Aqueous Sodium Sulfate Solutions Research Articles

Mercury Beating Heart: Modifications to the Classical Demonstration

By analogy with the classical variant of the mercury beating heart (MBH), we propose several demonstrations of the MBH with various solutions of electrolytes, where the beating is generated by external power supply. Details for performing the experiments of MBH are given in this article. Video clips are offered in addition to classical demonstrations with an overhead projector or video camera. Mercury oscillations were observed without physical contact of mercury with the electrodes. When an aqueous solution of sodium sulfate or alkali hydroxide was used as electrolyte, an amalgam formed (even without direct contact between the electrode and mercury drop) and a mechanism is proposed for this phenomenon.

Siloxane-containing polymer matrices as coating materials

Coating materials based on siloxane-containing polymer matrices that had been modified with fluoropolymer or acrylic resins and applied as organic components of hybrid systems were examined. The optimal recipes of the dispersion systems, applied as polymer matrix precursors, were determined on the basis of factorial experiments, designed as 22 with additional ‘star’ experimental points to obtain greater accuracy in the resulting regression equations. The siloxane cage formation was based on the following crosslinking reactions of functional polysiloxanes: (1) hydrosilylation of vinyl groups; (2) condensation of silanol groups. Moreover, the molecular modeling, using P3 semi-empirical methods, was applied to build the model structure of a siloxane-containing polymer matrix. The surface properties of these coatings were studied using wettability assessments (dynamic contact angle and surface-free energy evaluation), atomic force microscopy (AFM), and X-ray electron microscopy (ESCA-XPS). The morphology, roughness, and structural regularity are discussed to illustrate the effects of the organic component on the surface properties. The most significant changes were observed in the surface morphology of the coatings. The application properties of such coating materials for the protection of buildings were tested, based on studies of their water vapor permeability, water absorption, and weathering resistance (freezing/thawing, salt-saturated aqueous sodium sulfate solution). The effect of the chemical structure of the siloxane-containing polymer matrix on the properties of the resulting coatings was focused on the protection of porous building materials. A very good correlation of the application properties of these coating materials and their surface properties, such as high dynamic contact angle (DCA), low surface-free energy (SFE) and surface morphology, was observed and is discussed.

Assessing the Role of the Active-site Cysteine Ligand in the Superoxide Reductase from Desulfoarculus baarsii

Superoxide reductase is a novel class of non-heme iron proteins that catalyzes the one-electron reduction of O(2)(.) to H(2)O(2), providing an antioxidant defense in some bacteria. Its active site consists of an unusual non-heme Fe(2+) center in a [His(4) Cys(1)] square pyramidal pentacoordination. In this class of enzyme, the cysteine axial ligand has been hypothesized to be an essential feature in the reactivity of the enzyme. Previous Fourier transform infrared spectroscopy studies on the enzyme from Desulfoarculus baarsii revealed that a protonated carboxylate group, proposed to be the side chain of Glu(114), is in interaction with the cysteine ligand. In this work, using pulse radiolysis, Fourier transform infrared, and resonance Raman spectroscopies, we have investigated to what extent the presence of this Glu(114) carboxylic lateral chain affects the strength of the S-Fe bond and the reaction of the iron active site with superoxide. The E114A mutant shows significantly modified pulse radiolysis kinetics for the protonation process of the first reaction intermediate. Resonance Raman spectroscopy demonstrates that the E114A mutation results in both a strengthening of the S-Fe bond and an increase in the extent of freeze-trapping of a Fe-peroxo species after treatment with H(2)O(2) by a specific strengthening of the Fe-O bond. A fine tuning of the strength of the S-Fe bond by the presence of Glu(114) appears to be an essential factor for both the strength of the Fe-O bond and the pK(a) value of the Fe(3+)-peroxo intermediate species to form the reaction product H(2)O(2).

