Search Results (161)

Ecological porous concrete (EPC) offers both structural performance and ecosystem services, yet an inherent contradiction exists between the ecological benefits of high porosity and mechanical performance. Traditional design methods focusing solely on macro-scale porosity fail to achieve synergistic optimization. This review comprehensively synthesizes the intrinsic correlations between EPC’s multi-scale pore structures and key properties from micro-, meso-, and macro-scale perspectives, drawing upon representative studies across experimental, numerical, and theoretical approaches. The microscale reveals interfacial transition zone bonding, capillary pore effects, and alkalinity regulation for vegetation compatibility. The mesoscale clarifies the control of effective porosity, tortuosity, and pore throats on fluid transport and root penetration. The macro-scale analyzes skeletal pore support for plant growth, hydrology, and slope stability. A cross-scale collaborative design approach is proposed, featuring microscopic reinforcement, mesoscopic continuity, and macroscopic moderation. This paper provides theoretical support for EPC’s transition from empirical to precision design, promoting low-carbon and large-scale applications in revetments, Sponge Cities, and slope restoration. Full article

Focused-ion-beam scanning electron microscopy (FIB-SEM) provides site-specific access to buried interfaces, particle interiors, porous electrode architectures, and localized degradation regions in energy materials. This capability is particularly valuable for rechargeable batteries, solid-state ion conductors, alkali-metal electrodes, and reactive solid–liquid interfaces, where the structures governing transport and failure are rarely exposed at a free surface. However, the preparation and imaging steps that reveal these regions may also alter them. Ion milling, environmental transfer, vacuum exposure, scanning electron microscopy (SEM), cryogenic handling, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), electron energy-loss spectroscopy (EELS), and atom probe tomography (APT) can each modify local morphology, chemistry, or phase state. These effects are especially important when the intended evidence involves light elements, metastable phases, nanoscale coatings, reactive interphases, volatile species, or ion-conducting materials. This perspective develops a claim-specific framework for evaluating such results. Preparation- and imaging-induced changes are related to the material feature being interpreted and to the minimum control needed to distinguish the two origins. For porous electrodes, the relevant outputs include pore volume, connectivity, tortuosity, crack geometry, phase fraction, and active surface area. For reactive interfaces and solid electrolytes, the critical questions concern alkali-metal redistribution, surface amorphization, light-element contrast, implanted-species chemistry, and beam-induced phase formation. The discussion further compares conventional Ga-FIB, cryogenic FIB, Xe plasma FIB, low-energy Ar+ polishing, broad-ion-beam preparation, ultramicrotomy, and repeated particle-oriented FIB workflows. Reliable interpretation requires the preparation route, transfer conditions, imaging dose, analytical acquisition, and claim-specific controls to be reported together with the final microscopy result. Full article

Coal matrix pores are critical sites for gas storage and migration, ensuring effective gas drainage, safe coal mining and reliable evaluation of pore structures. To investigate coal matrix pore characteristics, this study examines coal samples from the Xiaobaodang and Sangshuping collieries (Samples 1 and 2, respectively) using focused ion beam scanning electron microscopy. Datasets were developed through systematic data acquisition, preprocessing and labelling, and the MDFA-DeepLabv3+ model was trained for pore segmentation. Spatial pore size distribution characteristics were derived by integrating 3D reconstruction theory. The final evaluation metrics yielded IoU, Dice, PA, Precision, and Recall values of 81.63%, 89.89%, 98.51%, 89.43%, and 90.34%, respectively. Sample 1 and Sample 2 have broadly similar coordination numbers, Euler numbers and tortuosity values, yet they show distinct differences in the proportion of pores by volume and total pore quantity. These findings provide a theoretical basis for the accurate evaluation of coal matrix pore characteristics and the optimisation of gas drainage design. Full article

