Cathodic electrodeposition of mixed molybdenum tungsten oxides from peroxo-polymolybdotungstate solutions

Mixed molybdenum tungsten trioxide films of varying stoichiometry (MoxW1 - xO3, 0 < x < 1) were prepared by cathodic electrodeposition on indium tin oxide (ITO)-coated glass substrates from aqueous peroxo-polymolybdotungstate solutions. Electrochemical quartz crystal microbalance (EQCM), cyclic voltammetry, and chronocoulometry were used to gain insight into the electrodeposition mechanism. The compositional and structural properties were characterized for MoxW1 - xO3 films deposited at intermediate potentials (-0.35 V vs Ag/AgCl) and sintered at 250 degrees C using energy-dispersive spectroscopy, X-ray diffraction, and Raman spectroscopy. These studies reveal that films consist of homogeneously mixed MoxW1 - xO3, with an enriched Mo content ranging in composition from 0.4 < x < 0.7 depending upon the mol % Mo present in the deposition solution. Chronoamperometry and spectroelectrochemical measurements were conducted to estimate lithium ion diffusion coefficients and coloration efficiencies for the mixed metal oxide films in 1 M LiClO4/propylene carbonate. The subtle interplay between structural and compositional properties due to the uniform mixing of Mo and W oxide components shows that electrochromic and lithium ion transport properties are moderately enhanced relative to those of single-component WO3 and MoO3 and demonstrate improved structural stability over pure MoO3 polymorphs during electrochemical cycling.     

Fundamental aspects of electrocatalysis

A theory for electrochemical electron transfer is proposed which explicitly accounts for the electronic structure of the electrode; it applies both to simple and to bond-breaking reactions. Interactions with narrow d-bands lead to changes in the local density of states of the reactant as its electronic level fluctuates due to solvent reorganization. More importantly, it can significantly reduce activation barriers, and in extreme cases induce dissociative adsorption. The model gives some justification to recent suggestions that the center of the d-band is a key factor for electrocatalysis, and it offers a route for calculating reaction rates using results from ab initio calculations as input.     

Low-dimensional manifolds in reaction-diffusion equations. 1. Fundamental aspects

The approach to equilibrium for systems of reaction-diffusion equations on bounded domains is studied geometrically. It is shown that equilibrium is approached via low-dimensional manifolds in the infinite-dimensional function space for these dissipative, parabolic systems. The fundamental aspects of this process are mapped out in some detail for single species cases and for two-species cases where there is an exact solution. It is shown how the manifolds reduce the dimensionality of the system from infinite dimensions to only a few dimensions.     

Cathodic electrodeposition of CdMn2O4 nanoplates and evaluation of the charge storage ability

Journal of Solid State Electrochemistry - The present work describes a facile route for the synthesis of CdMn2O4 nanoplates. The nanoplates were synthesized by cathodic electrogeneration of base...     

Cathodic electrodeposition and characterization of nanostructured Y2O3 from nitrate solution. Part I: Effect of current density

Particle, plate and flaky-like nanostructures of Y(OH)₃ and Y₂O₃ were prepared via cathodic electrodeposition from nitrate bath by applying different current densities. In the first step, yttrium hydroxide precursors were cathodically grown on the cathode surface at the current densities of 2, 1, 0.5, 0.25 and 0.1 mA cm^?2. The obtained hydroxide powders were heat-treated at 600°C for 3 h. The products were characterized by means of carbon, hydrogen and nitrogen (CHN), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and FT-IR spectroscopy. From the CHN, XRD and TG results, the mechanism of base electro generation at the applied conditions and the intercalation of nitrate ions in the deposit structure were proposed and confirmed. The results showed that the structural and morphological properties of the products are directly determined by the applied current density and it can be recognized as a main factor affecting in the cathodic electrodeposition of Y₂O₃.     

Cathodic chemistry of high performance Zr coated alkaline materials

A low level zirconia modification significantly stabilizes alternative higher energy cathodes under consideration to improve the energy storage capacity of alkaline batteries, and is demonstrated on materials including periodate, Fe(VI) "super-iron", manganese, nickel, bismuthate and silver oxide cathodes.     

