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.     

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.     

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.     

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.     

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     

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.     

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.     

Synthesis and Properties of a Novel Branched Polyether Surfactant

A novel branched polyether surfactant (TPE) was prepared by anion polymerization with different proportions of propylene oxide (PO) and ethylene oxide (EO) using 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane as a core. The structures and average molecular weight (M _n ) of the TPE were characterized by ¹H NMR and GPC. The cloud point was determined by turbidimetry in the presence of inorganic salts. Inorganic salts decreased the cloud point of TPE polyether in the following order: Na₂CO₃ > Na₂SO₄ > NaCl > CaCl₂ > MgCl₂. The effects of inorganic salts (NaCl, MgCl₂, CaCl₂, and NaSCN) and temperature on the surface activity of TPE in aqueous solution were investigated by surface tension measurements. The surface activity parameters and the thermodynamic parameters were calculated from surface tension data. Similar to the effect of increasing temperature, the salting-out inorganic salts such as NaCl, MgCl₂, and CaCl₂ favor the micellization and increase the maximum surface excess concentration, while the salting-in NaSCN has the opposite effect. The influence of NaCl on the morphology of micelles was investigated by TEM. The micellization is entropy-driven at low temperature and enthalpy-driven at higher temperature. The TPE polyether has large surface activity and can be used as a demulsifier to break up crude oil emulsions.     

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.     

Formation of anodic films on sputtering-deposited Al-Hf alloys

The growth of barrier-type anodic films at high efficiency on a range of sputtering-deposited Al-Hf alloys, containing from 1 to 95 at.% Hf, has been investigated in ammonium pentaborate electrolyte. The alloys encompassed nanocrystalline and amorphous structures, the latter being produced for alloys containing from 26 to 61 at.% Hf. Except at the highest hafnium content, the films were amorphous and contained units of HfO₂ and Al₂O₃ distributed relatively uniformly through the film thickness. Boron species were confined to outer regions of the films. The boron distributions suggest that the cation transport number decreases progressively with increasing hafnium concentration in the films, from ∼0.4 in anodic alumina to ∼0.2 for a film on an Al-61 at.% Hf alloy. The distributions of Al³⁺ and Hf⁴⁺ ions in the films indicate their similar migration rates, which correlates with the similarity of the energies of Al³⁺-O²⁻ and Hf⁴⁺-O²⁻ bonds. For an alloy containing ∼95 at.% Hf, the film was largely nanocrystalline, with a thin layer of amorphous oxide, of non-uniform thickness, at the film surface. The formation ratios for the films on the alloys changed approximately in proportion to the hafnium content of the films between the values for anodic alumina and anodic hafnia, ∼1.2 and 1.8 nm V⁻¹ respectively.     

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%.     

Electrical instability of composite aluminum oxide films

Composite films of hydrous + anodic Al₂O₃ have the peculiar property of losing field strength after anodization. After some time on open circuit a film that had supported several hundred volts will suddenly sustain no more than 10–20 V. A “reformation” to the original voltage brings the film to a stable state. Properties of this instability are described here. It is shown to result from diffusion of water into internal voids within the barrier oxide layer. The voids become filled with anodic oxide during the reformation.     

The Conductivity of Poly(o-anisidine), Poly(o-toluidine) and Their Copolymer with Various Inorganic Dopants in the Presence of Electrolyte

ABSTRACT

An attempt has been made to prepare poly(o-anisidine) (POA), poly(o-toluidine) (POT) and copolymer poly(o-anisidine)-co-poly(o-toluidine) (POA-co-POT) thin films dopped by several inorganic salts (sulphates and chlorides) with varying size of cations using aqueous solution of H₂SO₄ as electrolyte. The effect of dopant in the presence of electrolyte is rarely studied in the field of conducting polymers. Various inorganic salts as dopants, namely, K₂SO₄, Na₂SO₄, Li₂SO₄, MgSO₄, KCl, NaCl, LiCl, and MgCl₂ are used at room temperature. The films were electropolymerized in solution containing 0.1 M monomer(s), 1 M H₂SO₄ as electrolyte and 1 M inorganic salt, by applying sequential linear potential scan rate 50 mV/sbetween ? 0.2 to 1.0 V versus Ag/AgCl electrode. The electro-synthesized films were characterized by cyclic voltammetry, UV-visible spectroscopy, and conductivity measurements. It was observed that the UV-visible peaks usually appearing at about 802–826 nm with a shoulder at 410–426 nm shows a shift in presence of doping salt for emeraldine salt (ES) phase of POA, POT, POA-co-POT. In overall study, a significant increase in conductivity is observed for all mentioned dopants and among these K₂SO₄ is found to be the best in sulphate category and KCl in chloride category. The formation of copolymer has been confirmed by differential scanning calorimetry.     

