Sodium Nitrate Solutions Research Articles

STUDI EFEK MEMORI HIDROKSIDA GANDA TERLAPIS Zn-Al-NO3

Synthesis and memory effect’s study of Zn-Al Layered Double Hydroxides (LDH) containing nitrite anion had been performed. Zn-Al-NO3 LDH were synthesized by coprecipitating and hydrothermal methods with molar ratio of Zn:Al of 3:1. The conversion of Zn-Al-NO3 LDH to corresponding mixed metal oxide were carried out by heating Zn-Al-NO3 LDH at 400º C for 2 hours. The reconstruction of Zn-Al-NO3 LDH were carried out by reacting the mixed metal oxide with solution of sodium nitrate 0,01 mol.Zn0.702Al0.298(OH)2(NO3)0.298.1.882H2O were synthesized. Its mixed metal oxide were made. The results of XRD and FTIR analyses showed that Zn-Al-NO3 LDH could be reconstructed after calcination. This work may enable to recycle and reuse of LDHs after the structure damaged.

Synthesis and study of sodium triuranate Na2(UO2)3O3(OH)2

Sodium triuranate Na2(UO2)3O3(OH)2 was synthesized by the reaction between aqueous uranyl acetate solution and aqueous sodium nitrate solution under hydrothermal conditions at 200°C. The composition and structure of the synthesized compound were determined, and its dehydration and thermal decomposition were studied, by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis.

Effect of crystallization kinetics on the properties of spray dried microparticles

ABSTRACTA droplet chain technique was used to study the influence of the crystallization process on the morphology of spray dried microparticles. A piezoceramic dispenser produced a chain of monodisperse solution droplets with an initial diameter in the range of 60–80 µm. Aqueous solutions of sodium nitrate were prepared in concentrations ranging from 5 mg/ml to 5⋅10−5 mg/ml. The solution droplets were injected into a laminar flow with gas temperatures varying from 25 to 150°C, affecting the droplet temperature and the evaporation rate, accordingly. Dried particles with diameters between 0.3 and 18 µm were collected. The properties of the collected microparticles were studied and correlated with a particle formation model which predicted the onset of saturation and crystallization. The model accounted for the dependence of the diffusion coefficient of sodium nitrate in water on droplet viscosity. The viscosity trend for sodium nitrate solutions was determined by studying the relaxation time observed durin...

Analysis of the relationship between electrolyte characteristics and electrochemical machinability in PECM on invar (Fe-Ni)fine sheet

Pulsed electrochemical machining (PECM) has been conducted for invar (Fe-Ni) fine sheet consisting of 64 % Fe ions and 36 % Ni ions. Solutions of sodium chloride (NaCl), acetic acid (CH3COOH), sodium nitrate (NaNO3), and sodium nitrite (NaNO2) mixed with sodium tartrate (C4H4Na2O6) were used as an electrolyte. First, the electrical conductivities of all electrolytes have been measured. As the concentration of each electrolyte increased, the electrical conductivities of electrolytes increased except for the acetic acid. The electrochemical machinability has been investigated using four types of electrolytes. The results of PECM show that the electrolyte which has the high electrical conductivity value leads to the low electrochemical machinability. The pulse waves which indicate the electrical characteristics during the PECM has been observed and it is confirmed that the passivating oxide film occur in PECM. To compare the capability of changing in transpassive state, the anode surface has been investigated. This study presents the relationship between electrical conductivity and electrical machinability. Moreover, the capacity of changing in transpassive state has been investigated as compared with four types of electrolytes. This study shows the possibility of applying invar fine sheet in PECM and contributes to determining the electrolyte for the process.

