Porous Bulk Research Articles

Multiscale computational analysis of the steady fluid flow through a lymph node

Lymph Nodes (LNs) are crucial to the immune and lymphatic systems, filtering harmful substances and regulating lymph transport. LNs consist of a lymphoid compartment (LC) that forms a porous bulk region, and a subcapsular sinus (SCS), which is a free-fluid region. Mathematical and mechanical challenges arise in understanding lymph flow dynamics. The highly vascularized lymph node connects the lymphatic and blood systems, emphasizing its essential role in maintaining the fluid balance in the body. In this work, we describe a mathematical model in a steady setting to describe the lymph transport in a lymph node. We couple the fluid flow in the SCS governed by an incompressible Stokes equation with the fluid flow in LC, described by a model obtained by means of asymptotic homogenisation technique, taking into account the multiscale nature of the node and the fluid exchange with the blood vessels inside it. We solve this model using numerical simulations and we analyze the lymph transport inside the node to elucidate its regulatory mechanisms and significance. Our results highlight the crucial role of the microstructure of the lymph node in regularising its fluid balance. These results can pave the way to a better understanding of the mechanisms underlying the lymph node’s multiscale functionalities which can be significantly affected by specific physiological and pathological conditions, such as those characterising malignant tissues.

Fracture strain improving via structural austenitic stainless steel-coated 22MnB5 plates

A total of 316 austenitic stainless steel (ASS) coatings were deposited on 22MnB5 press-hardening steel plates by varying the substrate bias voltages using a magnetron sputtering technique and quenched in a flat mold with cooling water. The substrate bias current and ion-bombardment energy densities increased up to 0.5 mA/mm2 and 50 J/mm2 at a high voltage of −100 V, and, therefore, the variations in the coatings’ morphologies were owing to the increases in the ion bombardment. The porous bulk pattern appeared in the quenched ASS coating at −100 V, clearly different from the porous columnar structure of the others at −50 and −75 V. The γ-Fe and α-Fe phases were observed from the diffraction peaks, presented the ASS coating and 22MnB5 substrate, respectively. There was no intermetallic compound (IMC) peak detected. In addition, the diffusion layer of the quenched ASS-coated plate was observed, in which its morphology was different from the quenched martensite (M) plate, and proved to be the α-Fe microstructure by the very low α-Fe peak at the standard (110) position. The bright image of TEM and the select area electron diffraction pattern indicated the nanostructure of the quenched ASS coating. The nanohardness of the ASS coating, diffusion layer, and M plate (7.36, 3.60, and 6.25 GPa, respectively) was detected, indirectly proving an α-Fe structure of the diffusion layer. The fracture angles of the 316-coated plates significantly improved from 51.82° at −50 V, 53.77° at −75 V to 57.38° at −100 V, as the ASS structure changed to be porous bulk pattern. The clearance of IMC, coating’s porous bulk pattern, and the low hardness α-Fe diffusion layer benefited for the fracture strain by lengthening the pathway of the crack’s development and blocking the further crack’s propagation, respectively.

Microwave sintering construct 3D NiFeAl micro/nano porous bulk electrode for effective oxygen evolution reaction

The development of oxygen evolution reaction (OER) electrocatalysts is an important strategy to produce hydrogen energy by water splitting. Based on the Kirkendall effect and the capillary action of Al melting, this paper introduced a proper amount of Al into NiFe, and the 3D porous bulk high-efficiency OER electrodes were successfully prepared by microwave sintering. The 3D porous structure can provide abundant active sites for OER. The porous channel accelerates the penetration of O2 and electrolyte, shortens the diffusion path of reagents and products, and reduces the charge transfer resistance. It is worth noting that the NiFeAl porous bulk electrode shows excellent OER performance. The overpotentials are 205 mV and 251 mV at the current density of 10 mA cm−2 and 100 mA cm−2, respectively, and the Tafel slope is as low as 39.3 mV dec−1. Due to the existence of Al in the electrode and continuous etching and reconstruction in 1 M KOH solution, the stability test of the electrode lasts for more than 80 h, and the stability rate is even as high as 99.6%. In this work, a new view is put forward in developing an efficient and stable OER electrocatalysts for the preparation of transition metals.

