Porous Grains Research Articles

Dust mass in protoplanetary disks with porous dust opacities

Atacama Large Millimeter/submillimeter Array surveys have suggested that protoplanetary disks are not massive enough to form the known exoplanet population, based on the assumption that the millimeter continuum emission is optically thin. In this work, we investigate how the mass determination is influenced when the porosity of dust grains is considered in radiative transfer models. The results show that disks with porous dust opacities yield similar dust temperatures, but systematically lower millimeter fluxes, as compared to disks that incorporate compact dust grains. Moreover, we have recalibrated the relation between dust temperature and stellar luminosity for a wide range of stellar parameters. We also calculated the dust masses of a large sample of disks using the traditionally analytic approach. The median dust mass from our calculation is about six times higher than the literature result, and this is mostly driven by the different opacities of porous and compact grains. A comparison of the cumulative distribution function between disk dust masses and exoplanet masses shows that the median exoplanet mass is about two times lower than the median dust mass when grains are assumed to be porous and there are no exoplanetary systems with masses higher than the most massive disks. Our analysis suggests that adopting porous dust opacities may alleviate the mass budget problem for planet formation. As an example illustrating the combined effects of optical depth and porous dust opacities on the mass estimation, we conducted new IRAM/NIKA-2 observations toward the IRAS\,04370+2559 disk and performed a detailed radiative transfer modeling of the spectral energy distribution (SED). The best-fit dust mass is roughly 100 times higher than the value given by a traditionally analytic calculation. Future spatially resolved observations at various wavelengths are required to better constrain the dust mass.

The rotational disruption of porous dust aggregates from ab initio kinematic calculations

The size of dust grains in the interstellar medium follows a distribution where most of the dust mass is made up of smaller grains. However, the redistribution from larger grains towards smaller sizes, especially by means of rotational disruption, is still poorly understood. We aim to study the dynamics of porous grain aggregates undergoing an accelerated rotation, namely, a spin-up process that rapidly increases the angular velocity of the aggregate. In particular, we aim to determine the deformation of the grains and the maximal angular velocity up to the rotational disruption event by caused by centrifugal forces. We precalculated the porous grain aggregate by means of ballistic aggregation analogous to the interstellar dust as input for subsequent numerical simulations. We performed three-dimensional (3D) N-body simulations, mimicking the radiative torque spin-up process up to the point where the grain aggregates become rotationally disrupted. Our simulations results are in agreement with theoretical models predicting a characteristic angular velocity, $ disr $, on the order of $ rad\ $, where grains become rotationally disrupted. In contrast to theoretical predictions, we show that for large porous grain aggregates ($ nm $), the $ disr $ values do not strictly decline. Instead, they reach a lower asymptotic value. Hence, such grains can withstand an accelerated rotation more efficiently up to a factor of 10 because the displacement of mass by centrifugal forces and the subsequent mechanical deformation supports the buildup of new connections within the aggregate. Furthermore, we report that the rapid rotation of grains deforms an ensemble with initially 50:50 prolate and oblate shapes, respectively, preferentially into oblate shapes. Finally, we present a best-fit formula to predict the average rotational disruption of an ensemble of porous dust aggregates dependent on the internal grain structure, total number of monomers, and applied material properties.

In-vitro study of Ti6Al4V alloy fabricated by laser-based additive manufacturing for orthopedic implant applications

The Ti6Al4V alloy is widely used in orthopedic implants due to its excellent mechanical properties and biocompatibility. However, traditional manufacturing techniques are unable to fabricate complex geometrical shapes with tailored properties. This leads to premature failure due to wear, corrosion, and poor osseointegration. Recent advancements in laser-based additive manufacturing, particularly in direct metal laser sintering (DMLS), offer new opportunities to produce Ti6Al4V implants with tailored microstructures, mechanical properties, and biocompatibility. However, wear, corrosion, and cell viability behavior, required for evaluating the biomedical applicability of Ti6Al4V alloy produced through the DMLS route have not been reported. The present study fulfills this gap in the literature. Micro structural study revealed that DMLS-produced Ti6Al4V has a porous and fine grain structure (with mostly α′ phase) without any crack formation due to the controlled parameters during DMLS. Corrosion tests were conducted in simulated body fluid as an electrolytic media, while fibroblast cell lines were used to evaluate the cell viability. Compared to the conventional cast product, DMLS-produced Ti6Al4V alloy exhibited significantly higher porosity (4.8 times), scratch resistance (23.25%), wear resistance (11.53%), corrosion resistance (16.56%), and cell growth. (4.37%), thus making it a more suitable alloy for implants.

