Boiling Temperature and Reversed Deliquescence Relative Humidity Measurements for Mineral Assemblages in the NaCl + NaNO3 + KNO3 + Ca(NO3)2 + H2O System

Boiling temperature measurements have been made at ambient pressure for saturated ternary solutions of NaCl + KNO₃ + H₂O, NaNO₃ + KNO₃ + H₂O, and NaCl + Ca(NO₃)₂ + H₂O over the full composition range, along with those of the single salt systems. Boiling temperatures were also measured for the four component NaCl + NaNO₃ + KNO₃ + H₂O and five component NaCl + NaNO₃ + KNO₃ + Ca(NO₃)₂ + H₂O mixtures, where the solute mole fraction of Ca(NO₃)₂, x{Ca(NO₃)₂}, was varied between 0 and 0.25. The maximum boiling temperature found for the NaCl + KNO₃ + H₂O system is ≈134.9 ^∘C; for the NaNO₃ + KNO₃ + H₂O system is ≈165.1 ^∘C at x(NaNO₃) ≈ 0.46 and x(KNO₃) ≈ 0.54; and for the NaCl + Ca(NO₃)₂ + H₂O system is 164.7 ± 0.6 ^∘C at x{NaCl} ≈ 0.25 and x{Ca(NO₃)₂} ≈ 0.75. The NaCl + NaNO₃ + KNO₃ + Ca(NO₃)₂ + H₂O system forms molten salts below their maximum boiling temperatures and the temperatures corresponding to the cessation of boiling (dry-out temperatures) of these liquid mixtures were determined. These dry-out temperatures range from ≈300 ^∘C when x{Ca(NO₃)₂} = 0 to ≥ 400 ^∘C when x{Ca(NO₃)₂} = 0.20 and 0.25. Mutual deliquescence/efflorescence relative humidity (MDRH/MERH) measurements were also made for the NaNO₃ + KNO₃ and NaCl + NaNO₃ + KNO₃ salt mixture from 120 to 180 ^∘C at ambient pressure. The NaNO₃ + KNO₃ salt mixture has a MDRH of 26.4% at 120 ^∘C and 20.0% at 150 ^∘C. This salt mixture also absorbs water at 180 ^∘C, which is higher than expected from the boiling temperature experiments. The NaCl + NaNO₃ + KNO₃ salt mixture was found to have a MDRH of 25.9% at 120 ^∘C and 10.5% at 180 ^∘C. The investigated mixture compositions correspond to some of the major mineral assemblages that are predicted to control brine composition due to the deliquescence of salts formed in dust deposited on waste canisters in the proposed nuclear repository at Yucca Mountain, Nevada.     

Deliquescence behavior of internally mixed clay and salt aerosols by optical extinction measurements

Internal mixtures of montmorillonite, a clay component of mineral dust, with sodium chloride or ammonium sulfate were studied optically using cavity ring down spectroscopy. The effects of the addition of the clay to the optically observed deliquescence relative humidity (DRH) and water uptake of these salts were considered by investigating a series of different salt mass fractions. In most cases, montmorillonite alters the hygroscopic properties, lowering the DRH in comparison to the pure salt, and causes the particles to transition from solid to liquid at a lower relative humidity than is expected based on the salt alone. Predictions based on volume-weighted mixing rules were not accurate for most measurements around the DRH. We attribute deviations from theory to changes in the Gibbs free energy of the system caused by disturbances in the ion-ion interactions and lattice structure allowing water uptake prior to the DRH of the salt. Our optical results contradict some current measurements in the literature that suggest little change in the hygroscopic behavior of salts when insoluble mineral dust components are added.     

Deliquescence phase transition measurements by quartz crystal microbalance frequency shifts

Measurements of the hygroscopic properties of aerosols are needed to better understand the role of aerosols as cloud condensation nuclei. Several techniques have been used to measure deliquescence (solid to liquid) phase transitions in particular. In this study, we have measured the deliquescence relative humidity (DRH) of organic and inorganic salts, organic acids (glutaric and succinic acid), and mixtures of organic acids with ammonium sulfate using a quartz crystal microbalance (QCM). The QCM allows for measurement of the deliquescence phase transition due to inherent measurement differences between solids and liquids in the oscillation frequency of a quartz crystal. The relative humidity dependent frequency measurements can be used to identify compounds that adsorb monolayer amounts of water or form hydrates prior to deliquescence (e.g., lithium chloride, potassium and sodium acetate). Although the amount of water uptake by a deliquescing material cannot be quantified with this technique, deliquescence measurements of mixtures of hygroscopic and nonhygroscopic components (e.g., ammonium sulfate and succinic acid (DRH > 95%)) show that the mass fraction of the deliquescing portion of the sample can be quantitatively determined from the relative change in oscillation frequency at deliquescence. The results demonstrate the use of this technique as an alternative method for phase transition measurements and as a direct measurement of the mass fraction of a sample that undergoes deliquescence. Further, deliquescence measurements by the QCM may provide improved understanding of discrepancies in atmospheric particle mass measurements between filter samples and the tapered element oscillating microbalance given the similar measurement principle employed by the QCM.     

