Anisotropic Porosity Research Articles

Eco‐friendly Anode Materials for Lithium and Sodium‐ion Batteries from Wood Sources

AbstractThe intricate materials found in nature boast remarkable multifunctional properties honed through millions of years of evolution, resulting in the highest optimal organization in terms of function, structure, and chemistry. Leveraging the distinctive attributes of natural materials through biomimicry present a captivating avenue for research, brimming with vast potential for groundbreaking discoveries. Among the array of precursors available, wood stands out as a prominent candidate that covered over 30 % of the global land surface. Renowned for its captivating mechanical properties and anisotropic hierarchical porosity finely tuned to facilitate swift pathways, wood embodies attributes of abundance and biodegradability. Consequently, scientists have drawn inspiration from wood's exceptional characteristics to engineer batteries exhibiting remarkable electrochemical performance. For instance, the characteristic hierarchical multi‐channeled construction of wood serves as a blueprint for synthesizing energy storage materials endowed with heightened ion and electron diffusivity. Serving as an integrated carbonaceous scaffold featuring a hierarchical architecture and aligned channels, wood‐based anodes enhance ion and electron conductivities, while bolstering the kinetics of charge transfer in lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). This review underscores the recent strides made in utilizing wood as a hierarchically porous and renewable material for developing anode materials tailored for LIBs and SIBs. Additionally, it sheds light on the potential of wood‐derived anode materials for LIBs and SIBs to alleviate the strain on critical raw materials, while accentuating the additional environmental sustainability benefits derived from such innovations.

Experimental Studies on the Anisotropic Fatigue Behaviour of IN718 Fabricated via Wire Arc Additive Manufacturing

Wire and arc additive manufacturing (WAAM) offers promise in creating large complex structures due to its flexibility and high material deposition rates. The nickel-based alloy IN718 is favoured for WAAM due to its weldability and compatibility. However, WAAM can introduce issues like anisotropic grain structure, porosity, and residual stresses which can lead to directional variations in tensile, fatigue, and fracture behaviour. This paper studied the WAAM process of IN718, utilising cold metal transfer (CMT). The optimised CMT-WAAM parameters for IN718 were identified to as a wire feed speed of 8–10 m/min and a torch travel speed of 0.5–0.7 m/min, resulting in stable deposition and minimal defects. Nevertheless, columnar grain structures were observed in the build direction (BD), with coarse grains in the wall-length direction (WD). This anisotropic microstructure coupled with stress concentrators, contributes to the directional dependence observed in tensile properties, fatigue endurance, and crack growth. The investigation revealed superior ductility in the BD compared to the WD. Interestingly, the fatigue endurance testing showed a longer life in the WD compared with the BD, attributed to stronger stress concentrators in the BD specimens. However, when examining a cracked specimen, the fatigue crack propagated faster in the WD rather than the BD.

A simplified numerical method based on anisotropic porous media model for the precooler of the hypersonic precooled engine

The precooler is a key component of hypersonic precooled engine, and its actual structural have a high anisotropy in the axial, circumferential, and radial direction. Considering the non-uniform flow inside the precooler is crucial to study the flow and heat transfer characteristics of the precooler. The previous simplified method for the precooler has not fully considered the flow non-uniformity of the axial, radial and circumferential direction. In this paper, a simplified numerical method based on anisotropic porous media model for the precooler was proposed. The unique aspect of this method is the integration of anisotropic surface porosity of porous media model with the zero-dimensional heat transfer model. In addition, the influence of key structural parameters on the flow and heat transfer characteristics of precooler was studied. It is found that as the tube transverse pitch increases from 2 to 3.5, the total flow rate increases by 11%, and the heat exchange rate decreases by 25%. As the number of tube rows increases from 7 to 13, the heat exchange rate increases by 22%, but the total pressure loss coefficient increases from 0.046 to 0.082. In addition, the decrease of inner diameter of the precooler improves the heat exchange rate, but reduces the flow capacity of the precooler. These results indicate that the simplified numerical method is capable of simulating the behavior of precooler and provides some guidance on the design of precooler.

