Liquid Diffusion Coefficient Research Articles

Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry.

Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of (1)H spin-lattice relaxation rate R1(ω) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by (19)F spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the (1)H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the (1)H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R1 on square root of frequency. From the (19)F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids.

Effect of cation on diffusion coefficient of ionic liquids at onion-like carbon electrodes

While most supercapacitors are limited in their performance by the stability of the electrolyte, using neat ionic liquids (ILs) as the electrolyte can expand the voltage window and temperature range of operation. In this study, ILs with bis(trifluoromethylsulfonyl)imide (Tf2N) as the anion were investigated as the electrolyte in onion-like carbon-based electrochemical capacitors. To probe the influence of cations on the electrochemical performance of supercapacitors, three different cations were used: 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium and 1,6-bis(3-methylimidazolium-1-yl). A series of electrochemical characterization tests was performed using cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Diffusion coefficients were measured using EIS and correlated with quasielastic neutron scattering and molecular dynamics simulation. These three techniques were used in parallel to confirm a consistent trend between the three ILs. It was found that the IL with the smaller sized cation had a larger diffusion coefficient, leading to a higher capacitance at faster charge–discharge rates. Furthermore, the IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments.

Estimation of Binary Infinite Dilute Diffusion Coefficient Using Artificial Neural Network

In this study, the use of the three-layer feed forward neural network has been investigated for estimating of infinite dilute diffusion coefficient ( D12 ) of supercritical fluid (SCF), liquid and gas binary systems. Infinite dilute diffusion coefficient was spotted as a function of critical temperature, critical pressure, critical volume, normal boiling point, molecular volume in normal boiling point, molecule diameter, Lennard-Jones’s (LJ) energy parameter, temperature and pressure. For each set of SCF, liquid and gas systems a three-layer network has been applied with training algorithm of Levenberg-Marquard (LM). The obtained results of models have shown good accuracy of artificial neural network (ANN) for estimating infinite dilute diffusion coefficient of SCF, liquid and gas binary systems with mean relative error (MRE) of 2.88 % for 231 systems containing 4078 data points (mean relative error for ANN model in SCF, liquid and gas binary systems are 3.00, 2.99 and 1.21 %, respectively)

一种新的滑动剪切技术测量Al-Cu合金的互扩散系数

The diffusion coefficient is one of the most important physical parameters in liquid metals, and also an essential parameter for the material design and industrial application. However, available experimental data of the diffusion coefficients are actually not sufficient due to the difficulties of the diffusion measurement. In this work, a new kind of diffusion measurement technique: the sliding cell technique is presented. By employing this technique, the influence of the heating process on the isothermal liquid diffusion procedure is avoided, so that the measurement accuracy is significantly enhanced compared to the conventional long capillary technique. Using the novel technique, the liquid diffusion coefficients of the diffusion couple Al₇₀Cu₃₀ vs Al₉₀Cu₁₀ at 1023 K were measured. It is found that the measured diffusion coefficients show a clear composition dependent tendency. Such a tendency is useful for the understanding of the mechanism of atomic diffusion and the correlation between diffusion and atomic structure.

Electroreduction Property and MD Simulation of Nitrobenzene in Ionic Liquid [BMim][Tf2N]/[BMim][BF4

