Pore Closure Research Articles

Distinguishing of carbons and oxidation behaviour (Part 1): Exploring model-free kinetics and RAMAN spectroscopy as a synergistic approach for evaluating carbon-bonded-refractories

• Exploring the synergy of model free kinetics and Raman for industrial routine application on product performance. • Using carbon as a sensor to monitor and track oxidation within carbon bonded refractories. • Investigating microstructural changes using high temperature Raman to support oxidation reaction mechanism. • Utilising cluster analysis feature of the WiTec Raman software to distinguish carbons and the effects of aggregates on carbon signals. A rapid synergetic profiling approach to determining oxidation behaviour and distinguishing of carbons within a refractory composite was explored for steel end user application. The efficacy for both Raman spectroscopy and model free kinetics were studied and proved successful for adoption as routine techniques. With the model free approach, the complex reaction steps were profiled as a multi-step reaction with series of activation energy ranging from 230 KJ/Mol to 150 KJ/Mol. The complex oxidation behaviour was supported by high temperature Raman spectroscopy which corroborated the pore closure mechanism that plays a critical role in modulating reaction intensity. Raman tracked oxidation via its effect on the crystallite sizes of resin (∼ 5.5 nm to 8.5 nm) and intensity peak ratio of D to G peak within some limitations that are discussed in the study. Lastly, an empirical prediction of isothermal experiment from non-isothermal kinetics was validated and considered useful for determining the life of carbon especially in cases where under performance was suspected due to improper preheating by the end-user.

In situ detection method for Li-ion battery of separator pore closure defects based on abnormal voltage in rest condition

Lithium-ion batteries have been widely used in various fields, and safety accidents caused by defects in batteries often occur. However, there is little research on defect characteristics, models, and detection methods. In this study, a typical separator pore closure defect is simulated using an intentionally implanted polyethylene terephthalate tab on the anode. The effects of the lithium-ion blocking defect on the battery performance are investigated through experimentation and simulation. The research reveals the lithium-ion horizontal equalization mechanism that causes abnormal voltage variation in the defective battery, especially in the long-term rest condition. Furthermore, an in-situ detection method to diagnose defects based on abnormal voltage variations is proposed herein. The detection is conducted under a special cycle, and the voltage variation is described by two characteristic parameters. The method is proven to identify the defects and determine the relative size through numerical simulation and experiments of pouch batteries with different aging and defect degrees. In addition to the implanted defects, this method can diagnose inherent heterogeneity problems.

Inhomogeneous degradation induced by lithium plating in a large-format lithium-ion battery

With the demand for high-energy-density power sources for electric vehicles, large-format lithium-ion batteries are widely applied, considering their advantages in reducing the weight of inactive materials. However, large-format cells suffer from internal inhomogeneities, which become the bottleneck limiting their performance. Here, the inhomogeneous degradation in a large-format pouch cell is comprehensively investigated using a series of (non-)destructive techniques. Spatial-resolved deformation detection and ultrasonic diagnostics are utilized to study the evolution of inhomogeneity inside the large-format battery. Localized deformation and deposits are found to firstly appear at the tab-near regions and then propagate into central regions, which is identified by characterization tests to be induced by lithium plating. The inhomogeneous degradation mechanism inside the battery is summarized as an initiation-propagation process. During the process, lithium deposit is initiated by a local high current density, resulting in the local separator pore closure. Pore closure in the separator in return creates a high current density and overpotential in the adjacent area, leading to a continuous propagation of the lithium deposition area. Finally, an effective indicator—peak height in the differential voltage curve is proposed to detect the inhomogeneity in the battery, and thus offers guidance to the design and management of large-format cells.

A spin-crossover framework endowed with pore-adjustable behavior by slow structural dynamics

Host-guest interactions play critical roles in achieving switchable structures and functionalities in porous materials, but design and control remain challenging. Here, we report a two-dimensional porous magnetic compound, [FeII(prentrz)2PdII(CN)4] (prentrz = (1E,2E)−3-phenyl-N-(4H-1,2,4-triazol-4-yl)prop-2-en-1-imine), which exhibits an atypical pore transformation that directly entangles with a spin state transition in response to water adsorption. In this material, the adsorption-induced, non-uniform pedal motion of the axial prentrz ligands and the crumpling/unfolding of the layer structure actuate a reversible narrow quasi-discrete pore (nqp) to large channel-type pore (lcp) change that leads to a pore rearrangement associated with simultaneous pore opening and closing. The unusual pore transformation results in programmable adsorption in which the lcp structure type must be achieved first by the long-time exposure of the nqp structure type in a steam-saturated atmosphere to accomplish the gate-opening adsorption. The structural transformation is accompanied by a variation in the spin-crossover (SCO) property of FeII, i.e., two-step SCO with a large plateau for the lcp phase and two-step SCO with no plateau for the nqp phase. The unusual adsorption-induced pore rearrangement and the related SCO property offer a way to design and control the pore structure and physical properties of dynamic frameworks.

