Elongated Pores Research Articles

Multiscale analysis of carbon/carbon composite pores based on X-ray computed tomography

Pore defects formed during the impregnation and carbonization of carbon/carbon (C/C) composites were investigated. X-ray computed tomography (XCT) was used to analyze the pore characteristics of C/C composites during liquid-phase impregnation and carbonization (LIC), highlighting the pore structural evolution from impregnation to carbonization and the resultant porous morphology. The porosity, pore location, pore size, and pore shape of the samples were subjected to quantitative analysis. At the micro-scale within the fiber bundles, the pores exhibited an ellipsoidal and elongated shape. In the impregnated samples, the pores were all isolated, and the ellipsoidal and elongated pores accounted for the majority of the pores, but their volume accounted for less than 9 % of the total pore volume. At the macro-scale, pores were predominantly distributed along the surfaces of fiber bundles and between layers, representing the primary form of pore distribution. Analysis of the carbonized samples showed that elongated pores within fiber bundles extended along both the fiber depth and radial directions. Macroscopic pores between fiber bundles and layers extended along the fiber bundle surfaces. The carbonization process caused the micro- and macro-pore spaces to interconnect to form connected pores, which accounted for 79 % of the total pore volume, while the ellipsoidal and elongated pores in the isolated pores accounted for less than 18 % of the total pore volume, forming a porous medium.

Constructing hierarchically elongated porous structure in ultrathin ultrahigh molecular weight polyethylene membrane: Achieving high selectivity with remained permeability

Anisotropic pores with a high aspect ratio exhibit higher permeability as well as selectivity than circular pores. Herein, highly selective porous membranes exhibiting elongated slit-like pores and disk-like interlayer large pores are fabricated successfully by biaxial stretching and further constrained uniaxial stretching of ultrahigh molecular weight polyethylene gel films. The thickness and the surface roughness of the porous membrane decrease, and the pore size distribution become narrow during biaxial stretching, while the porous structure become elongated during constrained uniaxial stretching. The thickness decreases from 173.23 μm to 2.33 μm, which reduces the resistance to water passage and then increases the water permeability from approximately 540 L/ (m2 h bar) to 780 L/ (m2 h bar). Due to the presence of mineral oil, the porosity is maintained and even high ratios of constrained uniaxial stretching do not close the pores. The elongation of the porous structure resulted in a significant reduction of the membrane pore size. At a total stretching ratio of 144 times, the pore size of the porous membrane with only biaxial stretching is 0.098 μm, while that of the porous membrane with biaxial stretching and further constrained uniaxial stretching is 0.048 μm. The separation accuracy and stability of the porous membrane improve distinctly, ascribing that the small pore size can reject small particles and prevent the particles from entering the membrane. This study provides one novel strategy to regulate the porous structure of porous polymer membranes for improving the separation efficiency.

Porous ceramics derived from steel slag/coal gangue mixtures using cigarette butts as the pore‐forming agent

AbstractFabrication of ceramic materials with interconnected pores is necessary to improve thermal energy storage efficiency in high‐temperature infiltration technology. In the present study, industrial wastes such as coal gangue, steel slag, etc., were selected as the raw materials to prepare ceramics with interconnected pores. By adopting 50% cigarette butts as the pore‐forming agent, steel slag–coal gangue mixtures with a mass ratio of steel slag to coal gangue of 1:9 were sintered at 1100°C, and ceramics with interconnected elongated pores were prepared successfully. The highest apparent porosity and lowest volume density of the as‐prepared ceramics were ca. 73% and .74 g/cm3, respectively. Further measurements of the thermophysical properties indicated that no obvious mass loss was observed in the temperature range from ambient temperature to 800°C. The maximum values of specific heat and thermal conductivity were 1.38 J/(g K) and 1.661 W/(m K), respectively, and meanwhile the minimum compressive strength could exceed 3.5 MPa. These research results implied that the as‐prepared steel slag–coal gangue ceramics can provide long‐term service and offer excellent thermal stability over a wide temperature range. Therefore, they should have potential applications in high‐temperature infiltration technology.

