Search

Pack boriding with CeO2 was performed on the powder metallurgical (PM) near-α type titanium alloy at a temperature of 1273–1373 K for 5–15 h followed by air cooling. The microstructure analysis showed that the boride layer on the surface of the alloy was mainly composed of a monolithic TiB2 outer layer, inner whisker TiB and sub-micron sized flake-like TiB layer. The growth kinetics of the TiB2 and TiB layers obeyed the parabolic diffusion model. The diffusion coefficient of boron in the boride layers obtained in the present study was well within the ranges reported in the literature. The activation energies of boron in the TiB2 and TiB layers during the pack boriding were estimated to be 166.4 kJ/mol and 122.8 kJ/mol, respectively. Friction tests showed that alloys borided at moderate temperatures and times had lower friction coefficients, which may have been due to the fine grain strengthening effect of TiB whiskers. The alloy borided at 1273 K for 10 h had a minimum friction coefficient of 0.73. [ABSTRACT FROM AUTHOR]

Concrete with good mechanical properties and durability has always been a necessity in engineering. The addition of fibers and supplementary cementitious materials to concrete can enhance its mechanical and durability performance through a series of chemical and physical interactions. This study aims to investigate the effects of key parameters on the compressive strength, splitting tensile strength, and chloride penetration resistance of concrete combined with ground granulate blast furnace slag (GGBS) and macro polypropylene synthetic fiber (MSF). Based on the Taguchi method, a total of eighteen mixtures were evaluated, considering the effects of GGBS content, MSF content, water-to-binder (w/b) ratio, and chloride solution concentration on concrete properties. The results showed that the w/b ratio has a significant impact on the properties of concrete, which are enhanced by a decrease in w/b ratio. The GGBS content had little effect on the 28-day strength of concrete, which even decreased with a large GGBS content, but GGBS had a positive effect on the long-term strength of concrete. Moreover, the chloride penetration resistance of concrete was enhanced by an increase in the GGBS content. The MSF content had no obvious effects on the compressive strength and chloride penetration resistance of concrete, but it could enhance the splitting tensile strength to some extent, and this enhancement was more obvious over time. The chloride diffusion coefficient of concrete changed with the concentration of chloride solution, and the two increased simultaneously. [ABSTRACT FROM AUTHOR]

1H spin–lattice relaxation experiments have been performed for gels based on fish collagen in order to analyze water dynamics. The covered frequency range ranges from 10 kHz to 10 MHz; in some cases, the temperature has varied as well. The relaxation data have been reproduced in terms of two models of water motion—a model including two relaxation contributions associated with the diffusion of water molecules on the macromolecular surfaces and a second model being just a phenomenological power law. The concept of surface diffusion has led to a very good agreement with the experimental data and a consistent set of parameters, with the diffusion coefficients being about five orders of magnitude slower compared to bulk water for one of the pools and considerably faster for the second one (smaller by factors between 2 and 20 compared to bulk water). In some cases, the attempt to reproduce the data in terms of a power law has led to a good agreement with the experimental data (the power law factor varying between 0.41 and 0.57); however, in other cases, the discrepancies are significant. This outcome favors the concept of surface diffusion. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs) have become attractive vehicles for drug delivery in cancer therapy due to their ability to accumulate in tumours and mitigate side effects. This study focuses on the production of doxorubicin (DOX)-loaded NPs comprising Poly (lactic-co-glycolic acid)-Polyethylene glycol with varying PEG proportions and the examination of their impact on drug release kinetics. DOX-loaded NPs, composed of PLGA-co-PEG with PEG contents of 0%, 5%, 10%, and 15%, were synthesized by the solvent evaporation technique, exhibited spherical morphology, and had sizes ranging from 420 nm to 690 nm. In vitro drug release studies revealed biphasic profiles, with higher PEG contents leading to faster and more extensive drug release. The Baker–Lonsdale model demonstrated the best fit to the drug release data, indicating that the release process is diffusion-controlled. The diffusion coefficients for DOX determined ranged from 6.3 × 10−18 to 7.55 × 10−17 cm2s−1 and exhibited an upward trend with increasing PEG content in the polymer. In vitro cytotoxicity tests with CHO cells showed that unloaded NPs are non-toxic, while DOX-loaded PLGA-PEG 15% NPs induced a greater decrease in cellular viability compared to their PLGA counterparts. A mathematical relationship between the diffusion coefficient and PEG percentage was derived, providing a practical tool for optimizing DOX release profiles. [ABSTRACT FROM AUTHOR]

Reinforced concrete structures are prone to the corrosion of steel bars when exposed to chloride-rich environments, which can severely impact their durability. To address this issue, a comprehensive understanding of the factors influencing chloride ion diffusion in concrete is essential. This paper provides a summary of recent domestic and foreign research on chloride ion transport in concrete, focusing on six key factors: water–binder ratio, additive content, crack width, ambient temperature, relative humidity, and dry–wet cycles. The findings show that the diffusion coefficient of chloride ions in concrete increases with a higher water–binder ratio and decreases with increased additive content. Additionally, wider cracks result in a greater diffusion of chloride ions. The permeability resistance of concrete to chloride ions decreases with rising temperature and humidity, and dry–wet cycles further accelerate the diffusion of chloride ions. The article concludes by discussing various anti-corrosion measures, such as the use of corrosion inhibitors, surface coatings, and electrochemical treatments, to ensure the longevity of the structure. Finally, directions for future research are proposed. [ABSTRACT FROM AUTHOR]

In this research, the diffusion behaviors within the Ti-Fe-Cr ternary system were examined at the temperatures of 1273 K and 1373 K through the diffusion couple technique. This study led to the determination of both ternary inter-diffusion and impurity diffusion coefficients in the body-centered cubic (bcc) phase for the Ti-Fe-Cr alloy, utilizing the Whittle–Green and Hall methods. The statistics show that the average diffusion coefficients D ˜ F e F e T i and D ˜ C r C r T i measured at 1273 K were 1.34 × 10−12 and 3.66 × 10−13, respectively. At 1373 K, the average values of D ˜ F e F e T i and D ˜ C r C r T i were 4.89 × 10−12 and 1.43 × 10−12. By adopting the CALPHAD method, a self-consistent database for atomic mobility in the bcc phase of the Ti-Fe-Cr system was established. This database underwent refinement by comparing the newly acquired diffusion coefficients with data from the existing literature. Diffusion simulations for the diffusion couples were performed, drawing on the established database. The error between the simulated diffusion coefficient and the experimental measurement data is within 15%, and the simulated data of the component distance distribution and diffusion path are in good agreement with the experimental data. The simulations generated results that aligned well with the observed experimental diffusion characteristics, thereby affirming the reliability and accuracy of the database. [ABSTRACT FROM AUTHOR]

The dissolution of wool yarns in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim][OAc] has been investigated. Wool yarns were submerged into [C2mim][OAc] and dissolved for various times and temperatures before coagulating with water. Optical microscopy was used to track the yarn's cross-sectional area. We propose that there are two competing dissolution processes, one rate-limited by disulfide bonds at low temperatures (LTs), and a second by hydrogen bonds at high temperatures (HTs), with a crossover point between the two regimes at 70 ℃. The corresponding activation energies were ELT = 127 ± 9 kJ/mol and EHT = 34 ± 1 kJ/mol. The remaining area of the dissolved wool yarn could be shifted via time–temperature superposition to plot a single master curve of area against time for both regions. Finally, the dissolution could be modelled by a diffusion process, giving self-diffusion coefficients for the [C2mim][OAc] ions (0.64–15.31 × 10−13 m2/s). [ABSTRACT FROM AUTHOR]