Sequential compound fusion and kiss-and-run mediate exo- and endocytosis in excitable cells.

Vesicle fusion at preestablished plasma membrane release sites releases transmitters and hormones to mediate fundamental functions like neuronal network activities and fight-or-flight responses. This half-a-century-old concept—fusion at well-established release sites in excitable cells—needs to be modified to include the sequential compound fusion reported here—vesicle fusion at previously fused Ω-shaped vesicular membrane. With superresolution STED microscopy in excitable neuroendocrine chromaffin cells, we real-time visualized sequential compound fusion pore openings and content releases in generating multivesicular and asynchronous release from single release sites, which enhances exocytosis strength and dynamic ranges in excitable cells. We also visualized subsequent compound fusion pore closure, a new mode of endocytosis termed compound kiss-and-run that enhances vesicle recycling capacity. These results suggest modifying current exo-endocytosis concepts by including rapid release-site assembly at fused vesicle membrane, where sequential compound fusion and kiss-and-run take place to enhance exo-endocytosis capacity and dynamic ranges.

Application of Hot Isostatic Pressing in Nickel-Based Single Crystal Superalloys

Hot isostatic pressing (HIP) technology can effectively reduce microstructure defects such as micropores, which are formed during solidification and hominization heat treatment, and thus further improve the high temperature performance of nickel-based SX superalloys. This paper reviews the application of HIP treatment in nickel-based SX superalloys, focusing on the dislocation-creep closure and diffusion-creep closure mechanisms and the kinetics of annihilation of micropores by HIP. The effects of different scheme on pore closure and high temperature mechanical properties are compared. The advantages and disadvantages of different schemes are summarized. In addition, the application of HIP treatment in additive manufacturing (AM) of nickel-based SX superalloys is also discussed.

GM1 asymmetry in the membrane stabilizes pores

Cell membranes are highly asymmetric and their stability against poration is crucial for survival. We investigated the influence of membrane asymmetry on electroporation of giant unilamellar vesicles with membranes doped with GM1, a ganglioside asymmetrically enriched in the outer leaflet of neuronal cell membranes. Compared with symmetric membranes, the lifetimes of micronsized pores are about an order of magnitude longer suggesting that pores are stabilized by GM1. Internal membrane nanotubes caused by the GM1 asymmetry, obstruct and additionally slow down pore closure, effectively reducing pore edge tension and leading to leaky membranes. Our results point to the drastic effects this ganglioside can have on pore resealing in biotechnology applications based on poration as well as on membrane repair processes.

Formation of voids and their role in the recovery of sputtered AlN during high-temperature annealing

The structural recovery of AlN grown by reactive sputtering on a sapphire substrate during high-temperature annealing is studied by means of transmission electron microscopy and secondary ion mass spectrometry. The as-grown film shows high-density planar defects, such as basal and prismatic stacking faults, caused by the limited diffusion length of the adatoms and, thus, presents a columnar structure. The presence of high-density nanopipes is associated with the presence of unintentional oxygen impurities. Based on the atomic resolution transmission electron microscopy analysis, we show that basal and prismatic stacking faults vanish in the films via a climb mechanism and describe this process as the nucleation of jogs promoted by the diffusion of vacancies. The nanopipes present in the as-grown film transform into faceted voids and act as a beneficial source of excess vacancies that promote dislocation annihilation by climb. The transformation of nanopipes to faceted voids resembles the transition from open channel pores to close faceted pores, which has been observed in porous silicon and can be described in terms of a classical sintering theory.

