Changes In Pore Size Research Articles

Study on the characterization method and evolution law of the three-dimensional pore structure in frozen loess under loading

In this study, a functional relationship for frozen soil at different temperatures, confining pressures, and triaxial compressive strengths is established through macroscopic and mesoscopic comparative tests. Additionally, a three-dimensional pore network model at the mesoscopic scale is constructed. Morphological characterization parameters are introduced to quantify the pore structure, and the evolution of the pore structure in frozen soil during the stress process is analyzed, as well as the influence of temperature and confining pressure on the pore characteristics and failure morphologies. The results reveal that at the macroscale, frozen soil exhibits a power function relationship with temperature, confining pressure, and triaxial compressive strength. During mechanical loading, frozen soil undergoes compaction, pore development, and pore expansion stages, leading to changes in pore size and connectivity. Additionally, temperature and confining pressure significantly impact the pore characteristics and failure morphologies of frozen soil. At lower temperatures, frozen soil experiences severe bulging and brittle failure, accompanied by increased pore size, enhanced connectivity, and complex morphology. Increasing the confining pressure reduces the degree of bulging and damage, decreases the porosity and connectivity, enhances the complexity of the pore morphology, and results in a denser and more stable internal structure in frozen soil. Through this study, a better understanding of the damage behavior of frozen soil under different temperatures and confining pressures is achieved. Furthermore, this research provides a theoretical basis and reference for addressing related engineering problems.

The Influence of Different Aggregates on the Physico-Mechanical Performance of Alkali-Activated Geopolymer Composites Produced Using Romanian Fly Ash.

In light of the urgent need to develop environmentally friendly materials that, at some point, will allow the reduction of concrete and, consequently, cement consumption-while at the same time allowing the reuse of waste and industrial by-products-alkali-activated fly ash (AAFA) geopolymer composite emerges as a material of great interest. The aim of this study was to investigate the physico-mechanical performance of composites based on AAFA binders and the effect of different types of aggregates on these properties. The experimental results indicate variations in flexural and compressive strength, which are influenced both by the nature and particle size distribution of aggregates and the binder-to-aggregate ratio. The analysis of the samples highlighted changes in porosity, both in distribution and pore size, depending on the nature of the aggregates. This supports the evolution of physico-mechanical performance indicators.

STRUCTURE PARAMETER OF INTERFACIAL INTERACTION IN Cf/C COMPOSITES AND ITS CHANGE DURING PORE FORMATION PROCESS

The C<sub>f</sub>/C composite oxidation of polyacrylonitrile-based carbon fibers with a combined carbon matrix at 600°C up to a weight loss of 80 wt% has been investigated. The changes in the open porosity, specific surface area, apparent and true densities of the composite, as well as the ultimate strength and elastic modulus during three-point transverse bending tests have been analyzed. An analytical model for obtaining qualitative and semi-quantitative estimates of the change in integral pore size during oxidation of heterophase materials has been developed. The change in pore size is estimated through the evolution of open porosity P and materials specific surface area S. The model has been validated in the C<sub>f</sub>/C composite oxidation study. The composite's mechanical properties dependences on the value of the integral pore size are obtained and analyzed. The structural parameter P/S characterizes the change in the interphase interaction during pores formation and development. It is established that the failure mechanism depends on the value of the parameter P/S and dynamically changes with the oxidation of C<sub>f</sub>/C composite. The use of P/S parameter as a criterion for estimation and control of composite materials structural integrity in open systems is proposed.

Zinc oxide nanoparticle-reinforced sodium alginate/hydroxyapatite scaffolds for osteoporosis treatment in fragility fracture patients: Development and characterization using artificial neural networks (ANNs) modeling.