This article describes the swelling and release mechanisms of paracetamol in polyurethane nanocomposite hydrogels containing Cloisite® 30B (organically modified montmorillonite). The transport mechanism, swelling and release processes of the active substance in nanocomposite matrix were studied using gravimetric and UV-Vis spectroscopic methods. Swelling and release processes depend on the amount of clay nanoparticles in these systems and the degree of crosslinking of PU/PEG/Cloisite® 30B hydrogel nanocomposites. The presence of clay causes, on the one hand, a reduction in free volumes in the polymer matrices, making the swelling process less effective; on the other hand, the high swelling and self-aggregation behavior of Cloisite® 30B and the interactions of paracetamol both with it and with the matrix, cause a change in the transport mechanism from anomalous diffusion to Fickian-like diffusion. A more insightful interpretation of the swelling and release profiles of the active substance was proposed, taking into account the "double swelling" process, barrier effect, and aggregation of clay. It was also proven that in the case of modification of polymer matrices with nanoparticles, the appropriate selection of their concentration is crucial, due to the potential possibility of controlling the swelling and release processes in drug delivery patches. [ABSTRACT FROM AUTHOR]

Diffusion bonding has many advantages, but it also has its specifics. When creating heterogeneous joints, problems arise with the creation of intermetallic phases. For this reason, an interlayer is needed to prevent the creation of these unfavorable phases. It is important to ensure that the interlayer is of sufficient thickness to prevent the elements from diffusing through the entire interlayer and the intermetallic phases from being formed again. Conversely, too thick an interlayer causes an increase in the heterogeneity of the bond properties. The creation of the initial diffusion bonds in a heterogeneous diffusion joint of AISI 304 and AISI 316L steel with a 0.2 mm thick nickel interlayer was made in a Gleeble 3500. The experiments to determine the diffusion kinetics were carried out in a vacuum furnace, with subsequent evaluation by EDX (Energy Dispersive X-ray Spectroscopy) analysis. Subsequently, the diffusion coefficients of nickel into both steels were determined, and generalized equations were formulated to calculate the diffusion coefficients for temperatures in the range of 950 to 1150 °C and holding times in the range of 3600 to 18,000 s. Equations are also given to determine the width of the diffused zone between each steel and the Ni interlayer. [ABSTRACT FROM AUTHOR]

To avoid hydrogen flaking in rail production, it is of crucial importance to understand the differences in hydrogen diffusion and trapping between different production steps. Therefore, as-cast unfinished material was compared with two finished rails, hot-rolled and head-hardened, using electron backscattered diffraction (EBSD), electrochemical permeation, and thermal desorption spectroscopy (TDS). A significant increase in dislocation density was in the head-hardened rail compared with the other material states. This leads to an effective hydrogen diffusion coefficient of 5.8 × 10−7 cm2/s which is lower by a factor of four than the diffusion coefficients examined in the other states. Thermal desorption spectroscopy analyses show a clear difference between unfinished and finished rail materials. While a peak in activation energy between 32 and 38 kJ/mol is present at all states, only as-cast unfinished material shows a second peak with an activation energy of 47 kJ/mol, which is related to microvoids. The results show that in the investigated material, the effect of increasing dislocation density has a stronger influence on the effective diffusion coefficient than the presence of a second active trapping site. [ABSTRACT FROM AUTHOR]

In the hydrometallurgical process of zinc production, the residue from the leaching stage is an important intermediate product and is treated in a Waelz kiln to recover valuable metals. To ensure optimal results during the Waelz kiln process, it is necessary to pre-treat the residues by drying them first due to their higher water content. This work studies the residue's drying process using microwave technology. The study results indicate that microwave technology better removes the residue's oxygen functional groups and moisture. The dehydration process's effective diffusion coefficient increases as the microwave's heating power, the initial moisture content, and the initial mass increase. The Page model is appropriate for imitating the drying process, and the activation energy of the drying process for the residues is −13.11217 g/W. These results indicate that microwave technology efficiently dries the residues from the leaching stage. Furthermore, this study provides a theoretical basis and experimental data for the industrial application of microwave drying. [ABSTRACT FROM AUTHOR]

In this work, a novel flow–electric field coupling configuration was designed and implemented for enhancing Zn-Cd cementation. A series of tests was conducted to explore the optimization of the Zn-Cd cementation process and its mechanism. Firstly, the various characteristics of the sponge cadmium at various locations in the device were compared, and it was concluded that the optimum purity of the sponge cadmium obtained from the anode was up to 94.1%. The generation and stripping of the cadmium sponge was revealed for the first time by cross-sectional electron microscopy. The four stages of the apparent reaction in the system were analyzed in relation to the pH, cadmium concentration and cadmium sponge flaking at each flow rate. It was proved that the separation of cadmium sponge mainly occurred in the third phase. Secondly, by comparing the morphology and specific surface area of the cadmium sponge at different flow rates, the optimum flow field velocity was identified as 30 mL/s. At this point, the specific surface area reached a maximum of 1.151 m2/g. Six flow field configurations were compared and preferred. The results demonstrated that the LCAH (Low-Cathode-Anode-High) modulation resulted in a sparser structure of the cadmium sponge, which was more easily exfoliated from the zinc anode surface by fluid impact. This was considered to be the most beneficial flow field configuration for improving the cadmium cementation rate and reducing the cost of the reaction. Moreover, the reaction steps of the system were analyzed. Its rate-limiting step was initially empirically identified as the diffusion step and proven by calculating the activation energy of 12.6 kJ/mol. It was confirmed that the diffusion process under different flow field configurations followed the first-order kinetic principle. In addition, the system's reaction phases were compared. Calculations confirmed that the diffusion process under various flow field configurations followed first-order kinetics. The diffusion coefficient of LACH proved to be the highest in the comparative tests, and the evident experimental results supported this conclusion. [ABSTRACT FROM AUTHOR]

This paper presents an innovative and efficient methodology for the determination of the solid-state diffusion coefficient in electrode materials with phase transitions for which the assumption of applying the well-known formula from the work of Weppner et al. is not satisfied. This methodology includes a k-means machine learning screening of Galvanostatic Intermittent Titration Technique (GITT) steps, whose outcomes feed a physics-informed algorithm, the latter involving a pseudo-two-dimensional (P2D) electrochemical model for carrying out the numerical simulations. This methodology enables determining, for all of the 47 steps of the GITT characterization, the dependency of the Na+ diffusion coefficient as well as the reaction rate constant during the sodiation of an NVPF electrode to vary between 9 × 10 − 18 and 6.8 × 10 − 16 m2·s−1 and between 2.7 × 10 − 14 and 1.5 × 10 − 12 m2.5·mol−0.5·s−1, respectively. This methodology, also validated in this paper, is (a) innovative since it presents for the first time the successful application of unsupervised machine learning via k-means clustering for the categorization of GITT steps according to their characteristics in terms of voltage; (b) efficient given the considerable reduction in the number of iterations required with an average number of iterations equal to 8, and given the fact the entire experimental duration of each step should not be simulated anymore and hence can be simply restricted to the part with current and a small part of the rest period; (c) generically applicable since the methodology and its physics-informed algorithm only rely on "if" and "else" statements, i.e., no particular module/toolbox is required, which enables its replication and implementation for electrochemical models written in any programming language. [ABSTRACT FROM AUTHOR]

