Micropore Characteristics Research Articles

Evolution of axial cumulative strain and micro-pore structure characteristics of solidified mud under cyclic loading

Embankments and foundation geotechnical structures are frequently subjected to long-term cyclic loading due to traffic during their service life. Excessive cumulative deformation can lead to pavement cracking and uneven settlement of the subgrade. This study conducts a series of dynamic triaxial tests to analyze the effects of the number of cycles (N), effective confining pressure (σc), and dynamic stress amplitude (σd) on the axial cumulative strain (εd) characteristics of solidified mud samples. Additionally, it investigates the evolution model of εd of solidified mud and establishes a predictive model for this strain. In conjunction with the NMR tests, this research further investigates the effects of σc and σd on the pore distribution of solidified mud after loading. Ultimately, the correlation between microscopic pore structure indicators and εd is elucidated. The results indicate that the εd behavior of solidified mud under cyclic loading exhibits characteristics of plastic shakedown. Furthermore, the exponential hyperbolic function model more accurately characterizes the relationship between εd of the samples and N. Before and after cyclic loading, the micropores of the samples accounted for over 95 % of the total pore volume, predominantly concentrated in the radius range of r < 0.3 μm. A correlation exists between the average pore size of the sample and εd, which is primarily influenced by σd and σc.

Variability in soil characteristics in the field–bund transition area increases water loss potential in paddy fields

Water loss in paddy fields occurs through various pathways, and previous studies have primarily focused on water seepage in the field, often overlooking the potential for the field-bund area. In this study, 3 typical paddy fields in the plain river network area of southeastern China were selected to clarify the differences in the soil structure and hydraulic characteristics at different positions within the field–bund area: the field, inner bund, middle bund and outer bund. The interactions between basic soil properties and hydraulic characteristics were also evaluated. The results revealed that the outer bund presented the lowest soil porosity (6.92 %), followed by the field (7.52 %), middle bund (7.77 %), and inner bund (8.09 %). The soil pores in the field presented the smallest mean diameter and fractal dimension and the highest degree of anisotropy. The deep layer of the bund contained more macropores, and the soil pores exhibited greater spatial distribution heterogeneity. The bottom layer in the field and bund presented the lowest average Ks value of only 0.05 mm min−1, indicating the presence of a plow pan and a notable tendency for lateral seepage. Differences in the soil structure and hydraulic parameters between the field and bund created a driving force for lateral seepage and rendered the field–bund area a hotspot for water loss. For the analysis of the underlying water loss mechanism, the structural equation model represented 65 % of the total variance in the hydraulic parameters. The micropore characteristics had the greatest positive direct effect on the hydraulic parameters, with a standardized path coefficient of 0.39 (p < 0.001). The soil physical properties were not directly related to the hydraulic parameters but exerted an indirect effect through aggregate stability and micropore and macropore characteristics, with a total indirect standardized path coefficient of −0.41.

The Micropore Characteristics and Geological Significance of a Tuffaceous Tight Reservoir Formed by Burial Dissolution: A Case Study of the Carboniferous Tuff in the Santanghu Basin, NW China

The Micropore Characteristics and Geological Significance of a Tuffaceous Tight Reservoir Formed by Burial Dissolution: A Case Study of the Carboniferous Tuff in the Santanghu Basin, NW China

Advances in Understanding the Evolution Mechanism of Micropore Defects in Metal Materials under External Loads

Micropores are one of the critical factors affecting materials’ performance and service life. As the need for a deeper understanding of micropore evolution and damage mechanisms grows, assessing the mechanical properties of materials containing micropores and predicting the lifespan of related metal structural components becomes increasingly complex. This paper focuses on the evolution process, regularities, and research methods of micropores in metal materials. Based on recent research and practical applications, the key stages of micropore evolution are discussed, encompassing nucleation, growth, coalescence, collapse, interaction, and the influence of other microstructures. Firstly, the advantages and limitations of commonly used characterization methods such as scanning electron microscopy, transmission electron microscopy, and X-ray computed tomography are introduced in the study of micropore evolution. Subsequently, critical theoretical models for micropore evolution, such as the Gurson model and its extensions, are summarized. By using a multiscale approach combining the crystal plasticity finite element method, dislocation dynamics, and molecular dynamics, the factors influencing the micropore evolution, such as external stress conditions, internal microstructures, and micropore characteristics, are specifically elaborated, and the basic physical mechanisms of micropore evolution are analyzed. Finally, a comprehensive review and summary of current research trends and key findings are provided, and a forward-looking perspective on future research directions is presented.

