Intergranular Voids Research Articles

A 3D visualization method for identifying fabric characteristics during suffusion using transparent soil

Suffusion is a process by which fine particles move through the voids between coarse particles (intergranular voids) by seepage flow. Therefore, identifying the arrangement of coarse particles (coarse matrix), intergranular voids, and the spatial distribution of fine particles is a key issue for studying suffusion. Transparent soil is being increasingly used to replace real soil in laboratory model tests for studying the internal particle movements and pore fluid flow in soils. This study established an experimental setup for scanning a transparent soil specimen during seepage by a moving laser and made an attempt to construct a 3D digital mesostructural model of the specimen based on the images of the sequentially illuminated cross-sections. An example test on a gap-graded soil was conducted to show the performance of the presented method. It demonstrated that the coarse matrix and intergranular voids can be visualized and quantified at satisfactory precisions; moreover, the loss and redistribution of fine particles as well as important phenomena such as deposition at pore bodies and clogging of pore throats can also be visualized and identified qualitatively.

Relative density influence on the liquefaction potential of sand with fines

Liquefaction is a loss in soil’s resistance which can lead to disastrous and expensive consequences in terms of human lives and material damages, hence the interest of this laboratory study. The article explores the relative density influence in addition to the main parameter of the fines content on the liquefaction potential of soils. The study is based on a very large number of undrained monotonic triaxial tests undertaken on samples of reconstituted saturated sand and silt mixtures with 6 levels of initial relative density ranging from 15 to 90%. The materials used are levied from different level of deepness in the coastal region of Kharouba in the wilaya of Mostaganem. In this experiment, the sand-silt mixtures were separated to form the study samples. The aim of this work is, on one hand, to confirm and update the results of previous works (Bensoula et al., 2018) and on the other hand the study of the influence of relative density on the liquefaction potential of soils and the introduction of the concept of relative density threshold. The results of the tests confirm that the studied soil is most likely to be liquefied at a fines content between 0 and 30% depending on the equivalent intergranular voids and the equivalent relative density. These parameters are primordial for the characterization of soils sensitivity to liquefaction. In this study, the results showed that the resistance to liquefaction increases in a linear way with the relative density up to a threshold relative density value according to the fines content, which means that increasing the relative density improves the liquefaction resistance but only up to a threshold value of relative density given according to fines content

A method to fabricate supported catalytic packing: Polydopamine as a "Double-Sided Adhesive" to prepare the fully covered seeding layer

BackgroundIn recent years, Supported catalytic packings (SCPs) with zeolite coating on metallic substrates have received extensive attention due to their satisfactory heat/mass transfer properties. MethodsHerein, high-performance SCP with HZSM-5 coating was fabricated by secondary growth method with polydopamine (PDA)-assisted seeding, where PDA was used as a "double-sided adhesive" sandwiched between supports and seeds. The atom-economic reaction of cyclohexene and acetic acid for cyclohexyl acetate production was carried out to evaluate the catalytic performance of as-fabricated SCPs. Significant FindingsDue to the strong adhesion of PDA, the uniform and high-coverage seeding layer was achieved under the optimized seeding conditions, then continuous HZSM-5 coating that possessed high crystallinity, rough surface, and intergranular voids was formed. Compared with SCP prepared by secondary growth method with the traditional dip coating seeding method, the catalytic activity and stable operation time of PDA-assisted SCP were increased by 50% and 57%, respectively. Furthermore, PDA-assisted seeding method is easy to conduct, indicating its great potential in practical applications.

