Pore Shrinkage Research Articles

Evolution of Ultrathin CoFe-Nanomesh for Oxygen Evolution Reaction: From Slit Pores to Ink-Bottle Pores.

The time-dependent mechanism underlying the formation of Co0.8Fe0.2(OH)x-t nanomesh (nanomesh having 80 % Co and 20 % Fe, "t" represents materials synthesis time) has been identified towards the development of a highly effective catalyst for the oxygen evolution reaction (OER). Utilizing 2-ethyl imidazole (2-HEIM) as an etching reagent and the Ostwald ripening process enabled the evolution of nanomesh formation with a precise pore size of ink-bottle shape. Characterization techniques, including N2-adsorption/desorption, and transmission electron microscopy (TEM) analyses, confirmed the evolution of pore structure from layered double hydroxide-like structure to hierarchical slit-pores to uniform ink-bottle pores after 24 h of synthesis with limited pore shrinkage attributable to iron redeposition at the pore entrances. Atomic force microscopy (AFM) showed a gradual reduction in nanomesh thickness with an increase in synthesis time up to 24 h, indicative of successful exfoliation. The best catalyst (Co0.8Fe0.2(OH)x-24 h) was developed after 24 h of synthesis, having 3.8 nm ink-bottle-shaped pores on the basal plane of nanosheets with only 3-4 layers. Co0.8Fe0.2(OH)x-24 h nanomesh exhibited the best catalytic performance, characterized by a 330 mV overpotential, a mass activity of 309.1 A/g, and a turnover frequency of 2.28 s-1. Furthermore, electrochemical impedance spectroscopy indicated a low charge transfer resistance (5.9 Ω) and pseudoresistance (35.3 Ω), highlighting efficient electron transfer at the electrode/electrolyte interface and enhanced oxygen evolution reaction kinetics, respectively. An increased electrochemical surface area (70.74 cm2) and a high roughness factor of approximately 1010 underlined the importance of narrow mesopores in facilitating catalyst-electrolyte interactions and improving mass transport. The best material demonstrated remarkable stability during 25 h of electrolysis with a high average current density of 14.5 mA/cm2. Hence, this research underscores the critical role of pore morphology in nanomeshes for optimizing catalytic performance and providing stability under vigorous gas evolution due to catalysis.

Study on Microstructure and Properties of LZ50 Axle Steel Repaired by Laser Additive Remanufacturing

ER308L stainless steel welding wire was used for laser repair of LZ50 train axle steel sample. A large number of defects, such as microcracks, pore shrinkage and porosity, can be found in the re-manufacturing sample. A wave-like structure was formed at the boundary of the fusion zone between the augmented repair material and the base material, and the structure in this zone was consist of about 83% martensite and about 17% austenite, In the ER308L stainless steel welding wire repair zone, columnar equiaxed crystals with different lengths and morphology were formed, all of which pointed to the center of the molten pool. After repair, the tensile strength of the specimens decreased from 601.34MPa to 427.81MPa, and the elongation decreased from 16% to 5%, The fracture mode was a combination of ductile fracture and brittle fracture.

Application of Compressible Carbon in Cement to Mitigate Cement Pore Pressure Reduction and Improve Cement Bonding