Integration and characterization of a zeolite material in a microcomponent for measurements of environmental carbon dioxide

AbstractThis study demonstrates integration of a zeolite material in a ceramic microcomponent intended for use in sampling and analysis of environmental carbon dioxide (CO2). The zeolite material was integrated in bulk form, allowing for adsorption of large quantities of CO2 compared to previous integration attempts as thin films. To obtain a porous bulk material, an injectable slurry was developed, where expandable polymeric microspheres were added as a sacrificial template. By varying water and sphere contents of the slurry, it was possible to tune the porosity of the zeolite material between 55% and 72%. This in turn affected the flow resistance of the microcomponents, where an increase in the porosity of the filling from 62% to 72% reduced the flow resistance from 84 to 28 kPa min cm−3. In addition, the spheres facilitated complete fillings free from cracks. The zeolite material was seen to retain its ability to adsorb CO2 after processing, but it was not possible to quantify the level of retention compared to unprocessed zeolite.

Fabrication and characterisation of CrMnFeCoNi high entropy alloy electrocatalyst for oxygen evolution reaction

Water electrolysis is attracting increasing attention in becoming the main method for green energy production, which has long been hindered by the sluggish kinetics of oxygen evolution reaction (OER) and high cost of noble-metal (NM) containing electrodes. Template replication technique has been employed to fabricate porous CrMnFeCoNi high entropy alloy (HEA) bulk foams with > 95 % porosity. High entropy led to the formation of a single-phase solid solution of transition metals in the as-fabricated porous HEA bulk foam, and the lattice distortion brings about the outstanding OER performance that is close to that of the RuO2 reference sample. Effective electrochemically active surface area and amount of exposed active sites are increased by grinding into nanoparticles, which produced superior OER performance with a near-record low overpotential of ∼ 245 mV to drive a current density of 10 mA/cm2, a low Tafel slope of 73.6 mV/dec, a double layer capacitance of 102.3 mF, and excellent long-term stability over 24 h. This work demonstrates a cost-effective way to fabricate NM-free HEA electrocatalyst with complex structure and excellent stability in OER, which could help in advancing the research for alkaline water electrolysis.

Enhanced oil recovery via dissolution of low molecular weight PDMS in CO2 during immiscible gas injection in matrix-fracture system

Oil recovery in natural fracture reservoirs can be improved by reducing the capillary force during the gravity drainage process in matrix-fracture system. In the current study, a modified gas was generated via dissolution of low molecular weight poly(dimethyl siloxane) (PDMS, average Mw 3780 g/mol, 10000 – 50000 ppm) in CO2 to enhance oil recovery at 50 °C or 70 °C and 3000 psi. Cloud point measurements indicated that PDMS dissolved in CO2 at pressures less than 3000 psi, which was below the minimum miscibility pressure (MMP) of ∼3600 psi at 70 °C determined with the vanishing interfacial technique. The solution density increased from 669.6 kg/m3 for pure CO2 to 780.3 kg/m3 for CO2/PDMS (50000 ppm) at 70 °C and 3000 psi, thereby reducing the density difference between the CO2-rich fluid and crude oil (ρo=865.2 kg/m3) in matrix-fracture system. Also, CO2-oil interfacial tension (IFT) was reduced from 65 to 15 dyn/cm via the dissolution of 50000 ppm PDMS in CO2. Therefore, it led to the CO2 diffusion coefficient increased in both reservoir-fluid saturated porous media and bulk oil scenarios 3–4 fold and 4–7 fold respectively in comparison to pure CO2 injection. These PDMS-induced changes reduced the capillary effects in gas-invaded zone, which consequently led to an increase in oil recovery of 25% points (from 31% to 56%) compared to pure CO2 injection in the case of capillary continuity during gravity drainage tests. For the field-scale, because the PDMS can dissolve in CO2 at pressures and temperatures which are commensurate with CO2 EOR, it is a promising CO2-philic chemical for increasing CO2 density and improving CO2 diffusion coefficient in gas invaded zone compared to conventional CO2 injection.

