Diffusion Controlled Research Articles

Spatio-temporal characterization of nutrient and organic pollution along with nutrient-chlorophyll-a dynamics in the Geum River

River water pollution is one of the biggest environmental challenges in the world. Therefore, it is imperative to assess the spatial and temporal variability of surface water quality to manage water resources from pollution. This study aimed to identify spatio-temporal variations of Geum River surface water quality and the factors that influence it. Summer monsoon, land-use land-cover (LULC), and weirs are dominant factors determining the dynamics of river water quality. Empirical analysis showed that total phosphorus (TP), total nitrogen (TN), biological oxygen demand (BOD), and chemical oxygen demand (COD) had positive linear functional relations with the agricultural and built-up cover but negative linear relations with forest cover. The results showed that the total suspended solids (TSS), chlorophyll-a (CHL-a), TP, and COD levels were higher in the summer than in any other season. On the other hand, total nitrogen (TN) and electrical conductivity (EC) levels were lower during summer in the river due to the dilution effect. Pollutant-transport theory shows that TSS acts as a TP carrier (R2 = 0.83, p < 0.001). The empirical model suggested that TP (R2 = 0.76, p < 0.001) was the better predictor for CHL-a compared to TN (R2 = 0.13, p < 0.001) as well as showed strong P-limitation based on TN:TP ratios. The high average WQI values of the Geum River (except for S01 and S02) show a higher pollution level, indicating its unsuitability for drinking, irrigation, and industrial usage. Our results suggest that industrial and domestic sewage treatment and agricultural diffuse pollution control could improve the Geum river water quality.

Visible-Light-Promoted Photoaddition of N-Nitrosopiperidines to Alkynes: Continuous Flow Chemistry Approach to Tetrahydroimidazo[1,2-a]pyridine 1-Oxides.

The photoaddition of N-nitrosopiperidines to terminal alkynes was effected under visible-light irradiation, in which a novel synthetic access to tetrahydroimidazo[1,2-a]pyridine 1-oxides was achieved via the dehydrogenative cycloisomerization of β-nitroso enamine intermediates. The decomposition pathways of N-nitrosamines, alkynes, and β-nitroso enamine intermediates were better handled in a continuous flow setting through the diffusion control of chemical species that negatively affected the formation of tetrahydroimidazo[1,2-a]pyridine 1-oxides under batch reaction conditions.

Improving of hydrogen desorption kinetics of MgH2 by NaNH2 addition: Interplay between microstructure and chemical reaction

MgH2 based composites combined with NaNH2 were synthesized by mechanical milling for three different milling times ranging from 15 to 60 minutes. Microstructure and particle size of the samples were analyzed by SEM microscopy while desorption properties were followed by Thermal Desorption Spectroscopy (TDS). The kinetic properties of NaNH2-MgH2 composites were investigated by isoconversional kinetic method as implemented in code developed by our group. Composites show hydrogen desorption peaks shifted to lower temperatures in comparison to mechanically modified and as received MgH2. All NaNH2-MgH2 composites show enhanced kinetics with lowered apparent activation energy (Ea) in comparison to milled MgH2. The mechanism of desorption changes from Avrami–Erofeev n = 3 for as received MgH2 to Avrami–Erofeev n = 4 for composite materials. The change from 3 to 4 can be due to the modification of the nucleation process or a change in the dimensionality of the growth. Those high values of n disregard a diffusion control as a rate limiting step. It has been shown that there is a synergistic effect on the enhanced hydrogen storage performance of chemical reaction and structural changes caused by ball milling. This can be used as a starting point for synthesis of innovative hydrogen storage materials.

