ELECTRICAL CONDUCTIVITIES OF SOME METAL SALT FILMS UNDER ANODIC CONDITIONS

Recently determined electrical conductivities of anodic AgCl, A1C1₃, TiBr₄, and MgCl₂ films are compared to well established conductivities of anodic Ta₂O₅; and A1₂O₃. All of these films exhibit high-field barrier layer condition. The exponential constant, β. is about the same value for the salts as for oxides but the preexponential constants and conductivities are orders of magnitude larger for the salts. The salts, AlCl₃, TiBr₄, and MgCl₂, in addition, have a series ohmic resistance which is attributed to an outer, continuously-forming and dissolving, hydrated salt layer.     

ELECTRICAL CONDUCTIVITIES OF SOME METAL SALT FILMS UNDER ANODIC CONDITIONS

Recently determined electrical conductivities of anodic AgCl, AlCl₃, TiBr₄, and MgCl₂ films are compared to well established conductivities of anodic Ta₂O₅ and Al₂O₃. All of these films exhibit high-field barrier layer condition. The exponential constant, β is about the same value for the salts as for oxides but the preexponential constants and conductivities are orders of magnitude larger for the salts. The salts, AlCl₃, TiBr₄, and MgCl₂, in addition, have a series ohmic resistance which is attributed to an outer, continuously-forming and dissolving, hydrated salt layer.     

THE EFFECT OF PRESSURE ON AZEOTROPES

Recently determined electrical conductivities of anodic AgCl, A1C1₃, TiBr₄, and MgCl₂ films are compared to well established conductivities of anodic Ta₂O₅; and A1₂O₃. All of these films exhibit high-field barrier layer condition. The exponential constant, β. is about the same value for the salts as for oxides but the preexponential constants and conductivities are orders of magnitude larger for the salts. The salts, AlCl₃, TiBr₄, and MgCl₂, in addition, have a series ohmic resistance which is attributed to an outer, continuously-forming and dissolving, hydrated salt layer.     

A practical approach to produce Mg‐Al spinel based on the modeling of phase equilibria for NH4Cl‐MgCl2‐AlCl3‐H2O system

Based on chemical modeling of phase equilibria for the NH₄Cl‐MgCl₂‐AlCl₃‐H₂O system, a practical approach to produce Mg‐Al spinel (MgAl₂O₄) (widely used as refractory brick, supports in catalysts, and inert material for oxygen carriers) is proposed and proven feasible. This novel process includes coprecipitation of Mg₄Al₂(OH)₁₄·3H₂O from the NH₃‐MgCl₂‐AlCl₃‐H₂O system; calcination of Mg₄Al₂(OH)₁₄·3H₂O to obtain Mg‐Al spinel and recovery of NH₄Cl from NH₄Cl‐rich solutions by feeding MgCl₂‐AlCl₃. A MSMPR reactor was applied to investigate the effect of temperature, feed concentration, and NH₄Cl addition on coprecipitation of precursor Mg₄Al₂(OH)₁₄·3H₂O from MgCl₂‐AlCl₃ solutions with Mg/Al ratio = 2 through gradual addition of NH₄OH. The phase equilibria of the NH₄Cl‐MgCl₂‐AlCl₃‐H₂O system were determined over the temperature range 283.2 to 363.2 K using dynamic method. The experimental solubilities were regressed to obtain new Bromley‐Zemaitis model parameters. These newly obtained parameters were verified by predicting the quaternary system. A chemical model for the NH₄Cl‐MgCl₂‐AlCl₃‐H₂O system has been established with the OLI platform. All the results generated from this study will provide the theoretical basis for Mg‐Al spinel production. The high quality Mg‐Al spinel was prepared by calcination of precursor from 773.2 to 1273.2 K, and the NH₄Cl was successfully recovered through the common ion effect of MgCl₂‐AlCl₃ addition. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1855–1867, 2013     

Molecular weight distribution of polyethylene catalyzed by Ziegler–Natta catalyst supported on MgCl2 doped with AlCl3

