In this work, four empirical models of statistical thickness, namely the models of Harkins and Jura, Hasley, Carbon Black and Jaroniec, were compared in order to determine the textural properties (external surface and...In this work, four empirical models of statistical thickness, namely the models of Harkins and Jura, Hasley, Carbon Black and Jaroniec, were compared in order to determine the textural properties (external surface and surface of micropores) of a clay concrete without molasses and clay concretes stabilized with 8%, 12% and 16% molasses. The results obtained show that Hasley’s model can be used to obtain the external surfaces. However, it does not allow the surface of the micropores to be obtained, and is not suitable for the case of simple clay concrete (without molasses) and for clay concretes stabilized with molasses. The Carbon Black, Jaroniec and Harkins and Jura models can be used for clay concrete and stabilized clay concrete. However, the Carbon Black model is the most relevant for clay concrete and the Harkins and Jura model is for molasses-stabilized clay concrete. These last two models augur well for future research.展开更多
Energy conversion technologies like fuel cells and metal-air batteries require oxygen reduction reaction(ORR)electrocatalysts with low cost and high catalytic activity.Herein,N-doped carbon spheres(N-CS)with rich micr...Energy conversion technologies like fuel cells and metal-air batteries require oxygen reduction reaction(ORR)electrocatalysts with low cost and high catalytic activity.Herein,N-doped carbon spheres(N-CS)with rich micropore structure have been synthesized by a facile two-step method,which includes the polymerization of pyrrole and formaldehyde and followed by a facile pyrolysis process.During the preparation,zinc chloride(ZnCl2)was utilized as a catalyst to promote polymerization and provide a hypersaline environment.In addition,the morphology,defect content and activity area of the resultant N-CS catalysts could be regulated by controlling the content of ZnCl2.The optimum N-CS-1 catalyst demonstrated much better catalytic activity and durability towards ORR in alkaline conditions than commercial 20 wt%Pt/C catalysts,of which the half-wave potential reached 0.844 V vs.RHE.When applied in the Zn-air batteries as cathode catalysts,N-CS-1 showed a maximum power density of 175 mW cm^(-2) and long-term discharging stability of over 150 h at 10 mA cm^(-2),which outperformed 20 wt%Pt/C.The excellent performance could be due to its ultrahigh specific surface area of 1757 m2 g1 and rich micropore channels structure.Meanwhile,this work provides an efficient method to synthesize an ultrahigh surface porous carbon material,especially for catalyst application.展开更多
Micropores of shale are significant to the gas content and production potential of shale, which has been verified in the research of marine shale gas; while, few studies have been conducted on lacustrine shales. This ...Micropores of shale are significant to the gas content and production potential of shale, which has been verified in the research of marine shale gas; while, few studies have been conducted on lacustrine shales. This study collected 42 samples from three wells in the Late Cretaceous Qingshankou Formation of the southern Songliao Basin, NE China, and investigated these samples by the focused ion beam-scanning electron microscope(FIB–SEM) and nitrogen adsorption analysis techniques. Four types of micropores were identified in the samples, i.e., intergranular pore, intracellular pore, organic matter pore and microfracture. The pore structure type is characterized by open slit pores and "ink type" pores which are mainly 1.5–5 nm in diameter with mesopores as the main pores. The mesopores account for 74.01% of the pore volume and 54.68% of the pore surface area. Compared with the lacustrine shales from the Triassic Yanchang Formation in the Ordos Basin and Xujiahe Formation in the Sichuan Basin, the intergranular clay mineral interlayer pores are considered to be the main reservoir space for shale gas storage in the study area, followed by intraparticle pores, organic matter pores and microfractures. Maturity and micropore are the key controlling factors which affect the shale gas content of the Qingshankou Formation in southern Songliao Basin.展开更多
Based on an equivalent medium approach, this paper presents a model describing the nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores. The influences of pores＇ nonlinea...Based on an equivalent medium approach, this paper presents a model describing the nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores. The influences of pores＇ nonlinear oscillations on sound attenuation, sound dispersion and an equivalent acoustic nonlinearity parameter are discussed. The calculated results show that the attenuation increases with an increasing volume fraction of micropores. The peak of sound velocity and attenuation occurs at the resonant frequency of the micropores while the peak of the equivalent acoustic nonlinearity parameter occurs at the half of the resonant frequency of the micropores. Furthermore, multiple scattering has been taken into account, which leads to a modification to the effective wave number in the equivalent medium approach. We find that these linear and nonlinear acoustic parameters need to be corrected when the volume fraction of micropores is larger than 0.1%.展开更多
To accurately analyze the impact of casting pores in steel,high-resolution 3D X-ray tomography technology was used to gather detailed statistical information about micropores.These micropores were classified as gas,sh...To accurately analyze the impact of casting pores in steel,high-resolution 3D X-ray tomography technology was used to gather detailed statistical information about micropores.These micropores were classified as gas,shrinkage,and gas-shrinkage pores depending on their formation origin and morphology.Clustering tendencies and affinity parameters were defined to characterize the spatial correlations among these three types of pores.The 3D data from X-ray tomography scans were then integrated into finite element analysis(FEA)software to predict how micropore shape,size,and distribution influence stress distribution within the material.The results show that certain inflection points with small local radii within the cast pores are major contributors to stress concentration.Therefore,cast pores cannot be simply modeled as ideal spherical pores.The sphericity and volume of pores have a significant impact on the stress concentration of the model.Specifically,lower sphericity and larger pore volumes result in higher stress concentrations.Moreover,the internal pores of steel castings exhibit specific global distribution characteristics.Pores located on the surface of the specimen lead to significantly higher stress concentrations compared to those located inside the specimen.展开更多