Synergistic Removal of Zinc and Copper in Greenhouse Waste Effluent by Struvite

Struvite (MgNH4PO4·6H2O) can be recovered from wastewaters for mitigation of phosphorus content. However, the interaction of dissolved constituents with struvite is rarely evaluated. Removal of heavy metals and total organic carbon (TOC) in a greenhouse wastewater (GW) by struvite was investigated. Presynthesized struvite was added to GW and removal of Zn (689 μg/L), Cu (151 μg/L), and TOC (51 mg/L) monitored from 1 to 26 d. Metal uptake in sodium nitrate solutions was used to assess competition, and the influence of other GW constituents on sorption. Struvite was also directly precipitated from GW (PPT). Recovered GW solids had 64–247 mg/kg Zn, 12–54 mg/kg Cu, and 1721–8806 mg/kg TOC, with lowest loadings for PPT and highest for 26 d solids. X-ray absorption spectroscopy detected polymerized Zn-phosphate, induced by dissolved phosphorus in GW, and Cu copolymerization, initially limited by aqueous Cu-organic complexation. Sorbed Cu shifts Fourier transform infrared-sensitive phosphate bands and changes th...

Determination of acid sites in porous aluminosilicate solid catalysts for aqueous phase reactions using potentiometric titration method

A potentiometric acid–base titration method was developed to characterize the acid–base properties of H-Beta-25, H-Beta-300, H-Ferrierite-20 and Si-MCM-48 zeolites in aqueous solutions. The method is based on linearization of the titration curve. The zeolite powders were dispersed in a sodium nitrate solution which was then titrated with a standard solution of sodium hydroxide. Various acid sites were found in the studied zeolites, and both the protonation constants and the concentrations of these acid sites were determined. The chemical composition (aluminum and silicon), distribution of the aluminum sites, crystallinity as well as the acidic properties of the titrated zeolites were compared with those of the pristine zeolites by using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES), X-ray Diffraction (XRD), 27Al NMR spectroscopy and the commonly used gas phase Fourier Transform Infrared spectroscopy (FTIR) of pyridine adsorption method.

Electrolyte Jet Machining of Titanium Alloys Using Novel Electrolyte Solutions

Electrolyte Jet Machining (EJM) is a non-contact machining process whereby material is removed through highly localised electrochemical dissolution. Throughout the development of this technique, difficulties have been reported in the processing of titanium alloys due to the formation of an electrochemically inert non-conductive passivating layer. In this study, various electrolytes are investigated for the purpose of establishing more stable machining and controlled removal of the passivating layer. Surface finish, material removal rate and pit formations using solutions of sodium halides (bromide, chloride and fluoride respectively) are compared with those obtained using the more commonly used sodium nitrate solution. The concentration of electrolyte is varied in order to appraise the efficacy of each solution. Machined features produced are subject to typical characterisation methods. The removal mechanism for overcoming the passivating layer and the development of more stable machining regimes are explored. Sodium chloride machining is shown to increase mass removal rates by over 100% at concentrations less than 2.5M compared with that achievable using the commonly used sodium nitrate electrolyte. Doping sodium chloride electrolytes with sodium fluoride decreases the overcut effect in machined pits by half compared with the pits formed in chloride, bromide, and nitrate electrolytes.

The content of nitric oxide in blood plasma of health persons depending on age.

The article considers results of study of total concentration of nitrites and nitrates (NOx) in blood plasma of healthy individuals residing in St. Petersburg. The samples from 58 healthy individuals were analyzed and out of them - 31 aged 18-25 years and 27 aged 48-63 years. The concentration of NOx in blood plasma was determined using Griess reagent after reduction of nitrates under effect of NADH-dependent recombinant nitrate reductase from Arabidopsis thaliana. The surplus of NADH preventing Griess reaction was removed at the expense of of enzyme reaction in presence of lactate dehydrogenase and sodium pyruvate. The analysis and its calibration was carried out using additions of solution of sodium nitrate to samples of blood plasma without deproteinization. The data was obtained concerning variation of content of NOx in healthy individuals of various age. In particular, it is demonstrated that the level of total content of nitrogen oxide in the group of elder age was reliably higher (p=0.0001) as compared with donors aged 18-25 years.