Coupled dissolution-precipitation reactions as a potential method for mitigating contaminant transport in carbonate aquifers

• Coupled dissolution-precipitation reactions can reduce porosity and permeability in porous media. • Injection of oxalic acid into a calcitic 2D flow-through cell caused the formation of a barrier that limited solute transport and fluid flow. • Such a method could be used to contain contaminant transport in calcareous aquifers. Subsurface barriers are often used to mitigate the spread of contaminants in groundwater. Current methods typically involve the injection of slurries into aquifers, a process that clogs porosity and reduces hydraulic conductivity. An alternative way to achieve this effect in calcareous aquifers could be to inject a fluid that dissolves the existing carbonate minerals and induces the formation of phases that have higher molar volumes. While such mineral replacement reactions are known to affect hydraulic conductivity, their ability to impede contaminant transport has not been tested. In this study, we injected oxalic acid into a pseudo-2D flow through cell containing calcitic sand, which simulated a calcareous aquifer. The oxalic acid causes the dissolution of calcite, as well as the precipitation of calcium oxalate minerals, in a reaction zone that spreads out from the point of injection. We found that this process reduces the water discharge in the cell by up to 80%, and caused the flow velocity around the reaction zone to drop from 20 cm h −1 to <0.1 cm h −1 . Mineralogical analyses and electron microscopy indicate that permeability is reduced primarily by partitioning of the intergranular voids by micrometer sized calcium oxalate crystals. Our results suggest that coupled dissolution-precipitation reactions could be a feasible method for deploying subsurface barriers in aquifers.

Kaolin based protective barrier in municipal landfills against adverse chemo-mechanical loadings

In this work, we assess the self-sealing and swelling ability of the compacted granular bentonite (GB) under an inorganic salt environment and induced overburden stresses from the landfill waste. The laboratory permeation tests with high ionic strength salt solutions reveal that the GB fails to seal and exhibits a significant mechanical collapse under different applied stresses. The applicability of GB in the form of geosynthetic clay liners as the bottom liner facilities in landfills that produce high ionic strength salt leachates, therefore, remains a serious concern. We propose an additional barrier system based on kaolin, for the first time, to address this problem. The proposed kaolin-GB layered system performs satisfactorily in terms of its sealing and swelling ability even in adverse saline conditions and low overburden stresses. The kaolin improves the osmotic efficiency of the self and also helps the underlying GB layer to seal the inter-granular voids. The estimated design parameters by through-diffusion test suggest that the kaolin-GB layered system effectively attenuates the permeant flux and suitable as a landfill liner.

RELATIONSHIP BETWEEN MAGNETIC PROPERTIES AND MICROSTRUCTURE OF FERRITES DURING SINTERING IN RADIATION AND RADIATION-THERMAL CONDITIONS

The studies of correlation between magnetic properties and microstructure were conducted on samples of lithium-substituted ferrite, sintered in radiation and radiation-thermal conditions. Radiation-thermal sintering was performed for compacts irradiated with a pulsed electron beam with energy of (1.5–2.0) MeV, beam current per pulse of (0.5-0.9) A, irradiation pulse duration of 500 μs, pulse repetition rate of (5–50) Hz, and compact heating rate of 1000 C/min. Sintering in thermal furnaces (T-sintering) was carried out in a preheated chamber electric furnace. The paper shows that magnetic induction does not depend on the ferrite grain size. In this case, the coercive force is inversely proportional to the grain size and depends on the intragranular porosity of ferrite samples. In contrast to thermal sintering, radiation-thermal sintering does not cause capturing of intergranular voids by growing grains and enhances coagulation of intragranular pores.

