Nernst-Einstein Equation Research Articles

A model for predicting the relative chloride diffusion coefficient in unsaturated cementitious materials

An analytical model for predicting the relative chloride diffusion coefficient in cementitious materials at different degrees of water saturation is presented in this paper. The model is developed based on the Nernst-Einstein equation and conductivity of cementitious electrolyte, as well as on moisture distribution in the pore structure. Good agreement is found between the model and the experimental data. With the help of the model, the chloride diffusion coefficient of cementitious material at unsaturated state can be determined according to the chloride diffusion coefficient at saturated state, the degree of water saturation and the average pore diameter of the material. A detailed discussion about the inputs and outputs of the model is given in order to facilitate its application for engineering practice.

Prediction of self-diffusion coefficients of ions from various livestock antibiotics in water at infinite dilution

The development of antibiotic-resistant bacteria due to the existence and fate of Pharmaceutically Active Compounds (PHAC) used to treat bacterial diseases in humans as well as veterinary medicine to prevent disease in animals such as poultry, cattle, swine, and fish during animal food production and as growth promoters like antibiotics entering the environment turned out to be a problem when not removed in a normal wastewater treatment plant as it has increased effects on the disturbance of the natural bacterial ecosystem, presence of it in the effluent of sewage treatment plants as well as to surface and groundwater, and concerns for human health. Fate and transport of particles is an important matter that describe their physical form and behavior in different media with primary concern of determining the transport speed and combined effects of the chemicals in their discharge environments. In order to predict the fate and transport in the environment, one important parameter that indicates how individual molecules and ions move through a medium under a concentration gradient at a certain pressure and temperature is the diffusion coefficient. In relation to the previously published work on diffusion coefficient of various livestock antibiotics at infinite dilution, the present work extended the calculation to determine the self-diffusion coefficient of constituent ions from the studied antibiotics using the Nernst-Einstein Equation. Other parameters such as activation energy, pre-exponential factor, and hydrodynamic radius needed in describing the infinite dilution diffusion behavior were also calculated using Arrhenius-type equation and Stokes-Einstein Equation, respectively. The results may provide an adequate understanding of the mobility and behavior of these constituent ions from these livestock antibiotics when present in environmental water system, which may be of help for future studies for the removal of these antibiotics which can lead to the microbial resistance bacteria.

Estimation of diffusion coefficients of ascorbate-based ions at infinite dilution through electrolytic conductivity measurements

Ascorbic acid is a naturally-occurring organic compound that has high water solubility. One significant parameter that can describe the mobility and transport of ascorbic acid and its mineral salts in water systems is the diffusion coefficient. Molar conductivity data were determined from electrolytic conductivity data measured at different concentrations of ascorbate-based ions (dilute region) and temperatures (293.15 to 313.15 K). From these data, the infinite dilution diffusion coefficients of the ascorbic acid and mineral salts in water were estimated using the Nernst-Haskell Equation. The Nernst-Einstein Equation was used to predict the infinite dilution self-diffusion coefficients of the representative ascorbate-based ions ([H+], [Na+], and [Ca2+]). For most temperatures and concentrations considered, the Ca2+ cation had the highest molar conductivity but the [H+] cation had the highest correlated infinite dilution self-diffusion coefficient of 11.4105 × 10−9 m2/s at 313.15 K. The [Na+] and [Ca2+] cations had values of correlated infinite dilution self-diffusion coefficient of 2.6263 × 10−9 m2/s and 2.4045 × 10−9 m2/s at 313.15 K, respectively. The molar conductivity and diffusion coefficient of the ions at infinite dilution were in the order of [H+] > [Na+] > [Ca2+]. It was found that an increase in temperature also increases the diffusion coefficient. This study was able to estimate infinite dilution diffusion coefficient data for ascorbate-based ions. Thus, the results of this study can serve as a basis and reference for future researches to have a better understanding of the fate and transport of ascorbate-based ions in the environment.