Conjugated microporous polymers have excellent skeleton structures but poor electrical conductivity limits their applications in microwave absorption.To solve this problem,a strategy of molecular expansion and confini...Conjugated microporous polymers have excellent skeleton structures but poor electrical conductivity limits their applications in microwave absorption.To solve this problem,a strategy of molecular expansion and confining polymerization is proposed in this work to synthesize conductive hyper-crosslinked conjugated microporous polymer.The topology of the conjugated microporous polymer is changed into a three-dimensional skeleton structure with high specific surface area by using molecular expansion technique,and the controlled growth of polypyrrole in the channel constructs a unique network structure.The balance of excellent composite backbone structure,proper conductivity,attenuation capability and impedance matching enable the material to exhibit electromagnetic wave absorption performance.As a result,with low filler loading of 10 wt%,a strongest reflection loss of-52.68 d B and a maximum effective bandwidth of 5.76 GHz.Additionally,CST simulations of the radar scattering cross section have been carried out to verify the excellent material properties.This study provides new concepts for new conductive polymers and broadens the application of hyper-crosslinked conjugated microporous polymer in the field of electromagnetic wave absorption.展开更多
The Soft X-ray Imager(SXI)is part of the scientific payload of the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission.SMILE is a joint science mission between the European Space Agency(ESA)and the Chinese...The Soft X-ray Imager(SXI)is part of the scientific payload of the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission.SMILE is a joint science mission between the European Space Agency(ESA)and the Chinese Academy of Sciences(CAS)and is due for launch in 2025.SXI is a compact X-ray telescope with a wide field-of-view(FOV)capable of encompassing large portions of Earth’s magnetosphere from the vantage point of the SMILE orbit.SXI is sensitive to the soft X-rays produced by the Solar Wind Charge eXchange(SWCX)process produced when heavy ions of solar wind origin interact with neutral particles in Earth’s exosphere.SWCX provides a mechanism for boundary detection within the magnetosphere,such as the position of Earth’s magnetopause,because the solar wind heavy ions have a very low density in regions of closed magnetic field lines.The sensitivity of the SXI is such that it can potentially track movements of the magnetopause on timescales of a few minutes and the orbit of SMILE will enable such movements to be tracked for segments lasting many hours.SXI is led by the University of Leicester in the United Kingdom(UK)with collaborating organisations on hardware,software and science support within the UK,Europe,China and the United States.展开更多
The rich accumulation of methane(CH_(4))in tectonic coal layers poses a significant obstacle to the safe and efficient extraction of coal seams and coalbed methane.Tectonic coal samples from three geologically complex...The rich accumulation of methane(CH_(4))in tectonic coal layers poses a significant obstacle to the safe and efficient extraction of coal seams and coalbed methane.Tectonic coal samples from three geologically complex regions were selected,and the main results obtained by using a variety of research tools,such as physical tests,theoretical analyses,and numerical simulations,are as follows:22.4–62.5 nm is the joint segment of pore volume,and 26.7–100.7 nm is the joint segment of pore specific surface area.In the dynamic gas production process of tectonic coal pore structure,the adsorption method of methane molecules is“solid–liquid adsorption is the mainstay,and solid–gas adsorption coexists”.Methane stored in micropores with a pore size smaller than the jointed range is defined as solid-state pores.Pores within the jointed range,which transition from micropore filling to surface adsorption,are defined as gaseous pores.Pores outside the jointed range,where solid–liquid adsorption occurs,are defined as liquid pores.The evolution of pore structure affects the methane adsorption mode,which provides basic theoretical guidance for the development of coal seam resources.展开更多
Ensuring the consistency of electrode structure in proton-exchange-membrane fuel cells is highly desired yet challenging because of wide-existing and unguided cracks in the microporous layer(MPL). The first thing is t...Ensuring the consistency of electrode structure in proton-exchange-membrane fuel cells is highly desired yet challenging because of wide-existing and unguided cracks in the microporous layer(MPL). The first thing is to evaluate the homogeneity of MPL with cracks quantitatively. This paper proposes the homogeneity index of a full-scale MPL with an area of 50 cm~2, which is yet to be reported in the literature to our knowledge. Besides, the effects of the carbon material and surfactant on the ink and resulting MPL structure have been studied. The ink with a high network development degree produces an MPL with low crack density, but the ink with high PDI produces an MPL with low crack homogeneity. The polarity of the surfactant and the non-polarity of polytetrafluoroethylene(PTFE) are not mutually soluble,resulting in the heterogeneous PTFE distribution. The findings of this study provide guidelines for MPL fabrication.展开更多