ESTIMATION OF LIMITING EQUIVALENT CONDUCTIVITY AND IONIC RADIUS OF TETRABORATE ANION FROM CONDUCTIVITY MEASUREMENTS OF CONCENTRATED TETRABORATE SOLUTIONS

The conductivities of aqueous solutions of sodium sulphate and sodium tetraborate at different concentrations were measured. Using a novel method, these data were used to determine the limiting equivalent ionic conductivity and ionic radius of tetraborate ion. It was found that the limiting equivalent ionic conductivity of tetraborate ion is 34.58 ohm−1 cm2 and the ionic radius of tetraborate is 3.507±0.076 Å.

Small-scale top-spray fluidised bed coating: Granule impact strength, agglomeration tendency and coating layer morphology

The degree of agglomeration and impact strength of Na 2SO 4 cores (all in the size range of 200–300 μm) coated with aqueous solutions of sodium sulphate and dextrin as a function of several process and formulation variables have been investigated. The coating process was performed in a modified small-scale GEA Aeromatic-Fielder Strea-1 top-spray fluidised bed, and the impact strength was tested in bulks using a Pneumatic Impact Gun, in which granule samples of 0.5 g were exposed to ten repeated impacts at 10 m/s. Using an unreplicated double 2 4 − 1 fractional factor design, two regression models were derived from experimental data describing quantitatively the degree of agglomeration and impact strength respectively. The agglomeration model suggests in accordance with previous studies that increasing the nozzle pressure as well as coating-solution-dry-matter-concentration decreases the tendency of agglomeration. The consistency between the agglomeration model and new experimental data is concluded to be satisfactory. The impact strength model indicates increasing impact strength with increasing nozzle pressure, coating solution–dry-matter-concentration and bed temperature. These tendencies may be influenced by the large extent of droplet penetration, as observed in additional coating droplet penetration and coating layer morphology studies in the present paper. The validation of the impact strength model shows that the model clearly follows overall experimental tendencies. The derivation of these quantitative models may be seen as a first step towards the development of processes for production of unagglomerated enzyme granules with high mechanical strength and contribute to an improved understanding of fluid bed processes and products.

Hemodialysis membranes prepared from poly(vinyl alcohol): Effects of the preparation conditions on the morphology and performance

AbstractPoly(vinyl alcohol) was employed for the preparation of hemodialysis membranes with and without the addition of acetic acid and poly(ethylene glycol) with the phase‐inversion process. Aqueous solutions of sodium sulfate and sodium hydroxide were chosen as coagulant baths. The performances of the membranes were estimated by the measurement of the removal of uremic toxins (urea, uric acid, and creatinine) from human blood serum. The morphologies of the membranes were investigated and correlated to the membrane performance. Increasing the poly(ethylene glycol) concentration in the polymer solutions resulted in porous, spongelike structures because of the higher polarity of the polymer solutions and the enhancement of the diffusion rate of the nonsolvent (sodium sulfate and sodium hydroxide) into the polymer solutions. The porous structures of the membranes enhanced the removal of uremic toxins. The presence of acetic acid, with greater ionization strength, resulted in higher electrostatic interactions between positive and negative ions in the coagulation baths and polymer solutions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2490–2497, 2007

Effect of free solvent on the solvation of electrolytes and nonelectrolytes

An approach is developed for analyzing hydration of sodium and magnesium sulfate electrolytes over a wide range of concentrations up to 1.8 mol/L at temperatures from 278.15 to 318.15 K. The model of free water (water that does not enter hydrate complexes) is used to analyze the hydration numbers, mean compressibility of water in the hydration sphere, its temperature dependence, and several other solvation parameters that are determined with difficulty. A comparative analysis of the behavior of the βhVh = f(h) function is carried out for zwitterions and electrolytes. This function has an identical slope for amino acids, halides, and nitrates; that is, the adiabatic compressibility of water in the hydrate complex of an electrolyte or nonelectrolyte (β1hV1h) is independent of the solution concentration over a wide range of compositions. This suggests that the clathrate solvation mechanism operates both for a stoichiometric ion mixture and for zwitterions. Aqueous solutions of sodium sulfate and magnesium sulfate behave quite differently: they appreciably deviate from the solutions of the specified systems.