Ti‐based Ziegler–Natta catalysts supported on MgCl₂ doped with AlCl₃ were prepared by the reaction of MgCl₂/AlCl₃–ethanol adduct with TiCl₄. No AlCl₃ crystallites were found in the AlCl₃‐doped catalysts by WAXD analysis, suggesting that AlCl₃/MgCl₂ solid solution was formed. The effect of doping on the catalyst performance in ethylene polymerization was investigated. The results showed that the catalysts based on AlCl₃‐doped MgCl₂ support exhibited a slightly higher activity than did the MgCl₂‐supported catalyst and the molecular weight distribution (MWD) of polyethylene (PE) markedly increased (from 10.8 to 47.9) with the increase of AlCl₃ content in catalysts. The changes in catalyst's active center distribution were studied based on nonlinear fitting of the polymer GPC curves by multiple Flory functions. It was found that increase of types of active centers by introducing AlCl₃ into the support should be responsible for the broadening of MWD of PE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1768–1772, 2006     

Behavior of gas bubbles in aqueous electrolyte solutions

A system was investigated in which a swarm of air bubbles was dispersed in aqueous electrolyte solutions. the salts used were: NaCl, NaBr, NaI, Na₂SO₄, Na₃PO₄ LiCl, MgCl₂, MgSO₄, CaCl₂, AlCl₃ and Al₂(SO₄₃. The effects of the salts on the interfacial area of dispersion and on the oxygen transfer coefficient were investigated at various salt concentrations. The results showed a definite dependence of the surface area of dispersion on the valence of the ionic species and salt concentrations. A very satisfactory correlation was obtained for all the salts with the use of ionic strength as the correlating parameter. The mechanism of the coalescence-preventing action of the salts was discussed and explained on the basis of ion—water interactions. The oxygen mass transfer coefficient was found to be only slightly dependent on the presence of electrolytes in the range of concentrations used in this work. The importance and possible practical application of the results were briefly discussed.     

Amorphous-to-crystalline transition of silicon-incorporated anodic ZrO2 and improved dielectric properties

Sputter-deposited zirconium and Zr-16 at.% Si alloy have been anodized to various voltages at several formation voltages in 0.1 mol dm⁻³ ammonium pentaborate electrolyte at 298 K for 900 s. The resultant anodic films have been characterized using X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy, and electrochemical impedance spectroscopy. The anodic oxide films formed on Zr-16 at.% Si are amorphous up to 30 V, but the outer part of the anodic oxide films crystallizes at higher formation voltages. This is in contrast to the case of sputter-deposited zirconium, on which the crystalline anodic oxide films, composed mainly of monoclinic ZrO₂, are developed even at low formation voltages. The outer crystalline layer on the Zr-16 at.% Si consists of a high-temperature stable tetragonal phase of ZrO₂. Due to immobile nature of silicon species, silicon-free outermost layer is formed by simultaneous migrations of Zr⁴⁺ ions outwards and O²⁻ ions inwards. An intermediate crystalline oxide layer, in which silicon content is lower in comparison with that in the innermost layer, is developed at the boundary of the crystalline layer and amorphous layer. Capacitances of the anodic zirconium oxide are highly enhanced by incorporation of silicon due to reduced film thickness, even though the permittivity of anodic oxide decreases with silicon incorporation.     

Mechanically stable flat anodic titania membranes for gas transport applications

Anodic titanium oxide (ATO) membranes were produced by two-step anodic oxidation of titanium foil in ethylene glycol electrolyte containing NH₄F at the anodization voltage of 60?V. To provide the mechanical strength necessary for applying tubular anodic films as gas membranes, we utilized the formation of protective continuous TiO₂ layer at the top film surface prior to second anodization. As compared to conventional two-step anodic oxidation this technique decreases dissolution rates of titanium oxide phases with oxidation states lower than +4 (Ti₂O₃, Ti₃O₅), which are forming between titania nanotubes during anodization. The structural parameters of anodic titania films were determined by small-angle X-ray scattering and scanning electron microscopy techniques. According to SEM the proposed method resulted in growth of ATO films with a flat surface without nanotube endings, which enabled to use the films as gas separation membranes. The permeance of individual gases through ATO membranes were found to depend on gas molecular weight (M^?0.5), with absolute values twice exceeding theoretical permeabilities as it was predicted by Knudsen diffusion (up to 63?m³/(m²?×?bar?×?h) for nitrogen at 298?K). Here we ascribe this phenomenon to diffusion according to Knudsen-Smoluchoski mechanism (diffusion with slip, involving specular reflections of molecules), which is appropriate for membranes with straight pores and smooth internal pore surfaces.     

