Non-hydrostatic Conditions Research Articles

Effects of aluminum and barium stearates on hydrophobic material production

Despite their porous and hydrophilic structures, cement-based mortar and concrete materials are highly susceptible to water and aggressive ions, significantly reducing their lifespan. Applying hydrophobic admixtures to cement-based products can substantially enhance their water-repellent performance. This study investigated the mechanical and microstructural properties of aluminum stearate (Al St) and barium stearate (Ba St) based on their water repellency. Powder solutions of Al St and Ba St were combined with water-repellent admixtures of ordinary Portland cement (OPC) paste and mortars at 0.5 %, 1 %, and 1.5 % dosages to create bulk water-repellent mortars suitable for building protection and appropriate for any construction work. The effects of the admixtures on the hydration and structure of the mortars were assessed through scanning electron microscopy (SEM), thermogravimetric analysis/differential thermal gravimetry (TG-DTG), X-ray diffraction (XRD) analysis, and Fourier transform infrared (FTIR) spectroscopy. The effectiveness of these compounds against the action of water was determined using various methods, such as mercury intrusion porosimetry, capillary water absorption tests, contact angle measurements, and water absorption tests. These admixtures form water-repellent layers within the capillary pores, which can reduce mortar permeability, particularly under nonhydrostatic conditions. Here, water capillary coefficient of Al St and Ba St 0.5 % are 0.0003 and 0.0003 respectively which is much higher that OPC. Furthermore, the resistance of the water-repellent mortars to salt crystallization was evaluated. All water-repellent admixtures provided adequate water-repellent protection, even though the water-repellent compounds and their dosages altered several physical characteristics and hydration kinetics. These materials had higher water-repellent properties but lower compressive strengths than OPC such as Al St 0.5 % result is 99.28%at 7days and on the other hand Ba St %0.5 at 3 and 56 days test results increase 109.89 % and 104.65 % respectively. Furthermore, their RCPT and contact angle were larger than those of OPC like RCPT value of Ba ST 0.5 % increased significantly 19.31 % and Al St 1 % contact angle is 108.41°. Moreover, by promoting cement hydration, Al St and Ba St may mitigate the loss of strength in concrete. Nevertheless, no research has been conducted on Al St and Ba St as hydrophobic admixtures for modifying cement mortar. This can offer insightful information about improving the mortars' natural water-repellent qualities and durability. The experiments revealed that Al St and Ba St materials are suitable for construction applications, considering their technology and characteristics.

Pressure-induced structural phase transitions and metallization in cuprous oxide under different hydrostatic environments up to 25.3 GPa

High-pressure vibrational and electrical transport behaviors of cuprous oxide were systematically investigated in a diamond anvil cell through in-situ Raman spectroscopy and electrical conductivity measurements under different hydrostatic environments up to 25.3 GPa. Upon compression, Cu2O undergoes a series of structural transformations from Cu2O–I to Cu2O–Ia to Cu2O–Ib to Cu2O–II to Cu2O–III phases at the respective pressures of 1.7(2), 10.3(2), 12.9(3) and 21.0(2) GPa under non-hydrostatic condition. Meanwhile, the metallization of Cu2O at 19.5(3) GPa is well characterized by the variable-temperature electrical conductivity experiments. Under hydrostatic condition, the pressure delay of 0.6–1.6 GPa is detected in the phase transitions from Cu2O–Ia to Cu2O–Ib to Cu2O–II to Cu2O–III phases. Upon decompression, one huge discrepancy is observed in the Raman spectra and electrical conductivity before and after the metallization, which indicates the irreversibility of phase transitions under different hydrostatic environments.