Nitrogen saturation, soil acidification, and ecological effects in a subtropical pine forest on acid soil in southwest China

AbstractElevated anthropogenic nitrogen (N) deposition has caused nitrate (NO3−) leaching, an indication of N saturation, in several temperate and boreal forests across the Northern Hemisphere. So far, the occurrence of N saturation in subtropical forests and its effects on the chemistry of the typically highly weathered soils, forest growth, and biodiversity have received little attention. Here we investigated N saturation and the effects of chronically high N inputs on soil and vegetation in a typical, subtropical Masson pine (Pinus massoniana) forest at Tieshanping, southwest China. Seven years of N flux data obtained in ambient conditions and in response to field manipulation, including a doubling of N input either as ammonium nitrate (NH4NO3) or as sodium nitrate (NaNO3) solution, resulted in a unique set of N balance data. Our data showed extreme N saturation with near‐quantitative leaching of NO3−, by far the dominant form of dissolved inorganic N in soil water. Even after 7 years, NH4+, added as NH4NO3, was nearly fully converted to NO3−, thus giving rise to a major acid input into the soil. Despite the large acid input, the decrease in soil pH was insignificant, due to pH buffering caused by Al3+ mobilization and enhanced SO42− adsorption. In response to the NH4NO3‐induced increase in soil acidification and N availability, ground vegetation showed significant reduction of abundance and diversity, while Masson pine growth further declined. By contrast, addition of NaNO3 did not cause soil acidification. The comparison of NH4NO3 treatment and NaNO3 treatment indicated that pine growth decline was mainly attributed to acidification‐induced nutrient imbalance, while the loss in abundance of major ground species was the combining effect of N saturation and acidification. Therefore, N emission control is of primary importance to curb further acidification and eutrophication of forest soils in much of subtropical south China.

Efficient frequency conversion by stimulated Raman scattering in a sodium nitrate aqueous solution

Frequency conversion of laser beams, based on stimulated Raman scattering (SRS) is an appealing technique for generating radiation at new wavelengths. Here, we investigated experimentally the SRS due to a single pass of a collimated frequency-doubled Nd:YAG laser beam (532 nm) through a saturated aqueous solution of sodium nitrate (NaNO3), filling a 50 cm long cell. These experiments resulted in simultaneous generation of 1st (564 nm) and 2nd (599 nm) Stokes beams, corresponding to the symmetric stretching mode of the nitrate ion, ν1(NO3−), with 40 and 12 mJ/pulse maximal converted energies, equivalent to 12% and 4% efficiencies, respectively, for a 340 mJ/pulse pump energy. The results indicate that the pump and SRS beams were thermally defocused and that four-wave mixing was responsible for the second order Stokes process onset.

Properties of aqueous nitrate and nitrite from x-ray absorption spectroscopy.

Nitrate and nitrite ions are of considerable interest, both for their widespread use in commercial and research contexts and because of their central role in the global nitrogen cycle. The chemistry of atmospheric aerosols, wherein nitrate is abundant, has been found to depend on the interfacial behavior of ionic species. The interfacial behavior of ions is determined largely by their hydration properties; consequently, the study of the hydration and interfacial behavior of nitrate and nitrite comprises a significant field of study. In this work, we describe the study of aqueous solutions of sodium nitrate and nitrite via X-ray absorption spectroscopy (XAS), interpreted in light of first-principles density functional theory electronic structure calculations. Experimental and calculated spectra of the nitrogen K-edge XA spectra of bulk solutions exhibit a large 3.7 eV shift between the XA spectra of nitrate and nitrite resulting from greater stabilization of the nitrogen 1s energy level in nitrate. A similar shift is not observed in the oxygen K-edge XA spectra of NO3 (-) and NO2 (-). The hydration properties of nitrate and nitrite are found to be similar, with both anions exhibiting a similar propensity towards ion pairing.