Brainstem lesions are associated with diffuse spinal cord involvement in early multiple sclerosis

BackgroundEarly infratentorial and focal spinal cord lesions on magnetic resonance imaging (MRI) are associated with a higher risk of long-term disability in patients with multiple sclerosis (MS). The role of diffuse spinal cord lesions remains less understood. The purpose of this study was to evaluate focal and especially diffuse spinal cord lesions in patients with early relapsing-remitting MS and their association with intracranial lesion topography, global and regional brain volume, and spinal cord volume.MethodsWe investigated 58 MS patients with short disease duration (< 5 years) from a large academic MS center and 58 healthy controls matched for age and sex. Brain, spinal cord, and intracranial lesion volumes were compared among patients with- and without diffuse spinal cord lesions and controls. Binary logistic regression models were used to analyse the association between the volume and topology of intracranial lesions and the presence of focal and diffuse spinal cord lesions.ResultsWe found spinal cord involvement in 75% of the patients (43/58), including diffuse changes in 41.4% (24/58). Patients with diffuse spinal cord changes exhibited higher volumes of brainstem lesion volume (p = 0.008). The presence of at least one brainstem lesion was associated with a higher probability of the presence of diffuse spinal cord lesions (odds ratio 47.1; 95% confidence interval 6.9–321.6 p < 0.001) as opposed to focal spinal cord lesions (odds ratio 0.22; p = 0.320). Patients with diffuse spinal cord lesions had a lower thalamus volume compared to patients without diffuse spinal cord lesions (p = 0.007) or healthy controls (p = 0.002).ConclusionsDiffuse spinal cord lesions are associated with the presence of brainstem lesions and with a lower volume of the thalamus. This association was not found in patients with focal spinal cord lesions. If confirmed, thalamic atrophy in patients with diffuse lesions could increase our knowledge on the worse prognosis in patients with infratentorial and SC lesions.

Comprehensive extraction of valuable metals from waste ternary lithium batteries via roasting and leaching: Thermodynamic and kinetic studies

Considering the existing problems in the extraction of waste ternary materials, a method of reduction roasting - sulfuric acid leaching is proposed in this paper. The waste ternary battery material is mixed with carbon powder, reduced and roasted in an argon atmosphere to destroy the original crystal lattice of the ternary material, adjust the valuable metal ions to a valence state suitable for leaching, and reduce the difficulty of leaching. Moreover, recycling waste lithium batteries were systematically studied from the thermodynamic and kinetic aspects. Thermodynamic calculations indicate that the theoretical temperature for reduction roasting is 500–650 °C, and the roasting products are composed of lithium carbonate, nickel, cobalt, nickel oxide and manganese oxide, which has been confirmed by X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy analysis. The activation energy for the reduction roasting of the cathode material was calculated as 134.7 kJ/mol by thermogravimetry–differential scanning calorimetry and Kissinger formula. The roasted electrode materials were subjected to an acid leaching process. The effects of roasting and leaching conditions on the metal extraction from waste ternary batteries were investigated based on thermodynamic calculations, and the following optimal conditions were identified: 10% carbon content, 600 °C roasting temperature, 120 min roasting time, 2 mol/L sulfuric acid concentration, 85 °C leaching temperature, 10:1 liquid-to-solid ratio and 60 min leaching time. The extraction of lithium, nickel, cobalt, and manganese reached 98.3%, 97.2%, 98.8%, 96.1%, respectively, under the optimal conditions. The kinetic analysis of the acid leaching process adopted the shrinking core model and Arrhenius formula. The activation energies of lithium, nickel, cobalt, and manganese leaching were 23.9 kJ/mol, 25.2 kJ/mol, 23.0 kJ/mol, and 27.6 kJ/mol, respectively, which indicates that acid leaching is an internal diffusion control process. This study provides an economical and efficient process route and lays a theoretical and technological foundation for the extraction of cathode materials from waste ternary batteries.

