Role Of Pore Research Articles

On the application of reduced pressure test for the prediction of ductility of 46000 alloy: Role of pore's morphology and distribution

Bifilms have been proposed to be critical for forming casting defects. The reduced pressure test (RPT) and bifilm index (BI) have been widely studied and used in industry for melt quality assessment. However, the BI remains challenged in predicting the mechanical properties. This work investigated the usage of RPT for elongation prediction by analyzing the melt in two foundries. The results showed that the BI could be valid when the bifilms exist as fully inflated pores. In reality, bifilms present as pores with various morphology and distribution, generating local stress concentrations under tension. Consequently, the parameter areaeff, which considers the pores’ morphology and distribution, was proposed, and the resultant feff showed a good correlation with the elongation of the castings. These results guide the foundry to predict the elongation of the final castings and give directions for further research on the bifilm defects.

Clathrin mediates membrane fission and budding by constricting membrane pores

Membrane budding, which underlies fundamental processes like endocytosis, intracellular trafficking, and viral infection, is thought to involve membrane coat-forming proteins, including the most observed clathrin, to form Ω-shape profiles and helix-forming proteins like dynamin to constrict Ω-profiles’ pores and thus mediate fission. Challenging this fundamental concept, we report that polymerized clathrin is required for Ω-profiles’ pore closure and that clathrin around Ω-profiles’ base/pore region mediates pore constriction/closure in neuroendocrine chromaffin cells. Mathematical modeling suggests that clathrin polymerization at Ω-profiles’ base/pore region generates forces from its intrinsically curved shape to constrict/close the pore. This new fission function may exert broader impacts than clathrin’s well-known coat-forming function during clathrin (coat)-dependent endocytosis, because it underlies not only clathrin (coat)-dependent endocytosis, but also diverse endocytic modes, including ultrafast, fast, slow, bulk, and overshoot endocytosis previously considered clathrin (coat)-independent in chromaffin cells. It mediates kiss-and-run fusion (fusion pore closure) previously considered bona fide clathrin-independent, and limits the vesicular content release rate. Furthermore, analogous to results in chromaffin cells, we found that clathrin is essential for fast and slow endocytosis at hippocampal synapses where clathrin was previously considered dispensable, suggesting clathrin in mediating synaptic vesicle endocytosis and fission. These results suggest that clathrin and likely other intrinsically curved coat proteins are a new class of fission proteins underlying vesicle budding and fusion. The half-a-century concept and studies that attribute vesicle-coat contents’ function to Ω-profile formation and classify budding as coat-protein (e.g., clathrin)-dependent or -independent may need to be re-defined and re-examined by considering clathrin’s pivotal role in pore constriction/closure.

Pitting corrosion characteristics of sintered Type 316 L stainless steel: relationship between pores and MnS

In Type 316 L stainless steel fabricated from gas-atomized powder via spark plasma sintering, lack-of-fusion pores and MnS inclusions were identified as possible pitting initiation sites. Through potentiodynamic polarization with different working electrode areas, the distribution density of the identified pit initiation sites was compared with that of sites found on wrought Type 316 L stainless steel. Surface observations of the sintered Type 316 L after polarization suggest that pitting corrosion was initiated at a location where both MnS and pores existed. By reducing the porosity and removing MnS, the roles of pores and MnS inclusions in the initiation of pitting corrosion were investigated.