Impact of the uranium (VI) speciation in mineralised urines on its extraction by calix[6]arene bearing hydroxamic groups used in chromatography columns

Actinides determination in urine samples is part of the analyses performed to monitor internal contamination in case of an accident or a terrorist attack involving nuclear matter. Mineralisation is the first step of any of these analyses. It aims at reducing the sample volume and at destroying all organic compounds present. The mineralisation protocol is usually based on a wet ashing step, followed by actinides co-precipitation and a furnace ashing step, before redissolution and the quantification of the actinides by the appropriate techniques. Amongst the existing methods to perform the actinides co-precipitation, alkali-earth (typically calcium) precipitation is widely used. In the present work, the extraction of uranium(VI), plutonium(IV) and americium(III) from the redissolution solutions (called “mineralised urines”) on calix[6]arene columns bearing hydroxamic groups was investigated as such an extraction is a necessary step before their determination by ICP–MS or alpha spectrometry. Difficulties were encountered in the transfer of uranium(VI) from raw to mineralised urines, with yield of transfer ranging between 0% and 85%, compared to about 90% for Pu and Am, depending on the starting raw urines. To understand the origin of such a difficulty, the speciation of uranium (VI) in mineralised urines was investigated by computer simulation using the MEDUSA software and the associated HYDRA database, compiled with recently published data. These calculations showed that the presence of phosphates in the “mineralised urines” leads to the formation of strong uranyl-phosphate complexes (such as UO2HPO4) which compete with the uranium (VI) extraction by the calix[6]arene bearing hydroxamic groups. The extraction constant of uranium (VI) by calix[6]arene bearing hydroxamic groups was determined in a 0.04molL−1 sodium nitrate solution (logK=4.86±0.03) and implemented in an extraction model taking into account the speciation in the aqueous phase. This model allowed to simulate satisfactorily the experimental uranium extraction data and to support the preliminary conclusions about the role of the phosphates present in mineralised urines. These calculations also showed that the phosphate/calcium ratio is a key parameter as far as the efficiency of the uranium (VI) extraction by the calix[6]arene columns is concerned. It predicted that the addition of CaCl2 in mineralised urines would release uranium (VI) from phosphates by forming calcium (II)-phosphate complexes and thus facilitate the uranium (VI) extraction on calix[6]arene columns. These predictions were confirmed experimentally as the addition of 0.1molL−1 CaCl2 to a mineralised urine containing naturally a high concentration of phosphate (typically 0.04molL−1) significantly increased the percentage of uranium (VI) extraction on the calix[6]arene columns.

Effects of strong ionic polarization in the soil electric field on soil particle transport during rainfall

SummarySpecific ion effects are now thought to be important in nature. We studied the specific ion effects on soil particle transport during rainfall simulation (150 mm hour−1, 110 minutes) in sodium nitrate (NaNO3), potassium nitrate (KNO3) and caesium nitrate (CsNO3) solutions. The results showed marked differences in the intensity of soil particle transport in Na+, K+ and Cs+ systems. The differences increased sharply with the decrease in electrolyte concentration, which indicated strong specific ion effects on soil transport and suggested that the differences could not be explained by ionic size, hydration effect or dispersion force. The cationic non‐classical polarization in a strong electric field increases the Coulomb attractive force between the cation and clay surface, and further adversely decreases the strength of the electric field. With the absolute effective charge coefficients, γ, of Na+ (1.110), K+ (1.699) and Cs+ (2.506), we recalculated the true surface potentials of soil particles in NaNO3, KNO3 and CsNO3 solutions. The true surface potentials decrease sharply with the increase in ionic non‐classical polarization, and then the electrostatic repulsive pressure between particles in the soil should decrease sharply. Comparison of fitting the equation for transport intensity in NaNO3 solution with that in KNO3 and CsNO3 solutions showed clearly that the soil electric field controlled the aggregate breakdown and particle transport. The results suggested that the stronger the non‐classical polarization for cations in the soil, the weaker is the electrostatic field that forms and the soil erosion at the same solution concentrations.