Constraints on the spin-state transition of siderite from laboratory-based Raman spectroscopy and electrical conductivity under high temperature and high pressure

The vibrational and electrical transport properties of natural siderite are systematically investigated by means of in-situ Raman spectroscopy and alternating current impedance spectroscopy under conditions of 0.6–55.6 GPa, 298–873 K and different hydrostatic environments using a diamond anvil cell (DAC). Upon non-hydrostatic compression, all of these observable characteristic variations of siderite including the appearance of three absolutely new Raman peaks (L’, v4′ and v1′), the disappearance of Raman peaks (T, L and v4) and the discontinuity in the pressure-dependent electrical conductivity can provide robust evidence of electronic spin transitions of Fe2+ from high-spin to mixed-spin to low-spin states at the respective pressures of 42.5 GPa and 48.5 GPa. As far as hydrostatic condition, the electronic spin states from high-spin to mixed-spin to low-spin states occurred at the higher pressures of 45.7 GPa and 50.4 GPa, respectively, which implied the highly sensitive hydrostaticity of electronic spin transition pressures. Upon decompression, the reverse electronic spin transitions from low-spin to mixed-spin to high-spin states were detected at the respective pressures of 47.2 GPa and 28.7 GPa under non-hydrostatic condition, and as well as at the pressures of 49.4 GPa and 25.1 GPa under hydrostatic condition, respectively. The huge pressure hysteresis of 13.8 GPa and 20.6 GPa for the electronic spin state transition was revealed under non-hydrostatic and hydrostatic environments, respectively. In order to explore the effect of temperature on the electronic spin transition, a series of electrical conductivity experiments on siderite were performed over the temperature range of 323–873 K under conditions of three typical pressures of 47.7, 49.8 and 51.6 GPa. Furthermore, the functional relationships between the temperature and pressure describing the high-spin to mixed-spin to low-spin transitions for siderite were successfully established: P1 (GPa) = 39.318 + 0.015 T (K) and P2 (GPa) = 41.277 + 0.018 T (K), respectively. In conclusion, our acquired phase diagram of the electronic spin transition on siderite is beneficial to deep insight into the electronic spin behavior for those of iron-bearing carbonate minerals under high-temperature and high-pressure conditions.

Pressure-induced optical anisotropy of HfS2

The effect of pressure on Raman scattering (RS) in bulk HfS2 is investigated under hydrostatic and non-hydrostatic pressure conditions. The RS line shape does not change significantly in the hydrostatic regime up to P = 9.6 GPa, showing a systematic blueshift of the spectral features. In a non-hydrostatic environment, seven peaks appear in the spectrum at P = 7 GPa, which dominate the RS line shape up to P = 10.5 GPa. The change in the RS line shape manifests a pressure-induced phase transition in HfS2. The simultaneous observation of both low-pressure (LP) and high-pressure (HP) related RS peaks suggests the coexistence of two different phases over a wide pressure range. It is found that the HP-related phase is metastable and persists during the decompression cycle down to P = 1.2 GPa, while the LP-related features eventually recover at even lower pressure. The angle-resolved polarized RS performed under P = 7.4 GPa revealed a strong in-plane anisotropy of both the LP-related A1g mode and the HP peaks. The anisotropy is related to the possible distortion of the structure induced by the non-hydrostatic component of the pressure. The results are explained in terms of a distorted Pnma phase as a possible pressure-induced phase of HfS2.

Pressure-induced phase transition and metallization in zirconium disulfide under different hydrostatic environments up to 25.3 GPa

The pressurized behaviours of structure, vibration and electrical transport in zirconium disulfide have been systematically investigated in a diamond anvil cell (DAC) under different hydrostatic environments up to 25.3 GPa utilizing in-situ Raman spectroscopy, electrical conductivity measurement, high-resolution transmission electron microscopy (HRTEM) and first-principles theoretical calculations. Upon compression, our experimental results showed that ZrS2 underwent a phase transition accompanied by a semiconductor-to-metal transformation at 15.4 GPa under non-hydrostatic condition. Under hydrostatic condition, the corresponding phase transition occurred at a higher pressure of 17.5 GPa, indicating that the high-pressure phase transition is sensitive to the hydrostaticity in the sample chamber of DAC. Upon decompression, some absolutely new Raman peaks emerged at the pressures below 4.8 GPa and 2.9 GPa under non-hydrostatic and hydrostatic environments, respectively, which revealed an irreversible phase transition in ZrS2. Furthermore, our observations from selected-area electron diffraction patterns confirmed the irreversibility of the high-pressure phase transformation.