Oxygen Isotope Exchange in Proton-Conducting Oxides Based on Lanthanum Scandates

The method of oxygen isotope exchange with the gas phase equilibration have been used to obtain the temperature dependences of the oxygen surface exchange and diffusion coefficients with proton-conducting oxides La1–xSrxScO3–δ (x = 0; 0.04; 0.09) in the temperature range of 600−900°C at oxygen pressure 1.01 kPa. The paper determines that the diffusion and oxygen surface exchange coefficients increase with the increasing of the strontium content in the oxides. We have found out the rates of the individual stages of the oxygen exchange process on the surface of the oxides. It is shown that oxygen incorporation is rate-determining stage of the oxygen exchange on the surface of the undoped oxide, whereas for the strontium-doped oxides La1–xSrxScO3–δ (x = 0; 0.04; 0.09) with increasing of strontium concentration, the difference between the rates of dissociative adsorption and oxygen incorporation decreases so that for the oxide La0,91Sr0,09ScO3–δ the stage of dissociative adsorption of oxygen becomes rate-determining stage. The paper analyzes the possible reasons of these differences in oxygen surface exchange kinetics. Moreover, the paper using the obtained oxygen diffusion coefficients that have been recalculated in the oxygen-ionic conductivities according to the Nernst-Einstein equation performs the contributions of the oxygen-ion and proton components of the total conductivity of oxides La1–xSrxScO3–δ (x = 0; 0.04; 0.09) in the wet reducing atmosphere (pH2O = 2.35 kPa, pO2 = 10−15 Pa). Proton transference numbers are shown to be close to unit in the temperature range of 500–600 °С at the wet hydrogen-containing reducing atmosphere.

Properties of planetary silicate melts by molecular dynamics simulation

Because magmatic liquids play a fundamental role in the evolution of the terrestrial planets, a precise knowledge of their physical properties is requisite to better understand the formation and the dynamics of planetary interiors. In using an improved force field for silicates (Dufils et al., 2017), we report the results of a series of molecular dynamics simulations (MD) aiming to evaluate the equation of state (EOS), the viscosity, the electrical conductivity, and the elemental self-diffusion coefficients of various planetary melts representative of the Earth, Mars, the Moon and Mercury. The agreement between MD calculations and experimental data (when they exist) is remarkable, a finding which suggests that the MD simulations can be used on trust to extend the existing laboratory data on planetary melts (as it is proposed here for some lunar, martian and mercurian basalts) or to predict the thermo-physical properties of more exotic compositions (magma oceans, lava planets). Moreover, the MD simulations show that the evolution of the viscosity and of the electrical conductivity with the pressure depends in a complex manner on temperature and composition and that is difficult to extract general trends from these behaviors. Another advantage of the MD simulations is that the transport coefficients (viscosity, conductivity, and diffusivities) being evaluated along the same numerical experiment, one is able to test the validity of the Eyring and the Stokes-Einstein equations relating viscosity and diffusivity, as also as the Nernst-Einstein equation expressing the conductivity as function of the ionic diffusivities. It is shown that the Stokes-Einstein equation is suitable to describe planetary melts of low viscosity (≤1 Pa·s), whereas the Eyring relation leads to a better estimation at high viscosities (>100 Pa·s). Concerning the electrical conductivity, the Nernst-Einstein relation fails to reproduce the conductivity values obtained by MD simulation, a result which can be explained by the crucial role played by ion-ion correlations in silicate melts.

Temperature and Density Dependence of the Transport Properties of the Ionic Liquid Triethylpentylphosphonium Bis(trifluoromethanesulfonyl)amide, [P222,5][Tf2N

Viscosities (η), conductivities (κ, Λ), and ion self-diffusion coefficients (DSi) for triethylpentylphosphonium bis(trifluoromethanesulfonyl)amide, ([P222,5][Tf2N]), have been measured as a function of temperature and pressure in the ranges ([273–363] K, 243 MPa max), ([273–353] K, 251 MPa max), and (298–363 K, 225 MPa max), respectively. pVT data are also reported from (298 to 353) K to 50 MPa. The ratio of the ion self-diffusion coefficients is constant, independent of temperature and pressure. The results are discussed using velocity correlation, distinct diffusion, and resistance coefficients, and the Stokes–Einstein–Sutherland (SES: relating DSi and η) and Nernst–Einstein equations (NE: relating Λ and DSi). As is usual for ionic liquids the SES and NE plots for high-pressure isotherms and the atmospheric pressure isobar overlap quantitatively, that is the self-diffusion and distinct diffusion coefficients, and the molar conductivity, are functions of the viscosity. This can be used for the interpolat...