Heteroatom-doped hierarchically porous thick bulk carbon derived from a Pleurotus eryngii/lignin composite: a free-standing and high mass loading electrode for high-energy-density storage

It is critical to prepare self-supported carbonaceous electrode materials that enable high-mass loading and efficient ion/electron transport through a simple and sustainable method.

Optimizing the thermophysical qualities of innovative clay–rGO composite bricks for sustainable applications

This work concerned the development of a unique reduced graphene oxide (rGO) nano-filler to provide innovative opportunities in enhancing the thermophysical performance of clay composite bricks. Whereas, a series of clay–rGO composite bricks were produced, doped with various levels of rGO nanosheets (i.e., 0, 1, 2, 4, and 6 wt% clay). Each clay–rGO composite’s microstructure, shrinkage, morphology, density, porosity, and thermophysical characteristics were carefully investigated, and the thermal conductivity performance was optimized. Incorporation of different levels of rGO NPs to the clay matrix allowed all the peaks intensity to rise relative to the untreated one in the XRD pattern. Meanwhile, the inclusion of these doping resulted in a grew in the crystallite sizes and apparent porosity within the compositions. In this vein, shrinkage fracture of fabricated brick composites varied depending on dopants type and levels during the drying and firing processes. Moreover, there are some changes in chemical compositions, as well as wave shifts, suggesting that functional groups of rGO may have contributed to partially introduce carbonyl groups in clay–rGO composites. Besides, the porous topography and bulk density improved rapidly with respect to the plane of the rGO nanosheets within the composites. The differ-dense microstructure displayed in the SEM micrographs supports these outcomes. Remarkably, clay–(4%)rGO compound not only has an optimum thermal conductivity value (0.43 W/mK), but it also has a high heat capacity (1.94 MJ/m3K). These results revealed the exceptional features of rGO sheets such as large surface area with high porosity within the modified clay composites.

Novel Environmentally Responsive Polyvinyl Polyamine Hydrogels Capable of Phase Transformation with Temperature for Applications in Reservoir Profile Control.

Hydrogel has been widely used in reservoir regulation for enhancing oil recovery, however, this process can experience negative influences on the properties and effects of the hydrogels. Therefore, developing novel hydrogels with excellent environmental responsiveness would improve the formation adaptability of hydrogels. In this study, novel polyvinyl polyamine hydrogels were synthesized by a ring-opening addition reaction between polyvinyl polyamines and polyethylene glycol glycidyl ether. The results of atomic force microscopy and transmission electron microscopy showed that the polyvinyl polyamine gel had a porous and irregular bulk structure and was endowed with water storage. With the temperature rising from 30 °C to 60 °C, the transmittance of diethylenetriamine hydrogel decreased from 84.3% to 18.8%, indicating that a phase transition had occurred. After the polyvinyl polyamine hydrogel with low initial viscosity was injected into the formation in the liquid phase, the increase of the reservoir temperature caused it to turn into an elastomer, thereby migrating to the depth of the reservoir and achieving effective plugging. Polyvinyl polyamine hydrogel could improve the profile of heterogeneous layers significantly by forcing subsequent fluids into the low permeability zone in the form of elastomers in the medium temperature reservoirs of 40-60 °C. The novel environmentally responsive polyvinyl polyamine hydrogels, capable of phase transformation with temperature, exhibited superior performance in recovering residual oil, which was beneficial for applications in reservoir profile control and oilfield development.