Effect of rice husk volatiles in iron ore reduction and its kinetic study

ABSTRACT India is an agricultural country, whose main crop is rice. Processing and milling of rice crops generate waste which is not yet potentially utilized, at most, it can be used for combustion purposes only. Hence, this research attempts to utilize rice husk volatiles (RHv) as a reducing agent for iron ore pellets in iron and steel making. Selected rice husk (RH) consists of approximately 72% volatile matter. The reduction process was carried out at different temperatures at 800, 900, 1000, and 1100°C and time intervals of 15, 30, 45, 60, and 75 min in a double chamber vertical furnace, using RHv as a reducing agent. It has been observed that the reduction percentage of iron ore obtained in case of RHv is 79.01% at 1100°C in 75 min. Field Emission Scanning Electron Microscope (FESEM) and X-ray diffraction (XRD) analysis show the reduced pellets’ morphological characteristics and phase transformation, respectively. Kinetic analysis was done using the shrinking core model and it shows that at lower temperatures, that is, 800, 900, and 1000°C, reduction was diffusion control and followed by chemical reaction control at 1100°C. The activation energy obtained for diffusion and chemical control was 159 KJ/mol and 83.93 KJ/mol, respectively.

Ultrasonic-enhanced sulfuric acid leaching kinetics of high-grade germanium-containing materials

The study is based on the application of sulfuric acid in germanium leaching process, the leaching kinetic of high grade germanium-containing materials with sulfuric acid as solvent under ultrasonic assistance was studied. The influences of reaction temperature, sulfuric acid concentration and ultrasonic power on germanium leaching process were investigated.The results showed that when the sulfuric acid concentration was 110 g/L, the leaching temperature was 90 °C the leaching time was 30 min, the liquid-solid ratio was 10, and the ultrasonic power was 700 W, the germanium leaching effect was the best, and the leaching efficiency reached 92%.The leaching reaction process of germanium conforms to the unreacted shrinking core model. In the reaction process, loose product layer will be formed on the surface of the mineral, which hinders the diffusion of the leaching agent into the mineral. The leaching reaction control step of germanium in high-grade germanium-containing materials is internal diffusion control. According to the experimental data, the macro-kinetic model of the reaction was established, and the macro-kinetic equation was obtained with Ea (apparent activation energy) of 8.76 kJ/mol, A (pre-exponential factor) of 0.102.

The Influence of Fluorine-Containing Surfactants and Polymers on Regularities of Lead Dioxide Electrodeposition