Enhancing catalytic activity of multi-enzyme in vitro through substrate channeling effect is promis-ing yet challenging.Herein,conjugated microporous polymers(CMPs)-scaffolded integrated en-zyme cascade systems(I-ECSs...Enhancing catalytic activity of multi-enzyme in vitro through substrate channeling effect is promis-ing yet challenging.Herein,conjugated microporous polymers(CMPs)-scaffolded integrated en-zyme cascade systems(I-ECSs)are constructed through co-entrapping glucose oxidase(GOx)and horseradish peroxidase(HRP),in which hydrogen peroxide(H_(2)O_(2)) is the intermediate product.The interplay of low-resistance mass transfer pathway and appropriate pore wall-H_(2)O_(2) interactions facilitates the directed transfer of H_(2)O_(2),resulting in 2.4-fold and 5.0-fold elevation in catalytic activ-ity compared to free ECSs and separated ECSs,respectively.The substrate channeling effect could be regulated by altering the mass ratio of GOx to HRP.Besides,I-ECSs demonstrate excellent stabili-ties in harsh environments and multiple recycling.展开更多
The transport properties of fluid argon in micropores, i.e. diffusivity and viscosity, were studied by molecular dynamics simulations. The effects of pore width, temperature and density on diffusivity and viscosity we...The transport properties of fluid argon in micropores, i.e. diffusivity and viscosity, were studied by molecular dynamics simulations. The effects of pore width, temperature and density on diffusivity and viscosity were analyzed in micropores with pore widths from 0.8 to 4.0 nm. The results show that the diffusivity in micropores is much lower than the bulk diffusivity, and it decreases as the pore width decreases; but the viscosity in micropores is significantly larger than the bulk one, and it increases sharply in narrow micropores. The diffusivity in channel parallel direction is obviously larger than that in channel perpendicular direction. The temperature and density are important factors that obviously affect diffusivity and viscosity in micropores.展开更多
Thermal stabilization is an important process in carbon fibers＇ production, during which the polyacryloni-trile fibers are heated from 180℃ to 280 ℃ in air. In this study, the samples were characterized by X-ray di...Thermal stabilization is an important process in carbon fibers＇ production, during which the polyacryloni-trile fibers are heated from 180℃ to 280 ℃ in air. In this study, the samples were characterized by X-ray diffraction,Fourier infrared spectroscopy, differential scanning calorimetry, small angle X-ray Scattering（SAXS） and mechanicaltensile tests. A new rule was suggested by the results of structural characterization for the cyclization, dehydrogena-tion and oxidation reactions that were observed to be drastic from 200 ℃ to 220 ℃, from 220 ℃ to 250 ℃, and inthe later period of the thermal stabilization reactions, respectively. The sizes, shapes and distributions of the sealedmicropores were obtained from the SAXS data. The breaking elongation was significantly affected by the drasticcyclization and dehydrogenation reactions. The breaking force was affected considerably by the bigger micropores,especially from 220 ℃ to 250 ℃, owing to the drastic dehydrogenation reactions.展开更多
A novel hybrid material with microporous structure was fabricated from SBA-15 with mesopores via silane modification and hydrolysis. Two kinds of pores with diameters of 6.5 and 1.9 nm were found in the hybrid materia...A novel hybrid material with microporous structure was fabricated from SBA-15 with mesopores via silane modification and hydrolysis. Two kinds of pores with diameters of 6.5 and 1.9 nm were found in the hybrid material. Compared to that of SBA-15, the surface area of the hybrid material increased from 395.9 m2/g to 667.4 m2/g while its porous volume decreased. The new hybrid material was found to have high efficiency in removing NaCl from solution, and the maximum adsorption capacity of it was ca. 517.5 mg/g.展开更多
The healing behavior of micropores in powder metallurgy （P/M） 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the...The healing behavior of micropores in powder metallurgy （P/M） 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the pore size and enhance the relative density of material in varying degree due to different forging temperatures. As a re- sult of deformation and diffusion bonding at high temperature, the irregular pores were spheroidized and finally turned into stable inner grain pores. The comparison of compression behavior between P/M and wrought dense mate rials has shown that the pores can either be the obstacles of dislocation movement or be the nucleation sites accelera- ting the reerystallization according to the difference of deformation temperatures.展开更多
The bedrock weathered crust in front of the Altun Mountains in the Qaidam Basin,western China,is different from others because this is a salt-lake basin,where saline water fluid infiltrates and is deposited in the ove...The bedrock weathered crust in front of the Altun Mountains in the Qaidam Basin,western China,is different from others because this is a salt-lake basin,where saline water fluid infiltrates and is deposited in the overlying strata.A large amount of gypsum infills the bedrock weathered crust,and this has changed the pore structure.Using core observation,polarized light microscopy,electron probe,physical property analysis and field emission scanning electron microscopy experiments,the characteristics of the weathered bedrock have been studied.There are cracks and a small number of dissolved pores in the interior of the weathered crust.Matrix micropores are widely developed,especially the various matrix cracks formed by tectonics and weathering,as well as the stress characteristics of small dissolved pores,and physical properties such as porosity and permeability.This‘dual structure’developed in the bedrock is important for guiding the exploration of the lake basin bedrock for natural gas.展开更多
In order to deal with the increasingly serious environmental problems,it is important and necessary to lower the concentration of greenhouse gases,especially the CO_(2)gas.CO_(2)capture and storage are the relative su...In order to deal with the increasingly serious environmental problems,it is important and necessary to lower the concentration of greenhouse gases,especially the CO_(2)gas.CO_(2)capture and storage are the relative suitable options for the reduction of these harmful gas concentration.Through the variation of mass ratio of KOH to bio-char,the as prepared active carbon PC-4 exhibits a higher specific surface area of 2491.57 cm^(3)·g^(−1),with the ultra-micropores of 0.5 and 1.2 nm.At 298 K/1 bar,the CO_(2)adsorption capacity of PC-4 also represents the highest value of 5.81 mmol/g.This work demonstrates that the both the pore size and the specific surface area are equally important to enhance the CO_(2)adsorption.This work provides a sustainable method to develop high efficiency waste-based adsorbents to deal with environmental issues of CO_(2)gas.展开更多