Influence of textural variability on plastic response of porous crystal embedded in polycrystalline aggregate: A crystal plasticity study

Damage evolution in polycrystalline aggregates is complicated by the intricate interplay of crystallographic orientation of the porous grain and the surrounding anisotropic matrix. Therefore, formulation of design rules and damage models for polycrystalline materials proves daunting due to relative lack of thorough understanding of the underlying heterogeneity at the mesoscale. This work explores the orientation dependent void growth in a porous crystal embedded in an anisotropic polycrystalline matrix with different initial textures. Polycrystalline face-centered cubic based aggregate is simulated within the framework of crystal plasticity finite element method. Porosity is first modeled in the form of a single pre-existing spherical void in the central grain of the randomly oriented polycrystal. One-hundred crystallographic orientations of the central grain in three-dimensional Euler space are analyzed to reveal the orientation dependent trends of the porous grain. To account for textural variability, the analysis is repeated for polycrystals exhibiting preferred textures like Cube, Brass, Copper and Goss. In this manner, interesting orientation dependent trends in basic tenets of void growth like yield strength, coalescence strain and porosity evolution are unraveled across various polycrystalline textures. To account for spatial heterogeneity as well, porosity in the central grain is then re-distributed and the aforementioned analysis is repeated for all the crystallographic orientations of the central grain embedded in polycrystals with different textures. Owing to the large amount of data thus generated, statistical analysis is invoked to identify stimulating trends and key statistical variables governing the strength and toughness. Consequently, a statistical void growth model is also presented by assessing the CP simulation results and identifying suitable distribution function governing the growth of voids in polycrystals. The modeling framework is expected to inform porous plasticity models aimed at capturing damage evolution in porous grains embedded in polycrystalline materials exhibiting topological and crystallographic anisotropy.

Recycled Aggregate Integration for Enhanced Performance of Polymer Concrete.

The objective of the research outlined in this paper is to propose an eco-friendly solution that simultaneously contributes to improving the characteristics of polymer composites. The analyzed solution entails the use of recycled aggregate from crushed concrete rubble. The authors conducted experiments to test the consistency, density, flexural strength, compressive strength, and microstructure of polymer concrete (PC) with different proportions of recycled aggregate (RA). It was found that PC with RA had a higher compressive strength, 96 MPa, than PC with natural aggregate, 89.1 MPa, owing to the formation of a double-layer shell of resin and calcium filler on the surface of porous RA grains. Using a resin with a lower viscosity could improve the performance of PC with RA by filling the cracks and penetrating deeper into the pores. RA is a valuable material for PC production, especially when it contains porous grains with poor mechanical properties, which are otherwise unsuitable for other applications. This article also highlights the environmental and economic benefits of using RA in PC, as it can reduce waste generation and natural resource consumption.

Enhanced precision lapping techniques for fused quartz optical elements: Synergistic integration of mechanical and mechanochemical processes

Fused silica is a material of great importance in the field of precision optical equipment due to its excellent optical properties, e.g. photolithography, laser fusion devices, etc. However, the material's inherent hardness and brittleness render it a challenging material to process. Therefore, an enhanced precision lapping technique was proposed, i.e., a synergistic integration of mechanical and mechanochemical lapping processes. Firstly, a synergistic lapping tool with an outer layer of porous diamond abrasive and an inner layer of CeO2 abrasive was fabricated by hot press forming method. The reduction of layer thickness due to abrasion and detachment of the porous diamond abrasive layer was analyzed, and the lapping mechanism of porous diamond on fused silica materials was revealed. The surface creation mechanism of the CeO2 abrasive layer on fused silica material was analyzed by molecular dynamics simulation and the results were validated by enhanced precision lapping experiment. The results demonstrated that the surface atoms of fused silica are removed in a ‘remote disordered’ manner by conventional diamond abrasive grains, whereas the surface atoms of fused silica are removed in a ‘proximally ordered’ manner by the fine porous diamond abrasive grains through the micro-multi-flute cutting. Consequently, the grinding of a porous diamond abrasive layer can significantly reduce the processing damage, with the surface roughness of the lapping Ra reaching 199 nm. The lapping of CeO2 induces the formation of an oxygen bridge on the surface of fused silica, which then produces bending vibration. This is followed by the adsorption and diffusion of oxygen atoms, which form the -Ce-O-Si intermediate with the oxygen atoms shared with the fused silica. This process results in the formation of CeSiO3 and CaSiO3 compounds. The final surface quality with a surface roughness of Ra 21 nm was obtained by mechanochemical lapping of the cerium oxide abrasive layer. The single mechanical-mechanochemical composite ultra-precision lapping process provides technical support for the efficient and low-damage processing of hard and brittle components.

