Small Micropores Research Articles

Heterogeneity and permeability estimation of pore-throat structure at different scales in deep tight sandstone reservoirs: A case study of Paleogene Hetaoyuan Formation in Anpeng area, Nanxiang Basin, China.

Clarifying the pore-throat size and pore size distribution of tight sandstone reservoirs, quantitatively characterizing the heterogeneity of pore-throat structures, is crucial for evaluating reservoir effectiveness and predicting productivity. Through a series of rock physics experiments including gas measurement of porosity and permeability, casting thin sections, scanning electron microscopy, and high-pressure mercury injection, the quality of reservoir properties and microscopic pore-throat structure characteristics were systematically studied. Combined with fractal geometry theory, the effects of different pore throat types, geometric shapes and scale sizes on the fractal characteristics and heterogeneity of sandstone pore throat structure are clarified. On this basis, the estimation model of tight sandstone permeability was established. The results indicate that the reservoir physical properties in the study area are poor, the pore types are mainly dissolved pores, and the pore size is mainly distributed in the nano to submicron range. The fractal dimension fitting curve obtained based on the non-wetting phase model has obvious turning points, indicating that the pore-throat structure has multi-scale characteristics. The turning point of fractal dimension divides the pore-throat structure of tight sandstone into large-scale pore-throats with good connectivity (reticular or beaded pore-throats) and small-scale pore-throats with poor connectivity (dendritic or capillary pore-throats), indicating that tight sandstone has binary pore structure characteristics. The geometry of large-scale pore-throat is complex, which is difficult to meet the self-similar characteristics, with the average fractal dimension is 3.72. The small-scale pore-throat morphology is close to the capillary and has obvious fractal characteristics, with the average fractal dimension is 2.22. There are many small pores and micropores in the reservoir, and the pore volume has a significant positive correlation with the total porosity of the rock, but the contribution to the permeability is low. The development degree of large-scale pore throat is an important factor affecting the physical properties of tight sandstone. The turning point radius of fractal curve and the comprehensive fractal dimension can be used as good indicators for permeability estimation.

Effect of Carbonate Solvent Additives in Electrolyte on the Self-Discharge Phenomenon in Organic Electrical Double Layer Capacitors

As a result of industrialization, technological progress, and the growing global population, energy consumption worldwide is skyrocketing. Researchers are thriving to seek high power density storage device to meet these escalating energy demands. Electrical Double Layer Capacitors (EDLCs) also known as a supercapacitor, are energy storage devices that store energy by Coulombic attraction between ions, polarized solvent on the surface of the activated carbon electrodes to form an electric double layer without involving chemical reactions. EDLCs display some remarkable characteristics such as high-power density, ultrafast charge/discharge rates, and long cycle life, surpassing conventional lithium-ion batteries. These features make EDLCs ideal for a wide range of applications, including portable devices, energy backup systems, and electric vehicles.However, the self-discharge effect in EDLCs is a deadly drawback that decrease the shelf life of EDLCs and impeding its practical applications. This phenomenon refers to the spontaneous voltage decay between the electrodes when the capacitor is under open-circuit potential after being charged, leading to a reduction in the stored charge without any external connection. This voltage declination is a complex process therefore, various mechanisms have been proposed to elucidate this phenomenon. There are primarily four mechanisms leading to the self-discharge. First, the internal short-circuit caused by imperfect seal of EDLCs leading to ohmic leakage current. Second, the uneven distribution of pore sizes in activated carbon electrodes leads to a higher resistance for ions to penetrate deeper into the material, resulting in ion accumulation on the surface during short charging times. This accumulation causes an uneven distribution of electron energy in the electrode material. After disconnecting, electrons rearrange to achieve overall energy consistency, while ions gradually redistribute and move into the smaller micropores within the activated carbon electrode. This phenomenon is referred to as charge redistribution effect. Third, Faradic current in EDLCs occurs due to redox reactions, stemming from the decomposition of the electrolyte or chemical reactions involving impurities within the electrolyte. Lastly, during the charging process, ions accumulate at the electrode surface, creating a concentration gradient between the electrodes and the electrolyte. As a result, ions gradually diffuse back into the bulk electrolyte until reaching equilibrium. Addressing self-discharge is paramount in ongoing research efforts.Electrolyte solutions are critical components in EDLCs, providing a medium for ion transport between the electrodes. The electrolyte solution is typically composed of a supporting electrolyte dissolved in a solvent, and the choice of solvent can significantly impact the performance of the device. This study delves into the impact of electrolyte solvent additives in the electrical double layer of EDLCs, leading to varied self-discharge performances. In this report, five commonly-used organic carbonate solvents in EDLCs, were selected to investigate their effects on the self-discharge phenomenon. Cyclic carbonate solvents, such as EC and PC, are known to possess high dielectric constants, high viscosities and high flash points. In contrast, linear carbonates e.g., DEC, DMC, EMC have low viscosities, low dielectric constants and low flash point. By incorporating carbonate solvents into the 1M TEABF4/PC (Tetraethylammonium tetrafluoroborate/propylene carbonate) commercial electrolyte, the performance of five supercapacitors , minimal deviation in electrochemical analyses such as CV and GCD was observed. However, significant differences emerged in EIS, elucidating the varying degrees of self-discharge phenomena. These differences in self-discharge mechanisms across the five EDLCs stemmed from the distinct dielectric constants and molecule sizes of the five solvent additives (i) Low dielectric constant and large molecule size, as seen in DEC (239.4h) and EMC (165.1h), contributed to increased interfacial impedance which effectively prolonging self-discharge compared to commercial one (145.7h). Conversely, the DMC with smaller interfacial resistance initially exhibited lower voltage decline due to reduced charge redistribution effects. However, its rapid ion diffusion process from carbon pores to electrolyte resulted in the fastest self-discharge of DMC (124.7h). (ii) High dielectric EC competes for solvation coordination, reducing interfacial resistance and enhancing intermolecular interaction. This, in turn, leads to the formation of a denser electric double layer (EDL) with EC, therefore decelerating the self-discharge process (205.9h) in EDLCs. In summary, the study emphasizes the significance of solvent additive selection and demonstrates a simple, safe, and cost-effective method to prolonging the self-discharge duration of DEC to more than 1.5 times that of the commercial one, significantly inhibiting the critical self-discharge issue in supercapacitors. Figure 1

