Zinc dissolution in ammonium chloride electrolytes

The anodic dissolution of zinc RDE in NH₄Cl and NH₄Cl + ZnCl₂ electrolytes at pH 5.5 was studied. XPS and SEM data indicate that the zinc electrode is covered by a porous film composed of a mixture of metallic zinc and zinc hydroxide. The thickness of the film and the zinc hydroxide content is much higher in zinc-containing electrolytes than in NH₄Cl and, although the thickness and Zn(OH)₂ amount decrease with anodic polarization, the electrode is never free from oxidized compounds. Electrochemical results indicate that at low overpotentials the rate of zinc dissolution is determined by the removal of the oxidized blocking particles, while at high overpotentials Zn dissolution takes place through the porous layer.     

Initiation of copper dissolution in sodium chloride electrolytes

Initial stages of copper activation in chloride-ion containing neutral aqueous solution were studied. The results point that activation of copper passivity is initiated once the potential exceeds the breakdown value, occurring with well-defined incubation period, similar to that of other passive metals in chloride environments. The effect of applied potential and Cl⁻ ion concentration on the incubation period is presented. The results indicate that an incubation period for copper activation in chloride containing solutions can be associated with the formation of a two-dimensional CuCl layer on the metal surface. The incubation period is relatively long at negative potentials and it is decreases with a positive shift in the potential. At a certain potential, the incubation period is sharply decreased. The time-frame of incubation period is attributed to the formation rate of two-dimensional CuCl layer and its reduction rate. The formation of a stable salt film on the metal surface facilitates localized rapid dissolution of the copper.     

Transpassive dissolution of mild steel in NaNO3 electrolytes

A study has been made of the transpassive dissolution of mild steel in sodium nitrate solution over a range of current densities from 2 to 100 A cm^–2. The dissolution current efficiency and the anode potential free from the electrolyte IR component were measured in a flow cell; optical and scanning electron microscopy were then used to examine the sample surfaces after the dissolution tests. The results show that during the early stage of transpassive dissolution, the mild steel is covered with a compact, electronically conductive Fe₃O₄ film, and the current is consumed mainly in oxygen generation on the film/electrolyte interface. With increasing anode potential and current density, this film is gradually broken and the underlying metal surface becomes exposed to the electrolyte. At this stage, iron dissolution begins at a high rate. The film rupturing process is strongly dependent on nitrate concentration; the higher this is, the lower is the current density required to rupture the film.     

The anodic dissolution of nickel—II. Bromide and iodide electrolytes

The kinetics of the anodic dissolution of nickel were studied in acidic bromide and iodide solutions using a potentiostatic sweep technique. The rate of dissolution is almost unaffected by the halide at low concentrations due to the presence of a prepassive film. At higher halide concentrations the prepassive film is removed and active dissolution occurs. The reaction is first order in Br^?, zero order in I^? and independent of pH for pH < 2. The Tafel slope is 82 mV, in accord with earlier work in chloride solutions.     

The anodic dissolution of nickel—1: Perchlorate and fluoride electrolytes

A potentiostatic sweep technique has been used to study the anodic dissolution of nickel in acidic perchlorate, acetate and fluoride solutions. At slow potential sweep rates a prepassive film exists throughout the anodic region in perchlorate and acetate electrolytes. By the use of fast sweeps, or by the addition of F^?, film formation and growth is sufficiently reduced to reveal a linear anodic. Tafel region. The rate of active dissolution, which is independent of [H⁺] and [F^?], obeys the following rate law; i = 2Fka_w exp [βFE/RT], with β = 0·53.The following mechanism is proposed for active dissolution, with the first step rate-determining: (1) Ni + H₂O → NiOH_ads + H⁺ + e^?, (2) NiOH_ads → NiOH⁺ + e^?, (3) NiOH⁺ + H⁺ ? Ni²⁺ + H₂O. Prepassivation is thought to occur from the intermediate NiOH_ads through a solid state mechanism.     

Anodic dissolution of aluminium in organic electrolytes containing perfluoroalkylsulfonyl imides

Electrochemical dissolution of aluminium has been investigated in various solutions composed of organic solvents and 1 m lithium bis(perfluoroalkylsulfonyl) imide salts. Potentials of the onset of transpassive dissolution and repassivation as well as dissolution currents have been measured for several systems by using voltammetric methods. Empirical correlation between the composition of the solvent and the dissolution current has been established for mixtures of ethylene carbonate and ethylmethyl carbonate. The effect of the perfluoroalkyl chain length on the dissolution rate has also been studied and the result has been elucidated with the help of considerations on the structure of the ions. Mechanistic information obtained from electrochemical impedance spectra revealed that at least two adsorbed intermediates have to be included in the dissolution mechanism. Conditions of application of lithium perfluoroalkylsulfonyl imides in lithium ion batteries are briefly discussed.     