Lithium(Li)metal anodes have attracted extensive attention due to their ultrahigh theoretical capacity and low potential.However,the uneven deposition of Li near the unstable electrode/electrolyte interfaces leads to ...Lithium(Li)metal anodes have attracted extensive attention due to their ultrahigh theoretical capacity and low potential.However,the uneven deposition of Li near the unstable electrode/electrolyte interfaces leads to the growth of Li dendrites and the degradation of active electrodes.Herein,we directly fluorinate alkyne-containing conjugated microporous polymers(ACMPs)microspheres with fluorine gas(F_(2))to introduce a novel fluorinated interlayer as an interfacial stabilizer in lithium metal batteries.Using density functional theory methods,it is found that as-prepared fluorinated ACMP(FACMP)has abundant partially ionic C–F bonds.The C–F bonds with electrochemical lability yield remarkable lithiophilicity during cycling.The in situ reactions between the active C–F bonds and Li ions enable transfer of lithium fluoride microcrystals to the solid electrolyte interphase(SEI)layers,guaranteeing effective ionic distribution and smooth Li deposition.Consequently,Li metal electrodes with the fluorinated interlayers demonstrate excellent cycling performances in both half-batteries and full cells with a lithium bis(trifluoromethanesulfonyl)imide electrolyte as well as a nonfluorinated lithium bis(oxalate)borate electrolyte system.This strategy is highly significant in customizable SEI layers to stabilize electrode interfaces and ensure high utilization of Li metal anodes,especially in a nonfluorinated electrolyte.展开更多
Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1700℃for 3 h with corn starch,PMMA microspheres or rice husk powder as the porogenic agent.The effects of some porogenic agents ...Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1700℃for 3 h with corn starch,PMMA microspheres or rice husk powder as the porogenic agent.The effects of some porogenic agents and their additions(mass fraction of 0,5%,10%,15%and 20%,respectively)on the properties of the microporous mullite aggregates were analyzed by XRD,SEM and Image-Pro Plus software.The results show that the comprehensive performance of the sample with 10%rice husk powder is the best:the closed porosity is 7.1%;the bulk density is 2.63 g·cm^(-3);the compressive strength is 122 MPa;the median pore size is 15.16μm;and the thermal conductivity at 500℃is 2.30 W·m^(-1)·K^(-1).展开更多
Three lightweight Al_(2)O_(3)-MgO castables were fabricated with tabular alumina or microporous corundum as the aggregates,reactiveα-Al_(2)O_(3)micropowder,tabular alumina powder,and fused magnesia powder as the matr...Three lightweight Al_(2)O_(3)-MgO castables were fabricated with tabular alumina or microporous corundum as the aggregates,reactiveα-Al_(2)O_(3)micropowder,tabular alumina powder,and fused magnesia powder as the matrix,calcium aluminate cement as the binder,and MgO ultrafine powder(d50=5.4μm)and Al(OH)3 ultrafine powder(d50=8.2μm)as additives.The influence of aggregates and ultrafine powders on the properties,including pore size distribution,heat conductivity,thermal shock resistance,and slag resistance of lightweight refractory castables was investigated.The results show that the incorporation of microporous corundum reduces the bulk density of Al_(2)O_(3)-MgO castables,and MgO and Al(OH)3 ultrafine powders further increases the proportion of micropores in castables,which is beneficial to reducing the heat conductivity,and improving the thermal shock resistance and slag resistance of castables.Additionally,MgO ultrafine powder and Al(OH)3 ultrafine powder increase the fluidity and the strength of castables.展开更多
Fe-rich intermetallics, especially β-Fe phase, usually forming in the microstructure of cast aluminum alloys, are very detrimental to mechanical properties. In the present work, the effects of Fe content on phase tra...Fe-rich intermetallics, especially β-Fe phase, usually forming in the microstructure of cast aluminum alloys, are very detrimental to mechanical properties. In the present work, the effects of Fe content on phase transformation and microstructures were analyzed using a 3D X-ray microscope. Based on the highresolution 3D X-ray computed tomography, the 3D characteristics of Fe-rich intermetallics and micropores in the gravity-cast Al-6 Si alloys with different Fe contents were investigated. In addition, the effect of intermetallics on the microporosity was discussed. The results show that with increasing the Fe content from 0.10 wt.% to 0.60 wt.%, the volume fraction of Fe-rich intermetallics and the volume of the largest size Fe-rich intermetallic increased, and the 3D morphology of intermetallics changed from fine flake to network aggregation. As the Fe contents increased, the shrinkage pores were characterized, which were rather complex due to the micropores promoted by the intermetallics interactions.展开更多
文摘In this work, four empirical models of statistical thickness, namely the models of Harkins and Jura, Hasley, Carbon Black and Jaroniec, were compared in order to determine the textural properties (external surface and surface of micropores) of a clay concrete without molasses and clay concretes stabilized with 8%, 12% and 16% molasses. The results obtained show that Hasley’s model can be used to obtain the external surfaces. However, it does not allow the surface of the micropores to be obtained, and is not suitable for the case of simple clay concrete (without molasses) and for clay concretes stabilized with molasses. The Carbon Black, Jaroniec and Harkins and Jura models can be used for clay concrete and stabilized clay concrete. However, the Carbon Black model is the most relevant for clay concrete and the Harkins and Jura model is for molasses-stabilized clay concrete. These last two models augur well for future research.