Physical experiment and pore-scale investigation of the clogging of polydisperse particles in saturated porous media during artificial groundwater recharge

Groundwater recharge engineering practices are usually accompanied by the migration and deposition of polydisperse particles. Solid particles may be retained in the pore space leading to clogging of the porous media and reducing groundwater recharge efficiency. However, the mechanism behind this clogging phenomenon remains poorly understood. Specifically, the relation of particle clogging at pore-scale and macroscale is unclear. Here, the influence of polydisperse particle size on clogging development patterns was studied utilizing a series of laboratory-scale column experiments in conjunction with pore-scale scanning electron microscopy (SEM) experiments. Particles with median particle sizes (dp50) of 0.66, 4.05, 11.83 μm were injected separately into the sand column to simulate particle clogging that occurs during groundwater recharge. SEM was used to directly observe particles deposition on porous media grain surface after the column experiments. By counting the size distribution of the particles on the media grain surface, the response of the particle deposition to the surface morphology of the media grains was analysed. Compared to dp50 of 4.05 and 11.83 μm, the spatial distribution of particles deposited in the sand column was more uniform at dp50 of 0.66 μm. The smallest particles (dp50 = 0.66 μm) used in the experiments ultimately formed mixed clogging, which was the result of the combined effects of particle deposition and aggregation. The particle deposition with dp50 = 4.05 and 11.83 μm ultimately exhibited hyper-exponential distribution and formed mixed and superficial clogging, respectively. At the same time, the concave region of the media grain surface played a dominant role in particle deposition. For dp50 = 4.05 μm, 69.41 % of the particles were deposited in the concave region, and for dp50 = 11.83 μm, the proportion was 90.1 %. The results help to better manage particle clogging in groundwater recharge and other engineering applications (e.g., groundwater source heat pump, and filtration project). In addition, these findings provide a theoretical reference for the development of numerical models to help recognize the probability of particles of different sizes to be captured in porous media.

A Novel Ag-MgFe2O4 nanocomposite based hydroelectric cell: Green energy source illuminating the future

Hydroelectric cells demonstrate their capacity to produce electricity via the dissociation of water molecules, eliminating the requirement of electrolytes. The objective of this research is to synthesize Ag-MgFe2O4 nanocomposite using low-cost method and to study the green electricity generation by hydroelectric cell via the dissociation of water molecules. The nanocomposite displayed a cubic crystalline structure with an average crystallite size of about 29 nm, as determined by XRD. The lattice strain and crystal defects resulted from the insertion of the Ag in spinel ferrite from the W-H plot. The theoretical porosity of 54 % was further evaluated by XRD analysis and visually confirmed by FESEM imaging. The FTIR spectroscopy revealed functional groups present in ferrite observed from 428 cm−1 to 3450 cm−1 spectra. Strong water absorption near 3450 cm−1 showed materials sensitivity to water. FESEM imaging displayed the morphology, revealing porous grains with an average size of 93 nm. BET analysis of the prepared nanocomposite confirmed mesoporosity within the nanocomposite. Photoluminescence study confirmed radiative defects and oxygen deficiencies, as evidenced by emitted light maximum at 483 nm and broad peak from 456 nm to 526 nm. The voltage-current (V-I) polarization diagram for the Ag- MgFe2O4 nanocomposite-based hydroelectric cell showed an offload current of 18 mA, an open circuit voltage of 1.404 V, and an output power of 25.27 mW. In this context, the hydroelectric cell based on Ag- MgFe2O4 nanocomposite demonstrated increased porosity, radiative defects, and oxygen vacancies, all contributing to efficient water molecule dissociation for power generation. This represents a significant development in sustainable energy and highlights the practical possibilities of clean and renewable resources.