Power Density of a Magnesium Air Fuel Cell with Titanium Dioxide Added to Activated Carbon Derived from Marine Plastic Waste

Plastic waste is widely recognized as one of the major sources of marine pollution. Not only does it have a severe effect on marine ecology, but it also releases cancerogenic chemicals into the waterways. The amount of global plastic waste has doubled from 234 million tonnes in 2000 to 460 million tonnes in 2019, of which only 9% was recycled. In 2010, an estimated 275 million tonnes of plastic waste were collected from 192 countries located in coastal areas, with approximately 4.8–12 million tonnes ultimately finding their way into the seas and oceans. Global health, animal wildlife, and the environment are bearing a hefty price [1].In addition to increasing demand for portable energy storage in electronics and electric vehicles, batteries better than the current Li-ion batteries (LIBs) are a necessity. Magnesium (Mg) ion batteries have emerged as an attractive alternative because of the unique advantages of Mg metal. These include as large specific capacity, easy handling, high abundance, and theoretically smooth electrodeposition on Mg metal [2]. In addition, the reasons why magnesium is attracting attention as a battery include the following. A magnesium battery has been proposed as a promising multivalent-ion battery candidates due to its large specific capacity, high energy density, high security, low cost, low equivalent weight and low toxicity. Moreover, it shows many advantages in comparison with the widely used lithium ion batteries. Firstly, Mg ions are present in the form of +2 valence cations, implying that its energy storage density is twice of that of Li ion battery. Secondly, an Mg battery has a higher volume capacity than graphite and, even lithium ion batteries. Furthermore, an Mg element is an environmental element and abundant in the earth’s crust [3]. In this research, we developed electrode materials for magnesium air fuel cells using marine plastic waste, mainly Poly Ethylene Terephthalate, and aimed to apply them to energy storage device materials and reduce waste. The first step in the procedure was to produce activated carbon. Activated carbon is a carbon with micropores made from carbon materials such as coal and coconut shells by reacting them with gases and chemicals at high temperatures. Compared to charcoal, activated carbon has smaller micropores, larger specific surface area, and higher adsorption performance, and is used as a food additive and medicinal charcoal. Activated carbon was prepared by the two-step activation of organic materials (i.e., Poly Ethylene Terephthalate). The resulting activated carbon, conductivity aid, and binding material were added and mixed. Titanium dioxide was added as an additive. Currently, the annual production of titanium dioxide exceeds 4 million tonnes, and this molecule is used as an excipient in the pharmaceutical industry, in the production of sunscreen creams in the cosmetics industry, as a colorant in white plastics, and as a relatively inexpensive non-toxic food pigment approved by the relevant EU authorities regarding food additive safety, it is used in numerous household products. Its high dielectric constant gives the material many capabilities, such as its use as an antireflective surface and as a dielectric gate material in metal-oxide-semiconductor field-effect transistors [4]. The mixed activated carbon and titanium dioxide were prepared in three different ratios (1:1, 1:5, and 1:10) and mixed further. The mixture was then used to prepare two types of cathode materials. Magnesium-air fuel cells with sizes of 10 mm × 10 mm were also fabricated. Sodium polyacrylate was used as the solid electrolyte. The electrolyte was then prepared with a 1:25 ratio of sodium polyacrylate to a 3.0% NaCl concentration solution. The current and voltage were measured when connected to a solid electrolyte 1:25, 40kΩ~1Ω resistance, and the current density per reaction area, weight, and volume of the magnesium air fuel cell were calculated to obtain the power density. The maximum power density was 7.18 mW/cm2 at 1:25 without titanium dioxide added, 2.02 mW/cm2 at 1:1, 4.23 mW/cm2 at 1:5, and 4.06 mW/cm2 at 1:10 with titanium dioxide added.The results show that the power density was highest when titanium dioxide was not blended. Initially, it was considered that the power density would increase due to the high ionic conductivity of titanium dioxide, but this was not the case. The reason for this is thought to be that the redox reaction did not work due to the oxide film of titanium dioxide. In the future, titanium dioxide will be treated with hydrochloric acid to eliminate the oxide film so that the redox reaction can take place. Figure 1