НОВИЙ ПІДХІД ДО РЕМОНТУ НЕЖОРСТКИХ ДОРОЖНІХ ОДЯГІВ ПЕРЕХІДНОГО ТИПУ

Earlier, due to insufficient financing of the road industry, funds were allocated on a leftover basis for the repair of local roads, over time the condition of these roads has deteriorated significantly. So, given the ramified network of local roads, the issue of restoring the condition of local roads is a very urgent problem. Conducted exploratory studies of the application of stabilization technology to restore the condition of local roads show that this technology is progressive, since it allows reusing existing materials while ensuring the required strength of the pavement. However, design engineers rarely use this technology, probably due to insufficient research on this approach. The task is to investigate the possibility of using stabilization technology with the use of crushed stone layers of different composition and their maximum reuse, when repairing transitional pavements. Analysis shows that there are many cases where transitional structures have significant heterogeneity and low strength. This is formed due to a weak crushed stone base and waterlogging of the subgrade soils. Over time, soil particles penetrate into the crushed stone layer and weaken the contacts between the crushed stones, as a result of which rut, pits and subsidence form on the road, which significantly complicates the movement of vehicles. Studies of the composition of existing bases show that if in a dispersed system the amount of crushed stone grains is more than 50% by volume, then a contact frame is formed in the material. Intergranular voids are filled with soil or fine aggregate, processing with such a small amount of a mineral binder (cement or lime) allows it to be significantly strengthened, as well as to create bonds between the soil and crushed stone. Modern self-propelled soil mixing machines (recycler-stabilizer) allow in one pass to perform milling (loosening) and mixing of materials of existing transitional pavement to a depth of 40 cm. Taking into account the dependence of the distribution of normal stress in a two-layer half-space, it can be seen that stabilization of the foundation to a depth of 40 cm will allow the subgrade soil to work without exceeding the permissible shear deformations. The construction of the experimental site in Berezivka, Odessa region, confirmed the assumptions about the effectiveness of the proposed solution to restore the strength of transitional pavement. Keywords: non-rigid pavement of transition type, modulus of elasticity, stabilization, rubble, soil, cold recycling.

Phase-field simulation of the interaction between intergranular voids and grain boundaries during radiation in UO2

In the present work, a phase-field model is developed to simulate the interaction between voids and grain boundary (GB) by a set of modified Cahn-Hilliard and Allen-Cahn equations with spatially and temporally evolving field variables and order parameters. Both the evolution of grain growth and the effect of moving GBs on the formation of voids during radiation were captured in the present phase-field model. A flat GB with an artificial driving force was used to analyze the resistive pressure of the void during the interaction of the void and moving GB, and the interaction between GB and void with different radius was also simulated. The effects of moving GB on the void formation during radiation was also discussed in detail. In addition, the grain growth and voids formation during radiation in polycrystalline uranium dioxide were studied based on the modified phase-field model.

Numerical simulations of thermal conductivity in void-containing tungsten: Topological feature of voids

Tungsten, as a promising candidate for plasma-facing material in the advanced fusion reactors, has to suffer heat loading and high-energy particle irradiation. Since numerous voids form in the grain interior and on the grain boundary during irradiation, the thermal transfer capacity of tungsten would face a grand challenge. Herein, we systematically investigate the thermal conductivity of void-containing tungsten using finite element method. To understand the relation between the topological features of void and the corresponding thermal response within a wide temperature range, we analyze the thermal conductivity of tungsten by considering the arrangements, shapes and rotation angles of voids. The effects of intra- and inter-granular voids on the heat transmission are examined. The numerical results show how the thermal conductivity of single-crystal tungsten can be independent of void distribution pattern and how the void shape can lead to an anisotropic effective thermal conductivity. The predicted thermal conductivities are compared with those of well-known models and experimental data. Apart from voids, the proportion of grain boundary is also considered to analyze its effect on the thermal resistivity. Finally, we show how the spatial distribution of voids influences the heat flow inside the crystalline phase and across the grain boundary.

Proton irradiation-decelerated intergranular corrosion of Ni-Cr alloys in molten salt

The effects of ionizing radiation on materials often reduce to “bad news”. Radiation damage usually leads to detrimental effects such as embrittlement, accelerated creep, phase instability, and radiation-altered corrosion. Here we report that proton irradiation decelerates intergranular corrosion of Ni-Cr alloys in molten fluoride salt at 650 °C. We demonstrate this by showing that the depth of intergranular voids resulting from Cr leaching into the salt is reduced by proton irradiation alone. Interstitial defects generated from irradiation enhance diffusion, more rapidly replenishing corrosion-injected vacancies with alloy constituents, thus playing the crucial role in decelerating corrosion. Our results show that irradiation can have a positive impact on materials performance, challenging our view that radiation damage usually results in negative effects.