A new bath for the electrodeposition of aluminium. III. The electrochemical behaviour of the rotating aluminium disc electrode in pure AlCl3/THF-toluene solutions

The electrochemical behaviour of the rotating aluminium disc electrode in AlCl₃/tetrahydrofurantoluene solution was studied. The kinetic parameters controlling the electrode processes were investigated. The effect of the concentration of AlCl₃, the speed of rotation of the rotating disc electrode and the temperature on the cathodic and anodic current density was analysed. The results were compared with those for AlCl₃–LiAlH₄/THF-toluene solutions.     

Polyaniline Salts and Complexes as Catalyst in Bisindole Synthesis

Polyaniline salts are prepared by doping of polyaniline base with different Bronsted acids (H₂SO₄, HNO₃ and H₃PO₄), organic acid — p-toluene sulfonic acid (PTSA) and Iodine (I₂). Polyaniline complexes are also prepared using Lewis acids (BF₃, AlCl₃ and SnCl₂). Polyaniline salts and polyaniline complexes are characterized by physical, electrical and spectral methods. Polyaniline salts and polyaniline complexes are used as catalyst for the first time in bisindole synthesis. Bisindole (3,3′-bis(indolyl)phenylmethane) is obtained in excellent yields with simple and more environmental benign procedure. The use of polyaniline catalysts are feasible because of their easy preparation, easy handling, stability, easy recovery, reusability, good activity and eco-friendly.     

Anodic film growth on tantalum in dilute phosphoric acid solution at 20 and 85 °C

The effects of current density and temperature on the anodic films formed on tantalum in dilute H₃PO₄ (0.06%wt) solution have been studied by transmission electron microscopy, using ultramicrotomed sections, and Rutherford backscattering spectroscopy. Two-layered films have been identified, comprising an inner relatively pure Ta₂O₅ layer, adjacent to the metal/film interface, and an outer layer containing incorporated PO₄³⁻ anions. The total amount and depth of incorporated phosphorus species increase with increasing current density and decreasing temperature, in correspondence with the enhancement of the electric field. The formation conditions for the films include those relevant to the commercial anodising of tantalum for capacitors for which the extent of phosphorus incorporation is shown to be comparatively low.     

Role of indium in promoting anodic dissolution of Al-In alloys in non-aqueous electrolyte

Exploratory work on the anodic dissolution behaviour of aluminium and aluminium binary alloys in electrolytes in non-aqueous organic solvents is reported. Commonly used electrolytes for non-aqueous battery systems were selected on the basis of their conductivities and activities for anodic dissolution of Al and Al-alloy anodes. It is found that Al–In alloy electrodes exhibit an exceptionally active anodic dissolution behaviour in a 1 M solution of AlCl₃ in anhydrous acetonitrile. The steady-state Tafel polarization plots for dissolution of pure Al, Al–Sn, Al–Ga and Al–In alloy anodes are compared, and a.c. impedance spectra for an Al–In alloy anode in 1 M solution of AlCl₃ in CH₃CN are evaluated and discussed. The In component, like Ga or Hg, interferes with passivation of Al during its anodic dissolution and thus promotes an active condition on the metal surface leading to relatively high anodic dissolution current-densities at substantially negative electrode potentials.     

Characterization of polypyrrole films incorporating various anions

The conductivity of polypyrrole films has been enhanced by electrochemical post-deposition doping with various anions. The change of conductivity was found to depend on the type and concentration of the anion. Results for the polypyrrole films doped with anions of H₂SO₄, (C₂H₅)₄N(O₃SC₆H₄CH₃), KI, CH₃C₆H₄SO₃H · H₂O (p-toluene sulphonic acid monohydrate), AlCl₃, KBrO₃ and HNO₃ showed that in the case of H₂SO₄, (C₂H₅)₄ N(O₃SC₆H₄CH₃) and CH₃C₆ H₄SO₃ H · H₂O the conductivity can be enhanced by up to a factor of two, from a value of 67 S cm^–1 up to 165, 102 and 95 S cm^–1, respectively. Doping with I^– had a negligible effect on the conductivity which was about 71 S cm^–1, while in the case of AlCl₃, KBrO₃ and HNO₃ the conductivity of the polypyrrole decreased significantly for certain anion concentrations.     