Impact of Particle Size and Sintering Temperature on Calcium Phosphate Gyroid Structure Scaffolds for Bone Tissue Engineering.

Due to the chemical composition and structure of the target tissue, autologous bone grafting remains the gold standard for orthopedic applications worldwide. However, ongoing advancements in alternative grafting materials show that 3D-printed synthetic biomaterials offer many advantages. For instance, they provide high availability, have low clinical limitations, and can be designed with a chemical composition and structure comparable to the target tissue. This study aimed to compare the influences of particle size and sintering temperature on the mechanical properties and biocompatibility of calcium phosphate (CaP) gyroid scaffolds. CaP gyroid scaffolds were fabricated by 3D printing using powders with the same chemical composition but different particle sizes and sintering temperatures. The physicochemical characterization of the scaffolds was performed using X-ray diffractometry, scanning electron microscopy, and microtomography analyses. The immortalized human mesenchymal stem cell line SCP-1 (osteoblast-like cells) and osteoclast-like cells (THP-1 cells) were seeded on the scaffolds as mono- or co-cultures. Bone cell attachment, number of live cells, and functionality were assessed at different time points over a period of 21 days. Improvements in mechanical properties were observed for scaffolds fabricated with narrow-particle-size-distribution powder. The physicochemical analysis showed that the microstructure varied with sintering temperature and that narrow particle size distribution resulted in smaller micropores and a smoother surface. Viable osteoblast- and osteoclast-like cells were observed for all scaffolds tested, but scaffolds produced with a smaller particle size distribution showed less attachment of osteoblast-like cells. Interestingly, low attachment of osteoclast-like cells was observed for all scaffolds regardless of surface roughness. Although bone cell adhesion was lower in scaffolds made with powder containing smaller particle sizes, the long-term function of osteoblast-like and osteoclast-like cells was superior in scaffolds with improved mechanical properties.

In situ iron coating of amorphous boron and characterization of its energy release behavior

Boron was widely employed as metal fuel in solid propellants for its higher gravimetric and volumetric combustion enthalpies. However, the low melting point and high boiling point of B2O3 on the surface of boron particles significantly hinder its ignition and combustion performance, seriously preventing the full realization of its thermodynamic potential. To address this issue, B@Fe composite fuels with different iron contents from 1.59 % to 7.09 % were prepared via liquid phase reduction in this paper and the quasi-static high temperature oxidation, ignition and combustion reaction characteristics and corresponding mechanism were studied, in order to provide effective modification techniques in supporting the large-scale engineering application of boron as metal fuel. The study results show that B@Fe can effectively reduce the ignition temperature and maximum heat flow temperature of amorphous boron, and increase the maximum mass gain rate. The ignition temperature and maximum heat flow temperature have an exponential function with the iron coating content. Iron coated amorphous boron can effectively shorten the laser ignition delay time by more than 50 %, and significantly change the flame structure, flame evolution process and combustion duration. Both amorphous boron and iron-coated amorphous boron flame showed a multi-layer structure, including the outer green flame, the middle yellow flame and the central incandescent flame. However, with the increase of the iron coating content, the flame height increased from 5.5 cm to 6.3 cm, the flame structure changed from mushroom type to triangle type, and the central incandescent flame area increased significantly. The equivalent combustion duration increased from 975 ms to 1997 ms, and the flame temperature increased from 1288 to 1505 °C. The emission spectra of BO2 and BO lines are captured during combustion. B@Fe with the increase of iron content, a large number of small diameter micropores appear in the condensed combustion products(CCPs) of composite fuels, and a grid-like structure was formed. With the increase of iron coating content, the boron content of condensed combustion products decreases, and the oxygen content increases. The main components of CCP include B, B2O3, B6O, FeB, Fe2B and Fe3B. Based on the ignition combustion experiment of B@Fe composite fuel, ignition combustion analysis model of B@Fe composite fuel was established.