Permeability acts as a core parameter governing the efficient and cost-effective development of deep coalbed methane (CBM) reservoirs. The evolution of permeability in deep CBM formations is predominantly driven by the coupled deformation of pore and fracture systems under in-situ stress, yet the intrinsic mechanisms behind this process have not been fully elucidated. In this work, permeability tests were carried out on cataclastic coal specimens in three orientations under both loading and unloading conditions with confining pressures. Experimental results reveal that coal permeability decreases exponentially with increasing effective stress (R² is about 0.99; reduction is about 86%), exhibiting strong anisotropy and displays significant hysteresis during unloading. To interpret these phenomena, we establish a dual-pore fractal series model that uniquely integrates serial flow coupling between matrix pores and fractures and quantifies stress-driven changes in fractal dimension, tortuosity, and maximum pore size. The model successfully reproduces experimental results (mean relative error ≤ 4.2%) and provides mechanistic insights into stress-induced permeability evolution. Stress increases fractal dimension and tortuosity while reducing maximum pore size, rendering pore structures more complex and less conductive. Incomplete recovery of fractal parameters during unloading explains the observed hysteresis. This mechanistic framework, combining the experiment and theory, offers quantitative support for optimizing CBM extraction strategies. Full article

This study proposes a novel analytical model to predict one-dimensional moisture transport in concrete under cyclic drying and wetting conditions. The framework distinguishes between two physical mechanisms: diffusion-driven evaporation during drying and capillary-driven suction during wetting. Governing equations for weight loss and gain are derived for each respective phase. During the drying phase, weight loss follows a linear relationship with the square root of time, allowing the diffusion coefficient to be determined via evaporation tests. For the wetting phase, a modified sorptivity approach is employed, incorporating an error-function baseline to account for residual moisture. A calibration coefficient of ε is utilized to correct for varying conditions between standard water suction tests and environmental wetting, particularly for air-entrained concrete characterized by larger capillary volumes and complex tortuosity. Experimental validation was conducted on concrete with varying water-to-cement ratios. The model demonstrated excellent agreement with experimental data, maintaining relative errors below 10% for standard mixes. While higher-porosity samples exhibited greater scatter due to “water traps” and complex pore structures, the model effectively captured cumulative moisture trends over multiple cycles. This framework provides a robust tool for assessing the durability of concrete structures in unsheltered environments. Full article

Understanding the pore structure of high-rank coals is essential in evaluating gas storage and transport. Here, twelve semianthracite samples from the early Permian Shanxi Formation were investigated by proximate analysis, optical microscopy, low-temperature N₂ adsorption, and fractal analysis, coupled with diffusion coefficient modeling. The coals exhibit diverse pore types (plant-cellular, interparticle, and dissolution pores) shaped by coalification and minerals and show Type IV (a) isotherms with H4 hysteresis loops, indicating complex pore networks. Pore-size partitioning reveals that mesopores and macropores dominate total pore volume, whereas mesopores contribute most of the specific surface area. The pore structure exhibits strong fractal characteristics with an average comprehensive fractal dimension (F_c) of 2.628. The calculated gas diffusion coefficient decreases monotonically with increasing pressure from 1 MPa to 5.8 MPa, with a more pronounced decline at low pressure, indicating a clear pressure-dependent attenuation effect. Diffusion capacity is weakly related to average pore diameter but shows positive correlations with total pore volume and, particularly, macropore volume. Multiple linear regression further demonstrates that pore volume structure is the dominant control on diffusion under both low- and high-pressure conditions, with the relative importance ranked as macropores > mesopores > micropores. Macropores provide the main low-resistance transport framework, mesopores serve as transitional pathways linking storage and transport domains, whereas micropores mainly contribute to gas storage and may even suppress apparent diffusion when overly developed. These results reveal a clear functional differentiation of multiscale pore systems and highlight that gas migration in semianthracite is jointly governed by pore size distribution, connectivity, tortuosity, and fractal network topology. Full article

The Lower Permian Fengcheng Formation (P₁f) in the Mahu Sag, Junggar Basin, records an uncommon alkaline–lacustrine hybrid system where siliciclastic, volcaniclastic inputs, and endogenous carbonates jointly build strong reservoir heterogeneity. This study clarifies how depositional framework architecture and diagenetic evolution jointly control effective pore–throat connectivity and reservoir effectiveness. We examined 55 core samples from nine wells using X-ray diffraction (XRD), scanning electron microscopy (SEM), low-pressure N₂ adsorption (LPNA), high-pressure mercury intrusion (HPMI), and nuclear magnetic resonance (NMR) T₂ spectra, and identified five lithofacies: siliciclastic-dominated (SDF), volcaniclastic (VTF), mixed siliciclastic–carbonate (MSCF), carbonate-dominated (CDF), and alkaline mineral-rich (AMF). Reservoir quality is strongly lithofacies-dependent and cannot be inferred from pore volume alone. The SDF and CDF are both dominated by the >200 nm domain, but only the SDF preserves a coarse pore–throat framework that sustains effective flow; the MSCF is characterized by a stronger 10–50 nm contribution and a more tortuous network, and the VTF by enrichment of the 50–200 nm domain. In the SDF, quartz is preferentially associated with the >200 nm domain and dolomite with the 50–200 nm domain, consistent with coarse residual pores preserved by rigid grains and intercrystalline or dissolution-related pores, respectively. The AMF should be treated as two subtypes: the Na-borosilicate subtype shows high >200 nm volume but very high tortuosity, whereas the Na-carbonate subtype shows co-development of the 10–50 nm and >200 nm domains with lower threshold pressure and tortuosity, indicating better pore-body–throat matching and more favorable reservoir behavior. These findings provide a lithofacies-based framework for screening effective reservoir intervals in alkaline lacustrine hybrid systems. Full article

