Pore Structure Analysis Research Articles

Comprehensive Testing of Sulfate Erosion Damage of Concrete Structures and Analysis of Silane Coating Protection Effect.

In order to study the protection performance of silane coating on in-service concrete structures in a sulfate environment, we collect concrete samples in the field to simulate the concrete erosion process by accelerated erosion with wetting–drying cycles. We place the samples into protected, exposed and control groups corresponding to a corrosive environment with silane protection, corrosive environment without protection and general environment for three different service conditions. A combination of ultrasonic velocimetry, CT (Computed Tomography) scan imaging, NMR (Nuclear Magnetic Resonance) pore structure analysis, strength testing and other methods are used to analyze the strength, ultrasonic wave velocity, pore structure and other characteristics of the specimens during sulfate erosion. Based on the test results, the protective effect of silane coating on concrete structures under sulfate attack is quantitatively analyzed, and an index for judging the damage rate of specimens is proposed to quantitatively analyze the protective effect of silane coating. The research results show that the damage of the concrete structure under silane protection in a sulfate-attack environment can be reduced by more than 50%; its integrity damage index and strength damage index are easily affected by the location of local defects, which leads to a decrease in the protection efficiency of the surface silane coating.

Size-dependent analysis of porous multi-directional FG shell structures based on the modified couple stress theory using the unsymmetric finite element method

Size-dependent analysis of porous multi-directional FG shell structures based on the modified couple stress theory using the unsymmetric finite element method

Pore structure modification and characterization of carbon adsorbent prepared by high-sulfur anthracite blending coal

ABSTRACT High sulfur anthracite has high research value and application prospects in the preparation of carbon adsorbent due to its excellent coal quality conditions, but the pore structure changes and sulfur migration dynamics in the preparation process are not clear. In this paper, using SEM, pore structure analysis, Raman, FTIR and XPS, the feasibility of preparing carbon adsorbent from high-sulfur coal blending was analyzed from the perspective of apparent morphology, pore structure parameters, graphite crystal structure, and functional groups and content, while the occurrence form of sulfur in carbon adsorbent was explored. The results showed that the carbon adsorbent prepared from high-sulfur anthracite was mainly microporous, and the specific surface area was up to 1103.23 m2/g, which was the highest among the known high-sulfur coal materials. The degree of disorder of raw coal and the size of graphite crystal particles synergistically formed a rich pore structure. Sulfur in coal mainly exists in the form of thiophene and sulfide. An increase in the bituminous coal proportion promotes the transformation of carbon adsorbent to an alkaline environment. Thiophene sulfur is removed at 900°C, and sulfide is transformed into sulfoxide and sulfone under steam oxidation and Fe catalysis.

Effects of paramagnetic material on the characteristics of low field nuclear magnetic resonance signals and water measurement in different textured soils.

Nuclear magnetic resonance (NMR) technology has been applied in soil science due to the characte-ristics of high efficiency, rapidity, no damage to soil structure, and harmlessness to the human body. However, the effect of the presence of paramagnetic materials in soils on the characteristics of NMR signals was still unclear. In this study, we investigated the effects of paramagnetic material on the low field nuclear magnetic (LF-NMR) signals and soil water content measurement in soils with different texture. The results showed that the LF-NMR signal of soil water could reach about 150, while that of all the solid materials including soil minerals, organic matter and microbes was less than 0.3, which was relatively negligible. Compared with the NMR signals produced by solid materials in soils, soil texture and paramagnetic material had stronger impact on the measured LF-NMR signals of soil water. LF-NMR equipment had a relaxation time monitoring blind area, and the loss of NMR signal was mainly due to the acceleration of the relaxation process of hydrogen protons in water by magnetic materials, resulting in extremely fast LF-NMR signals feed back by water in small pores that could not be captured by monitoring equipment. For loamy fluvo-aquic soil (1.2%) and clay loamy black soil (1.3%) with low paramagnetic material contents, the loss of LF-NMR signals was not large, which was linearly related to soil water content. For clayey red soil with high content of clay (45.3%) and paramagnetic materials (4.0%), a part of the LF-NMR signals would be lost in the measurement, and the monitored LF-NMR signal was not linearly related to the soil water content. In addition, external addition of paramagnetic materials (3.0 g·L-1 MnCl2 solution) would further reduce the LF-NMR signals that could be monitored in black and red soils. The maximum signal loss rates of black soil and red soil were 41.0% and 46.7%, respectively, which greatly changed the quantitative relationship between it and soil water content. Therefore, the influence of paramagnetic materials on the LF-NMR signals should be reduced first through correction when using LF-NMR to measure the water content of clay soil with rich internal paramagnetic materials (>1.3%) or external addition of paramagnetic materials. Our results would provide valuable insights into the study of soil water content measurement and soil pore structure analysis using low field nuclear magnetic resonance technology.

