Spatial Distribution Of Pores Research Articles

Quantitative characterization of organic and inorganic pores in shale based on deep learning

Organic matter (OM) maturity is closely related to organic pores in shales. Quantitative characterization of organic and inorganic pores in shale is crucial for rock-physics modeling and reservoir porosity and permeability evaluation. Focused ion beam-scanning electron microscopy (FIB-SEM) can capture high-precision three-dimensional (3D) images and directly describe the types, shapes, and spatial distribution of pores in shale gas reservoirs. However, due to the high scanning cost, wide 3D view field, and complex microstructure of FIB-SEM, more efficient segmentation for the FIB-SEM images is required. For this purpose, a multiphase segmentation workflow in conjunction with a U-net is developed to segment pores from the matrix and distinguish organic pores from inorganic pores simultaneously in the entire 3D image stack. The workflow is repeated for FIB-SEM data sets of 17 organic-rich shales with various characteristics. The analysis focuses on improving the efficiency and relevance of the workflow, that is, quantifying the minimum number of training slices while ensuring accuracy and further combining the fractal dimension (FD) and lacunarity to study a simple and objective method of selection. Meanwhile, the computational efficiency, accuracy, and robustness to noise of the 2D U-net model are discussed. The intersection over the union of automatic segmentation can amount to 80%–95% in all data sets with manual labels as ground truth. In addition, calculated by the FIB-SEM multiphase segmentation, the organic porosity is used to quantitatively evaluate the OM decomposition level. Deep-learning-based segmentation shows great potential for characterizing shale pore structures and quantifying OM maturity.

Application of Petrographic and Stereological Analyses to Describe the Pore Space of Rocks as a Standard for the Characterization of Pores in Slags and Ashes Generated after the Combustion of Municipal Waste.

Slags and ashes generated in thermal waste treatment facilities require proper management. In line with the principles of the circular economy, new, more economical, and ecological possibilities for utilizing these substances are sought. These waste materials exhibit characteristics similar to rocks in many aspects. This study focuses on analyzing the similarities and differences between nine selected rocks and three samples of slags and ashes obtained from municipal waste incineration. The main research device used was a polarizing microscope, using reflected, transmitted, and fluorescent light. Additionally, low-pressure gas adsorption equipment, as well as helium and quasi-liquid pycnometers, were used for complementary analysis. The parameters analyzed mainly covered broadly defined petrographic properties of rocks and slags, with a particular emphasis on porosity, porous structure, and the spatial distribution of pores and fractures. The conducted analyses confirmed a significant similarity between slags and ashes and clastic sedimentary rocks such as sandstones and mudstones. The research results underscore the importance of petrographic microscopic studies for analyzing materials other than rocks. They also allow for exploring applications for slags and ashes in areas traditionally reserved for natural rock resources. The findings also indicate the necessity of using methods other than microscopic ones to describe the pore space of rocks. The lower measurement range of the optical microscope is limited to approximately 1 μm, covering only macropores. Other methods extend this characteristic to micro- and mesopores. Therefore, a combination of different methods is often employed to obtain a more comprehensive characterization of rock porosity.

Nondestructive Evaluation of the Isolated Pore Spatial Distribution State in a Special-Shaped C/SiC Composite Component

Nondestructive Evaluation of the Isolated Pore Spatial Distribution State in a Special-Shaped C/SiC Composite Component

Fracture and porosity evolution of coal under uniaxial compression: An in-situ X-ray tomography study

To investigate the meso-structure evolution and fracture mechanism of coal under uniaxial compression, an X-ray three-dimensional scanning microscopy in-situ loading test bench was used to conduct a uniaxial compression test of coal. CT data were obtained under different strain conditions and combined using 3D visualization software. According to the surface porosity under different axial forces shows stages in the Z axis, the 3D reconstruction of coal was divided into three regions to compare its structural evolution law. The results show that the uniaxial compression of coal presents staged fractures, and the distribution characteristics of fractures and pores are closely related to internal stress propagation. With the axial force loading, the internal fractures continued to expand, accompanied by the generation of micro-fractures. The development degree of penetrating fracture and lateral strain in region 1 were always higher than in region 2 and region 3, which is more obvious after the scan D; During the whole process of uniaxial compression, the three regions interacted with each other, and the energy transferred between regions has a “hysteresis”. The failure response of region 1 to axial force was earlier than that in region 2, and region 2 was earlier than region 3. However, the fracture evolution behavior of the same region, the three regions showed consistency; After scan D, the meso-structure changes of region 1 were more significant than the other two regions; The coal was locally deformed and destroyed under the action of axial force, resulting in isolated pores and micro-fractures. The spatial distribution of pores and fractures, the existence of micro-fractures and the interaction among different regions aggravated the uneven distribution of axial force in coal, which has a great influence on the fracture process of coal, so that the failure of coal present stages.

