Changes In Pore Size Research Articles

Structural origin of negative thermal expansion of cordierite honeycomb ceramics and crystal phase evolution with sintering temperature

The structural origin of the negative coefficient of thermal expansion (CTE) along the c-axis in cordierite is investigated using high temperature X-ray diffraction. The evolution of the lattice parameters, bond length, covalent character, and electron density distributions are analyzed with increasing temperature. The increase of covalent character of the tetrahedral bonds in the six-membered hexagonal ring is considered as the possible origin for the negative expansion. In addition, the bridging oxygen can act as a buffer absorbing thermal energy and prevents the increase in M1-O-M2 bond. The electron density distribution indicates that the linking oxygen strongly vibrates transversely across two coordinate M1-O-M2 linkages. The CTE and pore size and distribution change drastically at near 1300 °C due to the substantial increase in cordierite phase proportion and the formation of a liquid phase. Raw materials are consumed completely at 1450 °C and the CTE decreases to 1.3 ppm K−1.

Non-destructive Evaluation of Pore Size and Structural Change in Geopolymer Composite Materials with Added Fibres

This paper introduces a non-destructive method of analysis of the internal structure, occurrence and pore size in a specific volume of geopolymer composite material, with and without the addition of inorganic fibres in the form of meshes using computed tomography. A desktop micro-tomography device Skyscan 1272 was used for visualization and accurate analysis of the interlacing points in the basalt and carbon fibre meshes and for evaluating the adhesion of the fibres to the matrix of the composite material. An appropriate resolution was selected both for displaying the interlacing points in the inorganic fibres and for visualization and analysis of the geopolymer structures. The method makes it possible to evaluate the differences in the structure of the studied materials in a non-destructive way and to check the adhesion of the fibres to the base material.

Effects of biochar addition on soil hydraulic properties before and after freezing-thawing

Biochar as a soil amendment has attracted wide attention worldwide. However, the study of biochar on soil hydraulic properties during freeze-thawing remains insufficient. The purpose of this study was to determine the effect of straw biochar on soil water retention and soil hydraulic conductivity during a freeze-thaw period. Specifically, the effects of different biochar application rates (0, 30, 60, 90 and 120 t·hm−2) on the soil water characteristic curve (SWRCs), saturated hydraulic conductivity (Ksat) and hydraulic characteristic parameters were analysed through field trials. The response relationship between changes in the soil pore size and hydraulic characteristics was explored. The results showed that the combination of biochar amendment and freezing-thawing significantly increased the soil micro pore size (≥0.3–5 μm), soil voids (>100 μm) and total porosity (TP) and thereby improved the soil water retention capacity during the melting period. In addition, the use of biochar can promote the Ksat before and after freezing-thawing. However, increases in the carbon added during the melting period decreased the value of Ksat by 3.89%, 8.12%, 13.02% and 18.14% (p < 0.05) due to blockage of the soil pores by fine carbon particles. Compared with the control treatment, biochar significantly increased the field capacity (FC) and available water content (AWC) in soil. The largest relative change in the FC was obtained with an applied carbon amount of 60 t·hm−2, and this effect would improve the drought resistance capacity of the soil in the spring season. The excessive application of biochar led to an imbalance between the liquid and gas phases in soil, and thus, suggested biochar should not be applied in excess amounts to avoid negative effects on the soil structure. This study revealed the response mechanism of the hydraulic characteristics of the carbon-soil mixture during the freeze-thaw period and can provide a reference for the efficient utilization of soil water resources and the prediction of soil moisture in cold and dry areas.

Factors Influencing the Soil-Water Characteristics of Unsaturated Tropical Silty Sand

Fine grain soils have a complex engineering behaviour which depends but not limited to moisture content, changes in external pressure and characteristics of the pore medium. Sand often contains a considerable percent of silt which is expected to alter its natural behaviour. This composite matrix is referred to as silty-sand. To understand the behaviour of this matrix under varying moisture conditions, some of the factors influencing the soil-water characteristics of unsaturated silty sands were investigated. Representative samples were collected from a river bank after its index properties were predetermined in the laboratory. The samples were compacted at different moisture conditions and compactive efforts. With the pressure plate extractor device, the Soil-Water Characteristic (SWC) was obtained and SWC Curves plotted. Compaction at greater compactive effort (modified proctor) and optimum moisture content produced the largest air entry value and reduced air voids. The air entry values of the soils obtained ranged from 21 kPa to 57 kPa. Also changes in the shape of the SWCC were consistent with changes in pore size which occur by varying compaction conditions. Result shows that soil structure, compaction water content, compactive effort and percentage of fine particles are factors affecting the Soil-Water Characteristics.