Electrochemical synthesis allows one to influence the composition and properties of materials by changing the conditions of electrolysis and electrolyte composition. Lead dioxide due to the simplicity of its electrochemical synthesis, high corrosion resistance and relatively low cost is widely used in electrocatalysis, electroplating, lead-acid batteries, etc. The inclusion of fluorine-containing compounds in the metal oxide matrix provides antistatic, anti-adhesive, anti-corrosion properties, and at the same time the materials retain the properties of metal oxide: high electrical conductivity, resistance to mechanical wear and good adhesion to the substrate.In this work, the regularities of lead dioxide electrosynthesis in the presence of fluorine-containing surfactants with different fluor-carbon chain lengths and polyelectrolytes in the electrolyte were investigated.Electrodeposition was studied in 0.11 M CH3SO3H + 0.01 M Pb (CH3SO3)2. The surfactant was added to the deposition electrolyte in the form of aqueous solutions with a concentration of 3×10-4 M. Determination of current efficiency and partial oxidation current (IPb(II)) was performed by the method described in detail previously [1].The kinetic regularities of PbO2 electrodeposition are satisfactorily described in a four-stage mechanism applied to a wide range of electrolytes (both nitrate and methanesulfonate), including those containing ionic additives, colloidal TiO2 and polyelectrolytes [2,3]. As a rule, at low anodic polarizations (E <1.6 V) the reactions will take place with kinetic control, while at high polarizations the delivery of Pb2+ ions to the electrode surface will be the rate-determining stage. It was found that the addition of surfactants and polyelectrolytes in different ways affect the kinetics of electrodeposition of lead dioxide, without changing the mechanism of the process.The basis of the surface effects is the adsorption of additives on the electrode surface. The adsorption on the electrode of methanesulfonate and fluoride ions significantly affects the rate of the discharge-ionization stage. This effect is due to a number of factors that lead to changes in the concentration of reacting particles in the surface layer and the activation energy of the electrode process. Since the value of surface charge is positive, a decrease in the value of the potential in the plane of localization of the activated complex will increase the rate of the charge transfer stage, which is observed in practice in solutions containing short-chain perfluoroalkyl surfactants and low concentrations of Nafion® polymer. During the adsorption of a polyelectrolyte or anionic surfactant on the surface of the electrode, the value of such potential can not only decrease significantly, but even become negative due to recharging of the electric double layer. This possibility is indicated by the change in the electrokinetic potential of PbO2 from positive to negative by adding anionic surfactants and polymers to the electrolyte.The inhibition parameter reflects both the electrostatic and chemical interaction of the activated complex with the adsorption layer, which leads to an increase in the activation energy of the charge transfer stage. Increasing the volume concentration of the additive in the electrolyte leads to an increase in the degree of filling of the electrode surface, which will cause a decrease in the rate of the charge transfer stage due to blocking of active centers on the electrode surface.Since the process of formation of lead dioxide takes place together with the reaction of oxygen evolution, the dependences of PbO2 current efficiencies (CE) on the electrodeposition potential were investigated to assess the influence of surfactants on the lead dioxide electrodeposition.In the low polarizations area, the PbO2 CE remains virtually unchanged, close to 100%. In this area, the deposition process is controlled by kinetic stages. If the additive does not inhibit the deposition of lead oxide, CE is close to 100% and is almost independent of the current density. In the next part of the curve the process of electrodeposition of oxide occurs under mixed control. On the descending part of the dependence CE decreases due to the increase in the reaction rate of oxygen evolution when the limiting current of electrodeposition of oxide is observed (diffusion control). References A. Velichenko, T. Luk’yanenko, O. Shmychkova, L. Dmitrikova, Electrosynthesis and catalytic activity of PbO2-fluorinated surfactant composites, J. Chem. Technol. Biotechnol., 95, 3085, (2020). A. Velichenko, T. Luk’yanenko, N. Nikolenko, O. Shmychkova, P. Demchenko, R. Gladyshevskii, Composite electrodes PbO2-Nafion®, J. Electrochem. Soc., 167, 063501 (2020).O. Shmychkova, T. Luk’yanenko, A. Velichenko, Lead dioxide electrocrystallization from nitrate and methanesulfonate electrolytes: The influence of various dopants on initial stages, ECS Transactions, 77, 1617 (2017).

Efficient Water Softening in Heavy Oil Steamflood Operations

Summary Pigging of once through steam generators (OTSGs) has indicated various types of scales, the most predominant of these being silicates of hardness causing ions. It was noted that scaling propensity can potentially go up with higher steam quality (SQ) as the reject stream gets concentrated with ions. However, models suggested that there are benefits of higher SQ in enhancing fuel savings (8%) and electricity savings (2%) when SQ was increased by 20%. The challenges of higher SQ were noted in terms of increased scaling tendency and therefore the need for improved softening. In Field D, the service cycle, the backwash cycle, and the brining cycle were optimized leading to a gain in throughput and reduction in salt consumption. Service cycle improvement gained 30 to 130% in throughput between two regenerations, backwash cycle improvement by fluidizing the bed to nearly 35% helped gain 10% in throughput, and reduction of brining cycle from 75 to 48 minutes helped reduce salt consumption by 56% without impacting the throughput. In Field B, a 6-month pilot revealed that shallow shell resins where ion exchange is more efficient due to inert core (better intraparticle diffusion control) can enhance the throughput by 30 to 80% and simultaneously reduce the number of regenerations by 15 to 30%. Resin fouling is still a major challenge to contend with as oil can foul the resin and throughput can decline by 0.5 to 3 folds. In a plant operation, where there are multiple softener and brine vessels, there is a need to optimize them as a system. Reliability, availability, and maintainability (RAM) models are used in Field C to (a) address equipment configuration optimization with impact on capital capacity expansion project scope, (b) understand how net soft water delivery capacity was affected by increases in inlet hardness, and (c) assess through a comparison scenario if the large cost of addressing the valve issue in an upstream nutshell filter was worth the lost production opportunity related to unplanned downtime.