Achieving strong interfacial bonding of CFRP and magnesium alloy by modifying magnesium alloy surface via alkaline etching with EDTA addition

The interfacial properties of fibre metal laminates are closely related to the surface microstructure of metals. Herein, a hitherto unreported honeycomb-like micro/nano-porous structure was successfully fabricated on an AZ31B Mg alloy surface by incorporation of ethylenediaminetetraacetic acid disodium (EDTA-2Na) into an alkaline solution and achieved excellent interfacial bonding property between AZ31B and carbon fibre-reinforced plastic. The addition of EDTA-2Na can promote the formation of etched pores. The growing nano-scale etched pores join together to produce micro-scale pores and ultimately lead to the formation of a micro/nano-porous structure. The 60 min etched AZ31B/carbon fibre-reinforced plastic laminate exhibits a bonding strength of 25.87 MPa, which is an increase of 350.7% compared to that of the untreated sample. The significant increase in bonding strength is mostly ascribed to composite mechanical interlocking by the micro/nano-porous structure and chemical bonding through the formation of MgCO3 and MgO1+X. In addition, the characteristics of micro-pores also affect the bonding strength.

Influences of Different Acid Solutions on Pore Structures and Fractal Features of Coal

The effect of different acids on the pore structure and fractal characteristics of micropores and mesopores was determined with the help of low-temperature liquid nitrogen adsorption, X-ray diffraction, and the Frenkel–Halsey–Hill (FHH) model by using Yuwu coal as a sample and placing it in acidic environments, such as HF, HCl, HNO3, and CH3COOH. The results show that the acidization effects of HF and CH3COOH are separately dominated by the micropore and mesopore formation effects, while HCl and HNO3 mainly play their roles in expanding mesopores. After acidization, the surface fractal dimensions D1 and D1′ of micropores and mesopores in coal are always negatively correlated with the total specific surface area SBET, specific surface area Smic of micropores, and specific surface area Smes of mesopores. After being acidized by HF, D2 is negatively correlated with the total volume Vtot and the corresponding micropore volume Vmic, while acidization with HCl and HNO3 leads to the opposite result. After being acidized by CH3COOH, D2 has a negative correlation with Vtot and a positive correlation with Vmic. The structural fractal dimensions D2′ of mesopores in samples acidized by HF and CH3COOH are positively correlated with both the volume Vtot and mesopore volume Vmes, while it is the opposite for samples acidized by HNO3. D2′ of coal samples acidized by HCl is negatively correlated with Vtot while positively correlated with Vmes.

Evaluation of strength development and micro-pore characteristics of stabilized expansive soil

Evaluation of strength development and micro-pore characteristics of stabilized expansive soil

Evolution of micropores and second phases during hot deformation of 2050 Al-Li alloy

Microporosity and second phases are typical components for casting 2050 alloy. In this paper, the evolution of both microporosity and the second phases during hot deformation of casting 2050 Al-Li alloy was studied. Firstly, based on industrial CT technology, the typical morphology characteristics of micropores during the hot deformation process of the alloy were studied and related statistics were carried out. The results show that with the increase of deformation strain, the volume, volume ratio, and porosity of the micropores gradually decreased, and the roundness gradually increased. Secondly, the detailed evolution mechanism of the second phases during hot deformation was studied by SEM, XRD, and TEM. It was found that with the increase of deformation strain, the thin plate T1 phase gradually undergoes shearing and exhibits bend-shaped morphology in the SEM image, which was essentially a process of stress transfer from Al matrix to the T1 phase. Meanwhile, the T1 phase also experienced thinning and secondary precipitation. This is mainly attributed to the intensive interaction between the alloying elements within T1 phase and the dislocations pile-up around T1 phase during the hot deformation process. While for the large-size intermetallic phase AlCuFeMn, it breaks up gradually and oxide inclusion is generated at the broken site, which provides favorable conditions for the initiation and propagation of cracks during hot deformation. From TEM observation, it is found that there is Al6Mn intermetallic phase in the alloy matrix with different morphologies under different deformation strains. When the deformation strain reaches 70%, a large number of nanometer Al6Mn particles are dynamically precipitated near the dislocations.