Micro-karstification in a stalagmite, Küpeli Cave, southern Turkey

This article deals with micro-karstification forming abundant dissolution features in a stalagmite from Küpeli Cave in southern Turkey. Dissolution occurs when cave water enriched with CO2 from the atmosphere and soil seeps into the stalagmite. Water is transmitted from the surface of the stalagmite to the interior by the roughly vertical or diagonal notch-shaped pores formed by the enlargement of intercrystalline pores by dissolution. These slightly elongated pores appear embedded in different parts of the stalagmite and characterize different stages of dissolution during the stalagmite formation. Later, when this water reaches the relatively more permeable growth layer surfaces, it flows along these surfaces, and diffuse dissolution features form. These features include micro-scale pitted and etched surface structures, rounded and enlarged crystal boundaries and intercrystalline pores, and the breakdown of relatively large crystals into small crystals (micritization). When the percolating water is sufficiently saturated with calcium carbonate in the stalagmite, secondary calcite precipitation occurs as rim and pore-filling cements within the pores formed as a result of dissolution. In general, dissolution and calcite re-precipitation as cement are early diagenetic events and occur at different stages of stalagmite development due to seasonal variation in CO2 and CaCO3 contents of the water in the epikarst zone and within the stalagmite. These conditions were probably provided during the wet season.

Linking pore structure characteristics to soil strength and their relationships with detachment rate of disturbed Mollisol by concentrated flow under freeze–thaw effects

In mid-high latitude areas, seasonal freeze–thaw cycles generate significant effects on pore structure of soils, and in turn, affect soil mechanical properties and soil erosion processes. Furthermore, soil particles can be detached on ridged farmland by snowmelt or rainfall concentrated flow due to topographic relief during the spring snowmelt period. To explore the changes in pore structure characteristics under freeze–thaw effects on soil detachment rates under simulating concentrated flow, fifteen soil columns and twenty soil tanks underwent a freeze–thaw pre-treatment of zero, one, five, ten, and fifteen cycles. Soil structure characteristics were quantitatively obtained by scanning soil columns with industrial computer tomography at a 25-μm resolution. Soil strength was measured by a portable vane shear instrument on the surface of soil tanks. Detachment rates of soil tanks were measured in a flume under changeless flow shear stress (τ = 2.32 Pa). Results indicated that freeze–thaw effects significantly decreased soil strength by changing pore network structure, including increasing total imaged porosity and elongated-pore porosity. The detachment rate significantly rose with the rising freeze–thaw cycles (p < 0.05) and had a power relationship with the soil strength (R2 = 0.503, p < 0.05). Thus, the increase in detachment rate was mainly caused by the decrease in soil strength, which is dependent on large and elongated pores that formed during freeze–thaw cycles and on the geometrical characteristics of the pore network. The findings improve the understanding of the generation mechanism of soil erosion as a result of changes in pore structure characteristics during the spring snowmelt period.

Capillary flow in Y-shaped junctions with open- and closed-end branches

The capillary flow in asymmetric junctions can delay the liquid invasion of the wide branch, which has important implications for the liquid imbibition in porous media with elongated pores. For the capillary flow in Y-shaped junctions with two open-end branches of different radii, the delay time of the liquid invasion of the wide branch depends on the pressure at the junction. In Y-shaped junctions with open- and closed-end branches, the gas compression in the closed-end branch is required for determining the pressure at the junction. A closer investigation of the capillary flow in such junctions is necessary to predict the liquid imbibition in porous media that comprise continuous and discontinuous elongated pores. This study presents a theoretical model considering the effect of gas compression in closed-end branches and analyzes this effect on the capillary-flow dynamics. The analytical results obtained suggest that the initiation of capillary flow in the open-end wide branch is governed by the trapped-gas pressure in the closed-end narrow branch. In this case, the delay time of the liquid invasion of the open-end branch decreases with a decrease in the length of the closed-end branch; this is because the decreased length causes the pressure difference at the junction to approach that at the liquid–gas interface in the open-end branch early. Additionally, for open- and closed-end branches, the velocity of capillary flow in the open-end branch increases because the volume rate of flow in the closed-end branch decreases owing to the increase in the trapped-gas pressure in this branch.