A modeling study of transport through composite membrane with support pore location distributing randomly based on 2D Voronoi tessellations

Composite membrane consisting of selective layer and support is the mainstream membrane configuration. Support has drawn increasing attention in recent years. In this work, transport through composite membrane with support pore location distributing randomly was studied based on 2D Voronoi tessellations and the corresponding membrane performance calculation method was developed. For the calculation, firstly, irregular Voronoi regions are transformed into regular polygons with fixed number of edges meanwhile maintaining the region area. Then, the membrane performance can be obtained by combining the computation results of regular support surface pore spatial distribution and random support surface pore spatial distribution formulas. Poisson Voronoi diagrams, one of the most representative Voronoi diagrams, were mainly used to describe the support surface pore spatial distribution. The results indicate the importance of the number of support surface pores, which determines the average area of Voronoi regions. Support surface pores should be as many as possible. Another important conclusion is that a certain randomness of support surface pore structure (size and location) may not exert an influence on the composite membrane performance. That is, when calculating the composite membrane performance, the support surface pore spatial distribution and surface pore size distribution can be considered as being regular.

The Effects of Stochastic Circular Pores on Splitting Tensile Behavior of Concrete Based on the Multifractal Theory

Concrete naturally contains a large number of circular-like stochastic pores which weaken the tensile strength of concrete and change the crack propagation path. This study investigates the influences of the size distribution and the spatial distribution of stochastic pores on the fracture behavior of concrete based on the splitting tensile test. The mesoscale model of concrete containing coarse aggregate, mortar, interface transition zone (ITZ), and circular pores is established to simulate the crack initiation, propagation, and coalescence of concrete. Concrete samples with a single hole are prepared to verify the effectiveness of the numerical simulation method. Numerical tests are conducted on numerous mesoscale concrete samples with various porosities, pore size distributions, and pore spatial distributions. The numerical simulation results indicate that the tensile strength decreases with the increase of pore size at the same porosity. Based on multifractal theory, a quantitative indicator to describe the spatial distribution uniformity of concrete stochastic pores is proposed. There is a positive correlation between the spatial distribution uniformity of stochastic pores and the tensile strength. The stochastic circular pores can have a profound effect on the concrete’s fracture pattern, which results in three typical macro-crack patterns in the numerical simulation of the splitting tensile test. The presented results deepen the understanding of the influence of stochastic circular pores on the tensile mechanical properties of concrete and provide a reference for the design of concrete structures.

Laser powder bed fusion of oxidized microscale SiC-particle-reinforced AlSi10Mg matrix composites: Microstructure, porosity, and mechanical properties

Laser powder bed fusion (LPBF)-fabricated Al matrix composites reinforced with SiC particles are strongly influenced by SiC particle features. In this study, the microstructural features, mechanical properties, and porosity of moderate volume fraction (10 vol%) microscale SiC-particle-reinforced AlSi10Mg composites fabricated by LPBF under different oxidation temperatures of SiC particles were investigated. The results demonstrate that LPBF-deposited SiCp/AlSi10Mg composites mainly exhibited laser track segments in macroscale and fine cellular-like dendrite grains and (Al + Si) eutectic phases within the melt pool on a microscale. The transition layer of MgAl2O4 was present around the SiC particles in the oxidized-SiCp reinforced AlSi10Mg composites. In addition, the pore spatial distribution of the deposited composites using the microcomputed tomography test and the microstructural formation mechanism using Thermal Calc software were also studied. Using the finite element to model the deposited composites, it was found that the stress and strain distribution presented higher values than those without long-stripe precipitation phases in the deposited parts with long-stripe precipitation phases. The LPBF-fabricated oxidized-10 vol% SiCp/AlSi10Mg composite part with a relatively large ultimate tensile strength (∼405.3 MPa), relative density (∼98.89%), compressive strength (∼1046 MPa) and friction coefficient (0.32) were obtained. In particular, the ultimate tensile strength was larger than that of the other reported SiCp/AlSi10Mg composites with similar volume fractions and particle sizes.