Uncovering the Effects of Non-Hydrostaticity on Pressure-Induced Phase Transformation in Xenotime-Structured TbPO4

The pressure-induced phase transformations of rare earth orthophosphates (REPO4s) have become increasingly relevant in ceramic matrix composite (CMC) research; however, understanding of the shear-dependence of these transformations remains limited. This study employs diamond anvil cell experiments with three pressure media (neon, KCl, sample itself/no medium) to systematically assess the effect of shear on the phase transformations of TbPO4. Results show a lowering of the TbPO4 transformation onset pressure (Ponset) as well as an extension of the xenotime–monazite phase coexistence range under non-hydrostatic conditions. The TbPO4 Ponset under no medium (4.4(3) GPa) is the lowest REPO4 Ponset reported to date and represents a ~50% drop from the hydrostatic Ponset. Enthalpic differences likely account for lower Ponset values in TbPO4 compared to DyPO4. Experiments also show scheelite may be the post-monazite phase of TbPO4; this phase is consistent with observed and predicted REPO4 transformation pathways.

A new kinematic wave model that describes lateral subsurface flow and percolation in hillslopes

Kinematic wave (KW) models are commonly used for flood forecasting in large river basins, but have limitations in their ability to simulate percolation effects. Here, we suggest an extended KW model wherein the vertical pressure head is under non-hydrostatic conditions. The proposed model uses the Brooks Corey and Mualem models to estimate the water retention curve and unsaturated hydraulic conductivity and adopts the pressure head gradient as a new variable to calculate runoff based on changing water content distributions over time due to percolation. The increase in the pressure head gradient with rainfall infiltration is determined from the relationship between water storage and pressure head distribution, while the decrease in pressure head gradient due to percolation is modeled as exponential decay with time. A comparison of the proposed KW model and a numerical solution of the Richards equation shows that the proposed KW model can reproduce the storage effect caused by percolation, delaying runoff and reducing peak discharge. The agreement between the proposed KW model and the Richards equation is high for soils with high water retention. Conversely, the agreement becomes lower for soil with low water retention or deep soil layer thickness, where the complexity of water content distribution requires further refinement. The proposed model can easily be incorporated into distributed models while low computational cost with keeping the important percolation effects.

Structural instability in LaNbO4 under compression

In this work, we report a high-pressure study on fergusonite-type LaNbO4. Powder x-ray diffraction and Raman spectroscopic experiments support the occurrence of a phase transition between 11 and 14 GPa. The transition takes place from a monoclinic fergusonite-type structure (space group I2/a) to another monoclinic structure (space group P21/c). The phase transition is reversible, and the high-pressure phase is isomorphic to the high-pressure phase of HoNbO4. The high-pressure phase remains stable up to 33.3 GPa, the highest pressure reached in the present measurements. Density-functional theory calculations found that in the pressure range of the studies; the high-pressure phase has a higher enthalpy than the low-pressure fergusonite phase. We propose that the high-pressure phase is metastable and it is observed because of non-hydrostatic conditions in the experiments. The pressure dependence of unit-cell parameters of the low-pressure phase and the room-temperature equation of state are reported. The pressure dependence of various Raman and IR frequencies as obtained from experiment and theory is also reported. For the fergusonite phase, we have also obtained the isothermal compressibility tensor, elastics constants, and elastic moduli.

Comparison of hydrostatic and non-hydrostatic compression of glassy carbon to 80 GPa

Understanding new mechanisms for phase transformation in carbon is of considerable interest. This study investigates on the compression conditions required to create recoverable diamond during room-temperature high-pressure compression of glassy carbon. Under non-hydrostatic compression conditions when shear is present, glassy carbon transforms into an oriented graphitic structure at ∼45 GPa, and then forms mixed diamond and lonsdaleite nanocrystals when the pressure is higher than ∼80 GPa. In contrast, during hydrostatic compression no significant changes in the microstructure was observed, highlighting glassy carbon’s resilience under compression. Molecular dynamics modelling supports the proposed model that shear drives the phase transition mechanism and causes a temperature spike that drives crystallisation. Our work demonstrates that shear is key to high-pressure diamond formation in the absence of heating.