Electrochemical Micromachining of Bulk Metallic Glasses

Owing to unique structural and functional properties bulk metallic glasses (BMG) are very promising materials. Their outstanding durability aligned with high mechanical strength and/or soft magnetic properties make them suited for micro­-electro­mechanical systems (MEMS), diminutive spring-mass systems, micronsized yokes in positioning systems, magnetic cores or medical gadgets. For shaping the required micro-sized devices thermo-mechanical forming is so far applied, but this is only applicable to selected glassy alloys with appropriate thermal characteristics. An upcoming alternative which allows operating at room temperature is electrochemical micromachining (ECMM). As new technique voltage pulsed electrochemical micromachining with a micro-tool electrode is introduced and a specially designed four-electrode setup for machining glassy plates was developed. The multi-component and reactive nature of metallic glasses demands a strict control of the local electrochemical dissolution process based on the choice of a suitable electrolyte and the identification of the effects of the ideal ultra-short pulse voltage parameters. First studies focused on Zr-based BMGs. Their high susceptibility for pitting corrosion limits the choice of electrolytes to halide-free ones. The standard electrolyte for industrial ECM is a concentrated (250 g/l) sodium nitrate solution. When conducting machining experiments with ultra-short voltage pulses in the transpassive regime, it could be demonstrated that the electrochemical dissolution of the glassy alloy can be focused on the microscale. But machined structures were irregularly shaped and covered with corrosion products and no clear dependence from the machining parameters was given. The underlying reaction mechanism and the role of the amorphous alloy structure and of the alloy constituents are discussed [1,2]. Recent studies were conducted on selected Fe-based glasses. Surface structuring of the soft magnetic glassy alloy Fe65.5Cr4Mo4Ga4P12C5B5.5 (at.-%) using an electrolyte based on a methanolic sulfuric acid solution was successful. The transpassive dissolution process was utilized for a defined, localized material removal. By applying nanosecond pulses between a work piece and a tool electrode, micro-holes of high aspect ratio and depth of up to 100 µm can be machined. But methanolic solutions are highly toxic and flammable and thus, undesirable in industrial mass production. Water-based electrolytes are the better choice, but the BMG is forming a passive layer which is very stable throughout the machining process. The addition of an oxidizing agent (iron sulphate) is successfully introduced to reduce this passivation process. Further, the Fe(III) ion reduction dominates the W-tool cathode reactivity and thus, suppresses disturbing hydrogen evolution. The influence of the applied oxidizing agents is analyzed and robust parameters for a fast and repeatable forming process without corrosion products are evaluated. The impact of the crucial process parameters as voltage, heading velocity or pulse-pause-ratio on the surface structuring is discussed. Optimum hole and line micro-structures were machined on BMG surfaces in 0.1 M sulphuric acid solution with 0.1 M iron sulphate at parameters: pulse on/off voltage = 6.0/0.5 V, pulse period/length = 750/75 ns, machining velocity = 0.1 µm/s (deep hole) and pulse on/off voltage = 6.0/1.0 V, pulse period/length = 2400/300 ns, machining velocity = 0.05 µm/s (line) [3-5]. This work is funded by the German Research Foundation (DFG) under project numbers GE 1106/10 and 1106/11. [1] J. A. Koza, R. Sueptitz, M. Uhlemann, L. Schultz, A. Gebert: Electrochemical micromachining of a Zr-based bulk metallic glass using a micro-tool e lectrode technique, Intermetallics 19 (2011) 437-444 [2] A. Gebert, P.F. Gostin, R. Sueptitz, S. Oswald, S. Abdi, M. Uhlemann, J. Eckert: Polarization studies of Zr-based bulk metallic glasses for electrochemical machining , Journal of the Electrochemical Society 161 (4) (2014) E66-E73 [3] R. Sueptitz, K. Tschulik, C. Becker, M. Stoica, M. Uhlemann, J. Eckert, A. Gebert: Micro-patterning of Fe-based bulk metallic glass surfaces by pulsed electrochemical micro-machining (ECMM), Journal of Materials Research 27 (2012) 3033-3040 [4] R. Sueptitz, P. Dunne, K. Tschulik, M. Uhlemann, J. Eckert, A. Gebert : Electrochemical micromachining of passive electrodes, Electrochimica Acta 109 (2013) 562-569 [5] S. Horn, A. Freidank, M. Uhlemann, M. Stoica, J. Eckert, A. Gebert, Electrochemical micromachining of passive Fe-based bulk metallic glasses in aqueous solutions, Proceedings INSECT 2014, Saarbrücken, Germany (in press)

