Salt Diffusion Research Articles

Single Electrode Entropy Change for LiCoO2 Electrodes

Heat effects are known to be crucial for the performance of the Li-battery. In addition to the irreversible effects (e.g. Joule heat), reversible heat effects may play a role. These effects, i.e. the Soret and Seebeck effects, are however scarcely investigated. We report the initial and stationary state thermoelectric potentials of a pouch cell having electrodes where Li is intercalated in CoO2. The electrolyte consists of 1.0 M lithium hexafluoro phosphate dissolved in a mixture of equal volumes of ethylene carbonate and diethyl carbonate.The two identical electrodes were thermostatted at different temperatures, the average being always 298 K and the potential was measured over several days. We observe two time-dependent phenomena with characteristic times of 4.5 and 21.3 hours. We explain them by thermal diffusion of salt and esters. The Seebeck coefficient varies from -2.8 mV/K in the initial state to 1.5 mV/K in the state characterized by partial Soret equilibrium. The time-variation of the signal is used to compute Seebeck coefficients, the contributions to the heats of transfer, and the reversible heat effect at the LiCoO2-and carbon electrodes. The electrode heat effects in a Li-battery is surprisingly asymmetric, given the small entropy of the total reaction.The LiCoO2 electrode heat varies from 51 to - 46 kJ/mol, while the carbon electrode will vary from -73 to 56 kJ/mol. Uncertainties in computations are within 15%. This may explain why the reaction entropy depends largely on the state of charge. It may also be important for thermal modeling of the battery.

Effect of eddy diffusivity ratio on underwater optical scintillation index.

The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and spherical waves and investigate the effect of the eddy diffusivity ratio.

Water and salt transport properties of disulfonated poly(arylene ether sulfone) desalination membranes formed by solvent-free melt extrusion

This paper reports water and salt transport properties of sulfonated polysulfone desalination membranes prepared by solvent-free, melt extrusion. The 20mol% disulfonated poly(arylene ether sulfone) (BPS-20K) membranes were prepared by melt processing, using poly(ethyelene glycol) (PEG) M̅n (200 ~ 400g/mol) as plasticizers at concentrations of 20wt% to 30wt%, and different PEG extraction temperatures. Water and salt transport properties of BPS-20K membranes prepared by different processing routes correlated well with water uptake, as expected, based on free volume theory. The melt-extruded BPS-20K membranes show higher water uptake than those of solution cast membranes. As PEG molecular weight and concentration used during extrusion increases and as PEG extraction temperature increases, water uptake also increases. As water uptake increases, water and salt permeabilities and diffusivities increase, consistent with the findings of Yasuda et al. In general, BPS-20K membranes prepared by different processing routes followed the trade-off relationship between water permeability and water/salt permeability selectivity. These results indicate that differences in membrane processing history have significant effects on the transport properties of small molecules in these polymers, similar to other glassy polymers.

Effects of tannic acid on membrane fouling and membrane cleaning in forward osmosis.

The fouling behavior during forward osmosis (FO) was investigated. Tannic acid was used as a model organic foulant for natural organic matter analysis since the main characteristics are similar, and calcium ions were added at different concentrations to explore the anti-pollution capability of FO membranes. The initial permeate flux and calcium ions strength were varied in different operating conditions to describe membrane fouling with membrane cleaning methods. The observed flux decline in FO changed dramatically with the type of foulant and the type of draw solution used to provide the osmotic driving force. Calcium ions aggravated membrane fouling and decreased transmembrane flux. Membrane cleaning methods included physical and physicochemical approaches, and there was no obvious difference among the typical cleaning methods (i.e., membrane flushing with different types of cleaning fluids at various crossflow velocities and backwashing with varying osmotic driving forces) with respect to flux recovery. Ultrasonic cleaning damaged the membrane structure and decreased permeate flux, and reverse diffusion of salt from the draw solution to the feed side accelerated after cleaning.