Permeability of micro-scale structure in coal: Insights from μ-CT image and pore network modelling

For developing coalbed methane resources, it is necessary to quantify the heterogeneity embodied in pore size and spatial distribution, and on the basis of which the correlation between the gas transportability and pore structure could then be clarified in coal. In this study the μ-CT imaging technique was used to examine the micro-scale 3D pore structure in two Qinshui basin coals, and the permeability was estimated based on the reconstructed real pore structure. With CT image processing and 3D pore structure, the pore size, connectivity and the pore spatial distribution were displayed, and the connected pores and isolated pores were distinguished, and the proportion of connected pores of the two studied coals was estimated to be 54.22%–68.52% and 79.48%–91.86%, respectively. The surface porosity of 2D structure slice interprets the local pore connectivity, the minimum surface porosity in certain direction of 3D structure was close to 0 for the studied coals, which means that the pore structure is not connected and it has poor permeability in the direction of coal seam. The gas flow path and flow fluxe in 3D structure was visualized and quantified by gas transport simulation based on real coal pore structure, and the permeability and its anisotropy was evaluated. It indicates that the gas pressure appears to be distributed in a “cluster” shape, and the heterogeneity could be major reason for the low gas transport capacity in coal. The permeability of the two studied coals in the horizontal direction is significantly higher than that in the vertical direction, because the transport channels with low surface porosity in the vertical direction have the tendency to hinder the gas transport.

Neutron-tomographic study of the structural features of a bronze mirror found in the Akterek burial complex

This work presents a study on the structure of a bronze mirror found in the Akterek burial complex by using neutron radiography and tomography. The manufacturing features and the physical state of this mirror was analyzed by three-dimensional model. It turned out that the rim on the edge was made of a different alloy, and the border between the rim and the base of the mirror is also visually visible. The morphological features and spatial distribution of pores and voids formed during secondary casting with the application of various patterns and ornaments have been studied in detail. The neutron tomography data made it possible to study the remains of a thin layer of corrosion on the surface of the mirror.

Effect of multiple wetting and drying cycles on the macropore structure of granite residual soil

Soil usually experiences multiple wetting and drying cycles due to changes in climate conditions, which directly lead to changes in the soil pore structure, especially macropores, thus affecting the mechanical properties and permeability. In this paper, the macropore structure of granite residual soil during three wetting and drying cycles is examined by X-ray computed tomography (CT). The pore spatial distribution (including connected pores and isolated pores), pore number, pore porosity and hydraulic conductivity are analysed and quantified. The results show that the variation in the 2D porosity distribution curve continuously decreases in size and reaches the smallest size in the third cycle. Interestingly, the variation in the connected pore porosity is greater than that of the porosity obtained based on all pores as well as isolated pores. The cycles make the soil shrink, the drying effect reduces the connectivity of the pore space, and the number of isolated pores increases; the wetting effect contributes to the recovery of the lost pores and connections, and the pore space and porosity increase after wetting. In addition, the hydraulic conductivity decreases due to the connected porosity, the pore/throat radius decreases, and the connected macropores play a decisive role in the saturated hydraulic conductivity.

Study of triethanolamine on regulating early strength of fly ash-based chemically foamed geopolymer

This study investigates the role of triethanolamine (TEA) in regulating the early strength of ultra-lightweight (∼460 kg/cm3) fly ash-based chemically foamed geopolymer. The reaction kinetics, pore distribution and skeleton strength were examined using isothermal calorimetry, X-ray microtomography, and solid-state nuclear magnetic resonance spectroscopy, respectively. The three-dimensional pore spatial distribution patterns were statistically assessed by applying the Nearest-neighbor distance-based techniques. The results showed that TEA can regulate the early strength of geopolymer foam by rendering homogeneous pore sizes and spatial distributions even when the geopolymerization of the skeleton is retarded. Furthermore, 0.3 % TEA reduced the compressive strength of the skeleton by 13.4 %, from 105.8 MPa to 91.6 MPa, but doubled the specific strength of the geopolymer foam from 2271 N·m/kg to 4662 N·m/kg. The proposed mechanism suggests that foaming kinetics can be regulated for a homogeneous pore distribution by manipulating the complexing effect.