Aged PVDF and PSF ultrafiltration membranes restored by functional polydopamine for adjustable pore sizes and fouling control

Hydrophilic polyvinylidene difluoride (PVDF) and polysulfone (PSF) membranes modified by hydrophilic additives such as polyvinylpyrrolidone (PVP) are widely used in various industrial fields. However, the degradation and removal of hydrophilic additives caused by chemical cleaning agents can occur in a short-term aging, which impair the integrity and performances of the membranes. A restoration method is essential for improving the performances of initial aged membranes. In this study, the effects of polydopamine (PDA) coatings on the structural/surface characteristics, the filtration performance and fouling behaviors of aged PVDF and PSF membranes were investigated. Results indicate that the surface properties of aged membranes could be improved by PDA modification. However, the PDA coating structures for PSF and PVDF membranes are different, which are regulated by the different aperture ranges of aged membranes. A mechanism of external and internal PDA restoration for aged membranes with different aperture ranges was introduced. PDA deposited on/in aged PVDF membrane that had large aperture could achieve the synchronous repair of membrane external and pore surface, which not only enhance their surface hydrophilicity (contact angle goes from 80.2° to 58.7°) and zeta potential (from − 23.7 mV to − 30.5 mV at pH 7.5) but also these properties of the pore channel surface and narrow the enlarged pore size simultaneously (the average pore size changes from 220 nm to 170 nm), in turn improved the anti-fouling and rejection performances. By contrast, the PDA was formed as an individual layer on the surface of aged PSF membrane with smaller pore sizes and blocked some pores that showed reduced adsorption and accumulation of foulants on membrane surface, but less reduction of fouling was observed during fouling experiments.

The evolution of pores in thermal barrier coatings under volcanic ash corrosion using X-ray computed tomography

Characterization of the evolution of pores in thermal barrier coatings (TBCs) under volcanic ash (VA) corrosion is essential for assessing coating premature failure. As a nondestructive three-dimensional visualization method, X-ray computed tomography (CT) is used to quantitative investigate the pore structure in ceramic layer. An image morphological method combining Top-Hat and region growing method is applied to separate the pores and background. The change of porosity, pore size and shape resulting from VA corrosion were obtained, which is consistent with the results of mercury infiltration porosimetry (MIP) and scanning electron microscope (SEM).

Use of non-destructive tests to explain manifested pore structure changes in cryogenic concrete

The pore structure serves as a transport medium for external agents that cause concrete deterioration and controls the main properties of concrete. This work utilized non-destructive tests to explain pore structure changes in concrete assessed for direct liquefied natural gas (LNG) containment. It sought to investigate concrete mixture designs that are least susceptible to internal damage during cryogenic cooling. Concrete specimens were prepared using limestone and trap rock as coarse aggregates and river sand as fine aggregate. The effect of air-entrainment was also considered. Microcracking in the concrete specimens was monitored using coupled acoustic emission (AE) sensors during cryogenic cooling and warming. While proton nuclear magnetic resonance (NMR) measurements and x-ray computed tomography (XRCT) imaging were conducted on the specimens before and after the temperature swings. The manifestation of pore structure changes was assessed using water and ‘chloride permeability’ tests. Significant microcracking and changes in NMR porosity and mean pore size, and CT-calculated porosity corresponded to changes in water permeability trend but not ‘chloride permeability’ trend. Air entrainment caused a reduction in chloride penetrability. The results show the utility of the non-destructive tests in explaining pore structure changes in cryogenic concrete and identifies the damage-resistance potential of the concrete mixtures.