Coupling mechanism of THM fields and SLG phases during the gas extraction process and its application in numerical analysis of gas occurrence regularity and effective extraction radius

The analysis of the coupling mechanism of thermal-hydraulic-mechanical (THM) fields, and solid-liquid-gas (SLG) phases during gas extraction process is of profound significance to explore its numerical application in the gas occurrence regularity and its effective extraction radius. In this study, the Hudi coal mine in Qinshui basin is taken as the research area, the influencing factors of gas occurrence were analyzed, the differences in overburden load for gas pressure distribution and the factors influencing the effective extraction radius were further discussed by using the COMSOL software. The results show that the derivation of mathematical model in gas extraction shows that the process is a process the THM fields restrict each other, and the SLG phases influence each other. The longer the extraction time, the larger the influencing range of borehole, and the better the extraction effect. The larger the diameter of borehole, the larger the effective extraction radius, and the influence on gas extraction effect is smaller in the early stage and larger in the late stage. The borehole arrangement should be flexibly arranged according to the actual extraction situation. The higher the porosity, the higher the permeability, the better the gas extraction effect. The larger the overburden load of reservoir, the stronger the effective stress, which will result in the more severe the strain, and the closure of pore and fracture, which in turn will lead to the decrease of permeability and slow down the gas extraction. The relationship among extraction time, borehole diameter, negative pressure of gas extraction, permeability with effective extraction radius is exponential. This study has important theoretical and practical significance for clarifying and summarizing the gas occurrence regularity and its engineering practice.

Grain growth during capsule-free hot isostatic pressing

This paper provides a new insight to the capsule free hot isostatic pressing (HIP) of alumina and yttria-stabilized zirconia ceramics. The first part of the paper focuses on the pre-sintering stage, namely the impact of conventional (2, 5, 10 °C/min) and rapid heating rate (100 °C/min) on pore closure and grain growth. It is shown that the rapid heating neither changes the pore closure behavior nor restricts the grain growth compared to conventional pre-sintering. The second part investigates the influence of temperature, dwell time, and applied pressure on the microstructure development during HIP. Our findings indicate the existence of a kinetic window, providing the optimal HIP conditions (1200–1250 °C, 200 MPa, 1–4 h for investigated powders) for production of almost fully dense compacts with only minimal grain growth. Our results also show that the applied pressure (up to 200 MPa) does not facilitate the grain boundary mobility of the investigated materials even at a higher temperature (1300 °C) at which the grain growth normally occurs. The potential of optimized capsule-free HIP was demonstrated by preparation of a transparent c-YSZ sample by a combination of rapid pre-sintering and optimized post-HIP.

Activation and closed-state inactivation mechanisms of the human voltage-gated KV4 channel complexes

The voltage-gated ion channel activity depends on both activation (transition from the resting state to the open state) and inactivation. Inactivation is a self-restraint mechanism to limit ion conduction and is as crucial to membrane excitability as activation. Inactivation can occur when the channel is open or closed. Although open-state inactivation is well understood, the molecular basis of closed-state inactivation has remained elusive. We report cryo-EM structures of human KV4.2 channel complexes in inactivated, open, and closed states. Closed-state inactivation of KV4 involves an unprecedented symmetry breakdown for pore closure by only two of the four S4-S5 linkers, distinct from known mechanisms of open-state inactivation. We further capture KV4 in a putative resting state, revealing how voltage sensor movements control the pore. Moreover, our structures provide insights regarding channel modulation by KChIP2 and DPP6 auxiliary subunits. Our findings elucidate mechanisms of closed-state inactivation and voltage-dependent activation of the KV4 channel.

Modeling and simulation of current-clamp electroporation

Current-Clamp electroporation refers to the application of a constant current across a membrane which results in voltage fluctuations due to the creation of electropores. This method allows for the measurement of electroporation across a long timescale (minutes) and facilitates the comparison between experimental and theoretical studies. Of particular interest is the claim in the literature that current-clamp electroporation results in the creation of a single pore. We simulated current-clamp electroporation using the Smoluchowski and Langevin equations and identified two possible mechanisms to explain the observed voltage fluctuations. The voltage fluctuations may be due to a single pore or a few pores growing and shrinking via a negative feedback mechanism or the opening and closing of pores in a larger population of pores. Our results suggest that current-clamp conditions do not necessarily result in the creation of a single pore. Additionally, we showed that the Langevin model is more accurate than the Smoluchowski model under conditions where there are only a few pores.

Morphological and chemical evolution of transient interfaces during zinc oxide cold sintering process