Osteoporosis is a significant public health concern due to its association with fragility fractures. Despite experiencing such fractures, many patients remain at high risk of future fractures due to inadequate management and treatment of their underlying osteoporosis. This research presents a comprehensive intervention to enhance osteoporosis management in patients with fragility fractures. The intervention involves a thorough personalized assessment of fracture risk using clinical factors and bone density testing, followed by customized treatment based on the individual's fracture risk level. It also addresses non-compliance through patient education, counseling, reminders, and improved care coordination among acute, primary, and specialty providers. The aim is to create and characterize sodium alginate/hydroxyapatite (HA) scaffolds reinforced with zinc oxide nanoparticles (ZnO-NP) for bone tissue engineering. Freeze-drying was used to produce scaffolds with 0-15% ZnO-NP. Analyses confirmed the composite structure, uniform ZnO-NP distribution, and decreasing pore size with higher ZnO-NP content. Mechanical testing showed increased compressive strength with greater ZnO-NP. The scaffolds exhibited over 70% porosity, neutral pH, and increased apatite deposition and bioactivity with higher ZnO-NP. They also demonstrated decreased swelling and strong antibacterial activity against Escherichia coli and Staphylococcus aureus, making them a promising candidate for bone regeneration. Additionally, the researchers used an artificial neural network (ANN) to better understand the relationships between various scaffold properties, and the ANN-based predictions showed that changes in pore size and porosity affect the other properties, with acceptable error compared to experimental results.

EXPLORATION OF GEOPOLYMER BINDERS UTILIZING FLY ASH AND SEWAGE SLUDGE ACTIVATION: IMPACTS ON FRESH PROPERTIES, STRENGTH, DURABILITY, MICROSTRUCTURE AND THERMAL CONDUCTIVITY

EXPLORATION OF GEOPOLYMER BINDERS UTILIZING FLY ASH AND SEWAGE SLUDGE ACTIVATION: IMPACTS ON FRESH PROPERTIES, STRENGTH, DURABILITY, MICROSTRUCTURE AND THERMAL CONDUCTIVITY

Study on changes in pore size on single powder and reduction swelling index during the reduction of iron mill scale with hydrogen and forming gas.

Study on changes in pore size on single powder and reduction swelling index during the reduction of iron mill scale with hydrogen and forming gas.

Sol-gel synthesis of zirconia-based nanoparticles from the side product of tin mining

Indonesia has been one of the world’s primary source of tin since the early of 19th century. Bangka island has the largest tin abundant with a side product is zircon sand (ZrSiO4). The existence of zircon (ZrSiO4) is mostly associated with some of the valuable oxide compounds (VOC) and rare earth oxides (REO). The zirconia powders were synthesized from the zircon sand of PT. Timah Tbk by caustic fusion method followed by sol-gel method. The raw material zircon sand and as-synthesized zirconia were characterized through x-ray fluorescence (XRF), x-ray diffraction (XRD), surface area analysis and porositymeter, thermogravimetric and differential scanning calorimetry analysis (TG-DSC), fourier transform infra-red (FTIR) and scanning electron microscopy (SEM) techniques. The results show that zircon sand from PT Timah Tbk contains some of VOCs, such as ZrSiO4, ZrO2, HfO2, SiO2, Al2O3, TiO2, Fe2O3 and some REOs, such as La2O3, Y2O3, Nb2O5. The fusion temperatures varied from 600 to 800 °C which resulted in an increase of the purity of ZrO2 to 76% based on the XRF analysis. The surface area analysis and porositymeter results showed the significant change in specific surface area, pore size and pore volume of as-synthesized zirconia. The specific surface area increased dramatically from 0.28 m2/g to 173.97, 125.18, and 102.14 m2/g, at fusion temperatures of 600, 700, and 800 °C, respectively. The average particle size of as-synthesized zirconia showed the significant change from 21.31μm to 34.48 nm. The results of this work open new opportunities for the development of zirconia-based nanoparticles from the side product of tin mining.

Photo-responsive nanoporous liquid crystal polymer films for selective dye adsorption.

