Diffusion Behavior Research Articles

Diffusion behavior of Cr and V elements in the 50CrVA steel under high-temperature oxidation and surface treatment processes

Diffusion behavior of Cr and V elements in the 50CrVA steel under high-temperature oxidation and surface treatment processes

Rotational inertia-induced glassy transition in chiral particle systems.

The dense active matter exhibits characteristics reminiscent of traditional glassy phenomena, yet the role of rotational inertia in glass dynamics remains elusive. In this study, we investigate the glass dynamics of chiral active particles influenced by rotational inertia. Rotational inertia endows exponential memory to particle orientation, restricting its alteration and amplifying the effective persistence time. At lower spinning frequencies, the diffusion coefficient exhibits a peak function relative to rotational inertia for shorter persistence times, while it steadily increases with rotational inertia for longer persistence times. In the realm of high-frequency spinning, the impact of rotational inertia on diffusion behavior becomes more pronounced, resulting in a nonmonotonic and intricate relationship between the diffusion coefficient and rotational inertia. Consequently, the introduction of rotational inertia significantly alters the glassy dynamics of chiral active particles, allowing for the control over transitions between fluid and glassy states by modulating rotational inertia. Moreover, our findings indicate that at a specific spinning temperature, there exists an optimal spinning frequency at which the diffusion coefficient attains its maximum value.

The effect of skin diffusion kinetics of isopropyl ester permeation enhancers on drug permeation: Role of lateral spread and penetration characteristics

The purpose of present work was to study the effects of permeation enhancers’ two kinetic behaviors of simultaneous lateral diffusion and vertical penetration in the skin on its enhancing effect. The skin diffusion kinetics of isopropyl ester permeation enhancers were characterized by the innovative concentric tape peeling study and Raman imaging, which were quantitatively assessed through innovative parameters, namely, lateral-to-vertical penetration amount (CL-V) and lateral-to-vertical penetration distance (DL-V). The enhancement effect of permeation enhancers on drug flurbiprofen (FLU) was assessed by in vitro skin permeation tests, which were confirmed by transdermal water loss and skin resistance study. The relationship between kinetic parameters of permeation enhancers and permeation parameters of FLU was carried out by correlation analysis. The molecular mechanisms of effect of skin diffusion kinetics of permeation enhancers on drug permeation were characterized by molecular docking, modulated-temperature differential scanning calorimetry (MTDSC), Raman spectra, solid-state NMR and molecular dynamic simulation. The results indicated skin diffusion kinetics of short-chain (C8–C12) isopropyl ester permeation enhancers were governed by vertical penetration, while long-chain (C14–C18) ones were characterized by lateral spread. Quadratic correlation between CL-V and enhancement ratio of permeation-retention ratio of FLU (ERQ/R) (R2 = 0.95), DL-V and enhancement ratio of permeation area (ERA) of FLU (R2 = 0.98) indicating that varied skin diffusion kinetics of permeation enhancers directly influenced the barrier function of stratum corneum (SC) and further enhancing drug permeation. In terms of molecular mechanism, long-chain isopropyl ester enhancers had good miscibility with SC, leading to their high CL-V and DL-V, and causing strong interaction strength with SC and resulting in weaker skin barrier function for drug permeation. In summary, in comparison to short-chain isopropyl ester enhancers that relied on penetration, long-chain ones that depended on lateral spread exhibited greater enhancement efficacy, which guided the application of enhancers in transdermal formulations.

Facile controllable sequential electrochemical in-situ synthesis of Fe3O4/PPY hybrid electrode for supercapacitor

In this work, a facile sequential electrochemical synthesis strategy is employed for the precisely controlled in situ polymerization of pyrrole on an iron oxide substrate in the oxalic acid system. The use of porous iron oxide as a template allows for the modification of polypyrrole to create a large conductive network while preserving the integrity of the substrate. This process improves the poor conductivity of conventional metal oxides, allowing for the synthesis of a Fe3O4/PPY hybrid electrode material. The experiments elucidated the mechanism of pyrrole surface morphology coupled with the deposition amount threshold affecting the electrode performance. This was achieved by elucidating the regulation laws of key deposition process parameters (pyrrole monomer concentration, scanning rate, and number of cycles) on the diffusion and oxidation behaviors of pyrrole during the continuous polymerization process. Furthermore, the electrochemical behaviors of the Fe3O4/PPY hybrid electrode were better resolved. The results demonstrate that the deposition amount of PPY on the Fe3O4/PPY hybrid electrode material is within the optimized threshold (1 × 10−6∼3 × 10−6 g), exhibiting a regular and uniform surface morphology with no agglomeration, which indicates a competitive specific capacitance (215.12 mF cm−2 at 1.1 mA cm−2). This strategy of structure-modulated synergistic functional hybridization offers a new approach for designing efficient binder-free hybridized electrode materials.