Performance of layer-by-layer (LbL) polyelectrolyte forward osmosis membrane for humic acid removal and reverse solute diffusion

<p>Recent study claimed that forward osmosis (FO) process could handle the fouling problem due it driven force based on natural osmotic pressure. However, researchers observed that FO membrane had problem with reverse solute diffusion (RSD) of draw solution. Therefore, FO membrane properties must be improved either physically or chemically in order to overcome this problem. Among all, surface modification approach has been acknowledged as a best technique to alter the membrane properties without significantly change the bulk membrane properties. In this study, polyelectrolyte FO membrane has been produced through Layer by Layer (LbL) deposition method by using Poly (diallyl-dimethylammoniumchloride), PDADMAC and Poly (sodium 4-styrene-sulfonate), PSS as an active monomers. Humic acid (HA) as part of Natural Organic Matter constituents was used as the feed solution and NaCl as a draw solution. The chemical structure and morphology of the FO membrane were characterized by FTIR and FESEM, respectively. From this study, the highest water flux and humic acid rejection were achieved at 2.5M of draw solution with value of 2.56 L/m<sup>²</sup>.h and 99%, respectively. In general, the water flux increases as the concentration of draw solutions were increased. However, it was observed that reverse salt diffusion (RSD) become worse at higher concentration of draw solution.</p><p>Chemical Engineering Research Bulletin 19(2017) 75-79</p>

Pressure retarded osmosis process for power generation: Feasibility, energy balance and controlling parameters

The feasibility of pressure-retarded osmosis (PRO) for power generation was evaluated with consideration of the energy inputs and losses in the process. The effects of the concentration polarization, reverse salt diffusion, and external resistance at the membrane porous layer were quantified, for the first time, along the membrane module to determine their contributions to the energy loss in the PRO process. Concentration polarization was responsible for up to 40% of the energy loss during the PRO process. However, increasing the PRO membrane modules from 1 to 4 resulted in a variable increase of the energy output depending on the salinity gradient. The energy requirements for draw and feed solution pretreatment were estimated to be over 38% of the total energy inputs. Results showed that coupling seawater (SW) with river water (RW) was unable to generate sufficient energy to compensate for the energy inputs and losses during the PRO process. With 0.39kwh/m3 maximum specific energy in the PRO process, the energy yield of reverse osmosis brine (ROB)-wastewater (WW) salinity gradient was slightly greater than the total energy inputs, although using Dead Sea-SW/ROB salinity gradient was more promising. Overall, the primary current limitation is the lack of suitable PRO membranes that can withstand a high hydraulic pressure.

