Frozen Salt Solutions Research Articles

Revisiting concrete frost salt scaling: On the role of the frozen salt solution micro-structure

We simulate the glue-spall stress due to mechanical interactions between a frozen saline solution (brine-ice composite) and a non-air entrained concrete surface including the impact of the micro-structure of the frozen solution. The presence of brine channels at the ice/concrete interface was found to be a prerequisite to induce stress during freezing and hence for scaling to occur. Pure ice does not result in scaling as it does not have brine channels. Furthermore, the size of the brine channels and their distribution was found determinant for the magnitude of the glue-spall stress in the concrete and the experimentally observed pessimum effect of a medium salt concentration was explained based on the change of the microstructure of the brine-ice composite at different salt concentrations and temperatures. The predicted results are in good agreement with the experimental observations and the few numerical demonstrations related to frost salt scaling in the literature.

Thermal conductivity measurements of macroscopic frozen salt ice analogues of Jovian icy moons in support of the planned JUICE mission

ABSTRACT The study of thermal properties of frozen salt solutions representative of ice layers in Jovian moons is crucial to support the JUpiter ICy moons Explorer (JUICE) (ESA) and Europa Clipper (NASA) missions, which will be launched in the upcoming years to make detailed observations of the giant gaseous planet Jupiter and three of its largest moons (Ganymede, Europa, and Callisto), due to the scarcity of experimental measurements. Therefore, we have conducted a set of experiments to measure and study the thermal conductivity of macroscopic frozen salt solutions of particular interest in these regions, including sodium chloride (NaCl), magnesium sulphate (MgSO4), sodium sulphate (Na2SO4), and magnesium chloride (MgCl2). Measurements were performed at atmospheric pressure and temperatures from 0 to −70 °C in a climatic chamber. Temperature and calorimetry were measured during the course of the experiments. An interesting side effect of these measurements is that they served to spot phase changes in the frozen salt solutions, even for very low salt concentrations. A small sample of the liquid salt-water solution was set aside for the calorimetry measurements. These experiments and the measurements of thermal conductivity and calorimetry will be valuable to constrain the chemical composition, physical state, and temperature of the icy crusts of Ganymede, Europa, and Callisto.

Corrosion damage in frozen 3.5 wt.% NaCl solution

AbstractZn and frozen 3.5 wt.% NaCl solution were used to simulate galvanized steel structures exposed to the seawater in the Polar Regions. The conductivity of the frozen salt solution and the corrosion of the Zn were characterized by electrochemical impedance spectroscopy, galvanic current measurement, and surface analyses. The results indicated that the completely frozen 3.5 wt.% NaCl solution was still conductive and corrosive, and the galvanic effect between different metals could not be ignored. The corrosion damage risk of metallic structures, particularly in the joint regions, can be high under freezing marine conditions in the Polar Regions.

Análisis experimental de la difusión salina durante la desalación por congelación

The consequences on health and low life quality caused by the problem of water scarcity, as well as the interrelation between energy and water supply, call attention to water desalination by Freezing Melting (F/M), which is a well-known technique but unfortunately, not used for this application, which is considered the most sustainable, in terms of its lower energy demand compared with commercial desalination techniques (about 70% less than thermal desalination). However, it presents some problems regarding the saline trapping in the ice, therefore, in this work, an experimental analysis is carried out to achieve a better understanding of the saline displacement, using an aqueous solution of sodium chloride, frozen at different temperatures, and configurations containers, with a F/M progressive desalination. It has been found that, at a freezing temperature of 8oC, it is possible to purify up to an average of 78.12% of the frozen salt solution, obtaining an easy-to-separate brine.

Cryoelectrolysis-electrolytic processes in a frozen physiological saline medium.