NMR Transport Study of LiPF6 and NaPF6 in Glymes for Use in Supercapacitors

Electric double-layer capacitors (EDLC) store ionic charge electrostatically at the interface of high surface area electrodes such as carbon in a liquid electrolyte. Despite significant improvements in electrode and materials design, virtually all state-of-the-art nonaqueous electrochemical capacitors use the same electrolyte: tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile (ACN). This electrolyte has an exceptionally high conductivity which minimizes resistive losses and enables capacitors to operate at very high power. However, this electrolyte has a practical voltage window around only 2.7 V, beyond which the capacitor lifetime is significantly shortened. Since the energy stored in a capacitor increases quadratically with voltage, extending this electrochemical window could significantly improve the energy density. In this study we report on electrolytes consisting of LiPF6 or NaPF6 in tetraethylene glycol dimethyl ether (TEGDME or tetraglyme or G4), bis(2-methoxyethyl) ether (diglyme, or G2) and dimethoxyethane (DME or G1) which clearly show a 4 V electrochemical window. The extended voltage window doubles the energy density that can be achieved with any given capacitor electrode. Electrolyte conductivities range from 1-10 mS/cm, which are comparable to ionic liquids and adequate for moderate power applications. Futhermore, glyme-based electrolytes have good chemical stability and low flammability. Importantly, all salts and solvents are commercially available, which should enable these electrolytes to be as cost-effective and scalable as the current generation of commercial supercapacitor electrolytes. NMR experiments were performed on 0.1m LiPF6 and 0.1m/0.8m NaPF6, each dissolved in G1, G2, and G4. Using Pulsed Field Gradient (PFG) NMR, the solvent and ionic self-diffusion coefficients, D, of 1H, 7Li, 19F, and 23Na were measured, at both 25°C and 60°C. As NMR does not distinguish between the movement of single ions and ion pairs, it can be difficult to accurately determine the true conductivity of the material. However, the diffusion measurements were used to find the limiting conductivity, σNMR , of each material via the Nernst-Einstein equation: σNMR = F2[C]/(RT)*(Dcation+Danion) Direct comparison with conductivity values obtained by electrochemical impedance spectroscopy measurements yields the degree of ion association, α: α = 1 - (σdirect/σNMR) Both diffusion and conductivity decrease with increasing solvent size, primarily attributed to viscosity effects. However the degree of ion association is significant, determined to be 85% for both 0.1m LiPF6 and 0.1m NaPF6 in G2. In glyme solvents, ion association tends to decrease with increasing solvent molecular mass, and increase with increasing temperature. These results will be discussed in the context of practical use of glyme-based electrolytes for electrochemical capacitors.

Influence of moisture condition on chloride diffusion in partially saturated ordinary Portland cement mortar

Experiments have been carried out to study the influence of moisture condition, including moisture content and its distribution, on the chloride diffusion in partially saturated ordinary Portland cement mortar. The mortar samples with water-to-cement (w/c) ratios of 0.4, 0.5 and 0.6, cured for 1 year, were preconditioned to uniform water saturations ranging from 18 to 100%. The interior relative humidities of these partially saturated cement mortars, i.e. water vapour desorption isotherm (WVDI), were measured. The WVDI results in relation to the pore structures obtained from the mercury intrusion porosimetry tests of paste samples with the same w/c ratios were analyzed, which provided a basic insight into the moisture distribution in the non-saturated cement mortars. The relative chloride diffusion coefficients of cement mortars at various water saturations were determined based on the Nernst-Einstein equation and conductivity technique. It is found that the relative chloride diffusion coefficient Drc depends on the degree of water saturation Sw and WVDI. At a given Sw level, the Drc is larger for a higher w/c ratio. The role of the w/c ratio in the Drc–Sw relation, however, becomes less pronounced with increasing w/c ratio. There exists a critical saturation, below which the water-filled capillary pores are discontinuous and the Drc-value tends towards infinitely small. An increase of the w/c ratio results in a decrease of the critical saturation level.