Photo-responsive nanoporous polymer films (AZOF-R(NC6)) have been developed by a template method based on a hydrogen-bonding supramolecular liquid crystal (LC) and a light-sensitive azobenzene LC crosslinker in this work. Anionic nanopores were obtained after the removal of template NC6 using KOH solution. The AZOF-R(NC6) demonstrates charge-selective dye adsorption and the maximum adsorption capacity for Rh6G is 504.6 mg g-1. The AZOF-R(NC6) film without UV light treatment shows a 32% higher adsorption capacity for Rh6G than the AZOF-R(NC6) film treated with UV light within the initial 10 min. In addition, UV light can trigger the release of the adsorbed dye from the polymer film due to the pore size change arising from the trans-cis isomerization. Besides, the used polymer film can be effectively regenerated using a HCl solution. Such functional polymer films with highly ordered nanopores and photo-responsive properties hold great promise in selective adsorption and mass separations.

Investigation of the microscopic properties of natural structured clay

Conducting quantitative research on the microstructure of soft clay can reveal the essence of its soil mechanical behavior, which is of important practical significance for geological disaster risk assessment and prevention. To quantitatively investigate the microscopic properties of natural structured clay, soft clay soils from various sedimentary environments in the Hangzhou Estuarine Bay area were chosen as the research subject in this study. Subsequently, a comprehensive investigation into the microstructure of clay was conducted, involving X-ray phase analysis and SEM imaging analysis. The results revealed the following: (1) In comparison to the deep clay deposited in fluvial-lacustrine environments, the shallow mucky clay in marine sediments had a higher clay mineral content, accounting for 48%. Illite makes up the majority of it, with minor levels of kaolinite and montmorillonite being present. (2) The shallow mucky clay in the Hangzhou Estuarine Bay area had a typical agglomerate-flocculated structure. In contrast, the deeper clay showed a flocculated structure with less uniform particle sizes, strong stacking randomness, poor directional alignment of soil pores, and tends to form arrangements where edges are adjacent to faces or edges are adjacent to other edges. (3) Compared to the deep clay deposited in fluvial-lacustrine environments, the marine-deposited shallow mucky clay displayed orderly pore arrangements, strong directional alignment, significant pore shape variability, and minimal pore size changes between adjacent pores. The microstructure of soil plays a crucial role in determining the physical, mechanical, and other engineering properties of the soil. This study provides insightful information about the relationship between clay microstructure and geotechnical characteristics in Hangzhou and the surrounding areas.

4D evolutions of cracks, voids, and corrosion products in reinforced concrete materials

This research paper presents a comprehensive investigation into the corrosion process in reinforced concrete structures using advanced analytical techniques, namely non-destructive X-ray computed tomography (CT) imaging, scanning electron microscopy (SEM) images, energy dispersive x-ray spectrometry (EDS), and Raman spectroscopy. The CT image analysis allowed for the identification and quantification of pore structures, crack propagation, and corrosion progression at different stages of corrosion. CT scanning and data analysis offer valuable 4D (3D spatial + time) insights into corrosion in reinforced concrete, revealing changes in pore sizes, with smaller pores increasing and larger pores decreasing as corrosion progresses. Our investigation reveals dynamic changes in reinforced concrete pores during the accelerated corrosion test leading to new pore formation and cracking. The research identifies two distinct types of cracks: one filled with corrosion products and the other, zipper-like cracks, resulting from the connection of deformed pores without corrosion products. The SEM images and EDS analysis confirmed the absence of corrosion products within these unique zipper cracks, suggesting a different mechanism of crack formation compared to the first type of cracks. The results revealed two distinct categories of corrosion products: iron oxides and iron hydroxides, with their distribution correlated to the duration of accelerated corrosion testing. The integration and verification of results from X-ray CT imaging and Raman spectroscopy established a comprehensive understanding of corrosion-induced damage in the reinforced concrete specimen, shedding light on complex interactions among different corrosion products during the corrosion process. These findings offer crucial insights for better understanding of the corrosion process in reinforced concrete paving the way for future development of effective treatments and strategies to mitigate corrosion impact.