Correlation between porous structure analysis, mechanical efficiency and gamma-ray attenuation power for hydrothermally treated slag-glass waste-based geopolymer

The main objective of this work is to compare conventional Portland cement pastes (OPC) and alkali-activated geopolymer pastes in terms of compressive strength, phase composition, micro-porosity, and attenuation ability against harmful gamma irradiation. OPC pastes were cured at 20 °C in tap water for up to 28 days, while geopolymer pastes were prepared by recycling two different industrial byproducts. Equal masses of slag (GGBFS) and recycled glass powder (RGP) were activated by two concentrations of NaOH (5% and 10% mass of total binders). The obtained geopolymer pastes were treated in different manners; some pastes were treated in high humidity at 20 °C and 80 °C for 28 days, while other pastes were cured in an autoclave for different time intervals (2, 4, 8 and 12 hrs) and different steam pressures (4, 6 and 8 bar). A Gamma attenuation capacity test was performed to determine the linear attenuation coefficient (µ) for some selected hardened pastes. Two sources of gamma-ray were used (137Cs/661.6Kev &60Co/1332.5Kev). To correlate mechanical performance and attenuation behavior, the N2-adsorption/desorption technique was conducted to analyze the micro-porosity. The results indicated GGBFS-RGP geopolymer pastes activated by 5 wt% NaOH and thermally hydrated at 4bars for 8hrs possessed the highest compressive strength (86 MPa), highest attenuation ability (µ = 0.156 and 0.126 cm−1), highest BET "Brunauer-Emmett-Teller model" surface area (10048 cm2/g) and minimum BJH "Barrett-Joyner-Halenda model"-average pore diameter (23.6 nm) as compared with OPC pastes and other all geopolymer pastes. After the autoclaving process, calcium-silicate-hydrate (C-S-Hs), calcium-alumino-silicate-hydrate (C-A-S-Hs), calcium-alumino-hydrate (C-A-Hs), sodium-alumino-silicate-hydrate (N-A-S-Hs) and hexagonal zeolite phase has been achieved via X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscope (SEM/EDX).

A bio-inspired, plant-derived admixture for metakaolin blended cement mortars

Partially replacing ordinary Portland cement (OPC) with metakaolin (MK) can refine the pore structure, improve mechanical properties, and enhance the durability of concretes. However, MK tends to agglomerate due to its high surface area and high concentration of hydroxyl groups. To overcome this problem, this study exploits a plant-derived polyphenol, tannic acid (TA), as an eco-friendly admixture to disperse MK. Due to its similar chemical functional groups as the adhesive protein in the mussel byssus, TA can adhere to various surfaces like the mussel’s adhesive protein. An experimental program was carried out to characterize the TA treated MK and investigate the effects of the proposed method on the properties of the cement paste and mortar. After mixing with the MK, TA can be adsorbed on the surface of MK particles, achieving deflocculation and dispersion of mineral grains by electrostatic repulsion forces and steric effect, significantly improving the workability of the mortar. Pore structure analysis suggests that TA dispersion densifies the hydration products, as revealed by the much-reduced gel and interhydrate pores. The nanoindentation results indicated that all low-density calcium hydrate silicate (CSH) was converted to high density by the TA dispersion, leading to a drastic improvement in the compressive strength of the produced mortars. As a result, the 28 days compressive strength of cement mortar prepared with TA dispersed MK was enhanced by up to 97 % compared with the one prepared without MK substitution, which exhibits great potential in reducing the carbon footprint of cement-based construction materials.