In Situ NMR Imaging of Ion Transport in Li-Ion Batteries

The operation of battery management systems requires that the transient conditions experienced by a battery in electrified vehicle applications can be accurately described through battery modeling. Reliable data on the transport properties of electrolyte solutions, as functions of both salt concentration and temperature, are a prerequisite for such a task. The accurate characterization of the transport parameters is a complex problem, because the values of ionic diffusion coefficients in an electrolyte solution depend strongly on the salt concentration. At the same time, the salt concentration inside a battery is neither stationary nor homogeneous, during battery operation at high charge/discharge rates. It is, rather, a function of current density, time and distance from the electrodes. Recently, MRI was used for in operando characterization of materials used in Li-ion batteries. The main advantage of MRI over commonly used methods, such as NMR and electrochemical techniques, is its ability to provide spatially resolved details regarding the chemical and dynamic features of solution species. Therefore, such data enable a more accurate representation of the processes occurring in an electrolyte solution under an applied electrical potential, instead of values averaged over the entire volume of a sample cell. Using in situ MRI, we have unambiguously mapped the large concentration polarization experienced by an electrolyte solutions during battery operation.1 The concentration gradient created in the electrolyte solution of the cell under galvanostatic conditions will increase until a steady-state (time invariant) condition is achieved, when the diffusion flux compensates for the migration flux of the ions. Our results confirm that the concentration gradient developed under such conditions is proportional to the applied current (Fig. 1b) as described by the diffusion-migration equation (Eqn. 1), where i is the current density and F is the Faraday constant.2 We have shown previously that, while the degree of ion pairing is quite high (up to 67%) in electrolyte solutions under normal operating conditions, it is almost constant during a steady-state NMR gradient measurements (with salt concentrations varying from 0.8 to 1.2 M).3 Therefore, one can use averaged diffusion coefficients of charged and neutral species measured by pulsed field gradient NMR (PFG-NMR) in Eqn. 1. Also the total salt concentration, obtained directly by MRI should be used, instead of concentration of free ions.2 The inverse modeling of evolution of salt concentration profiles measured by in situ MRI under applied electric current also supported this conclusion.4 Therefore, by combining the PFG-NMR and the in situ MRI techniques into one experiment, one can simultaneously determine the distribution of salt concentration and the salt diffusivity in the electrolyte solution during a galvanostatic experiment (Fig. 2). It can be readily seen that the diffusion coefficient has a significant dependence on the salt concentration, with the values of D measured at opposite ends of the cell varying by more than 60%. Such changes obviously must be taken into account in order to provide an accurate description of mass-transport. The Li+ transference number (t+ ) can then be obtained by means of Eqn.(1). A slight decrease in t+ with concentration was observed, which can be explained by an increase in ion association. However, with the exception of data point at the lowest concentration, all of values of the Li+ transference numbers thus obtained fall within the experimental error and t += 0.31 ± 0.03. The formed concentration gradient affects not only the mass transport in electrolyte solution, but also the electrode lithiation. The electrolyte depletion prevents the active material in the solid from being lithiated in regions where electrolyte has been depleted. Furthermore, when the electrolyte concentration approaches zero, its conductivity drops, significantly hampering the process. The current tends to flow into the particles nearest the separator until they are completely lithiated, causing the intercalation reaction to occur preferentially at the front of the electrode. Implementation of pure phase-encoding MRI methods allows us to visualize non-uniform lithiation of the graphite electrode during cycling of Li-ion cell (Fig. 1c), leading to the next level of battery performance characterization.

Apparatus for Measuring Coupled Membrane and Diffusion Behavior of Unsaturated Sodium Bentonite

Core Ideas Coupled membrane and diffusion behavior was measured in unsaturated Na‐bentonite. A new testing apparatus advances the state of the art for coupled processes in clays. The membrane efficiency of Na‐bentonite increased as the degree of saturation decreased. Sodium bentonite (Na‐bentonite) has been shown to exhibit semipermeable membrane behavior—the ability to selectively restrict the migration of dissolved chemical species through the pores of the clay. However, experimental research to date has focused on the membrane behavior of Na‐bentonite almost exclusively under water‐saturated conditions (i.e., degree of saturation S = 1), even though membrane behavior under unsaturated conditions is expected to be more significant. Further, the limited number of studies that have been performed to evaluate membrane behavior in unsaturated soils have used only open systems to quantify membrane efficiency (ω), despite the testing advantages of using closed systems (e.g., more accurate measurement of ω, easier control of boundary conditions). Thus, a closed‐system testing apparatus capable of measuring coupled membrane and diffusion behavior in unsaturated Na‐bentonite was developed and then used to measure ω and salt diffusion in Na‐bentonite with S of 0.84 and 1.0. For a source solution (concentration difference) of 20 mM KCl, ω increased from 0.61 to 0.71 as S decreased from 1.0 to 0.84, which is consistent with the current conceptual understanding of membrane behavior and trends in the literature. In contrast, the effective diffusion coefficient for Cl− was essentially the same (i.e., ∼1.8 × 10−10 m2 s−1) for both specimens due to the small difference in S. The development of the testing apparatus advances the state of the art for laboratory measurement of coupled membrane and diffusion behavior in unsaturated clays commonly used as chemical containment barriers.