The two different common accessible ionic liquids [BMim][BF4] and [BMim][Tf2N] were mixed each other in a simple and economic way. In some compound ratios, the dynamic performance of nitrobenzene in electric reduction was superior to that of any single kind of ionic liquid has been appeared. The interaction and mass transfer of diffusion of nitrobenzene in composite ionic liquids with different volume ratios were studied with molecular dynamics (MD) simulation. The improvement of the electroreduction performance of nitrobenzene in composite ionic liquids was verified and was tried to explain. This provides a new idea for the modification and functionalization of ionic liquids in electrochemical field.The experimental results showed that kinematic viscosity and electroconductibility of different ionic liquid systems display a regular change. And the change law has been basically unchanged after adding water. The two different functional ionic liquids were complemented each other in a simple and economic way, which has compensated for the disadvantage of mono-component ionic liquids. At 25°C, electroreduction property of V[BMim][BF4]:V[BMim][Tf2N]=1:1 is the best in cyclic voltammetry experiments of nitrobenzene in different composite ionic liquids. Its electrochemical behavior is significantly affected by scan rate, temperature, concentration of nitrobenzene and concentration of water. The MD simulation results showed most of interaction energies between nitrobenzene and different ionic liquids with and without water is little difference. The variation trend of diffusion coefficients in different composite ionic liquids is consistent with that of interaction energies. Analyzing pair correlation functions showed that the bonding and nonbonding interactions are formed between the N, S and O atoms of ionic liquid and the N and O atoms of nitrobenzene. The diffusion is mainly caused by the nonbonding interaction between nitrobenzene and composite ionic liquid, and the interactions with water molecules are obviously greater than that without water. The conclusion is consistent with the experimental results.

Oxygen mass transfer and hydrodynamic behaviour in wastewater: Determination of local impact of surfactants by visualization techniques

Powerful techniques, based on the Planar Laser Induced Fluorescence (PLIF) technique, are deployed to locally visualize and quantify the impact of surfactants in wastewaters on hydrodynamics and oxygen mass transfer. Bubble diameter, aspect ratio, rise velocity, contamination angle, as well as flux, flux density, liquid side mass transfer and diffusion coefficients of transferred oxygen are determined based on these techniques applied in the wake of rising bubbles of diameter 1 mm and through planar gas/liquid interfaces. The initial experiments were performed in demineralized water containing small amounts of surfactant. Different concentrations of surfactant were added to finally reach the Critical Micelle Concentration (CMC). Bubbles have classically been found to be more spherical with a reduced rise velocity in the presence of surfactants up to the CMC. Above the CMC, these hydrodynamic characteristics were found to be almost constant, although the oxygen mass transfer decreased due to the presence of surfactants. Experimental results were markedly lower than predicted by the well-known Frössling equation with rigid surfaces. This is believed to be caused by a barrier of surfactants hindering the oxygen mass transfer at the interface. Similar hindrance of oxygen mass transfer applies to waters from sewage plants (filtered raw water and treated water), making accurate design of aeration tanks difficult.

A sliding cell technique for diffusion measurements in liquid metals

The long capillary and shear cell techniques are the usual methods for diffusion measurements in liquid metals. Here we present a new “sliding cell technique” to measure interdiffusion in liquid alloys, which combines the merits of these two methods. Instead of a number of shear cells, as used in the shear cell method, only one sliding cell is designed to separate and join the liquid diffusion samples. Using the sliding cell technique, the influence of the heating process (which affects liquid diffusion measurements in the conventional long capillary method) can be eliminated. Time-dependent diffusion measurements at the same isothermal temperature were carried out in Al-Cu liquids. Compared with the previous results measured by in-situ X-ray radiography, the obtained liquid diffusion coefficient in this work is believed to be influenced by convective flow. The present work further supports the idea that to obtain accurate diffusion constants in liquid metals, the measurement conditions must be well controlled, and there should be no temperature gradients or other disturbances.

Pressure and temperature dependence of diffusion coefficients in a model liquid and glass forming liquid

The self-diffusion coefficients in a model liquid and glass forming liquid have been studied as a function of temperature and pressure using the classical molecular dynamics (MD) method. Isothermal–isobaric (NPT) ensemble is carried out in our simulations. Special attention is paid to the glass-forming ability of the rapid-quench method under different pressures. We evaluate (1) glass transition and radial distribution function, (2) temperature dependence of diffusion coefficients in liquid and glass forming liquid, and (3) pressure dependence of diffusion coefficients in glass forming liquid. The simulations show (i) the greater the pressure, the higher the glass-transition temperature, by using the same high enough cooling rate from the melts; (ii) an Arrhenius dependence of diffusion coefficients D with reduced temperature T⁎ in liquid, that is, lnD~1/T⁎, and there being a process of slow change in glass forming liquid; (iii) an Arrhenius dependence of diffusion coefficients on pressure in glass forming liquid in the pressure range studied, that is, lnD~P⁎.

