materials; we will also present the electronic structure changes caused by Nb incorporation in BiVO4 and the application of external pressure. Through the analyses of the chemical-potential landscape, we have determined the single-phase stability zone of BiVO4 with the Nb doping. Application of external pressure improved the single-phase stability zone. We have also focused on the local structural distortions near the Nb doping site, especially on the BiO8 octahedra. We have shown here that pressure-induced symmetrization of BiO8 dodecahedron could lower the electron’s effective mass and therefore can help to improve the photo-conduction property of BiVO4. This work is supported by NSF-award # 1609811. We also acknowledge the computational time from Texas Advanced Computing Center (TACC).

Analysis of the effect of applying external mechanical pressure on next generation silicon alloy lithium-ion cells

This research will focus on characterising and analysing next generation batteries consisting of silicon-alloy/graphite blend anode combined with a nickel rich lithium nickel manganese cobalt oxide (NMC 622) as cathode. The study is performed on prototype pouch cells (1.4 Ah). Furthermore, the effect of applying external pressure on the pouch cell is investigated. The application of external pressure has a significant beneficial impact, more specifically a 19% increase in capacity combined with a significant decrease of 50% of the discharge ohmic resistance. To investigate and quantify the pressure variation over the state of charge (SoC) a dedicated set-up has been developed which allows to apply an external pressure while measuring the pressure variation. Up to 30 N of pressure variation is observed during static tests, while no pressure variation can be observed during short pulses, demonstrating its potential to use pressure as SoC estimator. Finally, a study on the effect of initial applied external pressure on the cells' lifetime has shown that the initial applied pressure, within the range of tested pressures, has little impact on the cells’ performance and lifetime.

Observation of subkelvin superconductivity in Cd3As2 thin films

We report the first experimental observation of superconductivity in Cd$_3$As$_2$ thin films without application of external pressure. Surface studies suggest that the observed transport characteristics are related to the polycrystalline continuous part of investigated films with homogeneous distribution of elements and the Cd-to-As ratio close to stoichiometric Cd$_3$As$_2$. The latter is also supported by Raman spectra of the studied films, which are similar to those of Cd$_3$As$_2$ single crystals. The formation of superconducting phase in films under study is confirmed by the characteristic behavior of temperature and magnetic field dependence of samples resistances, as well as by the presence of pronounced zero-resistance plateaux in $dV/dI$ characteristics. The corresponding $H_c-T_c$ plots reveal a clearly pronounced linear behavior within the intermediate temperature range, similar to that observed for bulk Cd$_3$As$_2$ and Bi$_2$Se$_3$ films under pressure, suggesting the possibility of nontrivial pairing in the films under investigation. We discuss a possible role of sample inhomogeneities and crystal strains in the observed phenomena.

Niobium Doping in BiVO4 : Interplay Between Effective Mass, Stability, and Pressure.

We have applied density functional theory to study the electronic structure changes caused by Nb incorporation in BiVO4 and the application of external pressure. The overall solubility of Nb in BiVO4 is usually high, and the presence of oxygen vacancies affect the dopability of Nb in BiVO4 . Through the analyses of the chemical-potential landscape, we have determined the single-phase stability zone of BiVO4 with the Nb doping. The most favorable Nb doping is simultaneous substitutions at both V- and Bi-sites. Even though Nb substitution at only V-site is next favorable, the band gap change is not very significant which agrees with an earlier experiment. However, it does change the electron effective mass by 20 % owing to the presence of Nb 4d bands in the conduction bands, which explains better catalytic activity by Nb-doped BiVO4 . In addition, application of external pressure the single-phase stability zone in the chemical-potential landscape. We have also focused on the local structural distortions near the Nb doping site, especially on the BiO8 octahedra. We have shown here that pressure-induced symmetrization of BiO8 dodecahedron lowers the electron's effective mass further and therefore can help to improve the photoconduction property of BiVO4 .

Generation of nanoparticles upon mixing ethanol and water; Nanobubbles or Not?

