Multiple-component oxides

One approach to the production of high-performance dielectrics relies on the use of mixed-metal, multiple-component oxides. These oxides provide convenient means for controlling the dielectric-constant breakdown-field product through incorporation of components that specifically contribute to performance via dielectric constant or breakdown. At the same time, the mixed materials can inhibit crystallization, resulting in deposition of amorphous films with extremely flat surfaces. Common candidates, base oxides for tuning these properties, are listed in Table 4.1. 

Note that the concentrations of additive oxides differ. No attempt has been made to scale this effect with additive concentration). This curious reduction effect is not easily understood but emphasizes the complex nature of the glasses including the possible cooperative involvement of the multiple components. Similarly complex phenomena might influence leaching behavior in the complex, multicomponent glasses of interest for radioactive waste storage. 

A wide variety of in situ techniques are available for the study of anodic hhns. These include reflectance, eUipsometry, X-ray reflectivity, and SXRD. X-ray reflectivity can be used to study thick surface layers up to 1000 A. The reflectance technique has been used to study oxide growth on metals, and it yields information on oxide thickness, roughness, and stoichiometry. It the only technique that can give information on buried metal-oxide interfaces. It is also possible to get information on duplex or multiple-layer oxide hhns or oxide hhns consisting of layers with different porosity. Films with thicknesses of anywhere from 10 to 1000 A can be studied. XAS can be used to study the chemistry of dilute components such as Cr in passive oxide hhns. 

STABREX is easier and simpler to use compared to any other oxidant available for industrial water treatment. The product is pumped directly from returnable transporters (PortaFeed Systems)17 with standard chemical feed equipment. Previously, the only practical ways to apply bromine were to oxidize bromide solutions on-site with chlorine in dual liquid feed systems, or with one of the solid organically-stabilized bromine products applied from sidestream erosion feeders. The former is cumbersome and complex, and the latter is prone to dusting and difficult to control. Other oxidants require complex handling and feed of toxic volatile gases, unstable liquids, multiple-component products, or reactive solids. Simplicity in use results in reduced risk to workers and to the environment. 

Vanadyl phosphates (VPO) and multiple component molybdate (MCM) are good examples of catalysts, and alpha alumina, amorphous silica and alumino-silicates are good examples of catalyst supports that can be fabricated in the form of 45 to 150 im diameter spray dried porous spheres with attrition resistance improved by a relatively thin peripheral layer rich in amorphous silica, amorphous alumina, or phosphorus oxides. The hard phase component or precursor is selected in each case so that it will not interfere with the catalytic performance of the catalyst. 

The metal sample on which the KMC algorithm operates can comprise a single or multiple components with one of the components having a substantially lower reversible potential than the others. Table 4.2 provides a list of reversible potentials for some oxidation-reduction reactions focused but are available in the literature. In general, while dissolution will proceed if an externally applied potential or local galvanic couple drives the potential of the sample above its reversible potential, selective dissolution will in general occur only for potentials that fall within the gap between the reversible potentials for the components of the alloy. 

The acid strength of Bronsted acid sites increased with Si/Al ratio. Tiimethylposphine oxide (TMPO) was adsorbed as a probe molecule from the gas phase to avoid solvent effects. The MAS NMR spectra of TMPO-adsorbed samples showed a line at <5 s 46 ppm, ascribed to physisorbed or weakly adsorbed TMPO and a group of signals between 80 and 50 ppm ascribed to TMPO adsorbed on Bronsted acid sites or chemisorbed species. The analysis of the spectra showed that the average P chemical shift of chemisorbed TMPO and consequently the acidic strength increased with the Si/Al ratio. The multiple components of the P MAS NMR spectra showed that there are several kinds of sites with different acid strength. The Si and Al MAS NMR spectra were also studied - Table 11. The A1 spectra showed the presence of extra-framework A1 as well as invisible Al. 

Bulk mixed metal oxide catalytic materials consist of multiple metal oxide components. Such mixed metal oxide catalysts find wide application as selective oxidation catalysts for the synthesis of chemical intermediates. For example, bulk iron-molybdate catalysts are employed in the selective oxidation of CH3OH to H2CO [122], bulk bismuth-molybdates are the catalysts of choice for selective oxidation of CH2=CHCH3 to acrolein (CH2=CHCHO) and its further oxidation to acrylic acid (CH2=CHCOOH) [123], selective ammoxidation of CH2=CHCH3 to acrylonitrile (CH2=CHCN) [123], and selective oxidation of linear CH3CH2CH2CH3 to cyclic maleic anhydride consisting of a flve-membered ring (four carbons and one O atom) [124]. The characterization of the surface... 

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