In this study, the influence of growth temperature variation on the synthesis of MoS2 using a direct MoO2 precursor was investigated. The research showed that the growth temperature had a strong impact on the resulting morphologies. Below 650 °C, no nucleation or growth of MoS2 occurred. The optimal growth temperature for producing continuous MoS2 films without intermediate-state formation was approximately 760 °C. However, when the growth temperatures exceeded 800 °C, a transition from pure MoS2 to predominantly intermediate states was observed. This was attributed to enhanced diffusion of the precursor at higher temperatures, which reduced the local S:Mo ratio. The diffusion equation was analyzed, showing how the diffusion coefficient, diffusion length, and concentration gradients varied with temperature, consistent with the experimental observations. This study also investigated the impact of increasing the MoO2 precursor amount, resulting in the formation of multilayer MoS2 domains at the outermost growth zones. These findings provide valuable insights into the growth criteria for the effective synthesis of clean and large-area MoS2, thereby facilitating its application in semiconductors and related industries. [ABSTRACT FROM AUTHOR]

In the present work, two mathematical diffusion models have been used to estimate the growth of the iron monoboride and diiron boride coating formed on AISI 420 steel. The boronizing of the steel was carried out with the solid diffusion packing method at a boronizing temperature of 1123 K–1273 K. Experimental results show the two-coating system consists of an outer monoboride and an inner diiron boride coating with a predominantly planar structure at the propagation front. The depth of the boride coating increases according to temperature and treatment time. A parabolic curve characterizes the propagation of the boride coatings. The two proposed mathematical models of mass transfer diffusion are founded on the solution corresponding to Fick's second fundamental law. The first is based on a linear boron concentration–penetration profile without time dependence, and the second model with time dependence (exact solution). For both models, the theoretical law of parabolic propagation and the average flux of boron atoms (Fick's first fundamental law) at the growth interfaces (monoboride/diiron boride and diiron boride/substrate) are considered to estimate the propagation of the boride coatings (monoboride and diiron boride). To validate the mathematical models, a programming code is written in the MATLAB program (adaptation 7.5) designed to simulate the growth of the boride coatings (monoboride and diiron boride). The following parameters are used as input data for this computer code: (the layer thicknesses of the FeB and Fe2B phases, the operating temperature, the boronizing time, initial formation time of the boride coating, the surface boron concentration limits, FeB/Fe2B and Fe2B/Fe growth interfaces, and the mass transfer diffusion coefficient of boron in the iron monoboride and diiron boride phases). The outputs of the computer code are the constants ε F e B and ε F e 2 B . The assessment of activation energies of AISI 420 steel for the two mathematical models of mass transfer is coincident ( Q F e B = 221.9 kJ∙mol−1 and Q F e 2 B = 209.1 kJ∙mol−1). A numerical analysis was performed using a standard Taylor series for clarification of the proximity between the two models. SEM micrographs exhibited a strong propensity toward a flat-fronted composition at expansion interfaces of the iron monoboride and diiron boride coating, confirmed by XRD analysis. Tribological characterizations included the Vickers hardness test method, pin-on-disc, and Daimler–Benz Rockwell-C indentation adhesion tests. After thorough analysis, the energies were compared to the existing literature to validate our experiment. We found that our models and experimental results agreed. The diffusion models we utilized were crucial in gaining a deeper understanding of the boronizing behavior of AISI 420 steel, and they also allowed us to predict the thicknesses of the iron monoboride and diiron boride coating. These models provide helpful approaches for predicting the behavior of these steels. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of SiC/Al-40Si composites prepared under high pressure were studied. As the pressure increases from 1 atm to 3 GPa, the primary Si phase in the Al-40Si alloy is refined. With increasing pressure, the composition of the eutectic point increases, the solute diffusion coefficient decreases exponentially, and the concentration of Si solute at the front of the solid–liquid interface of the primary Si is low, which contributes to the refining of the primary Si and inhibiting its faceted growth. The bending strength of SiC/Al-40Si composite prepared under 3 GPa was 334 MPa, which was 66% higher compared to the Al-40Si alloy prepared under the same pressure. [ABSTRACT FROM AUTHOR]

The actual protective performance of the coated reinforcement in coral concrete was investigated by measuring the chloride ion diffusion coefficient, electrochemical analysis, and numerical simulation. The test results show that the corrosion rate of coated reinforcement in coral concrete under the action of wet and dry cycles is kept at a low level, and the Rp value is always greater than 250 kΩ·cm2 during the test period, which is in the uncorroded state and has good protection performance. Moreover, the chloride ion diffusion coefficient D is in accordance with the power function relationship with the wet and dry cycle time, and a time-varying model of chloride ion concentration on the surface of coral concrete is established. The surface chloride ion concentration of coral concrete reinforcement was modeled as a time-varying model; the cathodic zone of coral concrete members was the most active, increasing from 0 V to 0.14 V from 0 to 20 years, with a large increase in potential difference before the 7th year, and a significant decrease in the increase after the 7th year. [ABSTRACT FROM AUTHOR]

One of the key problems that affect the durability of reinforced concrete structures is the corrosion of rebar induced by chloride. Despite the complicated transport mechanism of chloride ions in cementitious materials, diffusion is still the key mechanism of chloride ingress. The determination of the chloride diffusion coefficient will help to predict the chloride profile inside the cementitious materials and estimate the service life with regard to chloride-induced corrosion. However, this paper shows that the chloride diffusion coefficient in the literature is sometimes misunderstood. Such a misunderstanding results in the overestimation of the chloride resistance of cementitious materials. To clarify the chloride diffusion coefficient, this paper first presents the steady- and non-steady-state diffusion equations in cementitious materials. The factors that influence the diffusive flux are identified. The effective and apparent diffusion coefficients are then clearly explained and properly defined. We also point out the obscure definitions of the effective diffusion coefficient in the literature. The varied definitions of the effective diffusion coefficient are the result of the consideration of different factors affecting the diffusion process. Subsequently, this paper discusses two natural diffusion test methods that are frequently employed in cementitious materials to measure the chloride diffusion coefficient. The influencing factors considered by the measured diffusion coefficients are analyzed in detail. Then, the diffusion coefficients determined in some of the studies are reviewed. It is shown that three typical errors could occur when numerically determining the diffusion coefficients. [ABSTRACT FROM AUTHOR]

The diffusion phenomenon in the Ti–Ni binary system was investigated at a temperature of 1173 K. Microstructure and texture analysis revealed the formation of three stable intermetallic compounds, namely Ti2Ni, TiNi, and TiNi3, as well as two metastable intermetallic compounds, including Ti3Ni4 and Ti2Ni3, at the interfacial diffusion zone. The nucleation surface energy increase was analytically estimated, and marker experiments were conducted using thoria particles, both of which showed that Ti2Ni was the first compound to form at the Ti–Ni diffusion interface. At a temperature of 1173 K, using the Wagner method, the integrated diffusion coefficients for the Ti2Ni, TiNi, and TiNi3 phases were calculated to be 3.53 × 10−12, 18.1 × 10−15, and 6.2 × 10−15 m2/s, for, respectively. [ABSTRACT FROM AUTHOR]