Determination of film thicknesses of metal oxides prepared by atomic layer deposition on SBA-15

ZrO2 and CeO2 films were grown in SBA-15 by Atomic Layer Deposition (ALD) to loadings of 0.92 g oxide/g SBA-15. Scanning Transmission Electron Microscopy (STEM) with Energy Dispersive Spectra (EDS) showed that the oxides grew uniformly inside the mesopores. Film thicknesses were then analyzed as a function of the number of ALD cycles using three methods: 1) mass changes assuming bulk densities for the films; 2) changes in pore size from Barret-Joyner-Halenda (BJH) analysis with N2 adsorption isotherms; and 3) small-angle X-ray scattering (SAXS). Film thicknesses assuming bulk densities were between 6 and 8 times smaller than those obtained from BJH analysis. SAXS analysis gave film thicknesses that were approximately twice that obtained from bulk densities. Possible explanations of the discrepancies between these methods are discussed.

Poly(2-vinylpyridine)/MCM-41 Composites with Micropores and Switchable Mesopores for the Removal of Cr(VI).

Porous structure design and reversible regulation of pore size during adsorption-desorption are crucial to the removal of pollutants in water such as Cr(VI). In this paper, micropores and switchable mesopores were constructed on MCM-41 to further improve adsorption-desorption performance of Cr(VI) via the confinement effect of micropores and opening and closing of mesopores. 2-Vinylpyridine was introduced and polymerized into the pores and on the pore mouth of MCM41 modified by C═C group (AM41) under the irradiation of ultraviolet light. The obtained samples (PM41) possessed mesopores (2.73 nm) and micropores (1.36 nm), where mesopores could open or close under different pH and micropores showed the confinement effect because their pore size is close to Cr(VI) diameter (0.87 nm). Compared with MCM-41, the introduction of poly(2-vinylpyridine) enhanced obviously its adsorptive ability and it trapped most of the Cr(VI) (99%) in solution, 12 times higher than that of the parent sample. The change of pore size is favorable to the cycle performance, and after 3 times recycling, the removal rate of Cr(VI) by PM41-20 remained above 88%. Langmuir isotherm showed a better data correlation than the Freundlich model. Cr(VI) in solution was removed by electrostatic interaction between the pyridine group and Cr(VI) and the confinement effect from micropores.

Effect of Scanning Strategy on Surface Roughness of Directed Energy Deposited Inconel 718 Alloy

The additive manufacturing method based on powder feed type laser Directed Energy Deposition (DED) is projected to be able to create objects with intricate structures. The intricate thermal history that occurs during DED causes variations in the top surface roughness, which is an important quality index for DED and has a significant impact on the lifespan of the samples. Surface quality is always desirable, mostly in the case of dynamic loading applications. This article presents a methodical investigation into the top surface roughness of the Inconel 718 alloy during various scanning strategies in the DED. This alloy is utilized extensively in the aerospace, automotive, and military industries. Multilayer cuboid samples are fabricated using four scanning strategies. Using different scan strategy, no significant changes in pore size and amount of porosity was observed, but significant changes were observed for the surface quality of printed Inconel alloy.

Preparation, characterization and designing of porous Ti–6Al–4V through metal injection molding without space holder

Porous Ti–6Al–4V alloys have been widely applied in industry, serving as structural or functional materials. However, the conventional method of producing porous Ti–6Al–4V by metal injection molding (MIM) with a space holder has several drawbacks, such as long debinding time, sintering furnace contamination, uncontrolled porosity and pore size, poor mechanical properties and process instability. This study presents a novel method of fabricating porous Ti–6Al–4V by MIM without space holder that can overcome these challenges. The porosity, average pore size, tensile strength, and compressive strength were studied by scanning electron microscope characterization, optical micrograph analysis, and mechanical testing. Flexible changes in porosity (17 %–74 %), pore size (14 μm–84 μm), and tensile strength (15 MPa–457 MPa) could be achieved by adjusting the powder size and sintering temperature. A higher porosity can be achieved as compared to the previous studies. The relationships among particle size, sintering temperature, porosity, and tensile strength are investigated by multiple regression models, which facilitate the tailored design of porous Ti–6Al–4V alloys for industrial applications and enhance the combination of experimental and theoretical methods in the design of porous alloys using MIM.

Programmable all-DNA hydrogels based on rolling circle and multiprimed chain amplification products.

