Unimodal Pore Size Distribution Research Articles

Effects of Remolding Water Content and Compaction Degree on the Dynamic Behavior of Compacted Clay Soils

The stable and safe operation of highway/railway lines is largely dependent on the dynamic behavior of subgrade fillings. Clay soils are widely used in subgrade construction and are compacted at different remolding water contents and compaction degrees, depending on the field conditions. As a result, their dynamic behaviors may vary, which have not been fully investigated until now. To clarify this aspect, a series of cyclic triaxial tests were carried out in this study with three typical remolding water contents (w = 19%, 24%, and 29%), corresponding to the optimum water content as well as its dry and wet sides, and two compaction degrees (Dc = 0.8 and 0.9), which were selected according to the field-testing data. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were also conducted on typical samples to investigate the corresponding soil fabric variations. The findings indicate the following: (a) The soil fabric at the optimum remolding water content and its dry side was characterized by a clay aggregate assembly with a bimodal pore size distribution. In contrast, the soil fabric on the wet side of the optimum water content consisted of dispersed clay particles with a unimodal pore size distribution. (b) As the compaction degree increased, to ensure the optimum water content and its dry side, large pores were compressed to make them smaller, while small pores remained unchanged. Comparatively, all the pores on the wet side were compressed to make them smaller. (c) For each compaction degree, as the remolding water content increased, a non-monotonic changing pattern was identified for both the permanent strain and resilient modulus; the permanent strain first decreased and then increased, while, for the resilient modulus, an initial increasing trend and then a decreasing trend were identified. In addition, a larger changing rate of the permanent strain (resilient modulus) was observed on the dry side, indicating a larger effect of the remolding water content. (d) For each remolding water content, as the compaction degree increased, the permanent strain exhibited a decreasing trend, but an increasing trend was identified for the resilient modulus. Moreover, the rate of change in the permanent strain (resilient modulus) on the dry side of the optimum water content was larger than that on the wet side. In contrast, the minimum rate of change was identified at the optimum water content. The obtained results allowed for the effects of the remolding water content and compaction degree on the dynamic behavior to be analyzed, and they helped guide the construction and maintenance of the subgrade.

Porous ZrO2–ZrO2 ceramics with excellent mechanical strength and permeability for transpiration cooling

AbstractThe great development of transpiration cooling technology challenges the coolant medium seriously. In this paper, porous ZrO2–ZrO2 ceramics have been satisfactorily prepared to meet the requirements of the coolant medium in transpiration cooling. The results illustrate that porous ZrO2–ZrO2 ceramics have excellent compressive strengths; meanwhile, percentages of compressive strength difference (parallel and perpendicular to the mold‐pressing direction) have an upward trend due to the increasing fiber contents. Besides, the failure mode has a huge distinction between parallelity (45° oblique section) and perpendicularity (wedge shape). These ceramics have unimodal pore size distribution (2–10 µm), and their wettability has a substantial improvement reflected by contact angle from 118° to 0°. Permeability behavior across these ceramics has been accurately described using the Darcy–Forchheimer equation, while obtaining viscous and inertial resistance coefficients, respectively. This work can provide an essential reference for coolant medium in transpiration cooling.

Improved predictions of permeability properties in cement-based materials: A comparative study of pore size distribution-based models

Permeability is a fundamental physical property of a cement-based material and is closely related to its pore structure. This study developed an improved model for permeability prediction of cementitious materials with a function of the pore size distribution (PSD), in which PSD is simulated from single and compound lognormal distribution functions, respectively. The efficiency of the improved model is demonstrated by calculating permeability for mortars and pastes available in the literature. It is found that, first, for cementitious materials with unimodal PSD, the single lognormal distribution function is adequate to describe the pore structures. In contrast, for cementing mixtures presenting multimodal PSD, the compounded lognormal distribution function is highly recommended to cover a wide range of pore components. Second, the permeability model based on the compound PSD can predict well permeability to gas intrusion, whereas the single PSD-based model is applicable for calculating permeability via water intrusion. Furthermore, slippage effect and water saturation degree are introduced in the PSD-based model. Results prove that the corrected gas permeability model from the compound PSD performs well in estimating the gas permeability in unsaturated states. Finally, the compound PSD-based model is extended by considering varying porosities and relative humidities, which can be used to quantitively describe permeability when cementitious materials undergoing pore structure degradation induced by durability issues.

