Until recently, “room-temperature” (<100–150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)–(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of “first-generation” room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the “later generation” RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in “cocktails” of one’s choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost “universal” solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) “sister-systems”.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules.

/pdf/ionic-liquids-at-electrified-interfaces-4n93eaytys.pdf

Ionic Liquids at Electrified Interfaces

We have applied molecular dynamics to calculate thermodynamic and transport properties of a set of 19 room-temperature ionic liquids. Since accurately simulating the thermophysical properties of solvents strongly depends upon the force field of choice, we tested the accuracy of the general AMBER force field, without refinement, for the case of ionic liquids. Electrostatic point charges were developed using ab initio calculations and a charge scaling factor of 0.8 to more accurately predict dynamic properties. The density, heat capacity, molar enthalpy of vaporization, self-diffusivity, and shear viscosity of the ionic liquids were computed and compared to experimentally available data, and good agreement across a wide range of cation and anion types was observed. Results show that, for a wide range of ionic liquids, the general AMBER force field, with no tuning of parameters, can reproduce a variety of thermodynamic and transport properties with similar accuracy to that of other published, often IL-specif...

The general AMBER force field (GAFF) can accurately predict thermodynamic and transport properties of many ionic liquids.

Equilibrium molecular dynamics is often used in conjunction with a Green-Kubo integral of the pressure tensor autocorrelation function to compute the shear viscosity of fluids. This approach is computationally expensive and is subject to a large amount of variability because the plateau region of the Green-Kubo integral is difficult to identify unambiguously. Here, we propose a time decomposition approach for computing the shear viscosity using the Green-Kubo formalism. Instead of one long trajectory, multiple independent trajectories are run and the Green-Kubo relation is applied to each trajectory. The averaged running integral as a function of time is fit to a double-exponential function with a weighting function derived from the standard deviation of the running integrals. Such a weighting function minimizes the uncertainty of the estimated shear viscosity and provides an objective means of estimating the viscosity. While the formal Green-Kubo integral requires an integration to infinite time, we suggest an integration cutoff time tcut, which can be determined by the relative values of the running integral and the corresponding standard deviation. This approach for computing the shear viscosity can be easily automated and used in computational screening studies where human judgment and intervention in the data analysis are impractical. The method has been applied to the calculation of the shear viscosity of a relatively low-viscosity liquid, ethanol, and relatively high-viscosity ionic liquid, 1-n-butyl-3-methylimidazolium bis(trifluoromethane-sulfonyl)imide ([BMIM][Tf2N]), over a range of temperatures. These test cases show that the method is robust and yields reproducible and reliable shear viscosity values.

Reliable Viscosity Calculation from Equilibrium Molecular Dynamics Simulations: A Time Decomposition Method.

This paper describes the use of data analytics tools for predicting the fatigue strength of steels. Several physics-based as well as data-driven approaches have been used to arrive at correlations between various properties of alloys and their compositions and manufacturing process parameters. Data-driven approaches are of significant interest to materials engineers especially in arriving at extreme value properties such as cyclic fatigue, where the current state-of-the-art physics based models have severe limitations. Unfortunately, there is limited amount of documented success in these efforts. In this paper, we explore the application of different data science techniques, including feature selection and predictive modeling, to the fatigue properties of steels, utilizing the data from the National Institute for Material Science (NIMS) public domain database, and present a systematic end-to-end framework for exploring materials informatics. Results demonstrate that several advanced data analytics techniques such as neural networks, decision trees, and multivariate polynomial regression can achieve significant improvement in the prediction accuracy over previous efforts, with R2 values over 0.97. The results have successfully demonstrated the utility of such data mining tools for ranking the composition and process parameters in the order of their potential for predicting fatigue strength of steels, and actually develop predictive models for the same.

/pdf/exploration-of-data-science-techniques-to-predict-fatigue-562aevhl9b.pdf

Exploration of data science techniques to predict fatigue strength of steel from composition and processing parameters

Novel deep eutectic solvents (DES) based on three different hydrogen-bond donors (HBD), namely phenol, o-cresol, and 2,3-xylenol, and choline chloride (ChCl) were successfully synthesized with different mole ratios of HBD to ChCl. Melting temperature of these DES were measured. Compared with an ideal mixture of the two components, the freezing temperature of the DES depresses greatly from (120 to 127) K. The physical properties, such as density, viscosity, and conductivity of phenol-based and o-cresol-based DES were determined at atmospheric pressure and temperatures from (293.2 to 318.2) K at an interval of 5 K. The results show that the type of HBD, the mole ratio of HBD to ChCl, and temperature have great influences on the physical properties of DES. Densities and viscosities of DES formed by phenol and ChCl decrease with increases of temperature and phenol content. The conductivities of the DES are from (1.40 to 7.06) mS·cm–1, similar to that of room temperature ionic liquids. The conductivities of th...