Chemiluminescent wood

Wood materials incorporating new properties are of great interest, especially for advanced applications such as sustainable optics and photonics. In this work we describe a wood functionalization approach, comprising the incorporation of artificial chemiluminescent systems (phenyl oxalate ester‑hydrogen peroxide-fluorophore, and luminol-ferricyanide), resulting in light-emitting wood. By a detailed characterisation of the light emission features we point out the complex interaction between wood scaffold and chemiluminescent systems, especially the quenching effect of wood extractives (for the TCPO-H2O2-fluorophore system) and lignin (for the luminol-ferricyanide system). Moreover, we take advantage of the intrinsic anisotropic porosity and capillarity of wood tissue to study the chemiluminescent front propagation. Our results may inspire the development of novel light-emitting wood materials for a variety of applications, from fundamental studies of water uptake in wood to sensors and even design elements.

From cocoa waste to sustainable bioink: valorising pectin for circular economy-driven tissue engineering

Cocoa bean production, a cornerstone of many developing economies, currently adheres to a linear economic model, giving rise to sustainability concerns. The expansion of cocoa butter and liquor consumption has resulted in the increased generation of residual biomass, constituting 60–70 % of fresh fruit. The absence of management plans for this biomass in cocoa-producing countries poses a risk of phytosanitary issues. This study proposed a circular economy approach by valorising cocoa pod husk-derived pectin for tissue engineering. The study optimised an alkaline-based protocol to extract pectin from cocoa pod husk, resulting in ∼ 20 % yield with a ∼ 47 % degree of esterification. Methacrylation transformed extracted pectin into pectin methacrylate (PECMA), confirmed by FTIR-ATR and NMR analyses. PECMA hydrogels, crosslinked with CaCO3 and UV, exhibited rapid gelation and superior water uptake properties. SEM revealed distinct morphological differences with UV exposure, showing improved interconnectivity and anisotropic porosity while the mechanical testing demonstrated enhanced compressive modulus and rheological properties with UV crosslinking. PECMA-based bioink encapsulated chondrocytes, maintaining cell viability over 6 days. This innovative bioink, derived from cocoa waste, holds promise for sustainable tissue engineering applications.

Numerical investigation and experimental validation of water condensation in the gas diffusion layer with different properties

Liquid water in porous media hinders the transport of reactant to catalyst layer, where the electrochemical reactions occur, which in turn, reduces performance and lifetime of a proton exchange membrane fuel cell (PEMFC). In this study, two types of gas diffusion layer (GDL) materials are used to study the two-phase saturation distribution in a PEMFC. The correlations between the effective and anisotropic transport properties and porosity of the two GDLs are solved by the pore scale model. In addition, the anisotropic liquid water permeability and the relationship between saturation pressure and capillary pressure is determined by using the Lattice-Boltzmann method. Fuel cell performance as well as liquid water distribution in the GDL using neutron radiography are obtained for validation. Under wet conditions, the cell with Freudenberg GDL performs better than that using Toray GDL, especially at high current densities. The results of the two-phase model simulation show that the peak water saturation for Toray GDL occurs in the catalyst layer and can reach 40%, while the peak water saturation for Freudenberg GDL occurs inside the GDL directly under the ribs and only reaches 25% saturation. The combined results provide key insights to enable high power density operation of a PEMFC through GDL material optimization.