Effect of Cold Plasma Treatment of Carbon Nanostructures on the Hydrogen Sorption

Using X-ray diffraction and thermo-programmed desorption, the present study investigated the effect of treatment with pulsed high-frequency discharge in a hydrogen environment on the structure and sorption characteristics of the carbon synthetic nanoporous sorbent SCN (spherical carbonite saturated). Treatment with SCN by a pulsed gas discharge led to chemisorption of 0.4% hydrogen by weight, as well as 1.7 times greater physical sorption of hydrogen. We can assume this increase in sorption capacity is due to changes in the equivalent pore sizes that result from chemical interaction of the carbon atoms of SCN with hydrogen ionized during the discharge process. PACS: 61.43.Gt Powders; porous materials; 52.77.–j Plasma applications; 88.30.R– Hydrogen storage.

Effect of water salinity on the water retention curve of geosynthetic clay liners

The effect of water salinity on the water retention curve of geosynthetic clay liners (GCLs), under constant volume condition is examined. The results indicate that at a constant gravimetric moisture content the total suction increases as the salinity of the wetting liquid increases. Furthermore, the difference in total suction between the GCL hydrated by saline water and distilled water is greater than the difference in the osmotic potential of the wetting water. This behaviour is possibly caused by the matric suction being affected by the expected chemically induced pore size change of the bentonite component of the GCL.

Structure and features determined for pores created with femtosecond laser machining of polymers

A team of researchers characterized how high-density polyethylene acts in the presence of femtosecond laser pulses, including how pore size changes with molecular weight and melt viscosity.

Experimental investigations on the effects of ambient freeze-thaw cycling on dynamic properties and rock pore structure deterioration of sandstone

The issue of rock pore structure deterioration and dynamical mechanical properties has drawn much attention in recent years in the rock engineering community. In this study, a series of 140 freeze-thaw cycling tests are conducted on sandstone samples. The sandstone pore structure after freeze-thaw cycles was detected by Nuclear Magnetic Resonance (NMR), and the dynamic load test was carried out by Split Hopkinson Pressure Bar system (SHPB). The results are: with the increase of freeze-thaw cycles, the saturated mass and porosity of sandstone increase, the dynamic peak stress of sandstone decreases; while the peak strain and total strain increase gradually, and the macroscopic damages of rocks increase. The results of T2 distribution and pore size changes are that the pore sizes of sandstones increase, especially that of micro-pores and macro-pores increase obviously after 140 freeze-thaw cycles. Under the effect of freeze-thaw cycles, the sandstone pores become connected with each other, some of the micro-pores and mini-pores are changed into meso-pores and macro-pores. The number of marco-pores increases evidently, and the largest increase is 197.23%. The rock pore structures have changed, which would lead to the change of mechanic properties. As the number of freeze-thaw cycles increases, the rock dynamical peak stress gradually decreases and the peak strain and the overall strain increase gradually.

Toxic heavy metal ion adsorption kinetics of Mg(OH)2 nanostructures with superb efficacies

Presence of both Cd(II) and Pb(II) ions in water is highly toxic for human health. That is why WHO recommends maximum permissible values of cadmium and lead in drinking water as 0.003 mg.L−1 and 0.01 mg.L−1, respectively. Therefore, here we report for the first time the adsorption kinetics of Mg(OH)2 for adsorptions of Pb(II) and Cd(II). To the best of our knowledge, this is the very first attempt to evaluate the Langmuir and Freundlich isotherms of Mg(OH)2 nanostructures with different morphologies for adsorptions of Pb(II) and Cd(II). The changes in adsorption processes with temperature are also studied. The Mg(OH)2 nanostructures reduce the concentration of Cd(II) ions from as high as 1000 mg.L−1 to as low as 0.001 mg.L−1 and that of Pb(II) ions from as high as 1000 mg.L−1 to as low as 0.009 mg.L−1. These values are much lower than the permissible limits prescribed by WHO. To attain these very significant achievements the time dependent changes in pore size, pore size distribution and surface area are explored. Finally, the results obtained by XRD, FTIR, Raman, pore size, pore size distribution, BET surface area, FESEM, TEM, EDX and adsoption kinetics studies show that nanoplatelet Mg(OH)2 powders exhibit the highest respective adsorption efficacies of 3700 mg.g−1 and 3030 mg.g−1 for Pb(II) and Cd(II). Thus, the nanoplatelet Mg(OH)2 powders may possibly find huge usage in near future for water purification applications.