The role of pores in structure of polyethylenglycol diacrylate based‐inverse opal photonic crystal in binding protein applicable to optical biosensor

AbstractHere, the role of pores in the structure of inverse opal photonic crystals (IOPC) in binding proteins in comparison with their parent photonic crystal (PC) templates has been investigated. For this purpose, polyethyleneglycol diacrylate (PEGDA) coated with SiO2‐based PC (PEGDA/SiO2‐based PC) and PEGDA‐based IOPC were attached with fluorophore Alexa 488, which is a polyclonal secondary antibody, to investigate their fluorescence emission. Scanning electron microscopy (SEM) images showed face centered cubic (fcc) packing of the PEGDA/SiO2‐based PC. And it remained after the formation of PEGDA‐based IOPC. The presence of 3‐aminopropyl triethoxysilane (APTES) and Alexa 488 that immobilized the PEGDA‐based PC and PEGDA‐based IOPC was recognized by the appearance of bands at 850, 1175, and a dominant increase in the band at 1750 cm−1. Those were attributed to (N─H) wagging, (C─N) stretching, and (C═O) stretching vibrations, respectively. Reflectance spectra showed a blue shift of the Bragg photonic band gap of the PEGDA‐based IOPC in comparison with that of the PEGDA/SiO2‐based PC. The fluorescence images showed a significant increase in the fluorescence intensity of PEGDA‐based IOPC owing to the resonance effect. These obtained results indicated the role of pores in structure of PEGDA‐based IOPC in improvement of the attachment of Alexa 488 protein.

The role of pores in micro-zone distribution of Cd in a tropical paddy soil: Results from X-ray computed tomography combined energy dispersive spectroscopy analysis

Accurate description of Cd micro-zone distribution and accumulation is the prerequisite for revealing Cd transfer and transformation processes. However, to date, the role of soil pores in the Cd micro-zone distribution characteristics in undisturbed soil is still unclear. In this study, the obvious heterogeneous distribution of Cd in and around the soil pores at the cross-sectional surface of the tropical undisturbed topsoil was visualized by the combination of X-ray micro-computed tomography and scanning electron microscope-energy dispersive spectroscopy. For both the air space and water-holding pores, the micro-zone distribution characteristics of Cd around the pores were dominated by pore sizes. For macropores and mesopores, Cd preferred to distribute in the micro-zone within 167.5–335 µm from pores. But for micropores, the highest content percentage of Cd was exhibited in the micro-zone within 67–167.5 µm from pores. The random forest model revealed that the occurrence of Fe (13.83%) and P (13.59%) contributed most to Cd micro-zone distribution around air space pores. While for water-holding pores, Fe occurrence (18.30%) contributed more significantly than P (11.92%) to Cd micro-zone distribution. Our study provided new insights into Cd retention mechanism, which is help for accessing Cd migration and transformation.

Pore scale numerical investigation of counter-current spontaneous imbibition in multi-scaled pore networks

The multi-scaled pore networks of shale or tight reservoirs are considerably different from the conventional sandstone reservoirs. After hydraulic fracturing treatment, the spontaneous imbibition process plays an important role in the productivity of the horizontal wells. Applying the color-gradient model of Lattice Boltzmann Method (LBM) accelerated with parallel computing, we studied the countercurrent spontaneous imbibition process in two kinds of pore structures with different interlacing distributions of large and small pores. The effect of geometry configuration of pore arrays with different pore-scale and the capillary number Ca on the mechanism of counter-current spontaneous imbibition as well as the corresponding oil recovery factor are studied. We found that the wetting phase tends to invade the small pore array under small Ca in both types of geometry configurations of different pore arrays of four pore arrays zones. The wetting phase also tends to invade the pore array near the inlet for injecting the wetting phase no matter if it is a large pore array or small pore array except for the situation when the Ca is large to a certain value. In this situation, the small pore arrays show resistance to the wetting phase, so the wetting phase doesn't invade the small pore near the inlet, but invades the large pore preferentially. Both the geometry configurations of different pore arrays and Ca have a significant effect on the oil recovery factor. This work will help to solve the doubt about the selectivity of the multi-scaled pores of the wetting phase and the role of pores with different sizes in imbibition and oil draining in countercurrent spontaneous imbibition processes.