Although zinc oxide has a high melting point of 1975 °C, the recent development of the cold sintering process has shown that highly dense polycrystalline ceramics can be obtained at 150 °C or below. As such unusual densification does not yet have fully elucidated underlying mechanisms, this study aims to provide a comprehensive investigation of transient morphological and chemical interfaces during isothermal dwell. The chemical “transient” interface involves the formation of a zinc carboxylate complex by reacting the host zinc oxide powder and acetic acid solution, which is later consumed for the recrystallization on the lattice of an adjacent grain with a decomposition of the complex. Hence, the final outcome can be a residual-free zinc oxide phase. Regarding the morphological evolution, gas physisorption studies were conducted to quantify the area of solid–vapor interfaces and the Schlaffer model was used to analyze the activation energy for specific surface area reduction. Moreover, transmission electron micrographs revealed that the recrystallization occurs at the interface between crystalline grain and carbon-rich amorphous phase. After 30 minutes of isothermal dwell, the area of the amorphous phase was significantly decreased while grain size was increased, potentially indicating the recrystallization-induced grain growth and pore closure. The chemical transition at the zinc oxide surface was further investigated using ReaxFF molecular dynamics simulation, observing that acetate molecule acts as a bridging complex to connect zinc ions to the surface. Overall, understanding the evolution of the transient interface is a crucial subject to obtaining a residual-free cold-sintered sample with desired grain size and properties for application developments.

Structural basis of sodium-dependent bile salt uptake into the liver

The liver takes up bile salts from blood to generate bile, enabling absorption of lipophilic nutrients and excretion of metabolites and drugs1. Human Na+–taurocholate co-transporting polypeptide (NTCP) is the main bile salt uptake system in liver. NTCP is also the cellular entry receptor of human hepatitis B and D viruses2,3 (HBV/HDV), and has emerged as an important target for antiviral drugs4. However, the molecular mechanisms underlying NTCP transport and viral receptor functions remain incompletely understood. Here we present cryo-electron microscopy structures of human NTCP in complexes with nanobodies, revealing key conformations of its transport cycle. NTCP undergoes a conformational transition opening a wide transmembrane pore that serves as the transport pathway for bile salts, and exposes key determinant residues for HBV/HDV binding to the outside of the cell. A nanobody that stabilizes pore closure and inward-facing states impairs recognition of the HBV/HDV receptor-binding domain preS1, demonstrating binding selectivity of the viruses for open-to-outside over inward-facing conformations of the NTCP transport cycle. These results provide molecular insights into NTCP ‘gated-pore’ transport and HBV/HDV receptor recognition mechanisms, and are expected to help with development of liver disease therapies targeting NTCP.

Role of porosity in machinability of additively manufactured Ti-6Al-4V

Despite numerous benefits, the additively manufactured (AM) parts present poor surface quality and dimensional errors, requiring semi-finishing or finishing operations. Machining of AM metals presents multiple challenges due to porosity, anisotropy, microcracks, and uneven layer thickness. This paper studies the role of porosity in the machinability of AM porous Titanium alloy (Ti6Al4V). Microendmilling experiments are conducted using the AM Ti6Al4V with four porosity levels. The machining response is analyzed in terms of machining force, chip morphology, tool wear, and machined surface finish; and compared with that of solid/continuous Ti6Al4V. A new metric has been proposed to quantify and statistically correlate the random variations in the machining force with AM part porosity. At higher porosities, tool chipping increases due to thermo-mechanical shocks as the tool encounters random pore-material boundaries. This results in microburrs and an increase in surface roughness (Ra). The chip and surface morphology show pore closure phenomenon at lower porosity levels, while chip segmentation is observed at higher porosities. Overall, the findings of this research provide valuable insights into the cutting mechanism of AM porous metals. Moreover, the correlation between the machining response and the porosity-driven part quality could be instrumental in in-situ process monitoring/control of hybrid additive-subtractive processes.

Mechanisms and kinetics of pore closure in thick aluminum plate

Interrupted in situ tests at high temperature characterized with X-ray microtomography were employed to study porosity evolution under loading conditions representative of aluminum hot rolling. Coupling digital volume correlation and simulations, it is possible to access, for each pore, its morphological evolution, and the mechanical fields it experienced. The closure kinetics of hundreds of pores were studied, which is described as the pore volume as a function of the hydrostatic integration. Closure kinetics are a function of the shape of the pore. Focus is put on pores with a complex shape which are more detrimental to mechanical properties. Their closure kinetics are exponential due to the pore fragmentation during closure. The closure of complex pores is fostered by an initial orientation perpendicular to the loading direction and a low initial fragmentation. Based on the closure kinetics of 243 complex pores, a new pore closure model is proposed.