An analysis of thixotropic micropore variation and its mechanism in loess

The relationship between the thixotropic mechanism and the macroscopic thixotropic strength can be clarified by analyzing the changes in microstructure and pores in the loess thixotropic process. This approach is of significant importance for calculating the strength of compacted loess foundations. In the present study, a representative sample prepared from Xi’an loess was analyzed and eight resting ages were set. The micropore characteristics of the remolded loess and undisturbed loess at different resting ages were obtained using electron microscope observation and nuclear magnetic resonance testing. The results indicate that the thixotropy in the prepared loess samples is significant. It is also found that as the resting age grew, newly formed cements in the remolded loess continuously accumulated and filled in the microcracks between the aggregates. Consequently, the contact area of aggregates increased, thereby decreasing the width and length of the microcracks. The proportion of cementation pore and small microcracks gradually increased, while the proportion of large microcracks gradually decreased, indicating that thixotropy increased the cohesive force and friction force of soil structure at the mesoscale. This phenomenon also explains the increase of thixotropic strength at the macroscopic scale. The mesoscopic mechanism of loess thixotropic strength recovery is that the connection between soil particles is re-established after the break of the clay particle–water–charge system. Moreover, the elastic potential energy of soil particles generated by compression promoted the polymerization of clay particles dispersed in a pore water solution to produce flocculating aggregates during resting dissipation. The continuous consumption of clay particles expanded the processing time and flocs and continuously decreased the strength growth rate.

Biochar-based microporous nanosheets-mediated nanoconfinement for high-efficiency reduction of Cr(VI)

Biochar-based materials have been widely used to remove Cr(VI). However, current strategies mainly focus on slow adsorption through electrostatic and functional group properties, ignoring the confinement catalytic fast kinetics caused by inherent porous properties. Herein, we designed a confinement strategy to achieve high-efficiency Cr(VI) reduction by encapsulating the catalytic reaction of Cr(VI) and oxalic acid (OA) in the micropore of PCRN-3–10–2–800. The results showed that the removal rate constant of the PCRN-3–10–2–800/OA system was 14.3 and 146.8 times higher than that of the BC-800/OA system (low porosity) and PCRN-3–10–2–800 alone (adsorption), which was highest removal rate constant in the current reported materials under the same system. The structure-activity relationship indicated that the catalytic activity of Cr(VI) depended on the micropore characteristics of the catalyst. Density functional theory calculations confirmed that nanoscale space could enhance Cr(VI) adsorption and reduce the energy barrier of the rate-determining step. The electron paramagnetic resonance spectrum demonstrated the rapid conversion of Cr(VI) to Cr(III). Furthermore, the PCRN-3–10–2–800/OA system showed good applicability and high efficiency for Cr(VI) removal (nearly 100% in 5 min) in industrial electroplating wastewater treatment. This work first proposes a nanoconfinement-induced heavy metal reduction strategy and guides biochar's universality design in wastewater treatment.

Pore evolution and shear characteristics of a soil-rock mixture upon freeze-thaw cycling

The changes in pore structure within soil-rock mixtures under freeze-thaw cycles in cold regions result in strength deterioration, leading to instability and slope failure. However, the existing studies mainly provided qualitative analysis of the changes in pore or strength of soil-rock mixture under freeze-thaw cycles. In contrast, few studies focused on the quantitative evaluation of pore change and the relationship between the freeze-thaw strength deterioration and pore change of soil-rock mixture. This study aims to explore the correlation between the micro-pore evolution characteristics and macro-mechanics of a soil-rock mixture after frequent freeze-thaw cycles during the construction and subsequent operation in a permafrost region. The pore characteristics of remolded soil samples with different rock contents (i.e., 25%, 35%, 45%, and 55%) subjected to various freeze-thaw cycles (i.e., 0, 1, 3, 6, and 10) were quantitatively analyzed using nuclear magnetic resonance (NMR). Shear tests of soil-rock samples under different normal pressures were carried out simultaneously to explore the correlation between the soil strength changes and pore characteristics. The results indicate that with an increase in the number of freeze-thaw cycles, the cohesion of the soil-rock mixture generally decreases first, then increases, and finally decreases; however, the internal friction angle shows no apparent change. With the increase in rock content, the peak shear strength of the soil-rock mixture rises first and then decreases and peaks when the rock content is at 45%. When the rock content remains constant, as the number of freeze-thaw cycles rises, the shear strength of the sample reaches its peak after three freeze-thaw cycles. Studies have shown that with an increase in freeze-thaw cycles, the medium and large pores develop rapidly, especially for pores with a size of 0.2–20 μm. Freeze-thaw cycling affects the internal pores of the soil-rock mixture by altering its skeleton and, therefore, impacts its macro-mechanical characteristics.