Microstructural and isotopic analysis of shocked monazite from the Hiawatha impact structure: development of porosity and its utility in dating impact craters

U–Pb geochronology of shocked monazite can be used to date hypervelocity impact events. Impact-induced recrystallisation and formation of mechanical twins in monazite have been shown to result in radiogenic Pb loss and thus constrain impact ages. However, little is known about the effect of porosity on the U–Pb system in shocked monazite. Here we investigate monazite in two impact melt rocks from the Hiawatha impact structure, Greenland by means of nano- and micrometre-scale techniques. Microstructural characterisation by scanning electron and transmission electron microscopy imaging and electron backscatter diffraction reveals shock recrystallisation, microtwins and the development of widespread micrometre- to nanometre-scale porosity. For the first time in shocked monazite, nanophases identified as cubic Pb, Pb3O4, and cerussite (PbCO3) were observed. We also find evidence for interaction with impact melt and fluids, with the formation of micrometre-scale melt-bearing channels, and the precipitation of the Pb-rich nanophases by dissolution–precipitation reactions involving pre-existing Pb-rich high-density clusters. To shed light on the response of monazite to shock metamorphism, high-spatial-resolution U–Pb dating by secondary ion mass spectrometry was completed. Recrystallised grains show the most advanced Pb loss, and together with porous grains yield concordia intercept ages within uncertainty of the previously established zircon U–Pb impact age attributed to the Hiawatha impact structure. Although porous grains alone yielded a less precise age, they are demonstrably useful in constraining impact ages. Observed relatively old apparent ages can be explained by significant retention of radiogenic lead in the form of widespread Pb nanophases. Lastly, we demonstrate that porous monazite is a valuable microtexture to search for when attempting to date poorly constrained impact structures, especially when shocked zircon or recrystallised monazite grains are not present.

Enhancing the structural, optical, magnetic and ferroelectric properties of perovskite BiFeO3 through metal substitution

Nanocrystalline BiFeO3 materials with multiferroic properties were successfully prepared using the solution-combustion method, and the impact of Ni-substitution in bismuth ferrite was investigated in the present research. Structural phase identification was done through XRD and FTIR spectroscopy. The average crystallite size was determined to be 44.87 nm for the pristine sample and 32.52 nm for the Ni-substituted ferrite. An enhancement in lattice strain, leading to crystal defects, was observed with Ni substitution in bismuth ferrite. Elemental analysis by EDX revealed the presence of Ni, Fe, Bi, and O in the substituted ferrites. FESEM studies indicated a significant decrease in the size of agglomerated and porous grains from 137 nm to 102 nm with the substitution of Ni in pristine bismuth ferrite. A considerable increase in the band gap from 2.21 eV to 2.39 eV was observed with Ni-substitution in the prepared ferrite phase, possibly due to the decrease in crystallite size. The very low coercivity (1.509 Oe) of pristine bismuth ferrite indicates its superparamagnetic behaviour. An improvement in saturation magnetization (almost two times) and a slight increase in coercivity (2.042 Oe) were found with Ni-substitution at Fe3+ sites in bismuth ferrite compared to the pristine ferrite. At 10 KHz, Ni-substitution enhanced the dielectric constant and decreased the dielectric loss of the prepared bismuth ferrite materials. Ferroelectric investigation of the prepared ferrites indicated an improvement in the P-E loop of Ni-substituted bismuth ferrite with a reduced loop area, indicating low electrical leakage.

Seismic wave dispersion and attenuation resulting from multiscale wave-induced fluid flow in partially saturated porous media

SUMMARY Sedimentary rocks are typical heterogeneous porous media induced by fluid patches and pore fabric. It is well acknowledged that the wave-induced fluid flow (WIFF) at different scales will cause seismic wave dispersion and attenuation in a wide frequency range. Consequently, modelling wave dispersion and attenuation due to multiscale WIFF is of significance for reservoir characterization from multiscale geophysical measurement and interpretation. In this study, the multiscale WIFF in partially saturated porous media, including global, 3-D mesoscopic and squirt flows, are investigated. And we derive the wave equations by introducing the Rayleigh's spherical bubble oscillation and the porous grain models into Santos poroelasticity theory. Numerical simulations demonstrate that the multiscale model can interpret the transition of rock states as frequency increases and capture the broad-band seismic wave dispersion and attenuation characteristics, which are directly associated with the heterogeneity scale. Besides, the multiscale model can be degraded to a single- or dual-scale model under specific parameters. We validate the proposed model with board-band experimental data of partially saturated sandstones, confirming its comprehensive characterization of velocity dispersion and attenuation over a wider range of frequencies. Moreover, the model successfully interprets the unrelaxed state of partially saturated rock at ultrasound frequencies.