Boosting the Intrinsic Stability of Lithium Metal Anodes by an Electrochemically Active Encapsulating Framework

AbstractThe lithium metal anode (LMA) is a promising technology to promote the energy density of secondary batteries. However, the coupled growth of surface corrosion and deposited lithium with high reactivity causes capacity fading and safety hazards, especially at high temperatures. Great efforts have been focused on preventing the LMA from direct contact with electrolytes to extend its lifespan, but few pay attention to its stability at high temperatures, which is crucial to battery safety. Herein, a 3D Li22Sn5‐based interpenetrated skeleton is introduced into the bulk of LMA with mechanical kneading, which enables a LMA with fast and stable cycles at high temperatures and improved safety under thermal abuse. The Li22Sn5 skeleton acts as a solid electrolyte inside the bulk, allowing rapid Li+ ion transport and homogenous lithium stripping/plating into the porous bulk through Li/Li22Sn5 interface. The encapsulating framework expands the electrochemically active area and limits its exposure to the electrolyte, enabling a LMA with steady cyclability even at 60 °C. Trapping lithium inside the thermally stable skeleton postpones the catastrophic exothermal reactions between lithium and electrolytes. The strategy for constructing a 3D encapsulating lithiophilic framework is promising for creating safe and stable lithium metal batteries working under harsh circumstances.

Synthesis of nitrogen-doped reduced graphene oxide/magnesium ferrite/polyaniline composite aerogel as a lightweight, broadband and efficient microwave absorber

The fabrication of graphene-based microwave absorbing materials with low density, small filling ratio, broad bandwidth and strong absorption remains a huge challenge. In this work, nitrogen-doped reduced graphene oxide/magnesium ferrite/polyaniline (NRGO/MgFe2O4/PANI) composite aerogel was synthesized by a three-step method of solvothermal reaction, in situ chemical oxidation polymerization and hydrothermal self-assembly. The results showed that the obtained aerogels had a unique three-dimensional (3D) porous network structure and low bulk density (11.1–13.0 mg cm−3). It was worth noting that in the NRGO/MgFe2O4/PANI ternary composite aerogel, MgFe2O4 coated with a thin PANI layer was anchored on the surface of NRGO sheets. Furthermore, the NRGO/MgFe2O4/PANI ternary composite aerogel showed much better microwave absorbing capacity compared with pure NRGO aerogel and NRGO/MgFe2O4 binary composite aerogel. When the filling ratio was as low as 11.5 wt.%, the obtained ternary composite aerogel exhibited the maximum effective absorption bandwidth of 7.0 GHz at a matching thickness of 2.1 mm, and the minimum reflection loss of -42.9 dB at a thickness of 3.57 mm. Additionally, the probable microwave dissipation mechanism was also elucidated. It was believed that this study would pave the way for the construction of 3D graphene-based composites as lightweight, broadband and efficient microwave absorbents.

A self-supported 3D porous high entropy alloy with progressive formation of needle-shaped nanowires during reactions for maintained excellent electrocatalytic oxygen evolution

An efficient 3D porous bulk electrocatalyst is a feasible way to improve the conductivity. Herein, the preparation of a novel self-supporting 3D porous bulk FeCoNiMgB catalyst exhibits excellent electrocatalytic activity and stability properties towards OER. The self-supporting 3D porous framework structure catalyst possesses multiple advantages including large surface area, excellent conductivity, leading to the fast mass and charge transfers, low electrochemical impedance and fast water splitting reaction kinetics. As a result, the 3D porous bulk FeCoNiMgB catalyst requires substantially lower overpotential (234 mV) with a small Tafel slope (36.1 mV dec−1) as compared to pure FeCoNiMgB powders and RuO2 electrodes, as well as stable catalytic properties for over 72 h with no obvious evidence of degradation. Comparative structural characterization and DFT calculations reveal that the needle-shaped nanowires with Fe rich are formed from many open pores during the OER process, which helps to reduce the rate determining step energy barrier (O∗→OOH∗) for OER, and thus has excellent long-term electrochemical stability for continuous oxygen production under alkaline conditions. This work provides a new feasible and promising protocol to realize a novel self-supporting 3D porous bulk high entropy alloy catalyst as an inexpensive catalyst for efficient water splitting.