Acoustic droplet vaporization for on-demand modulation of microporosity in smart hydrogels.

Microporosity in hydrogels is critical for directing tissue formation and function. We have developed a fibrin-based smart hydrogel, termed an acoustically responsive scaffold (ARS), which responds to focused ultrasound in a spatiotemporally controlled, user-defined manner. ARSs are highly flexible platforms due to the inclusion of phase-shift droplets and their tunable response to ultrasound through a mechanism termed acoustic droplet vaporization (ADV). Here, we demonstrated that ADV enabled consistent generation of micropores in ARSs, throughout the entire thickness (∼5.5 mm), utilizing perfluorooctane phase-shift droplets. Size characteristics of the generated micropores were quantified in response to critical parameters including acoustic properties, droplet size, and shear elastic modulus of fibrin using confocal microscopy. The findings showed that the length of the generated micropores correlated directly with excitation frequency, peak rarefactional pressure, pulse duration, droplet size, and indirectly with the shear elastic modulus of the fibrin matrix. The ADV-generated micropores in ARSs were further compared with cavitation-mediated micropores in fibrin gels without droplets. Additionally, the Keller-Miksis equation was used to predict an upper bound for micropore formation in ARSs at varying driving frequencies and droplet sizes. Finally, our in vivo studies showed that host cell migration following ADV-induced micropore formation was frequency-dependent, with up to 2.6 times higher cell migration at lower frequencies. Overall, these findings demonstrate a new potential application of ADV in hydrogels. STATEMENT OF SIGNIFICANCE: Interconnected micropores within a hydrogel can facilitate many cell-mediated processes. Most techniques for generating micropores are typically not biocompatible or do not enable controlled, in situ micropore formation. We used an ultrasound-based technique, termed acoustic droplet vaporization, to generate microporosity in smart hydrogels termed acoustically responsive scaffolds (ARSs). ARSs contain a fibrin matrix doped with a phase-shift droplet. We demonstrate that unique acoustic properties of phase-shift droplets can be tailored to yield spatiotemporally controlled, on-demand micropore formation. Additionally, the size characteristics of the ultrasound-generated micropores can be modulated by tuning ultrasound parameters, droplet properties, and bulk elastic properties of fibrin. Finally, we demonstrate significant, frequency-dependent host cell migration in subcutaneously implanted ARSs in mice following ultrasound-induced micropore formation in situ.

Pore structure characteristics of different lithofacies of the Longmaxi shale, Western Hunan‐Hubei Region, China: Implications for reservoir quality prediction