Ranking and comparison of draw solutes in a forward osmosis process

Forward osmosis (FO) is an emerging technology which can possibly make the desalination process more cost and energy efficient. One of the major factors impeding its growth is the lack of an appropriate draw solute. The present study deals with the identification of potential draw solutes, and rank them. The comparison was carried out among ten draw solutes on the basis of four main parameters namely; water flux, reverse salt diffusion, flux recovery and cost. Each draw solute was given three 24 hour runs; corresponding to three different concentrations; and their flux and reverse salt diffusion values were calculated. A fresh membrane was used every time except for the fourth time which was the flux recovery experiment conducted for the lowest concentration and the change of flux and reverse salt diffusion values from the initial run was noted. The organic solutes inspected were urea and tartaric acid which showed appreciable values in other parameters viz. reverse salt diffusion, flux recovery and cost although they generated a lower flux. They ranked 5th and 8th respectively. All the experimented draw solutes were ranked based on their values corresponding to each of the four main parameters chosen for comparison and Ammonium sulfate was found to be the best draw solute.

Demulsification to control solute release from Pickering crystal-stabilized water-in-oil emulsions

Controlled demulsification was used to tailor the release of NaCl as a solute from water-in-oil (W/O) emulsion droplets encased in glycerol monostearate (GMS) crystalline shells. Under quiescent conditions at room temperature, the GMS shells behaved as an effective barrier against salt diffusion. A second surfactant, sorbitan monooleate (SMO), added to the emulsion post-preparation to controllably demulsify, resulted in concentration-dependent removal of the interfacially-bound GMS crystals resulting in aqueous droplet coalescence. As a result, NaCl was released from the now-unstable emulsions. Mechanistically, the SMO and GMS demonstrated competitive adsorption for the oil–water interface, with the SMO significantly reducing the displacement energy of the interfacially-bound GMS. Overall, secondary surfactant addition to Pickering emulsions was shown to have important implications for tailoring interfacial composition, and by extension, modulation of the release of solutes from fat crystal-stabilized W/O Pickering emulsions.

Fractal structures in freezing brine

The process of initial ice formation in brine is a highly complex problem. In this paper, we propose a mathematical model that captures the dynamics of nucleation and development of ice inclusions in brine. The primary emphasis is on the interaction between ice growth and salt diffusion, subject to external forcing provided by temperature. Within this setting two freezing regimes are identified, depending on the rate of change of the temperature: a slow freezing regime where a continuous ice domain is formed; and a fast freezing regime where recurrent nucleation appears within the fluid domain. The second regime is of primary interest, as it leads to fractal-like ice structures. We analyse the critical threshold between the slow and fast regimes by identifying the explicit rates of external temperature control that lead to self-similar salt-concentration profiles in the fluid domains. Subsequent heuristic analysis provides estimates of the characteristic length scales of the fluid domains depending on the time-variation of the temperature. The analysis is confirmed by numerical simulations.

Introduction to laser induced breakdown spectroscopy imaging in food: Salt diffusion in meat

This study illustrates the ability of laser induced breakdown spectroscopy (LIBS) to detect and map minerals in food. A LIBS system was used to spatially collect spectra of beef samples. Samples were brined in a 6% salt solution for 2 h and 24 h along with a control sample. Samples were measured by scanning the cross-section of each sample in a 90 × 90 square grid. Sodium (Na) distribution images with respect to emission peak at 589.05 nm were generated after pre-processing the spectral data which directly corresponds to salt levels. As expected, the control sample showed the lowest Na distribution whereas 2 h brined sample showed distribution along the sample's edges decreasing towards the centre. The 24 h brined sample showed increased diffusion. Overall, results show the ability of LIBS to map salt diffusion in meat via Na LIBS imaging, which could be used to optimize brining conditions.

SPH modelling of multi-fluid lock-exchange over and within porous media

Multi-fluid flow over and within porous media occurs frequently in nature and plays an important role in engineering applications. The modeling of these flows and validation against experimental or field observations have not been largely conducted in literature. An explicit numerical scheme for incompressible fluid using Smoothed Particle Hydrodynamics (EISPH) was employed and solved using two integration algorithms. To explore the capabilities and limitations of the model, case studies including percolation of a single fluid in a porous medium, gravity current of a single fluid over a porous medium, multi-fluid flow over an impermeable bed, and a porous medium were simulated and compared with experimental data. The EISPH method led to results overall similar to the observed experimental data. The model was able to reproduce the behaviour of the flow within media with different porosities. In addition, the model reproduced behaviour of multi-fluid flow at the interface between different fluids, such as reproducing Kelvin–Helmholtz vortices and diffusion of salt.