Pyrolysis combined with KOH activation to turn waste apple pruning branches into high performance electrode materials with multiple energy storage functions

In this paper, porous activated carbon is successfully prepared from waste apple pruning branches (PGZ), which demonstrates an ultra-high specific capacity of 505 F g −1 at a current density of 1 A g −1 with excellent rate performance (215 F g −1 at 50 A g−1). The assembled supercapacitor also exhibits excellent specific capacitance of 320 F g −1 (at 0.5 A g−1) and 160 F g −1 (at 20 A g−1), with a high energy density of 12.03 Wh kg −1 at a power density of 250.45 W kg −1 in 6 M KOH. In 1 M Na2SO 4 and 1 M Et4 NBF4/AC electrolytes, high energy densities of 18.8 Wh kg −1 and 44.1 Wh kg −1 could be achieved. It also exhibits high reversible lithium storage capacity of 636.2 mAh g −1 at 0.2 C and retains 390 mAh g −1 after 1000 cycles. Even at 0.8 C, the storage capacity is still as high as 327 mAh g −1, with 282 mAh g −1 retained after 1000 cycles. These excellent electrochemical properties are attributed to the hierarchical porous structure of the sample prepared under the optimum conditions. The large pores in the hierarchical structure will lead to high-speed capacitive properties due to their low ion transport resistance while the small mesopore and micropore provide a large electrode and electrolyte interface, which can facilitate charge transfer reaction. These outstanding performances highlights the first example of using waste apple pruning branches as a sustainable source of raw materials for the preparation of high value-added porous carbon materials with multiple energy storage functions.

Structural and physicochemical characteristics of starches from sorghum varieties with varying amylose content.

Six sorghum varieties containing different amylose were selected to investigate the structural and physicochemical characteristics of starches and endosperm texture of grains. The results showed that the outer layer endosperm of sorghum grain changed from waxy to corneous, and its starch granules were more compactly packed and exhibited the spindle-shaped holes with the increase of amylose content. Higher amylose starch granules exhibited fewer and smaller micropores on the surface and were more likely to deform and agglomerate into larger amorphous particles after heated. Amylose content of sorghum starches was negatively correlated to granule size, relative crystallinity, and the proportion of the long branch chains (DP = 25-36 and > 36), whereas positively correlated to the proportion of the short branch chains (DP = 6-12 and 13-24). Amylose content had negative correlations with T o , T p , ΔH, PV, and SDS (p < .05), positive corrections with FV, SB, and RDS (p < .05), and no correlations with T c , HPV, BD, and RS. It could be concluded that amylose content affected the endosperm texture of sorghum grain and had strong correlations with structural and physicochemical properties of sorghum starch. These findings may help identify uses for these sorghum varieties in baijiu production.

Time-fractional fabric to quantify non-Fickian diffusion in porous media: New vision from previous studies

The diffusion kinetics of different substances in porous media is a priori described by the second Fick's law of diffusion. Herein, we demonstrate that such a description sometimes yields erratic results. In contrast, the time-fractional diffusion equation is found to reflect the diffusion kinetics in the case of Fick's law failure. The analytic solutions of the time-fractional diffusion equation are based on the Mittag–Leffler function. At large times, it is shown that the utilization of the approximation of the Mittag–Leffler function for the large values of its argument for the description of the experimental data gives almost the same results as those obtained using the Mittag–Leffler function itself. The time-fractional diffusion is applied on a phenomenological basis. Nevertheless, we speculate that the deviations from Fick's law may be governed by strong adsorption of the diffusing species inside the small micropores of a porous material.

Microporosity evolution in polymer‐derived SiOC glasses pyrolyzed in different atmospheres

AbstractPolymer‐derived ceramics (PDCs) are a class of advanced materials obtained by pyrolysis in a controlled atmosphere of an organosilicon polymer. Their functional as well as mechanical properties originate from the peculiar nanostructures developed during the pyrolysis. Herein, we investigate the formation of transient microporosity in a model PDC (methyl‐silsesquioxane) obtained in Ar, Ar–5%H2, CO2, and air. It is shown that a common evolution can be detected up to 700°C. At this temperature, the structure of the material in terms of chemical bonds is marginally changed (only redistribution reactions take place), but the medium‐range order is clearly modified moving the system to a more disordered state (detected by small angle x‐ray scattering [SAXS]) and causing the formation of a large amount of open micropores sized at about 1.2–1.7 nm. In the 700–800°C range, the proper ceramization starts causing the formation of a new class of small (around 1 nm) open micropores. These partially annihilate at 900°C in Ar and Ar–H2 (i.e., in the second part of the ceramization process), whereas they totally collapse in CO2 due to the formation of a more silica‐like SiOC (less polymerized and viscous). Finally, SAXS points out the persistence of relatively large closed nanovoids of about 1 nm at 1250°C for the samples treated in Ar and Ar–H2. These might explain anomalies in terms of density, elastic modulus, and thermal conductivity of this class of ceramics as reported in the literature.