Turbulent partially cracked ammonia/air premixed spherical flames

The combustion of ammonia requires, for most energy conversion systems, a combustion promoter such as hydrogen to guarantee the start-up, stability and combustion efficiency. Partially cracked ammonia (PCA) can provide sufficient hydrogen concentrations to enhance the burning velocity in comparison with pure ammonia. However, little work exists on the use of PCA blends operating under relevant turbulent conditions. To that end the outwardly propagating spherical flame configuration was employed to determine the laminar and turbulent flame propagation characteristics of PCA (NH3/(H2+N2)) and corresponding binary (NH3/H2) mixtures across various turbulent combustion regimes. First, PCA and ammonia-hydrogen blends exhibit similar flame propagation rates under various turbulent intensities, even for the laminar case. The highest turbulent burning velocity was observed at leanest conditions, as opposed to laminar flames which exhibited highest flame speed at conditions above stoichiometry. Under rich conditions, no substantial flame enhancement due to turbulence was measured irrespective of the hydrogen content. This lack of flame enhancement under turbulent conditions is attributed to the effect of preferential diffusion with good agreement observed with trends in measured Markstein numbers. The normalized turbulent flame speed is dominated by the enhanced molecular diffusivity afforded by the presence of hydrogen up to 15 % enrichment, prior to decreasing upon further hydrogen addition under lean and stoichiometric conditions. This ‘bending’ phenomenon may be the contribution of several factors including; the transitioning between combustion regimes associated with low Damköhler numbers (Da) and flame thickening; merging of flamelets due to the presence of ammonia enhancing wrinkling; and combined changes in laminar burning velocity and preferential diffusional behavior. Furthermore, good agreement for turbulent flame speed is observed with a correlation that includes the influence of turbulent stretch (Ka) and non-equidiffusion (Le), with the agreement reducing with decreasing chemical to turbulent time scale ratios (Da << 1).

Electrochemical hydrogen permeation measurement during cyclic stress testing of a ferritic chromium steel

AbstractIn the present work, the hydrogen diffusion during cyclic stress testing in the ferritic chromium steel 1.4521 (X2CrMoTi18‐2) is investigated. Therefore, electrochemical hydrogen permeation measurements are carried out on a hollow cylinder geometry. Simultaneously an alternating stress is applied using a stress ratio of R=‐1. At low stress amplitudes, no influence on the diffusion behaviour of hydrogen is found. At a higher stress amplitude, close to the macroscopic yield strength, a delayed hydrogen permeation by a factor of two is observed. It is postulated that this observation is a result of the nucleation of new hydrogen traps during the measurement. Hydrogen content measurements using carrier gas hot extraction support this hypothesis.

Numerical Modeling of Energetic Charged-particle Transport with SPECTRUM Software: General Approach and Artificial Effects due to Field Discretization

Test-particle simulations are an important tool for magnetospheric and heliophysics research. In this paper, we present the Space Plasma and Energetic Charged particle TRansport on Unstructured Meshes (SPECTRUM) software as a novel tool for performing these types of simulations in arbitrary astrophysical environments, specified either analytically or numerically (i.e., on a grid). We discuss and benchmark SPECTRUM’s interface with meshed magnetohydrodynamic backgrounds, including output from the Block Adaptive Tree Solar-wind Roe-type Upwind Scheme (BATS-R-US) code. We also investigate the effects of field discretization on both deterministic and stochastic particle motion, with emphasis on space science applications, concluding that the discretization error typically enhances the diffusive behavior of the ensemble.