Effect of withdrawal rate on microstructure and lattice misfit of a Ni3Al based single crystal superalloy

A newly developed Re-containing Ni3Al based single crystal superalloy was prepared by seeding technique. We investigated the effect of withdrawal rate (1–400μm/s) on the microstructure and the γ/γ′ lattice misfit. With increasing withdrawal rate, the as-cast microstructure changed from planar to cellular and then to dendritic, accompanied by the significant refinement of dendrite arm and γ′ phases. The morphology of γ′ phases also transformed in response to different withdrawal rates, which was ascribed to the influence of the γ/γ′ lattice misfit. In association with the evolution of the microstructures, the liquid diffusion coefficients of Ni and Ni3Al based superalloys were estimated by Kurz–Fisher model.

Determination of binary diffusion coefficients of hydrocarbon mixtures using MLP and ANFIS networks based on QSPR method

In this article, at first, a quantitative structure–property relationship (QSPR) model for estimation of limiting diffusion coefficients of hydrocarbon liquids, DAB0, is developed. Particle swarm optimization variable selection (PSOvs) method, together with multi-linear regression (MLR) model, selects suitable descriptors from a pool of 1124 predefined descriptors. The MLR model is trained based on a data bank of 345 experimental binary diffusivities of hydrocarbons in infinite dilution solutions. The objective function of the optimizer for descriptor selection is the multi-variant RQK function. In addition, an artificial neural network (ANN) and an adaptive neuro-fuzzy inference system (ANFIS) are developed as two nonlinear black-box estimators of DAB0 based on the descriptors obtained from PSOvs algorithm. The estimation results of these three QSPR models (PSO-MLR, ANN and ANFIS) are compared with five semi-empirical correlations. Furthermore, using 402 experimental binary diffusion coefficient data at different concentrations and temperatures, another multi-layer perceptron network (MLPN) is constructed to predict the diffusion coefficients of binary hydrocarbon liquid systems at various concentrations and temperatures. The input variables of this network are DAB0, DBA0, and mole fraction of the component A. Average absolute relative deviations (AARD) of the developed MLP-QSPR model for training, test, and whole data are respectively, 5.86%, 7.79%, and 6.32%. Indeed this model has less than 5% AARD for more than 50% of the data points. Also, the results of the MLP model designed to estimate the binary diffusivities of concentrated hydrocarbon mixtures show that the average absolute relative error for the whole of test and training data is 6.3%. The comparison of the developed MLP model with experimental data and some of semi-empirical correlations indicates that the suggested modeling scheme based on QSPR and MLP method has very good accuracies for estimation/prediction of liquid hydrocarbon diffusivity not only in infinite dilution but also at concentrated solutions.

Effect of liquid diffusion coefficients on microstructure evolution during solidification of Al356.1 alloy

The effect of liquid diffusion coefficients on the microstructure evolution during solidification of primary (Al) phase in Al356.1 alloy was investigated by means of the phase-field simulation using two sets of diffusion coefficients in liquid phase, while fixing other thermophysical and numerical parameters. The first set is only with impurity coefficients of liquid phase in Arrhenius formula representing only the temperature dependence. While the second set is with the well-established atomic mobility database representing both temperature and concentration dependence. For the second set of liquid diffusion coefficients, the effect of non-diagonal diffusion coefficients on the microstructure evolution in Al356.1 alloy during solidification was also analyzed. The differences were observed in the morphology, tip velocity and composition profile ahead of the tip of the dendrite due to the three cases of liquid diffusivities. The simulation results indicate that accurate databases of mobilities in the liquid phase are highly needed for the quantitative simulation of microstructural evolution during solidification.