Fractal Analysis and Classification of Pore Structures of High-Rank Coal in Qinshui Basin, China

The influence of high-rank coal’s pore characteristics on the physical properties, gas-bearing properties, and exploitation of coal reservoirs is becoming more and more prominent. How to establish the classification to describe the pore networks combining quantitative and qualitative characteristics has emerged as a major problem, which may offer a scientific foundation to deepen the understanding of this issue. In this research, the structure and fractal characteristics of reservoir pores were determined after analyzing 20 high-rank coal samples from Xinjing Coal Mine in the Qinshui Basin with the application of the high-pressure mercury intrusion method (HPMI) and argon ion polishing–field emission scanning electron microscopy (AIP–FESEM). The results show that the tested coal samples were bipolar distributed, with transitional pores and micropores dominating the pore volume, followed by macropores. The Menger sponge fractal models manifested two or three distinct straight-line segments with demarcation points of 65 nm and 1000 nm. A natural classification with three major pore types of diffusion pores (D-pores), seepage pores (S-pores), and pico pores (P-pores), demarcated by pore size intervals of 65 nm and 1 nm and seven sub-types, was established to relate pores to pore networks based on these fractal characteristics and the kinetic characteristics of methane molecules. This classification scheme can characterize the relationship between pore types and the corresponding major occurrence and transport mechanisms of the gas. In addition, P-pores and D-pores are predominately nanoscale OM pores with three major genetic types of organic constituent interparticle pores (5–200 nm), metamorphic pores (<5 nm), and intermorphic pores (<5 nm). S-pores are more complex in origin and shape features, and the major types include outgas pores, plant tissue residual pores, mineral-related pores, and microfractures. The mean radius (Pa), total pore volume (Vt), apparent porosity (Φ), and volume ratio of macro- and mesopores were positively correlated with the fractal dimension D1 of S-pores (>65 nm). Since fractal analysis is a more comprehensive characterization of reservoir structure and quantitatively reflects the pore structure, undulating state, and roughness of the inner surface, fractal parameters can be used as an important index to describe the pore structure characteristics of high-rank coal reservoirs.

129Xe NMR analysis of pore structures and adsorption phenomena in rare-earth element phosphates

Rare-earth elements (REEs) are indispensable in various applications ranging from catalysis to batteries and they are commonly found from phosphate minerals. Xenon is an excellent exogenous NMR probe for materials because it is inert and its 129Xe chemical shift is very sensitive to its local physical or chemical environment. Here, we exploit, for the first time, 129Xe NMR for the characterization of porous structures and adsorption properties of REE phosphates (REEPO4). We study four different REEPO4 samples (REE = La, Lu, Sm and Yb), including both light (La and Sm) and heavy (Lu and Yb) as well as diamagnetic (La and Lu) and paramagnetic (Sm and Yb) REEs. 129Xe resonances are very sensitive to the porous structures and moisture content of the REEPO4 samples. In the samples treated at a lower temperature (80 °C), free water hinders the access of hydrophobic xenon into small mesopores, but the treatment at a higher temperature (200 °C) removes the free water and allows xenon to explore the mesopores. Based on a standard two-site exchange model analysis of the variable-temperature 129Xe chemical shifts, as well as its proposed, novel modification for paramagnetic materials, the average mesopore sizes were determined. The size was the largest (79 nm) for the La sample with mixed monazite (70%) and rhabdophane (30%) phases and the smallest (6 nm) for the Yb sample with pure xenotime phase. The mesopore sizes of the Lu and Yb samples (12 and 6 nm) differed by a factor of two regardless of their similar xenotime phase. The 129Xe NMR analysis revealed that the heats of adsorption of the samples are similar, varying between 8.7 and 10.1 kJ/mol. For diamagnetic samples, computational modelling confirmed the order of magnitude of the chemical shifts of Xe adsorbed on surfaces and therefore the validity of the two-site exchange model analysis. Overall, 129Xe NMR provides exceptionally versatile information about the pore structures and adsorption properties of REEPO4 materials, which may be very useful for developing the extraction processes and applications of REEs.