INFLUENCE OF FILLER QUALITY ON CONCRETE THERMAL CONDUCTIVITY

Studies on the effect of grain composition on the thermal conductivity of lightweight concrete, it was shown that the mineral composition of filler (aggregates) substantially reflects the thermal conductivity and density of concrete. The grains of the component have a slightly higher effect on the thermal conductivity than the material itself. The proof of this position is that the thermal conductivity of bulk materials is always slightly lower than cellular materials of the same average density. In an absolutely dry porous body, heat transfer can occur not only through thermal conductivity but also through the solid skeleton of the body, located in the air pores, but also by convection and radiation between the pore walls. With a pore diameter of less than 1 mm, convective heat transfer is practically zero, and the coefficient of radiant heat conductivity can be neglected only when the pore diameter is less than 0.5 mm. Therefore, with the same porosity, the thermal conductivity coefficient will be the greater, the larger the pores of the material. Therefore, the creation of a finely porous structure of lightweight concrete and the use of finely porous aggregates contributes to the production of concrete with reduced thermal conductivity. The proof can be the results of experiments and the curves presented. An increase in the pore size on the surface of the grains of the aggregates leads to an increase in intergranular voids of the mixtures. As a result of mineralogical-petrographic studies of artificial porous aggregates, it was established that aluminosilicate phases with a disordered structure — clay amorphized with firing and acidic glasses — predominate in expanded clay, agloporite, and expanded perlite. Slag is characterized by a predominance of crystalline phases - low-basic calcium silicates than calcium and magnesium aluminosilicates. The glassy phase is present only in the form of an impurity of 15 - 20%. When analyzing the experimental data, we came to the conclusion that the thermal conductivity of expanded clay increases with increasing density. However, at the same density, expanded clay of different batches of the same plant and especially of different plants, differ in the values of the coefficient of thermal conductivity.

Insitu investigation of tensile deformation behaviour of cold-rolled interstitial-free high-strength steel in scanning electron microscope

The progress of tensile deformation of cold rolled interstitial-free high-strength (IFHS) steel in the as-received and 10 pct tensile pre-strained conditions has been studied through testing of miniature sized specimens in scanning electron microscope. Strength and ductility of the steel obtained through insitu tests have been compared with the macro tensile test results. The insitu test results show that the yield strength and tensile strength of miniature sized specimens are less as compared to that of macro tensile test results. But, uniform strain in case of insitu tests is higher than that obtained in case of macro tensile specimens. The insitu tests reveal that intergranular cracking of surface grains and formation of both intergranular and transgranular voids precede the final ductile fracture. The areal density of voids is found to increase with increase of Von Mises equivalent plastic strain. Under pre-strained condition void nucleation strain of the steel is found to be lower as compared to the as-received condition.

Thermal and porosity properties of meteorites: A compilation of published data and new measurements

AbstractWe report direct measurements of thermal diffusivity and conductivity at room temperature for 38 meteorite samples of 36 different meteorites including mostly chondrites, and thus almost triple the number of meteorites for which thermal conductivity is directly measured. Additionally, we measured porosity for 34 of these samples. Thermal properties were measured using an optical infrared scanning method on samples of cm‐sizes with a flat, sawn surface. A database compiled from our measurements and literature data suggests that thermal diffusivities and conductivities at room temperature vary largely among samples even of the same petrologic and chemical type and overlap among, for example, different ordinary chondrite classes. Measured conductivities of ordinary chondrites vary from 0.4 to 5.1 W m−1 K−1. On average, enstatite chondrites show much higher values (2.33–5.51 W m−1 K−1) and carbonaceous chondrites lower values (0.5–2.55 W m−1 K−1). Mineral composition (silicates versus iron‐nickel) and porosity control conductivity. Porosity shows (linear) negative correlation with conductivity. Variable conductivity is attributed to heterogeneity in mineral composition and porosity by intra‐ and intergranular voids and cracks, which are important in the scale of typical meteorite samples. The effect of porosity may be even more significant for thermal properties than that of the metal content in chondrites.

Enhanced electrochemical performance of LiNi0.8Co0.1Mn0.1O2 with a 3D-SiO2 framework by a new negative pressure immersion method.