BackgroundCryoelectrolysis is a new minimally invasive tissue ablation surgical technique that combines the ablation techniques of electrolytic ablation with cryosurgery. The goal of this study is to examine the hypothesis that electrolysis can take place in a frozen aqueous saline solution.MethodTo examine the hypothesis we performed a cryoelectrolytic ablation protocol in which electrolysis and cryosurgery are delivered simultaneously in a tissue simulant made of physiological saline gel with a pH dye. We measured current flow, voltage and extents of freezing and pH dye staining.ResultsUsing optical measurements and measurements of currents, we have shown that electrolysis can occur in frozen physiological saline, at high subzero freezing temperatures, above the eutectic temperature of the frozen salt solution. It was observed that electrolysis occurs when the tissue resides at high subzero temperatures during the freezing stage and essentially throughout the entire thawing stage. We also found that during thawing, the frozen lesion temperature raises rapidly to high subfreezing values and remains at those values throughout the thawing stage. Substantial electrolysis occurs during the thawing stage. Another interesting finding is that electro-osmotic flows affect the process of cryoelectrolysis at the anode and cathode, in different ways.DiscussionThe results showing that electrical current flow and electrolysis occur in frozen saline solutions imply a mechanism involving ionic movement in the fluid concentrated saline solution channels between ice crystals, at high subfreezing temperatures. Temperatures higher than the eutectic are required for the brine to be fluid. The particular pattern of temperature and electrical currents during the thawing stage of frozen tissue, can be explained by the large amounts of energy that must be removed at the outer edge of the frozen lesion because of the solid/liquid phase transformation on that interface.ConclusionElectrolysis can occur in a frozen domain at high subfreezing temperature, probably above the eutectic. It appears that the most effective period for delivering electrolytic currents in cryoelectrolysis is during the high subzero temperatures stage while freezing and immediately after cooling has stopped, throughout the thawing stage.

Использование особенностей спектров ЭПР ионов переходных металлов при исследовании концентрирования солей в зависимости от условий замораживания

The EPR spectra of frozen salt solutions of paramagnetic cations were studied. The spectra structure and shape were demonstrated to be dependent on regimen and composition of freezing medium. The obtained experimental EPR spectra are theoretically described by spin Hamiltonian containing axially symmetric term of fine structure with manifestation of forbidden Δm = ±1 transitions. There was proposed to use EPR approaches in designing low temperature technologies for biological object preservation to analyze freezing regimens and possible cryoprotectants to forecast the minimization of cryoinjury effects with high salt concentrations during freezing. Probl Cryobiol Cryomed 2014; 24(3):212-221.

Detection and identification of salts and frozen salt solutions combining laser-induced breakdown spectroscopy and multivariate analysis methods: A study for future martian exploration

For the geochemical investigation of extraterrestrial surfaces laser-induced breakdown spectroscopy (LIBS) has been suggested as a powerful analytical tool, and is part of the payload on NASA’s rover Curiosity, which reached Mars in August 2012. Apart from soil in general, LIBS is capable of analyzing ice and salts within the soil. This study demonstrates the feasibility of LIBS for investigating and differentiating between different salts by applying three multivariate analysis (MVA) techniques. The focus was on the capability of the MVA techniques for LIBS data to discriminate between sulfates and chlorides with cations of the same kind as pure pressed pellets and in frozen salt solutions. Two data sets of LIBS spectra of eight different salts (CaCl2, CaSO4, KCl, K2SO4, MgCl2, MgSO4, NaCl, Na2SO4), pure and as frozen salt solutions, were acquired in a dedicated simulation chamber under martian atmospheric conditions. With principal components analysis (PCA) both data sets were analyzed with the aim of dividing the spectra of the ices into groups and revealing the most important lines in the spectra for discrimination and identification of the type of salt. PCA performance is improved by selecting the most relevant lines with emphasis on the sulfur and chlorine lines and additionally averaging the spectra before analysis. Moreover, a subsequent PCA with a subset of data can improve the discrimination ability for a sulfate and a chloride with the same type of cation. Soft independent modeling of class analogy (SIMCA) and partial least squares discriminant analysis (PLS-DA) were performed for both data sets. While SIMCA worked well for the pressed salt samples, its application to the spectra of the frozen salt solutions was not successful. A local PLS-DA of the LIBS spectra of salts with the same cation is capable of distinguishing sulfate and chloride.

Different photolysis kinetics at the surface of frozen freshwater vs. frozen salt solutions

Abstract. Reactions at air-ice interfaces can proceed at very different rates than those in aqueous solution, due to the unique disordered region at the ice surface known as the quasi-liquid layer (QLL) . The physical and chemical nature of the surfacial region of ice is greatly affected by solutes such as sodium halide salts. In this work, we studied the effects of sodium chloride and sodium bromide on the photolysis kinetics of harmine, an aromatic organic compound, in aqueous solution and at the surface of frozen salt solutions above the eutectic temperature. In common with other aromatic organic compounds we have studied, harmine photolysis is much faster on ice surfaces than in aqueous solution, but the presence of NaCl or NaBr – which does not affect photolysis kinetics in solution – reduces the photolysis rate on ice. The rate decreases monotonically with increasing salt concentration; at the concentrations found in seawater, harmine photolysis at the surface of frozen salt solutions proceeds at the same rate as in aqueous solution. These results suggest that the brine excluded to the surfaces of frozen salt solutions is a true aqueous solution, and so it may be possible to use aqueous-phase kinetics to predict photolysis rates at sea ice surfaces. This is in marked contrast to the result at the surface of frozen freshwater samples, where reaction kinetics are often not well-described by aqueous-phase processes.