Investigating the Adsorption Kinetics of Dimethoate, Malathion and Chlorpyrifos on Cellulose-Derived Activated Carbons: Understanding the Influence of Physicochemical Properties

In light of the escalating environmental concerns regarding pesticide accumulation, it is imperative to devise efficient strategies for their removal. Among the various options, activated carbons have emerged as promising candidates for adsorptive pesticide removal due to their many advantages, such as large surface area, well-developed porosity, and cost-effectiveness. However, the intricate relationship between the properties of these materials and their performance in pesticide adsorption remains largely unexplored. This study primarily focuses on examining the adsorption kinetics of three organophosphate pesticides: dimethoate, malathion (aliphatic), and chlorpyrifos (aromatic), using a range of cellulose-based activated carbon fibers with diverse specific surface areas, pore size distributions, and elemental compositions. By employing sophisticated data analysis tools, principal component analysis, and semi-empirical quantum chemical calculations, this study uncovers the importance of these distinct properties in efficiently removing structurally diverse pesticides. The results of the adsorption experiments suggested that these processes can be described using a pseudo-second-order kinetic model, which is confirmed via multiple linear regression. The obtained data suggest that the most effective carbon material for pesticide removal should have a pore diameter of approximately 4 nm, low oxygen content, a unimodal pore size distribution, and a high presence of sp2 domains. The insights from this research have the potential to guide the development of improved adsorbents and facilitate the rational selection of adsorbents tailored to specific pollutants based on their physicochemical properties and the pollutants’ chemical structure. By shedding light on the vital connection between adsorbent properties and performance, our findings significantly advance sustainable and effective pesticide removal, thereby fostering a cleaner and healthier environment.

Diclofenac sodium drug adsorption isotherm on carbon xerogels via an advanced two layers model with two energies

In this work, four carbon xerogels (XCs) adsorbents, which were prepared by the polymerization of formaldehyde (F) and resorcinol (R) using cesium carbonate (Cs) as catalyst at 4 M ratios R/Cs = XCs-100, XCs-500, XCs-1000 and XCs-2000, were utilized to interpret and understand the adsorption mechanism at a molecular level of non steroidal anti inflammatory drug (NSAID), namely diclofenac sodium (DCF). Hence, Four adsorption isotherms were utilized to present the evolution of the adsorbed quantity (Qa) as a function of drug concentration describing the DCF adsorption on the four carbons xerogels at T = 298 K and at pH = 7. In addition, two other adsorption systems, describing the adsorption of DCF on XCs-500, were plotted by varying two experimental conditions: temperature and solution pH. All these experimental data were adjusted and analyzed via the advanced two layers model with two adsorption energies (A2LM2E), which was chosen as the most adequate statistical physics model. Furthermore, stereographic and energetic parameters of A2LM2E namely: the number of DCF molecules per XCs sites (n), the adsorbed quantity at saturation (Qas) and the concentrations at half saturation (C1 and C2) were estimated by a multi-variable non-linear regression. The fitting results indicated that the DCF drug molecules were docked with mixed and non-parallel orientations on the different XCs adsorbents. The investigation of the adsorbed quantity at saturation indicated that Qas increased as follows: Qas (XCs-2000) < Qas (XCs-100) < Qas (XCs-1000) < Qas (XCs-500), showing that the XCs-500 was more efficient for the adsorption of DCF drug than the other adsorbents. The calculated molar adsorption energies ΔE1 and ΔE2 for the studied adsorption systems affirmed the exothermic and the physical characters of the adsorption mechanism since ΔE1 and ΔE2 values were positive and inferior to 40 kJ/mol. Lastly, the XCs-100, XCs-500, XCs-1000 and XCs-2000 adsorbents presented unimodal pore size distributions (PSDs) centered at a pore radius of 8.38 nm, 7.17 nm, 6.05 nm and 5 nm, respectively. Finally, the estimated thermodynamic parameters such as the adsorption entropy (Sa), the Gibbs free enthalpy (G) and the internal energy (Eint) indicated that DCF adsorption on XCs-500 was spontaneous and exothermic process.