Effect of surface roughness and industrial heat treatments on the microstructure and mechanical properties of Ti6Al4V alloy manufactured by laser powder bed fusion in different built orientations

The emergence of powder bed fusion in recent years has made it one of the most demanded additive manufacturing technologies for Ti6Al4V alloys in the biomedical and aerospace industries due to its ease of part fabrication with complex geometry. However, Ti6Al4V components require a post-processing treatment to optimize their mechanical properties for engineering applications. The present study offers an analysis of the effects of different industrial heat treatments (704 °C for 120 min, 740 °C for 130 min) on the microstructure and tensile properties of Ti6Al4V samples manufactured by laser powder bed fusion in different orientations (Z, 45°, XY and XZ). These heat treatments were selected to improve the mechanical properties of the as-built material and to obtain samples representative of real industrial applications. SEM observations illustrated that the α’ martensite grown in the columnar parent β-grains was converted into an α+β mixture after both heat treatments. EBSD showed that the newly formed α phase maintained, inside the parent β grains, the same orientation relationship as the as-built α′ martensite. However, on a macroscopic scale, the α phase exhibited no preferential orientation. The heat-treated samples, which exhibited approximately 10% lower ultimate tensile strength and yield strength than the as built samples but a 10–13% higher elongation, were practically isotropic in their mechanical response. What little anisotropy was left was mainly attributed to few elongated interlamellar pores. The sandblasting process was also investigated; it did not affect the static mechanical properties of the samples but it reduced the Ra values by 25%. Finally, Vickers microhardness vs. strength relationships were studied by considering the α-phase orientation.

The influence of structural properties on the adsorption capacities of microwave-assisted biochars for metazachlor removal from aqueous solutions

Biochars, carbonaceous materials prepared without the usage of chemical agents, are porous materials capable of adsorbing pollutants from ground- and surface waters. In this study, biochars prepared from various types of agricultural biomass were tested for the adsorptive removal of herbicide metazachlor from an aqueous environment. Banana wastes, red mombin seeds, corncob, cocoa pod husk, and coffee husk were used as precursors. Biochars were prepared with the aid of microwave treatment. The effect of precursor type on structure and adsorption was examined. Adsorption was controlled by a multistep mechanism, adsorption kinetics followed predominantly the pseudo-second-order model, adsorption isotherms suited to both Langmuir and Freundlich isotherms, depending on the particular biochar. Significant differences between the structural properties and adsorption capacities of the examined biochars were observed. The best adsorption properties for metazachlor uptake were observed for banana waste-based biochar, which had large, elongated pores, highest volume of micropores and one of the highest contents of polar functional groups. The maximum adsorption capacity, calculated from Langmuir isotherm, was 146.01 mg·g−1, The adsorption capacity at equilibrium, obtained by kinetic measurements, was 27.25 mg·g−1, the kinetic constant was 5.14·10−3 dm3·min−1 (both calculated from pseudo-second order model). Molecular modeling revealed that metazachlor molecules preferably entered two layer wide cavities containing one COOH group with their pyrazole rings.

Modulating the Pore Architecture of Ice-Templated Dextran Microparticles Using Molecular Weight and Concentration.