Summary A quality cement job is essential to ensure long-term zonal isolation in oil/gas and carbon storage wells. This may be affected by the cement hydration process, during which water is consumed, causing pore pressure reduction and shrinkage, which increases the risk of fluid/gas invasion, formation of microannuli, and even the risk of shear bond strength reduction. In this paper, we present the application of compressible carbon (CC) particles as a cement additive to mitigate cement pore pressure reduction and improve zonal isolation. We designed cement formulations with CC and evaluated them using API standard tests and industry-wide recognized tests to ensure they met functional requirements for well cementing, such as mixability, thickening time, rheology, compressive strength development, fluid loss, and free water. The concept is as follows: When cement is pumped into an annulus, the CC particles will compress under hydrostatic pressure. When the cement is hydrating, the CC will expand to mitigate the pore pressure reduction. To validate the proof of concept, we developed a benchtop high-pressure, high-temperature setup and a pilot-scale test setup. A cement formulation with 9% CC by volume was found to be stable and have controllable performance properties such as thickening time, fluid loss, and free water. We also designed and tested a control slurry without CC for comparison. Both the benchtop and pilot-scale tests demonstrated that adding CC into the cement formulation mitigated the pore pressure reduction during cement hydration. This may reduce the risk of fluid/gas invasion that could result in migration in the set cement. Comparing the cement containing carbon with the control system without carbon, the gas permeability was reduced. The bond strength obtained from shear bond tests improved significantly, which may reduce the risk of debonding and be an indication of the reduction of shrinkage. In addition, a better hydraulic seal was found in one test, but further investigation is needed. Similar mechanical properties such as compressive strength were measured for both cements with and without CC. The data showed that adding CC does not have a negative impact on the hardened cement properties. In fact, adding CC decreased Poisson’s ratio slightly. In this paper, we present the results of proof-of-concept testing for the novel application of CC in cement to improve zonal isolation by mitigating pore pressure reduction. We also present new benchtop and pilot-scale experimental setups to measure pore pressure changes during cement hydration.

Defect evolution and mitigation in metal extrusion additive manufacturing: From deposition to sintering

Material extrusion additive manufacturing of metals has found widespread application and is typically thought of as a facile technique to create metal components. This can be undertaken without the need for energy sources typically used in direct energy deposition and powder bed fusion processes. Despite recent advances in achieving net shape and improvements to material/component integrity, these processes are characterized by performance limiting defects which often emerge as a result of deposition strategy and are retained post sintering. Although the debinding and sintering steps have been investigated for metal injection molding technology, quantitative studies of defect evolution are lacking. This work proposes an approach to study the pore evolution behavior from deposition to sintering through X-ray Computed Tomography (XCT) image processing. Quantitative results of pore shrinking, partial and full closure through backtracking of individual pores from the sintered to the green state are presented. It is shown that where pores are larger than 4 × 10-6 mm3, equals to the D90 of the feedstock metal particles, these cannot be fully closed upon sintering and will survive to limit the performance of the final part. The average pore shrinkage is by a factor of 5.6 and partial closure happens in pores with minimum Feret diameter of 33 μm, equals to 160% of the D90 powder particle, or less. The utilization of overfill as a proposed technique in the literature for the elimination of macro pores is investigated, yielding disparate and unsatisfactory results. This discrepancy can be attributed to the insufficient formation of micro-channels within the pore structure during the deposition process of the aqueous feedstock, leading to regions of weak grain bonding. To evaluate the contribution of these to undermining material integrity, tensile tests of linear and circular deposition strategies are undertaken. Experiments show that track interface length plays a major role in determining elongation to failure and tensile strength. It is concluded that the limitation to the mechanical properties of metal paste extrusion components originates from the emergence of defects and their characteristics after the completion of the processing, as opposed to being influenced by the metallurgy prior or post sintering.

Effect of the incorporation of ashes from the Calbuco volcano on the porous function of an andosol

Soils derived from volcanic ashes represent >60% of the arable land in Chile. Permanent volcanic activity makes seeking solutions for the management of volcanic material deposited after an eruption essential. The aim of this research was to evaluate how incorporating ashes from the eruption of the Calbuco Volcano affected the structure of a volcanic soil in southern Chile. Undisturbed soil samples were collected in 2022, under three field conditions: soils from which the ashes were entirely removed after the eruption (c), soils in which the ashes were incorporated (c/i) and soils on which the ashes remained on the surface (s/i). The pore-size distribution and the air conductivity were determined based on the water retention curve (WRC), the coefficient of linear extensibility (COLE), the pore shrinkage index (PSI) and the air permeability (Ka). Under c/i field conditions, an increase in total porosity (TP) of 5.57 and 3.48% was found when compared to the control and s/i field conditions, respectively. The highest volume of plant available water capacity (PAWC) was observed in the s/i field conditions, which increased by 65% compared to the other soil conditions. The incorporation of ash into the first 20 cm of depth did not guarantee an increase in usable water for plants; nonetheless, changes in structure did generate a redistribution in the pore size. Therefore, it is essential to evaluate how volcanic ash deposits and their incorporation affect soil physical properties under field conditions.