基金financially supported by the National Key R&D Program of China (No. 2018YFB0104000 and No. 2019YFA0210300)National Nature Science Foundation of China (No.21571189 and No.21671200)+3 种基金Natural Science Foundation of Jiangsu Province (BK20200991)Hunan Provincial Science and Technology Plan Project of China (No. 2019GK2033, No. 2017TP1001, CPS2019K06 and No. 2018RS3009)Postdoctoral International Exchange Program Funding of China (No. [2018]115)China Postdoctoral Science Foundation (2019M652802)
文摘Energy conversion technologies like fuel cells and metal-air batteries require oxygen reduction reaction(ORR)electrocatalysts with low cost and high catalytic activity.Herein,N-doped carbon spheres(N-CS)with rich micropore structure have been synthesized by a facile two-step method,which includes the polymerization of pyrrole and formaldehyde and followed by a facile pyrolysis process.During the preparation,zinc chloride(ZnCl2)was utilized as a catalyst to promote polymerization and provide a hypersaline environment.In addition,the morphology,defect content and activity area of the resultant N-CS catalysts could be regulated by controlling the content of ZnCl2.The optimum N-CS-1 catalyst demonstrated much better catalytic activity and durability towards ORR in alkaline conditions than commercial 20 wt%Pt/C catalysts,of which the half-wave potential reached 0.844 V vs.RHE.When applied in the Zn-air batteries as cathode catalysts,N-CS-1 showed a maximum power density of 175 mW cm^(-2) and long-term discharging stability of over 150 h at 10 mA cm^(-2),which outperformed 20 wt%Pt/C.The excellent performance could be due to its ultrahigh specific surface area of 1757 m2 g1 and rich micropore channels structure.Meanwhile,this work provides an efficient method to synthesize an ultrahigh surface porous carbon material,especially for catalyst application.
基金financially supported by the National Natural Science Foundation of China (grant No. 41702171)a National Science and Technology Major Project (grant No. 2016ZX05034002)
文摘Micropores of shale are significant to the gas content and production potential of shale, which has been verified in the research of marine shale gas; while, few studies have been conducted on lacustrine shales. This study collected 42 samples from three wells in the Late Cretaceous Qingshankou Formation of the southern Songliao Basin, NE China, and investigated these samples by the focused ion beam-scanning electron microscope(FIB–SEM) and nitrogen adsorption analysis techniques. Four types of micropores were identified in the samples, i.e., intergranular pore, intracellular pore, organic matter pore and microfracture. The pore structure type is characterized by open slit pores and "ink type" pores which are mainly 1.5–5 nm in diameter with mesopores as the main pores. The mesopores account for 74.01% of the pore volume and 54.68% of the pore surface area. Compared with the lacustrine shales from the Triassic Yanchang Formation in the Ordos Basin and Xujiahe Formation in the Sichuan Basin, the intergranular clay mineral interlayer pores are considered to be the main reservoir space for shale gas storage in the study area, followed by intraparticle pores, organic matter pores and microfractures. Maturity and micropore are the key controlling factors which affect the shale gas content of the Qingshankou Formation in southern Songliao Basin.
基金supported by the National Natural Science Foundation of China (Grant No 10674066)State Key Laboratory of Acoustics (Grant No 200802)
文摘Based on an equivalent medium approach, this paper presents a model describing the nonlinear propagation of acoustic waves in a viscoelastic medium containing cylindrical micropores. The influences of pores＇ nonlinear oscillations on sound attenuation, sound dispersion and an equivalent acoustic nonlinearity parameter are discussed. The calculated results show that the attenuation increases with an increasing volume fraction of micropores. The peak of sound velocity and attenuation occurs at the resonant frequency of the micropores while the peak of the equivalent acoustic nonlinearity parameter occurs at the half of the resonant frequency of the micropores. Furthermore, multiple scattering has been taken into account, which leads to a modification to the effective wave number in the equivalent medium approach. We find that these linear and nonlinear acoustic parameters need to be corrected when the volume fraction of micropores is larger than 0.1%.
基金The National Natural Science Foundation of China(No.51578137).