Discrimination between Pore and Throat Resistances against Single-Phase Flow in Porous Media

This study investigates the critical agents that cause non-Darrian flow in porous media. Four porous media different in morphology but similar in topology were studied numerically. By varying the throat diameters, the distinct roles of pores and throats in total dissipation were investigated using direct numerical simulation. Forchheimer model was selected to analyze the non-Darcian flow. In our simplified geometry, the ratio KappKD can best be correlated by non-Darcy effect (E). Total dissipation is directly related to the porous medium resistance against fluid flow. The energy dissipated in pores and throats was calculated by summing the dissipation in each computational segment. Pores are more prone to disobey the Darcy model than throats due to irregularity in fluid flow, and they are introduced as the cause of Darcy-model cessation. By increasing the pore-to-throat ratio, the non-Darcian flow in the pores begins sooner. The results show that the energy dissipation due to eddies is negligible. The dissipation in pores and throats was simulated through separate power-law equations, and their exponents were also extracted. The exponent for the pore body is equal to two when the viscous forces are dominant, and it increases by increasing the inertia force. The dissipation due to pore bodies is more apparent when the size of pore and throats are of the same order of magnitude. The relative losses of pore body increase as the velocity increases, in contrast to throats.

A scanning electron microscopy study of projectile entry fractures in cortical bone; genesis and microarchitectural features

The present paper presents a scanning electron microscope (SEM) analysis of the genesis and microarchitecture of experimentally induced cortical entry fractures in porcine scapulae impacted at velocities ranging from 54 to 897 m/s. SEM observation was conducted on polyurethane replicas cast from negative silicone moulds. Analysis of the sequence of fracture processes operative during projectile impact revealed the presence of ring cracks at the site of impact, confirming that penetration in sandwich bones is achieved by cone crack propagation. Despite impulsive loading, two forms of plastic deformation were identified in the cortical bone surrounding the entry fracture up to a maximum velocity of 871 m/s. Microscopic radial and concentric cracks were associated with projectile impact, and the role of pores and pits as stress concentrators was captured. Possible underlying mechanisms for the observed plastic deformation are described, and the diagnostic utility of SEM analysis is presented.

Effect of dominated coal pores and fractures on water migration after low-pressure water injection based on CT images

A computational model for water migration in porous media is developed based on the CT images of coal samples to study the effect of dominant pores and fractures on water migration after low-pressure water injection. The pore and fracture structure in this model is regarded as porous media with a porosity ratio close to 1, and the fluid exchange between the pores and fractures and the matrix area is considered. The effect of pore and fracture structure on water migration is determined through numerical solution. Results show that the velocity of the fluid flowing into the matrix from the corner of the fracture increases significantly. Moreover, the efficiency of water migration in the radial fractures is high, and water tends to flow to the radial fractures. The pores mainly play a role in quickly absorbing and efficiently transporting water. The non-connected pores can increase the range of water migration and should not therefore be ignored. The role of pores and fractures in dominating water migration is most obvious at the front edge of water migration. The water migration is divided into three stages: high-velocity, transitional, and low-velocity migration stages. In addition, the distance difference between the saturation contours of water migration has a logarithmic relationship with time, and the macro fractures around the boreholes cause the increase in the distance difference between the two saturation contours.

Dielectric breakdown behavior of ferroelectric ceramics: The role of pores

Dielectric breakdown is a fundamental issue for ferroelectric ceramics. In this work, a phase-field method is introduced to study the breakdown behavior of ferroelectric ceramics with pores randomly distributed. Effects of the position and the size of pores on the breakdown behavior are analyzed. Results indicate that the position of pores, for example in grains or at grain boundaries, has a significant influence on the breakdown strength of ferroelectric ceramics. The nominal breakdown strength of ferroelectric ceramics with 2 % pores at grain boundaries is almost 50 % higher than 2 % pores in grains. Further, for ferroelectric ceramics with a certain porosity, the smaller the pore size, the higher the breakdown strength. As the nominal pore size decreases from 2.5 to 1, the nominal breakdown strength is enhanced from 0.73 to 1.16. Such results agree well with the widely accepted Gerson-Marshall model and previously published experimental observations.