Effect of curing conditions on the alkali-activated blends: Microstructure, performance and economic assessment

To enhance the application of alkali-activated materials in engineering, this study investigates the influence of cast-in-place and prefabrication by steam curing and autoclaved curing on alkali-activated materials with different slag-fly ash mass ratios. The selection of the three curing methods is based on current construction techniques: onsite construction (ambient curing), production of prefabricated cement-based components (steam curing), and production of aerated concrete blocks (autoclaved curing). In this paper, the dissolution ability of CaO, SiO2 and Al2O3 in fly ash and slag was first evaluated. Subsequently, the hydration products of the samples were analyzed using X-ray diffraction, thermogravimetric analysis, and a scanning electron microscope. Additionally, the degree of hydration of the samples was quantitatively analyzed using the selective dissolution method combined with 29Si NMR. The results showed that compared to ambient curing, autoclaved curing, which provides a high-temperature and high-pressure environment, enhances the reactivity of slag and fly ash. This enhancement is reflected in the increase in their solubility and the degree of reaction from 28.3% to 14.6%–69.9% and 63.7% respectively. The pore structure, compressive strength, and shrinkage of the samples were also evaluated. The results demonstrate that autoclaved curing enhances the formation of hydration products, reduces porosity, and increases compressive strength. Compared to ambient curing, steam curing can reduce the shrinkage rate from 64.8% to 68.4%, while autoclaved curing can decrease it from 87.9% to 95.1%. Based on the economic analysis, autoclaved curing can offset the total costs by reducing the usage of slag and lowering raw material expenses, demonstrating its cost-effectiveness. The obtained results can provide a theoretical foundation for the large-scale application of alkali-activated slag-fly ash materials in civil engineering construction.

Phase-field simulation of sintering process of ceramic composite fuel

Due to the limitation of existing experimental techniques, it is difficult to observe the evolution of microstructure in the sintering process in real time, resulting in a lack of in-depth understanding of the sintering mechanism of two-phase composite fuels. Therefore, it is greatly important to carry out theoretical simulation studies in the sintering process of composite fuels. In this work, a phase-field model of the two-phase sintering process of ceramic composite fuel is established, and the sintering process of UN-U<sub>3</sub>Si<sub>2</sub> composite fuel is simulated by using this method. The simulation results show that during the formation of sintering neck, the surface deformation of the grains with higher surface energy is significant. The size of the final equilibrium dihedral angle formed by the two-phase double grains depends on the ratio of the grain boundary energy to the surface energy of the two phases. The phenomenon of large grains swallowing small grains does not occur between the two unequal double grains. Subsequently, the pore shrinkage and the properties of the trident grain boundary among the two-phase three grains are investigated in the sintering process. It is found that the angle of the trident grain boundary formed by the two-phase three grains deviates from 120°. The high-energy barrier at the grain boundary hinders the diffusion of the pore vacancies along the grain boundary, resulting in a slow shrinkage rate of the pore vacancies at the trident grain boundary. In addition, the simulation results of the microstructure evolution of two-phase polycrystalline sintered tissue with different volume fraction ratios show that the grain boundary diffusion plays a major role in the two-phase sintering process. The grain growth of the phase with a higher volume fraction is dominant, and there exists a hindrance to the migration of grain boundaries between two-phase grains. The phenomenon of grain migration exists between grains of the same phase.

Membrane fouling and control in algae-rich water treatment

Microfiltration and ultrafiltration membrane technology has now become one of the important methods for algae-rich water treatment due to its better solid-liquid separation effect and microbial retention capacity, while the existence of membrane fouling has been restricting the full-scale promotion and application of low-pressure membrane technology. The main foulants causing membrane fouling in algal-rich water include algal cells, algal debris and algal organic matter AOM (EOM and IOM). In this paper, the mechanism of membrane fouling caused by algal foulants in MF/UF for high algal water treatment is analysed in terms of both individual and composite fouling. Both individual and composite effects of algal foulants can lead to severe membrane fouling, in which algal cells and algal debris mainly dominate the accumulation of filter cake, while AOM mainly leads to membrane pore blockage membrane fouling is exacerbated by compounding effects, with severe reversible and irreversible fouling caused by filter cake formation and membrane pore shrinkage. This paper also discusses several common membrane fouling control methods, including pretreatment (oxidation, coagulation, combined oxidation-coagulation and adsorption) and membrane modification, and it is found that these several membrane fouling control methods can achieve good results.