Mass transport in textiles is crucial. Knowledge of effective mass transport properties of textiles can be used to improve processes and applications where textiles are used. Mass transfer in knitted and woven fabrics strongly depends on the yarn used. In particular, the permeability and effective diffusion coefficient of yarns are of interest. Correlations are often used to estimate the mass transfer properties of yarns. These correlations commonly assume an ordered distribution, but here we demonstrate that an ordered distribution leads to an overestimation of mass transfer properties. We therefore address the impact of random ordering on the effective diffusivity and permeability of yarns and show that it is important to account for the random arrangement of fibers in order to predict mass transfer. To do this, Representative Volume Elements are randomly generated to represent the structure of yarns made from continuous filaments of synthetic materials. Furthermore, parallel, randomly arranged fibers with a circular cross-section are assumed. By solving the so-called cell problems on the Representative Volume Elements, transport coefficients can be calculated for given porosities. These transport coefficients, which are based on a digital reconstruction of the yarn and asymptotic homogenization, are then used to derive an improved correlation for the effective diffusivity and permeability as a function of porosity and fiber diameter. At porosities below 0.7, the predicted transport is significantly lower under the assumption of random ordering. The approach is not limited to circular fibers and may be extended to arbitrary fiber geometries. [ABSTRACT FROM AUTHOR]

Chloride ion diffusion properties are important factors that affect the durability of cementitious materials. Researchers have conducted much exploration in this field, both experimentally and theoretically. Numerical simulation techniques have been greatly improved as theoretical methods and testing techniques have been updated. Researchers have modeled cement particles mostly as circular shapes, simulated the diffusion of chloride ions, and derived chloride ion diffusion coefficients in two-dimensional models. In this paper, a three-dimensional random walk method based on Brownian motion is employed to evaluate the chloride ion diffusivity of cement paste with the use of numerical simulation techniques. Unlike previous simplified two-dimensional or three-dimensional models with restricted walks, this is a true three-dimensional simulation technique that can visually represent the cement hydration process and the diffusion behavior of chloride ions in cement paste. During the simulation, the cement particles were reduced to spheres, which were randomly distributed in a simulation cell with periodic boundary conditions. Brownian particles were then dropped into the cell and permanently captured if their initial position in the gel fell. Otherwise, a sphere tangential to the nearest cement particle was constructed, with the initial position as the center. Then, the Brownian particles randomly jumped to the surface of this sphere. The process was repeated to derive the average arrival time. In addition, the diffusion coefficient of chloride ions was deduced. The effectiveness of the method was also tentatively confirmed by the experimental data. [ABSTRACT FROM AUTHOR]

Niobates are very promising anode materials for Li+-storage rooted in their good safety and high capacities. However, the exploration of niobate anode materials is still insufficient. In this work, we explore ~1 wt% carbon-coated CuNb13O33 microparticles (C-CuNb13O33) with a stable shear ReO3 structure as a new anode material to store Li+. C-CuNb13O33 delivers a safe operation potential (~1.54 V), high reversible capacity of 244 mAh g−1, and high initial-cycle Coulombic efficiency of 90.4% at 0.1C. Its fast Li+ transport is systematically confirmed through galvanostatic intermittent titration technique and cyclic voltammetry, which reveal an ultra-high average Li+ diffusion coefficient (~5 × 10–11 cm2 s−1), significantly contributing to its excellent rate capability with capacity retention of 69.4%/59.9% at 10C/20C relative to 0.5C. An in-situ XRD test is performed to analyze crystal-structural evolutions of C-CuNb13O33 during lithiation/delithiation, demonstrating its intercalation-type Li+-storage mechanism with small unit-cell-volume variations, which results in its capacity retention of 86.2%/92.3% at 10C/20C after 3000 cycles. These comprehensively good electrochemical properties indicate that C-CuNb13O33 is a practical anode material for high-performance energy-storage applications. [ABSTRACT FROM AUTHOR]

The chloride diffusion coefficient (Dcl) is one of the most important characteristics of concrete durability. This study aimed to develop a prediction model for the Dcl of concrete incorporating supplemental cementitious material. The datasets of concrete containing supplemental cementitious materials (SCMs) such as tricalcium aluminate (C3A), ground granulated blast furnace slag (GGBFS), and fly ash were used in developing the model. Five machine learning (ML) algorithms including adaptive neuro-fuzzy inference system (ANFIS), artificial neural network (ANN), support vector machine (SVM), and extreme learning machine (ELM) were used in the model development. The performance of the developed models was tested using five evaluation metrics, namely, normalized reference index (RI), coefficient of determination (R2), mean absolute error (MAE), and root mean square error (RMSE). The SVM models demonstrated the highest prediction accuracy with R2 values of 0.955 and 0.951 at the training and testing stage, respectively. The prediction accuracy of the machine learning (ML) algorithm was checked using the Taylor diagram and Boxplot, which confirmed that SVM is the best ML algorithm for estimating Dcl, thus, helpful in establishing reliable tools in concrete durability design. [ABSTRACT FROM AUTHOR]

Mechanical properties determine the use of two-component polyurethane materials. The compatibility of two components in the polyether polyol-MDI molecular system greatly influences the formation of mechanical properties in polyurethane materials. In this paper, we studied and evaluated the compatibility and mechanical properties of two-component polyurethane at multiple scales by combining molecular dynamics simulation with macroscopic experiments, which is an important guideline for synthesizing and preparing two-component polyurethanes. We evaluated the stability of the two-component polyurethane system by calculating the solubility parameter, binding energy, and diffusion coefficient at four temperatures with three isocyanate contents. The Perl scripting language obtained the mechanical properties of the MDI-polyether polyol system. The MD calculation results show that the solubility parameter of two-component polyurethane negatively correlated with temperature, and the intermolecular binding energy and MDI diffusion coefficient positively correlated with temperature. When the mass ratio of polyether polyol to isocyanate was 1:0.6, the solubility parameter difference between the two was 1.43 (J/cm3)1/2, the intermolecular binding energy was 531.68 kcal/mol, and the two-component system was more stable. A macroscopic direct tensile test was employed to assess the polyurethane elastomers' tensile properties. Our results show that the tensile strength of polyurethane elastomers increased with the increase in isocyanate content and decrease in temperature. Furthermore, the elongation at the break decreased, and the modulus increased, which is consistent with the law of molecular simulation. [ABSTRACT FROM AUTHOR]