PRODUCTION AND RESEARCH OF SORBENTS FROM FOOD PLANT WASTES FOR WATER PURIFICATION

The article describes the results of research on production of modified types of sorbents based on waste food plants and the possibility of drinking water purification from Ca2+ and Mg2+ ions. Sunflower and buckwheat wastes widely spread in the East Kazakhstan region were selected for production of modified sorbent. Structural features of sunflower and buckwheat shells were studied. It was found that samples of the initial form of buckwheat and sunflower, washed with distilled water, consist of very dense and small micropores. It was found that the surface of the sorbents particles is changed by washing with alcohol solution, with pores and hillocks appearing on the surface of sunflower husk particles. In acid-base-treated sorbents, an increase in the number of macropores and a change in the general morphological structure are observed. As a result of defining the sorption capacity of sorbents produced by acid-alkaline activation, it is on average 0.06 mg/g in iodine and 1.3 mg/g in methylene blue higher than that of medical activated carbon. The results of materials sorption capacity study produced from sunflower husk, sequentially treated with 8.2% hydrochloric acid solution and 16,5% sodium hydroxide solution, indicated effect respect to Ca2+ and Mg2+ ions showed a high purification effect of 98.7% and 95.8%, respectively. The above-mentioned modified sorbent is proposed as a sorption material in the production of filters for drinking water purification.

Solvent-Driven Dynamics: Crafting Tailored Transformations of Cu(II)-Based MOFs.

Metal-organic frameworks (MOFs), a sort of crystalline porous coordination polymers composed of metal ions and organic linkers, have been intensively studied for their ability to take up nonpolar gas-phase molecules such as ethane and ethylene. In this context, interpenetrated MOFs, where multiple framework nets are entwined, have been considered promising materials for capturing nonpolar molecules due to their relatively higher stability and smaller micropores. This study explores a solvent-assisted reversible strategy to interpenetrate and deinterpenetrate a Cu(II)-based MOF, namely, MOF-143 (noninterpenetrated form) and MOF-14 (doubly interpenetrated forms). Interpenetration was achieved using protic solvents with small molecular sizes such as water, methanol, and ethanol, while deinterpenetration was accomplished with a Lewis-basic solvent, pyridine. Additionally, this study investigates the adsorptive separation of ethane and ethylene, which is a significant application in the chemical industry. The results showed that interpenetrated MOF-14 exhibited higher ethane and ethylene uptakes compared to the noninterpenetrated MOF-143 due to narrower micropores. Furthermore, we demonstrate that pristine MOF-14 displayed higher ethane selectivity than transformed MOF-14 from MOF-143 by identifying the "fraction of micropore volume" as a key factor influencing ethane uptake. These findings highlight the potential of controlled transformations between interpenetrated and noninterpenetrated MOFs, anticipating that larger MOF crystals with narrower micropores and higher crystallinity will be more suitable for selective gas capture and separation applications.

Quantitative characterization and evaluation of key physicochemical characteristics of steel slag

Steel slag is considered to improve the road performance of cold mixed asphalt (CMA) due to its superior physicochemical characteristics. To realize the potential application of steel slag in CMA pavement, the alkalinity, hydration activity, pore characteristics, and three-dimensional (3D) morphology were quantitatively characterized and evaluated based on the X-ray fluorescence (XRF), mercury intrusion porosimetry (MIP), 3D laser scanning, and 3D structured light measurement, respectively. The results show that the alkalinity of steel slag can not fully reflect its hydration activity. Most steel slag has high alkalinity with an alkalinity value greater than 2.5, while the activity index (AI) is generally less than 1.0. The pores of steel slag are mostly "ink-bottle" shaped, in which macropores are the most developed, and small pores and micropores are the least developed. The total pore volume of macropores is the largest, while the total pore area of small pores is the largest. The porosity of porous, less porous, and dense steel slag is 12.05%, 6.88%, and 1.28%, respectively. The adsorption and accommodation capacity of porous steel slag for fluids is the largest, followed by less porous and dense steel slag. All three steel slags have good 3D shapes, and their shape factor (SF), sphericity (S), needle degree (ND), and flake degree (FD) have distribution intervals of 0.81–1.19, 0.70–0.99, 1.01–1.90, and 1.01–1.51, respectively. Porous steel slag shows richer apparent morphology than less porous and dense steel slag. Their apparent morphology characterization indicators Ra, Rq, Rp, Rv, and Rt show a good linear positive correlation with porosity, which can be regarded as the classification criterion for apparent morphology. This study will help enrich the theoretical basis and control indicator system for applying steel slag in CMA pavement.