Achieving the coexistence of high energy density and fast-charging capability remains a fundamental challenge for lithium-ion batteries. Increasing electrode thickness and compaction density enhances energy density but simultaneously alters the pore structure and restricts lithium-ion transport, leading to concentration polarization, increased resistance, and lithium plating. In this work, we employ X-ray computed tomography (X-CT) and 3D reconstruction to establish quantitative relationships between particle size, compaction density, and key structural parameters (porosity, tortuosity, effective proportion of lithium-ion flux (f_eff)). Then, an electrochemical model is used to link the liquid-phase kinetic parameters (ionic conductivity (k₀) and liquid-phase diffusion coefficient), as corrected by the effective proportion of lithium-ion flux f_eff, to polarization and lithium-plating behavior, and the maximum current density without lithium plating under various fabrication conditions is finally determined. Results show that small-particle electrodes exhibit superior rate capability at moderate compaction levels, but suffer from rapidly increasing tortuosity and reduced transport efficiency under high compaction and large thickness. Moreover, a double-layer gradient electrode design effectively integrates the advantages of both large- and small-particle architectures, enabling high-rate operation without lithium plating. The double-layer gradient electrode (ρ = 1.6 g/cm³) exhibited ~50% higher performance at 1.5 C compared to the small-particle anode and enabled 2 C charging without lithium plating. This study offers a robust structural design strategy for optimizing thick-electrode architectures toward high-energy, fast-charging LIBs. Full article

Sol–gel processing provides an unusually controllable route to nanoporous solids, making silica aerogels the leading reference systems for extremely low thermal conductivity due to their high porosity, nanoscale pore sizes, and tunable solid frameworks. Under near-ambient conditions, thermal transport is multi-scale and multiphase, arising primarily from coupled solid conduction through the skeletal network and gas conduction within the pore space. Accordingly, aerogel design has emphasized suppressing solid-phase transport by reducing network connectivity, increasing tortuosity, and enhancing boundary scattering, while also limiting gaseous conduction through the control of pore size and gas pressure. This critical review provides an integrated overview of these mechanisms and the theory-to-experiment toolbox used to quantify the separate and combined contributions of the solid and gas phases to the effective thermal conductivity. We link key structural and environmental parameters (porosity, pore size distribution, density, backbone morphology, and pressure) to dominant transport regimes and the assumptions embedded in common models. Classical approaches, including effective-medium and percolation-based models, are assessed alongside phonon-scaling descriptions that incorporate characteristic length scales. Particular attention is given to the Knudsen effect and pressure-sensitive gas-conduction models, which are central to interpreting performance at atmospheric conditions and under vacuum or low-pressure operation. This review highlights inconsistencies across datasets and modeling practices, identifies persistent knowledge gaps, and outlines practical directions toward processable structure–property guidelines for manufacturing aerogels with targeted thermal performance, with regard to conduction-dominated heat transport mechanisms. Full article