A mechanistic explanation of shrinkage porosity in laser powder bed fusion additive manufacturing

This work focuses on the occurrence of shrinkage porosity and its manifestation in Alloy 718 during laser-powder bed fusion (PBF-LB) processing. Shrinkage porosity is a common defect in metal castings that degrades part performance. In traditional metal castings, the Niyama criterion is a reliable heuristic for predicting the formation of shrinkage porosity. However, the Niyama criterion’s applicability in the PBF-LB process remains unexplored, and there is no known and evaluated heuristic to predict shrinkage porosity in the PBF-LB manufactured parts. This work employs microstructure characterization and an analytical heat transfer model to develop a mechanistic explanation for the formation of shrinkage porosity in the PBF-LB process. The results show that the Niyama criterion could not effectively predict the occurrence of shrinkage porosity. Further, the formation of shrinkage porosity is primarily driven by secondary dendrite arm growth in the solidifying microstructure, where the transition to cellular growth at high cooling rates during solidification mitigates porosity by removing locations for pore formation. This means a heuristic based on solidification cooling rate could reliably predict the occurrence of shrinkage porosity. For practical use, shrinkage porosity process maps are presented for use in process design and control to directly aid shrinkage porosity mitigation in process planning. The process-shrinkage porosity relationship results also indicate that trends in PBF-LB manufacturing toward higher deposition temperatures and higher throughput are likely to aggravate the conditions for shrinkage porosity formation and further elevate the importance of the mitigation strategies presented in this work.

The impacts of CO2 mineralization reaction on the physicochemical characteristics of fly ash: A study under different reaction conditions of the water-to-solid ratio and the pressure of CO2

Utilizing fly ash (FA) directly to mineralize CO2 and injecting carbon sequestration products into goafs of coal mines is a novel and promising technology. The impact mechanisms of CO2 direct mineralization reactions on the characteristics of key groups, physical phases, surface micromorphology, particle size and pore structure of FA are discussed systematically in detail. The focus is imposed on the impacts of different reaction conditions (water-to-solid ratios and pressures of CO2). Based on the FT-IR, XRD and ESEM-EDS analysis, CO2 is transformed into carbonates of five vibrational models after mineralization and largely sequestered as calcite by portlandite, which forms a passivated layer on the FA surface. The particle size of carbonated FA particles gets smaller and less uniform, and the variation laws of the particle size at full scale are analyzed by particle size intervals. The variation process of the pore can be divided into the dissolution of FA for pore expansion, the low degree of CO2 mineralization reaction for further expanding the pore and the high reaction degree for pore shrinkage. This paper provides theoretical bases for improving the direct CO2 sequestration capacity and research directions for the subsequent application properties of carbon sequestration products.

High-efficiency recycling of Mo and Ni from spent HDS catalysts: Enhanced oxidation with O2-rich roasting and selective separation with organic acid leaching- complexation extraction

Spent petroleum refining catalyst is regarded as the important secondary resource for valuable metals. However, common recycling strategies, including soda roasting, acid and alkaline solutions leaching and chemically precipitation, produced large quantities of high salinity wastewater. This study proposed an efficient method to recovery of Mo and Ni from the spent hydrodesulfurization (HDS) catalyst via O2-rich roasting and organic acid leaching with the advantage of less salinity wastewater production. The transformation of Mo(IV) into soluble Mo(VI) was enhanced by O2-rich atmosphere roasting, and 98.64% of Mo(IV) was oxidized at 650 ℃ for 2 h in atmosphere containing 30% of O2. The oxidation process of Mo(IV) was agreed with the shrinkage pore model, and regulated by surface reaction and internal diffusion. 97.97% of Mo(VI) was leached from roasted product by oxalic acid, separated with complexation extraction agent of Ala-TBP and recovered as (NH4)8Mo10O34 and (NH4)2Mo3O10 by evaporative crystallization. Ni was leached out from spent catalyst with 1 mol/L acetic acid, and precipitated as NiC2O4 with oxalic acid. 95.92% of Mo and 96.77% of Ni were recovered from spent HDS catalyst with this recycling route. This study provided a high-efficient and eco-friendly method to recovery of valuable metals from spent catalyst.

