Solutions Of Strong Electrolytes Research Articles

Uniform Doping of Titanium in Hematite Nanorods for Efficient Photoelectrochemical Water Splitting.

Doping elements in hematite nanostructures is a promising approach to improve the photoelectrochemical (PEC) water-splitting performance of hematite photoanodes. However, uniform doping with precise control on doping amount and morphology is the major challenge for quantitatively investigating the PEC water-splitting enhancement. Here, we report on the design and synthesis of uniform titanium (Ti)-doped hematite nanorods with precise control of the Ti amount and morphology for highly effective PEC water splitting using an atomic layer deposition assisted solid-state diffusion method. We found that Ti doping promoted band bending and increased the carrier density as well as the surface state. Remarkably, these uniformly doped hematite nanorods exhibited high PEC performance with a pronounced photocurrent density of 2.28 mA/cm(2) at 1.23 V vs reversible hydrogen electrode (RHE) and 4.18 mA/cm(2) at 1.70 V vs RHE, respectively. Furthermore, as-prepared Ti-doping hematite nanorods performed excellent repeatability and durability; over 80% of the as-fabricated photoanodes reproduced the steady photocurrent density of 1.9-2.2 mA/cm(2) at 1.23 V vs RHE at least 3 h in a strong alkaline electrolyte solution.

Comparison of the Pitzer and Hückel Equation Frameworks for Activity Coefficients, Osmotic Coefficients, and Apparent Molar Relative Enthalpies, Heat Capacities, and Volumes of Binary Aqueous Strong Electrolyte Solutions at 25 °C

Detailed numerical analysis of literature data for five key thermodynamic properties (activity coefficients, osmotic coefficients, apparent molar relative enthalpies, heat capacities, and volumes) of well-characterized aqueous strong electrolyte solutions shows that equally good fits are generally obtained from the Pitzer and Huckel equations when both frameworks have the same number of adjustable parameters. Fifty-seven strong electrolyte systems with published values at 25 °C have been examined: the differences found between the two frameworks are never large and are only significant with the activity and osmotic coefficients of eight systems. Most of these eight exceptions involve a lanthanide salt that has been characterized by just one research group. For describing the solution thermodynamics of binary (single) strong electrolytes, the Pitzer equations are found to possess no fundamental theoretical advantage over an extended Huckel framework. On the other hand, slight additional flexibility inherent in the Pitzer formalism makes it more susceptible than the Huckel equations to the numerical effects of experimental error. Comparing the fits achieved by the Pitzer and Huckel equation frameworks can help to identify (a) the simple behavior characteristic of strong electrolytes even at high concentration and (b) signs of error in experimental data sets lacking confirmation by independent measurement.

Ion hydration effects in aqueous solutions of strong electrolytes, according to proton magnetic relaxation measurements

The concentration dependences of proton magnetic relaxation (PMR) rates measured at different temperatures in aqueous electrolyte solutions and concentrated seawater (SW) in a wide range of salt concentrations and for different seawater salinities are presented, along with the concentration dependences of PMR rates determined in salts dissolved directly in seawater. The coordination numbers of the basic ions in seawater were determined from the complete solvation limits and compared with those measured in single-component water-salt solutions. The attaining of complete solvation limits was determined using the PMR data for ions of different hydration signs.

Dielectric permittivity in a dense layer of the hydration shell of an ion in a strong-electrolyte solution

Based on the experimental data on the dielectric dispersion and the static dielectric permittivity of solutions of strong electrolytes, the effective value of the latter in the dense layer of the hydration shell of an ion has been calculated. The calculations have been carried out in terms of the three-layer model of the hydration complex. The calculations have shown that for the solutions of strong electrolytes the value of the static dielectric permittivity (dielectric constant) in the dense layer of the hydration shell of an ion proves to be close to 2 and is almost independent of the concentration and temperature.

The conductivity equation for solutions of strong electrolytes

Based on the statistical model of solutions, an equation for calculating the conductivity of solutions of strong electrolytes in a wide concentration range is derived. The calculated values of the key empirical parameter of the equation are compared with the results of the calculation within the Onsager theory.