The peculiarities of Ni and Fe diffusion in polycrystalline Cu and Cu-Fe alloys at a 650–750 °C temperature range were studied. It was shown that the bulk diffusion coefficients were in a good agreement with the available literature data obtained for different temperature concentration ranges. The obtained values of the Ni GB diffusion triple product could be described as s δ D b = 8.8 × 10 − 13 × e x p ( − 165   k J m o l − 1 R T ) m 3 s − 1 . The obtained values were an order of magnitude less than the values obtained by the radiotracer method. This fact was explained by the negative segregation of Ni at the Cu GB. A stronger negative segregation of Fe in the copper GB reduced the penetration depth of iron along the GB because of an additional (negative) "driving" force; this explained why there was no advanced grain boundary diffusion. Another peculiarity of the Fe diffusion that was confirmed was the significant supersaturation of the Cu-based solid solution near the Fe/Cu interface. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the chloride ion transport in coral aggregate seawater concrete (CASC) with varying water–cement ratios under different loads. The ultimate compressive strength was obtained by conducting compression testing of three groups of CASC with different water–cement ratios. Steady loads of 0%, 10%, and 20% of their respective ultimate compressive strengths were applied to the concrete specimens with different water–cement ratios. After being subjected to a seawater erosion test for 30, 60, 90, 120, and 180 days, the chloride ion concentration at different depths was measured to determine the chloride ion diffusion coefficient. Meanwhile, the chloride ion diffusion coefficients of CASC were verified by comparing them with results obtained from numerical simulations performed using COMSOL software. The test results show that the internal pore space of CASC expands, leading to acceleration of the chloride ion transport rate when applied loads are increased. The initial chloride ion concentration of CASC rises as the water–cement ratio rises, and the concentration gradient formed with artificial seawater lowers, decreasing the chloride ion transport rate. When the water cement ratio decreases and the load increases, the diffusion coefficient increases. Using the numerical simulation method of COMSOL software, it was proved that the model has good applicability and accuracy in predicting chloride ion transport in CASC. [ABSTRACT FROM AUTHOR]

Both the discrete and continuous particle packing models are used to design UHPC, but the influences of a water film covering the particle surfaces on the compactness of the particle system were not considered in these models. In fact, the water film results in a certain distance between solid particles (DSP), which affects the compactness of the particle system, especially for cementitious materials with small particle sizes. In the present study, the mixture design method for UHPC was proposed based on the Fuller distribution model modified using the DSP. Then, the components of cementitious materials and aggregates were optimized, and the UHPC matrices with high solid concentrations were obtained. The results showed that the solid concentration, slump flow, and compressive strength of the UHPC matrix reached 77.1 vol.%, 810 mm, and 162.0 MPa, respectively. By replacing granulated blast furnace slag (GBFS) with quartz powder (QP), the flexural strength of the UHPC matrix was increased without reducing its compressive strength. When the steel fiber with a volume fraction of 1.5% was used, the slump flow, compressive strength, tensile strength, and flexural strength of the UHPC reached 740 mm, 175.6 MPa, 9.7 MPa, and 22.8 MPa, respectively. After 500 freeze–thaw cycles or 60 dry–wet cycles under sulfate erosion, the mechanical properties did not deteriorate. The chloride diffusion coefficients in UHPCs were lower than 3.0 × 10−14 m2/s, and the carbonation depth of each UHPC was 0 mm after carbonization for 28 days. The UHPCs presented ideal workability, mechanical properties, and durability, demonstrating the validity of the method proposed for UHPC design. [ABSTRACT FROM AUTHOR]

This research paper is the result of observations made during tests according to various standards carried out on behalf of industry. The article presents diffusion coefficient values calculated according to the thermodynamic migration model for twenty different concrete mixes and some selected mixes of the codified approaches known as ASTM 1202, NT BUILD 443, NT BUILD 492, ASTM 1556. The method used here, according to the thermodynamic model of migration, allows determination of the value of the diffusion coefficient after short studies of the migration of chloride ions into concrete and was described in earlier works by one of the authors. Unfortunately, when using standard methods, the values of diffusion coefficients differ significantly from each other. In each concrete, diffusion tests were carried out in the conditions of long-term natural diffusion to verify the values determined by standard methods and according to the thermodynamic model of migration. The analysis conducted for this research paper reveals that the chloride permeability test method according to the standard ASTM C1202-97 has an almost 2.8-fold greater dispersion of the obtained results compared to the thermodynamic model of migration. It was observed that the standard NT BUILD 492 has a 3.8-fold dispersion of results compared to the method with the thermodynamic model of migration. The most time-consuming method is the standard method NT BUILD 443. The largest 3.5-fold dispersion of values concerning the reference value are observed in that method. Moreover, a method based on a thermodynamic migration model seems to be the best option of all analyzed methods. It is a quite quick, but laborious, method that should be tested for a larger number of concrete mixes. A great advantage of this method is that it is promising for a wide range of concrete mixtures, both plain concrete and concrete with various additives and admixtures, as well as high-performance concrete. [ABSTRACT FROM AUTHOR]

Nitride film as a hydrogen permeation barrier on zirconium hydride has seldom been studied. In this work, the zirconium nitride films were prepared on zirconium hydride in an atmosphere of N2 and N2 + H2 at 500~800 °C, with a holding time of 5 h and 20 h, and the mechanisms of film growth and hydrogen permeation were analyzed. The results showed that the film growth was mostly influenced by the temperature, followed by the reaction atmosphere and the holding time. The hydrogen could increase the nitrogen diffusivity during the formation of zirconium nitride films. The in situ nitriding conditions were optimized as 800 °C, N2 + H2 atmosphere, and 5~20 h. The chemical composition of ZrN-based films was mainly comprised of Zr and N, with a minor content of O. In addition, the film exhibited a major phase of ZrN, accompanied by the coexistence of ZrO2, ZrO, ZrN(NH2), and ZrN0.36H0.8, as well as O-H and N-H bonds based on the XPS analysis. The as-prepared ZrN base films in the present study exhibited superior hydrogen permeation resistance to other ZrO2 films previously reported. The hydrogen permeation resistance of the films could be attributed to the following mechanisms, including the chemical capture of hydrogen by the above-mentioned compounds and bonds; the physical barrier of continuous and dense film incurred from the volume effect of different compounds based on Pilling–Bedworth model and the different nitrogen diffusion coefficients at different temperatures. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of rhenium ions in the molten KF-KBF4-B2O3 salt was systematically studied, and pure metallic rhenium was obtained at the cathode. The processes of rhenium ions reduction and diffusion in molten KF-KBF4-B2O3 were determined using cyclic voltammetry, stationary galvanostatic and polarization curves analyses. The values of diffusion coefficients were 3.15 × 10−5 cm2/s and 4.61 × 10−5 cm2/s for R1 and R2, respectively. Rhenium electrodeposition was carried out at a constant potential. The process of rhenium cathode reduction in KF-KBF4-B2O3 at 773 K was found to be a one-step reaction Re(VII) → Re, and rhenium electrodeposition presumably occurred from two types of complex rhenium ions (KReO4 and K3ReO5). Both processes are quasi-reversible and controlled by diffusion. The obtained cathode deposit was analyzed by SEM, EDX, ICP-OES and XRD methods. The obtained deposit had a thread structure and rhenium was the main component. [ABSTRACT FROM AUTHOR]

V6O13 thin films were deposited on indium-doped tin oxide (ITO) conductive glass by a concise low-temperature liquid-phase deposition method and through heat treatment. The obtained films were directly used as electrodes without adding any other media. The results indicate that the film annealed at 400 °C exhibited an excellent cycling performance, which remained at 82.7% of capacity after 100 cycles. The film annealed at 400 °C with diffusion coefficients of 6.08 × 10−12 cm2·s−1 (Li+ insertion) and 5.46 × 10−12 cm2·s−1 (Li+ extraction) in the V6O13 film electrode. The high diffusion coefficients could be ascribed to the porous morphology composed of ultrathin nanosheets. Moreover, the film endured phase transitions during electrochemical cycling, the V6O13 partially transformed to Li0.6V1.67O3.67, Li3VO4, and VO2 with the insertion of Li+ into the lattice, and Li0.6V1.67O3.67, Li3VO4, and VO2 partially reversibly transformed backwards to V6O13 with the extraction of Li+ from the lattice. The phase transition can be attributed to the unique structure and morphology with enough active sites and ions diffusion channels during cycles. Such findings reveal a bright idea to prepare high-performance cathode materials for LIBs. [ABSTRACT FROM AUTHOR]