Silicon carbide sintered by magnesium additive: role of pores

Silicon carbide ceramics were prepared by hot press sintering using Mg additive. Pores are observed on boundaries between particles, grains, and substructures. The microstructures and pores in the ceramics were observed. Results show that pores between particles mainly located on boundaries along the major axis of elongated particles. Micronecks formed between particles in the initial stage, which divide voids between particles into micropores. The initial micronecks and pores are generous to distribute along the major axis of elongated particles. Pores shrunk in the intermediate stage then coarsened. Equiaxed nanopores are formed on grain boundaries between abnormal growth grains and normal grains. Elongated nanopores are formed adjacent to high-density defects.

Hot isostatic pressing in metal additive manufacturing: X-ray tomography reveals details of pore closure

Hot isostatic pressing (HIP) of additively manufactured metals is a widely adopted and effective method to improve the density and microstructure homogeneity within geometrically-complex metal structures fabricated with laser powder bed fusion (LPBF). The role of pores in the fatigue performance of additively manufactured metal parts is increasingly being recognized as a critical factor and HIP post-processing is now heralded as a method to eliminate pores, especially for high-criticality applications such as in the aerospace industry. Despite the widely reported positive influence on fatigue performance and high efficiency of pore closure, examples have been reported in which pores have not been entirely closed or have subsequently re-opened upon heat treatment. A variety of porosity distributions and types of pores may be present in parts produced by LBPF and the effectiveness of pore closure may differ depending on these pore characteristics. In this work, X-ray tomography was employed to provide insights into pore closure efficiency by HIP for an intentional and artificially-induced cavity as well as for a range of typical process-induced pores (lack of fusion, keyhole, contour pores, etc.) in coupon samples of Ti6Al4V. The same samples were imaged non-destructively before and after HIP and aligned carefully for side-by-side viewing. High pore closure efficiency is demonstrated for all types of cavities and pores investigated, but near-surface pores of all types are shown to be problematic to varying degrees, in some cases perforating the superficial surface and creating new external notches. Subsequent heat treatments (annealing after HIP) in some cases resulted in internal pore reopening for previously closed internal pores as well as a new “blistering” effect observed for some near-surface pores, which the authors believe is reported for the first time. Implications of these results for quality control and HIP processing of LPBF parts are discussed. Finally, the utility of using HIP to consolidate intentionally-unmelted powder in order to improve production rates of powder bed fusion has great potential and is preliminarily demonstrated.

Role of Pore and Pore‐Throat Distributions in Controlling Permeability in Heterogeneous Mineral Dissolution and Precipitation Scenarios

AbstractMineral dissolution and precipitation reactions can significantly alter the porosity and permeability of porous media. While porosity generally increases with dissolution and decreases with precipitation, permeability is controlled by the spatial locations of reactions in discrete pores and pore throats and in the greater pore network. Geochemical reactions have been observed to occur both uniformly and nonuniformly in porous media, driven by parameters such as mineral distribution, grain size, and Peclet and Damkohler numbers. Pore network modeling can be used to simulate the impact of pore‐scale alterations on permeability, requiring only pore and pore‐throat size distributions and pore connectivity. Here, the impact of variations in pore and pore‐throat size distributions on reactive permeability for uniform and nonuniform spatial distributions of reactions is evaluated. A series of pore network models are created and populated with pore and pore‐throat size distributions of varying types (skewed, normal, and uniform) to represent differences in network topology and characterization methods. The impacts of these distributions on reactive permeability are then simulated for uniform and nonuniform reaction conditions by increasing or decreasing pore and pore‐throat sizes in a prescribed manner to reflect dissolution and precipitation, respectively. Overall, simulations reveal that porosity‐permeability evolution varies with reaction scenario and is qualitatively consistent for the different pore and pore‐throat size distributions. Common macroscopic porosity‐permeability relationships work well for some reaction scenarios but are unable to reflect size‐dependent reactions. A new modified version of the Verma‐Pruess relationship is created and able to successfully reflect the porosity‐permeability evolution for size‐dependent reactions.