High-rate intercalation capability of NaTi2(PO4)3/C composite in aqueous lithium and sodium nitrate solutions

The nanodispersed NaTi2(PO4)3/C composite containing 20–25 wt.% of in-situ formed carbon, was synthesized by gel combustion procedure followed by a heat treatment at 650, 700 and 750 °C. The samples calcined at 700 and 750 °C displayed crystalline nasicon structure. They were subjected to the investigation of intercalation/deintercalation kinetics in aqueous NaNO3 and LiNO3 solutions, using cyclic voltammetry and galvanostatic charging/discharging measurements. As regards to the effect of electrolyte composition, the reactions were evidenced to be roughly twice faster in sodium nitrate than in lithium nitrate solution. Among the samples treated at 700 and 750 °C, better performance was evidenced for the sample treated at lower temperature. Coulombic capacity in NaNO3 solution at charging rate 1C amounted to ∼70 mAh g−1 and ∼55 mAh g−1 for the sample calcined at 700 and 750 °C, respectively, and displayed surprisingly slight dependence on charging rate up to even 100C.

Thermodynamic representation of aqueous sodium nitrate and nitric acid solution with electrolyte NRTL model

Nitric acid solution has been widely used in nuclear waste treatment processes. To support heat and mass balance calculations and process simulation, a comprehensive thermodynamic model is developed for sodium nitrate–water binary, nitric acid–water binary, and nitric-acid–sodium nitrate–water ternary systems. Based on symmetric electrolyte NRTL (eNRTL) activity coefficient model, the present work takes into account complete dissociation of sodium nitrate and partial dissociation of nitric acid in aqueous solution. With up to three temperature coefficients for each eNRTL binary interaction parameter, the model provides an accurate and thermodynamically consistent representation for phase equilibrium properties such as vapor pressure, boiling point, dew point and salt solubility, calorimetric properties such as enthalpy and heat capacity, and speciation properties. The model is validated with data covering temperature up to 473.15K and sodium nitrate concentration up to saturation for the sodium nitrate–water binary system, temperature up to 379.15K and nitric acid concentration up to pure acid for the nitric acid–water binary system, and sodium nitrate concentration up to 0.21 mole fraction and nitric acid concentration up to 0.3 mole fraction for the nitric acid–sodium nitrate–water ternary system.

Original Scientific Article. Assessment of Reagent Effectiveness and Preservation Methods for Equine Faecal Samples

Abstract The aim of our study was to identify the most suitable flotation solution and effective preservation method for the examination of equine faeces samples using the FLOTAC technique. Samples from naturally infected horses were transported to the laboratory and analysed accordingly. The sample from each horse was homogenized and divided into four parts: one was frozen, another two were preserved in different reagents such as sodium acetate-acetic-acid-formalin(SAF) or 5% formalin. The last part was examined as a fresh sample in three different flotation solutions (Sheather´s solution, sodium chloride and sodium nitrate solution, all with a specific gravity 1.200). The preserved samples were examined in the period from 14 to 21 days after collection. According to our results, the sucrose solution was the most suitable flotation solution for fresh samples (small strongyle egg per gram was 706 compared to 360 in sodium chlorid and 507 in sodium nitrate) and the sodium nitrate solution was the most efficient for the preserved samples (egg per gram was 382 compared to 295 in salt solution and 305 in sucrose solution). Freezing appears to be the most effective method of sample preservation, resulting in minimal damage to fragile strongyle eggs and therefore it is the most simple and effective preservation method for the examination of large numbers of faecal samples without the necessity of examining them all within 48 hours of collection. Deep freezing as a preservation method for equine faeces samples has not, according to our knowledge, been yet published.