Origin of preferred orientation in an isotropic material: High pressure synthesis of bc8-Si

High pressure experiments and ab initio calculations are used to investigate unexpected crystallographic preferred orientation in the bc8 phase of silicon formed under non-hydrostatic conditions. Microstructural characterization in two orthogonal directions reveals that the preferred orientation is only visible when the sample is viewed perpendicular to the compression axis. Curiously, the elastic constants of bc8-Si are almost perfectly isotropic, making it counter-intuitive that preferred crystallographic orientation is observed. This conundrum is resolved by tracking the phase transformation pathway and computing the three-dimensional Young's modulus. We find the preferred orientation most likely originates from the highly anisotropic simple-hexagonal phase and is passed on to subsequent daughter phases via displacive phase transformations. Our investigation of preferred orientation in bc8-Si complements other high pressure studies where preferred orientation in silicon phases is often observed but not explained.

Pressure-induced superconductivity and phase transitions in Bi2S3 under non-hydrostatic conditions

Despite extensive and systematic studies on pressure-induced phase transitions and superconductivity in sesqui-chalcogenide A2B3 (A=Sb, Bi; BS, Se, and Te) compounds, the detailed transporting properties of Bi2S3 have rarely been reported. Here, we discovered an unambiguous correlation between superconductivity and phase transitions in Bi2S3 under non-hydrostatic conditions. The rapid decrease in resistance below 10 GPa and the occurrence of superconductivity at approximately 25.5 GPa should be caused by the two unusual pressure-induced isostructural transitions. Subsequently, the superconducting transition temperature (TC) increased to around 7.3 K, which was accompanied by the amorphization of Bi2S3 above 43 GPa. Furthermore, divergence between the theoretical calculations and experimental measurements showed that the above phase transitions and pressure-induced charge transfer had a critical effect on the electronic properties of this compound. The results of this study indicated that high pressure could help to improve thermoelectric properties.

Pressure-Driven Structural and Electronic Transitions in a Two-Dimensional Janus WSSe Crystal.

In this work, we presented the first report on the high-pressure structural stability and electrical transport characteristics in WSSe under different hydrostatic environments through Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy (HRTEM) coupled with first-principles theoretical calculations. For nonhydrostatic conditions, WSSe endured a phase transition at 15.2 GPa, followed by a semiconductor-to-metal crossover at 25.3 GPa. Furthermore, the bandgap closure was accounted for the metallization of WSSe as derived from theoretical calculations. Under hydrostatic conditions, ∼ 2.0 GPa pressure hysteresis was detected for the emergence of phase transition and metallization in WSSe because of the feeble deviatoric stress. Upon depressurization, the reversibility of the phase transition was substantiated by those of microscopic HRTEM observations under different hydrostatic environments. Our high-pressure investigation on WSSe advances the insightful understanding of the crystalline structure and electronic properties for the Janus transition-metal dichalcogenide (TMD) family and boosts prospective developments in functional devices.

Pressure-induced reversible structural phase transitions and metallization in GeTe under hydrostatic and non-hydrostatic environments up to 22.9 GPa

The pressure-dependent vibrational and electrical transport properties of GeTe have been investigated in a diamond anvil cell through in-situ Raman spectroscopy and electrical conductivity measurements under hydrostatic and non-hydrostatic environments up to 22.9 GPa. Upon compression, two structural transformations from rhombohedral to cubic NaCl-type to orthorhombic GeTe occurred at 3.2 GPa and 12.3 GPa under non-hydrostatic condition. Similarly, two corresponding phase transitions were detected at much higher pressures of 5.0 GPa and 15.4 GPa under hydrostatic condition. Additionally, a 3.3 GPa of electronic transition accompanying by the rhombohedral to cubic NaCl-type transition was characterized by the variable-temperature electrical conductivity experiments. Upon decompression, the recoverable Raman spectra and resumable electrical conductivity suggested that the structural and electronic transitions of GeTe were reversible. The reversibility was further confirmed by the microscopic structural observations from high-resolution transmission electron microscopy, fast Fourier transform and atomic force microscopy.

Cold compression behavior of alumina particles with different grain sizes under high pressure

The cold compression behavior of alumina samples, with average grain sizes of 350 nm, 7.9 μm, and 18.2 μm, has been investigated under non-hydrostatic conditions by using a diamond anvil cell. After treatment with various pressures, the in situ axial X-ray diffraction patterns, transparency variations, and microstructures after decompression of the samples were also analyzed. The results showed that the submicron grains became easily translucent. The larger the grain size, the higher the pressure needed to compress the sample to transparency. On the other hand, for a similar grain size, the various geometrical shapes of the grains did not affect the pressure dependency on transparency. The elastoplastic characteristics of the alumina grains of different sizes under cold compression were found to be consistent with the transparency variation. As a conclusion, alumina particles under cold compression were found to be applicable in the pressure-assisted preparation of alumina transparent ceramics.