Phase transformation and energy dissipation of porous shape memory alloy structure under blast loading

Porous shape memory alloy (SMA) materials being porous structures combined with the behaviors of SMA material can offer tremendous potential for future energy absorbing structural components. Although several studies have been performed in recent past to examine the influence of pores towards phase transformation, they are limited to quasi-static loading conditions. Investigation of phase transformation and associated energy dissipation for porous structural component made of SMA materials is highly necessary for impact/blast loading. Therefore, using explicit finite element method, a predictive modeling framework is developed to solve the governing equations. A forward Euler algorithm is utilized to implement the thermo-mechanical constitutive model of SMA. Several porous SMA structures are idealized with array of macroscopic pores embedded in SMA plates. Parametric studies are performed to investigate the influence of pore sizes and arrangement on phase transformation behaviors and energy dissipation characteristics. The results provide key insights on the role of pores and their interaction in energy dissipation for SMA structures.

The role of pores and microstructural heterogeneity on the tooth root fatigue strength of sintered spur gears

The automotive industry employs a considerable amount of sintered parts, mainly as transmission and engine components. Gears are the parts that mostly benefit, in terms of cost saving, from the near net shape P/M technology. However, the porosity along with the heterogeneous microstructure can detrimentally affect the mechanical behaviour, especially the fatigue strength. The possibility of increasing sintered density up to 90% and more, the use of high strength alloys, as well as post sintering treatments have been extensively investigated obtaining consistent increases in the fatigue strength. The present study focuses on the effects of porosity and microstructure on tooth root bending fatigue of small module spur gears. The aim is to investigate the synergistic contribution of pore morphology and microstructure heterogeneity to the initiation of fatigue cracks and to the following crack paths. High density parts produced by high strength pre-alloyed powders were studied. Part of the specimens was case-hardened to obtain a martensitic/bainitic microstructure in the surface layer. Bending fatigue tests up to a fatigue endurance of three million cycles were performed. A careful fractographic analysis was conducted. The obtained results were discussed using the fracture mechanics approach of Murakami, considering the pores as pre-existing defects, whose propagation strongly depends on the microstructural heterogeneity.

Characterization and distribution of mechanically competent mineralized tissue in micropores of β-tricalcium phosphate bone substitutes

Although bone formation around and within implants has been intensively studied, the role of pores and pore geometry is still debated. Notwithstanding studies reporting the formation of bone and bone components within pores as small as a few micrometers (‘micropores’), bone ingrowth is believed to only occur in pores larger than 100 μm (‘macropores’). A thorough analysis of 10 different porous β-tricalcium phosphate cylinders (O: 8 mm; L: 13 mm) implanted for 2–24 weeks in an ovine model demonstrates ingrowth of mineralized tissue (MT) in pores as small as 1 μm. This tissue contained calcium phosphate, collagen, and interconnected cells. It formed within the first 3–4 weeks of implantation, extended over several hundred micrometers within the ceramic, and contributed to the majority of the early MT formation (including bone) in the defect. The indentation stiffness of the MT-ceramic composite was significantly higher than that of bone and MT-free ceramic. The presented results substantiate the importance of micropores for optimal bone healing, particularly at early implantation times.

INVESTIGATION OF ENVIRONMENTAL IMPACTS ON SANDSTONE BLOCKS AT LUXOR TEMPLE AND CONCEPTS FOR CONSERATION

Sandstone blocks were used in the construction of Luxor temple. However, they, especialy cement materials, were at a great risk because of being affected by various deterioration factors. Groundwater started to rise in and around the temple, causing serious deterioration aspects of the blocks. Therefore, the current study was conducted to focus on the role of pores and cement regarding the deterioration process of sandstone blocks in the temlpe. In order to conduct systematic investigation, it adopted SEM – EDX, PLM and XRD. Also, physical and mechanical properties were examined toevaluate the components of the sandstone, under the present environmental conditions. It also interpreted the nvestigations of onsite evaluation tests (non- and less-destructive). It also focused on other methods, e.g. humidity and salt analysis. The study ended develops some recommendations that fit sandstone address in Luxor Temple.