Thermodynamics of Strong Aqueous Electrolyte Solutions at t = 25 °C Described by the Hückel Equations

A theoretical framework based on the Hückel equation for activity coefficients has been developed, and the physicochemical properties of 57 binary strong electrolyte solutions at t = 25 °C have been correlated. These properties include the activity and osmotic coefficients, apparent molar relative enthalpies, apparent molar heat capacities, and apparent molar volumes. The correlating equations agree well with property values from the literature up to concentrations of m = 2.0 mol kg–1 for 1:1 electrolytes and m = 0.5 mol kg–1 for 2:1, 1:2, and 3:1 electrolytes. Certain electrolytes could not be satisfactorily represented, including polyprotic acids, 2:2 electrolytes, and the zinc and cadmium halides. In addition to quantifying Hückel equation parameters that can be used for the convenient calculation of physicochemical property values, the results provide a benchmark against which other theoretical frameworks with few adjustable parameters can be compared.

Theoretical analysis of aqueous solutions of mixed strong electrolytes by a smaller-ion shell electrostatic model

In spite of the great importance of mixed electrolytes in science and technology, no compelling theoretical explanation has been offered yet for the thermodynamic behavior of such systems, such as their deviation from ideality and the variation of their excess functions with ionic composition and concentration. Using the newly introduced Smaller-ion Shell treatment - an extension of the Debye-Hückel theory to ions of dissimilar size (hence DH-SiS) - simple analytic mathematical expressions can be derived for the mean and single-ion activity coefficients of binary electrolyte components of ternary ionic systems. Such expressions are based on modifying the parallel DH-SiS equations for pure binary ionic systems, by adding to the three ion-size parameters - a (of counterions), b+ (of positive coions), and b- (of negative coions) - a fourth parameter. For the (+ + -) system, this is "b++," the contact distance between non-coion cations. b++ is derived from fits with experiment and, like the other b's, is constant at varying ion concentration and combination. Four case studies are presented: (1) HCl-NaCl-H2O, (2) HCl-NH4Cl-H2O, (3) (0.01 M HX)-MX-H2O with X = Cl, Br, and with M = Li, Na, K, Cs, and (4) HCl-MCln-H2O with n = 2, M = Sr, Ba; and n = 3, M = Al, Ce. In all cases, theory is fully consistent with experiment when using a of the measured binary electrolyte as the sole fitting parameter. DH-SiS is thus shown to explain known "mysteries" in the behavior of ternary electrolytes, including Harned rule, and to adequately predict the pH of acid solutions in which ionized salts are present at different concentrations.

Electrokinetic and hydrodynamic properties of charged-particles systems

Dynamic processes in dispersions of charged spherical particles are of importance both in fundamental science, and in technical and bio-medical applications. There exists a large variety of charged-particles systems, ranging from nanometer-sized electrolyte ions to micron-sized charge-stabilized colloids. We review recent advances in theoretical methods for the calculation of linear transport coefficients in concentrated particulate systems, with the focus on hydrodynamic interactions and electrokinetic effects. Considered transport properties are the dispersion viscosity, self- and collective diffusion coefficients, sedimentation coefficients, and electrophoretic mobilities and conductivities of ionic particle species in an external electric field. Advances by our group are also discussed, including a novel mode-coupling-theory method for conduction-diffusion and viscoelastic properties of strong electrolyte solutions. Furthermore, results are presented for dispersions of solvent-permeable particles, and particles with non-zero hydrodynamic surface slip. The concentration-dependent swelling of ionic microgels is discussed, as well as a far-reaching dynamic scaling behavior relating colloidal long- to short-time dynamics.

Corrosion Mechanism of 316L Stainless Steel in a Expansion Joint of Blast Furnace Gas Pipeline in a Power Plant

Severe corrosion phenomenon appeared in an expansion joint of blast furnace gas (BFG) pipeline after booster fan in a power plant. The sediment adhered to the inner wall of the expansion joint was analyzed by ion chromatography. The corrosion site of expansion joint was examined by scanning electron microscope (SEM), and the behavior of electrochemical corrosion of stainless steel electrode was discussed through electrochemical impedance spectroscopy (EIS) and polarization curve. The results reveal that the leaching solution of the sediment is a kind of strong electrolyte solution. Along with the increase of immersion period, the impedance of stainless steel electrode decreases dramatically, the impedance spectroscopy experiences such a procedure that a single capacitive reactance arc gradually develops into the contraction of inductive reactance and then tends to be two capacitive reactance arc, which indicates that pitting corrosion transfers from induction period to evolution period until metastable pitting translates into stable pitting. There exists no passive area in polarization curves of stainless steel and shows the characteristics of active dissolution. In conclusion, the failure of the expansion joint stainless steel shows typical pitting characteristic.