Anodic film growth on Ru/Pt electrodes in HClO4 and HCl solutions

The voltammetric formation and potentiostatic growth of anodic films on Ru/Pt electrodes in HClO₄ and HCl solutions were studied by single negative potential sweeps and cathodic charging curves in the potential range from –0.25 to 1.1 V vs SCE. The growth of the anodic layer proceeds through the formation of two layers of different reduction reversibility. At potentials below 500 mV, the layer more reversibly reduced, grows slowly to a maximum coverage equivalent to one oxygen monolayer. The thicker, and more stable, layer increases with holding time to a maximum of about three oxygen monolayers during the period of time studied (7 h). At holding potentials above 500 mV, the reduction charge of the anodic layer reaches a constant value after polarization for 1 h. Growth starts with formation of two layers which, with time, become a single layer which is hardly reducible. The results suggest the eventual formation of anhydrous RuO₂, In HCl solutions, Cl^– adsorption inhibits the formation of the anodic layer, decreasing its growth rate but reaching no limiting thickness for 7 h. At holding potentials below 650 mV vs SCE, only a single layer is formed with slight structural changes. At potentials above 650 mV, the initially homogeneous film converts with holding time into a bilayer where the outer layer becomes hardly reducible. This layer is assumed to be a stable anionic hydroxy species (RuCl₅OH^2–) which dissolves as Ru₂O₂Cl₆(H₂O)^2–. In HClO₄ and HCl the layer growth follows a direct logarithmic law.     

Impact of dissolved wastewater constituents on peroxidase‐catalyzed treatment of phenol

The impact of dissolved wastewater constituents on the treatment of synthetic phenol solutions using horseradish peroxidase (HRP) and hydrogen peroxide was investigated under a variety of reaction conditions. The constituents studied included various inorganic salts, organic compounds and heavy metals. Higher H₂O₂ doses were required to treat phenol in the presence of sodium sulfite, thiosulfate and sulfide; however, enhanced levels of phenol conversion were achieved once sufficient H₂O₂ was supplied. Sulfide and cyanide inhibited phenol transformation. The inhibition of sulfide was overcome by supplying sufficient H₂O₂ to oxidize the sulfide to sulfur. However, increasing the H₂O₂ dose was ineffective in attempting to overcome the strong inhibiting effect of cyanide. Among the heavy metal ions tested, only Mn(II) substantially inhibited phenol removal when it was present at a concentration of 1 mmol dm^?3. The presence of inorganic salts including NaCl, CaCl₂, MgCl₂, NH₄Cl and (NH₄)₂SO₄ reduced phenol conversion as compared with the treatment in distilled‐deionized water. This can be attributed to the increased ionic strength of the solution. © 2002 Society of Chemical Industry     

Preparation and characterization of PbO2 electrodes doped with different rare earth oxides

PbO₂ electrodes doped with rare earth oxides (Re-PbO₂), including Er₂O₃, Gd₂O₃, La₂O₃ and CeO₂, were prepared by anodic codeposition in order to investigate the effect of rare earth oxide dopants on the properties of PbO₂ electrodes. The physicochemical properties of the Re-PbO₂ electrodes were analyzed by spectral methods and electrochemical measurements. The surface morphology of the Re-PbO₂ electrodes held the characteristics of the dopants and the crystal grain of PbO₂. The crystal structure of the PbO₂ electrodes was also influenced by doping with different rare earth oxides. The presence of Er₂O₃ and La₂O₃ in the PbO₂ films could enhance the direct anodic oxidation, which was helpful to mineralize 4-chlorophenol. The 4-chlorophenol decay on the Re-PbO₂ electrodes was analyzed and good fitting was found using the relation for the pseudo-first order reaction. Of the electrodes examined, the Er-PbO₂ electrode exhibited the best performance for the degradation of 4-chlorophenol. The removal rates of COD and 4-chlorophenol during the 9 h electrolysis at a current density of 20 mA cm⁻² were 80.7 and 100%, respectively, with the current efficiency being 16.0-10.1%.     