Fast Modeling of Vegetated Flow and Sediment Transport Over Mobile Beds Using Shallow Water Equations With Anisotropic Porosity

AbstractA two‐dimensional shallow water model based on the anisotropic porosity method is developed for predictions of water flows, sediment transport and bed morphological changes through rigid vegetation. Effects of the vegetation resistance and the spatial occupation are accounted for by adding an extra vegetation drag force and introducing porosity parameters. By defining a cell‐based porosity for the volumetric occupation and an edge‐based porosity for the flux exchange, the anisotropic property of the preferential flow can be well captured. Based on the finite volume method, the model is solved explicitly with a hybrid local time step/global maximum time step method and is parallelized using the Open MP techniques. The numerical grid convergence and quantitative accuracy of the model have been tested against a series of flume experiments for various configurations of rigid emergent vegetation over fixed or mobile beds. It is shown that using shallow water equations with anisotropic porosity, a constant drag coefficient can lead to numerical solutions of comparable accuracy as those complex empirical relations. Moreover, appropriate quantification of the stem‐scale turbulence effects brings significant improvement in modeling of the vegetation‐affected sediment transport.

A novel stabilized NS-FEM formulation for anisotropic double porosity media

Self-consistent extension of linear poroelasticity to overlapping scales of porosity within fluid-saturated anisotropic materials is developed. The coefficient matrix of poromechanical properties considering anisotropy is firstly derived from the corresponding intrinsic properties of its single porosity constituents. The momentum supply term arising from the mass transfer is also quantitatively analyzed. To provide further insight into the theory, numerical values of the poroelastic coefficients are calculated for sandstone that are consistent with the material parameters reported by prominent authors. Then, the node-based smoothed finite element method (NS-FEM) is extended to implement the coupled double porosity flow and deformation formulation. In order to provide numerical stability and accuracy, a modified nodal integration scheme based on multiple stress points over the smoothing domain (SD) and the polynomial pressure projection (PPP) scheme are further implemented in the NS-FEM. Next, four benchmark tests are simulated and compared with reference solutions, based on which the correctness of the proposed NS-FEM formulation is verified and the generalizability of the derived anisotropic double porosity model is confirmed. Finally, the elastoplastic response of double porosity media is investigated, including the impact of permeability anisotropy, the impact of permeability contrast, and the impact of strain-softening.

Mesoscale Models for Describing the Formation of Anisotropic Porosity and Strain-Stress Distributions during the Pressing Step in Electroceramics.

Porous ceramics are often produced by using pyrolisable additives to generate porosity during the sintering step. The examination of the experimental microstructures of the resulted porous ceramics revealed certain levels of anisotropy, even if the original soft additives used as pore forming agents were spherical. The paper shows that anisotropic porosity may result in ceramics when using equiaxed soft polymeric additives for generating porosity, due to the deformation of soft inclusions during the pressing step. It has been found, by means of analytical and numerical calculations, that uniaxial pressing of a mixture of solid particles with contrasting mechanical properties (hard/soft) generates modifications in the shape of the soft phase. As a result, anisotropic shape distribution of the soft inclusions in the green ceramic body and elongated porosity in the final ceramic product are obtained. The elongated pores are statistically oriented with the major axes perpendicular to the pressing direction and will generate anisotropy-related functional properties. Analytical calculations indicate the deformation of a single soft inclusion inside a continuum solid. Further, by finite element simulations performed in 2D planes along the transversal and radial directions of the pressing axis, a bimodal angular distribution of the long axes of the soft inclusions has been found.

Insight into the microstructural and durability characteristics of 3D printed concrete: Cast versus printed specimens

This study presents the comparison of microstructural and durability characteristics of 3D printed concrete (3DPC) depending on its production method (printing or casting). Printed samples with different numbers of layers, as well as a cast specimen with an identical mix composition, were produced and compared, with their microstructural pore and solid characteristics quantitatively and qualitatively investigated. For this purpose, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (micro-CT) were utilized to evaluate the microstructures of the 3DPC. In particular, quantitative approaches using micro-CT data were newly proposed for a better understanding of the microstructural characteristics of 3DPC. Moreover, their durability-related characteristics and transport properties, including freeze-thaw and thermal resistance, were examined and compared. Despite noticeable differences between the microstructures of the printed and cast specimens, including their anisotropic and inter-layer porosity and heterogeneity, confirmed by MIP, SEM and micro-CT, no significant differences in the transport (capillary water porosity and water sorptivity) or durability-related properties (frost and thermal attack) were found. This was due to the dense and homogenous microstructure of 3DPC, which is attributable to the high binder content and low w/b of the mixture. Moreover, the newly proposed evaluation provided reasonable quantitative and qualitative characteristics, which can be used to demonstrate and predict the material properties of 3DPC.