Leaching of yttrium and europium from fluorescent lamp phosphor powder using nitric acid: kinetics and optimization

ABSTRACT Rare earth elements (REEs) are recognized as one of the most critical elements and considered essential for the development of sustainable energy technologies, lasers, electronics, alloys, catalysts, and other applications. In order to meet the increasing demand to ensure those essential usages, the supply of REEs is however limited from the primary sources. Recovery of REEs from secondary resources, such as discarded electrical and electronic equipment, referred to as electronic waste (e-waste) is consequently crucial. Fluorescent lamps among such wastes are of special concern due to the high quantity of REEs present in them. This article discusses a potential hydrometallurgical method for recovering REEs (yttrium and europium) from fluorescent lamp waste via nitric acid leaching. The effects of leaching factors including acid concentration and temperature were examined. To assist the leaching yields of those metals, the effect of alkaline fusion was specifically examined. The kinetics of both processes, direct- and alkaline fusion-assisted leaching were investigated based on the shrinking core model. In the case of direct leaching, the metal dissolution was controlled by surface chemical reaction with apparent activation energies of 43.9 and 48.1 kJ/mol for yttrium and europium, respectively, in the temperature range 303–333 K. Pretreatment, viz., the alkaline fusion changed the subsequent leaching mechanism to diffusion control with apparent activation energies of 7.4 and 9.5 kJ/mol for the respective metal in the same temperature range. Optimization of the alkaline fusion-assisted acid leaching process was undertaken by applying response surface methodology (RSM) based on the central composite design (CCD). Under the alkaline fusion conditions such as soda/fluorescent powder mass ratio of 0.65 g/g, temperature of 1223 K and reaction time of 7200 s followed by acid leaching (nitric acid concentration – 3.5 M, temperature-323 K, pulp density – 30 g/L and leaching duration – 1200 s), the leaching efficiencies of 92.6% and 99.5% for yttrium and europium, respectively, could be achieved.

In-depth study on reaction kinetics of porous charred layer with high temperature alumina deposition in solid rocket motor

Current understanding of insulators abnormal ablation caused by alumina deposition in solid rocket motors (SRMs) is limited. The ability to calculate its thermochemical kinetic parameters and establish the corresponding ablation model determines the height of the thermal protection system design for advanced SRMs. In this work, the reaction mechanism of interaction between α-alumina and porous charred layer under deposition conditions was proposed firstly. Then the isothermal thermogravimetric experiments at 1750-1900 °C were carried out for the reaction system. The TG and DTG curves under various reaction conditions were treated by isoconversional method and model-fitting method, respectively, and the corresponding kinetic parameters and reaction models were calculated. Finally, based on the above research results, a deposition ablation model was established and the corresponding calculation code was compiled. Results show that the reaction of α-alumina/ porous charred layer system is formed by the superposition of four steps. The reaction model and kinetic parameters of each step reaction are as follows: steps 1 and 4 follows the diffusion control model (D3) with activation energies Ea of 109.6 kJ·mol−1, 47.9 kJ·mol−1 and frequency factors A of 47.9 min−1, 0.4 min−1, respectively, step 2 follows the chemical reaction control model (F1) with Ea of 48.5kJ·mol−1 and A of 14.8 min−1, and step 3 follows the contracting area model (R2) with Ea of 41.9kJ·mol−1 and A of 3.9 min−1. The insulator's ablation thickness calculated by the deposition ablation model established in this paper has an error of 16.01% compared to that in the experiment, indicating that it can be used to accurately calculate the ablation characteristics of insulators under the alumina deposition conditions in the future work.