Effect of CO2 absorption on ion and water mobility in an anion exchange membrane

We report the measured water uptake, density, ionic conductivity and water transport properties in Tokuyama A201 membrane in OH−, HCO3− and Cl− forms. The water uptake of the AEM varies with anion type in the order λ(OH−) > λ(HCO3−) > λ(Cl−) for samples equilibrated with the same water vapor activity (aw). The conductivity of the AEM is reduced by absorption of CO2. Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) measurements were utilized to characterize the diffusivity of water and HCO3− ion. The anion diffusion coefficient and membrane conductivity are used to probe the applicability of the Nernst-Einstein equation in these AEMs.

Influence of anisotropy on the electrical conductivity and diffusion coefficient of dry K-feldspar: Implications of the mechanism of conduction**Project supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (CAS) (Grant No. XDB 18010401), the Key Research Program of Frontier Sciences of CAS (Grant No. QYZDB-SSW-DQC009), the “135” Program of the Institute of Geochemistry of CAS,

The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa in a frequency range of 10−1 Hz–106 Hz. The measured electrical conductivity along the [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ± 0.06 eV and 2.51 ± 0.19 cm3/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the [001] axis is approximately three times higher than that along the [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst–Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.

A P2-Type Layered Superionic Conductor Ga-Doped Na2 Zn2 TeO6 for All-Solid-State Sodium-Ion Batteries.

Here, a P2-type layered Na2 Zn2 TeO6 (NZTO) is reported with a high Na+ ion conductivity ≈0.6×10-3 S cm-1 at room temperature (RT), which is comparable to the currently best Na1+n Zr2 Sin P3-n O12 NASICON structure. As small amounts of Ga3+ substitutes for Zn2+ , more Na+ vacancies are introduced in the interlayer gaps, which greatly reduces strong Na+ -Na+ coulomb interactions. Ga-substituted NZTO exhibits a superionic conductivity of ≈1.1×10-3 S cm-1 at RT, and excellent phase and electrochemical stability. All solid-state batteries have been successfully assembled with a capacity of ≈70 mAh g-1 over 10 cycles with a rate of 0.2 C at 80 °C. 23 Na nuclear magnetic resonance (NMR) studies on powder samples show intra-grain (bulk) diffusion coefficients DNMR on the order of 12.35×10-12 m2 s-1 at 65 °C that corresponds to a conductivity σNMR of 8.16×10-3 S cm-1 , assuming the Nernst-Einstein equation, which thus suggests a new perspective of fast Na+ ion conductor for advanced sodium ion batteries.

Atomic Diffusion and Electric Conductivity of Gum Arabic/Graphite Composite

In this work, we had adopted solid states reaction kinetic model to calculate diffusion coefficient of graphite Gr in Gum Arabic (GA) as the function of temperatures and concentration D(t, C). From the calculations we have found that the diffusion coefficient D increases with increasing temperature. At higher temperature the Gr atoms might get enough thermal energy to overcome the activation energy (Ea) barrier and hence can easily be transported to a new atomic position. Diffusion coefficient of Gr at high concentrations had exceeded that at low concentrations by more than two to three orders of magnitude. Such increase can be attributed to the large number of jumps or jump frequency which found to be directly proportion to the Gr concentration. Electric conductivity, calculated by Nernst-Einstein equation, at high concentration Gr had exceeded that at lower concentration. The decrease in conductivity with decreasing Gr concentration might be attributed to the effective charges interactions, which lead to enhance the recombination of charge carriers.