Modeling and Experimental Studies of Adsorptive Dewatering of Selected Aliphatic Alcohols in Temperature Swing Adsorption System

Based on experimental work, closely coupled with mathematical modeling, an analysis was performed of the adsorptive drying of selected water-aliphatic alcohol solutions. The experimental work involved ethanol, n-propanol, and n-butanol dehydration using two adsorbents, 3A and 4A zeolite molecular sieves. The isothermal model developed in this paper incorporates an overall linear mass driving force, including liquid film mass transfer and intraparticle diffusion coefficients, a variable axial diffusivity, and experimentally determined Langmuir-Freundlich isotherms. Breakthrough curves generated by the model were compared with those obtained experimentally, giving a fairly good fit. The model simulations enabled determination of the water content profiles in adsorbent beds.

Diffusion coefficient of three-dimensional Yukawa liquids

The purpose of this work is an investigation of the diffusion coefficient of the dust component in complex plasma. The computer simulation of the Yukawa liquids was made on the basis of the Langevin equation, which takes into account the influence of buffer plasma on the dust particles dynamics. The Green–Kubo relation was used to calculate the diffusion coefficient. Calculations of the diffusion coefficient for a wide range of the system parameters were performed. Using obtained numerical data, we constructed the interpolation formula for the diffusion coefficient. We also show that the interpolation formula correctly describes experimental data obtained under microgravity conditions.

The influence of intra-droplet heat and mass transfer limitations in evaporation of binary hydrocarbon mixtures

The influence of intra-droplet heat and mass transfer limitations during the evaporation of binary hydrocarbon mixtures is investigated. Liquid transport processes are described with a 1D formulation (diffusion limit model – DLM) taking into account temporal and spatial gradients of the substance properties. The vapor liquid equilibrium is described with a γ–φ model and the activity coefficients are calculated using the NRTL approach. A suitably normalized segregation factor for each component based on the time-integrated evaporation rate is introduced and used for the analysis of n-heptane/n-decane and n-heptane/iso-octane droplets varying the ambient conditions and the initial liquid compositions. Simulations with the DLM approach are compared to results obtained with a 0D model (rapid mixing model – RMM), which assumes homogeneous droplets in the infinite-diffusivity limit. Simulation results are also compared to experimental data where available. Biot numbers for heat and mass transfer as well as Lewis numbers for the liquid phase are evaluated and their differences are analyzed. A constant Lewis number based approach to calculate the liquid diffusion coefficients is investigated in detail as an alternative to the computationally expensive calculation of the individual diffusion coefficients at each inner droplet location. A suitable strategy to precompute the Lewis number as a function of temperature and composition is presented and the results are compared to the detailed calculations.

Diffusion coefficients and VLE data of aqueous phosphoric acid

In this work, transport and thermodynamic properties of phosphoric acid/water mixtures were determined experimentally over a wide range of concentrations. Liquid binary diffusion coefficients were measured using the Taylor dispersion technique at various temperatures and concentrations. The second part of this work concerns itself with the (vapour+liquid) phase equilibrium of phosphoric acid and water up to concentrations of 105wt% at different pressures.

Modeling diffusion-governed solidification of ternary alloys – Part 1: Coupling solidification kinetics with thermodynamics

A method incorporating the full diffusion-governed solidification kinetics and the ternary phase diagram into a multiphase volume average solidification model is presented. The motivation to develop such a model is to predict macrosegregation in castings. A key feature of this model, different from most previous ones which usually assume an infinite solute mixing in liquid (e.g. lever rule, Gulliver–Scheil), is that diffusions in both liquid and solid phases are considered. It is known that models with assumption of an infinite liquid mixing lead to erroneous estimation of the solidification path at the initial stage. Here solidification of a ternary alloy (Fe–0.45wt.%C–1.06wt.%Mn) is examined. As the two chosen alloy elements (C and Mn) have large differences in the solute partition coefficient, liquidus slope and liquid diffusion coefficient, the solidification path shows differently from those predicted by infinite liquid mixing models. The first part of this two-part investigation evaluates the full diffusion-governed kinetics and its influence on solidification path and microsegregation. Applications of the model for the calculation of solidification and macrosegregation are presented in the accompanying paper [Part 2].