Synthesis and characterization of porous maghemite as an anode for Li-ion batteries

The synthesis of porous maghemite via a simple glycerol-mediated solution method was successfully accomplished. Thermal analysis, X-ray diffraction and Mössbauer spectroscopy results disclosed the formation of maghemite. The morphological and structural features of maghemite were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and nitrogen adsorption–desorption. The powder showed Brunauer–Emmett–Teller surface area of 285m2g−1 with micro-, meso- and macropores.The anode body was doctor bladed using primary powder with a binder and a conductive agent. Galvanostatic charge–discharge cycling of the porous maghemite exhibited a specific reversible capacity of approximately 1180mAhg−1 at 100mAg−1 current density, which was two times higher than that of common nanomaghemite with average particle size of 19nm. The cell showed stability even at the high current charge–discharge rates of 3000mAg−1 and more than 94% retention. After multiple high current cycling regimes, the cell recovered to nearly full reversible capacity of ~1120mAhg−1 at 100mAg−1. The reason for this remarkable performance of the present anode was thought to be dependent upon the role of pores in increasing the surface area and resistance against volume changes during lithium insertion/extraction.

Study of durability of Portland cement mortars blended with silica nanoparticles

In this paper the effects of nanosilica (NS) on porosity, capillary suction (UNE 8398:2008), compressive strength (ASTM C 349), and sulfate resistance (ASTM C 1012) were evaluated for mortars made with Portland cement (control) and partially replaced with a commercial NS suspension, in percentages by weight of 0%, 1%, 3%, 5%, and 10%. Mortars with a water/binder (w/b) ratio of 0.55 and addition of superplasticizer, for flow correction, were prepared. NS showed that, it has an important role in pore refining, decreasing the total volume of pores and their diameters. Samples containing NS showed an important positive effect on the capillary suction and sulfate resistance. In the case of expansion due to sulfate attack, mortars with 5% and 10% of NS decreased expansion by 90% and 95% respectively after 2years of immersion.

Effects of phosphorus concentration on Cr(VI) sorption onto phosphorus-rich sludge biochar

To investigate effects of phosphorus content on Cr(VI) sorption onto phosphorus-rich biochar, sewage sludge of different phosphorus concentrations from 4 to 60 mg·g−1 by dry weight were prepared and carbonized to make biochar for batch sorption experiments. Test results revealed that different phosphorous concentration of raw sludge had respective impacts on surface area, pore surface area, average pore diameter and pH value of derived biochar. The adsorption kinetics of phosphorus-rich biochar could be described by the pseudo-second-order model. The sorption isotherm data followed Langmiur model better than Freundlich model. Biochar produced from sludge with phosphorus concentration of 20 mg·g−1 gave the largest chromium sorption capacity, which could be attributed to its largest surface area and pores surface area comparing with those of biochars from sludge with other phosphorus concentrations. The chromium loaded biochar was analyzed using Fourier Transform Infrared Spectroscopy and X-ray Diffraction measurement. The results indicated that chemical functional groups hydroxyl and methyl on surface of biochar were involved in Cr(VI) binding and its reducing to Cr(III). Then, a portion of Cr (III) in form of various phosphate precipitates was bound onto biochar surface and the rest was released into the solution. The experimental results suggested that phosphorus played an important role in pore and surface area development of sludge biochar during pyrolytic process. It also could react with Cr(III) on the biochar surface that impacted on capacity of Cr(VI) removal from solution by sludge biochar. Therefore, phosphorus concentration in sludge should be considered when sludge pyrolytic residue would be reused for heavy metals sorbing.