Chloride penetration resistance is one of the most important performance measures for the evaluation of the durability of concrete under a chloride environment. Due to differences in theory and experimental conditions, the durability index (chloride diffusion coefficient) obtained from laboratory accelerated migration tests cannot reflect the real process of chloride ingress into concrete in the natural environment. The difference in test methods must be considered and the transfer parameter k t should be introduced into the service life prediction model when the test results of accelerated methods are used. According to the test data of coastal exposure in South China, the attenuation rule of the chloride diffusion coefficient of different cement-based materials changed with time and was analyzed in this paper. Based on the diffusion coefficient–time curve, the theoretical natural diffusion coefficients of 28 d and 56 d were deduced, which were compared with the chloride diffusion coefficients obtained from the non-steady-state rapid migration method (RCM) at the same age. Therefore, the transfer parameter k t that expounds the relationship between concrete resistance to chloride permeability under a non-stationary electrical accelerated state and natural diffusion in the marine environment can be calculated; thus, the RCM testing index can be used to evaluate the long-term performance of the concrete structure in the marine environment. The results show that the value of k t was related to environmental conditions, test methods, and binder systems. [ABSTRACT FROM AUTHOR]

The structure, vibrational density of states, and transport coefficients of liquid alumina were studied using molecular dynamics simulations. At the temperature of 2500 K, 3000 K, 3500 K, and 4000 K, systems with three different densities were constructed, respectively, including the configurations with densities of 2.81 g/cm3 and 3.17 g/cm3, and the relaxed ones with nearly zero pressure at each temperature. With the changes in temperature or density, the transformations on the structural, vibrational and transport properties were discussed. The Born–Mayer–Huggins type of atomic interactions was used, with newly optimized parameters. The analysis of the interatomic correlations indicated that the short-range order of liquid alumina was mainly constructed by AlO4 tetrahedra, also a certain number of AlO3 and AlO5 was present. Meanwhile, the structural transitions on the elemental units occurred as either the temperature or density increased. Two primary frequency bands were observed in each vibrational density of states spectrum, with the higher frequency bands produced by the O atom vibrations, and the lower frequency ones generated by the Al atom vibrations. Self-diffusion coefficients were estimated using the linear behavior of the mean-squared displacement at long time, while by using the Green–Kubo relation during equilibrium molecular dynamics simulations, thermal conductivities and viscosities were calculated. Significantly, the viscosity at 2500 K with a density of 2.81 g/cm3 was equal to 25.23 mPa s, which was very close to the experimental finding. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) are at the forefront of energy storage and highly demanded in consumer electronics due to their high energy density, long battery life, and great flexibility. However, LIBs usually suffer from obvious capacity reduction, security problems, and a sharp decline in cycle life under low temperatures, especially below 0 °C, which can be mainly ascribed to the decrease in Li+ diffusion coefficient in both electrodes and electrolyte, poor transfer kinetics on the interphase, high Li+ desolvation barrier in the electrolyte, and severe Li plating and dendrite. Targeting such issues, approaches to improve the kinetics and stability of cathodes are also dissected, followed by the evaluation of the application prospects and modifications between various anodes and the strategies of electrolyte design including cosolvent, blended Li salts, high-concentration electrolyte, and additive introduction. Such designs elucidate the successful exploration of low-temperature LIBs with high energy density and long lifespan. This review prospects the future paths of research for LIBs under cold environments, aiming to provide insightful guidance for the reasonable design of LIBs under low temperature, accelerating their widespread application and commercialization. [ABSTRACT FROM AUTHOR]

With the increasing energy crisis and environmental problems, there is an urgent need to seek an efficient renewable energy source, and hydrogen energy is considered one of the most promising energy carriers. Magnesium is considered a promising hydrogen storage material due to its high hydrogen storage density, abundant resources, and low cost. However, sluggish kinetic performance is one of the bottlenecks hindering its practical application. The kinetic process of hydrogenation/dehydrogenation can be influenced by both external and internal factors, including temperature, pressure, elementary composition, particle size, particle surface states, irregularities in particle structure, and hydrogen diffusion coefficient. The kinetic performance of the MgH2/Mg system can be effectively improved by more active sites and nucleation centers for hydrogen absorption and desorption. Herein, we briefly review and discuss the experimentally observed nucleation and growth behavior of Mg/MgH2 during de/hydrogenation of MgH2/Mg. In particular, the nucleation and growth behavior of MgH2 during the hydrogenation of Mg is discussed from the aspect of temperature and hydrogen pressure. [ABSTRACT FROM AUTHOR]

As an effective flux, CaF2 is beneficial in improving the fluidity of slag in the steel-making process, which is crucial for dephosphorization. To reveal the existence form and functional mechanism of CaF2 in phosphosilicate systems, the microstructures and transport properties of CaO-SiO2-CaF2-P2O5 quaternary slag systems are investigated by molecular dynamics simulations (MD) combined with experiments. The results demonstrate that the Si-O coordination number does not vary significantly with the increasing CaF2 content, but the P-O coordination number dramatically decreases. CaF2 has a minor effect on the single [SiO4] but makes the structure of the silicate system simple. On the contrary, F− ions could reduce the stability of P-O bonds and promoted the transformation of [PO4] to [PO3F], which is beneficial for making the P element-enriched phosphate network structure more aggregated. However, the introduction of CaF2 does not alter the tetrahedral character of the original fundamental structural unit. In addition, the results of the investigation of the transport properties show that the self-diffusion coefficients of each ion are positively correlated with CaF2 content and arranged in the order of F− > Ca2+ > O2− ≈ P5+ > Si4+. Due to CaF2 reducing the degree of polymerization of the whole melts, the viscosity decreases from 0.39 to 0.13 Pa·s as the CaF2 content increases from 0% to 20%. Moreover, the viscosity of the melt shows an excellent linear dependence on the structural parameters. [ABSTRACT FROM AUTHOR]

The permeability of different strength grades of submerged non-dispersible concrete with different granulated slag admixtures in a saline soil environment simulated by different erosion solutions was investigated. The variation patterns of the chloride ion diffusion coefficient and pore characteristics were tested using NEL and MIP. The microscopic morphology of the specimens in different erosion environments and with slag doping was observed using SEM. The results showed that the impermeability of concrete in sulfate and complex salt environments was significantly reduced. The resistance of concrete to chloride ion penetration increased with the increase in strength grade, and the Cl− diffusion coefficient of C35 was 5–30% lower than those of C30 and C25 underwater non-dispersible concrete at 360 d. Meanwhile, the admixture of granulated blast-furnace slag optimized the pore size distribution and improved the matrix compactness and permeability. [ABSTRACT FROM AUTHOR]