Predicting Deliquescence Relative Humidities of Crystals and Crystal Mixtures

The presence of water in the form of relative humidity (RH) may lead to deliquescence of crystalline components above a certain RH, the deliquescence RH (DRH). Knowing the DRH values is essential, e.g., for the agrochemical industry, food industry, and pharmaceutical industry to identify stability windows for their crystalline products. This work applies the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) to purely predict the DRH of single components (organic acids, sugars, artificial sweeteners, and amides) and multicomponent crystal mixtures thereof only based on aqueous solubility data of the pure components. The predicted DRH values very well agree with the experimental ones. In addition, the temperature influence on the DRH value could be successfully predicted with PC-SAFT. The DRH prediction also differentiates between formation of hydrates and anhydrates. PC-SAFT-predicted phase diagrams of hydrate-forming components illustrate the influence of additional components on the hydrate formation as a function of RH. The DRH prediction via PC-SAFT allows for the determining of the stability of crystals and crystal mixtures without the need for time-consuming experiments.     

Low-Temperature Sol-Gel Synthesis of Single-Phase ZrTiO4 Nanoparticles

Ceramic ZrTiO₄ powders were prepared by a sol-gel method using zirconium oxychloride and titanium tetraisopropoxide. In situ high temperature X-ray diffraction results show that crystallization of the amorphous gel starts at 400 ^∘C. Single-phase ZrTiO₄ nanoparticles were obtained after heat treatment at 450 ^∘C for one hour. An average particle size of 46 nm has been determined by nitrogen adsorption analysis. After pressing these sinteractive powders, pellets with controlled pore size distribution were obtained by sintering at temperatures as low as 400 ^∘C. The analysis of pores by mercury porosimetry gives an average porosity of 45%. The electrical resistivity, determined by impedance spectroscopy measurements at 24 ^∘C under different humidity environments, shows the ability of these pellets to adsorb water vapor in the porous surfaces. Pellets fabricated with the nanosized powders prepared by the sol-gel technique are proposed as good candidates to be used in humidity sensing devices.     

Equilibrium phase diagrams of aqueous mixtures of malonic acid and sulfate/ammonium salts

Tropospheric aerosols are usually complex mixtures of inorganic and organic components. Although the thermodynamic properties of inorganic aerosols have been widely studied, the effect of organics on such properties is still under discussion. In this study, solubility in water, water activity (a(w)) of aqueous solutions, deliquescence relative humidity (DRH), eutonic composition, and eutonic DRH were determined for bulk mixtures of malonic acid (MA) with ammonium sulfate (AS) and ammonium bisulfate (ABS) at 25 degrees C over the full range of composition (from 0 wt % to the solubility limit of the mixture components). The data were used to construct equilibrium phase diagrams, which show the phase of the mixtures as a function of total composition, dry mixture composition, water content, and ambient relative humidity (RH). This work complements previous reports on the thermodynamic properties of AS/MA mixtures because the range of concentrations investigated is larger than in any other published single study. On the other hand, this is the first report on the a(w), deliquescence, and water absorption of ABS/MA mixtures. The eutonic composition for AS/MA mixtures was found to be 66.8 MA dry wt % (MA dry wt % = MA mass x 100/(AS mass + MA mass) with a DRH of 0.437. The eutonic composition for the ABS/MA mixtures was lower than for the AS/MA mixtures: 20.9 MA dry wt % with a DRH of 0.327. Measured a(w) of liquid AS/MA and ABS/MA solutions is compared with an extended Zdanovskii-Stokes-Robinson expression, obtaining a good agreement (error < 5-6%). The expression was used to predict water uptake of mixtures and might be useful to interpret particle hygroscopic growth experiments. Comparison of the AS/MA and ABS/MA systems indicates that ABS reduces the DRH and enhances water uptake, relative to mixtures with AS. The results confirm that ambient particles containing sulfate and water-soluble organic compounds can remain liquid or partially liquid at very low ambient RH conditions, especially if the sulfate is not completely neutralized.     