Lithofacies and micropore characteristics of shale reservoir directly affect the exploration and development of natural gas. To determine the development potential of shales of the Longmaxi Formation in the Western Hunan‐Hubei Region, the lithofacies types and micropore structure characteristics of the Longmaxi Formation shales have been systematically studied in this paper, based on ordinary thin sections, argon ion polishing–scanning electron microscopy, physical property testing, x‐ray diffraction whole‐rock and clay mineral analysis, isothermal nitrogen, and carbon dioxide adsorptions. According to the principle of ‘laminar structure + total organic carbon (TOC) + mineral composition of felsic, clay, and carbonate minerals’, eight types of shale lithofacies were identified. The effective porosity of the Longmaxi shale ranges from 1.8% to 14.4%, with a peak range from 3% to 6%, while the permeability ranges from 0.001 to 1.27 mD, with an average of 0.106 mD. Combined with the isothermal adsorption experiments, the proportion of mesopores is the largest in the Longmaxi shale, followed by macropores and micropores. Moreover, the pore diameters of mesopores are concentrated between 3 and 10 nm, while those of micropores are concentrated between 0.4 and 0.9 nm. The pore volume of shale is most developed when the content of brittle felsic minerals is 50% ~ 75% and the content of clay minerals is 25% ~ 50%, and the TOC content is positively correlated with the pore volume and specific surface area. There are significant differences in the pore development characteristics of different lithofacies. The shale reservoir space analysis indicates that micropores are controlled by TOC content and clay minerals, while the macropores are controlled by depositional intergranular pores, TOC content, and felsic content, as well as diagenetic pyrite mould pores, microfractures pores, and intercrystalline pores. On the other hand, mesopores are related to a mix of depositional and diagenetic factors with dominant contribution of intergranular pores, intercrystalline pores, organic pores, and intergranular shrinkage fractures pores. It is found that the pore development of massive organic‐rich siliceous shale lithofacies has the best reservoir quality, including well‐connected intergranular pores, intercrystalline pores, organic pores, and shrinkage fractures. Therefore, the massive organic‐rich siliceous shale lithofacies is the dominant fine‐grained reservoir lithofacies in the studied area. Based on understating the pore characteristics of different lithofacies, this study can provide a scientific basis for the prediction of favourable sweet spots of shale gas reservoir in the Longmaxi Formation, western Hunan‐Hubei Region.

Investigation on strong vertical permeability and micro-pore characteristics of Jinan red clay using X-ray micro-tomography

Due to the peculiarity of the spring domain strata in Jinan, the phenomenon of serious water seepage appears in the process of excavation. The macro permeability of soil is closely correlated with its microstructure. In this study, using the X-ray micro-tomography (micro-CT) system and a self-designed soil seepage device, the internal pore structure of Jinan red clay and the water flow inside the sample under different seepage stages were observed. The microstructure of water phase and air phase in the sample was segmented by the watershed algorithm. Calculation and comparison of pore and throat size distributions and coordination number (CN) at different seepage stages were conducted by establishing pore network model (PNM). Meanwhile, the seepage experiment simulations were conducted based on the 3D pore structure of red clay. The results show that the preferentially flow of Jinan red clay is obvious due to the existence of the vertically developed macropore channel. The fine particles (mainly silt particles) are washed away during seepage, thereby expanding the pore channels. The maximum pore radius and pore connectivity have important influence on seepage characteristics of Jinan red clay, but the correlation between porosity is small.

Insights in mechanism of drying shrinkage by pore-scale modeling of heat-moisture and stress-strain distribution for high-moisture porous media

Drying shrinkage occurs accompanying with heat-moisture transfer during drying process of high-moisture porous media and forming mechanism of drying shrinkage is complicated and influenced by micro-pore structure characteristics of porous media. In order to explore the forming mechanism of shrinkage caused by drying, the pore-scale modeling of heat-moisture and stress-strain distributions for high-moisture porous media was directly established considering the effect of micro-pore structure characteristics of porous media in drying process and analyzed using self-developed pore network simulation algorithm. Simulation results indicated that the drying curves (moisture vs drying time, average temperature vs drying time, and shrinkage vs drying time) were in a good agreement with hot-air drying experimental measurement using apple slices as the typical representation of high-moisture porous media. The phenomenon of dry spots, wet spots, irregular drying front, and irregular asymmetric shrinkage were reflected through pore network simulation. Capillary stress was a key factor affecting drying shrinkage and capillary stress was negative related to the porosity of materials and positive related to the coordination number of materials. Capillary stress produced by materials with uniform diameter distribution was larger, followed by the distribution of normal distribution materials and experimental materials. The findings in current elucidate the mechanism of drying shrinkage and provide insights into drying optimization of high-moisture porous media.