Soft, biocompatible, and tunable materials offer biomedical engineers and material scientists programmable matrices for a variety of biomedical applications. In this regard, DNA hydrogels have emerged as highly promising biomaterials that offer programmable self-assembly, superior biocompatibility, and the presence of specific molecular identifiable structures. Many types of DNA hydrogels have been developed, yet the programmability of the DNA building blocks has not been fully exploited, and further efforts must be directed toward understanding how to finely tune their properties in a predictable manner. Herein, we develop physically crosslinked all-DNA hydrogels with tunable morphology and controllable biodegradation, based on rolling circle amplification and multiprimed chain amplification products. Through molecular engineering of the DNA sequences and their nano-/microscale architectures, the precursors self-assemble in a controlled manner to produce soft hydrogels in an efficient, cost-effective, and highly tunable manner. Notably, we develop a novel DNA microladder architecture that serves as a framework for modulating the hydrogel properties, including over an order of magnitude change in pore size and up to 50% change in biodegradation rate. Overall, we demonstrate how the properties of this DNA-based biomaterial can be tuned by modulating the amounts of rigid double-stranded DNA chains compared to flexible single-stranded DNA chains, as well as through the precursor architecture. Ultimately, this work opens new avenues for the development of programmable and biodegradable soft materials in which DNA functions not only as a store of genetic information but also as a versatile polymeric biomaterial and molecularly engineered macroscale scaffold.

Experimental study on the influence of ultrasonic excitation duration on the pore and fracture structure and permeability of coal body

The study aims to explore the effect of ultrasonic duration on the pore structure and seepage characteristics of coal. Herein, we adopted a self-developed ultrasonic excitation experiment system using low-field nuclear magnetic resonance (NMR) technology and NM-4B non-metallic ultrasonic wave velocity detector. The study investigated NMR relaxation time T2 patterns and the number of pores of each size, internal structural damage, and seepage characteristics of the coal body before and after ultrasonic fracturing. Based on the Warren-Root model, the permeability model of coal under ultrasonic fracturing was established, revealing the changing law of ultrasonic fracturing at different times on the change of pore scale, connectivity, and nuclear magnetic permeability of the coal body. The mechanism of ultrasonic fractured coal body evolution at different times was clarified. The results showed that the ultrasonic fracturing at different times improved the number and volume of all size pores in the coal body, expanded primary fractures, and developed newborn fractures. The rate of change in pore size, porosity, wave velocity, and coal permeability had a linear relationship with the fracturing time. The growth rate of seepage pore volume proportion was positively correlated to the decreased rate of adsorption pore volume proportion. The fracturing duration leads to the interconnection of micropores within the coal body, forming medium and large pore fractures. This transformation between pores and fractures enhances the pore structure and seepage characteristics of the coal body. The coal rock permeability model can be used to calculate the permeability of a coal body, which follows the same change law as nuclear magnetic permeability. When evaluating the index using absolute and relative errors, the range of relative error is 0.97%–7.91%. The error variation range is small, indicating that the established model can effectively reflect the change law of porosity and permeability of the coal body responding to ultrasonic fracturing. The ultrasonic fracturing rendered the ultrasonic cavitation takes micropores as fracturing units, developed pores of all sizes, connected closed pores, increased free fluid space proportion, and improved the coal permeability.

Study on production performance characteristics of horizontal wells in low permeability and tight oil reservoirs

Low permeability and tight oil reservoirs are rich in microscale pores and contain a large amount of dissolved gas. With the progress of production, the volatile gas gradually forms a continuous gas phase and has an important impact on the productivity of oil wells. In this paper, the characteristics of oil and gas separation in the production process of low permeability and tight reservoirs are described, a productivity prediction vector model is established considering the characteristics of starting pressure in the percolation process, and the coupled influence of "oil film thickness - high pressure effect - multi-element gas effect" on dissolved gas flow is analyzed. Results show that: (a) The horizontal section length and production pressure difference of horizontal wells are the key factors affecting the productivity of low permeability or tight oil reservoirs, while the influence of wellbore radius and reservoir thickness is not obvious. (b) The increase in the length of the horizontal section effectively increases the well control range, increases the oil drainage volume, and thus improves the productivity. (c) With the development of low permeability or tight oil reservoirs, the reservoir pressure and oil saturation have decreased. This results in a decrease in oil film thickness and an increase in volatile gas content. With the change of volatile gas pressure and the change of percolation pore size, the Knudsen number changes in a large range, resulting in the change of the microscale transport mechanism of volatile gas.