Influence of position and building orientation on the static properties of LPBF specimens in 17-4 PH stainless steel

Laser Powder Bed Fusion (LPBF) is among the most valid solutions for Additive Manufacturing thanks to its high flexibility and accuracy, even though LPBF products can present mechanical properties negatively affected by anisotropic grain morphologies, porosity and heterogeneous solute distribution.Growth direction of parts has a clear effect on mechanical properties. Although the subject has been addressed in literature by numerous Authors, many conflicting results can be found. This work is aimed at providing further knowledge in this regard, even assessing the influence of the building position over the building plate, in case of LPBF of 17-4 PH stainless steel powder in full-melting mode. The investigation comprised static tensile tests to assess the influence of building direction (0° or 90°) and position of specimens on the building plate. Scanning Electron Microscope (SEM) observations were made on specimens after tests so to observe the fracture surfaces and, eventually, statistical evidences were provided to support the conclusions of the work.

Calcium phosphate-based biomaterials trigger human macrophages to release extracellular traps

As central part of the innate immune response, immune cells fight against invaders through various mechanisms, such as the release of extracellular traps (ETs). While this mechanism is mainly known for neutrophils in biomaterial contact, the release of macrophage extracellular traps (METs) in response to biomaterials has not yet been reported. An important application area for biomaterials is bone, where healing of defects of a critical size requires the implantation of grafts, which are often composed of calcium phosphates (CaPs). In this study, the response of human monocyte-derived macrophages in vitro to two different CaPs (α-tricalcium phosphate (α-TCP) and calcium deficient hydroxyapatite (CDHA)) as well as different pore structures was investigated. Scaffolds with anisotropic porosity were prepared by directional freezing, while samples with isotropic pore structure served as reference. It was revealed that ETs are released by human monocyte-derived macrophages in direct or indirect contact with CaP scaffolds. This was caused by mineral nanoparticles formed during incubation of α-TCP samples in culture medium supplemented with human platelet lysate, with an anisotropic pore structure attenuating MET formation. METs were significantly less pronounced or absent in association with CDHA samples. It was furthermore demonstrated that MET formation was accompanied by an increase in pro-inflammatory cytokines. Thus, this study provided the first evidence that macrophages are capable of releasing ETs in response to biomaterials.

The impact of effective tortuosity on carbonate acidizing and the validation of Damköhler and Péclet dimensionless phase space

Acid stimulation is one of the main methodologies to enhance well productivity and increase permeability lost by near-wellbore formation damage through matrix acidizing. The desired outcome of acidizing carbonate rocks is to form deep conductive flow channels called “wormholes”. The productivity enhancement depends on how deep these wormholes penetrate into the reservoir. The porous medium is characterized by three fundamental parameters which are anisotropic or isotropic porosity, permeability, and percolation. Here we test the hypothesis that effective tortuosity - a key parameter for microstructure characterization in porous media - has a significant effect on wormhole formation. Significant progress has been made by empirical work on carbonate acidizing to increase the stimulation efficiency, but further improvements are possible by developing a deeper understanding of the impact of effective tortuosity on wormhole initiation and development. We use Indiana limestone core-flooding experiments to inject diluted hydrochloric acid (HCl) at different acid concentrations and injection rates. Effective tortuosity was calculated for the tight Indiana limestone and was compared with an earlier study on the highly porous Mount Gambier limestone to evaluate the effect of tortuosity on wormhole formation. Our results suggest that the inverse Damköhler and Péclet phase space, traditionally used for evaluating criteria for wormhole formation, needs to be extended by tortuosity as a third dimension to capture the effect of microstructure for the initiation of wormhole phenomenon. Incorporating this extension will improve the prediction of wormhole initiation conditions for all carbonate rock types by using a universal dimensionless phase space.