An extension of the McAllister model to correlate kinematic viscosity of electrolyte solutions

This paper presents a new model for correlating kinematic viscosity of binary strong electrolyte solutions. The new model, based upon Eyring theory, considers that molecular interactions among anion, cation, and molecule occur in a certain way. The new equation correlates the viscosity of different aqueous electrolyte solutions within an absolute percentage error of 0.49% with a standard deviation of 0.4%. Comparison to existing correlations also appears in this work.List of symbolsG*Gibbs energy of activation [J/mol]hPlanck constant [6.624×10−27ergs/molecule, 6.624×10−25gmm2/(smolecule)]aiConstant of Eq. (23)biConstants of Eq. (24)MMolecular weight, g/molnNumber of molesNAvogadro's number [6.023×1023] molecules/mol or number of data points in Eqs. (4)NPNumber of experimental data pointsRUniversal gas constanttTemperature, [°C]TTemperature [K]VMolar volumen [cm3/mol]xMole fractionGreek lettersδGij*Temperature dependent parameter of the new viscosity equationδGji*Temperature dependent parameter of the new viscosity equationδGijk*Temperature dependent parameter of the new viscosity equationμDynamic viscosity, mPasνKinematic viscosity, mm2/sSubscriptsi, j, kSpecies i, j, and kmMixturemixMixture

Chemistry and applications of polysaccharide solutions in strong electrolytes/dipolar aprotic solvents: an overview.

Biopolymers and their derivatives are being actively investigated as substitutes for petroleum-based polymers. This has generated an intense interest in investigating new solvents, in particular for cellulose, chitin/chitosan, and starch. This overview focuses on recent advances in the dissolution and derivatization of these polysaccharides in solutions of strong electrolytes in dipolar aprotic solvents. A brief description of the molecular structures of these biopolymers is given, with emphases on the properties that are relevant to derivatization, namely crystallinity and accessibility. The mechanism of cellulose dissolution is then discussed, followed by a description of the strategies employed for the synthesis of cellulose derivatives (carboxylic acid esters, and ethers) under homogeneous reaction conditions. The same sequence of presentation has been followed for chitin/chitosan and starch. Future perspectives for this subject are summarized, in particular with regard to compliance with the principles of green chemistry.

Specific Rate of Protein Crystallization Determined by the Guggenheim Method

The biological function of a protein is intimately related to its three-dimensional molecular structure. Although X-ray diffraction from single crystals can be employed to solve for the molecular structure, use of this method is often impeded by the slow rate of precipitation of crystals from the pH buffered, aqueous solutions of strong electrolytes which ordinarily serve as growth media. The rate of crystallization can be measured as a function of growth solution conditions by growing the crystals in a dilatometer. As the crystallization progresses, the rate of change of the system volume caused by the difference in density between the crystals and the solution is reflected in the rate of change of the height of the fluid in the capillary side arm of the dilatometer. In the case of the proteins, lysozyme, and canavalin, this height changes exponentially with time, which serves to define a first-order rate constant or specific crystallization rate, k. A dozen such experiments may be needed to determine how \(k\) depends upon pH, electrolyte concentration, and temperature. Each experiment can require 4 or 5 days to reach equilibrium. If height measurements are made equally spaced in time, however, early time data can be combined according to the Guggenheim procedure, and the value of k can be determined without the experiment having to reach equilibrium. By using this method, the time required to complete an experiment can be reduced by as much as 50 %.

The destruction of quartz, amorphous silica minerals, and feldspars in model experiments and in soils: Possible mechanisms, rates, and diagnostics (the analysis of literature)

The dissolution of quartz and amorphous SiO2 proceeds via the adsorption of water molecules on the surface of these minerals with the further formation of four silanol groups around the silicon atom and the detachment of the molecules of orthosilicic acid from the surface. The rates of quartz dissolution at pH 7 and 3 constitute 10−15.72 and 10−16.12 mol/m2 s, respectively. They increase by three orders of magnitude upon the rise in pH from 7 to 10; they also increase in the solutions of strong electrolytes and in the presence of the anions of polybasic organic acids. The dissolution of feldspars begins from the release of alkali metals and calcium from the surface of crystal lattices of these minerals into the solution in the course of the cation exchange reaction. This is a fast process, and it does not control the rate of the feldspar dissolution that depends on the concentrations of protonated (in the acid medium) and deprotonated (in the alkaline medium) complexes with participation of the surface Si-O-Si and Al-O-Si groups of the mineral lattices. The rate of dissolution of K-Na feldspars decreases from n × 10−11 to n × 10−12 mol/m2 s upon the rise in pH from 3 to 5; it also increases in the plagioclase series with an increase in the portion of anorthite molecules and in the presence of the anions of polybasic organic acids in the solution. The rate of dissolution of feldspars in the model experiments is by 1–3 orders of magnitude higher than that obtained by different methods for native soils. This may be related to the adequacy of determination of the specific surface and its changes with time in native soils.