Controlling external versus internal pore modification of ultrafiltration membranes using surface-initiated AGET-ATRP

The activators generated electron transfer (AGET) method coupled with atom transfer radical polymerization (ATRP) is shown to be a simple and well controlled approach for surface-initiated polymerization of 2-hydroxyethyl methacrylate (HEMA) on regenerated cellulose (RC) membranes. The AGET-ATRP method has been optimized with respect to the initiator concentration, the polymerization reaction time and the reducing agent (activator) concentration. Control of polymer grafting on the external membrane surface versus the internal pore surface of RC ultrafiltration membranes was investigated using different pore filling solvents having a wide range of viscosity and reactivity during ATRP initiator immobilization via acylation of RC hydroxyl groups. The effectiveness of the pore filling solvent in limiting grafting inside the membrane pores was found to depend on both its viscosity and reactivity. Rejection of BSA and dextran was used to probe changes in pore size. Glycerol was found to be the most effective pore filling solvent, indicated by a significant degree of modification of the membrane surface with grafted polyHEMA but only a very minor increase in solute rejection.

Effect of meso- and micropore structures on the hydrogen storage properties of nanoporous carbon materials

We report on the pore structure and hydrogen storage properties of nanoporous carbon (NPC) prepared by KOH activation of rice husk ash. The specific surface area of the NPC increased from 220 to 2770 m2/g with an increase in KOH/rice husk ash weight ratio from 1:1 to 7:1. In addition, the micropore volume of the NPC increased from 0.08 to 0.73 cm3/g with an increase in KOH quantity. Furthermore, the mesopore volume also increased from 0.08 to 2.17 cm3/g. Results of pore size distribution studies indicated NPC pore size widening from the micropore to the mesopore scale with the addition of further KOH. The stored hydrogen content of the NPC therefore increased with the development of the pore structure. From these results, we propose that this change in pore size is responsible for the increase in stored hydrogen content in NPCs.

SNARE Copy Number Determines the Size and Kinetic Properties of Nascent Fusion Pores

The first step in neurotransmitter and hormone release is the formation of a fusion pore. Capacitance measurements revealed that pore size can range from 0.5 to 2 nm in neuroendocrine cells. However, the mechanisms that determine pore size and dynamics are largely unknown due to the low abundance and ephemeral nature of these crucial structures. Here, we reduced the number of available SNAREs in neurons and observed changes in transmitter release suggestive of alterations in fusion pore properties. To address this possibility, we first employed reconstituted nanodisc/liposome-based fusion assays, using optical sensors to detect cargo flux through nascent pores. Ensemble and single vesicle measurements revealed that increasing the number of SNARE complexes enhances the rate of release of a given cargo, and enables the escape of larger cargos. To determine whether this was due to changes in pore size versus stability, we developed a novel reconstitution approach, based on nanodiscs and planar lipid bilayer electrophysiology, that affords µsec time resolution at the single event level. Remarkably, both parameters were affected by SNARE copy number. Increasing the total number of v-SNAREs per nanodisc from three to five caused a two-fold increase in pore size and decreased the rate of pore closure by two orders of magnitude. Moreover, trans-SNARE pairing was dynamic as perturbation of v-/t-SNARE zippering disrupted the stability of fusion pores, particularly at the base of the SNARE complex. In summary, trans-SNARE complexes are metastable and the number of SNAREs recruited to drive fusion dictates fundamental properties of individual pores.

Dynamics and number of trans-SNARE complexes determine nascent fusion pore properties.

SummaryThe fusion pore is the first crucial intermediate formed during exocytosis, yet little is known regarding the mechanisms that determine the size and kinetic properties of these transient structures1. Here, we reduced the number of available SNAREs in neurons and observed changes in transmitter release suggestive of alterations in fusion pores. To address this, we employed reconstituted fusion assays using nanodiscs to trap pores in their initial open state. Optical measurements revealed that increasing the number of SNARE complexes enhanced the rate of release from single pores, and enabled the escape of larger cargos. To determine whether this was due to changes in nascent pore size versus stability, we developed a novel approach, based on nanodiscs and planar lipid bilayer electrophysiology, that affords μsec time resolution at the single event level. Remarkably, both parameters were affected by SNARE copy number. Increasing the number of v-SNAREs per nanodisc from three to five caused a two-fold increase in pore size and decreased the rate of pore closure by more than three orders of magnitude. Moreover, trans-SNARE pairing was highly dynamic: flickering nascent pores closed upon addition of a v-SNARE fragment, revealing that the fully assembled, stable, SNARE complex does not form at this stage of exocytosis. Finally, a deletion at the base of the SNARE complex, that mimics the action of botulinum neurotoxin A, dramatically reduced fusion pore stability. In summary, trans-SNARE complexes are dynamic, and the number of SNAREs recruited to drive fusion determine fundamental properties of individual pores.