Mathematical analysis of the effect of process conditions on the porous structure development of activated carbons derived from Pine cones

This paper presents the results of a study on the influence of the degree of impregnation and activation temperature on the formation of the porous structure of activated carbons (ACs) obtained from Pine cones by the chemical activation process using potassium hydroxide as an activator. The advanced new numerical clustering based adsorption analysis (LBET) method, together with the implemented unique numerical procedure for the fast multivariant identification were applied to nitrogen and carbon dioxide adsorption isotherms determined for porous structure characterization of the ACs. Moreover, the Quenched Solid Density Functional Theory (QSDFT) method was chosen to determine pore size distributions. The results showed a significant influence of the primary structure of Pine cones on the formation of the porous structure of the developed ACs. Among others, it was evidenced by a very high degree of surface heterogeneity of all the obtained ACs, irrespective of the degree of impregnation with potassium hydroxide and the activation temperature. Moreover, the analysis of carbon dioxide adsorption isotherms showed, that the porous structure of the studied ACs samples contains micropores accessible only to carbon dioxide molecules. The results also showed a significant advantage of the LBET method over those conventionally used for porous structure analysis based on Brunauer–Emmett–Teller (BET) and Dubinin–Raduskevich (DR) equations, because it takes into account surface heterogeneities. The novel analyses methods were more fully validated as a reliable characterization tool, by extending their application to the isotherms for ACs developed from the same precursor by phosphoric acid activation, and for samples arising from these ACs, further subjected to additional post-treatments. The effect of the raw material used as precursor was moreover analysed by comparison with previous reported results for other ACs. The complementarity of the results obtained with the LBET and QSDFT methods is also noteworthy, resulting in a more complete and reliable picture of the analyzed porous structures.

Thermal conductivity and pore structure analysis of alkali-activated foam cement with supercritical CO2 modified slag: Feasibility evaluation for geothermal applications

• Foam cement with AAMs modified by CO 2 can be used as energy pile filling materials. • CO 2 modified AAMs decrease dry density and increase water adsorption of foam cement. • CO 2 modified AAMs increase the thermal conductivity of foam cement. Geothermal energy is a clean and renewable energy that can be extracted by energy piles. Low density filling materials with relatively high thermal conductivity are ideal for energy pile construction, due to the low cost and high heat exchange efficiency of filling materials. In this study, three types of low density filling materials (Class G foam cement, alkali-activated foam cement, and supercritical CO 2 (ScCO 2 ) modified alkali-activated foam cement) were tested to evaluate their performances to serve as candidate filling materials for energy piles. The thermal conductivities of the three materials were measured and showed that the minimum thermal conductivity was 0.22 W·mK −1 (foam cement without slag), and the maximum thermal conductivity was 0.32 W·mK −1 (foam cement with 5 % CO 2 modified slag). By analyzing the cement hydration products and distribution of pores, adding slag improved the hydration of cement, which caused a longer foaming time and increased the porosity of samples. ScCO 2 modification of slag increased the porosity and the thermal conductivities of the samples. In summary, slag with ScCO 2 modification can promote the thermal conductivity of foam cement, which is beneficial to the application of shallow energy piles.