Investigating the coupled influence of flow fields and porous electrodes on redox flow battery performance

At the core of redox flow reactors, the design of the flow field geometry –which distributes the liquid electrolyte through the porous electrodes– and the porous electrode microstructure –which provides surfaces for electrochemical reactions– determines the performance of the system. To date, these two components have been engineered in isolation and their interdependence, although critical, is largely overlooked. Here, we systematically investigate the interaction between state-of-the-art electrode microstructures (a paper and a cloth) and prevailing flow field geometries (flow through, serpentine and four variations of interdigitated). We employ a suite of microscopic, fluid dynamics, and electrochemical diagnostics to elucidate structure-property-performance relationships. We find that interdigitated flow fields in combination with paper electrodes –which features a uniform microstructure with unimodal pore size distribution– and flow-through configurations combined with cloth electrodes –which have a hierarchical microstructure with bimodal pore size distribution– provide the most favorable trade-off between hydraulic and electrochemical performance. Our analysis evidences the importance of carrying out the co-design of flow fields and electrode microstructures in tandem.

Influence of Support Material on the Structural Evolution of Copper during Electrochemical CO2 Reduction

The electrochemical CO2 reduction reaction (CO2RR) provides the combined benefit of reducing anthropogenic CO2 emissions while supplying a wide variety of valuable chemical feedstock chemicals.[1] While many transition metals are CO2RR active catalysts, only copper can form products requiring more than two electrons in the electrochemical conversion of CO2. This includes a multitude of high-value-added products such as ethylene, ethanol, or propanol.[1-3] The selectivity of the CO2RR is strongly influenced by the structure and morphology of the copper catalysts. Consequently, structural properties such as copper nanoparticle size, display an influence on CO2RR product selectivity.[4] This creates a substantial problem as copper is highly susceptible to reorganization during the electrochemical CO2RR, which inhibits the retention of apparently favorable surface structures during the CO2RR.[5] As a consequence, structure-selectivity relations can neither be reliably described nor completely understood. This problem is exacerbated by a lack of understanding of the underlying reasons that drive reorganization and therefore degradation of the catalyst. At reductive potentials, as used in the electrochemical CO2RR, coalescence and subsequent agglomeration are assumed to be the dominant degradation mechanism, while oxidative potentials generally trigger support corrosion and dissolution. Strategies for stabilization to retain activity and selectivity are therefore essential. Nevertheless their importance in the electrochemical CO2RR, stabilization methods are largely missing. For other reactions, such as the oxygen reduction reaction, various studies showed an increase in overall stability by containing the catalysts in a confined space.[6-8] This work presents the stabilizing effect of three different carbon support materials with unique morphologies on copper nanoparticles (CuNPs). Through the use of a non-porous Vulcan, a Ketjenblack with a diverse pore size distribution and highly defined mesoporous graphitic spheres (MGS) with a unimodal pore size distribution, the influence on structural characteristics of the carbon material on the stabilization of the CuNPs can be presented. The representative copper catalysts were prepared by colloidal synthesis or incipient wetness impregnation and evaluated through micro-flow cell measurements with online gas chromatography (GC) analytics and pre-/post catalytic high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), visualizing changes in the catalyst structure and morphology after the reaction. We demonstrate the successful stabilization of CuNPs by pore confinement against particle coalescence and subsequent agglomeration for up to 20 h of electrochemical CO2RR conditions, with GC analysis providing great insight into the influence of particle size, morphology, and location of the CuNPs on CO2RR product selectivity. Intriguingly, a high share of CO2RR products was observed for stabilized < 4 nm CuNPs putting the established particle size effect for the CO2RR, where the hydrogen evolution reaction was predominantly observed on nanoparticles below 15 nm, into question.[4] These results present new ways of stabilizing CuNPs and highlight the need for post-catalytic evaluation of the catalysts' morphological state to precisely derive performance-structure indicators.Work accepted and soon to be published in ChemElectroChemdoi.org/10.1002/celc.202200924Literature:[1] S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramollo, I. Chorkendorff, Chem Rev. 2019, 119, 7610–7672.[2] Y. Hori, Modern Aspects of Electrochemistry No. 42, Springer, 2008.[3] K. P. Kuhl, E. R. Cave, D. N. Abram, T. F. Jaramillo, Energy Environ. Sci. 2012, 5, 7050–7059.[4] R. Reske, H. Mistry, F. Behafarid, B. Roldan Cuenya, P. Strasser, J. Am. Chem. Soc. 2014, 136, 6978–6986.[5] W. T. Osowiecki, J. J. Nussbaum, G. A. Kamat, G. Katsoukis, M. Ledendecker, H. Frei, A. T. Bell, A. P. Alivisatos, ACS Appl. Energy Mater. 2019, 2, 7744–7749.[6] Y. Li, F. Cui, M. B. Ross, D. Kim, Y. Sun, P. Yang, Nano Lett. 2017, 1312–1317.[7] Y. T. Guntern, J. R. Pankhurst, J. Vavra, M. Mensi, V. Mantella, P. Schouwink, R. Buonsanti, Angew. Chem. 2019, 131, 12762–12769.[8] C. Galeano, J. C. Meier, V. Peinecke, H. Bongard, I. Katsounaros, A. A. Topalov, A. Lu, K. J. J. Mayrhofer, F. Schüth, J. Am. Chem. Soc. 2012, 134, 20457 – 20465. Figure 1

