Anodic oxides structure

Berger S, Tsuchiya H, Schmuki P (2008) Transition from nanopores to nanotubes self-ordered anodic oxide structures on titanium—aluminides. Chem Mater 20(10) 3245-3247... 

Peroxodisulfuric acid, H2S2O8, is a colourless solid mp 65° (with decomposition). The acid is soluble in water in all proportions and its most important salts, (NH4)2S208 and K2S2O8, are also freely soluble. These salts are, in fact, easier to prepare than the acid and both are made on an industrial scale by anodic oxidation of the corresponding sulfates under carefully controlled conditions (high current density, T < 30°, bright Pt electrodes, protected cathode). The structure of the peroxo-disulfate ion [now preferably called hexaoxo-/r-peroxodisulfate(2-)]0 l is OaSOOSOa " with... 

Less important oxides are Ag203, obtained impure by extended anodic oxidation of silver, and Ag30, obtained hydrothermally from Ag/AgO at 80°C, 4000 bar, which is a metallic conductor with the anti-BiI3 structure containing an hep array of silvers with oxide ions occupying 2/3 of the octahedral holes [32]. 

The conformational changes are stimulated by cathodic compaction of the structure, by anodic oxidation and swelling, or, in absence of any external electric field, by thermal energy.177,178,188 In any case, they are a combination of the polymer-solvent interactions. So A can be expressed as a sum of three terms... 

Carboxylic acids can be converted by anodic oxidation into radicals and/or carbo-cations. The procedure is simple, an undivided beaker-type cell to perform the reaction, current control, and usually methanol as solvent is sufficient. A scale up is fairly easy and the yields are generally good. The pathway towards either radicals or carbocations can be efficiently controlled by the reaction conditions (electrode material, solvent, additives) and the structure of the carboxylic acids. A broad variety of starting compounds is easily and inexpensively available from natural and petrochemical sources, or by highly developed procedures for the synthesis of carboxylic acids. 

For this version, the micro structured AlMg3 platelets were coated with silver by CVD in [43], In [44], the platelets were either totally made of silver (as constmction material) or of AlMg3 and then coated by PVD with silver. In the latter version, two sub-versions were made with and without anodic oxidation to a generate nano-porous surface structure. 

GP 1] [R 1] A comparison of four micro reactors with different Pt loadings (Pt impregnated on anodically oxidized alumina support) and different Pt structures confirmed that cluster size has an impact on the single Pt-atom activity (6 vol.-% NHj, 88 vol.-% O2, balance He 0.51 ms 260-380 °C) [28, 98]. At low Pt loadings, isolated atoms are formed. Calculated ammonia consumption rates amount to 20 s at 300 °C. At high Pt loadings, clusters are formed. Turn over frequencies (TOP) of about 40 s are determined. 

A nanoporous structure on the surface of the micro channels can be realized via anodic oxidation, thereby considerably enlarging the catalyst surface [17]. Catalysts... 

The surface of the micro channels was anodically oxidized to create a pore structure and thereafter wet-chemically impregnated [61]. The liquid reaction solution was fed by an HPLC pump hydrogen was metered by a mass-flow controller. Pressure was kept constant... 

Arenz M, Stamenkovic V, Blizanac BB, Mayrhofer KJJ, Markovic NM, Ross PN. 2005. Carbon-supported Pt-Sn electrocatalysts for the anodic oxidation of H2, CO, and H2/CO mixtures. Part 11 The structure-activity relationship. J Catal 232 402-410. 

Anodic oxidation often involves the formation of films on the surface, i.e. of a solid phase formed of salts or complexes of the metals with solution components. They often appear in the potential region where the electrode, covered with the oxidation product, can function as an electrode of the second kind. Under these conditions the films are thermodynamically stable. On the other hand, films are sometimes formed which in view of their solubility product and the pH of the solution should not be stable. These films are stabilized by their structure or by the influence of surface forces at the interface. 

In addition to the stoichiometry of the anodic oxide the knowledge about electronic and band structure properties is of importance for the understanding of electrochemical reactions and in situ optical data. As has been described above, valence band spectroscopy, preferably performed using UPS, provides information about the distribution of the density of electronic states close to the Fermi level and about the position of the valence band with respect to the Fermi level in the case of semiconductors. The UPS data for an anodic oxide film on a gold electrode in Fig. 17 clearly proves the semiconducting properties of the oxide with a band gap of roughly 1.6 eV (assuming n-type behaviour). 

Raja KS, Misra M, Paramguru K (2005) Formation of self-ordered nano-tubular structure of anodic oxide layer of titanium. Electrochim Acta 51 154—165... 

A vast body of literature tackles the different aspects of anodic oxidation, including the growth, structure, morphology, and proper-... 

An analogous expression assuming space charge effects and the double layer structure of the anodic oxide has been obtained by Goruk et al.5 and Bray.57... 

The true role of incorporation of anions in the formation of anodic alumina is being intensively discussed. Baker and Pearson183 have considered the anion effect in modifying the structure of anodic oxides to be due to the coordinative ability of anions to replace alumina tetrahedra in the body of the oxides. Dorsey184,185 has postulated that in porous oxides, anions stabilize the network of alumina tetrahedra and octahedra. 

According to El-Mashri et al.,190 the A106 A104 ratio determines the hydration capacity of anodic oxides. Tetrahedral sites are hydrated easily to form a boehmite-like structure, which is known to be composed of double layers of Al-centered octahedra, weakly linked by water molecules to other layers.184 As the oxide formed in H3P04 contains about 70% tetrahedral aluminum bonds, its hydration ability should be higher than that of the oxide formed in tartrate solution. However, this has not been found in practice, which is interpreted by El-Mashri et al. as being due to some reduction of A104 by incorporated phosphate species. 

A group of scientists have studied current transients in biased M-O-M structures.271,300 The general behavior of such a system may be described by classic theoretical work.268,302 However, the specific behavior of current transients in anodic oxides made it necessary to develop a special model for nonsteady current flow applicable to this case. Aris and Lewis have put forward an assumption that current transients in anodic oxides are due to carrier trapping and release in the two systems of localized states (shallow and deep traps) associated with oxygen vacancies and/or incorporated impurities.301 This approach was further supported by others,271,279 and it generally resembles the oxide band structure theoretically modeled by Parkhutik and Shershulskii62 (see. Fig. 37). 

If measurements are made in thin oxide films (of thickness less than 5 nm), at highly polished Al, within a small acceptance angle (a < 5°), well-defined additional maxima and minima in excitation (PL) and emission (PL and EL) spectra appear.322 This structure has been explained as a result of interference between monochromatic electromagnetic waves passing directly through the oxide film and EM waves reflected from the Al surface. In a series of papers,318-320 this effect has been explored as a means for precise determination of anodic oxide film thickness (or growth rate), refractive index, porosity, mean range of electron avalanches, transport numbers, etc. 

It is to be expected that a more profound investigation of EL and PL can give important information concerning electronic structure of anodic oxide films. 

The appearance of oxidation peaks in the CV is a direct evidence of PF f and BF 7 anions incorporation within the SWNT structure. The macromolecule Cn should then bear a positive charge as a result of subsequent oxidation following. In the case of PF 7 the anodic oxidation is ... 

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