On the CO2 Capture in Water-Free Monoethanolamine Solution: An ab Initio Molecular Dynamics Study

Monoethanolamine (MEA) based liquids are widely used materials for postcombustion CO2 capture. We report here an extensive ab initio molecular dynamic (AIMD) simulation study on CO2 sorption in water-free MEA liquid with a range of CO2 contents at 313 K. The simulation reveals the detailed CO2 capture mechanism that leads to the initial formation of a zwitterion species and the ultimate proton transfer from the zwitterion to a nearby MEA molecule. The ion pairs formed in the liquid result in strong electrostatic interactions among the molecules in the liquid. The variation of liquid density, volume, diffusion coefficient, power spectrum, and average heat of sorption at the selected CO2 loadings was systematically assessed. The results indicate that initially the volume of the MEA solution expands gradually and tops at 60% of CO2 loading. After that, the volume declines as a result of strong Coulomb interactions among the ion pairs at higher CO2 loadings. The calculated liquid densities and the average heats of sorption are in quantitative agreement with the available experimental values. The simulated power spectrum of the water-free liquid also resembles the infrared spectrum of 30% aqueous MEA solution. The characteristic features in the simulated power spectra are slightly blue-shifted upon CO2 uptake.

Universal model for accurate calculation of tracer diffusion coefficients in gas, liquid and supercritical systems

In this work it is presented a new model for accurate calculation of binary diffusivities (D12) of solutes infinitely diluted in gas, liquid and supercritical solvents. It is based on a Lennard–Jones (LJ) model, and contains two parameters: the molecular diameter of the solvent and a diffusion activation energy. The model is universal since it is applicable to polar, weakly polar, and non-polar solutes and/or solvents, over wide ranges of temperature and density. Its validation was accomplished with the largest database ever compiled, namely 487 systems with 8293 points totally, covering polar (180 systems/2335 points) and non-polar or weakly polar (307 systems/5958 points) mixtures, for which the average errors were 2.65% and 2.97%, respectively. With regard to the physical states of the systems, the average deviations achieved were 1.56% for gaseous (73 systems/1036 points), 2.90% for supercritical (173 systems/4398 points), and 2.92% for liquid (241 systems/2859 points). Furthermore, the model exhibited excellent prediction ability. Ten expressions from the literature were adopted for comparison, but provided worse results or were not applicable to polar systems. A spreadsheet for D12 calculation is provided online for users in Supplementary Data.

Modeling investigation of mass transfer of gas–liquid concurrent flow processes

This paper presents a modeling investigation of mass transfer of gas–liquid concurrent flow processes to explore the effect of bubble scale. CO2 capture with MEA aqueous solution is selected as a working system to evaluate the modeling results. The rate-controlling step is first determined and the effects of bubble size, gas–liquid volume ratio and diffusion coefficient on mass transfer coefficients are respectively discussed, with bubble size ranging between 10μm and 1cm and gas–liquid volume ratio ranging between 6.5:1 and 321:1. For both gas-resistance-controlled and liquid-resistance-controlled processes, as bubble size decreases from 1cm to 10μm, the overall mass-transfer coefficient increases by three orders of magnitude and volumetric mass-transfer coefficient increases by six orders of magnitude, indicating the decrease in bubble size intensifies the mass transfer processes both by reducing mass transfer resistance and increasing interfacial area obviously. The modeling results are in good agreement with the experimental data. This study could be useful for designing micro-devices and optimizing gas–liquid microdispersion processes.

Electrodeposition of metals in microgravity conditions

Metal electrodeposition may produce irregular deposits with various morphologies. For liquid electrolytes a precise study of these deposits may be complicated by convective motion due to buoyancy. Microgravity conditions give a straightforward mean to avoid this effect: we present here a study of electrodeposition in the microgravity environment provided by parabolic flights. Two electrochemical systems were studied: copper deposition from copper sulfate aqueous solution and lithium deposition from an ionic liquid containing LiTFSI.Concentration variations in the electrolyte were measured by laser interferometry. For copper, concentration variations were in good agreement with theory. For lithium, an induction time was observed for the concentration evolution in ground experiments: due to this induction time and to the low diffusion coefficient in ionic liquid, concentration variations were hardly measurable during the 20s parabolic flight.