The multi-scale pore structure of superfine pulverized coal. Part 2. Mesopore and closed pore morphology

Superfine pulverized coal exhibits extraordinary properties in thermal conversion processes like pyrolysis and combustion. The exploration of closed pores is of great significance for studying of the macromolecular structure, and developing advanced clean combustion technologies. In this work, the influences of coal rank and particle size on the mesopore characteristics (i.e., pore size, volume, and specific surface area), especially closed pores, were obtained by combining nitrogen adsorption and synchrotron-based small-angle X-ray radiation (SAXS). In addition, combined with the closed pore volume measured by He density and SAXS, research focuses on the formation and opening mechanisms of closed pores in different rank coals at a molecular level. The results indicate that both the bituminous (NMG) and anthracite coal (HN) have a few large open pores (>100 nm), with large amount of small mesopores and micropores (<2 nm). The HN coal has more open mesopores which have a smaller pore size than NMG coal. The closed pore proportion of HN coal in the studied pore size range is between 2 and 52 %, while that of NMG coal is between 47 and 67 %. In addition, both coals have a certain amount of closed pores formed by shear force and ash blockage, while the matrix compression also contribute to certain types of closed pores in NMG. These findings contribute to illustrating the closed pore structure in coal at the molecular level, which sheds light on constructing comprehensive macromolecular pore models of coal and thus promoting the development of clean coal utilization technologies.

Strength properties, microstructural evolution, and reinforcement mechanism for cement-stabilized loess with silica micro powder

Natural loess has poor engineering properties because of its own loose and porous nature. To meet the needs of engineering construction, this study attempted to add silica micro powder mixed with cement into loess to improve its mechanical properties. The direct shear test, triaxial shear test, and scanning electron microscope (SEM) test were used to evaluate the strength characteristics and micropore structure modifications of silica micro powder and cement stabilized loess. The results showed that the addition of silica micro powder alone increased the shear strength of loess, while when silica micro powder was mixed with cement, the improvement in strength increased significantly. 3% cement with 10% silica micro powder is the optimum content to stabilize loess. The shear strength of the stabilized loess for 28 days under 200 kPa confining pressure was 2255 kPa, which was 34.9% higher than that of plain loess. Under the same cement content, the cohesion of loess increased with the increase of silica micro powder content, and the internal friction angle increased first and then decreased. The increase in curing age and the decrease in water content were positively correlated with shear strength, and the prediction formula of shear strength parameters of stabilized loess is established. In the SEM test, through qualitative analysis, it is found that the unreacted silica powder mainly physically filled the pores of loess, while the reacted silica micro powder and cement mainly combine with hydration products, which together enhanced the compactness of loess. From the quantitative analysis, it can be seen that with the addition of silica micro powder and cement, the macropores and mesopores between loess particles are transformed into small pores and micropores, the orientation of pores is enhanced, and the loess structure becomes more compact, which further revealed the mechanism of silica micro powder combined with cement to stabilize loess. The results of this study demonstrate that silica micro powder mixed with cement can effectively improve the mechanical properties of natural loess, providing a promising approach for reinforcing loess in engineering applications.

Aeolian sand stabilized by using fiber- and silt-reinforced cement: Mechanical properties, microstructure evolution, and reinforcement mechanism