Study of the electrostatic repulsion of the carboxylic surface in the diffusion layer by scanning electrochemical microscopy

AbstractThe behavior of electrostatic repulsion in the diffusion layer on the electrode is significant for understanding electrochemical processes with a diffusion control step. In this work, the electrostatic repulsion at the carboxylic acid‐containing surface of a 3‐mercaptopropionic acid self‐assembled monolayer (MPA SAM) in the diffusion layer on the tip electrode was revealed by scanning electrochemical microscopy (SECM). A direct surface repulsion system was designed between [Fe(CN)6]4− and the carboxylate groups in the diffusion layer. The pH‐modulated electrostatic repulsion of the carboxylic surface led to the repulsion of [Fe(CN)6]4− during diffusion, interrupting the regeneration of [Fe(CN)6]4− to [Fe(CN)6]3− on MPA SAM. Therefore, the approaching curve underwent a characteristic inversion from positive feedback to negative feedback dramatically. Electrostatic repulsion of the carboxylic surface was confirmed by linear sweep voltammetry and substrate generation/tip collection. Furthermore, the electrostatic repulsion of the carboxylic surface was visualized by SECM imaging technology. This work has contributed to broadening the recognition of electrostatic repulsion in the diffusion layer.

Dynamic Urea Bond‐Mediated Polymerization for Solvent‐Free Low‐ Ð Linear Polyurethanes of Controlled Molar Mass: Hypothesis of Diffusion Control

Dynamic urea bond-mediated polymerization (DUBMP) has been employed for the synthesis of linear, branched, telechelic, and random-block polyurethanes (PUs) with low molar-mass dispersity relative to conventionally synthesized PUs (Đ < 1.5). However, the reason for the improved control of the molar mass and reduction in dispersity, promoted by DUBMP, has not been explained. In this paper, the DUBMP synthesis of linear PU based on low-molar-mass poly(ethylene glycol) (PEG) and isophorone diisocyanate is studied comprehensively. The lower viscosity of the PEG-based PU allows DUBMP to reach high conversions (≈0.97) for the first time, while molar mass and Đ vary substantially with reaction conditions, despite yielding similar/equal conversion values. Both molar mass and Đ increase with an increase in reaction temperature, or with a reduction of the amine/isocyanate molar ratio. Therefore, evidence suggests that DUBMP provides diffusion control due to the lower mobility of the longer chains associated with an isocyanate-deactivator-rich environment. An increase in the reaction temperature, and/or a decrease in the amine/isocyanate molar ratio, reduces the diffusion control, leading to higher Đ values and molar mass. Tuning of the reaction conditions allows obtaining PU of controlled molar mass (11 kDa ≤ Mw ≤ 42 kDa) and 1.3 < Đ < 1.75.

OPTIMIZATION AND KINETICS STUDIES OF THE DISSOLUTION OF DOLOMITE IN SULPHURIC ACID (H2SO4) VIA BOX-BEHNKEN EXPERIMENTAL DESIGN

Background: The recovery of any valuable component from dolomite as a double carbonate mineral depends on its dissolution efficiency. Aim: This study aimed to optimize and provide a simplified novel approach to the kinetics of dolomite dissolution in sulphuric acid solution using the Box-Behnken experimental design. Methods: The dolomite sample was dissolved in a sulphuric acid solution at seventeen different experimental conditions. The residue containing impurities was removed via filtration, while precipitation was carried out at the optimum conditions. Results and Discussion: The relationship between the independent and dependent variables best fits into the two-factor interaction model with a coefficient of determination of 0.9492, adjusted R² of 0.9187, and predicted R² of 0.7514. The total residual sum of 3x10-13 and adequate precision of 18.769 show that the predicted dissolution efficiency is much closer to the experimental values. The analysis of variance revealed that the individual effect of acid concentration, temperature, and dissolution time all positively contribute to the dissolution. The interactive effect of acid concentration with temperature and the interactive effect of temperature with dissolution time also positively influences the dissolution efficiency. Following the dissolution of dolomite in sulphuric acid, a white precipitate was formed at room temperature, which dissolved back at a temperature of 70 oC, agitation speed of 900 revolutions per minute, and within 10 minutes. A predictive approach using a two-factor interactive model was applied to generate the kinetic data. Conclusions: The established model equation is suitable for predicting dolomite dissolution in sulphuric acid. The application of the shrinking core model to the generated data shows that the reaction between dolomite and sulphuric acid is film diffusion control with a first-order reaction (0.6587) and activation energy of 27.5 KJmol-1k-1.