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.     

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.     

Development and application of a holistic model for the steady state growth of porous anodic alumina films

A holistic model was developed and applied to anodic alumina films galvanostatically grown in sulphuric acid solution at different anodising conditions thus characterised by different structural characteristics. The O²⁻ and Al³⁺ species transport numbers near the metal|oxide interface were determined that depended on both temperature and current density. The rate of film thickness growth was found to be proportional to the O²⁻ anionic current through the barrier layer near the metal|oxide interface. The results introduced a new growth mechanism theory embracing the rarefaction of barrier layer oxide lattice towards the metal|oxide interface. The oxide density near the metal|oxide is closely independent of anodising conditions and is related to the transformation of Al lattice to a transient oxide lattice about 37% rarer than that of γ-Al₂O₃ that is further suitably transformed to denser, amorphous or nanocrystalline material as this oxide is shifted to the oxide|electrolyte interface and becomes the pore wall material. This gradual lattice density variability can explain many peculiar properties of anodic alumina films.     

Sulphate-based solid electrolytes: properties and applications

Sulphate-based solid electrolytes can have conductivities as high as 3 (Ω cm)^?1, as is the case in pure Li₂SO₄ at a temperature of 800°C. For binary systems highly conducting phases can be found down to at least 415°C. If additional components are added conductivities exceeding 10^?3 (Ω cm)^?1 can be obtained at room temperature.The conductivity is due to cation mobility and, in contrast to other solid electrolytes such as beta-alumina and AgI-based double salts, both mono- and divalent cations are mobile.Phase diagrams for the systems containing Li₂SO₄ combined with Na₂SO₄, K₂SO₄, Rb₂SO₄, Cs₂SO₄, MgSO₄, CaSO₄, and ZnSO₄ have been constructed. A number of galvanic cells using anodes made from Mg, Ca, and Zn have been tested at elevated temperatures. A Mg|Li_1.72Mg_0.14SO₄|MnO₂ cell gave an open-circuit voltage of 2.3 V and a power density of 400 W/kg at 745°C. Ag|electrolyte|I₂ cells have been tested at room temperature.     

Metal salts interaction with acrylic acid–maleic acid copolymer: An infrared spectroscopic study

A study was carried out in which aqueous solutions of acrylic acid–maleic acid copolymer (mole ratio of monomers: 3:2) were diluted with solutions of various salts [NaCl, MgCl₂, CaCl₂, SrCl₂, ZnCl₂, Al(NO₃)₃ and Fe(NO₃)₃]. This copolymer was found to interact with all these salts to make solutions of enhanced acidity that infrared spectroscopy suggested was a result of charge stabilization of the polyanion by counterions occupying atmospheric or site‐bound locations. The cations of the salts NaCl, MgCl₂, CaCl₂ and SrCl₂ appeared to occupy atmospheric positions only; in contrast, with poly(acrylic acid) they showed some site binding. Zinc ions, on the other hand, gave identical bridging bidentate interactions with both polymers. The cations from the trivalent salts Al(NO₃)₃ and Fe(NO₃)₃ were atmospheric and site bound (bridging bidentate), respectively, and these were also different from their interactions with poly(acrylic acid). The addition of Fe(NO₃)₃ to the copolymer caused gelation, as with poly(acrylic acid), but formation of the gel was slower and did not result in phase separation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1680–1684, 2000     

Surface functionalization of anodized tantalum with Mn3O4 nanoparticles for effective corrosion protection in simulated inflammatory condition

The study highlights the corrosion behavior of untreated and treated tantalum with addition of trimanganese tetraoxide (Mn₃O₄) nanoparticles in simulated inflammatory media. The anodic layer was produced on pure tantalum by anodization in electrolytes composed of ammonium fluoride, ethylene glycol, and water. Nanoparticles were deposited uniformly on the surface of the anodized tantalum with the electrophoretic deposition (EPD) method. The results revealed that the anodic/EPD coating possessed more compact microstructure and higher bond strength than the anodic coating. Simulated inflammatory medium was based on phosphate-buffered saline with additions of H₂O₂ and HCl. Potentiodynamic polarization and electrochemical impedance spectroscopy studies showed that the anodic and Mn₃O₄ layers protected the tantalum from corroding in an acidic inflammatory condition. Finally, the corrosion protection mechanism of Mn₃O₄ NPs in inflammatory condition was presented.