Synthesis of molecularly printed methyl methacrylate-based polymers for the detection of di(2-ethylhexyl) phthalate and dibutyl phthalate

Molecularly imprinted polymers (MIP) were obtained by precipitation polymerization for the detection of DEHP and DBP from polymer packaging in drinking water. MIP was obtained by cross-linking DEHP and DBP with methyl methacrylate (MMA) and trimethylolpropane trimethacrylate (TRIM). FTIR, SEM-EDS, UV-Vis and SAA were used to determine properties of polymers (MIP_DEHP, MIP_DBP). The obtained materials were characterized by a mesoporous structure with small, uniform, and porous grains. The surface area and total pore volume of MIP_DEHP were more than twice smaller than MIP_DBP, with a slightly larger pore diameter. Lower C content may indicate the formation of MIP_DEHP and MIP_DBP. The FTIR method confirmed the presence of functional groups –CH, –CO, –C=C and –C=O. The adsorption capacity of MIP_DEHP and MIP_DBP was 0.68 mg/g and 1.06 mg/g, respectively, and was consistent with the Freundlich isothermal adsorption model.

Measuring porous media velocity fields and grain bed architecture with a quantitative PLIF-based technique

Porous media flows are common in both natural and anthropogenic systems. Mapping these flows in a laboratory setting is challenging and often requires non-intrusive measurement techniques, such as particle image velocimetry (PIV) coupled with refractive index matching (RIM). RIM-coupled PIV allows the mapping of velocity fields around transparent solids by analyzing the movement of neutrally buoyant micron-sized seeding particles. The use of this technique in a porous medium can be problematic because seeding particles adhere to grains, which causes the grain bed to lose transparency and can obstruct pore flows. Another non-intrusive optical technique, planar laser-induced fluorescence (PLIF), can be paired with RIM and does not have this limitation because fluorescent dye is used instead of particles, but it has been chiefly used for qualitative flow visualization. Here, we propose a quantitative PLIF-based methodology to map both porous media flow fields and porous media architecture. Velocity fields are obtained by tracking the advection-dominated movement of the fluorescent dye plume front within a porous medium. We also propose an automatic tracking algorithm that quantifies 2D velocity components as the plume moves through space in both an Eulerian and a Lagrangian framework. We apply this algorithm to three data sets: a synthetic data set and two laboratory experiments. Performance of this algorithm is reported by the mean (bias error, B) and standard deviation (random error, SD) of the residuals between its results and the reference data. For the synthetic data, the algorithm produces maximum errors of B & SD = 32% & 23% in the Eulerian framework, respectively, and B & SD = −0.04% & 3.9% in the Lagrangian framework. The small-scale laboratory experimental data requires the Eulerian framework and produce errors of B & SD = −0.5% & 33%. The Lagrangian framework is used on the large-scale laboratory experimental data and produces errors of B & SD = 5% & 44%. Mapping the porous media architecture shows negligible error for reconstructing calibration grains of known dimensions.

Assembling molybdenum-doped platinum clusters into a coral-like nanostructure for highly enhanced oxygen reduction

Regulating the electronic and geometric structures of electrocatalysts is an effective strategy to boost their catalytic properties. Herein, a coral-like nanostructure is assembled with Mo-doped Pt clusters to form a highly active catalyst toward the oxygen reduction reaction (ORR). The advantages of a Mo-doped porous skeleton, grain boundaries, and MoOx species on the Pt cluster surfaces synergistically boost the electrocatalytic performance. This unique architecture delivers 3.5- and 2.8-fold higher mass and specific activities, respectively, than commercial Pt/C. Density functional theory calculations reveal that the Mo-doped Pt clusters have an optimized Pt–O bond length of 2.110 ​Å, which weakens the adsorption energy of the intermediate O∗ to yield great ORR activity. Moreover, the catalyst shows a decay in the half-wave potential of only 8 ​mV after 10,000 cycles of accelerated durability testing. The high stability arises from the increased dissociation energy of Pt atoms and the stable architecture of the coral-like structure of clusters.