First-principles study on the diffusion behavior of Cs and I in Cr coating

First-principles study on the diffusion behavior of Cs and I in Cr coating

The diffusion behavior of H3O+ in insulation systems composed of paper cellulose and modified natural ester insulating oil

The oil-paper insulation system will be affected by the synergistic effects of moisture and acids during long-term stable operation of the transformer. The moisture in the oil can be combined with the H+ionized from the acid molecules in the form of H3O+ by coordination, thus changing the proportion of acid distribution in the insulating oil and paper cellulose. Natural ester insulating oil, as a new development trend to replace mineral oil, can be significantly improved by adding nanoparticles to them. The diffusion behavior of H3O+ in paper cellulose and nano-SiO2-modified soybean oil-based natural ester insulating oil insulating system has been investigated using molecular dynamics in this article. The results indicate that the incorporation with nanoparticles is effective in mitigating the impact of temperature on the diffusion behavior of H3O+ in oil-paper insulation. Compared with the unmodified model, the nano-modified model results in a significant reduction in the concentration distribution of H3O+ in paper cellulose. The hydroxyl and ether bonds in paper cellulose will interact with H3O+ to generate hydrogen bonds and destroy its original hydrogen bonding network, while nanoparticles can inhibit diffusion by adsorbing H3O+ through hydroxyl oxygen atoms.

Measurement of Diffusion Coefficients and Assessment of Atomic Mobilities in HCP Mg-Ag-Sn Alloys

Reliable thermodynamic and kinetic databases are essential for designing and developing novel magnesium (Mg) alloys for elevated-temperature applications in the automotive and aerospace industries. This study investigated diffusion behaviors of HCP Mg-Ag-Sn alloys by four sets of three diffusion couples annealed at 450, 500, and 550 °C, respectively. Interdiffusion and impurity diffusion coefficients at the three annealing temperatures were extracted using the forward-simulation method. The determined diffusion coefficients, combined with prior results in the literature, were then used to assess atomic mobilities for the HCP phase of the Mg-Ag-Sn system. This assessment was conducted using the DICTRA and the TCMG5 thermodynamic database within the Thermo-Calc software. Comprehensive comparisons between calculated and experimental diffusion coefficients yielded an excellent agreement. The atomic mobilities were also further validated by appropriate predictions of concentration profiles and diffusion paths observed in independent diffusion couple experiments performed at 525 °C for 18 hrs. It has been found that the addition of Sn and Ag both increase the diffusivity of Ag in HCP Mg and Sn in HCP Mg in the stable temperature range of HCP Mg, respectively. This improved understanding of the kinetics in the Mg-Ag-Sn ternary system is essential for controlling diffusion-dependent properties such as coarsening and, therefore, the mechanical properties of Mg-Ag-Sn alloys at elevated temperatures.

Structural and electrical properties of tetragonal tungsten bronze K4Bi2Nb10O30-Ba4Na2Nb10O30 solid solutions across two proximate phase transitions

Tetragonal tungsten bronzes allow for broader compositional engineering compared to perovskites. Here we investigate solid solutions between Ba4Na2Nb10O30 (BNN) and K4Bi2Nb10O30 (KBiN). A transition from orthorhombic to tetragonal symmetry was observed at 30–35 % KBiN. An expansion of the in-plane and a contraction of the out-of-plane parameter were observed with increasing KBiN content. Ferroelectricity, shown by a maximum in permittivity, was observed up to 20–35 % KBiN, while diffuse dielectric behaviour was exhibited from 40 % KBiN. Non-linear P-E loops are evident up to 35 % KBiN, and vaguely present for 40 % KBiN. The most prominent ferroelectric character, assigned by large remanent polarisation and opening of the strain hysteresis response was exhibited at 35 % KBiN. A ferroelastic-paraelastic phase transition between 30 % and 35 % KBiN and a ferroelectric-paraelectric phase transition around ∼40 % KBiN were inferred. Thus, the two distinct phase transitions mimic the temperature dependent structural evolution observed for BNN.

Adsorption and Diffusion Behavior of Xe/Kr Gas on Al2O3 and Stilbene Surface

Adsorption and Diffusion Behavior of Xe/Kr Gas on Al2O3 and Stilbene Surface

Excluded volume effects on tangentially driven active ring polymers.