A Short Review of Membrane Fouling in Forward Osmosis Processes.

Interest in forward osmosis (FO) research has rapidly increased in the last decade due to problems of water and energy scarcity. FO processes have been used in many applications, including wastewater reclamation, desalination, energy production, fertigation, and food and pharmaceutical processing. However, the inherent disadvantages of FO, such as lower permeate water flux compared to pressure driven membrane processes, concentration polarisation (CP), reverse salt diffusion, the energy consumption of draw solution recovery and issues of membrane fouling have restricted its industrial applications. This paper focuses on the fouling phenomena of FO processes in different areas, including organic, inorganic and biological categories, for better understanding of this long-standing issue in membrane processes. Furthermore, membrane fouling monitoring and mitigation strategies are reviewed.

Effect of Counter Ions on the Diffusion Characteristics of a Compacted Bentonite

Salt diffusion studies through compacted bentonites are important for designing the waste disposal facilities and assessment of the existing facilities. As the behavior of plastic clays is governed by the physical chemistry of the clay surface–electrolyte interactions, the effect of physicochemical parameters on diffusion rates of the bentonites is required to be studied. In this paper, transient through diffusion tests were conducted with different salts that contain different monovalent cations and a divalent cation. The influence of hydrated size and valence of the cations on the contaminant migration was studied experimentally. A Java based inverse analysis suit, CONTRADIS, was utilized for estimating the mass transport parameters from the experimental observations. The effect of hydrated size and valence of the cations on the mass transport parameters of the bentonite was qualitatively analyzed using diffuse double layer theory. The diffusion coefficient was found to vary about one order magnitude with the hydrated size of the cation. The significance of the variation in mass transport parameters was analyzed using the simulated concentration profiles along the depth of the clay liner.

Exploration of an innovative draw solution for a forward osmosis-membrane distillation desalination process.

Forward osmosis (FO) has emerged as a viable technology to alleviate the global water crisis. The greatest challenge facing the application of FO technology is the lack of an ideal draw solution with high water flux and low reverse salt flux. Hence, the objective of this study was to enhance FO by lowering reverse salt flux and maintaining high water flux; the method involved adding small concentrations of Al2(SO4)3 to a MgCl2 draw solution. Results showed that 0.5M MgCl2 mixed with 0.05M of Al2(SO4)3 at pH 6.5 achieved a lower reverse salt flux (0.53gMH) than that of pure MgCl2 (1.55gMH) using an FO cellulose triacetate nonwoven (CTA-NW) membrane. This was due possibly to the flocculation of aluminum hydroxide in the mixed draw solution that constricted membrane pores, resulting in reduced salt diffusion. Moreover, average water fluxes of 4.09 and 1.74L/m2-h (LMH) were achieved over 180min, respectively, when brackish water (5g/L) and sea water (35g/L) were used as feed solutions. Furthermore, three types of membrane distillation (MD) membranes were selected for draw solution recovery; of these, a polytetrafluoroethylene membrane with a pore size of 0.45μm proved to be the most effective in achieving a high salt rejection (99.90%) and high water flux (5.41LMH) in a diluted draw solution.