In-Liquid Plasma-Mediated Manganese Oxide Electrocatalysts for Quasi-Industrial Water Oxidation and Selective Dehydrogenation.

The production of renewable feedstocks through the coupled oxygen evolution reaction (OER) with selective organic oxidation requires a perfect balance in the choice of a catalyst and its synthesis access, morphology, and catalytic activity. Herein we report a rapid in-liquid plasma approach to produce a hierarchical amorphous birnessite-type manganese oxide layer on 3D nickel foam. The as-prepared anode exhibits an OER activity with overpotentials of 220, 250, and 270 mV for 100, 500, and 1000 mA·cm-2, respectively, and can spontaneously be paired with chemoselective dehydrogenation of benzylamine under both ambient and industrial (6 M KOH, 65 °C) alkaline conditions. The in-depth ex-situ and in-situ characterization unequivocally demonstrate the intercalation of potassium in the birnessite-type phase with prevalent MnIII states as an active structure, which displays a trade-off between porous morphology and bulk volume catalytic activity. Further, a structure-activity relationship is realized based on the cation size and structurally similar manganese oxide polymorphs. The presented method is a substantial step forward in developing a robust MnOx catalyst for combining effective industrial OER and value-added organic oxidation.

Micro-sized porous bulk bismuth caged by carbon for fast charging and ultralong cycling in sodium-ion batteries

Micro-sized porous bulk bismuth caged by carbon for fast charging and ultralong cycling in sodium-ion batteries

PH-Responsive Reversible Granular Hydrogels Based on Metal-Binding Mussel-Inspired Peptides.

Taking advantage of their thixotropic behavior, microporosity, and modular properties, granular hydrogels formed from jammed hydrogel microparticles have emerged as an exciting class of soft, injectable materials useful for numerous applications, ranging from the production of biomedical scaffolds for tissue repair to the therapeutic delivery of drugs and cells. Recently, the annealing of hydrogel microparticles in situ to yield a porous bulk scaffold has shown numerous benefits in regenerative medicine, including tissue-repair applications. Current annealing techniques, however, mainly rely either on covalent connections, which produce static scaffolds, or transient supramolecular interactions, which produce dynamic but mechanically weak hydrogels. To address these limitations, we developed microgels functionalized with peptides inspired by the histidine-rich cross-linking domains of marine mussel byssus proteins. Functionalized microgels can reversibly aggregate in situ via metal coordination cross-linking to form microporous, self-healing, and resilient scaffolds at physiological conditions by inclusion of minimal amounts of zinc ions at basic pH. Aggregated granular hydrogels can subsequently be dissociated in the presence of a metal chelator or under acidic conditions. Based on the demonstrated cytocompatibility of these annealed granular hydrogel scaffolds, we believe that these materials could be developed toward applications in regenerative medicine and tissue engineering.

Optimization of bioactivity and antibacterial properties of porous Ti-based bulk metallic glass through chemical treatment

Optimization of bioactivity and antibacterial properties of porous Ti-based bulk metallic glass through chemical treatment

Porous bulk superhydrophobic nanocomposites for extreme environments

Porous bulk superhydrophobic nanocomposites for extreme environments

Characteristics of CO2 hydrate formation and dissociation at different CO2-water ratios in a porous medium