The conformational and dynamical properties of active ring polymers are studied by numerical simulations. The two-dimensionally confined polymer is modeled as a closed bead-spring chain, driven by tangential forces, put in contact with a heat bath described by the Brownian multiparticle collision dynamics. Both phantom polymers and chains comprising excluded volume interactions are considered for different bending rigidities. The size and shape are found to be dependent on persistence length, driving force, and bead mutual exclusion. The lack of excluded volume interactions is responsible for a shrinkage of active rings when increasing driving force in the flexible limit, while the presence induces a moderate swelling of chains. The internal dynamics of flexible phantom active rings shows activity-enhanced diffusive behavior at large activity values while, in the case of self-avoiding active chains, it is characterized by active ballistic motion not depending on stiffness. The long-time dynamics of active rings is marked by rotational motion whose period scales as the inverse of the applied tangential force, irrespective of persistence length and beads' self-exclusion.

Anomalous and ultraslow diffusion of a particle driven by power-law-correlated and distributed-order noises

We study the generalised Langevin equation (GLE) approach to anomalous diffusion for a harmonic oscillator and a free particle driven by different forms of internal noises, such as power-law-correlated and distributed-order noises that fulfil generalised versions of the fluctuation-dissipation theorem. The mean squared displacement and the normalised displacement correlation function are derived for the different forms of the friction memory kernel. The corresponding overdamped GLEs for these cases are also investigated. It is shown that such models can be used to describe anomalous diffusion in complex media, giving rise to subdiffusion, superdiffusion, ultraslow diffusion, strong anomaly, and other complex diffusive behaviours.

Using Brownian model to study the effect of temperature on diffusion coefficient

This study employs molecular simulation techniques, particularly the Brownian motion model, to investigate the influence of temperature on diffusion coefficients. Leveraging Einsteins relationship for calculating diffusion coefficients and a one-dimensional random walk model, we systematically explore the impact of simulation direction, particle quantity, and simulation duration on diffusion behavior. The research extends its scope to three-dimensional Brownian motion simulations, offering insights into the stochastic motion of particles in a fluid. The primary objective is to analyze the relationship between temperature and diffusion coefficients. Through rigorous linear regression analysis, a significant and strong linear association is identified, demonstrating that an increase in temperature correlates with an increase in the diffusion coefficient. The research not only contributes to the fundamental understanding of molecular motion but also provides practical recommendations for simulation parameters, especially in resource-constrained computational environments. The study acknowledges certain limitations in the current Brownian motion algorithm and proposes avenues for future research to enhance computational efficiency and precision. This abstract encapsulates the key methodologies, findings, and implications of the research, laying the foundation for a comprehensive exploration of temperature-dependent diffusion coefficients in molecular systems.

Crystal plane orientation-dependent surface atom diffusion in sub-10-nm Au nanocrystals.

Surface atom diffusion is a ubiquitous phenomenon in nanostructured metals with ultrahigh surface-to-volume ratios. However, the fundamental atomic mechanism of surface atom diffusion remains elusive. Here, we report in situ atomic-scale observations of surface pressure-driven atom diffusion in gold nanocrystals at room temperature using high-resolution transmission electron microscopy with a high-speed detection camera. The topmost layer of atoms on (001) plane initially diffuse in a column-by-column manner. As diffusion proceeds, the remaining atomic columns collectively inject into adjacent underlayer, accompanied by nucleation of a surface dislocation. In comparison, atoms on (111) plane directly diffuse to the base without collective injection. Quantitative calculations indicate that these crystal plane orientation-dependent atom diffusion behaviors contribute to the larger diffusion coefficient of (111) plane compared to (001) plane in addition to the effect of diffusion activation energy. Our findings provide valuable insights into atomic mechanisms of diffusion-dominant morphology evolution of nanostructured metals and guide the design of nanostructured materials with enhanced structural stability.

Coal particle size-dependent gas diffusion coefficient

The tests on gas (CH4 or CO2) desorption-diffusion in coal particles, together with the analytical unipore or bidisperse diffusion model, are widely used to study the gas diffusion behavior, but the fitted diffusion coefficient always increases with particle size, which makes it difficult to determine an identical diffusion coefficient for coal particles. In this work, five sets of anthracite particles with different sizes are prepared, and tests on CO2 desorption-diffusion in different coal particles are carried out. Four continuum models (including an analytical unipore diffusion model, an analytical bidisperse diffusion model, a numerical unipore diffusion model, and a dual-porosity model) and a discrete fracture model are established. The continuum models can all fit the experimental results well, while the fitted diffusion coefficients always increase with particle size. Based on the identical matrix’s side length, matrix diffusion coefficient, and fracture diffusion coefficient, the discrete fracture model fits the experimental results of different coal particles successfully, and the size effect of diffusion coefficient is resolved. The diffusion coefficient fitted by the continuum models is the equivalent diffusion coefficient of matrix diffusion and fracture diffusion, so the equivalent diffusion coefficient increases with fracture path (i.e., particle size), and the size effect of diffusion coefficient occurs. The results provide an insight into the size effect of diffusion coefficient and make it possible to determine an identical diffusion coefficient for coal particles of different sizes.