Evolution of pore structure in nanoparticle deposits from unimodal to bimodal pore size distributions: Focus on structural features of dendritic structures

Nanoparticle deposits can exhibit various structures, including compact and dendritic structures, depending on the deposition conditions. While previous studies have characterized deposit structures using factors such as porosity and spatial autocorrelation index, the pore size distribution (PSD), which is an essential structural property, has only been explored in compact structures. In this study, we investigate the PSDs of the entire nanoparticle deposits, ranging from compact to dendritic structures. Deposits are formed using an off-lattice Monte Carlo simulation, and deposition conditions are represented by two dimensionless numbers (KnD, χF). The diffusive Knudsen number (KnD) ranges from 10−1.5 to 101.5, while the dimensionless translational energy of a particle (χF) ranges from 10−3 to 101.5. We use the Delaunay triangulation algorithm for fast PSD calculation, and validate the calculation method using theoretical values of ideal structures and experimental literature data. Our results show that bimodal PSDs appear under thermally-dominated conditions with high values of KnD, while unimodal PSDs with a constant mode radius (∼2.5 rp) are observed under highly advective conditions with high values of χF. We present the geometric mean radii and mode radii of pores as color-filled contours to show their variation trends with KnD and χF. Additionally, we propose a simple model that predicts dendrite width by combining the overall porosity and mode radii of pores. Our model's predictions reasonably match the dendrite width data obtained using a density-based clustering algorithm.

Pore system of the multiple lithofacies reservoirs in unconventional lacustrine shale oil formation