Laser-beam powder bed fusion of cost-effective non-spherical hydride-dehydride Ti-6Al-4V alloy

Hydride-dehydride (HDH) Ti-6Al-4V powders with non-spherical particle morphology are typically not used in laser-beam powder bed fusion (LB-PBF). Here, HDH powders with two size distributions of 50–120 µm (fine) and 75–175 µm (coarse) are compared for flowability, packing density, and resultant density of the LB-PBF manufactured parts. It is shown that a suitable laser power-velocity-hatch spacing combination can result in part production with a relative density of > 99.5% in LB-PBF of HDH Ti-6Al-4V powder. Size, morphology, and spatial distribution of pores are analyzed in 2D. The boundaries of the lack-of-fusion and keyhole porosity formation regimes are assessed and results showed parts with a relative density of > 99.5% could be LPBF processed at a build rate of 1.5–2 times of the nominal production rates in LPBF machines. The synchrotron x-ray high-speed imaging reveals the laser-powder interaction and potential porosity formation mechanism associated with HDH powder. It is found that lower powder packing density of coarse powder and high keyhole fluctuation result in higher fractions of porosity within builds during the LB-PBF process.

Chemical reactions of carbonate-rich mudstones with aqueous CO2 and their impacts on rock's local microstructural and chemo-mechanical properties

Assessment of the structural integrity of carbonate-rich rocks subjected to acidic brine strongly relies on the understanding of the coupling between the chemical changes and the alteration of the mechanical properties of rocks. This study aims at an integrated microscale chemo-mechanical and microstructural characterization of carbonate mudstones exposed to CO2-rich brine under high pressure and high temperature conditions. Digital image analysis was performed on X-ray micro-computed tomography (micro-CT) images to realize microstructural evolution and spatial distribution of pores and different material phases. This approach showed three distinct regions of porosity and carbonate content (resulting from dissolution and precipitation of calcium carbonates), which are critical for understanding the mechanical alteration of the rocks being investigated. Detailed analysis of the micro-CT images also revealed the preferred precipitation of calcium carbonates in pores parallel to the flow/reaction direction. Microscale chemo-mechanical testing performed using coupled grid nanoindentation and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) complemented the micro-CT results: dissolution zones close to the reacted surface were found to have lower hardness and indentation modulus while an increased values in adjacent precipitation zones was observed. Also, the thickness of the precipitation zones was found to be considerably higher in the direction of the bedding planes, which needs special attention in laminated rocks like shales and mudstones. The microstructural and mechanical properties of the microscale regions and the layered structure are expected to influence the overall mechanical properties and integrity of the rock. These results enhance our understanding of the microscale origin of the macroscopic mechanical alteration of carbonate-rich mudstones subjected to acidic brine.

Pores integrated fractal (PIF) analysis on transportation in porous media considering spatial distribution of pores and genuine tortuosity

A pores integrated fractal model is established to represent the microscopic structures of porous media in consideration of the spatial distribution of pores and the genuine tortuosity in various transportation processes. Transport equations are obtained based on the PIF model, providing high precision for predicting the effective thermal conductivity, the permeability and diffusion coefficient in porous materials. Spatial distributions of pores in realistic samples are acquired, based on which the influence of the equivalent pore distributions is specifically analyzed in the study. In the premise of the same porosity, broader range of pore size, dominant pores in dozens of micron or bimodal distribution of pores are crucial factors that influence the heat conduction and permeation in porous media. It is noted that the PIF model has significant values in the design of porous structure with improved transportation characteristics and in the accurate prediction of vital parameters in complex porous media.