Electrochemistry of proton-conducting ceramic materials and cells

Journal of Solid State Electrochemistry -     

Fundamental and engineering thermal aspects of energy and environment

Journal of Thermal Analysis and Calorimetry -     

Theory of damped quantum rotation in NMR spectra. I. Fundamental aspects

The damped quantum rotation (DQR) theory, formulated originally for methyl-like atomic groupings, is now extended to hindered (N>3)-fold molecular rotors, such as the cyclopentadienyl, benzene, and cycloheptatrienyl rings in solid phase environments. It heightens the significance of the Pauli principle in shaping up the stochastic dynamics of such objects, reflected in NMR line shapes. The corresponding NMR line-shape equation is derived; its stochastic part is shown for the first time to have the double commutator form for any values of the quantum-mechanical (coherence-damping) rate constants entering it. Constraints on the relative magnitudes of such constants are determined under which the DQR line-shape equation is converted into the phenomenological Alexander-Binsch equation describing classical jumps of the rotor. When all the quantum rate constants happen to be equal, the phenomenological model of equal jump rates between any two of the N (equivalent) orientations of the rotor is reproduced. On the other hand, the seemingly most plausible (for N>3) nearest-neighbor hopping model does not have any peculiar grounds in the DQR approach. For the special instances of stochastic molecular motions addressed in this work, the extended DQR formalism affords a quantification of the "degree of classicality" represented by a complete set of the relevant quantum rate constants. In view of our earlier experimental findings for the methyl rotors, the very occurrence of the nonclassical DQR effects seems unquestionable even for the objects of the size of benzene. The question of under what circumstances such effects can be big enough to be detected experimentally will be addressed in Part II of this work.     

Fundamental aspects of rubber-elasticity in real networks

Based on the van der Waals-equation of state a characterization of the elastic properties of molecular networks in the total range of strain is presented by the use of Mooney-Rivlin plots. This discussion elucidates the importance of finite chain extensibility as well as global interactions for a quantitative interpretation of the deformation properties of molecular networks. An interpretation of the so-called Mooney-Rivlin coefficients in terms of the van der Waals-parameters delivers at least a novel, yet very consistent understanding of simple extension of swollen networks.     

Fundamental aspects and applications of glow discharge spectrometric techniques

Glow discharges are kind of plasmas which are used in many fields of application, including analytical spectrometry. This review addresses both the fundamental aspects and analytical applications of glow discharges. In the first part, a systematic overview of the most important plasma processes is presented. To obtain better insight into the complexity of the glow discharge, both mathematical modeling and experimental plasma diagnostics can be carried out. Therefore, the models that were developed for a glow discharge are presented and typical results (e.g. three-dimensional density profiles, fluxes and energy distributions of the various plasma species, the electric field and potential distributions, information about collision processes in the plasma and about sputtering at the cathode, etc.) are summarized. Moreover, the most important plasma diagnostic techniques for glow discharges are discussed. In the second part, an overview is given of the various analytical applications of glow discharges.     

Fundamental aspects and applications of fourier-transform ion-cyclotron resonance spectrometry

The operating principles, features, advantages, applications and potential of Foourier-transform ion-cyclotron resonance (F.t./i.c.r. or F.t.m.s.) mass spectrometry are discussed. It is shown that F.t./i.c.r. technology creates a high-performance mass spectrometer with high speed, high sensitivity, ultrahigh mass resolution, very wide mass range and unparalleled versatility.     

Microanalytical investigation of fibre-reinforced ceramic materials

Summary Microanalytical investigations have been made on samples of ceramic fibres (SiC fibres, (Nicalon) C fibre coated with TiN) and fibre-reinforced ceramics (SiC- and glass-matrices). High resolution Auger electron spectroscopy (HRAES), electron probe microanalysis (EPMA) and scanning electron microscopy were employed for these examinations. Analysis was best performed with HRAES on account of its lateral and depth resolution. Some of the problems involved in this technique are discussed e.g. electron beam effects. AES depth profiles of ceramic fibres are reported and compared with the surface analysis of fibres in the composites after being broken in situ.

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Mikroanalytische Untersuchungen faserverstärkter keramischer Werkstoffe

     

Fundamental aspects of oxidation of electroexplosive nickel nanopowder

Fundamental aspects of the process in which a nickel nanopowder produced by an electric explosion of conductors is oxidized under heating in air at a linearly increasing temperature and in the isothermal mode were studied. It is shown that the dispersion composition of the powder, structure of the metallic core of nickel particles, and characteristics of the oxide shell affect the kinetic parameters of the process. An explanation is suggested for specific features of the macrokinetic reaction mode caused by the joint influence exerted by the relative amounts of fractions of different-size particles in the powder and by the characteristic of the oxide layer. The reaction kinetics is simulated, with the size distribution function of nickel particles taken into account.     