Unconventional lacustrine shale formations are characterized by strong heterogeneity and intensive lithological variations in the vertical direction. Nevertheless, most studies focused merely on the organic-rich intervals due to the successful exploration and development of marine shale gas resources. This study systematically analyzed the overall pore system of the Triassic Chang 7 lacustrine shale formation in the Ordos Basin, China, using geochemical, petrological, mineralogical and petrophysical methods. In addition, the statistical analysis method of spearman rank correlation was employed for the intensive data analysis. The results showed that rock components and diagenetic processes have significantly different effects on the development of multi-lithologic pore systems in lacustrine shale formations. Organic-rich laminated shale (ORLS) and argillaceous siltstone (AS) show a bimodal, while the medium organic matter massive shale (MOMMS), fine sandstone A (FSA), and coarse sandstone B (CSB) exhibit unimodal pore size distribution. Organic matter negatively affects the pore volume and positively influences the pore throat, while clay minerals generally play a negative role except for ORLS. Quartz is conducive to the pore development of the reservoir except that it blocks some pore space in ORLS. Meanwhile, feldspar boosts the pore volume of all reservoirs and inhibits the pore throat of ORLS and MOMMS. Calcite and dolomite have negative effects on the entire pore system. Pyrite and siderite could facilitate pore throat preservation but inhibit pore space development. The diagenetic analysis shows that thermal maturation of organic matter and mineral dissolution play important roles in promoting pore development, while cementation and mechanical compaction have counteracting effects. The assemblage of ORLS and CSB acts as the most favorable reservoirs for lacustrine shale oil exploration under ideal conditions. The pore size distribution of the lacustrine shale oil reservoir with random multi-lithologies shows that macropores and mesopores are the main reservoir space. This study contributes to a better understanding of sweet spot prediction in the notoriously complicated lacustrine shale formation.

Relationship between thermal and electrical conductivity curves of soils with a unimodal pore size distribution: Part 1. A unified series-parallel resistor model

Soil thermal conductivity (λ) and electrical conductivity (σ) characterize heat and electricity conduction through soils. Both λ and σ are affected by similar factors, such as soil water content (θ), texture, bulk density (ρb), temperature, structure, and organic matter content. Little is known about the quantitative relationship between λ and σ, and how soil texture and ρb modify the relationship. In this part one of a two-part series, we examine the correlation between λ(θ) and σ(θ) curves and develop a new model for normalized σ curves of soils with a unimodal pore size distribution. We introduce an Ohm’s law analogy to describe the λ and σ curves conceptually, based on a cubic cell unit model. A unified series–parallel resistor model considering θ and ρb effects is established for both λ(θ) and σ(θ) curves by considering heat and electrical conduction pathways (solid, solid–liquid, and liquid pathways) in the hydration, menisci, and continuous liquid ranges. Simultaneous measurements of θ, λ and σ with thermo-TDR sensors on two soils are used to examine the model performance at various values of ρb and θ. The modeled and measured λ (θ) and σ (θ) curves provide consistent trends, and the normalized λ and σ values vs. degree of saturation confirm the existence of an earlier reported “mirror image” phenomenon between the functions.

Relationship between thermal and electrical conductivity curves of soils with a unimodal pore size distribution: Part 2. Estimating bulk electrical conductivity from thermal conductivity

Soil thermal conductivity (λ) and electrical conductivity (σ) influence heat conduction and electrical conduction through soils. In Part 1 of this two-part series, we demonstrated that for soils with a unimodal pore size distribution, the λ and σ curves were interrelated and could be described with a unified series–parallel resistor model. Based on the conceptual model presented in Part 1, the “mirror image” phenomenon in the λ-σ relationship was further evaluated. Starting with the Lu et al. (2007) λ model, the “mirror image” phenomenon was used to derive a new normalized σ model. The new σ model was dependent on degree of water saturation (S), and shared the same shape parameters as those in the λ model. Here, the new σ model is examined using new datasets consisting of simultaneous thermo-TDR sensor measurements of soil water content (θ), λ and σ. New model σ values interpolated between known dry and saturated σ values agreed well with measured σ values, with RMSE values within 0.102 dS m−1 and bias values between −0.083 and 0.014 dS m−1 for a variety of soil samples. Using repeated in situ λ measurements made in soils during an evaporative drying period, the new σ model estimated normalized σ values with RMSEs within 0.015 dS m−1. The new σ model offers an effective way to estimate σ of unsaturated soils.