The dissolution and recrystallization of polyethylene crystals suspended in various solvents

The dissolution and recrystallization of crystals of polyethylene suspended in p-xylene, n-dodecane, and decalin, are described. It is shown that differential thermal analysis (DTA) can be applied to suspensions of polymer crystals to determine the dependence of dissolution temperature on concentration, temperature of crystallization, and solvent. In addition, DTA can be used to follow the course of isothermal recrystallization of a suspension as a function of time and temperature, as well as recrystallization occurring during heating at a constant rate. The results of DTA, coupled with those obtained by electron microscopy and low angle X-ray analysis, make it possible to present a general picture of the behaviour of suspended polyethylene crystals. Recrystallization normally occurs by a dissolution-redeposition mechanism, and evidence for thickening by creep-up is limited to certain special conditions. A detailed discussion of recrystallization is presented which involves both thermodynamic and kinetic arguments.     

Building action of various types of inorganic electrolytes

The builder effects of a series of condensed phosphates and other types of electrolytes on the detergency for standard soiled cloth have been measured. The detergency highly depends on the type of electrolytes and, in general, increases with increasing pH of detergent solutions. The building action of phosphates is greater than that of other electrolytes when it is compared at the same pH. The alkalinity, including alkali buffering capacity, of various electrolytes and the sequesteration capacity of phosphates for calcium ion have also been determined. From the results, the building action of inorganic electrolytes in a detersive system has been discussed in connection with the suspension stability of colloidal particles reported in previous papers. The following factors are at least important in the building action of inorganic compounds: (a) the suspension of soil particles in a detergent solution, (b) the sequesteration of heavy metal ions, and (c) the alkalinity including buffering action to keep the solution alkaline. Condensed phosphates, in particular sodium tripolyphophate, have an ability to satisfy these three factors although their alkalinity is not so strong.     

Effect of nitrite anions on the rate of iron dissolution in acid electrolytes

The effect of the concentration of nitrite ions, potential, pH and solution stirring on the dissolution rate of iron was studied. Nitrite ions were shown to accelerate active dissolution. The accelerating action of the oxidant depends on the ratio of the rates of electroreduction at the electrode surface and homogenous chemical reduction in the reaction layer adjacent to the electrode. A possible mechanism of oxidant action on the iron dissolution is considered. The electroreduction process is assumed to generate at the iron surface an activated complex accelerating metal dissolution.     

Effect of inorganic electrolytes on dissolution behavior of mixed anionic-amphoteric surfactant systems

The effects of some inorganic electrolytes on the dissolution behavior of anionic-amphoteric mixed surfactant systems have been studied in terms of dissolution temperature of a hydrated solid surfactant; these systems are sodium dodecyl sulfate (SDS) - N^α,N^α-dimethyl-N^ɛ-lauroyl lysine (DMLL), including different inorganic electrolytes (NaCl, NaSCN, or CaCl₂). The dissolution temperatures of mixed surfactant systems are lower than those of pure surfactant solutions and become less than 0 C at a certain mole fraction of surfactants. As the concentration of NaCl increases, the dissolution temperatures of systems at a DMLL mole fraction lower than 0.4 increase, while those of systems at a ratio higher than 0.9 remain almost the same. With increasing concentration of NaSCN, the dissolution temperatures of systems at a DMLL mole fraction lower than 0.4 increase, while those of systems at a ratio higher than 0.9 decrease. For CaCl₂ systems, there exists a maximum in the dissolution temperature at a certain composition, because addition compound formation between anionic and zwitterionic surfactants occurs due to the presence of calcium ions.     

Electrospun carbon nanofiber web electrode: Supercapacitor behavior in various electrolytes

Carbon nanofibers (CNFs) draw great interest due to their noticeable mechanical, electrochemical, and physical properties. In this study, polyacrylonitrile‐based CNFs are obtained via electrospinning technique. Thermal oxidation and low temperature (950 °C) carbonization are applied to the electrospun web in order to achieve CNF. Through the process, Fourier transform infrared‐attenuated total reflectance spectroscopy and Raman spectroscopic results are investigated. The electrochemical properties of the self‐standing CNF webs are examined with electrochemical impedance spectroscopy and cyclic voltammetry. In addition, various electrolyte solutions are studied to investigate the capacitive behavior of CNF webs. Electrolyte type variation has a significant effect on the capacitance results and high capacitance values are achieved in aqueous solution. According to the differing electrolyte types, specific capacitance values (C_sp) are recorded between 204 and 149 F g^?1 where maximum specific capacitance is obtained in 0.5 M H₂SO₄ as 204 F g^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45723.     

Substitution of silver by various metal ions in modified AgI solid electrolytes

The substitution process of silver by various metals in RbAg₄I₅ and other solid electrolytes of the AgI-modified type has been investigated. This process is of technological interest since it permits the use of copper, zinc or cadmium instead of silver as anode materials in solid state batteries which utilize these electrolytes.     