The electrodeposition of thorium in natural materials for alpha spectrometry

A technique has been developed for the electrodeposition of thorium on stainless stell planchettes following standard radiochemical separation and uptake in acetate buffer. The method has been used on over 130 samples including calcrete, clay, granite and shell matrices. To assess the efficiency at ultra low levels, three solutions of carrier free²²⁸Th (<1.5–10⁻⁷ μg in 5 ml electrolyte) and four solutions of²²⁹Th (4.4–10⁻⁴ μg in 5 ml) were studied. The efficiencies of the former avaregad 66 per cent; those of the²²⁹Th varied from 41 to 91%.     

Microbeam analysis of irradiated materials: practical aspects.

Among the microanalytical techniques, electron probe microanalysis (EPMA) is one of the most powerful. Its performances can be used to provide an accurate characterization. In the present article the differences between the EPMA of highly irradiated materials and standard EPMA are highlighted. It focuses on the shielded EPMA specificities. Then, the article presents the difficulties encountered during the sample preparation and the analysis (mainly due to the radioactive background). In spite of these difficulties, some valuable results can be provided by a shielded EPMA on the in-pile behavior of nuclear irradiated fuel. Some results of specific examples analyzed by EPMA in nuclear fuel research are presented.     

Fundamental aspects of chiral separations by capillary electrophoresis

A review is presented that surveys the basic theory of direct separation of enantiomers by capillary electrophoretic (CE) techniques. These separations are based on the formation of diastereomeric complexes between the enantiomeric analytes and a chiral selector added to the electrolyte solution. The review covers a comprehensive treatment of the equations needed for optimization of selectivity coefficients, resolution and analysis time in the zone electrophoretic mode. In this context, it takes into account combined equilibria of complexation and protonation/deprotonation as well as complexation and paritition into micelles. On the basis of these equations, the benefits of charged selectors and the optimization potential inherent to pH tuning can be documented. In addition, the review deals with some basic aspects of chiral isoelectric focusing and briefly discusses indirect enantioseparation. In a subsequent section a survey is given on particularfeatures of the various types of chiral selectors. Finally, the recent developments in preparative enantioseparation in continuous free-flow system and by use of isoelectric membranes are discussed.     

Fundamental aspects of electrospray droplet impact/SIMS

A new ionization method, electrospray droplet impact ionization (EDI), has been developed for matrix-free secondary-ion mass spectrometry (SIMS). The charged droplets formed by electrospraying 1 M acetic acid aqueous solution are sampled through an orifice with a diameter of 400 microm into the first vacuum chamber, transported into a quadrupole ion guide, and accelerated by 10 kV after exiting the ion guide. The droplets impact on a dry solid sample (no matrix used) deposited on a stainless steel substrate. The secondary ions formed by the impact are transported to a second quadrupole ion guide and mass-analyzed by an orthogonal time-of-flight mass spectrometer (TOF-MS). Ten pmol of gramicidin S could be detected with the presence of as much as 10 nmol of NaCl. The ion signal for arginine disappeared with decrease in the substrate temperature below 150 K owing to the formation of ice film over the sample surface. While 10 fmol of gramicidin S could be detected for 30 min, the ionization/desorption efficiency for EDI becomes smaller with an increase in the molecular weight (MW) of a biological sample. The largest protein samples detected to date are cytochrome c and lysozyme. The high sensitivity for EDI is due to the fact that samples only a few monolayers thick are subject to desorption/ionization by EDI, with little fragmentation. A coherent phonon excitation may be the main mechanism for the desorption/ionization of the solid sample.     

Fundamental comparison between non-equilibrium aspects of ICP and MIP discharges

A characterization theory is constructed to relate external control parameters to averaged values of internal plasma properties. It is based on a study on the effect of transport fluxes on elementary balances. This theory is used to compare the inductively coupled plasma (ICP) with the TIA (`torche a injection axiale', a microwave plasma) and to predict properties of He plasmas. The theory is validated by means of laser experiments on the ICP and TIA. Thomson (TS), Rayleigh (RyS) and Raman (RnS) scattering are used to get insight into spatially resolved plasma parameters. TS gives the electron number density and temperature, whereas the combination of RyS and RnS provides the densities of (entrained) air molecules and argon atoms (main gas). In particular, the influence of steep gradients and the air entrainment turn out to be of crucial importance for those situations in which the characterization theory does not properly predict the values of plasma parameters.