Aging behavior and mechanism of polyvinylidene fluoride membrane by intensified UV irradiation and NaOCl: A comparative study

Membrane technology plays a critical role in solving worldwide water scarcity and security issues. However, membrane aging causes deterioration or complete failure of membrane performance. In this work, polyvinylidene fluoride (PVDF) membrane aging induced by ultraviolet (UV) and NaOCl were investigated and compared. The skin layer was completely destroyed in 2d by UV irradiation under a dry state, which further caused deformation in the sublayer and pore shrinkage. The water layer on the membrane surface protected the skin layer from damage by UV till 8d under the wet state. NaOCl had a moderate influence, the flux was firstly decreased as the hydrophobicity of the membrane increased, and then increased due to pore enlargement. Membrane aging also resulted in a lower virus rejection, which highlighted the biosafety concern in membrane-based wastewater treatment. Infrared and two-dimensional correlation spectroscopy confirmed that the hydrophilic additive was first oxidated in both processes. β-PVDF segment changed before α-PVDF under UV, during which the CC bond was formed by the dehydrofluorination reaction. But the α-PVDF segment was attacked firstly by NaOCl, the radical reaction occurred both at CH2-CF2 and CH=CF segments. This work studied two aging patterns in the membrane lifecycle and demonstrated the aging mechanism, which shed light on membrane development and maintenance in the future.

Agglomeration behavior of colloidal nano-silica and its effect on pore structure, mechanical properties and shrinkage of cement mortar

The pozzolanic activity of colloidal nano-silica (CNS) can promote cement hydration, thereby improving the performance of the cement-based materials. However, the CNS itself presents highly electronegative, upon contact with cementitious materials, the electrostatic repulsion between CNS particles is lost due to the high ionic strength and the presence of multivalent cations in cement paste, which could lead to the destabilization of CNS and the formation of CNS aggregate (CNSA). Furthermore, similar to CNS, the chemical composition of CNSA is still amorphous silica because no chemical reaction occurs during the CNS agglomeration process. In theory, CNSA has similar nano effect and chemical activity effect to CNS and it can obviously accelerate the hydration rate of cement, improve the mechanical properties and pore structure of cement-based materials. This study aims to investigate the agglomeration behavior of CNS in cement pore solution (i.e. particle size distribution, zeta potential, residue Ca2+, microstructure) and its impact on the workability, pore structure and mechanical properties of cement mortar. It is proved that CNSA was formed by the complex of CNS and Ca2+ by electrostatic adsorption. And CNS content played a significant role on obtaining stable and narrow dispersion of CNSA in cement pore solution and the optimal content was found out to be 0.4 wt% where the particle size of the CNSA was still in the nanometer scale and stable at 200 nm. Cement mortar properties were also significantly improved through addition of 0.4 wt% CNS. While the basic workability was maintained, the 28-day compressive strength and flexural strength of cement mortar were improved by 8.94 % and 8.75 % respectively, the 28-day porosity was reduced by 8.76 %.

Nanoporous silicon fiber networks in a composite anode for all-solid-state batteries with superior cycling performance

All-solid-state batteries comprising Si anodes are promising materials for energy storage in electronic vehicles because their energy density is approximately 1.7 times higher than that of graphite anodes. However, Si undergoes severe volume changes during cycling, resulting in the loss of electronic and ionic conduction pathways and rapid capacity fading. To address this challenge, we developed composite anodes with a nanoporous Si fiber network structure in sulfide-based solid electrolytes (SEs) and conductive additives. Nanoporous Si fibers were fabricated by electrospinning, followed by magnesiothermic reduction. The total pore volume of the fibers allowed pore shrinkage to compensate for the volumetric expansion of Li12Si7, thereby suppressing outward expansion and preserving the Si-SE (or conductive additive) interface. The network structure of the lithiated Si fibers compensates for electronic and ionic conduction pathways even to the partially delaminated areas, leading to increased Si utilization. The anodes exhibited superior performance, achieving an initial Coulombic efficiency of 71%, a reversible capacity of 1474 mAh g−1, and capacity retention of 85% after 40 cycles with an industrially acceptable areal capacity of 1.3 mAh cm−2. The proposed approach can reduce the constraint pressure during charging/discharging and may have practical applications in large-area all-solid-state batteries.