LiNi0.8Co0.1Mn0.1O2 is one of the most promising cathode materials for lithium ion batteries; however, during the charge/discharge process, it suffers from capacity fading, which is considered to be due to intergranular cracking. Herein we develop an original concept to alleviate this problem via negative pressure immersion treatment. A 3D-SiO2 framework is formed in the intergranular voids and at grain boundaries (functioning as the buffer zone and transfer-bridge) and the SiO2 protective layer is completely and homogeneously coated on the surfaces of the pristine particles through a hydrolytic condensation reaction involving tetraethoxysilane (TEOS). The 3D-SiO2 framework has two advantages: firstly, acting as a buffer zone, the framework can effectively inhibit the generation and extension of intergranular cracking; secondly, like the SiO2 protective layer on the surface of the particles, the 3D-SiO2 framework can impede side reactions between primary particles (grains) and electrolyte inside the particles. As a result, the as-modified LiNi0.8Co0.1Mn0.1O2 exhibits enhanced cycling performance with 92.4% capacity retention after 100 cycles at 1 C (200 mA h·g-1), while the capacity retention values for the pristine particles and normal coating treatment particles are only 55.4% and 82.6%, respectively. Moreover, the thermal stability (60 °C) is distinctly enhanced and the rate performance is significantly improved at high rates (2, 3 and 5 C).

Biomineralization of calcium carbonate by marine bacterial strains isolated from calcareous deposits

Biomineralization induced by microbial enzymes, which catalyse CaCO3 precipitation, is a promising field of research for various applications in building eco-materials. Especially, this could provide an eco-friendly process for protection of coastal areas against erosion. In the present investigation, fourteen bacterial strains were isolated and characterized from both natural seawater and calcareous deposits formed on a cathodically protected steel mesh in marine environment. All of them induced calcium carbonate precipitation in various media by producing urease and/or carbonic anhydrase enzymes. The calcium carbonate minerals produced by bacteria were identified by microscopy and µ-Raman spectroscopy. In parallel, an experimental set-up, based on a column reactor, was developed to study biomineralization and microbial capacity of Sporosarcina pasteurii to form sandy agglomerate. These well-known calcifying bacteria degraded the urea present in liquid medium circulating through the column to produce calcium carbonate, which acted as cement between sand particles. The bio-bricks obtained after 3 weeks had a compressive strength of 4.2 MPa. 20% of the inter-granular voids were filled by calcite and corresponded to 13% of the total mass. We successfully showed that bio-column system can be used to evaluate the bacterial ability to agglomerate a sandy matrix with CaCO3.

Diffusion bonding of Cu atoms with molecular dynamics simulations

Diffusion bonding of copper disks is an important step during the assembly of accelerating structures -the main components of power radio-frequency linear accelerators-. During the diffusion bonding copper disks are subjected to pressure at high temperatures. Finding the optimal combination of pressure and temperature will enable an accurate design of manufacturing workflow and machining tolerances. However, required optimization is not possible without good understanding of physical processes developed in copper under pressure and high temperature. In this work, the combined effect of temperature and pressure on closing time of inter-granular voids is examined by means of molecular dynamics simulations. In particular, a nano-void of 3.5–5.5 nm in diameter representing a peak and a valley of surface roughness facing each other was inserted between identical copper grains. The simulations performed at T = 1250 K, the temperature used in experimental condition, and the 300–800 MPa pressure range indicated the dislocation-mediated enhancement of atomic diffusion leading to full void closure.

Preparation and characteristics of porous anorthite ceramics with high porosity and high‐temperature strength

AbstractHigh‐temperature properties including compressive strength, thermal shock behavior, and thermal conductivity of porous anorthite ceramics with high specific strength were tested and analyzed. The results showed that the prepared materials merit high‐temperature compressive strength, thermal stability, and conductivity. With the appropriate fabrication parameters, even though containing 0.33 g/cm3 bulk density and 88.2% porosity, its compressive strength could reach 2.03 MPa at 1000°C, 147% of that at room temperature; the residual strength ratio kept as 114.7% after a thermal shock at 1200°C. The X‐ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that anorthite grains refinement and intergranular voids filling by liquid phase were main factors for the high strength. From room temperature to 1200°C, its thermal conductivity only varied from 0.085 to 0.258 W·(m·K)−1. High porosity, a large number of nanoregions in anorthite grains and amorphous phase in grain boundary were main reasons for low thermal conductivity.