Diffuse noxious inhibitory controls and conditioned pain modulation: a shared neurobiology within the descending pain inhibitory system?

Diffuse noxious inhibitory controls and conditioned pain modulation: a shared neurobiology within the descending pain inhibitory system?

Rheology of partially molten plagioclase containing wetting silica-rich anhydrous melt

Abstract This work explores the effects of melt chemistry on diffusion controlled creep of partially molten labradorite plagioclase (An50) at anhydrous conditions. Using sol-gel and hot pressing techniques we produced: (1) nominally melt-free samples, with &amp;lt;1 vol. per cent residual glass confined solely to multiple-grain junctions; (2) two types of partially molten samples, containing respectively ∼1 and ∼5 vol. per cent silica-rich partial melts, wetting numerous grain boundaries by thin (&amp;lt;10 nm) amorphous films. Energy dispersive X-ray analysis showed that the amorphous phases of the latter materials contained ∼85 and 95 wt. per cent SiO2, thus representing different polymerization degrees. Infrared spectroscopy showed that the initial traces of water (∼0.05 wt. per cent) were dried out by annealing in air above 1100 °C. Uniaxial creep tests performed at temperatures and flow stresses ranging, respectively, between 1100–1250 °C and 3–60 MPa showed dominantly linear viscous flow, with a strong grain size dependence indicating grain boundary diffusion control. Counter-intuitively strength and activation energy increased with the content of melts. However, for the sample suite silica content covaries with melt proportion, and thus our results suggest that the kinetics of grain boundary diffusion controlled creep strongly depends on melt chemistry. Instead of acting as shortcut for diffusion, thin films of highly viscous amorphous phases may in turn considerably hinder grain boundary transport properties.

High stability of Mo-F dual-doped O3-type NaNi1/3Fe1/3Mn1/3O2 cathode material for sodium-ion battery

Aiming for promoting the capacity and cycling stability of O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM), the cathode material of sodium ion batteries (SIBs) with the most potential for industrialization, Na(Ni1/3Fe1/3Mn1/3)0.99Mo0.01O1.99F0.01 (NFM-MoF), Na(Ni1/3Fe1/3Mn1/3)0.99Mo0.01O2 (NFM-Mo) and NaNi1/3Fe1/3Mn1/3O1.99F0.01 (NFM-F) were successfully synthesized by solid phase method. The electrochemical performance of the doped samples was compared with that of the pristine NFM. The mechanism of the single- or dual-doping was explored by XRD Rietveld refinement and XPS. The NFM-MoF exhibits the highest initial specific discharge capacity of 137mAhg−1 at 1 C with a retention of 91.97% after 100 cycles and the smallest polarization (0.32 V), which could be contributed to the highest Ni2+ content and highest DNa+ (7.335 ×10−13 cm2·s−1) caused by the synergistic effect of Mo and F dual-doping. The highest Fe3+ content in the NFM-Mo leads to the higher initial discharge capacity of 136 mAhg−1 at 1 C with a relative lower retention of 83.38%, which is due to the structure instability resulting from Fe migration and the lowest Mn content, than that of the NFM-F (85.31%). It illustrates that the Mn4+ plays a crucial role in stabilizing the structure during Na+ migrating. The superiority of the discharge capacity of the NFM-Mo become narrow with rates rise, due to its lower DNa+ (4.229 ×10−13 cm2·s−1) than that of the NFM-F DNa+ (5.681 ×10−13 cm2·s−1). It verifies that it is a diffusion control process at high rates. Mo and F dual-doping in NFM was proved to amplify the benefit of Ni2+ increasing, meanwhile restrain undesirable Fe increasing due to the synergistic effect.