The coupling between the key parameters of rock and soil particle composition and slurry diffusion paths exerts a significant influence on actual grouting effectiveness. Based on the spherical penetration grouting model for Bingham cement grout, this study optimizes the fractal permeability model by coupling the characteristic particle size, porosity, and tortuosity, overcoming the deficiency of single-factor porosity consideration in existing permeability models. Unlike existing studies that only use experimentally measured permeability coefficients, this study employs a physically meaningful permeability model that realizes the synergistic coupling of soil particle composition, pore microstructure, and macroscopic permeability, and further establishes a penetration grouting mechanism that integrates the actual slurry diffusion path tortuosity into the classical spherical diffusion framework. A novel high-precision volume measurement method for grouting stone bodies based on point cloud 3D reconstruction is proposed, and a COMSOL-based visual numerical simulation program is developed by embedding the above coupling permeability model. The accuracy of the optimized mechanism is verified by a combination of model tests, numerical simulations, and theoretical analysis, which makes up for the existing grouting mechanism for loose gravelly soil failing to consider the synergistic influence of rock–soil particle composition parameters and the actual diffusion path. The research results indicate the following: (1) Adopting loose gravelly soil—which is more consistent with actual field conditions—as the grouted medium can effectively predict the reinforcement effect of heterogeneous media in grouting engineering. (2) Compared with theoretical values calculated by mechanisms that ignore the effect of the diffusion paths, those derived from the grouting mechanism that couples the rock and soil characteristic particle size with the Bingham cement grout diffusion path are closer to the experimental values. (3) The visual simulation results exhibit high morphological consistency with the actual grouting stone bodies, and the vast majority of the grout diffusion range falls within the numerical simulation domain. The findings of this study provide targeted theoretical and technical guidance for grouting design under complex geological conditions of loose gravelly soil layers. Full article

High-velocity fluid flow in porous media frequently exhibits non-Darcy behavior, where inertial losses lead to nonlinear pressure gradient velocity behavior. Predicting the Forchheimer coefficient β remains challenging because β varies sensitively with pore geometry and is often not constrained by porosity and permeability alone. This study develops a structure-based method to estimate β using intrinsic descriptors obtained from the Darcy regime flow characterization and image-based geometry analysis. A set of two-dimensional granular porous media was generated with controlled variations in porosity, particle size distribution, and grain size variability. Single phase simulations are simulated with a body-force multiple-relaxation-time lattice Boltzmann method. The transition from Darcy flow to non-Darcy flow is identified from the velocity and pressure gradient response, and β is determined by fitting the inertial flow regime. Two tortuosity responses were observed. In uniform media, hydraulic tortuosity remained nearly constant in the Darcy regime and then gradually decreased. In disordered media, hydraulic tortuosity first increased with the onset of recirculation and then decreased as dominant flow paths became stable. Based on these results, a dimensionless inertial factor was correlated with porosity, intrinsic hydraulic tortuosity, and a pore structure index derived from specific surface area and hydraulic pore size. The resulting model predicts β from permeability and structural descriptors. The resulting correlation provides β estimates from Darcy permeability and geometry descriptors. Validation with quasi-two-dimensional microfluidic pillar array data showed that the model captured both the magnitude and relative ordering of β for the tested geometries. The proposed framework should be regarded as a proof of concept for idealized granular porous media and quasi-two-dimensional structured systems. Full article

Accurate characterization of water saturation in tight sandstone gas reservoirs is the key to reservoir evaluation and productivity prediction. In view of the limitations of the traditional Archie formula in describing the strongly heterogeneous pore structure and the insufficient consideration of the coupling effect of pore throat geometry and fractal characteristics in the existing models, this paper innovatively combines the fractal theory with the trapezoidal pore throat model to construct a new water saturation interpretation model. By introducing parameters such as fractal dimension (D_f), tortuosity fractal dimension (D_T) and trapezoidal factor (φ_i), the model systematically quantifies the control mechanism of microscopic pore throat distribution, capillary force field evolution and stress sensitivity (rock elastic modulus E = 1.05 × 10³ MPa) on water saturation. The model was verified by the sealed coring and nuclear magnetic resonance experimental data of 10 groups of typical tight sandstone cores in Sulige gas field, Ordos Basin. The results show that: (1) The absolute error range between the water saturation calculated by the model and the measured value of the closed coring is 0.89–11.27%, indicating that the model has high accuracy and good applicability. (2) There is a significant negative correlation between reservoir water saturation and reservoir temperature and displacement pressure difference: for every 20 °C increase in temperature, water saturation decreases by about 4.5%; when the displacement pressure difference increases by 1 MPa, the water saturation decreases by about 6.3%. (3) The study further shows that under the condition of constant displacement pressure difference, the water saturation of the reservoir is positively correlated with the effective stress and negatively correlated with the maximum/minimum pore throat radius ratio. Rock mechanics parameters also have an impact on water saturation—the lower the elastic modulus, the higher the Poisson’s ratio, the greater the reservoir water saturation. The model can accurately predict the water saturation of the reservoir and provide an effective tool and support for the fluid quantitative evaluation and development scheme optimization of tight sandstone gas reservoirs. Full article