Compressive strength and composite pore structure parameters of iron ore tailings ball concrete

• Concrete with iron tailings ball as coarse aggregate is studied. • Compressive strength and pore structure of tailings ball concrete are analyzed. • The new fractal model well reflects the pore structure of tailings ball concrete. • The sensitive pore size is 0–160 µm for tailings ball concrete. • Composite pore structure parameter (P) for compressive strength is found. To investigate the relation between the pore structure and compressive strength of tailings ball concrete, compressive strength tests were subjected to normal concrete and different groups of tailings ball concrete (masterbatch and natural sand admixture as variables). The pore structure characteristics parameters of concrete were obtained with Rapidair457 concrete pore structure analyzer. The fractal dimension was calculated to analyze the intrinsic connection between the fractal dimension and pore structure of concrete, which were divided into three ranges to find sensitive pore size ranges. The results show that the compressive strength of tailings ball concrete increases and then decreases with increasing sand admixture. The masterbatch optimizes the pore structure and thus improves the compressive strength. Compared with other fractal calculation models, the solid mass fractal correction model takes into account not only coarse aggregates do not participate in the fractal, but also the influence of pores and solids, which better reflects the complexity of the internal structure of concrete. The small pore size in the range of 0 ∼ 160 µm is most influential to the compressive strength of tailings ball concrete. The composite pore structure parameter P is defined based on the three parameters of modified solid fractal dimension, air content at sensitive pore size range and specific surface area. The compressive strength and the parameter P satisfy a quadratic function relationship, and it can better characterize the compressive strength of tailings ball concrete with both these three factors considered.

Fractal analysis of pore structures in transitional shale gas reservoirs in the Linxing area, Ordos Basin

Studying complex pore structures and fractal characteristics of gas shale provides significant guidance for clarifying the mechanism of shale gas accumulation and realizing its efficient development. In this paper, 12 samples of Taiyuan Formation shale are used as the research object, and the fractal theory is combined with mercury intrusion porosimetry and N2 adsorption technology to innovatively solve the problem of splicing point selection, which can reveal the full-scale pore size distribution of shale. The results demonstrate that the most common types of pores in the chosen samples are pores between or within clay minerals, micropores and mesopores inside organic matter, and microfractures, based on scanning electron microscopy imagery analyses. The pores of shale samples have fractal geometries. The fractal dimension DM1 values in the mercury intrusion porosimetry experiments range from 2.3060 to 2.6528. Two fractal dimensions, DN1 and DN2, may be obtained using the Frenkel-Halsey-Hill fractal method. DN1 values vary from 2.4780 to 2.6387, whereas DN2 values range from 2.5239 to 2.7388. Most macropores in shale samples have a size range of about 0.2 mm, with a wide pore size distribution, and the largest peak of the micro-mesopore volume is generally about 50 nm. The fractal dimension correlates positively with the corresponding pore volume, although the correlation between volume and composition is weak. The relatively strong correlation between fractals and the basic compositions of shale proves the fractal theory’s relevance in defining pore inhomogeneity. This study would contribute to the development of a fractal perspective-based method for pore splicing while also expanding our understanding of pore morphology and structure in transitional shale.

Recycling waste glass aggregate in concrete: Mitigation of alkali-silica reaction (ASR) by carbonation curing

Concerns on low rate of glass recycling are rising due to the environmental issues caused by landfills of waste glass. Glass utilization in concrete is a promising approach to vastly improve the glass recycling rate. However, the glass in concrete causes deleterious alkali-silica reaction (ASR), which cracks the concrete and weakens its durability and is the biggest challenge for this approach. To address this challenge, this study proposes the use of carbonation curing to mitigate ASR of mortar prepared with recycled glass (named glass mortar, GM) for the first time. The effects of glass content and carbonation curing regime on mechanical properties and the resistance to ASR-induced volume change of GM were experimentally investigated. It was found that although the increase of glass content had negative impact on compressive strength and resistance to ASR of GM, with optimized carbonation curing, the 28-day compressive strength was improved by up to 40%, and the ASR-induced expansions was significantly reduced by up to 85%. In addition, the underlying mechanisms of ASR mitigation by carbonation curing were further elucidated through characterization tests including thermogravimetric analysis, pore structure analysis, and pore solution analysis. The test results demonstrated that carbonation curing mitigated the ASR in GM by reducing calcium hydroxide content and the volume of pore solution, densifying the microstructure, and reducing the pH and free alkali metal content in the pore solution. This research is hopeful to promote the application of recycling glass in the concrete industry.