HypothesisThe debate as to whether nanoparticles that are formed upon mixing ethanol and water are nanobubbles or other nanoparticles has continued over the past decade. In this work, we test the hypothesis that long lived bulk nanobubbles are produced upon mixing ethanol and water, using techniques that probe the density and the pressure response of the nanoparticles. ExperimentsNanoparticles were generated spontaneously upon mixing high-purity ethanol and high-purity water. The size distribution of these nanoparticles was obtained using nanoparticle tracking analysis. The mean density of the nanoparticles was determined using resonant mass measurement, and the response of the nanoparticles to the application of external pressure was measured using dynamic light scattering. FindingsThe ethanol-water mixture was found to produce only positively buoyant particles, with a mean density of 0.91 ± 0.01 g/cm3, and the external pressure had only a minimal effect on the size of these nanoparticles. Degassing the solvents before mixing led to a significant reduction in the number of nanoparticles produced. Allowing the solutions to re-gas restored their ability to produce nanoparticles. These experiments reveal that ethanol-water mixing produces nanoparticles that result from the accumulation of material at the interface of dissolving bubbles.

Study of PEM Fuel Cell End Plate Design by Structural Analysis Based on Contact Pressure

A fuel cell stack is configured to power any load ranging from watts to megawatt by varying cells connected in series. During stack assembly, major emphasis must be placed on application of adequate external pressure for reducing the ohmic losses, the purpose of which is to achieve proper contact between the cell components and minimize the contact resistance. Present work aims to study the influence of geometry of the cell, bolt configuration, gasket thickness mismatch, and material properties of different components of average and distribution contact pressure. The geometries are evaluated for end plate designs with a view to understand the pressure distribution and contact resistance in each case. Among different designs, extruded hexagon is found to perform well with an average contact pressure of 0.13 MPa and contact resistance of 28 Ω-cm2. Greater gasket thickness requires higher forces to be applied before the GDL makes contact with BPP. The effect of gasket thickness mismatch is evaluated for different values to identify its appropriate value. The pressure is applied using bolts and position and number of bolts is determined for homogeneous contact pressure on the active area. This study provides a framework for future end plate design of fuel cells.

High pressure affects on optical characteristics of AlGaAs/GaAsP/AlGaAs nano-heterostructure

This paper gives a detailed report on the tunability of optical gain characteristics of type-I n-Al0.45Ga0.55As/GaAs0.84P0.16/p-Al0.45Ga0.55As nano-scale hetrostructure under the external pressures applied along [001] and [100] directions. In order to find the carriers wavefunctions, their localizations and sub-band dispersions in the heterostrcuture, a 6 ×6 K –L Hamiltonian was solved. In addition, the optical and momentum matrix elements were also calculated followed by the calculation of TE and TM optical gain under the applied pressure along [001] and [100] directions. According to the quantitative analysis of the simulated results, it can be suggested that the application of external pressure along [001] direction within TE mode is one of the preferable approaches for the efficient improvement in the gain characteristics of the n-Al0.45Ga0.55As/GaAs0.84P0.16/p-Al0.45Ga0.55As nano-scale hetrostructure based laser performance in the NIR (near ifrared region).

Effect of hydrostatic pressure on the magnetic and magnetocaloric properties of Fe-doped MnCoGe alloys

Detailed structural and magnetic investigations have been performed on two equally Fe-doped MnCoGe alloys of nominal compositions Mn0.875Fe0.125CoGe and MnCo0.875Fe0.125Ge. The presence of martensitic phase transition (MPT) in both alloys is clear from the temperature variation of structural and magnetic properties. The nature of MPT is found to be complete in the Mn site Fe-doped alloy. On the other hand, a partial nature of the MPT is observed for the Co site Fe-doped alloy. The application of external hydrostatic pressure hardly affects the magnetic and structural transition temperatures. Both alloys show a significant amount of the magnetocaloric effect in ambient as well as in high pressure situation around their magnetic and structural transition regions.

Synthesis of solid acid catalysts for esterification with the assistance of elevated pressure

Abstract Acidic catalysts dedicated for esterification processes were prepared by immobilization of (3-mercaptopropyl)trimethoxysilane (MPTMS) on mesoporous silica and niobiosilicate material using a new methodology, i.e. solvothermal technique with increased pressure. The structure and surface properties of the samples obtained were examined using N2 adsorption/desorption, XRD, TEM, XPS and elemental analysis. The impact of modification technique as well as the presence of niobium in the sample on the acidity of final materials was investigated. It was found that the application of external pressure during the solvothermal modification of mesoporous silica with MPTMS allows obtaining materials with a greater number of acidic sites. These samples showed a high activity and stability in esterification of acetic and propionic acid with n-butanol and n-hexanol.