Accounting for frame of reference and thermodynamic non-idealities when calculating salt diffusion coefficients in ion exchange membranes

Accurate evaluation of salt diffusion coefficients from transport rate data in ion exchange membranes requires accounting for frame of reference and non-ideal thermodynamic effects. Due to a lack of models and experimental data quantifying membrane ion activity coefficients, it has been impossible to evaluate the impact of non-ideal thermodynamic effects on observed salt diffusion coefficients. Here, a framework is presented that includes both frame of reference (i.e., convection) and non-ideal thermodynamic effects in calculating salt diffusion coefficients in ion exchange membranes. Effective concentration averaged NaCl diffusion coefficients were determined as a function of upstream NaCl concentration in commercial ion exchange membranes from NaCl permeability and sorption measurements via the solution-diffusion model. Frame of reference effects were evaluated using a version of Fick's law that accounts for convection. The factors necessary to account for non-ideal thermodynamic effects were developed using Manning's counter-ion condensation theory. At low upstream NaCl concentrations, frame of reference and non-ideal thermodynamic effects on diffusion coefficients were negligible. However, at higher upstream NaCl concentrations (e.g., >0.1M), both effects contribute measurably to NaCl diffusion coefficients. Correcting for frame of reference effects increased apparent NaCl diffusion coefficients. However, correcting for thermodynamic non-idealities of the ions sorbed into the membranes reduced apparent NaCl diffusion coefficients. Fortuitously, for the materials considered in this study, frame of reference and non-ideal thermodynamic effects nearly cancel each other.

Transient reflection from mud during molecular diffusion of salt

Harbor basins and estuarine environments experience drastic salinity fluctuations in the water near the water-sediment interface, which can significantly affect how sound interacts with a low-velocity mud bottom. This presents challenges in applications including mine detection, port protection and shallow water sonar. In a previous investigation of this system, a mud sample that was saturated with fresh water was instantaneously exposed to salt water. Laboratory measurements of plane wave reflection from the water-mud interface were obtained using a time-gated broadband impulse as time evolved. Results suggested molecular diffusion of salt into the sample had altered the reflected pulse’s amplitude and caused a depth-dependent impedance profile in the mud. The sediment was discretized into layers much thinner than a wavelength and a multi-layer steady-state model was used to predict the reflection from the diffusing mud. As the effective diffusion length reached a critical value, predictions of the steady-state model began to deviate from the measurements, indicating that a transient solution was required. A model of the transient reflection of a finite-length pulse from a half space with an arbitrary impedance will be presented and model results compared with laboratory measurements. [Work supported by ONR.]

Influence of extrinsic operational parameters on salt diffusion during ultrasound assisted meat curing

The present study investigated the effect of geometric parameters of the ultrasound instrument during meat salting in order to enhance salt diffusion and salt distribution in pork meat on a lab scale. The effects of probe size (∅2.5 and 1.3cm) and of different distances between the transducer and the meat sample (0.3, 0.5, and 0.8cm) on NaCl diffusion were investigated. Changes in the moisture content and NaCl gain were used to evaluate salt distribution and diffusion in the samples, parallel and perpendicular to ultrasound propagation direction. Results showed that 0.3cm was the most efficient distance between the probe and the sample to ensure a higher salt diffusion rate. A distance of 0.5cm was however considered as a trade-off distance to ensure salt diffusion and maintenance of meat quality parameters. The enhancement of salt diffusion by ultrasound was observed to decrease with increased horizontal distance from the probe. This study is of valuable importance for meat processing industries willing to apply new technologies on a larger scale and with defined operational standards. The data suggest that the geometric parameters of ultrasound systems can have strong influence on the efficiency of ultrasonic enhancement of NaCl uptake in meat and can be a crucial element in determining salt uptake during meat processing.

Effect of freezing/thawing process on salting kinetics and thermal properties of beef

ABSTRACTIn this study, changes in water activity (aw) values and moisture and salt contents of fresh or frozen/thawed beef samples were detected during the salting process. The salt diffusion coefficients (Deff) in meat samples were calculated, and changes in thermal properties of meat proteins were identified. aw values in both fresh and frozen/thawed meat samples were significantly decreasing during the salting process. Salt contents of the samples significantly increased during the salting process while moisture contents decreased significantly. The Deff value of freshly salted samples was calculated as and as for frozen/thawed samples. It was found out that the freezing/thawing process significantly increased the salt Deff value by 50% compared with that of fresh meat. From the thermal analysis of the samples, the denaturation peak temperatures decreased or were no longer observed as a result of the decrease of the moisture content and increase of the salt concentration of the tissue.