Investigation on Compressibility and Microstructure Evolution of Intact Loess at Different Wetting States

Loess is widely deposited in arid and semi-arid areas and is characterized by low dry density, developed pore space, and loose structure, which is not commensurate with high structural strength and shear strength in the dry state. Many natural phenomena and experimental results show that intact loess is very sensitive to the change of water content, and a slight increase in water content can cause a rapid reduction in strength. Abundant information is available in the literature for the collapsibility of loess. However, research on the evolution of loess compressibility during wetting, which is very helpful in understanding loess collapsible deformation caused by long-term irrigation, remains minimal. To this end, in this article, the evolution of the compressibility of intact loess at different wetting stages is investigated by oedometer tests, and microstructure and pore size distribution (PSD) were characterized on intact loess specimens at different water contents before and after oedometer tests by scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP) methods. The results show that the compression index (Cc) and secondary compression index (Cα) of intact loess depend on water content and vertical stress and change abruptly when vertical stress exceeds yield stress. Cα/Cc values of intact loess are not constant, which increases with vertical stress to a peak and then gradually decreases to 0.025. Wetting and loading can cause damage to the microstructure of intact loess; specifically, loading leads to the collapse of the overhead structure and the transformation from a bimodal PSD into a unimodal PSD, and wetting intensifies the collapse of the microstructure to form a compacted interlocking structure and promotes the transformation of medium pores into small pores.

The fabric evaluation of two Indian bentonites subjected to different suctions and consolidation pressures

The study highlighted the fabric evaluation (i.e., pore size distribution (PSD) and morphology) of monovalent and divalent Indian bentonites, subjected to different suctions and consolidation pressures. Oedometer tests were conducted on bentonites specimens in two different initial conditions, i.e., slurry and compacted conditions. The slurry and compacted specimens were prepared at water contents equal to liquid limit (LL) and optimum moisture content (OMC), respectively. The water retention properties of the bentonites were determined in both unconfined (slurry) and confined (compacted) conditions using pressure plate apparatus and WP4C dew-point potentiameter. The influence of different consolidation pressures and suctions on pore structure and morphology of the bentonites were investigated by mercury intrusion porosimetry (MIP) and Field Emission Scanning Electron Microscope (FESEM) observations. For both the bentonites, the bimodal pore size distribution was observed over the applied consolidation pressure between 7.2 kPa and 2289.6 kPa in both slurry and compacted specimen conditions. However, an increase in consolidation pressure lead to a significant decrease in macropore volume. The compression index of the bentonites was found to be strongly correlated with a percentage decrease in macropore intruded volume (R2 = 0.91) and total intruded pore volume (R2 = 0.89), however, independent of micropores volume. The FESEM images and MIP results evidenced that for both the bentonites more homogeneous morphology and effective filling of the pores took place in slurry conditions as compared to initially compacted specimens. For the same void ratio, the hydraulic conductivity of slurry specimens was noted to be slightly lower than the compacted specimens. In slurry conditions at suctions below 3 MPa, the water retention capacity of monovalent bentonite was noted to be higher than that of divalent bentonite, whereas the opposite trend was found in compacted conditions. Irrespective of slurry or compacted conditions, the increase in suction lead to the transformation of bimodal PSD into a unimodal pore family for divalent bentonite, whereas trimodal to unimodal PSD was noted for monovalent bentonite in compacted specimens. The initial state (slurry or compacted) and the boundary condition of the specimen, as well as fabric (pore size distribution and morphology) of the bentonites, were found to have a notable influence on the compressibility, hydraulic conductivity and water retention properties.

Relationship between Thermal and Electrical Conductivity Curves of Soils with a Unimodal Pore Size Distribution: Part 2. Estimating Bulk Electrical Conductivity from Thermal Conductivity

Relationship between Thermal and Electrical Conductivity Curves of Soils with a Unimodal Pore Size Distribution: Part 2. Estimating Bulk Electrical Conductivity from Thermal Conductivity

Comparison of SEM-Assisted Nanoporometric and Microporometric Morphometric Techniques Applied for the Ultramicroporous Polymer Films