Atomistic insights into the thermodynamics, structure, and dynamics of ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate via molecular dynamics study

Molecular dynamics (MD) simulations were performed to compute the properties of the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate, [hmim][PF6], at three different temperatures (298, 323, and 348K) and atmospheric pressure. Thermodynamic, structural, and dynamical properties, such as average density, isobaric thermal expansion coefficient, isothermal compressibility factor, radial distribution function (RDF), spatial distribution function (SDF), mean square displacement (MSD) and velocity autocorrelation function (VACF) were computed and interpreted. The ionic self-diffusion coefficients were calculated using both the Einstein and Green–Kubo formulas and it was found that the cation diffuses faster than the anion and contributes more in the electric current. The ionic self-diffusion coefficients obtained from the Green–Kubo method agreed reasonably well with the experimental data in compared to the Einstein method. Also, the self-diffusion coefficients obtained from the two methods were used to calculate the ionic conductivity from the Nernst–Einstein equation. The effects of the system size and simulation run-time on determining diffusivity using the Einstein method were also investigated. The RDFs show that anions interact preferentially with the cation ring especially in direction of the acidic hydrogen atom of the imidazolium ring. This interaction was identified as hydrogen bonding interaction and observed using SDF.

Ion-Pairing and Electrical Conductivity in the Ionic Liquid 1-n-Butyl-3-methylimidazolium Methylsulfate [Bmim][MeSO4]: Molecular Dynamics Simulation Study.

Molecular dynamics simulations are performed on ionic liquid (IL) 1-n-butyl-3-methylimidazolium methylsulfate. The calculated densities, diffusion coefficients, and electrical conductivities are in very good agreement with the experiment. While the Nernst-Einstein equation largely overestimates the electrical conductivities compared to experiment, its correction for the joint translation of counterions substantially improves its accuracy. Taking into account the role of correlated motions of ions, expressed in terms of the collective mean-squared-displacement, predicts electrical conductivities in close agreement with the experiment. An examination of different dynamical processes shows that three types of motions occur in this IL. Short relaxation times (<1 ps) and low activation energies (≈4 kJ mol-1) are associated with local structural properties such as hydrogen bonding. The second class, such as structural relaxation of hydrogen bonds, has longer relaxation times (a few ten picoseconds) and higher activation energies (≈10 kJ mol-1). The slowest motions (relaxation times of a few ten nanoseconds and activation energies of ≈35 kJ mol-1) belong to the correlated motions of counterions. Ion-pairing, diffusion, and electrical conductivity belong to this third class. Closeness of the relaxation times and activation energies of the third class processes reveal that exchange of counterions in an ion's solvation shell governs the macroscopic dynamic properties of IL.

Diffusion of hydrous species in model basaltic melt

Water diffusion in Fe-free model basaltic melt with up to 2wt% H2O was investigated at 1658–1846K and 1GPa in piston-cylinder apparatus using both hydration and diffusion couple techniques. Diffusion profiles measured by FTIR are consistent with a model in which both molecular H2O (H2Om) and hydroxyl (OH) contribute to water diffusion. OH diffusivity is roughly 13% of H2Om diffusivity, showing little dependence on temperature or water concentration. Water diffusion is dominated by the motion of OH until total H2O (H2Ot) concentration reaches 1wt%. The dependence of apparent H2Ot diffusivity on H2Ot concentration appears to be overestimated by a previous study on MORB melt, but H2Ot diffusivity at 1wt% H2Ot in basaltic melt is still greater than those in rhyolitic to andesitic melts. The appreciable contribution of OH to water diffusion in basaltic melt can be explained by enhanced mobility of OH, probably associated with the development of free hydroxyl bonded with network-modifying cations, as well as higher OH concentration. Calculation based on the Nernst-Einstein equation demonstrates that OH may serve as an effective charge carrier in hydrous basaltic melt, which could partly account for the previously observed strong influence of water on electrical conductivity of basaltic melt.