Experimental analysis of pore structure and fractal characteristics of soft and hard coals with same coalification

Accurate and quantitative investigation of the physical structure and fractal geometry of coal has important theoretical and practical significance for coal bed methane (CBM) development and the prevention of dynamic disasters such as coal and gas outbursts. This study investigates the pore structure and fractal characteristics of soft and hard coals using nitrogen and carbon dioxide (N2/CO2) adsorption. Coal samples from Pingdingshan Mine in Henan province of China were collected and pulverized to the required size (0.20–0.25 mm). N2/CO2 adsorption tests were performed to evaluate the specific surface area (SSA), pore size distribution (PSD), and pore volume (PV) using Braunuer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), and Density Functional Theory (DFT). The pore structure was characterized based on the theory of fractal dimensions. The results unveiled that the strength of coal has a significant influence on pore structure and fractal dimensions. There are significant differences in SSA and PV between both coals. The BJH-PV and BET-SSA obtained by N2-adsorption for soft coal are 0.029–0.032 cm3/g and 3.523–4.783 m2/g. While the values of PV and SSA obtained by CO2-adsorption are 0.037–0.039 cm3/g and 106.016–111.870 m2/g. Soft coal shows greater SSA and PV than hard coal, which is consistent with the adsorption capacity ({V}_{mathrm{L}}). The fractal dimensions of soft and hard coal are respectively different. The Ding coal exhibits larger D1 and smaller D2, and the reverse for the Wu coal seam is observed. The greater the value of D1 (complexity of pore surface) of soft coal is, the larger the pore surface roughness and gas adsorption capacity is. The results enable us to conclude that the characterization of pores and fractal dimensions of soft and hard coals is different, tending to different adsorption/desorption characteristics. In this regard, the results provide a reference for formulating corresponding coal and gas outburst prevention and control measures.

Early-age mechanical properties and hydration degrees of magnesium phosphate cement paste in freezing winter of cold regions

Magnesium phosphate cement (MPC) paste is a good patching material for concrete repair works. This study focused on early-age mechanical properties and hydration degrees of MPC paste in freezing winter of two types of cold regions, which are highland regions and high-latitude regions. MPC pastes with different mix proportions under different curing modes were experienced a series of experiments, including fluidity and setting time, compressive strength, pore structure characterization, thermogravimetric analysis, X-ray diffraction and electron microscopic scanning. Results showed that for winter applications, MPC pastes in simulated highland temperature conditions performed better than those in true high-latitude temperature conditions, illustrated by pore structure analyses and hydration products analyses. The best M/P ratios for highland applications and high-latitude applications were respectively 4 and 5, which respectively delivered 24 h strengths at about 50 MPa and 25 MPa. Even in severe cold winter, the setting of MPC paste depended on the hydration speed instead of the frozen action. Mixing water temperature was good for early-age hydration of MPC paste which cured for six hours in natural cold environment, however, the effect vanished at 24 h. Both the amounts of struvite and unhydrated phosphate, which could be quantitatively assessed by TG-DSC tests or qualitatively assessed by XRD test, were good indicators of the hydration degree of MPC paste in cold weather. These results provided valuable suggestions for winter applications of MPC paste in different types of cold regions.