A study of the diffusion permeability coefficient of a tubular membrane unit in an aqueous solution of sodium sulfate

Experimental data on the diffusion permeability coefficient of sodium sulfate in a fluoroplastic membrane were obtained and analyzed.

Simultaneous solubility of SO 2 and NH 3 in (salt + H 2O) and enthalpy change upon dilution of (SO 2 + NH 3 + salt + H 2O) in (salt + H 2O) {salt = (NH 4) 2SO 4 or Na 2SO 4}: Experimental results and model predictions

The simultaneous solubility of sulfur dioxide and ammonia in aqueous solutions of (ammonium sulfate or sodium sulfate) was measured by a synthetic method in the temperature range from 313.6 to 373.2 K and at pressures up to 2.5 MPa. Furthermore, the enthalpy change upon diluting aqueous solutions of sulfur dioxide, ammonia and (ammonium sulfate or sodium sulfate) in aqueous solutions of the same salt was measured in a batch calorimeter at about 313 and 352 K. The experimental results are used for comparison with predictions from a thermodynamic model for the vapor–liquid equilibrium and the enthalpy of dilution of those chemical reacting systems. In that model, activity coefficients are calculated from Pitzer's molality-scale-based Gibbs excess energy model, where all interaction parameters are either adopted from previous investigations on the properties of the binary and ternary sub-systems (if available) or they are neglected (if they are not available).

Partial molar volumes and adiabatic compressibilities at infinite dilution of aminocarboxylic acids and glycylglycine in water and aqueous solutions of sodium sulphate at (288.15, 298.15 and 308.15) K

The partial molar volume and partial molar adiabatic compressibilities at infinite dilution of dl-aminobutanoic acid, dl-norvaline, β-alanine, 4-aminobutanoic acid, 5-aminopentanoic acid, 6-aminohexanoic acid and glycylglycine have been obtained in water and aqueous solutions of (0.5, 1.0 and 1.5) mol · kg −1 sodium sulphate at (288.15, 298.15 and 308.15) K from measurements of density and ultrasonic velocity. A qualitative interpretation of the results has been given using the Kirkwood model and nature of the interactions in solutions. A model, derived from Scaled Particle Theory, has been used for quantitative explanation of partial molar volumes and for the understanding the volumes of interaction. The results distinguish the behaviour of α-amino acids from that of α,ω-amino acids, and of the “less polar” 5-aminopentanoic acid from that of the analogous, but “more polar”, glycylglycine in solution. These findings are in agreement with previous studies in aqueous solutions and they support the water-structure making ability of sodium sulphate.

Precipitation of barium sulfate: Experimental investigation about the influence of supersaturation and free lattice ion ratio on particle formation

The precipitation of barium sulfate from aqueous solutions of barium chloride and sodium sulfate was investigated experimentally in a continuous Y-Mixer to avoid any mixing influence. Initial supersaturation and the initial ratio R = c B a free 2+ / c S O 4 , free 2 − of the free lattice ions after complete educt mixing were varied over a broad range. The variation of the free lattice ions has a strong influence on the obtained particle size distribution. At low supersaturations precipitation experiments with barium or sulfate ion excess lead to smaller mean particle diameters compared to experiments done under stoichiometric conditions. At higher supersaturations a sulfate ion excess has no effect on the detectable particle size. Streaming potential measurements reveal that the particle charge increases only with increasing barium ion excess. Higher repulsive electrostatic forces are caused by specific adsorption of the lattice ions on the particle surface and aggregation of primary particles can be avoided. By variation of supersaturation a broad range of particle sizes can selectively be produced, ranging from micrometer sizes down to nanoparticles smaller than 50 nm. The variation of supersaturation and of free lattice ion ratio at constant supersaturation has a great influence on crystal morphology.

Characterization of Silicate Complexes in Aqueous Sodium Sulfate Solutions by FAB-MS

When the sodium ion (Na+) concentration is increased above 0.5 mol-dm−3 (M), the concentrations of dissolved silica in aqueous sodium chloride (NaCl) and sodium nitrate (NaNO3) solutions decrease because of the salting out effect. On the other hand, the concentration of the dissolved silica in aqueous sodium sulfate (Na2SO4) solutions increases monotonously as the concentration of Na+ is increased above 0.5 M. The purpose of this study is to determine the reasons why the salting-out effect is not observed in Na2SO4 solutions. FAB-MS (Fast Atom Bombardment Mass Spectrometry) was used to sample directly the silica species dissolved in aqueous Na2SO4, NaCl, and NaNO3 solutions. In the FAB-MS spectra of these solutions, the peak intensity ratios of the linear tetramer to the cyclic tetramer largely increased for Na+ concentrations between (0.1 and 1) M. This shows that some characteristics of the Na2SO4 solutions are similar to those of the NaCl and NaNO3 solutions. In Na2SO4 solutions, however, when the concentration of Na+ is higher than 1 M, the peak intensity of the dimer is much higher than those of the other silicate complexes. In Na2SO4 solutions, the SO42− ion undergoes partial hydrolysis to form HSO−4 and OH− is produced. In particular, in the range where the concentration of SO42− is high, the pH of the solution increases slightly. This higher pH yields more dimers from the hydrolysis of silicate complexes. This increase in dimer production agrees with the observation that silica dissolves in sodium hydroxide (NaOH) solutions mainly as a dimer when the concentration of NaOH is less than 0.1 M. In Na2SO4 solutions at high concentrations, a salting-out effect is not observed for silica. This is due to the increase in the concentration of OH−, which accelerates the hydrolysis of silica and results in dimer formation.

Preparation of barium sulfate particles using filtration dispersion precipitation method in O/W system

In this paper, a new method to synthesize BaSO 4 nano-particles in O/W system with filtration dispersion technology was developed. The nano-particles of barium sulfate were prepared using a type of filtration dispersion device with a plate porous disc as a dispersion medium. Working systems of barium chloride aqueous solution/30% TBP (in kerosene) with sulfuric acid were applied. The influence of the reactant concentration and the operation conditions were investigated. The morphology of the particles was observed by SEM, and the particle-size distributions were measured. The nano-particles prepared in O/W system were compared with those prepared by dispersing aqueous barium chloride solution into aqueous sodium sulfate solution with the same filtration dispersion device. The results showed that mono-dispersed BaSO 4 particles can be prepared using the filtration dispersion method in O/W systems. The surfaces of all the particles were smooth. The mean diameter of the particles was in the 100–400 nm range and decreased with the increase of flux of the two phases. The ratio of the two phases greatly affects the morphology of particles because of the excess concentration of [SO 4 2−]. The particle size was also much smaller when the mixed two feeds were aqueous solutions.

Membrane distillation crystallization of concentrated salts—flux and crystal formation

Membrane distillation crystallization (MDC) can be used to process highly concentrated aqueous solutions. In MDC, membrane distillation (MD) is used to recover water and to generate the desired supersaturation in the crystallizer where product crystals can be precipitated. This paper discusses factors influencing flux at close to saturation and the formation of salt crystals. The flux behaviour was investigated using two aqueous salt solutions of sodium sulfate (Na 2SO 4) and sodium chloride (NaCl) which have different solubility–temperature coefficients. For both salts it was observed that MD was operable at high concentrations at feed temperatures of 50 and 60 °C with fluxes up to 20 L m −2 h −1. It was found that both concentration and temperature polarization influenced the performance of MD. When operated in batch concentration mode without the crystallizer the flux gradually declined due to vapour pressure suppression and concentration polarization, up to a critical degree of saturation. The flux data could be predicted by heat and mass transfer modeling or by a simple empirical relationship involving the overall vapour pressure driving force and the degree of saturation. Beyond the critical degree of saturation, rapid flux decline was observed due to crystal deposition and scale formation on the membrane which reduced the membrane permeability. The Na 2SO 4 solution was able to operate at slightly higher degrees of saturation, which may be because the negative solubility–temperature coefficient favours solubility in the polarization layer. In MDC the temperature and saturation level both in the MD and the crystallizer are critical operating parameters. Anhydrous sodium sulfate crystals can be produced by means of MDC with a relatively narrow crystal size distribution and average size of 60–80 μm.

Inhibitive Effect of Benzotriazole on Copper Surfaces Studied by SECM

The inhibitive effect of benzotriazole on a commercial copper surface (phosphorus-deoxidized copper) was studied by a scanning electrochemical microscope (SECM) in an aqueous sodium sulfate solution using ferrocenemethanol (FcMeOH) as the redox mediator. The formation of the inhibitive film was followed as a function of time and as a function of the potential of the copper substrate. The results were analyzed using the existing models in the literature. The results show that the potential has a crucial effect on the growth of the [Cu(I)-BTA] film. At a potential close to the dissolution range of copper, the surface changes gradually from almost ideally conductive to almost ideally insulating surface in the presence of benzotriazole, but at more negative potentials the effect is diminished and finally deceased. Quartz crystal microbalance experiments showed that the mass of an adsorbed layer must correspond to a multilayer. © 2004 The Electrochemical Society. All rights reserved.

Naphthalene sulphonic acids—new test compounds for characterization of the columns for reversed-phase chromatography

Non-substituted naphthalene sulphonic acids are strong acids, which are completely ionised in aqueous and aqueous-organic solutions. Because of repulsive electrostatic interactions, they are more or less excluded from the pores of the column packing materials commonly used in reversed-phase chromatography. The ionic exclusion can be suppressed by increasing the ionic strength of the mobile phase. In aqueous sodium sulphate solutions, very good selectivity was observed for isomeric naphthalene di- and tri-sulphonic acids, allowing reversed-phase separations of these strongly ionic compounds without addition of ion-pairing reagents to the mobile phase. The retention of the isomeric acids increases proportionally to the dipole moment, which can be explained by its effect on increasing exposure of the naphthalene ring to hydrophobic interactions with the non-polar stationary phases. Chromatographic behaviour of isomeric naphthalene di- and tri-sulphonic acids was investigated on 25 different columns for reversed-phase chromatography. The elution order of the isomers is the same on all the columns, but very strong stationary phase effects were observed on the retention and on the band asymmetry, depending on polar interactions with residual silanol groups and other polar adsorption centres in the stationary phases. These effects are independent of the organic solvents, as the tests are performed in purely aqueous mobile phases and allow classification of the columns into several groups.

Salt solubility and deposition in high temperature and pressure aqueous solutions

AbstractSolubility and deposition rate experiments were performed in aqueous sodium sulfate and potassium sulfate solutions at elevated temperatures and pressures typical of the supercritical water oxidation (SCWO) process. The test cell was a six‐port chamber in the form of a modified 1.91 cm (3/4 in.) diameter Swagelok cross with an internally heated cylinder (hot finger) mounted in its center. Solubilities were acquired by maintaining the surface temperature of the hot finger about 10°C above the gradually increasing bulk temperature of the solution flowing by it until salt precipitated on the hot finger. Solubility temperatures for sodium sulfate and potassium sulfate in water were measured for salt concentrations of up to 10% mass fraction. In the deposition rate experiments, the solution flowing past the hot finger was preheated to a temperature close to the solubility temperature and the salt layer–solution interface formed on the hot finger was maintained slightly above the solubility temperature to drive deposition. Deposition rates from SCWO streams containing up to 8% mass fraction salt were obtained by measuring the mass of the salt deposited on the hot finger after each (6 to 12 min) run. Solubility data are compared to those from other studies and a simple deposition rate model is developed and compared with the deposition rate data. Natural convection dominated transport and the system pressure was 25 MPa at all conditions. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2038–2049, 2004

A New Optically Reflective Thin Layer Electrode (ORTLE) Window: Gold on a Thin Porous Alumina Film Used to Observe the Onset of Water Reduction