Pore closure in thick aluminum plate: From industrial hot rolling to individual pore observation

Pores are often present in large aluminum ingots after casting. To ensure the mechanical reliability of the final thick plates, these pores must be closed during the forming process, hot rolling in the present case. This study aims at understanding the effects of rolling parameters on the volume evolution of pores. To do so, X-ray microtomography is used to track real casting pores during deformation. Nevertheless, thick plates are too large to enable a fine characterization of the evolution of pores during the process. The size and shape of the samples as well as the mechanical boundary conditions must be optimized to meet imaging constraints. This paper focuses on the reproduction of complex loading paths. Multi-scale FE simulations are used to reproduce the loading conditions of thick plate rolling with uniaxial tests on samples of a few millimeters. Uniaxial tests are then characterized with tomography on a synchrotron X-ray beamline. In each sample, tens of pores are individually tracked, giving access to their volume evolution. The local loading path experienced by each pore is determined with FE simulation. It is shown that the volume evolution of a real pore correlates with the hydrostatic integration which is the integral of stress triaxiality along cumulated strain. This confirms that the closure of complex casting pores is enhanced by a high relative reduction and high values of L/H ratio during rolling similarly to what was observed numerically on simpler shapes.

The Influence of Pore Distribution of Coal Char in the Char Fragmentation and Included Minerals Partitioning: A Percolation Modeling

The processes of char fragmentation, including mineral partitioning and particulate matter (PM) formation during dense and porous char combustion, were observed by a site percolation model. This model simulated the diffusion-controlled regime of char combustion, and the size distributions of included minerals in typical bituminous coal were determined by the computer-controlled scanning electron microscope (CCSEM), and the data were put into the char matrix randomly. The model presents the influence of initial pore distribution on char oxidation and fragmentation, the impact of the char conversion process on the extent of fragmentation, the change of ash distributions with the char conversion, and the particulate matters (PM) size distribution, which is derived from the consequence of the competition between char fragmentation and included minerals partitioning and coalescence. The results indicate that with increasing initial char porosity (φ), the number of large size pores increases but the number of pores decreases, which leads to open pores increasing, close pores decreasing, and the surface reaction area increasing. While φ ≥ 0.4, char fragmentation obviously occurs during the stage in which the rates of char conversion are 0.4–0.6, and it looks as though the maximum value of fragmentation will transfer to an earlier conversion stage if it has a larger φ. The enhanced φ shows a positive effect on the increase in the number and concentration of PM < 10 μm (nominally aerodynamic diameter), this is attributed to char fragments more drastically, and the probability of mineral coalescence reduces a lot.

Hysteretic hERG channel gating current recorded at physiological temperature

Cardiac hERG channels comprise at least two subunits, hERG 1a and hERG 1b, and drive cardiac action potential repolarization. hERG 1a subunits contain a cytoplasmic PAS domain that is absent in hERG 1b. The hERG 1a PAS domain regulates voltage sensor domain (VSD) movement, but hERG VSD behavior and its regulation by the hERG 1a PAS domain have not been studied at physiological temperatures. We recorded gating charge from homomeric hERG 1a and heteromeric hERG 1a/1b channels at near physiological temperatures (36 ± 1 °C) using pulse durations comparable in length to the human ventricular action potential. The voltage dependence of deactivation was hyperpolarized relative to activation, reflecting VSD relaxation at positive potentials. These data suggest that relaxation (hysteresis) works to delay pore closure during repolarization. Interestingly, hERG 1a VSD deactivation displayed a double Boltzmann distribution, but hERG 1a/1b deactivation displayed a single Boltzmann. Disabling the hERG 1a PAS domain using a PAS-targeting antibody similarly transformed hERG 1a deactivation from a double to a single Boltzmann, highlighting the contribution of the PAS in regulating VSD movement. These data represent, to our knowledge, the first recordings of hERG gating charge at physiological temperature and demonstrate that VSD relaxation (hysteresis) is present in hERG channels at physiological temperature.

Tuning the High-Pressure Phase Behaviour of Highly Compressible Zeolitic Imidazolate Frameworks: From Discontinuous to Continuous Pore Closure by Linker Substitution.

The high‐pressure behaviour of flexible zeolitic imidazolate frameworks (ZIFs) of the ZIF‐62 family with the chemical composition M(im)2−x (bim)x is presented (M2+=Zn2+, Co2+; im−=imidazolate; bim−=benzimidazolate, 0.02≤x≤0.37). High‐pressure powder X‐ray diffraction shows that the materials contract reversibly from an open pore ( op ) to a closed pore ( cp ) phase under a hydrostatic pressure of up to 4000 bar. Sequentially increasing the bim− fraction (x) reinforces the framework, leading to an increased threshold pressure for the op ‐to‐ cp phase transition, while the total volume contraction across the transition decreases. Most importantly, the typical discontinuous op ‐to‐ cp transition (first order) changes to an unusual continuous transition (second order) for x≥0.35. This allows finetuning of the void volume and the pore size of the material continuously by adjusting the pressure, thus opening new possibilities for MOFs in pressure‐switchable devices, membranes, and actuators.