Magnetization, high pressure, and magnetocaloric studies of MnRuxRh1-xAs (x = 0.05, 0.1): Experimental and theoretical approaches

The magnetic properties of the MnRuxRh1-xAs system with x = 0.05, 0.10 were studied under hydrostatic pressure up to 1.2 GPa in the 80–420 K temperature range. The (p,T) magnetic phase diagram was determined. The ferromagnetic component in an intermediate (AF2+f) domain was stabilized with pressure for both samples, and the critical field variation versus pressure was determined. In addition, dc magnetization measurements were performed in magnetic fields up to 10 T, and the magnetic field–induced phase transitions were pointed out. The reverse and conventional magnetocaloric effect for both compounds was analyzed. Electronic band structure computations for the MnRuAs and MnRhAs parent compounds were performed by using the Korringa–Kohn-Rostoker method. The results indicate that significant changes of electronic states in the vicinity of EF on the application of external pressure tend to favor a ferromagnetic-type ordering of the Mn magnetic moments.

Nuanced superconductivity in endohedral gallide Mo8Ga41

We report on synthesis and characterization of gallide cluster based Mo8Ga41 superconductor. Transport and magnetization measurements confirm the superconducting transition temperature to be 9.8 K. The upper critical field (Hc2), lower critical field (Hc1), Ginzburg–Landau coherence length ( ξGL) and penetration depth(λ) are estimated to be 11.8 T, 150 G, 5.28 nm, 148 nm respectively. The electronic band structure, density of states and phonon dispersion curve calculations are obtained by using Density Functional Theory. The core level x-ray Photoelectron Spectroscopy (XPS) reveals the binding energy information of the constituting elements Mo and Ga in Mo8Ga41. The valence band spectra from XPS are in good agreement with calculated density of states (DOS). The zero field critical current density (Jc) at T = 2 K is ∼3 × 105 A/cm2 which is indicative of efficient flux pinning in the as grown compound. About two fold enhancement in critical current density with application of external pressure (1.1 GPa) is observed with marginal decrease in transition temperature. The fitting of current density to double exponential model confirms possibility of two gap superconductivity in Mo8Ga41.

Pressure-Induced Transition of Bisamide-Substituted Diacetylene Crystals from Nonphotopolymerizable to Photopolymerizable State.

Mechanoresponsive diacetylenes (DAs) exhibiting a transition of crystalline orientation from light-inert to light-active state upon applied force are reported. Amide units are introduced to DAs where hydrogen bonding is utilized to control intermolecular interactions. Application of external pressure (2-150 MPa) to DAs results in an emergence of new crystal phases with changing the d-spacing which possibly reduces the reaction barrier. Accordingly, the dramatic crystalline transition from "perfectly off" to "on" state to undergo the light-induced topochemical polymerization of bulk DA crystals is obtained. Subsequent UV irradiation at a wavelength of 254 nm enables the polymerization of the pressed region, changing its color from white to blue which suggests the selective formation of polydiacetylene (PDA) polymorphs. In addition, by utilizing the mechanoresponsive crystallinity with low-enough activation pressure, a new strategy for PDA patterning is demonstrated based on the selective transfer of information by means of force to a DA film. This phenomenon can be applicable to a new nanoimprinting technique where no mechanical deformation of resist materials but phase transition is induced by the mold.

High-pressure studies on heavy-fermion antiferromagnet CeCuBi2

We report in-plane electrical resistivity studies of CeCuBi2 and LaCuBi2 single crystals under applied pressure. At ambient pressure, CeCuBi2 is a c-axis Ising antiferromagnet with a transition temperature K. In a magnetic field applied along the c-axis at K a spin-flop transition takes place T. Applying pressure on CeCuBi2 suppresses TN at a slow rate. extrapolates to zero temperature at GPa. The critical field of the spin-flop transition displays a maximum of 6.8 T at GPa. At low temperatures, a zero-resistance superconducting state emerges upon the application of external pressure having a maximum Tc of 7 K at 2.6 GPa in CeCuBi2. High-pressure electrical-resistivity experiments on the non-magnetic reference compound LaCuBi2 reveal also a zero resistance state with similar critical temperatures in the same pressure range as CeCuBi2. The great similarity between the superconducting properties of both materials and elemental Bi suggests a common origin of the superconductivity. We discuss that the appearance of this zero resistance state superconductivity may be related to the Bi layers present in the crystalline structure of both compounds and, therefore, could be intrinsic to CeCuBi2 and LaCuBi2, however further experiments under pressure are necessary to clarify this issue.