Natural gas desorption versus laboratory gas adsorption with pore shrinkage

To perform hydro-mechanical experiments on sorptive geomaterials, the gas is injected into bulk of the specimen to re-saturate it representing its in-situ state, and adsorption is monitored until gas equilibrium is reached. We show in this study that this experimental procedure does not reflect the in-situ state of the sample leading to potentially significant errors. We measured the carbon dioxide (CO2) adsorption capacity of the coal specimen (free of gas) and its powder with different particle sizes and compared the results with field desorption data. Experimental results indicate an increase in coal adsorption capacity with decrease in coal particle size. Interestingly, the field data exhibits much higher desorbed gas amount compared to laboratory-measured adsorption capacity of coal powder with smallest measurable particle size under the same gas pressure. To shed light on the observation of field desorption – laboratory adsorption hysteresis, the micro-scale gas adsorption experiments combined with X-ray micro-Computed Tomography (XRCT) measurements were conducted where an intact specimen was imaged before (dry state) and after Krypton injection. The analysis of the XRCT images indicates that the Krypton adsorption closes/reduces the aperture of pre-existing fractures in the specimen. In addition, the Krypton diffuses only in a small region near pre-existing fractures despite its adsorption measurement indicating gas equilibrium and specimen saturation. This observation proposes that significant portion of pores exposed to Krypton experienced a size reduction by swelling resulting in partial saturation of the specimen. This patrial saturation at laboratory conditions evidently cannot resemble the in-situ state of gas sorption capacity.

Self-graphenized biochar with huge pore volume prepared from pre-boiled Ulva lactuca for electrochemical supercapacitor with high energy density

To enhance energy density of water-based electrochemical supercapacitor, a highly self-graphenized bicohar with huge pore volume is pyrolyzed from the biomass Ulva lactuca (UL) pre-boiled in Mg(CH3COO)2 solution. During the pyrolysis process, the MgO converted from the Mg(CH3COO)2 re-crystallized in the biomass UL inhibits the pore shrinkage and helps to inherit the pristine pore system. The resultant biochar HUB-2.0 exhibits high specific surface area (SSA) of 2296.7 m2 g−1 and huge pore volume of 4.59 m3 g−1. It is also featured with moderate self-graphenization and heteroatoms self-doped surface in the connected pore system inherited from the precursor. It achieves a specific capacitance of 445.0 F g−1 at 0.5 A g−1 in the three-electrode system with the electrolyte 1.0 M H2SO4. A superior energy density of 27.17 Wh kg−1 is also calculated at a power density of 222.8 W kg−1 in the two-electrode system with the neutral electrolyte Na2SO4. The work provides a fast and efficient method to prepare the biochar with balanced properties to achieve superior electrochemical supercapacitor performance, especially for high energy density.

Optimization of SiO2 reflective layer thickness for improving the performance of structured CsI scintillation screen based on oxidized Si micropore array template in X-ray imaging.

Structured scintillation screen based on oxidized Si micropore array template can effectively improve the spatial resolution of X-ray imaging. The purpose of this study is to investigate the effect of SiO2 layer thickness on the light guide and X-ray imaging performance of CsI scintillation screen when the structural period is as small as microns. Cylindrical micropores with a period of 4.3 µm, an average diameter of 3.3 µm and a depth of about 40 µm were prepared in Si wafers. SiO2 layer was formed on the pore walls after thermal oxidation. Increasing SiO2 layer thickness would be beneficial to the propagation of scintillation light along the cylindrical channels. What was not previously anticipated was that the pore size gradually shrank as the SiO2 layer thickened. The pore shrinkage would reduce the filling rate of CsI in the templates and thus would reduce the production of scintillation light. The structured CsI scintillation screens with different SiO2 layer thicknesses were fabricated by filling CsI scintillator into the oxidized silicon micropore array template. The morphology, crystallinity, X-ray excited optical luminescence, and X-ray imaging performance of the screens were studied. The results show that the spatial resolutions of X-ray images measured using the structured CsI scintillation screens with different SiO2 layer thicknesses are close to each other, and they are all about 110 lp/mm. However, the X-ray excited optical luminescence of the screen and detective quantum efficiency of X-ray imaging vary with the thickness of the SiO2 layer. The optimal thickness is about 350 nm.