Porous Minerals Improve Wheat Shoot Growth and Grain Yield through Affecting Soil Properties and Microbial Community in Coastal Saline Land

Soil salinization has become a major environmental factor severely threatening global food security. The application of porous minerals could significantly ameliorate soil fertility and promote plant productivity under salt stress conditions. However, the effects of porous minerals on improving the salt resistance of grain crops in coastal saline soils is not fully studied. In this work, the shoot growth and grain yield of wheat plants grown in coastal saline fields, respectively amended with the four naturally available porous minerals, diatomite, montmorillonite, bentonite and zeolite, were assessed. The application of porous minerals, especially zeolite, significantly improved the biomass and grain yield of wheat plants under saline conditions, as demonstrated by the augmented plant fresh mass (14.8~61.2%) and increased seed size (3.8~58.8%) and number (1.4~57.5%). Soil property analyses exhibited that porous-mineral amendment decreased soil sodium content and sodium absorption ratio, and increased soil nutrients in both the rhizosphere and nonrhizosphere of wheat plants. Further quantitative-PCR and 16S high-throughput sequencing analysis revealed that porous-mineral application also remarkably increased the abundance of bacterial 16S rRNA (0.8~102.4%) and fungal 18S rRNA (89.2~209.6%), and altered the composition of the soil microbial community in the rhizosphere of wheat. Our findings suggest that zeolite could be used as an ideal salt soil amendment, and the changes in soil properties and microorganisms caused by the application of porous minerals like zeolite improved the salt resistance of wheat plants in coastal saline land, leading to increased shoot growth and seed production.

Grain wear properties and grinding performance of porous diamond grinding wheels

Conventional diamond grinding wheels present challenges such as poor self-sharpening and difficulties in achieving ductile domain machining when processing hard and brittle materials, reducing machining quality and efficiency. This paper introduces a novel grinding wheel composed of porous diamond abrasive grains for better ultra-precision machining. Thermochemical etching is used to produce porous diamond grains of varying corrosion levels, and the cutting and wear mechanisms of these grains are investigated through molecular dynamics simulations and single-grain scratch tests. Compared to conventional diamond grains, the increased "micro-edge" and "multi-edge" features of porous diamond grains effectively reduce cutting force and heat. Notably, corrosion pore sizes ranging from 2 μm to 5 μm reduce cutting damage. Conventional diamond abrasive grains primarily incur damage through crystal surface dissociation and block crushing, whereas porous diamond abrasive grains experience damage mainly due to micro-crushing and micro-fracture. Ultra-precision grinding tests on 4H–SiC revealed that conventional abrasives produced cracks and pits on the grinding surface. In contrast, abrasives with a 2 μm eroded aperture exhibited predominantly ductile removal with minimal cracks and pits present. Abrasives with a 5 μm eroded aperture displayed desirable characteristics. This research offers valuable technical insights for enhancing the grinding performance of diamond wheels.

Protonation Process of Porous Silica Cluster Surface using Molecular Dynamics Method

Using molecular dynamic simulation, we developed an algorithm to protonate the surface of an amorphous porous silica grain particle model and study its effect. In this work, the silica grain model can be used to study cosmic dust coagulation. The surface of the silica cluster was protonated by placing H atoms on oxygen atoms having only a single bond, namely, the non-bridging oxygens. The H atoms are placed opposite the Si–O bond with a distance of around 1 Å to form silanol (Si–O–H) group termination on the silica surface. The angular conformation of the silanol was optimized by relaxing the surface at low temperature. We evaluated the number of silanol groups, the angular distribution of the Si-O-H bond, and the average distance between Si-O particles using the radial distribution function (RDF). The result of the study shows that minimizing the energy of the silica surface changes the angular distribution of the silanol from 180° to about 110° and between 140°-160°. However, the average distance between Si-O particles remains at 1 Å, which demonstrates the correctness of the atomic interaction model. The addition of protons on the silica surface is an essential factor in the simulation of cosmic dust collision since the modification of the surface chemistry may alter the contact surface energy, thus changing the probability of particle coagulation.