A new anisotropic poroelasticity model to describe damage accumulation during cyclic triaxial loading of rock

SUMMARY Crustal rocks undergo repeated cycles of stress over time. In complex tectonic environments where stresses may evolve both spatially and temporally, such as volcanoes or active fault zones, these rocks may experience not only cyclic loading and unloading, but also rotation and/or reorientation of stresses. In such situations, any resulting crack distributions form sequentially and may therefore be highly anisotropic. Thus, the tectonic history of the crust as recorded in deformed rocks may include evidence for complex stress paths, encompassing different magnitudes and orientations. Despite this, the ways in which variations in principal stresses influence the evolution of anisotropic crack distributions remain poorly constrained. In this work, we build on the previous non-linear anisotropic damage rheology model by presenting a newly developed poroelastic rheological model which accounts for both coupled anisotropic damage and porosity evolution. The new model shares the main features of previously developed anisotropic damage and scalar poroelastic damage models, including the ability to simulate the entire yield curve through a single formulation. In the new model, the yield condition is defined in terms of invariants of the strain tensor, and so the new formulation operates with directional yield conditions (different values for each principal direction) depending on the damage tensor and triaxial loading conditions. This allows us to discern evolving yield conditions for each principal stress direction and fit the measured amounts of accumulated damage from previous loading cycles. Coupling between anisotropic damage and anisotropic compaction along with the damage-dependent yield condition produces a reasonable fit to the experimentally obtained stress–strain curves. Furthermore, the simulated time-dependent cumulative damage is well correlated with experimentally observed acoustic emissions during cyclic loading in different directions. As such, we are able to recreate many of the features of the experimentally observed directional 3-D Kaiser ‘damage memory’ effect.

Sintering anisotropy of binder jetted 316L stainless steel: part II – microstructure evolution during sintering

ABSTRACT Green density of binder jetted parts are typically equal or lower than the powder tap density. Also, anisotropic green porosity distribution is expected because of the characteristics of the binder jetting (BJ) printing process. In this study, the microstructure evolution in terms of phases and porosity characteristics was studied. A transition from irregular-shape interconnected porosity in pre-sintered samples to closed quasi-spherical porosity for samples sintered at 1370°C was observed. EBSD phase map showed ∼2.73% of δ-ferrite in sample sintered at 1370°C. The anisotropic porosity distribution was revealed by a higher area fraction of aligned large pores (>35 µm), within the cross-section perpendicular to the building direction. Chemical analysis showed an increase of C, O and N on the green sample, while a strong decrease was found after sintering when compared with the powder chemistry. δ-ferrite onset, from phase equilibrium calculations, varies from ∼1250°C (sintered sample chemistry) to ∼1350°C (powder chemistry).

Impacts of Anisotropic Porosity on Heat Transfer and Off-Gassing during Biomass Pyrolysis

Impacts of Anisotropic Porosity on Heat Transfer and Off-Gassing during Biomass Pyrolysis

Modeling of heat transfer in an element with anisotropic porosity

The paper presents the results of modeling the heat transfer process in a channel filled with a porous medium. Moreover, the porosity changes according to the specified law along one of the coordinates. It is shown that an element with anisotropic porosity has better heat transfer characteristics in comparison with an element with a homogeneous porous structure.