Mechanism of ion transport in hybrid materials based on MF-4SC perfluorinated sulfonation-exchange membranes and acid zirconium phosphate nanoparticles

The relationship between the transport properties of various salt forms (H⁺, Li⁺, Na⁺, Cs⁺) of MF-4SC hybrid membranes containing nanoparticles of crystalline acid zirconium phosphate Zr(HPO₄)₂ at various relative humidities are investigated with the use of impedance studies and NMR spectroscopy. Modification of the membranes leads to a marked increase in ion mobility, and the maximum effect is observed under reduced humidity conditions. The conductivity of a modified membrane at a relative humidity of 10% is 1.6 × 10^?4 Ω^?1 cm^?1, that is, almost 1.5 orders of magnitude greater than the conductivity of an initial membrane under the same conditions.     

Proton conductivity in phenolsulfonic acids and their salts

The geometric parameters and energies of crystal hydrates of aromatic sulfonic acids and their salts, as well as the pathways of proton transport in them, were calculated by the DFT (B3LYP) method with the 6-31G** basis set. For aromatic sulfonic acids, the proton relay mechanism was shown to be energetically more favorable than rotation of the HSO group or direct proton transfer. Calculations show that an increase in the number of water molecules located near the HSO₃ group from one to four decreases the barrier from 6 to 0.3 kcal/mol. Hence, a moderate increase in humidity should enhance the conductivity, which is fully consistent with experimental data. Calculations predict that the salts where all protons are substituted by metal atoms are unlikely to show good conductivity. Conversely, mixed salts, for example, H₃C₆(OH)(NaSO₃)(HSO₃) and H₃C₆(OH)(RbSO₃)(HSO₃), are expected to be thermally stable and resistant to deliquescence with an increase in the humidity of a medium and to have good conductivity.     

Crystallinity and fluorine substitution effects on the proton conductivity of porous hydroxyapatites

Porous calcium hydroxyapatite (p-HAp) was prepared by wet chemical methods. The poorly crystalline structure and the high surface specific area (235 m²/g) of this hydroxyapatite have effects on the variation of the electrical properties. Good linearity of logarithm of conductivity versus the relative humidity in the range from 19% to 88% (RH) was observed using the complex impedance spectroscopy. The proton conduction was affected by the relative humidity related to H₂O adsorption on the material surfaces. The fluorine substitution in p-HAp also modifies the crystalline and the proton conduction properties.     

Mobility of protons in 12-phosphotungstic acid and its acid and neutral salts

The proton mobility in 12-phosphotungstic heteropolyacid (PWA) and its salts (Cs₂HPW₁₂O₄₀·xH₂O, Cs₃PW₁₂O₄₀·xH₂O, (NH₄)₃PW₁₂O₄₀·xH₂O) was investigated by impedance spectroscopy and nuclear magnetic resonance with pulsed field gradient under wide range of relative humidity. Values of two diffusion components observed in PWA as well as in its acid cesium salt differ in one order of magnitude. Also there are two components in the impedance spectra of these compounds. Thus, we suggest, the proton transport take place both inside the grains and along its boundaries. Self-diffusion coefficients, observed in the neutral cesium and ammonium salts, are close to each other and equal to the fast diffusion coefficient in acid cesium salt. At the same time, there is the only relaxation component in the impedance spectra of neutral salts. Thus, it can be concluded, that in case of neutral salts of PWA, there is no proton transport inside the grains of these compounds, and their high proton conductivity caused by fast proton transport along the grain boundaries.     

Sea salt deliquescence and crystallization in atmosphere: an in situ investigation using x‐ray phase contrast imaging