Identification of the state of palladium in various hydrogenation catalysts by XPS

Various commercial supported palladium hydrogenation catalysts were studied by XPS and treated at ambient pressure with hydrogen and air. Unused catalysts exhibit a significant fraction of divalent Pd (oxide) which is reduced by hydrogen treatment at room temperature. Exposure to air in systems with carbonate, alumina, silica or active carbon as support causes the formation of a solid solution of oxygen in Pd characterized by a Pd 3d chemical shift of ca. + 0.4 eV. The absolute binding energy of Pd depends strongly on the matrix, indicating a significant contribution of extra-atomic screening, which prevents a direct comparison of reference samples and supported catalysts. Using the oxidation of CO to CO₂ at 300 K as in situ chemical probe it was confirmed that Pd supported on carbonate, silica and alumina exists in the same metallic state which could be activated for the test reaction irrespective of the variation in XPS binding energies.     

Suspension stability of solid particles in the presence of various types of electrolytes

Stabilities of titanium dioxide and ferric oxide suspensions in the presence of various types of electrolytes have been studied by measuring their sedimentation volume, rate of sedimentation and optical absorption as a measure of the degree of suspension. The stabilizing ability in suspensions with condensed phosphates is relatively high as compared with that with electrolytes other than the phosphates. This would indicate strong adsorption of phosphate ions onto the surface of the particle. A correlation is found between the extent of stability of a suspension and the electrophoretic mobility of the particle suspended in electrolyte solution, except with silicates. With polyphosphates (Na_n+2P_nO_3n+1) the stabilizing effect is noticeable at n≥2, while with metaphosphates (Na_nP_nO_3n) it becomes noticeable and constant at n≥4. The stabilities of titanium dioxide and ferric oxide suspensions containing silicates are high in spite of low electrophoretic mobilities of their suspended particles, which are comparable with the stability operated by tripolyphosphate or a typical dispersing agent. The suspension stability data of acid and neutral condensed phosphates and of the electrolytes used commonly as builders in the presence of a surfactant have also been included.     

Toluene combustion over palladium supported on various metal oxide supports

Metal–support interaction in the catalytic combustion of toluene was studied using metal oxides with different acid–base properties as supports for Pd. The catalytic performance was correlated with XPS data and the reaction order for oxygen. These studies revealed that the affinity for oxygen of Pd surface changed according to the acid–base character of metal oxide over MgO, Al₂O₃, SiO₂, SnO₂, Nb₂O₅, and WO₃. However, ZrO₂ exhibited exceptional character in that metal Pd was unusually stabilized, which was derived from the weak interaction between Pd and support surface. The reason for high toluene combustion activity of Pd/ZrO₂ was ascribed to the stabilization of metal Pd on ZrO₂.     

Quantitation of the dissolution of battery-grade copper foils in lithium-ion battery electrolytes by flame atomic absorption spectroscopy

Atomic absorption spectroscopy (AAS) was shown to be an effective method to quantitatively evaluate the stability of battery-grade copper foils in lithium-ion battery electrolytes at open-circuit. The results showed that copper stability was different between “fresh” electrolyte and electrolytes that had been “aged” for 6 months. In the “fresh” electrolyte, the copper foils showed a small amount of dissolution (up to ∼50 ppm) during their storage for up to 20 weeks. In the “aged” electrolyte, a large amount of copper dissolution (up to several hundred ppm) was found. The study showed that the condition of the electrolytes was critical to the stability of the copper foils.     

A fluorescence study on dissolution of polymeric glasses prepared in various molecular weights

Poly(methyl methacrylate) (PMMA) discs in various molecular weights, M_w, were prepared by free-radical polymerization of methyl methacrylate (MMA). Pyrene (P) was introduced during polymerization as a fluorescence probe to monitor the gelation and dissolution processes in chloroform vapor and solvent, respectively. In-situ steady state fluorescence (SSF) experiments were performed to monitor vapor uptake and chain desorption processes. Direct illumination of PMMA discs were performed to excite the P molecules embedded inside the PMMA glass. Variation in P intensity, I, was monitored during the swelling of the PMMA material exposed to chloroform vapor. It was observed that PMMA film swells like a crosslinked polymeric gel at early times by obeying the Li-Tanaka equation. Swelling time constants, τ_c, of PMMA discs were measured and found to have a strong correlation with the molecular weight, of PMMA. In a separate experiment, when the PMMA discs were in chloroform, desorption of PMMA chains from glass discs was monitored by observing the change of pyrene fluorescence intensity. A diffusion model with a moving boundary was employed to quantify the fluorescence data observed from dissolving PMMA discs made at various molecular weights. It was observed that desorption coefficient, D, decreased by increasing M_w by obeying the D≈M_w ⁻¹ law. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, New Orleans, LA. Department of Physics, 80626 Maslak, Istanbul. Turkey.