This study focuses on porous polyimide (PPI) lubricating materials for high-speed aerospace bearings. Based on their real microstructure, three-dimensional digital model reconstruction and mesoscale seepage characteristics were investigated. First, a sequence of two-dimensional slice images of PPI was obtained using micro-focus X-ray computed tomography (CT). Through image filtering, threshold segmentation, and three-dimensional reconstruction, a highly faithful digital model of the pore structure was constructed, and a quantified pore-network model was further extracted. Second, a multiple-relaxation-time lattice Boltzmann model based on the D3Q27 discrete scheme was established, and its accuracy and stability in complex boundaries and pressure-driven flows were verified using classic benchmark cases. Subsequently, the validated numerical model was applied to the reconstructed PPI pore structure to simulate and systematically analyze the single-phase seepage behavior of lubricating oil. The results show that the lubricant seepage exhibits a strong “preferential flow path” effect, with most of the flow transported through a small number of large-size throats. A clear quantitative relationship exists between the microscopic flow field structure—including velocity distribution, flow paths, and pressure gradient—and the pore-topology features, such as throat-size distribution, connectivity, and tortuosity. This verifies the mesoscale mechanism that “structure governs flow.” The complete technical chain established in this work—“real-structure reconstruction–numerical model validation–seepage mechanism analysis”—provides a reliable theoretical and numerical tool for gaining deeper insight into the lubricant transport behavior in porous polyimide and offers guidance for the microstructural design and optimization of this material. Full article

Upper E_s4 lacustrine calcareous shale in the Dongying Depression is characterized by strong pore–throat heterogeneity that limits shale-oil producibility. This study quantifies multiscale pore–throat complexity using high-pressure mercury intrusion-based fractal analysis (segmented fractal dimensions D₁–D₃ and a weighted comprehensive fractal dimension, D_c) and evaluates its control on oil occurrence and mobilization using low-field 2D NMR (T₁–T₂) and confocal microscopy before and after high-temperature, high-pressure spontaneous imbibition. Reservoirs show clear scale segmentation, with micropore fractality governing quality differentiation. Imbibition promotes desorption and redistribution from adsorbed to free oil, but effective mobilization is primarily controlled by pore–fracture connectivity: samples with well-connected networks can mobilize both adsorbed and free oil efficiently, whereas poorly connected systems exhibit desorption without effective production, implying that thermal stimulation alone is insufficient without fracture-assisted flow pathways. Movable-oil saturation decreases systematically with increasing D_c, indicating that higher roughness and tortuosity intensify capillary retention and Jamin trapping. D_c provides an actionable criterion for sweet-spot ranking and for designing stimulation–imbibition coupling and water-based EOR strategies in lacustrine calcareous shale-oil reservoirs. Full article

This research examines how atmospheric plasma spraying torch power and coating thickness jointly affect the adhesion strength, microstructure, porosity, and flexural behavior of $A{l}_2{O}_3$ coatings on 100Cr6 steel substrates. Optical microscopy, SEM and EDS mapping, 3D surface-roughness analysis, Vickers hardness testing (HV2) on polished cross-sections, and three-point bending of extracted beams were employed to develop a processing–structure–property map. This multi-technique approach enables the cross-validation of processing–structure–property relationships and supports a robust identification of the optimal power–thickness condition by jointly considering porosity (densification), adhesion strength, flexural response and failure mode. All conditions resulted in an average surface roughness Ra of approximately 1.0 µm. Increasing torch power to 45 kW generally reduced cross-sectional porosity, except at 500 µm, where globular pores appeared. Hardness (HV2) increased with power and peaked at the intermediate thickness (500 µm); adhesion up to 63 MPa was recorded for the 300 µm/45 kW coating. Flexural strength was highest at 500 µm and was consistently greater at 45 kW than at 39 kW. Fractography showed a shift in failure mode from interface-driven delamination at 39 kW to more cohesive, tortuous intra-coating cracks at 45 kW, aligned with improved splat bonding and crack-path deflection. An intermediate thickness of 500 µm deposited at 45 kW is thus identified as an optimal condition to balance densification and crack-path tortuosity, leading to enhanced hardness and flexural performance. Full article