Influence of electrolytes on contact angles of droplets under electric field

The change of contact angle is one of the major subjects in the studies of electrowetting on dielectrics. A larger change in contact angle with a less applied electric potential has been pursued by the researchers on digital microfluidics. From previous research it is concluded that the effect of free charges in electrolytes on contact angles can almost be neglected. In this article, obvious influences of free charges on contact angles are presented and discussed. To verify the influence of free charges, both weak electrolyte (boric acid) and strong electrolyte (sodium chloride) are used as sources of free charges in our experiment. It was found that the increase of ion concentration enhances the contact angle variation due to the attraction between the bound surface charges in the dielectric layer and the free counter-ions in the solution. The saturated contact angle occurs with a lower electric potential compared with de-ionized water due to the shielding of the electric field by the free counter-ions. When a strong electrolyte is used, the contact angle varies at a much higher rate than with de-ionized water, and the huge amount of accumulated free ions shields the driving field, causing the contact angle to saturate at a much lower electric potential. The saturated contact angle in strong electrolyte solution is markedly larger than those in weak electrolyte solutions and de-ionized water.

The effects of electrolyte concentration on film composition and homogeneity in electrodeposition

We have investigated the effects of electrolyte concentration on the composition and homogeneity of thin films of the ternary alloy CoNiCu grown by single-bath electrodeposition techniques. The material was chosen owing to its academic and industrial applications but our results are more generic and will apply to other alloys grown this way. We compare weak (low species concentrations) and strong (high species concentrations) electrolyte solutions using identical electrolyte ratios. By choosing the concentration of the more noble species, in this case Cu, to be 25 times less than that of the other species, we controlled alloy composition as a function of potential. Films grown from the strong electrolyte solution were largely invariant in composition, whereas the weak solution produced highly potential sensitive alloy compositions. We found a trade-off between the accessible alloying range and thickness homogeneity across the film. This was shown to be due to the convective evolution of the diffusion layer using schlieren imaging.

Viscosity of electrolyte solutions: a mode-coupling theory

We present a versatile theoretical method for calculating the steady-state viscosity and shear relaxation function of strong electrolyte solutions. In this method, the ions are described on a primitive model level as charged Brownian spheres, and the essential ion–ion hydrodynamic interactions (HIs) are accounted for in the shear relaxation effect of the ionic atmosphere. The method combines a many-component mode-coupling theory (MCT) approach by Nägele et al (1998 J. Chem. Phys. 108 9893) with a simplified solution scheme, leading to an analytic expression for the shear relaxation contribution to the viscosity. This expression accounts for both the excluded volumes of the ions and their HIs. We show that the limiting law results for the viscosity of electrolyte mixtures by Falkenhagen and by Onsager and Fuoss are recovered at very low concentrations, and we discuss HIs corrections appearing at higher concentrations. Our numerical results for a 1:1 electrolyte reveal a strong enlargement of the viscosity caused by the HIs. The high-frequency viscosity gives the largest contribution to the total viscosity at higher concentrations.