Coupled THM formulation and wellbore analytical solution in naturally fractured media during injection/production

The heat extraction efficiency, storage, and safety of carbon dioxide (CO2) sequestration and methane (CH4) injection/post-production in naturally fractured formations have attracted significant interest. However, these studies require the examination of complex thermal-hydraulic-mechanical (THM) interacting processes, which include muti-discipline coupling and phase changes. Energy transfer mechanisms and thermally induced hydraulic and mechanical responses are critical for energy extraction efficiency , surface design optimization, and safety evaluation. The THM response in the wellbore, where fluids are injected and circulated, provides key information for design evaluation. A fully coupled formulation was developed based on a dual-porosity model to simulate the THM responses of a wellbore in naturally fractured aquifers under non-isothermal, two-phase fluid flow, and non-hydrostatic loading conditions. Local thermal non-equilibrium (LTNE) conditions are imposed for energy transportation between the fracture and matrix systems in the fissured porous solid skeleton. Different physical parameters reflecting various rock types and fracture characteristics are defined for the corresponding THM behavior models. Analytical solutions for the temperature perturbation and pressure changes in single-phase fluid flow in the vicinity of a wellbore in fissured media are developed to simulate the injection and production processes. Simulating a non-isothermal fluid circulation problem along a wellbore, an newly proposed mixed Type I (Dirichlet) and II (Neumann) boundary condition is imposed to study the heat exchange efficiency between wellbore fluid and the fissured NFM. The analytical solution has the advantages of being simple, explicitly possessing direct physical parameters, and serving as a tool for validating numerical solutions. The impacts of the newly proposed boundary condition on the near-well responses and THM results from the newly developed solution may be used to simulate the injectivity, storage capacity, reproduction, and design of supercritical carbon (scCO2) and CH4 are discussed.

Effect of nonhydrostatic pressure on the superconducting kagome metal CsV3Sb5

High-pressure single-crystal x-ray diffraction experiments reveal that the superconducting kagome metal ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ transforms from hexagonal ($P6/mmm$) to monoclinic ($C2/m$) symmetry above 10 GPa if nonhydrostatic pressure conditions are created in a diamond anvil cell with silicon oil as the pressure-transmitting medium. This is contrary to the behavior of ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ under quasihydrostatic conditions in neon, with the hexagonal symmetry retained up to at least 20 GPa. Monoclinic distortion leaves the kagome planes almost unchanged, but deforms honeycomb nets of the Sb atoms. While the onset of the distortion almost coincides with the reentrance of superconductivity, our ab initio density-functional calculations reveal only minor changes in the electronic structure compared to the quasihydrostatic case. In particular, Fermi surface reconstruction driven by the formation of interlayer Sb-Sb bonds is observed in both monoclinic and hexagonal ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ structures at high pressures and comes out as the likely cause for the reentrant behavior.

Photoluminescence of Cr3+ in β-Ga2O3 and (Al0.1Ga0.9)2O3 under pressure

The effects of pressure on single crystals of Cr-doped gallium oxide (β-Ga2O3:Cr3+) and aluminum gallium oxide [(Al0.1Ga0.9)2O3] were examined by measuring the wavelength shift in the spectral R lines. Photoluminescence (PL) spectra of these materials were collected from samples in diamond anvil cells at pressures up to 9 GPa. The β-Ga2O3:Cr3+R lines were found to shift linearly under hydrostatic pressure. The (Al0.1Ga0.9)2O3R lines also show a linear shift but the R1 line shifted less than for β-Ga2O3:Cr3+. The ratio of R2 to R1 peak areas vs pressure is dominated by nonradiative recombination. X-ray diffraction measurements of (Al0.1Ga0.9)2O3 indicate that its equation of state is similar to that of β-Ga2O3. β-Ga2O3:Cr3+ was examined under non-hydrostatic conditions by using mineral oil as a pressure transmitting medium. Similar to the case in ruby, the R1 line is much more sensitive to non-hydrostatic stress than R2. Spatially resolved PL of a sample at 8 GPa in mineral oil showed significant variations in the R1 emission wavelength. These results suggest that the R1 line can serve as a sensitive probe of alloy composition and non-hydrostatic stress, while the R2 line is insensitive to these perturbations.