Fractal analysis of CT images of tight sandstone with anisotropy and permeability prediction

For developing unconventional oil and gas resources, it is necessary to quantify the heterogeneity embodied in both pore-size distribution (PSD) and pore spatial distribution, on the basis of which the relationship between the seepage characteristics and the microstructure of heterogeneous porous media could then be clarified. In this work, micro computed tomography (μCT) and image processing technology were applied to characterise matrix pore structure in tight sandstone. Fractal theory was used to investigate the image-based heterogeneity of tight porous media. On the basis of the verification that the PSD of the tight rock is statistically self-similar at a certain scale, we investigated the relationships between porosity and fractal dimension, and between 2D and 3D fractal dimensions, respectively. The results showed that the pore structure characteristic parameters with anisotropy, i.e., the ratio of the minimum pore size to the maximum pore size λ max /λ min and a proportionality constant C KT , could be obtained by liner fitting fractal dimension and porosity. Moreover, the 2D PSD characteristics of the ‘standard cross section’ were consistent with the 3D PSD characteristics of pore network. A fractal permeability model was established by treating the connected pores in the matrix as a bundle of conical micropipes. The permeability values predicted by the proposed model agreed well with those predicted by finite volume method simulation under the condition where irreducible pores were removed. A sensitivity analysis indicated that increasing the heterogeneity of the PSD and pore spatial distribution reduced the flow capacity of the matrix, particularly for low-porosity porous media. • A method to verify the fractal self-similarity of pore size distribution in CT images. • D f-2 vs D f-3 of microstructure in heterogeneous porous media was explored. • Fractal anisotropic model for permeability prediction in heterogeneous porous media.

Model representation and quantitative analysis of pore three‐dimensional morphological structure based on soil computed tomography images

AbstractComputed tomography technology has contributed greatly to the visualization of soil internal structure. Complex topological structure and spatial distribution of pores have become a focal area for studying the spatiotemporal evolution of soil structure. This is significant for understanding soil functions and ecological processes. Image‐processing software, such as ImageJ and Image Pro‐Plus, is widely used to visualize and quantify soil pores. However, it does not account for the irregularity and heterogeneity of pore structure, leading to low segmentation accuracy and inaccurate description of pore morphology. Therefore, we used the simplified convolutional network (SCN) method to segment the pore structure and proposed a parallel thinning method to extract the pore skeleton structure. Thereafter, using three‐dimensional modelling and quantitative analysis, we initially examined the spatiotemporal evolution of soil pores during freeze–thaw cycles. Based on the custom rule model and soil pore real model, we evaluated the performance of the distance transform method and parallel thinning method in extracting the pore skeleton structure. The parallel thinning method more effectively described the topological characteristics of pores, and the pore skeleton model had better centrality, refinement and connectivity. Quantitative analysis of pore characteristics illustrates that, although freeze–thaw cycles can affect pore structure at different scales, they do not regularly affect pore macroporosity and the three‐dimensional fractal dimension. These results illustrate that the soil pore structure of the viscous layer is sensitive to freeze–thaw cycles and provides preliminary evidence that seasonal freeze–thaw cycles can cause a soil water retention effect and weaken resistance to erosion. This study presents a novel technique for examining soil function at the pore scale and a theoretical foundation for future research on soil structure and hydrology.Highlights Freeze–thaw cycles have important effects on soil pore characteristics and thus on soil ecology. We provide novel evidence of pore structural changes in response to freeze–thaw cycles. Soil macropore skeleton was extracted using the parallel thinning method. Seasonal freeze–thaw cycles reconfigured the soil macropore model.

(Invited) Imaging Li Metal Transformations Garnet Solid Electrolyte Interfaces with Machine Learning

Reversible lithium metal anodes that can achieve high rate capabilities are necessary for next generation energy storage systems. Recently, there has been renewed interest in using solid electrolyte separators with lithium metal anodes. Solid electrolyte can act as a barrier for unwanted physical and chemical decomposition that lead to unstable electrodeposition (e.g. dendrite and filament growth). However, numerous experimental investigations have revealed that the strength of the separator cannot mitigate unstable electrodeposition and electrically shorting. Instead, the formation and growth of filaments is tied to unique chemo-mechanical properties that exists at buried solid|solid interfaces. Herein, in situ tomography of Li|LLZO|Li cells is carried out to track morphological transformations in Li metal electrodes and buried solid|solid interfaces during stripping and plating processes. Optimized experimental parameters enable high resolution, high contrast reconstructions that enable lithium metal visualization. Quantitative analysis tools (machine learning, image processing) are developed that enable quantification of physical descriptors of lithium metal (spatial current density, porosity, spatial distribution of pores) during cycling. Hotspots in lithium metal are correlated with microstructural anisotropy in the solid electrolyte. Modeling studies show large heterogeneity in transport and mechanical properties of electrolyte at the electrode|electrolyte interfaces. Local domains showing lower effective properties (transport and mechanical) are identified to be regions where failure modes can initiate due to non-uniform stress and flux distributions.