Electrolytic Nature of Aqueous Sulfuric Acid. 1. Activity

According to the literature, when H(2)SO(4) dissolves in water, (1) it retains its molecular formula and tetrahedral structure of two O atoms and two OH groups bonded to a central S atom, and (2) it ionizes partially, as a 1-1 electrolyte, to H(+) (H(3)O(+)) and HSO(4)(-); the latter ion further dissociates at low concentrations (<0.1 M) to H(+) and SO(4)(2-). Using the Debye-Hückel (DH) limiting law at very low concentration, and the smaller-ion shell (SiS) model of strong electrolyte solutions-an extension of the DH model for ion size dissimilarity-up to moderate concentration, I examine the theory-experiment fit of the mean ionic activity coefficient (γ(±)) of the acid as a function of concentration (at 0 to ∼6 m) and of temperature (at 0-60 °C). The fit is impossible if H(2)SO(4) in water is assumed to be a 1-1 or 1-2 electrolyte, but is excellent when the acid is treated instead as a strong 1-3 electrolyte; that is, aqueous sulfuric acid behaves as a fully dissociated H(3)A acid. At 25 °C, the SiS best fit is achieved with the H(+) diameter being 1.16 Å (as obtained for strong mineral 1-1 protonic acids) and with the A(3-) ionic diameter being 5.77 Å. On the basis of the present study, H(2)SO(4) in water may be H(4)SO(5) (dubbed "sulfoxuric", or parasulfuric acid) completely ionized to 3H(+) and the ("bisulfoxate", or parabisulfate) anion HSO(5)(3-). The calculated standard potential of a newly proposed half-cell reaction, H(2) + HSO(5)(3-) ↔ H(+) + SO(4)(2-) + H(2)O + 2e(-), at 25 °C, is -1.0933 V.

Electrolytic Nature of Aqueous Sulfuric Acid. 2. Acidity

In part 1 of this study, I reported that the Debye-Hückel limiting law and the smaller-ion shell (SiS) model of strong electrolyte solutions fit nicely with the experimental mean ionic activity coefficient (γ(±)) of aqueous sulfuric acid as a function of concentration and of temperature when the acid is assumed to be a strong 1-3 electrolyte. Here, I report that the SiS-derived activity coefficient of H(+), γ(H(+)), of the 1-3 acid is comparable to that of aqueous HCl. This agrees with titration curves showing, as well-known, that sulfuric acid in water is parallel in strength to aqueous HCl. The calculated pH is in good accord with the Hammett acidity function, H(0), of aqueous sulfuric acid at low concentration, and differences between the two functions at high concentration are discussed and explained. This pH-H(0) relation is consistent with the literature showing that the H(0) of sulfuric acid (in the 1-9 M range) is similar to those of HCl and the other strong mineral monoprotic acids. The titration of aqueous sulfuric acid with NaOH does not agree with the known second dissociation constant of 0.010 23; rather, the constant is found to be ~0.32 and the acid behaves upon neutralization as a strong diprotic acid practically dissociating in one step. A plausible reaction pathway is offered to explain how the acid may transform, upon base neutralization, from a dissociated H(4)SO(5) (as 3H(+) and HSO(5)(3-)) to a dissociated H(2)SO(4) even though the equilibrium constant of the reaction H(+) + HSO(5)(3-) ↔ SO(4)(2-) + H(2)O, at 25 °C, is 10(-37) (part 1).

An Investigation of Zdanovskii’s Rule for Predicting the Water Activity of Multicomponent Aqueous Strong Electrolyte Solutions

The effectiveness of Zdanovskii’s rule as a fundamental method of predicting water activities in mixed aqueous strong electrolyte solutions has been investigated. Unfortunately, when literature data available for more than 100 ternary systems (i.e., two electrolytes plus water) were examined, sufficient measurements were rarely available to test Zdanovskii’s rule conclusively. This is because few mixed systems have been studied by more than one (independent) investigator and, in these few cases, the differences between reported water activities are generally much larger than typical estimates of experimental uncertainty. Most of the electrolyte systems considered in this work are found statistically to conform with Zdanovskii’s rule but often only within a worryingly large tolerance in residuals. However, when data are taken from a single source, deviations from Zdanovskii’s rule, significant in comparison to the stated experimental precision, can often be attributed equally well to small, unrecognized, systematic errors. This dilemma can only be resolved by more experimental measurements of sufficient accuracy to achieve better agreement between independent observers. Our findings imply that (a) confidence in deviations from Zdanovskii’s rule typically depends on a subjective judgment of data quality and (b) Zdanovskii’s rule, albeit often difficult to validate, provides an impressively general method for estimating water activities in mixed aqueous strong electrolyte solutions, with a certainty that, objectively, is as good as or better than current experimental capability.

Potassium-cesium molybdenum oxide bronzes

The electrochemical synthesis of potassium-cesium molybdenum oxide bronzes in ionic melts of the potassium-cesium molybdates of the ternary system K2MoO4-Cs2MoO4-MoO3 is investigated. Two regions for compositions of the electro-crystallization of two alkaline bronzes KxCsyMoO3 are revealed. The electrical conductance of corrosion-proof bronzes in solutions of strong electrolytes is studied, along with the application of a 2D protective coating to metals.