Numerical Simulation of JCO-E Pipe Manufacturing Process and Its Effect on the External Pressure Capacity of the Pipe1

Large-diameter thick-walled steel pipes during their installation in deep-water are subjected to external pressure, which may trigger structural instability due to pipe ovalization, with detrimental effects. The resistance of offshore pipes against this instability is affected by local geometric deviations and residual stresses, introduced by the line pipe manufacturing process. In the present paper, the JCO-E pipe manufacturing process, a commonly adopted process for producing large-diameter pipes of significant thickness, is examined. The study examines the effect of JCO-E line pipe manufacturing process on the external pressure resistance of offshore pipes, candidates for deepwater applications using nonlinear finite element simulation tools. The cold bending induced by the JCO forming process as well as the subsequent welding and expansion (E) operations are simulated rigorously. Subsequently, the application of external pressure is modeled until structural instability (collapse) is detected. Both the JCO-E manufacturing process and the external pressure response of the pipe, are modeled using a two-dimensional (2D) generalized plane strain model, together with a coupled thermo-mechanical model for simulating the welding process.

Modeling and Mastering the Forging of Crystallizing Metal

The rational use of metal is determined by the use of alternative methods to produce blanks, including forging a crystallizing metal. Application of external pressure to the melt during crystallization completely eliminates gas porosity, which improves the mechanical characteristics of the products, and substantially increases the crystallization rate, which improves the life of dies. The results of mathematical modeling underlie the selection of thermomechanical conditions for forging of metals (iron, steel, and aluminum alloys) that crystallize under pressure. A number of liquid metal forging processes are mastered.

Reactive Forging − Pressure Assisted Thermal Explosion Mode of SHS for Processing Dense In Situ Composites and Structural Parts: A Review

Over the last decades, there has been a decisive shift from basic science to applied research that brought about the development of a number of unconventional combustion processes that allow for simultaneous synthesis and consolidation of otherwise difficult‐to‐process high temperature materials. External pressure application during thermal explosion (TE) mode of self‐propagating high‐temperature synthesis (SHS) can produce dense products provided the combination temperature and pressure are sufficient for consolidation. In the developed TE‐based reactive forging (RF) method, a self‐sustained reaction is ignited by rapid heat transfer from press die and rams, and a moderate consolidation pressure is applied when the combustion product still contains a sufficient amount of liquid or very soft phase. Plastic flow of the product results in filling the shape of the die thus producing a near‐net‐shape part. Reactive forging (RF) is especially efficient in combination with the developed short distance infiltration (SDI) approach based on the presence of a low melting phase component (e.g., Al, Mg, Ti–Ni eutectics) in the non‐dense reactant blend that is squeezed into the pores under the applied pressure thereby increasing the interparticle contact area and enhancing exothermic heat release rate. Compared to traditional reactive melt infiltration, SDI has the advantage of the considerably shorter infiltration distances (μm vs. mm–cm). Close temperature monitoring during RF and RF/SDI processing provides a deeper insight into the SHS reaction mechanisms. The “heat sink” action of the pressure die after TE results in rapid cooling of the consolidated products and correspondingly fine microstructures and high mechanical properties. Examples of successful application of the RF/SDI processing of homogeneous and functionally graded in situ composites based on binary (Al2O3, TiB2, TiC, TiN) and ternary (MgAl2O4, Ti3SiC2, Ti3AlC2) ceramics, as well as intermetallic–ceramic and metal–ceramic interpenetrating phase composites are described. Nanostructuring of reactant blends results in lower SHS ignition temperatures, and thus can be utilized for two‐stage ignition of multi‐component composite materials and structures with tunable ignition delay. Pressure assisted SHS is a “green,” cost‐effective, and thus perspective manufacturing route of near‐net‐shape structural parts. Examples of successful application of RF and RF‐SDI approach to fabrication of ceramic matrix–diamond grinding wheels, light armor tiles and high melting temperature nozzles are presented.