文摘To accurately analyze the impact of casting pores in steel,high-resolution 3D X-ray tomography technology was used to gather detailed statistical information about micropores.These micropores were classified as gas,shrinkage,and gas-shrinkage pores depending on their formation origin and morphology.Clustering tendencies and affinity parameters were defined to characterize the spatial correlations among these three types of pores.The 3D data from X-ray tomography scans were then integrated into finite element analysis(FEA)software to predict how micropore shape,size,and distribution influence stress distribution within the material.The results show that certain inflection points with small local radii within the cast pores are major contributors to stress concentration.Therefore,cast pores cannot be simply modeled as ideal spherical pores.The sphericity and volume of pores have a significant impact on the stress concentration of the model.Specifically,lower sphericity and larger pore volumes result in higher stress concentrations.Moreover,the internal pores of steel castings exhibit specific global distribution characteristics.Pores located on the surface of the specimen lead to significantly higher stress concentrations compared to those located inside the specimen.
基金financially supported by the National Natural Science Foundation of China(No.52273267)the Fundamental Research Funds for the Central Universities(Nos.30920041102 and 30920021107)。
文摘Conjugated microporous polymers have excellent skeleton structures but poor electrical conductivity limits their applications in microwave absorption.To solve this problem,a strategy of molecular expansion and confining polymerization is proposed in this work to synthesize conductive hyper-crosslinked conjugated microporous polymer.The topology of the conjugated microporous polymer is changed into a three-dimensional skeleton structure with high specific surface area by using molecular expansion technique,and the controlled growth of polypyrrole in the channel constructs a unique network structure.The balance of excellent composite backbone structure,proper conductivity,attenuation capability and impedance matching enable the material to exhibit electromagnetic wave absorption performance.As a result,with low filler loading of 10 wt%,a strongest reflection loss of-52.68 d B and a maximum effective bandwidth of 5.76 GHz.Additionally,CST simulations of the radar scattering cross section have been carried out to verify the excellent material properties.This study provides new concepts for new conductive polymers and broadens the application of hyper-crosslinked conjugated microporous polymer in the field of electromagnetic wave absorption.
基金funding and support from the United Kingdom Space Agency(UKSA)the European Space Agency(ESA)+5 种基金funded and supported through the ESA PRODEX schemefunded through PRODEX PEA 4000123238the Research Council of Norway grant 223252funded by Spanish MCIN/AEI/10.13039/501100011033 grant PID2019-107061GB-C61funding and support from the Chinese Academy of Sciences(CAS)funding and support from the National Aeronautics and Space Administration(NASA)。
文摘The Soft X-ray Imager(SXI)is part of the scientific payload of the Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)mission.SMILE is a joint science mission between the European Space Agency(ESA)and the Chinese Academy of Sciences(CAS)and is due for launch in 2025.SXI is a compact X-ray telescope with a wide field-of-view(FOV)capable of encompassing large portions of Earth’s magnetosphere from the vantage point of the SMILE orbit.SXI is sensitive to the soft X-rays produced by the Solar Wind Charge eXchange(SWCX)process produced when heavy ions of solar wind origin interact with neutral particles in Earth’s exosphere.SWCX provides a mechanism for boundary detection within the magnetosphere,such as the position of Earth’s magnetopause,because the solar wind heavy ions have a very low density in regions of closed magnetic field lines.The sensitivity of the SXI is such that it can potentially track movements of the magnetopause on timescales of a few minutes and the orbit of SMILE will enable such movements to be tracked for segments lasting many hours.SXI is led by the University of Leicester in the United Kingdom(UK)with collaborating organisations on hardware,software and science support within the UK,Europe,China and the United States.
基金supported by the National Natural Science Foundation of China(52164015)the Technology Funding Projects of Guizhou Province([2022]231).
文摘The rich accumulation of methane(CH_(4))in tectonic coal layers poses a significant obstacle to the safe and efficient extraction of coal seams and coalbed methane.Tectonic coal samples from three geologically complex regions were selected,and the main results obtained by using a variety of research tools,such as physical tests,theoretical analyses,and numerical simulations,are as follows:22.4–62.5 nm is the joint segment of pore volume,and 26.7–100.7 nm is the joint segment of pore specific surface area.In the dynamic gas production process of tectonic coal pore structure,the adsorption method of methane molecules is“solid–liquid adsorption is the mainstay,and solid–gas adsorption coexists”.Methane stored in micropores with a pore size smaller than the jointed range is defined as solid-state pores.Pores within the jointed range,which transition from micropore filling to surface adsorption,are defined as gaseous pores.Pores outside the jointed range,where solid–liquid adsorption occurs,are defined as liquid pores.The evolution of pore structure affects the methane adsorption mode,which provides basic theoretical guidance for the development of coal seam resources.
基金supported by China National Postdoctoral Program for Innovative Talents (BX20230121)China Postdoctoral Science Foundation (2023M741163)Shanghai Super Postdoctoral Incentive Program (2023741)。
文摘Ensuring the consistency of electrode structure in proton-exchange-membrane fuel cells is highly desired yet challenging because of wide-existing and unguided cracks in the microporous layer(MPL). The first thing is to evaluate the homogeneity of MPL with cracks quantitatively. This paper proposes the homogeneity index of a full-scale MPL with an area of 50 cm~2, which is yet to be reported in the literature to our knowledge. Besides, the effects of the carbon material and surfactant on the ink and resulting MPL structure have been studied. The ink with a high network development degree produces an MPL with low crack density, but the ink with high PDI produces an MPL with low crack homogeneity. The polarity of the surfactant and the non-polarity of polytetrafluoroethylene(PTFE) are not mutually soluble,resulting in the heterogeneous PTFE distribution. The findings of this study provide guidelines for MPL fabrication.