Pore structure analysis of directionally solidified porous copper

Directionally solidified porous copper is considered as a potential candidate in the field of microchannel heat sinks. By the Bridgman-type directional solidification method, a porous copper ingot was fabricated. Evolution of the porosity, pore number density, average pore diameter and average interpore spacing at different ingot heights was investigated. The results show that with the increase of ingot height, the porosity firstly increases and then basically remains unchanged from the ignot height of 65 mm; the pore number density rapidly decreases at first, and the decreasing speed becomes slower when the ignot height higher than 85 mm; the average pore diameter increases and then remains unchanged from the ingot height of 85 mm; the average interpore spacing increases, and the increasing speed of average interpore spacing becomes slower with the increase of height to higher than 85 mm. In order to study the evolution of diameter and spatial distribution of pores, the distribution ranges of pore diameter, nearest-neighbor distance and radial cumulative pore number were analyzed. As the ingot height increases, the distribution ranges of pore diameter and nearest-neighbor distance firstly increase and then tend to be stable. There are no pore clusters and for long distance, the spatial distribution of pores is uniform at different ingot heights. Pore structure and 3D pore morphology of porous copper were observed with the help of light illumination and X-ray tomography. Pore nucleation, pore interruption, pore coalescence, diameter change of pores and lateral displacement of pores were found to exist in the pore structure.

Characterization of Porous Cementitious Materials Using Microscopic Image Processing and X-ray CT Analysis

The use of lightweight concrete has continuously increased because it has a primary benefit of reducing dead load in a concrete infrastructure. Various properties of lightweight concrete, such as compressive strength, elastic modulus, sound absorption performance, and thermal insulation, are highly related to its pore characteristics. Consequently, the identification of the characteristics of its pores is an important task. This study performs a comparative analysis for characterizing the pores in cementitious materials using three different testing methods: a water absorption test, microscopic image processing, and X-ray computed tomography (X-ray CT) analysis. For all 12 porous cementitious materials, conventional water absorption test was conducted to obtain their water permeable porosities. Using the microscopic image processing method, various characteristics of pores were identified in terms of the 2D pore ratio (i.e., ratio of pore area to total surface area), the pore size, and the number of pores in the cross-sectional area. The 3D tomographic image-based X-ray CT analysis was conducted for the selected samples to show the 3D pore ratio (i.e., ratio of pore volume to total volume), the pore size, the spatial distribution of pores along the height direction of specimen, and open and closed pores. Based on the experimental results, the relationships of oven-dried density with these porosities were identified. Research findings revealed that the complementary use of these testing methods is beneficial for analyzing the characteristics of pores in cementitious materials.

Electron Beam Additive Manufacturing of Ti6al4v: Importance of Powder Reuse on Metal Porosity, Pore Size and Spatial Distribution

Porosity is one of the primary concerns in metal powder bed fusion Additive Manufacturing (AM). While investigations concerning defects in metal AM are common, there is limited understanding concerning the spatial distribution of pores in the metal, and how they evolve with powder reuse. In this study, the porosity in Ti6Al4V produced by Electron Beam Melting (EBM) AM was characterized by X-ray Micro Computed Microtomography (μCT) over a series of 30 build cycles (~480 hr cumulative build time). Investigated were the volume fraction of pores (i.e. the porosity), their size, shape, and location distribution. The most prevalent pores identified were those originating from the gas atomized powder and pores caused by incomplete fusion of the melt pool. The overall average volumetric porosity was 0.10±0.02%, with no significant dependence on powder reuse. A general tightening of the pore size distribution was seen with reuse including slight increases in the 10th and 50th percentile and a reduction in the 90th percentile. However, some consistency in the size distribution was noted, with some builds developing extreme size pores. An inverse relationship between pore diameter and sphericity was found, with large pores posing greater effective stress concentration. Regarding spatial distribution, the largest pore density developed around 0.5 mm adjacent to the surface of parts, at the transition between the contour and melt beams. Based on results of this study, µCT is recommended for quality control of metal parts, and models that account for these defects in defining the damage tolerance of components are needed.