Effect of Desorption Damage on the Kinetic Characteristics of Coal Particle Gas Desorption.

There is a positive feedback mechanism of desorption, pulverization, and redesorption in the process of coal and gas outburst. The coal pore structure changes to some extent in the process of coal pulverization and has a related impact on the dynamic parameters of coal particle gas desorption. To understand the impact of desorption damage on the dynamic characteristics of coal particle gas desorption, in this paper, a self-developed coal particle gas desorption test device is used to measure the amount of methane desorption of different coal samples repeatedly desorbed under the same adsorption equilibrium pressure. The results show that the methane desorption kinetic curves of the four coal samples based on desorption damage basically have the same trend. Nie's diffusion model can better describe the methane desorption characteristics of coal particles. After desorption, the methane desorption amount, initial desorption velocity, diffusion ability, and ultimate amount of methane desorption of the coal samples are greater than those before desorption. The desorption damage affects the relevant dynamic parameters of the coal particle gas diffusion model, and its impact on the outburst coal is greater than that on raw coal. In addition, the pore size distribution and change characteristics of the coal samples before and after desorption are analyzed quantitatively via a low-temperature liquid nitrogen adsorption test and fractal dimension-related theory. It was found that the pore volume peak area of the coal samples affected by desorption damage within each pore size range was significantly larger than that before desorption. Among them, micropores have the most significant impact on the desorption damage of coal samples, and the peak area of the pore volume of protruding coal is greater than that of raw coal, indicating that the internal pores of coal after desorption damage are more developed than those of raw coal.

Modeling properties of autoclaved aerated concrete (AAC) by different pore size

AbstractAutoclaved aerated concrete (AAC) is a very popular and porous material, which is foamed in a production process by using aluminum powder. The research program explores the influence of different particle size distributions for properties of AAC with different densities. The compressive strength, thermal conductivity, and shrinkage can be improved by changing the pore size. The research program focused on different density classes of AAC. The pore sizes were changed by using different aluminum powder, different water‐to‐solid ratio, and different starting temperature of the concrete mix. All tests were made on a technological scale and all properties were tested according to EN 771‐4:2011+A1:2015 standard. All samples were tested for dry density, compressive strength, thermal conductivity, shrinkage, and phase composition. The change in pore size can influence not only the AAC properties but also the amounts of raw materials used in the production process and CO2 consumption in its cycle life.

Persistent Homology as a Heterogeneity Metric for Predicting Pore Size Change in Dissolving Carbonates

AbstractAccurate prediction of physical alterations in carbonate reservoirs under dissolution is critical for development of subsurface energy technologies. The impact of mineral dissolution on flow characteristics depends on the connectivity and tortuosity of the pore network. Persistent homology is a tool from algebraic topology that describes the size and connectivity of topological features. When applied to 3D X‐ray computed tomography (XCT) imagery of rock cores, it provides a novel metric of pore network heterogeneity. Prior works have demonstrated the efficacy of persistent homology in predicting flow properties in numerical simulations of flow through porous media. Its ability to combine size, spatial distribution, and connectivity information make it a promising tool for understanding reactive transport in complex pore networks, yet limited work has been done to apply persistence analysis to experimental studies on natural rocks. In this study, three limestone cores were imaged by XCT before and after acid‐driven dissolution flow‐through experiments. Each XCT scan was analyzed using persistent homology. In all three rocks, permeability increase was driven by the growth of large, connected pore bodies. The two most homogenous samples saw an increased effect nearer to the flow inlet, suggesting emerging preferential flow paths as the reaction front progresses. The most heterogeneous sample showed an increase in along‐core homogeneity during reaction. Variability of persistence showed moderate positive correlation with pore body size increase. Persistence heterogeneity analysis could be used to anticipate where greatest pore size evolution may occur in a reservoir targeted for subsurface development, improving confidence in project viability.