文摘Enhancing catalytic activity of multi-enzyme in vitro through substrate channeling effect is promis-ing yet challenging.Herein,conjugated microporous polymers(CMPs)-scaffolded integrated en-zyme cascade systems(I-ECSs)are constructed through co-entrapping glucose oxidase(GOx)and horseradish peroxidase(HRP),in which hydrogen peroxide(H_(2)O_(2)) is the intermediate product.The interplay of low-resistance mass transfer pathway and appropriate pore wall-H_(2)O_(2) interactions facilitates the directed transfer of H_(2)O_(2),resulting in 2.4-fold and 5.0-fold elevation in catalytic activ-ity compared to free ECSs and separated ECSs,respectively.The substrate channeling effect could be regulated by altering the mass ratio of GOx to HRP.Besides,I-ECSs demonstrate excellent stabili-ties in harsh environments and multiple recycling.
基金Project supported by the National Natural Science Foundation of China (No. 20176048).
文摘The transport properties of fluid argon in micropores, i.e. diffusivity and viscosity, were studied by molecular dynamics simulations. The effects of pore width, temperature and density on diffusivity and viscosity were analyzed in micropores with pore widths from 0.8 to 4.0 nm. The results show that the diffusivity in micropores is much lower than the bulk diffusivity, and it decreases as the pore width decreases; but the viscosity in micropores is significantly larger than the bulk one, and it increases sharply in narrow micropores. The diffusivity in channel parallel direction is obviously larger than that in channel perpendicular direction. The temperature and density are important factors that obviously affect diffusivity and viscosity in micropores.
文摘Thermal stabilization is an important process in carbon fibers＇ production, during which the polyacryloni-trile fibers are heated from 180℃ to 280 ℃ in air. In this study, the samples were characterized by X-ray diffraction,Fourier infrared spectroscopy, differential scanning calorimetry, small angle X-ray Scattering（SAXS） and mechanicaltensile tests. A new rule was suggested by the results of structural characterization for the cyclization, dehydrogena-tion and oxidation reactions that were observed to be drastic from 200 ℃ to 220 ℃, from 220 ℃ to 250 ℃, and inthe later period of the thermal stabilization reactions, respectively. The sizes, shapes and distributions of the sealedmicropores were obtained from the SAXS data. The breaking elongation was significantly affected by the drasticcyclization and dehydrogenation reactions. The breaking force was affected considerably by the bigger micropores,especially from 220 ℃ to 250 ℃, owing to the drastic dehydrogenation reactions.
基金Supported by the National Natural Science Foundation of China（No.U1362113） and the Project of PetroChina Company Limited.
文摘A novel hybrid material with microporous structure was fabricated from SBA-15 with mesopores via silane modification and hydrolysis. Two kinds of pores with diameters of 6.5 and 1.9 nm were found in the hybrid material. Compared to that of SBA-15, the surface area of the hybrid material increased from 395.9 m2/g to 667.4 m2/g while its porous volume decreased. The new hybrid material was found to have high efficiency in removing NaCl from solution, and the maximum adsorption capacity of it was ca. 517.5 mg/g.
基金Item Sponsored by National Basic Research Program of China(2012CB619600)
文摘The healing behavior of micropores in powder metallurgy （P/M） 316L stainless steel during hot forging and subsequent heat treatment was studied. The results showed that hot forging can improve the homogeneity of the pore size and enhance the relative density of material in varying degree due to different forging temperatures. As a re- sult of deformation and diffusion bonding at high temperature, the irregular pores were spheroidized and finally turned into stable inner grain pores. The comparison of compression behavior between P/M and wrought dense mate rials has shown that the pores can either be the obstacles of dislocation movement or be the nucleation sites accelera- ting the reerystallization according to the difference of deformation temperatures.
基金the National Major Project of Science and Technology in developing great oil&gas field and coal bed gas(Grant No.2016ZX05007-006)the Study on water-cut control and production stabilization in the old gasfields and efficient development in new gasfields in Qaidam Basin(Grant No.2016E-0106GF)。
文摘The bedrock weathered crust in front of the Altun Mountains in the Qaidam Basin,western China,is different from others because this is a salt-lake basin,where saline water fluid infiltrates and is deposited in the overlying strata.A large amount of gypsum infills the bedrock weathered crust,and this has changed the pore structure.Using core observation,polarized light microscopy,electron probe,physical property analysis and field emission scanning electron microscopy experiments,the characteristics of the weathered bedrock have been studied.There are cracks and a small number of dissolved pores in the interior of the weathered crust.Matrix micropores are widely developed,especially the various matrix cracks formed by tectonics and weathering,as well as the stress characteristics of small dissolved pores,and physical properties such as porosity and permeability.This‘dual structure’developed in the bedrock is important for guiding the exploration of the lake basin bedrock for natural gas.