Proton mobility in sulfonic acid functionalized mesoporous materials studied by MAS PFG NMR diffusometry and impedance spectroscopy

The proton mobility in sulfonic acid functionalized mesoporous MCM-41, MCM-48 and KIT-6 was studied by impedance spectroscopy and MAS PFG NMR diffusometry. Highest proton conductivities were found at 140 °C as 19 S m−1, 0.48 S m−1, and 37 S m−1, for MCM-41, MCM-48 and KIT-6, respectively. The self-diffusion coefficients of water molecules in functionalized MCM-41 and KIT-6 were found to be smaller than the diffusivity of the bulk water, however, for functionalized MCM-48 they appeared to be larger. For comparison, we calculated diffusion coefficients of the charge carrier from the conductivity values by means of the Nernst-Einstein equation. It turned out that for MCM samples the NMR water diffusivity includes inter-particle contributions and succeeds the charge carrier diffusivity by some order of magnitudes. The reason is that the root-square displacement of the water molecules within the diffusion observation time (20–100 ms) is larger than the mesoporous particle size, which amounts 1–4 μm for the MCM materials. In contrast, for KIT-6 consisting of larger particles of up to 50 μm, it became possible to detect the intra-particle diffusion within the material particles, because the root-square displacement of the species is smaller than the size of the particles. A two-component behavior of the NMR diffusivity can be observed, and the slower component describes the self-diffusion within the particles. The observed intra-particle NMR diffusivity is in agreement with the charge carrier diffusivity. From this, one may conclude that the NMR technique observes the charge carrier diffusivity of hydroxonium or Zundel ions without water fluctuations. Therefore, we claim that the intra-particle proton conduction in functionalized mesoporous materials is a “packed-acid mechanism” without water fluctuation.

(Keynote) Investigation the Effect of CO2 Absorption in Anion Exchange Membrane By Electrical Conductivity and NMR

The anion exchange membrane (AEM) has attracted considerable attention in the application of fuel cell technology. Compared with proton exchange membrane fuel cells, AEM fuel cells (AEMFCs) have advantages in cost, catalyst stability, efficiency and system size1. However, one challenge in the application of AEMFCs is the absorption of CO2 from the cathode air supply, which forms carbonate and bicarbonate species and reduces the ionic conductivity of membrane. In this study, to better understand the effect induced by CO2 on AEM performance, the ion transport mechanism was investigated by using electrical conductivity and Nuclear Magnetic Resonance (NMR) techniques. A typical commercial anion exchange membrane Tokuyama A201 has been used for all experiments. OH- form membranes are prepared by soaking in low concentration (10-4 M) KOH solution. CO3 2- and HCO3 - form membranes are used after soaking in 1M K2CO3 or KHCO3 solution. Both electrical conductivity and NMR experiments have been performed on a series of OH- form, CO3 2- and HCO3 - form samples with different water contents from 20 °C to 80 °C. Figure 1 shows the electrical conductivity of HCO3 - form A201 at different relative humility as a function of temperature, which displays an increasing trend as the relative humility and temperature increase. Also note the low values of conductivity relative to that expected from a hydroxyl ion conductor. This is in accord with previous reports that indicate a significant decrease in conductivity upon uptake of CO2 into hydroxide-form membranes. 1H and 13C pulse-field-gradient NMR are used to characterize the speciation and diffusion coefficient D(NMR) of water, CO3 2- and HCO3 - respectively. Difference in ionic conductivity and diffusion coefficient of each species in the membrane between three different forms can be observed. The estimated diffusion coefficient D(σ) from ionic conductivity obtained by using Nernst-Einstein equation is sometimes different from that measured by NMR. The comparison between D(NMR) and D(σ) provides valuable information on ionic transport mechanism 2. Obtaining dynamic information on the behavior of CO2– derived species in the membrane will allow modeling to the distribution of such species in the membrane. Acknowledgement. We gretefully acknowledge the support of this work by the Office of Naval Research. We also appreciate the assistance of Tokuyama Soda in providing A201 membrane samples. Reference: 1. X. M. Ren, S. C. Price, A. C. Jackson, N. Pomerantz and F. L. Beyer, Acs Appl Mater Inter, 6, 13330 (2014). 2. S. Ochi, O. Kamishima, J. Mizusaki and J. Kawamura, Solid State Ionics, 180, 580 (2009). Figure 1