Formation of Deep Eutectic Solvents by Phenols and Choline Chloride and Their Physical Properties

Densities of two selected ionic liquids (ILs), 1-butyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide, [bmim][NTf2], and 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)imide, [bmpyr][NTf2], were determined in the temperature range from (293.15 to 353.15) K. From the experimental density values, the thermal expansion coefficient was calculated. The specific conductivity was measured in the range from (303.15 to 353.15) K. Our experimental results were compared with available literature data. Also, viscosity of these ionic liquids was measured from room temperature up to 353.15 K. Using the obtained data, the temperature effect on the viscosity was analyzed. Since there are limited literature data on physicochemical properties of ionic liquids, data obtained in this study can provide valuable contributions for better understanding of ILs behavior.

Physicochemical Characterization of 1-Butyl-3-methylimidazolium and 1-Butyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide

Thermal and conductometric studies of the CeBr3–MBr binary systems (M = Li, Na)

Molten salt technology is a catchall phrase that includes some very diverse technologies; electrochemistry, heat transfer, chemical oxidation/reduction baths, and nuclear reactors. All of these technologies are linked by the general characteristics of molten salts that can function as solvents, have good heat-transfer characteristics, function like a fluid, can attain very high temperatures, can conduct electricity, and also may have chemical catalytic properties. The Janz molten salt database is the most comprehensive compilation of property data about molten salts available today and is widely used for both fundamental and applied purposes. Databases are traditionally viewed as “static” documents that are used in a “search and retrieval” mode. These static data can be transformed by informatics and data mining tools into a dynamic dataset for analysis of the properties of the, materials and for making predictions. While this approch has been successful in the chemical and biochemical sciences in searching for and establishing structure-property relationships, it is not widely used in the materials science community. Because the design of the original molten salt database was not oriented toward this informatics goal, it was essential to evaluate this dataset in terms of data mining standards. Two techniques were used—a projection (principal components analysis (PCA)) and a predictive method (partial least squares (PLS))—in conjunction with fundamental knowledge acquired from the long-term practice of molten salt chemistry.

Extracting information from the molten salt database

Electrical conductivity of liquid binary NdBr3 – alkali metal bromide mixtures was measured as a function of temperature over the whole composition range. Prior to these measurements, NdBr3 and alkali bromides were reinvestigated: a new assessment of literature data was made because of the discrepancy with reference values on NdBr3, LiBr and CsBr. The classical Arrhenius equation describes well our electrical conductivity data for mixtures. These results are discussed in terms of complex formation in the melts.

/pdf/electrical-conductivity-of-molten-binary-ndbr-3-alkali-1qpl5q6u4u.pdf

Electrical Conductivity of Molten Binary NdBr 3 - Alkali Bromide Mixtures

This paper continues our research program on lanthanide halide-alkali metal halide systems. Differential scanning calorimetry (DSC) was used to investigate the phase equilibria of the CeBr3-KBr system. This system is characterized by the two congruently melting compounds K3CeBr6 and K2CeBr5 and the three eutectics located at the CeBr3mole fractions 0.193 (837 K), 0.295 (855 K) and 0.555 (766 K). K3CeBr6 forms at 775 K and melts congruently at 879 K with the related enthalpies 54.5 and 41.7 kJ mol−1, respectively. K2CeBr5 melts congruently at 874 K with the enthalpy 82.4 kJ mol−1. The electrical conductivity was measured of all CeBr3-KBr mixtures and of the pure components down to temperatures below solidification. The experimental determinations were conducted over the entire composition range in steps of about 10 mol%. The specific electrical conductivity decrease with increasing CeBr3 concentration, with significantly larger conductivity changes in the potassium bromide-rich region. The results are discussed in terms of possible complex formation.

https://www.degruyter.com/downloadpdf/j/zna.2007.62.issue-3-4/zna-2007-3-413/zna-2007-3-413.xml

Slobodan Gadzuric

Papers

Physicochemical Characterization of 1-Butyl-3-methylimidazolium and 1-Butyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide

Thermal and conductometric studies of the CeBr3–MBr binary systems (M = Li, Na)

Extracting information from the molten salt database

Electrical Conductivity of Molten Binary NdBr 3 - Alkali Bromide Mixtures

Phase Diagram and Electrical Conductivity of CeBr3-KBr