Northwest China has a large amount of aeolian sand, which exhibits poor gradation, low cohesive force, and loose structure; thus, this sand is difficult to be directly used as engineering construction materials. To solve this problem, this study mixed fiber, silt, and cement to stabilize aeolian sand. The effects of the fiber content (0%, 0.5%, 1%, 2%, 3%, and 4%), fiber length (6, 12, and 19 mm), silt content (10%, 15%, and 20%), and curing time (7, 14, and 28 d) were evaluated by conducting indoor unconfined compressive strength tests, and the strength prediction and constitutive models were established. In addition, the microstructural and pore variation characteristics were studied by performing scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and nuclear magnetic resonance (NMR) tests, and the stability mechanism was elucidated. The results showed that the addition of fibers and silt can significantly improve the strength and ductility of cement-stabilized aeolian sand. Under the optimal mixing conditions (fiber length: 12 mm; fiber content: 2%; silt content: 15%), the strength of the sample increased by 274.2% (reaching 1684 kPa) compared with that of cement-stabilized aeolian sand (450 kPa). A positive correlation was observed between the curing time and strength development of the samples. The established strength prediction model effectively predicted the strength variations in the specimens, whereas the constitutive model accurately reflected the stress-strain relationship of the specimens. The SEM results revealed that the coupling effect of fibers, silt, and cement makes the specimens more compact and improves the overall stability. The results of the NMR showed that the numbers of macropores and mesopores decreased significantly and that the numbers of small pores and micropores increased with 2% fiber content; the porosity of the specimen was 12.3%, which was 28.6% lower than that of ordinary-cement-stabilized aeolian sand. This study advocates making full use of local silt to stabilize aeolian sand, which has significant advantages in terms of improved mechanical properties, environmental protection, and reduced project costs compared with traditional cement-stabilized aeolian sand. The results of this study have important theoretical and practical significance for the engineering and design of projects in aeolian sand areas.

Understanding the Increase in H2/Air PEM Fuel Cell Performance of Pt Based Cathode Catalysts with the Tailored Pore Structure of Mesoporous Graphitic Spheres

To reach its climate neutrality goal by 2050, the European Union has agreed on ceasing the sale of new petrol and diesel-driven vehicles by the end of 2035. Therefore, interest in carbon-neutral transport options, such as battery-electric vehicles (BEV) or fuel-cell-electric vehicles (FCEV) has tremendously increased. Especially for heavy-duty applications, proton exchange membrane fuel cells (PEMFCs) can be a viable solution, as they exhibit a higher gravimetric power density compared to BEVs.[1] However, cost and supply constraints of the catalyst active material, i.e. platinum, are still a major hurdle to make PEMFCs competitive with incumbent technologies. While this has been addressed by a reduction of the Pt loading, this induces some major drawbacks regarding the overall performance due to the decrease in catalyst activity towards the oxygen reduction reaction (ORR) and the increase in proton and oxygen mass transport resistances to the Pt surface.[2] It has been shown that those issues can be mitigated by using cathode catalyst materials with a mesoporous carbon support, as they exhibit a high ORR activity while additionally facilitating the transport of protons and gaseous oxygen to Pt nanoparticles that are located inside the pores of the carbon support particles.[3] Previous studies have demonstrated that by using a multi-step catalyst synthesis procedure where Pt nanoparticles are incorporated into a mesoporous graphitic sphere (MGS) support and subjected to a pore-confined growth by a subsequent high-temperature treatment, a precisely defined catalyst structure is achieved with a good H2/air performance as well as high stability towards catalyst degradation.[4] In order to correlate the impact of a precisely defined mesoporous carbon structure on the overall H2/air performance, single cell tests were performed using 5 cm2 membrane electrode assemblies (MEAs) with cathode loadings of 0.1 mgPt cmMEA -2 using different commercially available 20 wt.% Pt/C catalysts as well as a 28 wt.% Pt/C catalyst based on lab-scale synthesized carbon supports: i) Ketjen black (KB, TEC10E20E, TKK); ii) Vulcan (Vu, TEC10V20E, TKK); and, iii) mesoporous graphitic spheres (MGS). The latter was produced following the procedure by Knosalla et al.[5] A full MEA characterization was included to measure the electrochemically active surface area (ECSA) by CO-stripping, the H2/air performance at different operating conditions (high and low relative humidity and high pressure), the H2/O2 performance, and the O2 and H+ transport resistance in the cathode by limiting current measurements and electrochemical impedance spectroscopy (EIS), respectively. Finally, the catalyst morphology has been studied ex/situ using three/dimensional reconstruction by electron tomography and by gas adsorption measurements (argon at 87 K and water at 298 K).It was found, that the mesoporous carbon support significantly improves the H+ and O2 transport, resulting in an improved H2/air performance compared to both commercial catalyst materials (see. Fig. 1 MGS vs. KB or Vu). Interestingly, the MGS retains also a high ORR catalyst mass activity (imass ≈ 400 A/gPt) which is similar to the one of Pt/KB cathode catalysts (with higher internal microporous structure), leading to the good H2/air performance also at low current densities. The overall optimal performance of Pt/MGS suggests that these materials have a defined porous internal network structure which combines the beneficial effect of a facilitated O2 and H+ transport through larger mesopores while still shielding the Pt surface from ionomer contact by incorporation of Pt nanoparticles into smaller micropores.

Pore Space Partition Synthetic Strategy in Imine-linked Multivariate Covalent Organic Frameworks.