Shear stress induced phase transitions of cubic Eu2O3 under non-hydrostatic pressures

Pressure-induced phase transitions in cubic Eu2O3 subjected to non-hydrostatic conditions have been studied by in situ high-pressure synchrotron angle dispersive x-ray diffraction and Raman scattering measurements up to 30.1 and 43.8 GPa, respectively. Both x-ray diffraction and Raman spectroscopy results indicate that the pressure-induced transition routines of cubic Eu2O3 depend on the nature of stress loading. In contrast to our previous high-pressure studies of cubic Eu2O3 under hydrostatic pressure, where cubic Eu2O3 transforms directly into a hexagonal structure, the x-ray diffraction data show that cubic Eu2O3 begins to transform into the monoclinic phase at a non-hydrostatic pressure of about 4.3 GPa, while the monoclinic to hexagonal phase transition is initiated at about 6.4 GPa. These phase transitions have also been confirmed by Raman spectroscopy; the hexagonal phase is stable up to at least 43.8 GPa; and the material decompressed from high pressures is composed of a monoclinic phase, showing that the cubic Eu2O3 to monoclinic phase transition is irreversible due to the constructive nature. Pressure coefficients of Raman peaks and Grüneisen mode parameters of cubic, monoclinic, and hexagonal phases followed under pressure were determined. Furthermore, this study provides evidence for the shear stress-induced cubic to monoclinic phase transition in cubic Eu2O3 and the corresponding mechanism.

Pressure-induced structural phase transitions in natural monazite

The behavior of natural monazite $(\mathrm{La},\phantom{\rule{0.16em}{0ex}}\mathrm{Ce},\phantom{\rule{0.16em}{0ex}}\mathrm{Nd})\mathrm{P}{\mathrm{O}}_{4}$ at high pressure is investigated by Raman spectroscopy. Changes in the Raman spectra indicate a phase transition from monazite to a post-monazite phase. Single-crystal x-ray diffraction measurements of the decompressed sample reveal that the post-monazite phase has a distorted barite-type structure with space group $P{2}_{1}/n$. This phase transition is irreversible under quasihydrostatic conditions, and is reversible under nonhydrostatic conditions. Therefore, it is expected that the post-monazite phase cannot be found as a metastable phase at ambient conditions in impact craters due to nonhydrostatic conditions during shock metamorphism, supporting recent mineralogical observations in impact craters.

Structural Behavior of Minrecordite Carbonate Mineral upon Compression: Effect of Mg → Zn Chemical Substitution in Dolomite-Type Compounds.

We report the structural behavior and compressibility of minrecordite, a naturally occurring Zn-rich dolomite mineral, determined using diamond-anvil cell synchrotron X-ray diffraction. Our data show that this rhombohedral CaZn0.52Mg0.48(CO3)2 carbonate exhibits a highly anisotropic behavior, the c axis being 3.3 times more compressible than the a axis. The axial compressibilities and the equation of state are governed by the compression of the [CaO6] and [ZnO6] octahedra, which are the cations in larger proportion in each layer. We observe the existence of a dense polymorph above 13.4(3) GPa using Ne as a pressure-transmitting medium, but the onset pressure of the phase transition decreases with the appearance of deviatoric stresses in nonhydrostatic conditions. Our results suggest that the phase transition observed in minrecordite is strain-induced and that the high-pressure polymorph is intimately related to the CaCO3-II-type structure. A comparison with other dolomite minerals indicates that the transition pressure decreases when the ratio Zn/Mg in the crystal lattice of pure dolomite is larger than 1. Density functional theory (DFT) calculations predict that a distorted CaCO3-II-type structure is energetically more stable than dolomite-type CaZn(CO3)2 above 10 GPa. However, according to our calculations, the most stable structure above this pressure is a dolomite-V-type phase, a polymorph not observed experimentally.