Hydrate-based CO2 sequestration (HBCS) is a new concept to store a huge amount of CO2 in geological sediments in the form of crystalline solids. This technique can address several environmental challenges of the current geologic carbon sequestration approaches. This study aims to evaluate and compare the characteristics and kinetics of CO2 hydrate formation and dissociation in the porous medium (three-phase) and bulk (two-phase) conditions at different CO2-water ratios. The experimental results indicate that the pressure drops and consequently hydrate nucleation and growth are limited in the porous medium due to the presence of solid particles, limited CO2 mass transfer, and heat transfer. Calculation of CO2 mass consumption and rate of gas uptake during hydrate formation also support the limited CO2 consumption and gas uptake rate in the porous medium, compared to the bulk condition. The calculated driving force for each test condition suggests its critical importance in the kinetics of CO2 hydrate formation. On the other hand, limited CO2 diffusion to the aqueous phase, hydrate nucleation at the solid-CO2-water interface, and better protection of newly formed hydrates are among the main reasons for the success of hydrate formation at the CO2-limited ratio only in the porous medium. Lastly, three steps during hydrate dissociation via thermal stimulation, such as heat transfer driving, kinetic driving, and fluid flow driving, are no longer discernable in the porous medium due to the limited heat and mass transfer during the process.

Influence of Radial Stiffness Gradients on Porous Composite Bulk Mechanics

Functionally gradient materials, characterized by a smooth compositional change over space, have gained attention in recent years due to their tunable properties and ability to reduce mechanical stress concentrations. Specifically, attaining high stiffness without compromising toughness is a challenge, as the properties are inversely related. Varying moduli gradients, as seen abundantly in biological materials, do not present this trade‐off, facilitating increased rigidity without altering maximum elongation. Herein, the application of stiffness gradients in porous structures is investigated through compressive mechanical testing, computerized tomography imaging, and finite element modeling. Gradients are compared to several alternative designs to investigate the importance of a smooth material transition and increased radial stiffness. All groups are compressed to 50% strain and the pre‐ and postpore closure modulus, toughness, and dimensional change in the transverse and radial directions are measured. The findings indicate that a mechanical gradient with increasing radial stiffness allows for balance of mechanical integrity and favorable recovery characteristics, crucial for long‐lasting performance. Furthermore, the structures with an increasing radial stiffness outperform those with a decreasing radial stiffness in all aspects. The results emphasize the mechanical advantages and optimization potential of a radial stiffness gradient for a wide range of load‐bearing applications.

Visualization of thermo-magnetic natural convective heat flow in a square enclosure partially filled with a porous medium using bejan heatlines and Hooman energy flux vectors: Hybrid fuel cell simulation

The aim of the article is to study the magneto-convective laminar incompressible flow within a differentially heated square enclosure partly filled with porous medium saturated with ionized helium gas in the presence of a transverse magnetic flux, as a model for emerging fuel cell designs. A Darcy model is utilized for porous medium bulk drag effects. Visualization of heat line and energy flux vectors is computed via Bejan's heat line approach and the Hooman energy flux vector method. The horizontal (i.e., bottom and top) wall boundaries are considered adiabatic and impermeable, while the side walls (cold and hot walls) are maintained at different but constant temperatures. The nonlinear coupled conservation equations under prescribed boundary conditions are solved with a finite difference-based vorticity-stream function approach. Appropriate convergence criteria factors are deployed. Furthermore, validation with earlier studies for the purely fluid, non-magnetic case i. e. in the absence of porous medium (Da) and Hartmann number (Ha) effects, is included. A parametric examination of the impact of Rayleigh number (Ra), Darcy number (Da) and Hartmann number (Ha) on temperature contours, heat lines, energy flux vectors and streamline patterns for ionized helium gas (Prandtl number, Pr = 0.71) is conducted. An increment in Hartmann magnetic number decreases the magnitudes of heat lines, suppresses heat transmission in the enclosure and curtails flow circulation. Enhancing the magnetic parameter and Rayleigh number however boosts the average heat transfer rate. Average Nusselt number at the left hot wall is elevated with increasing permeability of the porous medium and Rayleigh number. Mid-section velocities are enhanced in the porous layer but depleted in the non-porous layer of the enclosure with greater Rayleigh number. The simulations find provide some insight into applications in emerging hybrid electromagnetic fuel cells enabling better visualization of the thermal/fluid characteristics via the novel heat flow visualization heat-function and energy flux vectors analogy.