Partitioning the pores of covalent organic frameworks (COFs) is an attractive strategy for introducing microporosity and achieving new functionality, but it is technically challenging to achieve. Herein, we report a simple strategy for partitioning the micropores/mesopores of multivariate COFs. Our approach relies on the predesign and synthesis of multicomponent COFs through imine condensation reactions with aldehyde groups anchored in the COF pores, followed by inserting additional symmetric building blocks (with C2 or C3 symmetries) as pore partition agents. This approach allowed tetragonal or hexagonal pores to be partitioned into two or three smaller micropores, respectively. The synthesized library of pore-partitioned COFs was then applied for the capture of iodine pollutants (i.e., I2 and CH3I). This rich inventory allowed deep exploration of the relationships between the COF adsorbent composition, pore architecture, and adsorption capacity for I2 and CH3I capture under wide-ranging conditions. Notably, one of our developed pore-partitioned COFs (COF 3-2P) exhibited greatly enhanced dynamic I2 and CH3I adsorption performances compared to its parent COF (COF 3) in breakthrough tests, setting a new benchmark for COF-based adsorbents. Results present an effective design strategy toward functional COFs with tunable pore environments, functions, and properties.

Synthesis and Direct Observation of Molecules of 2D Polymers: With High Molecular Weights, Large Areas, Small Micropores, Solubility, Membrane Forming Ability, and High Oxygen Permselectivity.

If ideal 2D polymer (2DP) macromolecules with small pores that are similar in size to gas molecules, large areas, small thickness, and excellent membrane-forming ability are synthesized, ultimate gas separation membranes would be obtained. However, as far it is known, such ideal well-characterized 2DP macromolecules are not isolated. In this study, an ideal 2DP macromolecule is synthesized by using the successive three reactions (Glaser coupling, SCAT reaction, and the introduction of octyl groups), in which the conjugated framework structure is maintained, from a fully conjugated 1D polymer. Because this exfoliated 2DP is soluble, the macromolecular structure can be fully characterized by 1H-NMR, GPC, SEM, AFM, and its dense membrane with no defects can be fabricated by the solvent cast method. This soluble 2DP macromolecule has very small micropores (6.0Å) inside the macromolecule, a large area (30×68nm by SEM and AFM), high molecular weight (Mn=2.80×105 by GPC), and a small thickness (4.4Å by AFM). This membrane shows the highest oxygen permselectivity exceeding Robeson's upper line because of the high molecular sieving effect of the controlled small micropores.

Experimental study on frost heave characteristics and micro-mechanism of fine-grained soil under dynamic load for heavy-haul railway subgrades in seasonally frozen regions

In seasonally frozen regions, there is frequent uneven frost heave of heavy haul railway subgrades, which reduces the smoothness of the track and affects the operational safety of trains. To clarify the frost heave characteristics and micro-mechanism of subgrade filling under the action of unidirectional freezing and dynamic loading, unidirectional freezing tests were performed on a fine-grained subgrade filling under open conditions, and the frost heave characteristics under different initial water contents and dynamic loads were analyzed. The particle image velocimetry (PIV) technique was applied to analyze the development of local deformation at different locations in the samples. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were performed on the samples before and after freezing to reveal the development mechanism of the microstructure. The test results showed that with the increase in the initial water content and load amplitude, the frost heave increased, while the water replenishment and frost depth decreased. Combined with the PIV results, it was found that the soil in the frozen and unfrozen areas exhibited frost heave and compressive deformation, respectively, during the freezing process, further revealing the local deformation law of the soil. The samples mainly contained small pores and micropores before freezing and small pores and medium pores after freezing, indicating that the effect of freezing and swelling had the greatest influence on the small and medium pores inside the soil. The higher the initial water content, the higher the porosity of the sample after freezing; with the increase in the load amplitude, the porosity of the frozen samples decreased. The negative temperature effect of the change in phase from water to ice drove the particle movement, thereby increasing the inter-particle pore space, leading to a macroscopic frost heave deformation of the soil samples. Our results can serve as a basis in the maintenance and safety of railway subgrades in cold regions.

Synthesis of a Two-dimensional Multi-functional Macromonomer and Oxygen Permselectivity of Its Supramolecular and Covalent Polymer Membranes

Abstract Although polymers having small micropores are promising for good gas permselective membranes, such polymers tend to have no membrane-forming ability. In this study, a polymer including micropores was synthesized from two-dimensional fully-conjugated macromonomer (2DM) with multi-acetylene and hydroxyl groups. In spite of the low molecular weight, its solvent-cast membrane (supra-poly(2DM)) showed good oxygen permselectivity. In addition, soluble high molecular weight network poly(2DM) membrane obtained from supra-poly(2DM) membrane showed higher oxygen permselectivity due to the increased number of micropores.