The Salt Lake Basin Bedrock Weathered Crust Gas Reservoir in the Altun Mountains Front of the Qaidam Basin, China

AbstractThe bedrock weathered crust in front of the Altun Mountains in the Qaidam Basin is different from other bedrock weathered crust, because the Qaidam Basin is a salt lake basin, the saline water fluid is infiltrated and deposited in the overlying strata, and a large amount of gypsum is filled in bedrock weathered crust, the pore structure is changed. Use core observation, polarized light microscopy, Electron probe, physical property analysis and field emission scanning electron microscopy experiments. Cracks and a small number of dissolved pores in the interior of the weathered crust, the matrix micropores are widely developed. The characteristics of matrix micropores and cracks have been studied, especially the various matrix cracks formed by tectonic and weathered, as well as the stress characteristics of small dissolved pores, physical properties such as porosity and permeability, This “dual structure” developed in the bedrock is important for guiding the exploration of the lake basin bedrock natural gas.

Synthesis, properties and application of o-carborane-based π-conjugated macrocycles

Two o-carborane-based π-conjugated macrocycles were synthesized. Single-crystal structures revealed their micropore characteristics. These macrocycles exhibit aggregation-induced emission and selective identification.

The Control of Shale Composition on the Pore Structure Characteristics of Lacustrine Shales: A Case Study of the Chang 7 Member of the Triassic Yanchang Formation, Ordos Basin, North China

The pore structure characteristics of shales are controlled by their mineral and organic matter compositions. However, the contributions of different components to the pore structure characteristics of lacustrine shales remain poorly understood. In this study, fifteen Chang 7 Member shales of the Yanchang Formation, Ordos Basin, were investigated through total organic carbon (TOC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and low-pressure N2 and CO2 adsorption analyses to study the control of shale composition on the pore structure characteristics of lacustrine shales. The results show that the average TOC content of the Chang 7 Member shales is 9.63 wt.%. XRD analysis shows that minerals in the Chang 7 Member shales consist of quartz, feldspars, clay minerals, and pyrite. The clay minerals were dominated by illite, chlorite, and interstratified illite/smectite. The mesopore characteristics of the Chang 7 Member shales and micropore characteristics of organic-lean shales are mainly controlled by clay minerals, whereas the micropore characteristics of organic-rich samples are controlled by both clay minerals and organic matter. SEM observations show that the phyllosilicate framework pores are the main pore type in the Chang 7 Member shales. The results of this study provide important insights into compositional control on the pore structure characteristics of lacustrine shales.

Effects of micropore structure of activated carbon and wet conditions on nitrogen oxide removal performance of foam composites

In this study, the influences of the activated carbon type and wet conditions on the nitrogen oxide (NOx) removal performance of foam composites were investigated. To this end, foam composites with interconnected pores and a large specific surface area were prepared using activated carbon and titanium dioxide (TiO2). Two types of activated carbon (palm and pitched-based) with different micropore structures were used. The NOx removal performance of each specimen was evaluated according to the wet conditions. In addition, the micropore characteristics of the specimens were analyzed and compared with the NOx removal performance. The analyzed results revealed that the micropore structure of activated carbon has a significant influence on the NOx removal performance. In addition, as the moisture content of each specimen increased, the NOx removal performance of the foam composite showed a tendency to decrease.

Surface pore characteristics of original coal dust produced in underground mining sites and their impact on the moisture content

In underground coal mines, the efficiency of water-based dust suppression technologies is heavily limited by the poor wettability of coal dust. To explore the effect reasons of the surface pore parameters of coal dust on its wettability, in this study, 18 original coal dust (OCD) samples produced in underground mining sites were collected from various underground coal mines in north China. The surface micropore (pore size <2 nm) and mesopore (2 nm < pore size <50 nm) characteristics of the OCD samples were measured with the nitrogen (N2) adsorption/desorption method. Subsequently, the correlations between the pore characteristics of the OCD samples and their moisture contents and initial contact angle (ICA) were established and discussed. The results demonstrate that the pore structures of the OCD samples are significantly developed, and the impermeable pores with one open end are the dominant pore types in the OCD. The micropore structure of the OCD samples considerably affects its moisture content, thus influencing its wettability. As the increase of micropore size, micropore volume, and specific surface area (SSA), the moisture content of the OCD samples linearly decreased (R2 =0.55), linearly increased (R2 =0.66), and linearly increased (R2 =0.65), respectively. The large capillary force caused by the developed SSA accounts for the significant moisture conservation property of the micropore structures, which improves the wettability of the OCD. The variation of the ICA with the pore parameters well verifies this conclusion.