Electrical conductivity of hydrous andesitic melts pertinent to subduction zones

AbstractAndesitic magmatism and rocks are widespread at convergent plate boundaries. Electrically conductive bodies beneath subduction zone arc volcanoes, such as the Uturuncu Volcano, Bolivia, may correspond to active reservoirs of H2O‐bearing andesitic magma. Laboratory measurements of electrical conductivity of hydrous andesitic melts are required to constrain the physicochemical conditions of these magma reservoirs in combination with magnetotelluric data. This experimental study investigates electrical conductivity of andesitic melts with 0.01–5.9 wt % of H2O at 1164–1573 K and 0.5–1.0 GPa in a piston cylinder apparatus using sweeping‐frequency impedance spectroscopy. Electrical conductivity of andesitic melt increases with increasing temperature and H2O concentration but decreases with pressure. Across the investigated range of H2O concentration, electrical conductivity varies by 1.2–2.4 log units, indicating stronger influence of H2O for andesitic melt than for rhyolitic and dacitic melts. Using the Nernst‐Einstein equation, the principal charge carrier is inferred to be Na in anhydrous melt but divalent cations in hydrous andesitic melts. The experimental data are regressed into a general electrical conductivity model for andesitic melt accounting for the pressure‐temperature‐H2O dependences altogether. Modeling results show that the conductive layer at &gt;20 km depths beneath the surface of the Uturuncu Volcano could be interpreted by the presence of less than 20 vol % of H2O‐rich andesitic melt (with 6–9 wt % H2O).

Effects of Li Salt Anions and O2 Gas on Li Dissolution/Deposition Behavior at Li Metal Negative Electrode for Non-Aqueous Li-Air Batteries

To clarify the relationship between Li+ transport rate in glyme-based electrolytes and Li deposition/dissolution behavior at Li metal negative electrode (NE) in Li-air batteries (LAB) systems, 1.0 M tetraglyme (G4) electrolytes were prepared containing a Li salt of LiSO3CF3, LiN(SO2CF3)2, or LiN(SO2F)2. Two aspects of Li+ transfer between the two phases, i.e., G4 electrolyte | Li metal NE, were evaluated, namely i) Li+ supplying rate and ii) Li+ charge transfer rate through solid electrolyte interphase (SEI) films. The former was investigated by self-diffusion coefficients D of Li+, anions, and G4 solvent together with ionic conductivity σ, viscosity, density, and apparent dissociation degree αapp of the Li salts estimated by the Nernst–Einstein equation. The latter was evaluated with Li | Li symmetric and LAB (Li | O2) cells containing the electrolytes. The Li deposition/dissolution reaction basically depended on the Li+ supplying rate in the Li | Li cell; however Li dendrites were formed. Conversely, the LAB cell performance was controlled by Li oxide layers formed on the NE, resulting in similar discharge/charge properties without Li dendrites. The effects of surface-oxidation was also confirmed with Li | Li cells containing O2 gas, where both SEI and charge transfer resistances were reduced.

Quantification of Nanopore Networks: Application to Amorphous Polymers

We present numerical recipes to quantify the properties of pore networks in nanoporous materials, to be used as a postprocessing tool for Molecular Dynamics. The method we demonstrate allows determination of the total porosity, the porosity accessible to the solvent, the pore size distribution, and both pore network conductivity and tortuosity, by using atom type and coordinates. The pore diameter distribution is obtained from the chord distribution and demonstrated to be more accurate. The tortuosity of pore system is estimated based on Nernst–Einstein equation and does not require diffusion calculation. In the case study we investigate the impact of water adsorption on pore structure of two different amorphous polymers. We find out, quantitatively, that as the polymer absorb water, its porosity and average pore size increase, followed by an increase in conductivity and a decrease in tortuosity, which finds validation in experimental studies.