Hydrogen is a main factor in cold cracking or hydrogen-induced cracking. The most crack susceptible region of a steel welded joint is the heat affected zone (HAZ). The formulation and functional-analytical solution of the one-dimensional problem of hydrogen diffusion in an inhomogeneous butt-welded joint considering weld and joint dimensions and initial hydrogen distribution as well as hydrogen diffusion coefficients and solubilities are presented. It is shown that the peak hydrogen concentration in the HAZ of inhomogeneous joints varies in direct proportion to the initial hydrogen concentration in the weld metal. It is inversely proportional to the ratio of hydrogen solubilities in the weld metal and the HAZ metal and is nonlinear in the diffusion coefficient ratio of these metals. The peak hydrogen concentration in the HAZ can exceed 170% of the average initial concentration in the joint if martensitic steel is welded using low-carbon low-alloy welding consumables. The utilization of austenitic consumables leads to a dramatic reduction in the hydrogen concentration in the HAZ in comparison with the non-austenitic consumables. No direct relationship was found between the hydrogen concentration in the HAZ and the hydrogen evolution from the joint surface. [ABSTRACT FROM AUTHOR]

It is important to clarify the reaction behavior of 2CaO·SiO2 (C2S) during hot metal dephosphorization. In this study, C2S was prepared and added to steel slag to investigate the reaction of C2S particles with CaO–SiO2–FeO–P2O5 slag at 1723 K. The diffusion coefficient of phosphorus in C2S was calculated. In addition, the influence of the addition of BaO to C2S was discussed. The results show that the diffusion coefficient of phosphorus in C2S is 9.23 × 10−14 m2·s−1. The Ca in C2S can be replaced by Ba. Small particles in the solid solution were easily generated from the C2S body by the addition of BaO, which is beneficial for improving the phosphorus partition between the C2S solid phase and the liquid phase of the slag. [ABSTRACT FROM AUTHOR]

In this work, a simple two-parameters correlation based on the Rice and Gray, Lennard-Jones, and Stockmayer theories was devised for the calculation of binary diffusion coefficients ( D 12 ) of any type of solutes at infinite dilution in polar and non-polar solvents. This equation can be relevant for systems with polar solvents, since most models in the literature fail when strong intermolecular forces predominate in solution. The new correlation embodies the Stockmayer potential without requiring the dipole moments of any component, which significantly enlarges its application. It was validated with the largest D 12 database of polar and non-polar dense systems, with 8812 data points (NDP) spanning 553 systems, of which 133 have water as solvent (NDP = 1266), 89 contain polar solvents excluding water (NDP = 1405), 177 have supercritical carbon dioxide (SC-CO2) as solvent (NDP = 5028), and 154 have non-polar or weakly polar solvents excluding SC-CO2 (NDP = 1113). Overall, the model achieved an average deviation of only 3.43%, with accurate and unbiased behavior even for polar systems. [ABSTRACT FROM AUTHOR]

Wasted concrete was often used as a recycled aggregate instead natural stone in fresh concrete to reduce the environmental impact in a decade. However, because of the residual mortar interface, the performance of recycled aggregate was weaker. In this paper, the recycled aggregate was prewetted, and the effects of prewetted degree on the workability, strength, and durability of concrete were studied. The properties of the interfacial transition zone (ITZ), including microhardness, pore structure, and width, were also investigated. The results show that the workability intensity increased with the increase in prewetted degree from 0% to 100%, while the strength was first increased and then decreased with the optimal value of 43.3 MPa when the prewetted degree was 50–65%. The water absorption and chloride ion diffusion coefficient were also decreased by approximately 10% at minimum with the prewetted degree around 55% because of the declined fraction of pores larger than 50 μm and smaller porosity. The width of ITZ was first sharply decreased with a prewetted degree of 50–65%, then increased again with higher moisture, while microhardness of the ITZ showed the opposite trend and reached 82.7 MPa at maximum, at 50%. The appropriate moisture (50–65%) improved the pore structure and hydration products with an internal curing effect. When the moisture content was too high, the excess water was released from aggregate to the matrix, causing a higher water–cement ratio at ITZ; the porosity and the number of macrospores were increased to weaken the performance of concrete. [ABSTRACT FROM AUTHOR]

Estimating the effective properties of a particulate system is the most direct way to understand its macroscopic performance. In this work, we accurately evaluate the third-order approximations involving the three-point microstructural parameter ζ , which can be calculated from a triple integral involving 1-, 2-, and 3-point correlation functions. A GPU-based parallel algorithm was developed for quickly computing the n-point correlation functions, and the results agree well with analytical solutions. The effective thermal conductivity and diffusion coefficient are calculated by the third-order approximates for the random-packing systems of a super-ellipsoid. By changing the parameters of the super-ellipsoid, the particle-shape effect can be predicted for both the thermal conductivity and diffusion coefficient. [ABSTRACT FROM AUTHOR]

This paper aims to develop a chloride transport model of engineered cementitious composites (ECC) that can consider the influence of both exposure time and crack width. ECC specimens with crack widths of 0.1 mm, 0.2 mm and 0.3 mm were soaked into NaCl solution with periods of 30, 60, 90 and 120 days. The free chloride content profile was measured and used for the development of the transport model. Regression analysis was applied to build the time and crack width dependent models of apparent diffusion coefficient and surface chloride content. The results show that the crack width has significant influence on the free chloride concentration profile when it is above 0.2 mm and the time-dependent constant n decreases linearly with the crack width. The chloride transport model was obtained by subscribing the models of apparent diffusion coefficient and surface chloride content into the analytical solution of Fick's second law. The model was further validated with the experimental results, showing a deviation within 20%. The findings of the presented study can enhance the current understanding on the chloride transportation in ECC. [ABSTRACT FROM AUTHOR]

The adsorption properties of Aloe vera (Aloe barbadensis Miller) for the uptake of Methylene Blue (MB) from water were investigated after pre-treating the material with water–ethanol solutions at different ethanol concentrations: 0% v/v (AV0), 25% v/v (AV25), and 50% v/v (AV50). The pre-treated materials were characterized as follows: the pHZC was evaluated to be 6, 5.7, and 7.2 for AV0, AV25, and AV50, respectively; from BET-BJH analysis the mesoporous nature of the material and an increase from 108.2 (AV0) to 331.7 (AV50) m2/kg of its solid surface area was observed; TG analysis revealed a significat increase in volatile compounds from the untreated (5.4%) to the treated materials (8.9%, 10.3%, and 11.3% for AV0, AV25, and AV50, respectively). Adsorption batch tests were then performed to investigate the equilibrium, the kinetics, and the thermodynamics of the process. Results suggested that the Langmuir model was in agreement with the experimental results, and values for qmax of 199 mg/g, 311 mg/g, and 346 mg/g were calculated for AV0, AV25, and AV50, respectively. The kinetic results were used to develop a mathematical model to estimate the effective diffusion coefficient for each type of Aloe adopted. Effective diffusion coefficients of 5.43·10−7 cm2/min, 3.89·10−7 cm2/min, and 5.78·10−7 cm2/min were calculated for AV0, AV25, and AV50, respectively. It was found that pre-treatment, on the one hand, enhances the adsorption capacity of the material and on the other, reduces its affinity toward MB uptake. [ABSTRACT FROM AUTHOR]