Influence of volume compression on the unloading deformation behavior of red sandstone under damage-controlled cyclic triaxial loading

A reasonable evaluation of unloading deformation characteristics is of great significance for the effective analysis of deformation and stability of surrounding rocks after underground excavation. In this study, the damage-controlled cyclic triaxial loading tests were conducted to investigate the pore compaction mechanism and its influences on the unloading deformation behavior of red sandstone, including Young's modulus, Poisson's ratio, volumetric strain, and irreversible strain. The experimental results show that the increases of volumetric and irreversible strains of rocks can be attributed to the compaction mechanism, which almost dominates the entire pre-peak deformation process. The unloading deformation consists of the reversible linear and nonlinear strains, and the irreversible strain under the influence of the porous grain structure. The pre-peak Young's modulus tends to increase and then decrease due to the influence of the unloading irreversible strain. However, it hardly changes with the increasing volumetric strain compaction under the influence of reversible nonlinear strain. Instead, the initial unloading tangent modulus is highly related to the volumetric strain, and clearly reflects the compaction state of red sandstone. Furthermore, both the reversible nonlinear and irreversible unloading deformations are independent of confining pressure. This study is beneficial for the theoretical modeling and prediction of cyclic unloading deformation behavior of red sandstone.

Construction of a thermally stable ZIF-8 membrane embedded inside a porous support for H2/CO2 separation: Close interlocking between membrane grains and porous support grains

Zeolitic imidazolate framework-8 (ZIF-8) membranes have emerged as promising wall candidates for use in membrane reactors. These membranes can improve the water gas shift (WGS) reaction performance because of their exceptional thermal stability and marked H2/CO2 sieving ability. Here, we propose a modified counter diffusion scheme to form an unprecedented, thermally stable ZIF-8 membrane: Pre-deposition of a zinc precursor (zinc acetate dihydrate) and subsequent solvothermal reaction with a methanolic solution of the ligand (2-methylimidazole). It appears that the pre-deposition and drying of the Zn precursor on and inside a porous support were key to retarding the diffusion of the Zn source, thus leading to the primary contact between the Zn source and ligand molecules within the porous support. As a result, it is likely that a continuous ZIF-8 layer was formed on the top surface and, more preferentially, at the interface with the grains of the porous support, reaching an infiltration depth of approximately 80 μm. Accordingly, this allowed for the effective blocking of the support pores by ZIF-8 grains, as well as their high dispersion. Notably, the resulting ZIF-8 membrane exhibited a maximum H2/CO2 separation factor of ca. 8.7 at a WGS reaction temperature of 300 °C. Unlike the conventional membrane architecture, ZIF-8 grains were densely embedded inside the porous support, thus reducing the risk of mechanical damage. Furthermore, the unique membrane structure was desirable for securing superior thermal stability for reliable and sustainable H2/CO2 separation at 300 °C for up to 72 h.

Hiding Dust around ϵ Eridani

With a Jupiter-like exoplanet and a debris disk with both asteroid and Kuiper Belt analogs, ϵ Eridani has a fascinating resemblance to our expectations for a young solar system. We present a deep Hubble Space Telescope/Space Telescope Imaging Spectrograph coronographic data set using eight orbit visits and the point-spread function calibrator δ Eridani. While we were unable to detect the debris disk, we place stringent constraints on the scattered light surface brightness of We combine this scattered light detection limit with a reanalysis of archival near- and mid-infrared observations and a dynamical model of the full planetary system to refine our model of the ϵ Eridani debris disk components. Radiative transfer modeling suggests an asteroid belt analog inside of 3 au, an intermediate disk component in the 6–37 au region, and a Kuiper Belt analog colocated with the narrow belt observed in the millimeter (69 au). Modeling also suggests a large minimum grain size requiring either very porous grains or a suppression of small grain production, and a radially stratified particle size distribution. The inner disk regions require a steep power-law slope (s −3.8 where s is the grain size) weighted toward smaller grains and the outer disk prefers a shallower slope (s −3.4) with a minimum particle size of >2 μm. These conclusions will be enhanced by upcoming coronagraphic observations of the system with the James Webb Space Telescope, which will pinpoint the radial location of the dust belts and further diagnose the dust particle properties.