Separation of Sucrose and Reducing Sugar in Cane Molasses by Nanofiltration

Recovery of sugars from cane molasses is a promising approach to increase the added value of molasses and reduce its environmental pollution. In this work, for the first time, nanofiltration (NF) was used for the separation of sucrose and reducing sugar in cane molasses by a cascade diafiltration-concentration process. The retention difference between sucrose and reducing sugar by all the tested NF membranes was not distinct at 25 °C, while due to the thermal-induced pore size change and enhanced solute diffusivity, the NF retention behavior changed significantly at 60 °C, and the DL membrane with a sucrose retention of 96% and a reducing sugar retention 5% was selected for the process optimization and modeling. High temperature (55–60 °C), low permeate flux (below 15 Lm−2 h−1), and high sugar concentration resulted in a low retention of reducing sugar due to the dominant diffusive mass transfer, which was desirable for the molasses separation by NF. Mathematical modeling could well predict the diafiltration and concentration processes if using right sugar retention data. The deviations between prediction lines and experimental data in the cross-flow filtration of real solution were mainly caused by the permeate flux variation rather than membrane fouling. After diafiltration, the ratio of sucrose in total molasses sugar increased from 76.1 to 87.9%, while in the permeate of the second concentration step, the ratio of sucrose was only 2.4%. Thus, the retentate of diafiltration could be directly used for sucrose crystallization to avoid the accumulation of reducing sugar and salts, and the permeate of the second concentration step could be concentrated by NF270 at room temperature to produce syrup drinking.

Pore Size Manipulation in 3D Printed Cryogels Enables Selective Cell Seeding

AbstractCryogels are macroporous materials that display remarkable properties, such as high pore interconnection, large surface to volume ratio, and high mechanical stability, making them good candidates for 3D cell culture. However, shaping cryogels remains challenging because of the harsh conditions of synthesis at temperatures as low as −80 °C. In this paper, a solution for the 3D printing of functionalized cryogels is proposed. A microfabricated dispensing probe allowing the last second mixing of cryogel precursors as well as control of the temperature of the extruded material during printing is presented. This dispensing tool allows multilayer 3D printing of cryogels with on demand local pore size change through the control in temperature of the dispensed solution. Moreover, thanks to advanced functionalization of the scaffold, cells can be cultured in 3D within the printed scaffold and exhibited spreading. The ability to tune the pore size of the printed cryogels allows to select during printing where cells will get seeded.

New Method for In-situ Measurement of Pore Size Deformation of Barrier Textiles under Biaxial Loading

The pore size is one of the vital morphological characteristics of barrier fabrics as it decisively affects their permeability and retention properties. Apart from fabric construction and material aspects, the pore size also depends on applied mechanical loads, which occur during typical usage life cycles. Among others, barrier fabrics such as surgical gowns are exposed to loads during their use. These loads have a significant effect on the fabric morphology which influences the permeability properties as well. In this study, a newly developed in situ pore size measurement method was used to measure the changes in pore size that occur in high density barrier woven fabrics under biaxial loadings and after cyclic loading. It was observed that, under tension, pore size distributions changed and mean flow pore sizes increased. Results revealed that the developed in situ measurement method has a great potential for the determination of pore size changes in barrier textiles under biaxial loading.

Autoclaved materials with chalcedonite addition

Silicate products along with autoclaved aerated concrete are a healthy and ecological building material. Silicates and AAC are the effect of the reaction of the components from which they are formed under hydrothermal conditions. This process is called autoclaving from the name of the devices in which it runs. The tests have shown the effect of the tested additives on the particular properties of autoclaved lime-sand products and lime-sand-cement products. The addition of chalcedonite powder increased both the bulk density and compressive strength of lime-sand products and lime-sand-cement products. Composition modifications contributed to changing the microstructure of the products. In the samples with the addition of chalcedonite powder, fuller tobermorite crystals developed in comparison with the traditional sample. Additives contributed to changes in pore structure and size.