Naphthalene, as one of the representative polycyclic aromatic hydrocarbons, widely exists in contaminated sites and is a potential threat to human health due to its high mobility in soil. The interaction between naphthalene and clay minerals is of great significance to the environmental behavior of naphthalene and the design of remediation technology. In this study, montmorillonite and kaolinite were selected as representative clay minerals. Naphthalene adsorption behavior on mineral surfaces and water-wet kaolinite surfaces was investigated using molecular dynamics (MD) simulation. The interaction energy was calculated to represent the interaction between naphthalene and soil fractions, and the relative concentration and density distribution of naphthalene was analyzed to describe the distribution of naphthalene on the clay surfaces. The self-diffusion coefficient of naphthalene was obtained to represent its mobility under different water content. The electron density calculation was performed to reveal the different adsorption behavior of naphthalene on different surfaces of kaolinite. The simulation results show that montmorillonite had a stronger interaction with naphthalene due to larger electrostatic interaction energy compared to kaolinite, and naphthalene distributed more intensively on the montmorillonite surface. With regards to kaolinite, naphthalene tended to be absorbed on the alumina octahedral surface rather than the silicon tetrahedral surface due to the weak hydron bond interaction. The results indicate that water impeded the adsorption of naphthalene, and the optimal initial thickness of water film, which was 10 Å, was put forward for the application of thermal remediation technology. Furthermore, the average interaction energies between water and mineral surfaces largely depended on the water content, and the competitive adsorption between water and naphthalene only occurred under absorbed and bound water conditions. Overall, the knowledge of naphthalene–soil fractions interaction gained in this study is critical to the understanding of the environmental behavior of naphthalene and the reference for remediation technology. [ABSTRACT FROM AUTHOR]

The transport mechanism of chloride ions in concrete is relatively complicated since the erosion process is influenced by many factors. To investigate the effect of exposure conditions on the chloride ion diffusion property, three exposure conditions (long-term immersion in static sodium chloride solution, long-term immersion in circulating sodium chloride solution and dry–wet cycles in circulating sodium chloride solution) were considered in chloride ion diffusion experiments. Experimental results indicated that the chloride ion content at a certain depth increased with erosion age. The chloride ions in static sodium chloride solution transported more rapidly than those under dry–wet cycle conditions. Moreover, the chloride ion content of concrete under dry–wet cycles of the circulating sodium chloride solution was slightly higher than that under long-term immersion in the circulating solution. Based on Fick's second law, empirical equations for the chloride diffusion coefficient and chloride content at the surface of concrete were proposed by fitting experimental data, and the values of correlation coefficients of different exposure conditions were suggested. By comparison with the experiment results, it was verified that the calculation formula had better applicability. This method could be used to predict and analyze the chloride ion content under different exposure conditions. [ABSTRACT FROM AUTHOR]

The Li+ diffusion coefficients in Li+-adsorbed graphene systems were determined by combining first-principle calculations based on density functional theory with Kinetic Monte Carlo simulations. The calculated results indicate that the interactions between Li ions have a very important influence on lithium diffusion. Based on energy barriers directly obtained from first-principle calculations for single-Li+ and two-Li+ adsorbed systems, a new equation predicting energy barriers with more than two Li ions was deduced. Furthermore, it is found that the temperature dependence of Li+ diffusion coefficients fits well to the Arrhenius equation, rather than meeting the equation from electrochemical impedance spectroscopy applied to estimate experimental diffusion coefficients. Moreover, the calculated results also reveal that Li+ concentration dependence of diffusion coefficients roughly fits to the equation from electrochemical impedance spectroscopy in a low concentration region; however, it seriously deviates from the equation in a high concentration region. So, the equation from electrochemical impedance spectroscopy technique could not be simply used to estimate the Li+ diffusion coefficient for all Li+-adsorbed graphene systems with various Li+ concentrations. Our work suggests that interactions between Li ions, and among Li ion and host atoms will influence the Li+ diffusion, which determines that the Li+ intercalation dependence of Li+ diffusion coefficient should be changed and complex. [ABSTRACT FROM AUTHOR]

In this paper, the effects of dispersed 3~10 nm NbC precipitates on hydrogen diffusion in X80 pipeline steel were investigated by means of high resolution transmission electron microscopy (HRTEM), electrochemical hydrogen permeation, and thermal desorption spectroscopy (TDS). The relationship between hydrogen diffusion and temperature was determined for Nb-free X80 and 0.055 wt% Nb X80 steel. The temperature dividing reversible and irreversible traps was measured, and the quantity of hydrogen captured by different traps was calculated. Three types of hydrogen trap were designed and applied in the test, and the results revealed that irreversible hydrogen traps formed by nanosized and coherent NbC precipitates markedly hindered hydrogen diffusion, and prolonged breakthrough time in Nb-bearing X80 steel. [ABSTRACT FROM AUTHOR]

Microencapsulated rejuvenator has been attracted much attention for self-healing bitumen. The diffusion coefficient is one of the key parameters to estimate the feasibility of rejuvenator to age bitumen. The objective of this research was to evaluate diffusion behaviors of microencapsulated rejuvenator in aged bitumen by a FTIR-ATR method. Various microcapsule samples were mixed in bitumen to form thin films. The core material of microcapsules used as rejuvenator was diphenylsilane (DPS), its fairly specific absorption band at 843 cm-1 was selected as a marker band to calculate the diffusion coefficient (D). The microstructure parameters, including contents, mean size and mean shell thickness of microcapsules, were considered to understand the diffusion behaviors under different temperatures (20, 30, 40 and 50 °C) in bitumen. The results showed that a larger mean size of microcapsules did not greatly affect the D values under the same temperature. In contrast, a higher mean shell thickness decreased the D values because of the decrement of damage probability of microcapsules under the same content. With the same microcapsule sample in bitumen, the D values presented a trend of linear increase when the content of microcapsules was increased. All these results indicated that the microstructure affected the diffusion behaviors based on the concentration of released rejuvenator. A preliminary model of diffusion behaviors of microencapsulated rejuvenator in bitumen was given based on the Arrhenius equation considering the microstructure of microcapsules, the amount of released rejuvenator and the age degree of bitumen. This model may be a guide to the construction and application of self-healing bitumen using microcapsules. [ABSTRACT FROM AUTHOR]

The development of cracking in concrete structures leads to significant permeability and to durability problems as a result. Approaches to controlling crack development and crack width in concrete structures have been widely debated. Recently, it was recognized that a high-performance fiber-reinforced cement composite (HPFRCC) provides a possible solution to this inherent problem of cracking by smearing one or several dominant cracks into many distributed microcracks under tensile loading conditions. However, the chloride permeability of HPFRCC under compressive loading conditions is not yet fully understood. Therefore, the goal of the present study is to explore the chloride diffusion characteristics of HPFRCC damaged by compressive loads. The chloride diffusivity of HPFRCC is measured after being subjected to various repeated loads. The results show that the residual axial strain, lateral strain and specific crack area of HPFRCC specimens increase with an increase in the damage induced by repeated loads. However, the chloride diffusion coefficient increases only up to 1.5-times, whereas the specific crack area increases up to 3-times with an increase in damage. Although HPFRCC shows smeared distributed cracks in tensile loads, a significant reduction in the diffusion coefficient of HPFRCC is not obtained compared to plain concrete when the cyclic compressive load is applied below 85% of the strength. [ABSTRACT FROM AUTHOR]