X‐ray phase contrast imaging (PCI) based on synchrotron radiation was introduced for the first time as an in situ imaging way to investigate sea salt phase change, i.e. deliquescence and crystallization in atmospheric environment. A performance on the deliquescence of pure NaCl, which is the dominant component in sea salt, demonstrated that this technique can directly observe the change of core particle and differentiate the outer water layer clearly in solid‐aqueous system of ~100 µm scale. The imaging results showed that sea salt particle deliquesced on a large scale of relative humidity (RH) between 34 and 97% RH as a solid–liquid drop, while no clear deliquescence RH was observed during the process. According to the drop size growth curve, sea salt deliquescence can be divided into three steps, namely water accumulating step (34–75% RH), bulk melting step (75–86% RH) and delay dissolving step (>86% RH), which are most probably dominated by grouped components as MgCl₂/CaCl₂/MgSO₄, NaCl and Na₂SO₄/KCl/K₂SO₄, respectively. Instead at a sole RH, the crystallization of sea salt solution occurred at a range of 46–58% RH, which well agreed with the theory proposed by Ge et al. The aqueous‐solid condition provided by sea salt deliquescence and crystallization may greatly enhance the heterogeneous chemical reactions in atmosphere. Copyright © 2012 John Wiley & Sons, Ltd.     

Anisotropic electrical conductivity of drawn elastomeric ionene–TCNQ salts

Elastomeric ionene–TCNQ salts with favorable electrical, mechanical, and processing characteristics were drawn mechanically. The electrical conductivity parallel and perpendicular to the drawing axis was investigated. Correlation between anisotropic conductivity and the change in microstructure was discussed. The resistivity ρ at 25°C of the simple salt (EI-TCNQ₀) and the complex salt (EI-TCNQ_0.5) were on the order of 10⁵ and 10² Ω cm, respectively. In the drawn TCNQ salts, the ρ parallel to the drawing axis increased greatly; on the other hand, the ρ perpendicular to this axis increased slightly or was similar to the ρ of the undrawn TCNQ salts. The anisotropy in the ρ of EI-TCNQ_0.5 between the two directions reached 40 times. The activation energy also increased in the direction parallel to the drawing axis. In the undrawn TCNQ salts, the continuous conduction paths exist isotropically. With drawing, the continuous conduction paths, particularly in the direction parallel to the drawing axis, break or make a structural change. The anisotropic conductivity disappeared with time in EI-TCNQ₀; however, it was present in EI-TCNQ_0.5 even after 200 days under ambient conditions.     

Hydrogen Gas Sensing of High Electrical Conducting-P2O5-SiO2 Glasses Prepared by Sol-Gel Process

High proton-conducting P₂O₅-SiO₂ glass was applied to the electrolyte of the hydrogen concentration cell for hydrogen gas sensing. 5P₂O₅·95SiO₂ glass was prepared using the sol-gel method and its electrical conductivity and electromotive force were measured at 50°C as a function of both the ambient humidity and hydrogen gas concentration. The electrical conductivities increased with increasing humidity and reached 10^–2 S/cm at 90% relative humidity. The electromotive force of the hydrogen concentration cell, where the glass was used as a membrane, showed good Nernstian response to hydrogen pressure in the high relative humidity region.     

Electrical conductivity of systems based on Na3AlF6-SiO2 melt

The electrical conductivity of molten binary and ternary mixtures based on the NaF-AlF₃-SiO₂ system was investigated by means of a tube-cell (composed of pyrolytic boron nitride) with stationary electrodes. An impedance/gain-phase analyser (National Instruments; a high-performance modular chassis controlled by Labview? software) was used for the cell impedance measurement. The conductivity was found to vary linearly with temperature in all the mixtures investigated. The concentration dependence of electrical conductivity (isotherms) thus obtained was divided into two parts. The first represents the concentration region of up to 10 mole % of SiO₂, the second the region with a higher concentration of SiO₂ (from 10 mole % to 40 mole %). While the conductivity decreased considerably with the concentration of SiO₂ in the second part, it increased surprisingly in the low concentration range. From these results, the influence of electrolyte composition and temperature on the electrical conductivity was examined.     

Phase transitions and surface morphology of surfactant-coated aerosol particles

Probe molecule spectroscopy and hygroscopic growth curves characterize the morphology of surfactant-coated aerosol particles as a function of relative humidity (RH). This study focuses on particles composed of either potassium iodide or sodium chloride and sodium dodecyl sulfate (SDS). At high RH, these mixed particles assume a reverse micelle type structure, and at low RH, they comprise a solid core of either KI or NaCl coated with SDS and water. The deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of the inorganic fraction of the mixed particles are very similar to those of the pure salts. The surface polarity and morphology sampled by the coumarin 314 probe molecule ranges from that of a water-organic interface to that of an ionic surface and depends strongly on the RH and the amount of SDS. When the SDS coverage of the droplet just prior to efflorescence reaches approximately one monolayer, a thin soap film persists on the surface to values of RH much lower than the ERH. Both the electronic spectroscopy and photoelectric charging efficiency show a separate efflorescence for this layer at RH < 5%. The spectroscopy further reveals that there is a hysteresis associated with this low RH phase transition for both KI and NaCl cores.     