Effect of C–S–H seed/PCE nanocomposites and triisopropanolamine on portland cement properties: Hydration kinetic and strength

The purpose of this study is to investigate the effectiveness of the addition of triisopropanolamine (TIPA) and C–S–H seed/PCE nanocomposites (CPNs) on the strength evolution and hydration kinetics of cement and the relative mechanism. The setting results and isothermal conductivity calorimetry (ICC) results reveal that the addition of CPNs and TIPA significantly shortened the setting time of the cement paste and accelerated the hydration process. Simulations from the kinetic model further demonstrates that the curves of each hydration process (KNG, KI and KD) in the cement paste were influenced by CPNs and TIPA, and the rate of hydration in NG, I and D process is elevated with the admixture. This suggests that the enhancement of hydration behavior and hydration kinetics is closely related to the accelerated nucleation of nanoparticles and the promotion of clinker phase dissolution. Hydrate analysis confirms that CPNs and TIPA ensure the sustained hydration of C4AF, which contributes to the conversion of AFt (ettringite) to AFm (monosulfate). The strength evolution results show that the presence of CPNs and TIPA enhanced the early age strength development at 12 h, 24 h and 72 h and ensured the stability of the strength at the end of 28 days. Although the air content elevates with increasing TIPA incorporation, the analysis of pore structure still reflects its refinement by the additives. Owing to the above, the mechanical strength develops steadily in the later stages and the negative impacts of the increased air content and AFm content are mitigated. These findings are expected to provide novel guidance for the application of CPNs and TIPA to facilitate the performance of the Portland cement at early and later stages.

Mechanism of Methane Adsorption/Desorption in Low-Rank Vitrain and Durain Coal Affected by Pore Structure and Wettability: A Case Study in Dafosi Area, South Ordos Basin, China

Water content and water–coal interface wettability are always the difficult issues of coalbed methane adsorption/desorption. In order to study the effects of the pore structure and wettability of different macro coal components on methane adsorption and desorption, we compared and analyzed the wettability difference between vitrain and durain, and revealed the influence of wettability on methane adsorption and desorption through a pore structure analysis, wettability measurements, an adsorption–desorption experiment and adsorption heat calculations under different conditions, taking the No. 4 coal in Dafosi Coal Mine of the Huanglong coalfield as the research object. The results show that both vitrain and durain are relatively hydrophilic substances. However, vitrain has a low ash content, high volatility, and less oxygen, and the pores are mainly semi-closed pores compared with dark coal. Vitrain also has poor connectivity, poor sorting, a small pore diameter, and a coarser surface, resulting in poor surface wettability. The large specific surface area (SSA) and relatively poor wettability of vitrain leads to more adsorption sites in methane, which makes the adsorption capacity of vitrain greater than that of durain, but the good pore connectivity of durain causes the strong desorption capacity of durain. The isosteric adsorption heat of the adsorption process is greater than that of the desorption process, indicating that there is a desorption hysteresis phenomenon which is essentially due to the lack of energy in desorption. Surfactants change the wettability of the coal surface, and different surfactants have different effects on methane adsorption and desorption. Relatively speaking, the methane desorption of coal samples treated with G502 and 6501 are better. The research results provide scientific reference for the study of gas–water transport in the desorption process of low-rank CBM, and provide evidence for the methane desorption model of vitrain and durain.

Pore structure analysis of tight reservoirs in He-8 Member of Upper Paleozoic in the southwestern Ordos Basin, China

Quantitative characterization of the pore structure in tight reservoir can provide basic parameters for the evaluation of the reservoir quality. By using the cast thin-section petrography, scanning electron microscopy, mercury injection capillary pressure, and constant-rate mercury injection, we have evaluated the distribution characteristics of pore throat and its contribution to permeability. In addition, we have established the relationship between different pore-throat structure parameters and reservoir physical, which provides theoretical support for reservoir evaluation of the He-8 Member in the study area. The results indicate that the pore structure exerts a great control on the quality of the reservoir. Large pore throats (>0.15 μm) are the main contributors to the high seepage capacity of the reservoir. Throat radius, throat distribution, and pore-throat ratio are the key factors controlling the quality of tight reservoir. The He-8 Member of the Upper Paleozoic in the study area is dominated by tight reservoirs, accompanied by a small number of conventional reservoirs.

Zirconia-Doped Methylated Silica Membranes via Sol-Gel Process: Microstructure and Hydrogen Permselectivity

In order to obtain a steam-stable hydrogen permselectivity membrane, with tetraethylorthosilicate (TEOS) as the silicon source, zirconium nitrate pentahydrate (Zr(NO3)4·5H2O) as the zirconium source, and methyltriethoxysilane (MTES) as the hydrophobic modifier, the methyl-modified ZrO2-SiO2 (ZrO2-MSiO2) membranes were prepared via the sol-gel method. The microstructure and gas permeance of the ZrO2-MSiO2 membranes were studied. The physical-chemical properties of the membranes were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscope (SEM), and N2 adsorption–desorption analysis. The hydrogen permselectivity of ZrO2-MSiO2 membranes was evaluated with Zr content, temperature, pressure difference, drying control chemical additive (glycerol) content, and hydrothermal stability as the inferred factors. XRD and pore structure analysis revealed that, as nZr increased, the MSiO2 peak gradually shifted to a higher 2θ value, and the intensity gradually decreased. The study found that the permeation mechanism of H2 and other gases is mainly based on the activation–diffusion mechanism. The separation of H2 is facilitated by an increase in temperature. The ZrO2-MSiO2 membrane with nZr = 0.15 has a better pore structure and a suitable ratio of micropores to mesopores, which improved the gas permselectivities. At 200 °C, the H2 permeance of MSiO2 and ZrO2-MSiO2 membranes was 3.66 × 10−6 and 6.46 × 10−6 mol·m−2·s−1·Pa−1, respectively. Compared with the MSiO2 membrane, the H2/CO2 and H2/N2 permselectivities of the ZrO2-MSiO2 membrane were improved by 79.18% and 26.75%, respectively. The added amount of glycerol as the drying control chemical additive increased from 20% to 30%, the permeance of H2 decreased by 11.55%, and the permselectivities of H2/CO2 and H2/N2 rose by 2.14% and 0.28%, respectively. The final results demonstrate that the ZrO2-MSiO2 membrane possesses excellent hydrothermal stability and regeneration capability.

Application of electrospun polyimide-based porous nano-fibers separators in ionic liquid electrolyte for electrical double-layer capacitors

This paper studies the preparation and characterization of polyimide (PI)-based porous nano-fibers as separator for supercapacitor. PI-based porous nano-fibers were fabricated by electrospinning soluble PI and polyvinyl pyrrolidone (PVP), followed by solution induced phase separation process under ultrasonic-assisted vibration. The morphology and structure of PI-based separator was investigated by means of scanning electronics microscope, pore structure and specific surface area analysis. The electrochemical performances were characterized by alternative current impedance, cyclic voltammetry and constant current charge/discharge test in an ionic liquid electrolyte. The results indicate that PI nano-fibers derived from PI: PVP mass ratio = 1: 1 electrospun fibers exhibit high specific surface area (212.4 m 2 g −1 ), wide stability electrochemical windows (0.0–4.55 V) and high electrolyte uptake (430 wt . %). The graphical abstract is about the tittle Application of electrospun polyimide-based porous nano-fibers separators in ionic liquid electrolyte for electrical double-layer capacitors. • PI-based porous nano-fibers were prepared via PI/PVP blended electrospinning and solvent induce phase separation process. • PI-based nano-fibers are suitable for the adsorption, diffusion and infiltration of ionic liquids with a large ionic size. • PI-based porous nano-fibers separators exhibit high electrolyte uptake (430 wt %), wide stability electrochemical window (0.0 V–4.55 V) in ionic liquids electrolyte.