基金the National Natural Science Foundation of China(NSFC)(Nos.12205100 and 11665017)the Key Scientific Research Project in Colleges and Universities of Henan Province,China(No.23B140002)the Key Project of College Students'Innovation and Entrepreneurship Training Program 2022 of North China University of Water Resources and Electric Power(No.2022XA050)。
文摘In order to deal with the increasingly serious environmental problems,it is important and necessary to lower the concentration of greenhouse gases,especially the CO_(2)gas.CO_(2)capture and storage are the relative suitable options for the reduction of these harmful gas concentration.Through the variation of mass ratio of KOH to bio-char,the as prepared active carbon PC-4 exhibits a higher specific surface area of 2491.57 cm^(3)·g^(−1),with the ultra-micropores of 0.5 and 1.2 nm.At 298 K/1 bar,the CO_(2)adsorption capacity of PC-4 also represents the highest value of 5.81 mmol/g.This work demonstrates that the both the pore size and the specific surface area are equally important to enhance the CO_(2)adsorption.This work provides a sustainable method to develop high efficiency waste-based adsorbents to deal with environmental issues of CO_(2)gas.
基金Science Foundation for Distinguished Young Scholars in Tianjin,Grant/Award Number:19JCJQJC61700National Natural Science Foundation of China,Grant/Award Numbers:51773147,51973151,52130303National Key R&D Program of China,Grant/Award Number:2022YFB3805702。
文摘Lithium(Li)metal anodes have attracted extensive attention due to their ultrahigh theoretical capacity and low potential.However,the uneven deposition of Li near the unstable electrode/electrolyte interfaces leads to the growth of Li dendrites and the degradation of active electrodes.Herein,we directly fluorinate alkyne-containing conjugated microporous polymers(ACMPs)microspheres with fluorine gas(F_(2))to introduce a novel fluorinated interlayer as an interfacial stabilizer in lithium metal batteries.Using density functional theory methods,it is found that as-prepared fluorinated ACMP(FACMP)has abundant partially ionic C–F bonds.The C–F bonds with electrochemical lability yield remarkable lithiophilicity during cycling.The in situ reactions between the active C–F bonds and Li ions enable transfer of lithium fluoride microcrystals to the solid electrolyte interphase(SEI)layers,guaranteeing effective ionic distribution and smooth Li deposition.Consequently,Li metal electrodes with the fluorinated interlayers demonstrate excellent cycling performances in both half-batteries and full cells with a lithium bis(trifluoromethanesulfonyl)imide electrolyte as well as a nonfluorinated lithium bis(oxalate)borate electrolyte system.This strategy is highly significant in customizable SEI layers to stabilize electrode interfaces and ensure high utilization of Li metal anodes,especially in a nonfluorinated electrolyte.
文摘Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1700℃for 3 h with corn starch,PMMA microspheres or rice husk powder as the porogenic agent.The effects of some porogenic agents and their additions(mass fraction of 0,5%,10%,15%and 20%,respectively)on the properties of the microporous mullite aggregates were analyzed by XRD,SEM and Image-Pro Plus software.The results show that the comprehensive performance of the sample with 10%rice husk powder is the best:the closed porosity is 7.1%;the bulk density is 2.63 g·cm^(-3);the compressive strength is 122 MPa;the median pore size is 15.16μm;and the thermal conductivity at 500℃is 2.30 W·m^(-1)·K^(-1).
基金the National Natural Science Foundation of China(grant no.51774218 and 51374162)for providing financial support for this work.
文摘Three lightweight Al_(2)O_(3)-MgO castables were fabricated with tabular alumina or microporous corundum as the aggregates,reactiveα-Al_(2)O_(3)micropowder,tabular alumina powder,and fused magnesia powder as the matrix,calcium aluminate cement as the binder,and MgO ultrafine powder(d50=5.4μm)and Al(OH)3 ultrafine powder(d50=8.2μm)as additives.The influence of aggregates and ultrafine powders on the properties,including pore size distribution,heat conductivity,thermal shock resistance,and slag resistance of lightweight refractory castables was investigated.The results show that the incorporation of microporous corundum reduces the bulk density of Al_(2)O_(3)-MgO castables,and MgO and Al(OH)3 ultrafine powders further increases the proportion of micropores in castables,which is beneficial to reducing the heat conductivity,and improving the thermal shock resistance and slag resistance of castables.Additionally,MgO ultrafine powder and Al(OH)3 ultrafine powder increase the fluidity and the strength of castables.
基金supported by the Industry Base Enhanced Project(TC160A310-10-01)Guangdong Sci&Tech Project(2013A090100002)Guangzhou Sci&Tech Project(2014Y2-00214)
文摘Fe-rich intermetallics, especially β-Fe phase, usually forming in the microstructure of cast aluminum alloys, are very detrimental to mechanical properties. In the present work, the effects of Fe content on phase transformation and microstructures were analyzed using a 3D X-ray microscope. Based on the highresolution 3D X-ray computed tomography, the 3D characteristics of Fe-rich intermetallics and micropores in the gravity-cast Al-6 Si alloys with different Fe contents were investigated. In addition, the effect of intermetallics on the microporosity was discussed. The results show that with increasing the Fe content from 0.10 wt.% to 0.60 wt.%, the volume fraction of Fe-rich intermetallics and the volume of the largest size Fe-rich intermetallic increased, and the 3D morphology of intermetallics changed from fine flake to network aggregation. As the Fe contents increased, the shrinkage pores were characterized, which were rather complex due to the micropores promoted by the intermetallics interactions.