Polythermal study of electrophysical characteristics of poly(vinyl alcohol) polymer-salt films

Dielectric constant, dielectric loss tangent, and electrical conductivity were studied as functions of temperature for poly(vinyl alcohol) (PVA) films doped with ammonium metavanadate or polyoxometalate Mo132: (NH₄)₄₂[Mo ₇₂ ^VI Mo ₆₀ ^V O₃₇₂(HCOO)₃₀(H₂O)₇₂]30HCOONH₄·250H₂O. The electrophysical characteristics were measured and analyzed as dependent on the concentration and nature of the salt component and ambient humidity. The conductivity of polymer-salt compositions as a function of salt component concentration has a maximum, which is typical of electrolyte solutions. A conductivity mechanism was suggested: electron conductivity due to radical species at relatively low temperatures and proton conductivity at higher temperatures. Inflections on the electrical conductivity versus temperature and other property plots are due to removal of water from the compositions and thermal destruction.     

Alkali salts of (ω-sulphoxyalkyl)-acrylates and -methacrylates: Radical polymerization and copolymerization

A new preparation of alkali salts of (ω-sulphoxyalkyl)-acrylates and -methacrylates, by reaction of alkali salts of acrylic and methacrylic acids with cyclic sulphates, is described; spectral characterization of the products is described. The kinetics of the radical polymerization of sodium (2-sulphoxyethyl)methacrylate (SSEM) were studied; monomer reactivity ratios for copolymerization with methacrylic acid were: r₁ = 1.1 ± 0.15 and r₂ = 0.73 ± 0.05. Dark electrical surface conductivity of some homopolymers and copolymers with methacrylic acid was found to be 10⁴–10¹¹$\text{Ω}{}^{\mathrm{?1}}$, depending on relative humidity.     

Nafion-based composite solid electrolytes containing water-soluble fullerene C<Subscript>60</Subscript> derivatives

Nafion-based composite solid polyelectrolytes containing fullerene C₆₀ and its water-soluble derivatives fullerenol-C₆₀ and tris-malonate-C60 were studied by the impedance spectroscopy method. It was found that introduction of these dopants in Nafion leads to a substantial increase in proton conductivity of the composites in the region of low relative humidity. The reasons for the influence of dopants on proton conductivity of composites were discussed.     

Dilithium bis[(perfluoroalkyl)sulfonyl]diimide salts as electrolytes for rechargeable lithium batteries

A series of four different dilithium salts of structure F₃CSO₂N(Li)SO₂-(CF₂)_x-SO₂N(Li)SO₂CF₃, with x = 2, 4, 6, 8 were synthesized and characterized in polyethylene-oxide-based solid polymer electrolytes. Each salt may be thought of as two bis[(perfluoroalkyl)sulfonyl]imide anions linked together by a perfluoroalkyl chain of a particular length. Taken together, this homologous series provides an opportunity to study the effects of linker chain length and degree of fluorination in dianionic (and ultimately polyanionic) salts on the properties, particularly the conductivity, of the salts in various solvating media. SPEs in polyethylene oxide were characterized using scanning calorimetry, X-ray diffraction, ¹H and ¹⁹F NMR, and electrochemical impedance spectroscopy for SPEs prepared using ethylene-oxide-oxygen-to-lithium (EO:Li) ratios of 10:1 and 30:1. Trends in SPE ionic conductivity with anion structure revealed an unexpected trend whereby ionic conductivity is generally rising with increased length of the perfluoroalkylene linking group in the dianions. This trend could be the result of a decrease in dianion basicity that results in diminished ion pairing and an enhancement in the number of charge carriers with increasing anion fluorine content, thereby increasing ionic conductivity.     

Phase Behavior of Aqueous Na–K–Mg–Ca–Cl–NO<Subscript>3</Subscript> Mixtures: Isopiestic Measurements and Thermodynamic Modeling

A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻ and NO₃⁻ ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 °C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 °C. The measurements have been performed using Oak Ridge National Laboratory’s (ORNL) previously designed gravimetric isopiestic apparatus, which can also detect solid phase precipitation. In addition to various Na–K–Mg–Ca–Cl–NO₃ systems, results are reported for LiCl solutions. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid–liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor–liquid and solid–liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems.