Aqueous Sodium Sulfate Solutions Research Articles

Electrochemical Dissolution and Passivation of Cu-Ni Alloys in Sodium Sulphate Aqueous Solution

The electrochemical behaviour of two copper-nickel alloys is studied in 0.1 M Na2SO4 using cyclic voltammetry, potentiodynamic and current time transient techniques. The microstructure of the compounds formed during anodic sweep is characterized using x-ray diffraction analysis. The forward sweep is characterized by the existence of two well-defined potential regions; the selective dissolution and the simultaneous dissolution potential regions. The first potential region consisted in two anodic peaks A1 and A2 corresponding to the formation of Ni(OH)2 and NiO, and Cu2O, respectively. The second potential region consisted in two anodic peaks A3 and A4 corresponding to the formation of CuO and Ni2O3, respectively. It is found that the Cu-Ni system in sulphate solution follows the dissolution-redeposition mechanism of the dissolution of metals from the alloys. The X-ray diffraction analysis confirmed the existence Ni2O3 and CuO on the electrode surface of nickel rich alloy polarized to potential more noble than the potential of A4 and the existence of Cu2O and NiO on the surface of copper-rich alloy polarized to a potential in the A2 region. Atomic Force microscope images show surface enlargement beyond the critical potential Ecrit.

Modeling of direct contact membrane distillation process: Flux prediction of sodium sulfate and sodium chloride solutions

Membrane distillation (MD) can be used to process highly concentrated aqueous solutions to recover water. In this study we tried to model direct contact membrane distillation process in three different temperature systems using mass and energy balance. Data used in this study were the water flux behavior using two aqueous salt solutions of sodium sulfate (Na2SO4) and sodium chloride (NaCl) which were extracted from C.M. Tun et.al in a MD set up. Membrane flux behavior and other model parameters for a GVHP hydrophobic membrane were calculated. Initial concentration of sodium sulfate and sodium chloride was 2M and 4.5M, respectively, which was tested in three temperature systems of feed/permeate, 60/20, 60/30 and 50/30. It was found that both concentration and temperature polarization influenced the performance of MD. Mean relative absolute error for systems 60/20, 60/30 and 50/30 was 7.29%, 7.52% and 8.75% for sodium sulfate and 4.34%, 10.99% and 5.01% for sodium chloride, respectively.

Influence of Growth Conditions on Magnetite Nanoparticles Electro-Crystallized in the Presence of Organic Molecules

Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am2kg−1, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe3−δO4, with a small excess of Fe3+, 0.05 ≤ δ ≤ 0.15.

Volumetric properties, structural effects, and hydration of amino acids in aqueous salt solutions

The dependence of the standard partial volumes of glycine, α-alanine, and serine on the ionic strength of aqueous sodium chloride and sulfate solutions is modeled by the extended Masson equation: {ie534-1}. The error of less than 0.2 cm3/mol is a result of using five values of the A and B parameters: the two values of A are determined by the type of salt and the three values of B by the type of amino acid. A new variation of the additive-group approach is proposed for {ie534-2}. The partial volumes of the CH3 group (α-alanine) and the CH2 group (serine) are found not to depend on the salt concentration. The partial volume of the CH2 group of glycine grows with concentration. The structural characteristics of the hydrated complexes of the NH 3 + and COO− groups are calculated: the hydration numbers, the molar volumes of water inside and outside the hydration sphere, and the intrinsic volume of NH 3 + in COO− in solution. Given the same ionic strength, the aqueous sodium sulfate solution produces a somewhat stronger dehydration of the charged groups.

Presence of Hydrophobic Groups May Modify the Specific Ion Effect in Aqueous Polyelectrolyte Solutions

Enthalpies of dilution of aqueous solutions of aliphatic 6,12- and 12,12-ionene bromides and fluorides and enthalpies of mixing with low molecular-weight salts, such as sodium fluoride and bromide, are determined. In the second part of the study, the various x,y-ionenes (x, y are numbers of methylene groups between the adjacent charges) with fluoride, bromide, and iodide counterions are mixed with aqueous sodium sulfate solution. The polyelectrolytes examined in this part of the work are 3,3-, 6,9-, 6,12-, and 12,12-ionenes. A comparison with theoretical results, based on the Poisson-Boltzmann cell model, is presented. The theory predicts for the enthalpy of dilution to be exothermic and the enthalpy of mixing endothermic, while experiments show that signs of the heat effects depend on the nature of the counterion of the added salt, as also on the hydrophobicity (numbers x, y of methylene groups) of the ionene. We show that the salts when ordered by heat effects produced by mixing of NaF and NaBr with 3,3-, 6,9-, or 6,12-ionene fluorides and bromides follow the opposite ordering than in the case when the same alkali halide salts are mixed with more hydrophobic 12,12-ionene salts. The results for the enthalpy of mixing of ionenes under study with Na2SO4 follow the same order as obtained for monovalent salts.

Fabrication of bioactive titania coating on nitinol by plasma electrolytic oxidation

Surface modification was attempted on Nitinol (NiTi) by plasma electrolytic oxidation (PEO) in aqueous solutions of sodium sulphate and sodium hydroxide (Na2SO4-NaOH) using an AC power supply. A thick and porous oxide layer with micron-sized pores was formed on the Nitinol substrate, with the thickness of the oxide layer ranging from a few μm to over 10μm, depending on the processing time. X-ray diffraction (XRD) analysis confirmed that the oxide formed was anatase. Potentiodynamic polarization tests in Hanks’ solution showed that the corrosion resistance of PEO-coated Nitinol was much higher than that of the substrate. More importantly, the apatite-forming ability of the PEO-treated NiTi was found to be enhanced. This could be attributed to the anatase crystalline structure of the titanium oxide and the porous structure that facilitates the anchorage of the hydroxyapatite particles.

The mechanism for the stability of graphene oxide membranes in a sodium sulfate solution

The stability of graphene oxide (GO) membranes in a sodium sulfate aqueous solution is reported. The mechanism for the stability was interpreted with the assistance of molecular dynamic (MD) simulations as follows: GO disperses uniformly in water because it is hydrated. However, the hydration of GO is weakened when Na2SO4 is present because the Na+ and SO42− ions are preferentially hydrated over GO. Thus the movement of GO in the Na2SO4 solution becomes restricted and it is difficult for the GO in a GO membrane to uniformly disperse in a Na2SO4 solution even with ultrasonic treatment.

Thermodynamic properties of aqueous sodium sulfate solutions to 773 K and 3 GPa derived from acoustic velocity measurements in the diamond anvil cell

The thermodynamic properties of a 1 m Na(2)SO(4) solution have been determined to 773 K and 3 GPa from acoustic velocity measurements in externally heated diamond anvil cell using Brillouin spectroscopy. The measured acoustic velocities were inverted to obtain the density of the aqueous electrolyte solution with an accuracy of 0.3%-0.5%, and an equation of state (EoS) valid in the 293-773 K and 0.4-3 GPa range is proposed. The new EoS reproduces the experimental acoustic velocity data with a maximal deviation of 1.5% and allows deriving all thermodynamic properties of the aqueous solution, including isobaric heat capacity (C(P)), thermal expansion (α(P)), and compressibility (β) with an accuracy better than 3%-8%. The addition of dissolved sulfate species decreases the compressibility of water, consistent with the structure-maker character of SO(4)(2-) ions in solution that enhance the hydrogen-bond network of the solvent.

Electrodegradation of tetracycline on BDD anode

The anodic oxidation of tetracycline was performed in an up-flow reactor, operating in batch mode with recirculation, using as anode a boron-doped diamond electrode. The influence on the degradation rate of tetracycline initial concentration and recirculation flow rate were investigated. Assays were performed at constant current density, 300Am−2, using as electrolyte a sodium sulfate aqueous solution, 5gL−1. At the experimental conditions tested, HPLC results have shown an almost complete removal of tetracycline after 2h assay. The removals of the organic load, measured as chemical oxygen demand (COD) and total organic carbon (TOC), increased with tetracycline initial concentration and recirculation flow rate. At the highest recirculation flow rate tested, 100Lh−1, with an initial tetracycline concentration of 150mgL−1, after 4h assay, the removals of COD, TOC and absorbance (measured at 276.5 and 360.0nm) were 93%, 87%, 99% and 100%, respectively. Regarding the total Kjeldahl nitrogen elimination, it takes place mainly via transformation of organic nitrogen into ammonium, nitrate and nitrite. The total nitrogen removal increased with initial tetracycline concentration and showed also a tendency to increase with recirculation flow rate.

Solute- and Temperature-Responsive “Smart” Grafts and Supported Membranes Formed by Covalent Layer-by-Layer Assembly

Polymers like poly(N-isopropylacrylamide) (PNIPAM) exhibit lower critical solution temperature (LCST) behavior. A variety of reports have shown that brush grafts of PNIPAM on surfaces exhibit similar temperature responsiveness. We recently described an alternative synthetic approach to such surfaces that affords surfaces with similar LCST-like behavior. We also noted how such surfaces' wettability can change in response to the identity and concentration of solutes. Here we show that this synthetic procedure can be extended to glass surfaces and to more complex surfaces present in porous glass frits. Functionalized glass surfaces exhibit solute-dependent wetting behavior analogous to that previously reported. We further show that the resulting responsive nanocomposite grafts on such frits exhibit "smart" responsive permeability with a greater than 1000-fold difference in permeability to water versus aqueous solutions of sodium sulfate. This "smart" permeability is ascribed to the solute-dependent wettability behavior of the responsive PNIPAM component of the nanocomposite graft, which is sensitive both to the identity and concentration of the solute anion and to temperature.

Novel insight into neutral medium as electrolyte for high-voltage supercapacitors

This paper is focused on neutral aqueous medium, i.e.lithium, sodium and potassium sulfate solutions in a wide range of concentrations (0.1–2.5 mol L−1) as promising electrolytes for electrochemical capacitors because they are cheap, non-corrosive and allow applying diverse current collectors. These properties make the capacitor assembling process much easier and cheaper. Additionally, such electrolytes are electrochemically stable and environmentally friendly. Electrochemical investigations carried out especially for 1 mol L−1Li2SO4 aqueous solution confirmed the possibility of efficient capacitor work in a wider voltage range, i.e. even at 2.2 V without any significant capacitance fade during 15 000 cycles. The physicochemical properties of ions (i.e. solvation, diffusion or mobility) and their influence on the capacitor electrochemical behaviour are considered.

Ethylene glycol-mediated synthesis of PbO nanocrystal from PbSO 4: A major component of lead paste in spent lead acid battery

Lead sulfate (PbSO 4) is a major component of lead paste of spent lead acid batteries, normally over 60%. In traditional pyrometallurgical process, the decomposition of PbSO 4 requires a relatively high temperature and the use of coal as both the reducing agent and as the source of thermal energy, thereby causing emissions of SO x , lead particles and CO 2. In this study, lead sulfate was desulfated by adding an aqueous solution comprising citric acid and tri-sodium citrate with the modulation of ethylene glycol (EG) in order to control the morphology. The treating agent reacted with lead sulfate to form an aqueous solution of sodium sulfate and a precipitated precursor of lead carboxylate crystals. The precursor was characterized by XRD, SEM, SDT and FTIR. The morphology of the EG-mediated precursor showed a regular columnar shape. On calcining at relatively low temperatures, EG-mediated precursor was transformed into fine particles of lead oxide. The characteristics of calcined products were investigated by XRD, SEM, and TEM. The results showed that nanostructured crystals of lead oxide could be easily prepared by combustion of EG-mediated precursor at 350 °C with a lead recovery of about 98%. This paper has paved the way for obtaining nanostructured PbO from waste battery scrap.

Effect of porosity of phosphate coating on corrosion resistance of galvanized and phosphated steels Part I: Measurement of porosity of phosphate

AbstractThe corrosion resistance of phosphated and painted steels is associated with the integrity of phosphate and paint layers. In this work, a methodology to measure the porosity of phosphated coatings based on cathodic polarization technique with an electrolyte of a sodium sulfate aqueous solution was developed. The morphology and mass of phosphate layers were determined. Phosphating was performed using the spraying and immersion techniques, varying the refiner content of bath in the immersion operation. The phosphate coatings obtained by immersion with a refiner showed the lowest values of porosities among the samples studied. The phosphate layers, obtained by spraying, immersion without a refiner, and immersion with a half content of refiner, showed the lowest porosity on electrogalvanized steel. The phosphate layer obtained by immersion with a refiner displayed the lowest porosity on the substrate of ungalvanized steel.

Evaporation of Na2CO3-Na2SO4 solutions: A method to evaluate the distribution between bulk and surface crystallization

Precipitation of sodium salts in black liquor evaporators causes problems by forming scales on the evaporator surface, reducing heat transfer and cleaning intervals. Most problems are connected with the crystallization of sodium carbonate and sodium sulfate. As the solubility of these salts is exceeded, a crystal mass must form somewhere. Crystallization can occur either in the bulk solution, on the heat transfer surface, or on other surfaces. It is always desirable to create bulk crystals. If crystals form and remain on the surfaces, a layer of scales will build up with time. A method for estimating the distribution of crystal masses between the bulk and on surfaces has been developed in this work. The method is primarily based on inline density measurements combined with inline measurements of the system’s water mass. It has been applied to aqueous solution of sodium carbonate and sodium sulfate in a research black liquor falling film evaporator. Experiments have proven that the method gives valuable information on the crystallization process. It shows where crystals are formed during primary nucleation, as well as during the subsequent continuous crystallization. In an industrial black liquor evaporator, the metastable limit can be passed if it is operated under non-steady-state conditions. During evaporation, upon passing the metastable limit, the experiments showed that the surface crystallization is as high as or higher than the bulk crystallization. During the subsequent crystallization process, when concentration is further increased, the crystallization rate is higher in the bulk solution than on the surfaces.

An Experimental Study on Strength Deterioration of Cement Mortars by Wetting-Drying Cycles in Sodium Sulfate Aqueous Solution

An Experimental Study on Strength Deterioration of Cement Mortars by Wetting-Drying Cycles in Sodium Sulfate Aqueous Solution

Chitosan Sub-micron Particles Prepared Using Sulfate Ion Salt as Bacteriostatic Materials in Neutral pH Condition

In this paper, the newly developed ion exchange phase separation method to create chitosan sub-micron particles is introduced: 1) chitosan was dissolved in a lactic acid aqueous solution. 2) the obtained chitosan solution was added stepwise in a sodium sulfate aqueous solution and cooled down to 5℃ to become slightly turbid through agglutination. 3) desalinating and deacidifying of the mixture was carried out by a dialyzing tube method. IR spectroscopy and elemental analysis indicated that the agglutination of chitosan was induced by crosslinking effect with an electrostatic interaction between sulfate anions and amino groups in the glucosamine unit although large excess of Na2SO4 caused undesirable further agglutination of the resultant chitosan particles. As a result, the proper amount of Na2SO4 was approximately 1.0 - 10.0 equivalent for the amino group to create the chitosan particles with a sub-micron size. In addition, we investigated an antibacterial activity test for Escherichia coli of the obtained chitosan particles. The significant antibacterial activity was observed in incubation even at neutral pH condition while the chitosan microbeads (size: ca 200 ∫m) prepared by the conventional method and chitosan granules (size: ca 600 ∫m) as starting materials showed almost no antibacterial activity in the same condition.

Effect of chloride ions on electrochemical properties of anodized AV and D16 aluminum alloys in aqueous and glycerin-containing aqueous sodium sulfate solutions

The effect of chloride ions (0.01 N NaCl) on the electrochemical properties of anodized (in chromic anhydride or sulfuric acid) AV and D16 aluminum alloys in aqueous sulfate (0.5% Na2SO4) and glycerin-containing aqueous sulfate (0.5% Na2SO4, 33% glycerin) solutions is studied. Depending on the conditions of anodizing and the composition of the alloy and environment, currents on the anodized alloys in the passive range are shown to be smaller by one to four orders of magnitude compared to those on nonanodized alloys. Anodizing increases the resistance of alloys against pitting corrosion. Alloys anodized in sulfuric acid and then treated in dichromate are not susceptible to pitting corrosion. Alloys anodized in chromic anhydride are less resistant against pitting.

Effect of Water Polarizability on the Properties of Solutions of Polyvalent Ions: Simulations of Aqueous Sodium Sulfate with Different Force Fields.

We show that aqueous sodium sulfate solutions exhibit an unrealistically large degree of ion pairing and clustering when modeled using nonpolarizable force fields, with clusters resembling precipitate readily forming in a 0.5 m solution at ambient conditions. This aggregation behavior was found to be persistent in nonpolarizable water for a range of parameters of the sulfate anion. In contrast, a polarizable potential performs satisfactorily, producing a well dissolved salt with a degree of association that is consistent with activity data for real solutions. Most of this improvement is due to polarization of water molecules in the vicinity of the divalent sulfate anion, which enhances its solvation.

The formation of protein concentration gradients mediated by density differences of poly(ethylene glycol) microspheres

A critical element in the formation of scaffolds for tissue engineering is the introduction of concentration gradients of bioactive molecules. We explored the use of poly(ethylene glycol) (PEG) microspheres fabricated via a thermally induced phase separation to facilitate the creation of gradients in scaffolds. PEG microspheres were produced with different densities (buoyancies) and centrifuged to develop microsphere gradients. We previously found that the time to gelation following phase separation controlled the size of microspheres in the de-swollen state, while crosslink density affected swelling following buffer exchange into PBS. The principle factors used here to control microsphere densities were the temperature at which the PEG solutions were reacted following phase separation in aqueous sodium sulfate solutions and the length of the incubation period above the ‘cloud point’. Using different temperatures and incubation times, microspheres were formed that self-assembled into gradients upon centrifugation. The gradients were produced with sharp interfaces or gradual transitions, with up to 5 tiers of different microsphere types. For proof-of-concept, concentration gradients of covalently immobilized proteins were also assembled. PEG microspheres containing heparin were also fabricated. PEG-heparin microspheres were incubated with fluorescently labeled protamine and used to form gradient scaffolds. The ability to form gradients in microspheres may prove to be useful to achieve better control over the kinetics of protein release from scaffolds or to generate gradients of immobilized growth factors.

Crystallization in a Pilot Evaporator: Aqueous Solutions of Na2CO3 and Na2SO4

Sodium carbonate and sodium sulfate cause problems by forming scales in black liquor evaporators, reducing heat transfer and cleaning intervals. An experimental investigation of the crystallization behavior during evaporation of different aqueous solutions of sodium carbonate and sodium sulfate has been carried out. The analysis is based on changes in heat transfer coefficients and crystal masses. The results from this work show large variation in the distribution of the crystal mass, depending on the composition of the solution. Solutions with the crystalline form of either dicarbonate or sodium carbonate exhibit high propensity to form scales on the heat transfer surface. Solutions with the crystalline form of burkeite, however, do not show the same attraction to the heat transfer surface; they are more likely to crystallize in the circulating solution. Thus, the heat transfer is not as affected as for dicarbonate or sodium carbonate.