Parameter-Robust Preconditioning for Oseen Iteration Applied to Stationary and Instationary Navier--Stokes Control

We derive novel, fast, and parameter-robust preconditioned iterative methods for steady and time-dependent Navier--Stokes control problems. Our approach may be applied to time-dependent problems which are discretized using backward Euler or Crank--Nicolson, and is also a valuable candidate for Stokes control problems discretized using Crank--Nicolson. The key ingredients of the solver are a saddle-point type approximation for the linear systems, an inner iteration for the $(1,1)$-block accelerated by a preconditioner for convection--diffusion control, and an approximation to the Schur complement based on a potent commutator argument applied to an appropriate block matrix. A range of numerical experiments validate the effectiveness of our new approach.

Diffusion control and surface control mechanism in hierarchical nanostructured porous zinc‐basedMOFmaterial for supercapattery

In this paper, we are reporting the zinc-based metal-organic framework nanomaterials for their application as a supercapattery device. The facile hydrothermal technique had been utilized to synthesize the MOF material. The surface morphology, crystallinity, and porosity were investigated with X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller, and energy dispersive X-ray analysis. To study the ability of the synthesized material for the storage of charges, electrochemical characterizations such as cyclic voltammetry (CV), galvanostatic charge (GCD), and electrochemical impedance spectroscopy (EIS) were performed in 1.0 M potassium hydroxide electrolyte. The specific capacity has been calculated from GCD curves and the material delivers 200 C/g at a current density of 0.7 A/g. This material revealed excellent performance in three-electrode assembly and therefore coupled with activated carbon (Zn-MOF//AC) to analyze the real energy and power density. This asymmetric assembly (supercapattery) had been tested with CV, GCD, and EIS. From all these characterizations, it was founded that the device was able to store charges of 172 C/g along with the excellent energy density and power density of 38.05 Wh/kg and 240 W/kg, respectively. The supercapattery revealed exceptional cyclic stability of 93.6% even after 2500 GCD cycles along with 100% of columbic efficiency. Furthermore, the diffusion-controlled and surface-controlled contributions were investigated for the assembled supercapattery, and it is found that the device stores energy through both the contributions. The maximum diffusive contribution by the device was 70.13% at the scan rate of 10 mV/s, which reaches to 42.75% at 100 mV/s scan rate. Likewise, the surface control contribution of the device was 29.86% at 10 mV/s, which rises up to 57.24% at 100 mV/s scan rate. These variations are attributed to the scan rates, which allow the ions to interact fast/slow with electrodes. Our analysis indicates that the synthesized material can be utilized as an interesting high-performance electrode material for supercapattery devices.

Peeling dynamics of fluid membranes bridged by molecular bonds: moving or breaking.

Biological adhesion is a critical mechanical function of complex organisms. At the scale of cell–cell contacts, adhesion is remarkably tunable to enable both cohesion and malleability during development, homeostasis and disease. It is physically supported by transient and laterally mobile molecular bonds embedded in fluid membranes. Thus, unlike specific adhesion at solid–solid or solid–fluid interfaces, peeling at fluid–fluid interfaces can proceed by breaking bonds, by moving bonds or by a combination of both. How the additional degree of freedom provided by bond mobility changes the mechanics of peeling is not understood. To address this, we develop a theoretical model coupling diffusion, reactions and mechanics. Mobility and reaction rates determine distinct peeling regimes. In a diffusion-dominated Stefan-like regime, bond motion establishes self-stabilizing dynamics that increase the effective fracture energy. In a reaction-dominated regime, peeling proceeds by travelling fronts where marginal diffusion and unbinding control peeling speed. In a mixed reaction–diffusion regime, strengthening by bond motion competes with weakening by bond breaking in a force-dependent manner, defining the strength of the adhesion patch. In turn, patch strength depends on molecular properties such as bond stiffness, force sensitivity or crowding. We thus establish the physical rules enabling tunable cohesion in cellular tissues and in engineered biomimetic systems.