Estimation of anisotropic hydraulic conductivity using geophysical data in a coastal aquifer of Karnataka, India

AbstractEstimation of hydraulic parameters is essential to understand the interaction between groundwater flow and seawater intrusion. Though several studies have addressed hydraulic parameter estimation, based on pumping tests as well as geophysical methods, not many studies have addressed the problem with clayey formations being present. In this study, a methodology is proposed to estimate anisotropic hydraulic conductivity and porosity values for the coastal aquifer with unconsolidated formations. For this purpose, the one‐dimensional resistivity of the aquifer and the groundwater conductivity data are used to estimate porosity at discrete points. The hydraulic conductivity values are estimated by its mutual dependence with porosity and petrophysical parameters. From these estimated values, the bilinear relationship between hydraulic conductivity and aquifer resistivity is established based on the clay content of the sampled formation. The methodology is applied on a coastal aquifer along with the coastal Karnataka, India, which has significant clayey formations embedded in unconsolidated rock. The estimation of hydraulic conductivity values from the established correlations has a correlation coefficient of 0.83 with pumping test data, indicating good reliability of the methodology. The established correlations also enable the estimation of horizontal hydraulic conductivity on two‐dimensional resistivity sections, which was not addressed by earlier studies. The inventive approach of using the established bilinear correlations at one‐dimensional to two‐dimensional resistivity sections is verified by the comparison method. The horizontal hydraulic conductivity agrees with previous findings from inverse modelling. Additionally, this study provides critical insights into the estimation of vertical hydraulic conductivity and an equation is formulated which relates vertical hydraulic conductivity with horizontal. Based on the approach presented, the anisotropic hydraulic conductivity of any type aquifer with embedded clayey formations can be estimated. The anisotropic hydraulic conductivity has the potential to be used as an important input to the groundwater models.

Biomimetic Wood‐Inspired Batteries: Fabrication, Electrochemical Performance, and Sustainability within a Circular Perspective

AbstractNature's hierarchical materials offer exceptional multifunctional properties thanks to their evolution over millions of years to reach the most optimized organization in terms of function, structure, or chemistry. Exploiting the unique features of natural materials through biomimicry offers an exciting research field with large potential for new discoveries. Wood, as one of the most fascinating biomaterials, combines unique mechanical properties, an anisotropic hierarchical porosity optimized to provide rapid, and low tortuosity pathways for nutrient/water transport, abundance, and biodegradability. Accordingly, wood has inspired scientists to mimic its outstanding properties in artificial analogues to develop batteries with remarkable electrochemical performance. For instance, its sophisticated structure can be transferred to solid‐state materials through biomimetic templating to increase the lifespan and energy density of batteries, while its inherent hierarchical multi‐channeled structure allows the synthesis of current collectors with enhanced ion and electron diffusivity. This Review highlights the recent progress into the application of wood as a hierarchically porous and renewable material to develop different battery components, including the cathode, the anode, the separator, and current collectors. The potential of wood‐inspired batteries to lessen the pressure over critical raw materials and additional environmental sustainability benefits are highlighted within a circular economy perspective.

Fluid flow through anisotropic and deformable double porosity media with ultra-low matrix permeability: A continuum framework

Fractured porous media or double porosity media are common in nature. At the same time, accurate modeling remains a significant challenge due to bi-modal pore size distribution, anisotropy, multi-field coupling, and various flow patterns. This study aims to formulate a comprehensive coupled continuum framework that could adequately consider these critical characteristics. In our framework, fluid flow in the micro-fracture network is modeled with the generalized Darcy's law, in which the equivalent fracture permeability is upscaled from the detailed geological characterizations. The liquid in the much less permeable matrix follows a low-velocity non-Darcy flow characterized by threshold values and non-linearity. The fluid mass transfer is assumed to be a function of the shape factor, pressure difference, and (variable) interface permeability. The solid deformation relies on a thermodynamically consistent effective stress derived from the energy balance equation, and it is modeled following anisotropic poroelastic theory. The discussion revolves around generic double porosity media. Model applications reveal the capability of our framework to capture the crucial roles of coupling, poroelastic coefficients, anisotropy, and ultra-low matrix permeability in dictating the pressure and displacement fields.