Interfaces Between Nanoparticle and Biomacromolecular Network: Dynamic Behaviors, Confinement and Entropy

AbstractBiomacromolecular networks, crucial components of biological systems, are of great importance in biological and nanomedical science, in which the interfaces between nanoparticle and macromolecular networks are intriguing and drawing great attention. Herein, this review seeks to present the state‐of‐art progress and perspective of the dynamic behaviors, confinement and entropy at the nanoparticle‐biomacromolecular network interfaces. The basic biomacromolecular networks in living systems, recent research on networks with dynamic bonds and various diffusion behaviors of nanoparticles within biomacromolecular networks are summarized. In particular, entropic effects in the confined environments of biological networks are discussed, along with how they impact the mechanical properties and dynamical behaviors. The interesting research and findings included in this review might offer the scientific community a better understanding of how this field has developed thus far, and are anticipated to trigger more systematic and fundamental research to elucidate the underlying physics and broaden the potential applications of macromolecular networks, biological and artificial.

Bonding Behavior and Mechanism of Composite Interface Between Carbon Steel/Stainless Steel Laminates at Different Temperatures and Strain Rates

Compared to hot roll and explosive bonding, there are relatively few studies on warm/cold roll bonding under low temperature conditions. In this article, the warm/cold roll bonding simulation experiment is conducted to research the deformation, interface bonding rate, microstructure, element diffusion behavior, metallographic structure, and phase of carbon steel/stainless steel. The results show that the plastic deformation remains consistent below 400 °C but exhibits temperature sensitivity above 400 °C. The lower strain rate can increase the bonding rate, while insulation treatment may reduce the bonding rate. The formation of cracks is inhibited at 25 °C and 45% reduction rate due to the challenge of cracking the surface oxide film. Temperature significantly affects bonding, with improved performance observed above 600 °C. Uneven element distribution of bonding area may be related to the precipitated compounds, while insulation treatment increases the mutual diffusion ability of elements. The increase in temperature leads to an increase in pearlite, a decrease in ferrite, and decarburization occurs within the carbon steel matrix. The carbon elements diffuse from carbon steel to the surface of stainless steel. The increase in temperature increases the content of surface compounds.

Controlling amine monomers via UiO-66-NH2 defect sites to enhance forward osmosis membrane performance for lithium recovery

The excessive thickness of the separation layer and the presence of cracks cause low water flux and poor lithium recovery in conventional forward osmosis (FO) membranes. According to the influence of the diffusion behavior of amine monomers in interfacial polymerization, the use of an interlayer optimizes the separation layer structure of traditional thin-film composite FO membrane. However, it is difficult to accurately control the separation layer structure by simply adjusting the amount of the interlayer material loaded. Herein, FO membranes with defect-containing metal–organic framework (MOF) interlayers were constructed. By adjusting the concentrations of competitive ligands, the MOFs showed different degrees of linker loss, which exposed the metal ions in the MOFs to different extents. The defective sites of the constructed MOFs increased the interaction between the interlayer and m-phenylenediamine (MPD), and density functional theory (DFT) simulations also revealed an increase in the binding energy of the two materials. Therefore, MPD attachment and diffusion were controlled by changing the proportion of defects in the MOFs, thereby finely regulating the separation layer structure. Additionally, tannic acid (TA) was predeposited to improve the stability of the interlayer. The prepared membrane exhibited water fluxes of 33.84 and 65.81 LMH and reverse salt fluxes of 0.58 and 2.38 gMH in the active layer facing feed solution (AL-FS) and active layer facing draw solution (AL-DS) modes, respectively. Excellent lithium ion recovery and fouling resistance was also demonstrated in battery wastewater treatment.