Ellipsometric measurements of the barrier layer in composite aluminum oxide films

The composite oxide film (hydrous + anodic) formed on aluminum foil was chemically stripped to remove only the outer hydrous layer. Ellipsometry of the remaining barrier film showed it to be thinner and have a higher refractive index than conventional anodic barrier films grown to the same voltage. Reanodization to improve film stability gave a further increase in refractive index which indicated that the barrier film had contained some voids. The barrier film is almost entirely crystalline γ-Al₂O₃ and the higher field strength compared with conventional amorphous anodic films on aluminum is believed to be a characteristic of the denser oxide.     

Reduced temperature-dependent thermal conductivity of magnetite thin films by controlling film thickness

We report on the out-of-plane thermal conductivities of epitaxial Fe₃O₄ thin films with thicknesses of 100, 300, and 400 nm, prepared using pulsed laser deposition (PLD) on SiO₂/Si substrates. The four-point probe three-omega (3-ω) method was used for thermal conductivity measurements of the Fe₃O₄ thin films in the temperature range of 20 to 300 K. By measuring the temperature-dependent thermal characteristics of the Fe₃O₄ thin films, we realized that their thermal conductivities significantly decreased with decreasing grain size and thickness of the films. The out-of-plane thermal conductivities of the Fe₃O₄ films were found to be in the range of 0.52 to 3.51 W/m · K at 300 K. For 100-nm film, we found that the thermal conductivity was as low as approximately 0.52 W/m · K, which was 1.7 to 11.5 order of magnitude lower than the thermal conductivity of bulk material at 300 K. Furthermore, we calculated the temperature dependence of the thermal conductivity of these Fe₃O₄ films using a simple theoretical Callaway model for comparison with the experimental data. We found that the Callaway model predictions agree reasonably with the experimental data. We then noticed that the thin film-based oxide materials could be efficient thermoelectric materials to achieve high performance in thermoelectric devices.     

Highly efficient supported AlCl3-based cationic catalysts to produce polyα-olefin oil base stocks

The main aim of this research is to decrease the amount of AlCl₃ content that is very corrosive and hazardous in the catalytic system, required for the α-olefin oligomerization without substantial change of final oil features. This was successfully achieved by supporting AlCl₃ on different carriers. More precisely, a series of supported bimetallic catalysts was synthesized by immobilization of AlCl₃ and TiCl₄ onto Al₂O₃, SiO₂, and mixed supports, that is, Al₂O₃/FeCl₃ and SiO₂/FeCl₃. It was found that silica and alumina-based catalysts had higher catalytic activities compared to support free AlCl₃; however, this enhancement for silica-based supports was more significant. According to gel permeation chromatography (GPC) results, the use of single supports, that is, Al₂O₃ and SiO₂, increased oligomer's molecular weight, while the application of mixed supports resulted in the decrease of molecular weight of the oligomers. Viscosity characteristics of the synthesized oligomers have also been studied at two different temperatures of 40 and 100°C (KV⁴⁰ and KV¹⁰⁰). The viscosity index (VI) values, derived from KV⁴⁰ and KV¹⁰⁰, of the prepared oligomers were in the range of 126–145. The molecular weight and termination mechanisms of the oligomers were studied by ¹H-NMR spectroscopy. The obtained results disclosed that the employed reaction conditions led to the production of oligomer chains with various structures including vinylidene (Vd), and di and three-substituted vinylene (2Vn, 3Vn) structures.     

Interfacial origin of enhanced energy density in SrTiO3-based nanocomposite films

SrTiO₃-based films doped with different Al-precursors were prepared by sol-gel methods and the dielectric strengths and leakage currents of the materials were investigated. The best performance was found in SrTiO₃ films doped with Al₂O₃ nanoparticles (nano-Al₂O₃). When 5 mol% of nano-Al₂O₃ was added to SrTiO₃ films with Al electrodes, the dielectric strength was enhanced to 506.9 MV/m compared with a value of 233.5 MV/m for SrTiO₃ films. The energy density of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films was 19.3 J/cm³, which was also far higher than that of the SrTiO₃ films (3.2 J/cm³). These results were attributed to interfacial anodic oxidation reactions, which were experimentally confirmed by cross-sectional transmission electron microscope studies and theoretically modelled based on Faraday's laws. The films with added nano-Al₂O₃ featured many conducting paths at the interfaces between the host phase and the guest nano-Al₂O₃, which promoted ion transport and contributed to the strong anodic oxidation reaction capability of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films.