Performance analysis of a triple-effect absorption cooling cycle using aqueous (lithium, potassium, sodium) nitrate solution as a working pair

A triple-effect absorption cooling cycle using aqueous (lithium, potassium, sodium) nitrate solution (Alkitrate) as a working fluid in the high temperature stage is simulated in this work. This cycle takes advantage of the thermal potential of high temperature heat sources and has a configuration consisting of a H2O/LiBr double-effect cycle coupled with a single-effect cycle that uses Alkitrate as a working fluid. Heat is exchanged between the two cycles by thermal fluids which flow in the external circuits. The conventional working fluid H2O/LiBr suffers from serious problems of corrosion and thermal decomposition at temperatures of over 180 °C, which restricts its use in the high temperature components of a triple-effect absorption cooling cycle. At the nominal operating conditions selected, namely a heat source temperature TH of 250 °C and a cooling-water temperature TC of 30 °C the coefficient of performance achieved with the Alkitrate topping cycle is 1.73. The correct operation of the cycle is demonstrated by drawing the cycle in the Dühring diagram, where the safety margin for the crystallization of the working fluid is adhered to.Results show that the Alkitrate triple-effect cycle has a slightly higher efficiency as compared to the H2O/LiBr triple-effect cycle at generator temperatures of over 180 °C. Moreover, the practical operation of a H2O/LiBr triple-effect cycle at temperatures higher than 180 °C suffers from the above mentioned problems related to the thermal stability and corrosion of the working pair.

Visualization of Double-Diffusive Convection and Unsteady Solidification on a Vertical Circular Cylinder

This paper describes experimental results on the solidification process over the vertically positioned circular cylinder, placed in an aqueous solution of sodium nitrate, where the aqueous solution in the vessel is heated from the bottom. After the initiation of solidification by cooling the cylinder below the liquidus temperature, the pure ice formation on the cylinder causes the rejection of solute into the surrounding aqueous solution. The solute enriched vertical fluid layer over the ice then falls on the bottom of the vessel due to its higher density, and accumulates there. This process results in the formation of solute rich and hot horizontal layer (heavy layer), underlying the relatively cold but less concentrated fluid layer (light layer). As this process advances, however, because of the continuing influx of solute rich fluid, the lower heavy layer occupies more space, and the interface of the two layers rises slowly. The pH indicator method has been successfully employed in order to visualize the flows during this process. In this report, we document the evolution of both temperature and flow fields in the aqueous solution quantitatively, as the solidification progresses and the density discontinuity of the two layers rises.

Nitrate Concentration near the Surface of Frozen Aqueous Solutions.

Photolysis of nitrate plays an important role in the emission of nitrogen oxides from snow and ice, which affects the composition of the overlying atmosphere. In order to quantify these reactions, it is necessary to know how much nitrate is available for photolysis near the surfaces of snow and ice. The concentration of nitrate excluded from frozen solutions of nitric acid, sodium nitrate, and magnesium nitrate was measured with attenuated total reflection infrared spectroscopy. Liquid water and nitrate were observed at and near the bottom surface of frozen aqueous solutions during annealing from -18 to -2 °C. At -2 °C, the nitrate concentration was determined to be ∼1.0 mol/L for frozen NaNO(3) and Mg(NO(3))(2) solutions and ∼0.8 mol/L for frozen HNO(3) solutions. At lower temperatures, nitrate concentration ranged from 1.6 to 3.7 mol/L. Ideal thermodynamics overestimates nitrate concentration at colder temperatures where the brine is highly concentrated for all solutions. The nitrate concentration at ice surfaces is well described by bulk freezing point depression data close to the melting point of ice and for nitric acid at colder temperatures. Effects of temperature and counterions and implications for modeling snow chemistry are discussed.