One of the most important applications of polymeric porous nanomaterials is the design of nanoporous structures for operation in patch-clamp systems allowing to establish a gigaohm contact, as well as for the measurements of biomolecules, informational macromolecules, including DNA, translocating through the nanopore arrays. Development of nanopore sequencing techniques leads to fundamentally new big data arrays, but their representativeness and validity, as well as the validity of counting of biomacromolecular particles based on ultramicropore arrays, strongly depends both on the pore size (in engineering lithography unimodal pore size distribution is optimal) and the accuracy of the size distribution measurements using instrumental methods. However, the former is unattainable when using soft matter or stretchable, plastic and elastic polymer materials and films, while the latter depends on the metrological parameters of the instrumental and algorithmic porosimetry techniques. Therefore in this paper the question about the applicability of polymer materials with pore arrays for the studies of biomacromolecules and bionanostructures is proposed to be answered using a comparative analysis of two different porosimetry approaches with the resolution not lower than electron microscopic one.

Shrinkage Behavior, Thermal Expansion Behavior, and Electrical Conductivity Study of Samarium Doped Ceria Electrolytes

Ceria-based electrolytes generally have high sintering temperatures (~1500 °C)1,2, which increases the cell fabrication cost and decreases the mechanical stability of the cell due to rapid grain growth. In this work, the Ce0.9Sm0.1O2 (SDC) electrolyte is synthesized by microwave-assisted co-precipitation method using ethanol as a solvent. The sintering behavior of the green compact is studied using a dilatometer. Linear shrinkage and shrinkage rate behavior study shows a low sintering end temperature (1200 °C) and a final relative density of ~92%. A maximum linear shrinkage of -15.70% is observed at 1200 °C. A uni-modal shrinkage rate curve is seen, which confirms uni-modal pore size distribution in the powder. After 1388 °C, a dedensification is observed (+ 0.29% linear shrinkage), which might be associated with the reduction of Ce4+ to Ce3+ (please see Figure 1). Initial sintering results suggest that the synthesis method used has significantly lowered the SDC electrolyte's sintering temperature. Although the densification is completed at 1200 °C, the microstructure may change with further increase in the sintering temperature, affecting electrical conductivity. Inspired by the initial results, a detailed study on the effect of sintering temperature (1200 °C to 1500 °C) on the microstructure and electrical conductivity of SDC will be carried out and presented in the paper. S. Medisetti et al., Nano-Structures & Nano-Objects, 11, 7–12 (2017) https://www.sciencedirect.com/science/article/pii/S2352507X16301275.G. Accardo et al., J. Appl. Biomater. Funct. Mater., 14, 35–41 (2016) https://journals.sagepub.com/doi/abs/10.5301/jabfm.5000265. Figure 1

Synthesis of Nanocrystalline Powders in the CеO2〈ZrO2〉–Al2O3 System by the Citrate Sol–Gel Method

Weakly aggregated, highly dispersed precursor powders with a specific surface area of 350–360 m2/g have been prepared by the citrate sol–gel method in the CеO2〈ZrO2〉–Al2O3 system. Heat treatment of the precursors in the temperature range 700–1000°C led to the formation of powders based on a fluorite-like Ce0.7Zr0.3O2 solid solution with a crystallite size under 30 nm. The presence of alumina has been shown to inhibit the Ce0.7Zr0.3O2 crystallite growth process. Using low-temperature nitrogen adsorption measurements, we have studied texture characteristics of the powders obtained at 1000°C: they have a specific surface area of 90 and 105 m2/g and a specific pore volume of up to 0.380 cm3/g, with a unimodal pore size distribution in the range 2.5–10 nm. We examine the effect of thermal “aging” at a temperature of 1000°C for 50 h on the structure and particle size of the powders. Based on the experimental data obtained, we propose a process for the synthesis of nanocrystalline mesoporous powders in the CеO2〈ZrO2〉–Al2O3 system for the preparation of supports of an active phase (Pt, Pd, or Rh) in three-way catalysts.