Optimizing Sieving Effect for CO2 Capture from Humid Air Using an Adaptive Ultramicroporous Framework.

Excessive CO2 in the air can not only lead to serious climate problems but also cause serious damage to humans in confined spaces. Here, a novel metal-organic framework (FJI-H38) with adaptive ultramicropores and multiple active sites is prepared. It can sieve CO2 from air with the very high adsorption capacity/selectivity but the lowest adsorption enthalpy among the reported physical adsorbents. Such excellent adsorption performances can be retained even at high humidity. Mechanistic studies show that the polar ultramicropore is very suitable for molecular sieving of CO2 from N2 , and the distinguishable adsorption sites for H2 O and CO2 enable them to be co-adsorbed. Notably, the adsorbed-CO2 -driven pore shrinkage can further promote CO2 capture while the adsorbed-H2 O-induced phase transitions in turn inhibit H2 O adsorption. Moreover, FJI-H38 has excellent stability and recyclability and can be synthesized on a large scale, making it a practical trace CO2 adsorbent. This will provide a new strategy for developing practical adsorbents for CO2 capture from the air.

Experimental study on stress-dependent multiphase flow in ultra-low permeability sandstone during CO2 flooding based on LF-NMR

Oil production performance in the unconventional reservoirs is significantly affected by the flooding agent and occurrence environment. In this study, the in-situ stress and displacement pressure effects are considered, the response of CO2/Oil and pore structure was monitored by online low field nuclear magnetic resonance (LF-NMR). The results show that the pore structure was composed of adsorption pore (AP＜3 m s), percolation pore (3 m s＜PP＜30 m s), and migration pore (30 m s＜MP). The stress sensitivity of adsorption pore is more obvious than that of percolation pore and gradually weakened responding to the increase of in-situ stress. The increased in-situ stress narrowed and closured pore throats and limited the migration of CO2/Oil, and the pore transformed from gas-channeling type into homogeneous type and the hydraulic conductivity of CO2 and oil decreased non-linearly responding to the pore shrinkage. The percolation pore and migration pore dominate the oil recovery, and the decreased MP resulted in the non-linearly and dynamic reduction of oil recovery. The higher relative permeability was presented and the end-point oil saturation non-linearly increased with the increasing in-situ stress. The increased displacement pressure effectively improved the oil recovery and dynamic gas channeling, and the incremental oil recovery was primarily contributed by the PP and MP due to the increased CO2 swept area. The positive effect of displacement pressure on oil recovery gradually reduced with the increase of in-situ stress. The findings provide a significant insight on the application of CO2-EOR in ultra-low permeability reservoirs.

高純度アルミニウムおよびA6061アルミニウム合金におけるポアの成長挙動と水素脱離挙動

An increase in the volume fraction of pores in aluminum alloys causes a decrease in the elongation and the strength of alloys. To improve the mechanical properties of aluminum alloys, it is important to understand the growth and shrinkage behavior of pores. In this study, we analyzed the relationship between hydrogen desorption behavior and the growth/shrinking behavior of pores in A6061 alloys and pure aluminum using thermal desorption analysis and synchrotron radiation X-ray tomography. In pure aluminum, the fine pores began to annihilate at temperatures above 500°C and the relatively large pores coarsened. In contrast, the pores shrank with increasing temperature in A6061 alloy. The influence of second-phase particles has been discussed as a possible explanation for the difference in the nature of pores at elevated temperatures in pure aluminum and A6061 alloys. As in the A6061 alloy, much of the hydrogen desorbed from the pores due to heating is released externally from the second-phase particles on the aluminum surface, resulting in pore shrinkage due to the internal pressure drop of pores.