Spectroscopic studies of the heterogeneous reaction between O3(g) and halides at the surface of frozen salt solutions

Springtime ozone depletion events have been linked to elevated levels of bromine in the polar boundary layer. It has also been suggested that iodine may play an important role in boundary layer chemistry. However, the mechanism(s) for initial halogen activation is not well understood. We report results of experiments using glancing‐angle laser‐induced fluorescence (LIF) and glancing‐angle Raman spectroscopy to investigate the heterogeneous reaction of gas‐phase ozone with bromide and iodide ions at the surface of frozen salt solutions. The results suggest that halides that have been excluded to the ice surface during the freezing process react in the dark and under non‐acidified conditions to produce molecular halogen species. At environmentally relevant bromide concentrations, the reaction proceeds ∼60 times more rapidly at ice surfaces than at the surface of aqueous solutions. At an ozone concentration of ∼8 × 1015 molec cm−3, and sea water concentrations of bromide and iodide, we estimate uptake coefficients γ(Br−) = (1.3 ± 0.5) × 10−8 and γ(I−) = (1.6 ± 0.5) × 10−9. We estimate that at atmospheric ozone concentrations, the uptake coefficients will be approximately a factor of ten greater.

Photo-chemical synthesis and deposition of noble metal nanoparticles

Highly dispersed nanoparticles of transition and noble metals are utilized for hydrocarbon reactions and rearrangements important to the chemical industry. The need to obtain 1 to 3 nm particles with narrow size distributions has prompted the development of alternative processing methods. In this paper, a novel, dry method to synthesize nanoparticles from a frozen salt solution is reported. Pd nanoparticles were synthesized by photo-chemical decomposition of palladium acetate (PdAc) within a host matrix of chloroform using an excimer laser operating at 248 nm. Frozen composite targets were ablated at fluences ranging from 0.25 J/cm2 to 0.75 J/cm2 at a processing pressure of 10 mTorr. The ejected nanoparticles were deposited on continuous carbon coated and lacey carbon transmission electron microscopy (TEM) grids at ambient temperature. Characterization was performed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDXS). High-resolution TEM analysis showed definitive evidence that the size distributions of the nanoparticles were narrow, exhibiting mean diameters ranging from 2.15 nm to 2.62 nm.

Concentration Dependence of Mössbauer Parameters of SnCl−3and SnBr−3Complex Ions

Mössbauer parameters of frozen salt solutions could be correlated with apparent degree of dissociation, γ. KSnCl3 and KSnBr3 were dissolved in 0.5 M H2SO4, whereas NH4 SnCl3 was dissolved in 0.5 M HClO4. Mössbauer studies were made at different concentrations.

Bulk standards for low-temperature biological x-ray microanalysis

Although sections of frozen salt solutions have been used as standards for x-ray microanalysis, such solutions are less useful when analysed in the bulk form. They are poor thermal and electrical conductors and severe phase separation occurs during the cooling process. Following a suggestion by Whitecross et al we have made up a series of salt solutions containing a small amount of graphite to improve the sample conductivity. In addition, we have incorporated a polymer to ensure the formation of microcrystalline ice and a consequent homogenity of salt dispersion within the frozen matrix. The mixtures have been used to standardize the analytical procedures applied to frozen hydrated bulk specimens based on the peak/background analytical method and to measure the absolute concentration of elements in developing roots.

Ice sublimation from frozen salt solutions

The sublimation method of drying is finding ever wider application in scientific and technical fields. For example, one of the newest fields employing this method is cryochemical synthesis of inorganic materials, with sublimation dehydration as the basis of the process. Sublimation of ice from rapidly frozen salt solutions produces powders with a component distribution close to that existing in the solution. We will consider the problem of ice sublimation from salt solutions frozen in the form of a plate, cylinder, and sphere in a flow of noncondensing gas at a pressure of 0.01 ≤ P ≤ 1.02 bars. The noncondensing gas contains vapors of the subliming material at a partial pressure of pf. Comparison of theoretical and experimental data reveals completely satisfactory agreement. The mass output coefficient, which is usually determined experimentally for mass-exchange processes with phase transitions, can be found in a manner analogous to the heat-liberation coefficient for a volume content of noncondensing gas between 25 and 100%.