Spray freeze drying (SFD) is an ice templating method used to produce highly porous particles with complex pore architectures governed by ice nucleation and growth. SFD particles have been advanced as drug carrier systems, but the quantitative description of the morphology formation in the SFD process is still challenging. Here, the pore space dimensions of SFD particles prepared from aqueous dextran solutions of varying molecular weights (40-200 kDa) and concentrations (5-20%) are analyzed using scanning electron microscopy. Coexisting morphologies composed of cellular and dendritic motifs are obtained, which are attributed to variations in the ice growth mechanism determined by the SFD system and modulation of these mechanisms by given precursor solution properties leading to changes in their pore dimensions. Particles with low-aspect ratio cellular pores showing variation of around 0.5-1 μm in diameter with precursor composition but roughly constant with particle diameter are ascribed to a rapid growth regime with high nucleation site density. Image analysis suggests that the pore volume decreases with dextran solid content. Dendritic pores (≈2-20 μm in diameter) with often a central cellular region are identified with surface nucleation and growth followed by a slower growth regime, leading to the overall dendrite surface area scaling approximately linearly with the particle diameter. The dendrite lamellar spacing depends on the concentration according to an inverse power law but is not significantly influenced by molecular weight. Particles with highly elongated cellular pores without lamellar formation show intermediate pore dimensions between the above two limiting morphological types. Analysis of variance and post hoc tests indicate that dextran concentration is the most significant factor in affecting the pore dimensions. The SFD dextran particles herein described could find use in pulmonary drug delivery due to their high porosity and biocompatibility of the matrix material.

The application of human periodontal ligament stem cells and biomimetic silk scaffold for in situ tendon regeneration

BackgroundWith the development of tissue engineering, enhanced tendon regeneration could be achieved by exploiting suitable cell types and biomaterials. The accessibility, robust cell amplification ability, superior tendon differentiation potential, and immunomodulatory effects of human periodontal ligament stem cells (hPDLSCs) indicate their potential as ideal seed cells for tendon tissue engineering. Nevertheless, there are currently no reports of using PDLSCs as seed cells. Previous studies have confirmed the potential of silk scaffold for tendon tissue engineering. However, the biomimetic silk scaffold with tendon extracellular matrix (ECM)-like structure has not been systematically studied for in situ tendon regeneration. Therefore, this study aims to evaluate the effects of hPDLSCs and biomimetic silk scaffold on in situ tendon regeneration.MethodsHuman PDLSCs were isolated from extracted wisdom teeth. The differentiation potential of hPDLSCs towards osteo-, chondro-, and adipo-lineage was examined by cultured in different inducing media. Aligned and random silk scaffolds were fabricated by the controlled directional freezing technique. Scaffolds were characterized including surface structure, water contact angle, swelling ratio, degradation speed and mechanical properties. The biocompatibility of silk scaffolds was evaluated by live/dead staining, SEM observation, cell proliferation determination and immunofluorescent staining of deposited collagen type I. Subsequently, hPDLSCs were seeded on the aligned silk scaffold and transplanted into the ruptured rat Achilles tendon. Scaffolds without cells served as control groups. After 4 weeks, histology evaluation was carried out and macrophage polarization was examined to check the repair effects and immunomodulatory effects.ResultsHuman PDLSCs were successfully isolated, and their multi-differentiation potential was confirmed. Compared with random scaffold, aligned silk scaffold had more elongated and aligned pores and promoted the proliferation and ordered arrangement of hPDLSCs. After implantation into rat Achilles tendon defect, hPDLSCs seeded aligned silk scaffold enhanced tendon repair with more tendon-like tissue formation after 4 weeks, as compared to the scaffold-only groups. Higher expression of CD206 and lower expression of iNOS, IL-1β and TNF-α were found in the hPDLSCs seeded aligned silk scaffold group, which revealed its modulation effect of macrophage polarization from M1 to M2 phenotype.ConclusionsIn summary, this study demonstrates the efficacy of hPDLSCs as seed cells and aligned silk scaffold as a tendon-mimetic scaffold for enhanced tendon tissue engineering, which may have broad implications for future tendon tissue engineering and regenerative medicine researches.

Evolution of directionally freeze-cast Fe2O3 and Fe2O3+NiO green bodies during reduction and sintering to create lamellar Fe and Fe-20Ni foams

Directional freeze-casting (FC) of powder suspensions followed by freeze-drying and sintering is a versatile and scalable processing route for creating metallic foams with highly elongated pores. Because of the high propensity for oxidation of metal powders, the use of precursor oxide powders is studied here with an additional step of H2-reduction of oxides to metal before sintering. However, the large volume shrinkage due to oxide reduction causes foam deformations, making it difficult to optimize the FC parameters to obtain a particular foam structure. We use quasi in situ X-ray microtomography to analyze the three-dimensional structural evolution of directionally freeze-cast, lamellar Fe2O3 and Fe2O3+NiO green bodies as they are reduced by H2 at 725 °C to Fe and Fe-20Ni (at%), respectively, and sintered at 900 °C. These temperature and gas conditions result in sequential reduction and sintering steps that can be individually analyzed. Foam porosity, pore width, lamellae thickness, and macroscopic shrinkage are quantified by image analysis. Oxide green body structures match typical FC relationships: porosity increases with decreasing powder content in the FC suspension, and the lamellae spacing period, or FC wavelength, decreases with increasing freezing velocity. Upon H2-reduction, lamellae in Fe foams buckle due to mismatch stresses from spatially-inhomogeneous reduction rates, leading to anisotropic deformation. Buckling is absent in Fe-20Ni foams due to the faster reduction kinetics of Ni/NiO that lead to more spatially uniform reduction. Reduction is responsible for 73–86% of the total volumetric shrinkage, with sintering causing the remaining shrinkage, which is nearly isotropic for all foams. The observed relationships between FC parameters, green body and metal foam structure can help guide the design and optimization of metal foams for specific technological applications.

Microstructure analysis of porous lead zirconate–titanate films

AbstractPorous ferroelectric lead zirconate–titanate (PZT) films with different internal structures are synthesized using a sol–gel technique and spin‐on deposition on platinized silicon substrates. The films’ porosity is engineered using various structure‐directing agents: polyvinylpyrrolidone with a molecular weight of 360 000 (1–6.6 wt.%) and block copolymer surfactants Brij 30 and Brij 76 (30–60 wt.%). The films’ structures are characterized by transmission electron microscopy. The PVP‐based films contain large, elongated pores with diameters as large as 100 nm. By contrast, the films prepared from solutions with block copolymers exhibit a small pore size depending on the surfactant molecular weight (10–19 nm for Brij 30 and 20–27 nm for Brij 76), with a mostly uniform distribution of channel‐like pores within the film volume. Despite their highly porous structures, all of the films show a columnar‐grain perovskite structure with grains as large as several micrometers and curved grain boundaries. The films demonstrate ferroelectric behavior with dielectric hysteresis, and their permittivity decreases with increasing porosity. Thus, the Brij 30 and Brij 76 copolymer surfactants can be used to engineer fine porous structures in PZT films for various applications in electronics.

In-situ SAXS study on pore structure change of PAN-based carbon fiber during graphitization

Graphitization (1400 °C–2200 °C) of polyacrylonitrile (PAN)-based carbon fiber in a small furnace with direct electric heating by Joule effect was studied in situ by small angle X-ray scattering (SAXS) with X-ray synchrotron radiation. The two-dimensional SAXS images display an anisotropic shape indicating the existence of needle-like or elongated ellipsoid-shaped pores oriented along the fiber axis. The one-dimensional scattering curves display obvious positive deviation from Porod's law indicating the existence of micro-fluctuation of electron density in the skeleton of the fiber which give rise to additional scattering. After correcting the deviation from Porod's law, the pure pore scattering was derived, and the pore structure parameters were computed. The results show that with increasing temperature the orientation angle decreases whereas the orientation degree increases. The long axis decreases whereas the short axis increases leading to a lower axial ratio. The size distribution becomes broader and there is a maximum value of porosity and specific surface area at 1900 °C. The change of pore structure in the fiber with temperatures can be approximately divided into two stages corresponding to denitrification condensation (1400 °C–1900 °C) and structure rearrangement (1900 °C–2200 °C) during graphitization, respectively. The corresponding mechanism was analyzed. Reciprocal relationship between the orientation of the needle-like or elongated ellipsoid-shaped pores in carbon fiber and the scattering images (inspired from Macromolecules, 2000, 33, 1848–1852; Polymer, 2001, 42, 1601–1612; Journal of Light Scattering (In Chinese), 2021, 33, 328–334). The left is schematic diagram and the right is actual sample and SAXS images. Where φ is the orientation angle of pore, L is the long axis of pore, r is the short axis of pore, q 12 and q 3 are the components of the reciprocal space vector q (q = 4π·sinθ/λ, 2θ is the scattering angle, λ is the incident X-ray wavelength) in the directions perpendicular and parallel to the principal axis of the pore, respectively. • In-situ SAXS study on PAN-based carbon fiber during graphitization (1400 °C–2200 °C). • Obvious positive deviation from Porod's law for all measured SAXS curves. • Change of pore structure of fiber in two stages dividing by 1900 °C.

Anisotropy evolution of elastomeric foams during uniaxial compression measured via in-situ X-ray computed tomography

We have characterized the three-dimensional evolution of microstructural anisotropy of a family of elastomeric foams during uniaxial compression via in-situ X-ray computed tomography. Flexible polyurethane foam specimens with densities of 136, 160 and 240 kg/m3 were compressed in uniaxial stress tests both parallel and perpendicular to the foam rise direction, to engineering strains exceeding 70%. The uncompressed microstructures show slightly elongated ellipsoidal pores, with elongation aligned parallel to the foam rise direction. The evolution of this microstructural anisotropy during deformation is quantified based on the autocorrelation of the image intensity, and verified via the mean intercept length as well as the shape of individual pores. Trends are consistent across all three methods. In the rise direction, the material remains transversely anisotropic throughout compression. Anisotropy initially decreases with compression, reaches a minimum, then increases up to large strains, followed by a small decrease in anisotropy at the largest strains as pores collapse. Compression perpendicular to the foam rise direction induces secondary anisotropy with respect to the compression axis, in addition to primary anisotropy associated with the foam rise direction. In contrast to compression in the rise direction, primary anisotropy initially increases with compression, and shows a slight decrease at large strains. These surprising non-monotonic trends and qualitative differences in rise and transverse loading are explained based on the compression of initially ellipsoidal pores. Microstructural anisotropy trends reflect macroscopic stress-strain and lateral strain response. These findings provide novel quantitative connections between three-dimensional microstructure and anisotropy in moderate density polymer foams up to large deformation, with important implications for understanding complex three-dimensional states of deformation.

Effects of pore structure characterized by synchrotron-based micro-computed tomography on aggregate stability of black soil under freeze-thaw cycles

Soil structure affects soil quality, which in turn influences agricultural productivity. In north-eastern China, periodic melting of the frozen layer is very common in late autumn and early spring. Such freeze-thaw cycles affect soil structure, aggravating soil erosion and affecting soil quality. The objective of this study was to evaluate the effects of aggregate pore characteristics on the aggregate stability of black soil under freeze-thaw cycles. Undisturbed topsoil samples were submitted to 0, 1, 3, 5, 7, 10, 15, and 20 freeze-thaw cycles under controlled laboratory conditions. Then, 5–7 mm aggregates were collected from each treatment for synchrotron-based X-ray micro-computed tomography (SR-μCT) scanning with 3.25 μm voxel resolution at the Shanghai Synchrotron Radiation Facility (SSRF); 3D micro tomography images were then reconstructed using ImageJ software. Aggregate stabilities against slaking (MWDFW) and mechanical breakdown (MWDWS) were also measured after each treatment. The relationships between pore parameters and aggregate stability were then analyzed using the method of partial least squares regression (PLSR). 2D and 3D image visualization showed that the aggregate microstructures developed increasingly porous and connected pore networks following repeated freeze-thaw cycles. Quantitative analysis showed that total porosity, porosity of elongated pores (EP), and porosity of equivalent pore size >100 μm (P>100) significantly increased with an increasing number of freeze-thaw cycles. Such cycles decreased the aggregate stability, which was closely associated with pore characteristics. According to PLSR, the pore characteristics accounted for 86 % and 81 % of the variation in MWDFW and MWDWS, respectively. Total porosity, EP, and P>100 were identified as the primary factors controlling the air content, water entrance, and failure stress of interior aggregates, all of which could weaken aggregate stability. These results improve the understanding of pore characteristics and aggregate stability, which are key factors influencing soil erosion and soil quality during the seasonal freeze-thaw period.

Pea starch exhibits good expansion characteristics under relatively lower temperatures during extrusion cooking.

Extrusion processing characteristics of pea starch were studied as impacted by various extrusion cooking processing variables, including, moisture content (15%, 17.5%, and 20% w.b.), temperature (120, 135, and 150 °C), and screw speed (150, 200, and 250rpm), in a co-rotating twin-screw extruder. Physicochemical properties such as radial expansion ratio (ER), unit density (UD), water absorption index (WAI), and water solubility index (WSI) were measured. ER of the extrudates ranged between 2.52 and 3.63. These values of ER were significantly high, although relatively lower compared to the highest values reported in the literature for corn and rice extrudates. The UD values for all the extrudates ranged from 0.12 to 0.35g/cm3 , WAI, and WSI values ranged from 10.98 to 12.10g/g and from 0.12% to 7.73%, respectively. Both screw speed and moisture content had significant impacts on the ER (P <0.01). The highest ER was observed for the extrusion cooking conditions of the lowest moisture content level (15%), lowest barrel temperature (120 °C), and lowest screw speed (150rpm). The cross-sectional microstructure of the extrudates showed that the samples with a high ER had thick and elongated pores. The results of this study indicate that pea starch is a viable ingredient for making puffed extruded products. PRACTICAL APPLICATION: The food industry can utilize the information generated from this study in the development of extruded expanded food products with pea starch. The specific information related to process conditions can assist the food industry in determining the ideal conditions for extrusion cooking in the production.

The effect of application of digestate and agro-food industry sludges on Dystric Cambisol porosity.

The spatial arrangement and pore size distribution play an important role in accumulation and protection of exogenous organic matter (EOM) in the soil, but how different organic materials contribute to modify pore structure is poorly understood. We aimed at exploring possible changes in the complexity of the soil phase during fertilization with different doses of digestate and sludges sourced from the agro-food industry. For this purpose, the short-term effects—one year, of soil fertilization, were investigated in several sampling periods and within two depths (0–25 cm and 25–40 cm). Changes in the specific surface area (SSA), total pore volume (VMIP), total pore area (SMIP), average pore radius (RMIP) and pore size distribution (PSD) were monitored using N2 adsorption/desorption (NAD) and mercury porosimetry (MIP) methods. Our results showed that the intensity of observed changes depended on the type and dose of organic material, soil depth and sampling date. Accumulation of EOM increased with soil depth, masking a large proportion of SSA. Deeper soil layer was more susceptible to changes in the pore size distributions due to the formation of new elongated pores. We concluded that this specific structural porosity was related to the decomposition of organic matter during the formation of soil aggregates.

Analysis of the intra-aggregate pore structures in three soil types using X-ray computed tomography

The pore structure of soils can control important physical and biological processes in soil-plant-microbial systems. However, quantifying the intra-aggregate pore structure is challenging. This study investigated the soil pore structure in aggregates from three typical zonal soil types (alpine meadow soil, chestnut soil and red soil) from cold, temperate and subtropical regions of China, respectively, using X-ray microscopic computed tomography (CT) with a resolution of 7 μm. The results indicated that the chestnut soil aggregates had higher porosity than the alpine meadow and red soil aggregates due to the presence of grass/shrub roots. The soil pores of the chestnut soil aggregates were mostly small, relatively regular and densely distributed. Alpine meadow soil aggregates had many large, elongated pores, which was attributed to the freeze–thaw cycles in alpine regions. The alpine meadow aggregate pores had the largest mean equivalent diameter, mean surface area and mean volume of the evaluated soil types. Red soil aggregates had low porosity and poor connectivity, which were attributed to the high temperatures and abundant precipitation in subtropical regions. Moreover, the soil aggregate pores of the three soil types were found to be dominated by micropores, especially the chestnut soil (90.39% of the number of pores). Soil texture significantly influences the total porosity of soil aggregates. Higher soil organic matter content may result in aggregate pores that are more irregular in shape. A soil pore architecture with high continuity likely facilitated greater water flow to the deeper soil layers in the alpine meadow soil than in the red and chestnut soils. However, in the chestnut soil aggregates, the water could be unavailable for uptake by plants due to the relatively poor soil pore structure. The results for the red soil aggregates are indicative of the poor structure and tendency toward rapid erosion of red soils.

Porous Titanium Cylinders Obtained by the Freeze-Casting Technique: Influence of Process Parameters on Porosity and Mechanical Behavior

The discrepancy between the stiffness of commercially pure titanium and cortical bone tissue compromises its success as a biomaterial. The use of porous titanium has been widely studied, however, it is still challenging to obtain materials able to replicate the porous structure of the bones (content, size, morphology and distribution). In this work, the freeze-casting technique is used to manufacture cylinders with elongated porosity, using a home-made and economical device. The relationship between the processing parameters (diameter and material of the mold, temperature gradient), microstructural features and mechanical properties is established and discussed, in terms of ensuring biomechanical and biofunctional balance. The cylinders have a gradient porosity suitable for use in dentistry, presenting higher Young’s modulus at the bottom, near the cold spot and, therefore better mechanical resistance (it would be in contact with a prosthetic crown), while the opposite side, the hot spot, has bigger, elongated pores and walls.

The Characteristics of Poral Space as Habitat of Soybean Roots and Rhizobium Nodules

The objective of the paper was to emphasize the characteristics of the poral space (quantified according to their size and shape) of an intensely irrigated soil, representing the habitat for soybean roots and Rhizobium bacteria nodulation. The studied site is located in Southern Bărăgan Plain, Perișoru region. The soil is Vermic Chernozem (according to SRTS-2012) formed in carbonate loess like deposits. The climate is temperate continental with an average annual temperature of 10.8°C, and an average annual precipitation of 480 mm. The poral space was quantitatively evaluated at microscopic scale, using image analysis on oriented soil thin sections with the help of an image-analyzer computer. The image analysis allowed the quantitative evaluation at microscopic scale of the undisturbed structure and the adjacent porosity, in 2-D dimension (in thin sections). The pores were divided according to their shape in three classes (regular, irregular and elongated pores), and further each shape class was divided into seven size classes according to the equivalent pore diameter (ranging between 100 and &gt;1000 µm). The result showed, unspecific conditions in the studied Chernozem, thus: Ap horizon was more compacted than the underlined Apt, consequently the total porosity was lower (0.21 m2 m-2 ) into the top Ap horizon, comparing to the underlined Apt (0.33 m2 m-2 ). In agreement with the data obtained by means of image analysis (pores quantified according to their size and shape), the oriented thin sections gave a clear representation of the genesis, location and the characteristics of the poral space. The soybeans roots developed mainly into the areas with intense biological activity. The soil macro- and mesofauna proved to be good habitat builders for soybean roots and the Rhizobium nodules, even in the conditions of a droughty period with the irrigation application delay.