Catalytic performance of Ni/CaO-Ca12Al14O33 catalyst in the green synthesis gas production via CO2 reforming of CH4

Dry Reforming of Methane over 15wt.% Ni/CaO-Ca12Al14O33 catalyst was performed in a microreactor in the temperature range 600−800°C under atmospheric pressure, at WHSV of 120 Lg−1h−1 and by time on stream of 12 h for producing synthesis gas. The novel catalyst was prepared by Ni wet impregnation of a mixed calcium-aluminum-oxide (CAO) ceramic support. Similarly, a Ni/γ-Al2O3 reference catalyst was prepared. Characterizations were conducted by TGA-FTIR, XRD, SEM-EDS, N2 physisorption, H2-TPR, CO2-TPD, and CO2-TPRn techniques. After calcination(500°C)/reduction(700°C) steps in situ formed CaO promoter was highly dispersed on Ca12Al14O33 carrier, which induced strong basicity. A good anchorage of NiO on CAO support was evidenced by reduction peaks at 490°C and 650°C on the H2-TPR profile. The reduced mesoporous catalyst presented high SBET, large pores volume, and unimodal pore size distribution. High reactants conversions, good H2 and CO selectivity, and H2/CO molar ratio close to unity at 800°C were achieved. Although the catalytic activity of Ni/γ-Al2O3 reference catalyst was slightly better than that of Ni/CaO-Ca12Al14O33 catalyst the stability was worse owing to the excessive carbon build-ups, whereas the novel catalyst displayed a very low carbon deposit on spent catalyst at 600 and 700°C, and negligible coke deposit at 800°C. It was established that the basicity of CaO-Ca12Al14O33 support can play a key role in preventing coke deposition during DRM. The Ni CaO-Ca12Al14O33 can serve as sorbent for CO2 capture and simultaneously for its catalytic conversion in a valuable fuel.

Microstructure observations in compacted clays subjected to thermal loading

The response of clayey materials to thermal variation has been the subject of extensive studies, given the wide range of engineering applications which involve subjecting soils to substantial temperature fluctuations. A number of hypotheses have been proposed to explain the volumetric changes induced in the clays as a result of temperature variations. Most associate the observed volumetric changes to re-orientation as well as changes in the clay microstructure, with no microstructural experimental evidences to date. The work presented in this note is a first attempt at studying the evolution of the internal structure of two types of clays, an Illite and a Kaolin, compacted dry of optimum, submerged until saturation, reconsolidated to various vertical effective stresses and then subjected to thermal loading. A series of thermal oedometer, mercury intrusion porosimetry (MIP) and tomography tests were conducted in order to induce, detect, and quantify microstructural alterations within the clay as a consequence of temperature changes. Results of heating and cooling tests on Illite showed a thermal contraction which could be attributed to the deformation/collapse of macro-pores in its dual-porosity structure assemblage. The magnitude of the observed contraction varied with the level of pre-imposed effective vertical stresses. Higher effective vertical stresses resulted in larger shear stresses at the contacts of clay-assemblages, and thus in easier deformation of the macro-pores. The Kaolin samples which presented a unimodal pore size distribution, with a relatively small dominant pore size (0.25 μm), did not exhibit changes in the microstructure which could be captured by the MIP.

Compaction behaviour of lime-treated metakaolin

Metakaolin has been widely used as pozzolanic additive to improve the pozzolanic activity of lime-based products. In this study, the normal standard Proctor compaction test was performed on metakaolin with (5% lime) and without (0% lime) lime addition. The changes in stiffness, suction, and microstructure with remoulding water content were investigated on statically compacted samples. Results show that lime-treated metakaolin exhibits a 1.5-peak compaction curve, while untreated metakaolin exhibits common one-peak compaction curve. The uncommon shape of the compaction curve of the treated metakaolin can be explained by the non-fully developed soil suction when water is not continuous. Treated and untreated samples compacted at both dry and wet of optimum show uni-modal pore-size distribution characteristics, indicating the absence of aggregates. This is related to the specific thermal treatment, forming separate metakaolin platelets and leading to a modified uniform structure with diffuse platelets. The soil stiffness is rather dominated by the number of particle contacts or soil dry density, the effect of suction being insignificant. For the suction changes, on the dry side, the effect of pore-size distribution prevails facing the effect of water content, while on the wet side it is the effect of water content that becomes dominating.