AbstractThe fabrication and unique characteristics of a new type of thin layer electrode, an optically reflective thin layer electrode (ORTLE), are described. The electrode was fabricated by the anodization of a thin layer of aluminum sputtered onto a plain glass microscope slide to create a 750 nm‐thick porous alumina film. A thin film of gold was then sputtered atop the porous and transparent alumina film. The gold layer remained porous to allow solution into the pores but was optically thick and reflective. Reflectance measurements made through the microscope slide did not interrogate the bulk solution, but show spectral features that shift with the optical properties of the material filling the pores of the alumina film. A simple series of experiments, in which the potential of the ORTLE was stepped negatively to various values in an aqueous sodium sulfate solution, shows that interference fringes shift measurably in the ORTLE spectrum at potentials several hundred millivolts positive of the potential at which gas evolution was visible to the naked eye.

An electrochemical study of the oxidation of 1,3,5-Tris[4-[(3-methylphenyl)phenylamino]phenyl]benzene

An investigation into the oxidative electrochemistry of 1,3,5-Tris[4-[(3-methylphenyl)phenylamino]phenyl]benzene (TMPB) is described. In particular, the heterogeneous electron-transfer kinetics in N, N-dimethylformamide (DMF) and dichloromethane (DCM) are studied using the high-speed microband channel electrode. Experiments to investigate the standard electrochemical rate constants, k 0, transfer coefficients, α, and formal potentials, E f 0, of the observable oxidations of TMPB in both DMF and DCM solutions containing 0.10 M tetrabutylammonium perchlorate (TBAP) are reported for 12.5 μm platinum microband electrodes using a range of linear flow velocities from 12 to 25 m s −1. The measured values of k 0 for the two measurable oxidations in DMF are 1.03 ± 0.41 and 1.02 ± 0.20 cm s −1, and for the three oxidations in DCM are 0.44 ± 0.04, 0.17 ± 0.03 and 0.08 ± 0.02 cm s −1, respectively. The values of α for these oxidations in DMF are 0.48 ± 0.06 and 0.52 ± 0.02, and in DCM are 0.52 ± 0.02, 0.62 ± 0.03 and 0.53 ± 0.07, respectively. The respective formal oxidation potentials (all measured vs Ag) are 0.533 ± 0.002 and 0.766 ± 0.003 V in DMF, and 0.161 ± 0.002, 0.495 ± 0.002 and 1.128 ± 0.004 V in DCM. The presence of the monocation radical in DCM is confirmed by ESR measurement. Experiments are also presented to explore the voltammetry of TMPB in microdroplets of toluene and also in the solid-phase, when in contact with aqueous solutions of sodium fluoride, perchlorate, nitrate and sulphate. It was found that, when TMPB is dissolved in a toluene microdroplet, anion insertion accompanies the first oxidation for the case of perchlorate and nitrate, with anion-facilitated dissolution occurring for sulphate and fluoride. More complex reactions occur at more positive potentials. In the solid-phase, however, slow anion-facilitated dissolution still occurs for fluoride and sulphate, and rapid direct dissolution takes place in the case of perchlorate.

Electrode reactions at sub-micron oil ∣ water ∣ electrode interfaces

Our electrochemical system is a hemispherical droplet of nitrobenzene including ferrocene, which is mounted on a glassy carbon electrode in a sodium sulfate aqueous solution. It is composed of a hemispherical oil ∣ water interface, a disk-shaped oil ∣ electrode interface, a water ∣ electrode interface and a ring oil ∣ water ∣ electrode interface. The voltammetric current of the droplet showed two anodic waves for the oxidation of ferrocene. The current at 0.5 V was proportional to the radii of the droplet and concentration of ferrocene, and was independent of the potential sweep rate as well as the concentration of sulfate. These facts indicate that the electrode reaction should occur at the thin ring on the electrode into which the water and the oil phase merge. A model of a microband electrode was suggested and was applied to the limiting current to evaluate the width of the three-phase interface. The evaluated width, 0.23 μm, is much larger than the molecular size.