The keys for effective distribution of intergranular voids of peapod-like MnO@C core-shell for lithium ion batteries

Conversion reaction-based transition metal oxides have shown high reversible capacity compared to conventional intercalation reaction-based materials. However, their practical applications have been impeded by a poor cycle life resulted from their low electrical conductivity and huge volume changes. During the past decade, remarkable advances have been achieved in the preparation of nanostructured transition metal oxides for conversion reaction anodes. Among the various shaped nanomaterials, core-shell structure with a carbon shell showed excellent electrochemical performance. Herein, we prepared peapod-like MnO@C nanowires as one special type of core-shell structure, and we elucidated the structure-properties relationship in peapod-like MnO@C nanowires for Li-ion batteries. The morphology of the manganese oxide particles inside the carbon layer could be simply controlled by adjusting the parameters in the carbonization process. The optimized composites exhibited excellent cycling performance without decreasing the capacity, and outstanding rate properties. The optimized structure can maximize the advantages such as structural durability against the stress involving huge volume changes, as well as minimize the side reaction at the surface.

Highly Reversible Conversion Anodes Composed of Ultralarge Monolithic Grains with Seamless Intragranular Binder and Wiring Network

Conversion anodes enable a high capacity for lithium-ion batteries due to more than one electron transfer. However, the collapse of the host structure during cycling would cause huge volume expansion and phase separation, leading to the degradation and disconnection of the mixed conductive network of the electrode. The initial nanostructuring and loose spatial distribution of active species are often resorted to in order to alleviate the evolution of the electrode morphology, but at the cost of the decrease of grain packing density. The utilization of ultralarge microsized grains of high density as the conversion anode is still highly challenging. Here, a proof-of-concept grain architecture characterized byendogenetic binder matrix and wiring network is proposed to guarantee the structural integrity of monolithic grains as large as 50-100 μm during deep conversion reaction. Such big grains were fabricated by self-assembly and pyrolysis of a Keggin-type polyoxometalate-based complex with protonated tris[2-(2-methoxyethoxy)-ethyl]amine (TDA-1-H+). The metal-organic precursor can guarantee the firm adherence of numerous Mo-O clusters and nuclei into a highly elastic monolithic structure without evident grain boundaries and intergranular voids. The pyrolyzed TDA-1-H+ not only serves as in situ binder and conductive wire to glue adjacent Mo-O moieties but also acts as a Li-ion pathway to promote sufficient lithiation on surrounding Mo-O. Such a monolithic electrode design leads to an unusual high-conversion-capacity performance (1000 mAh/g) with satisfactory reversibility (reaching at least 750 cycles at 1 A/g). These cycled grains are not disassembled even after undergoing long-term cycling. The conception of the intragranular binder is further confirmed by consolidating the MoO2 porous network after in situ stuffing of MoS2 nanobinders.

Reactivity of solid BaCe0.9Y0.1O3-δ towards melted WO3

High-temperature impregnation of solid single-phase Y-doped BaCeO3 with melted WO3 was performed towards the evaluation of the possibility of formation of chemically stable material with relatively high electrical conductivity in this system. Impregnation was performed at 1470 °C as a function of time. Due to the relatively high reactivity in solid BaCe0.9Y0.1O3-δ - liquid WO3 system the reactive and the inner layers were distinguished and analysed. The obtained results clearly indicate the decomposition of Y-doped BaCeO3 in contact with melted WO3. X-ray diffraction method together with SEM observation, EDS analysis and EIS measurements results were applied to discuss the mechanism of this multi-stage process and the influence of the reaction time on materials structure and microstructure. As it was observed, partial incorporation of tungsten into the barium cerate structure can process not only on the surface of the materials but also in the inner layer of the synthesised materials. This donor-type doping of the perovskite structure finds reflection in both, materials electrical properties and chemical stability towards CO2/H2O. The decrease of proton defects concentration was observed together with the significant increase of the materials chemical stability in comparison to un-modified single-phase BaCe0.9Y0.1O3-δ. The calculated values of activation energy of conductivity confirm the change in the conduction mechanism. Also, the presence of an additional phase in the intergranular voids of doped BaCeO3 was postulated.