Silicate-based oxide

For optical applications, inorganic silicate-based oxide [2], non-oxide sulfide [3], and hybrid [4] and nanocomposite thin films [5] have been extensively studied, for passive or active optical components in integrated optical applications, including power splitters, Er " -dof>ed optical amplifiers for dense wavelength division multiplexer (DWDM) systems, and Au nanoparticle (NP)-doped optical sensors. However, sol-gel-derived materials may often differ from their melt-quenched analogues, even for the simple compoimd Si02- In these... 

Boron, oxide additives in silicate-based glasses, x-ray photomission spectroscopic spectra. 151/ Bridges... 

Sharp, Z.D. 1990 A laser-based microanalytical method for the in situ determination of oxygen isotope ratios of silicates and oxides. Geochimica et Cosmochimica Acta 54 1353-1357. 

C21-0078. The only important ore of mercury is cinnabar, HgS. In contrast, zinc is found in several ores, including sulfides, carbonates, silicates, and oxides. Explain these observations in terms of hard and soft acids and bases. 

With decreasing temperature, as we have seen, the intrinsic defect population decreases exponentially and, at low T, extrinsic disorder becomes dominant. Moreover, extrinsic disorder for oxygen-based minerals (such as silicates and oxides) is significantly alfected by the partial pressure of oxygen in the system (see section 4.4) and, in the region of intrinsic pressure, by the concentration of point impurities. In this new region, term Qj does not embody the enthalpy of defect formation, but simply the enthalpy of migration of the defect—i.e.,... 

There are, however, two limitations associated with preparation and application of zeolite based catalysts. First, hydrothermal syntheses Umit the extent to which zeolites can be tailored with respect to intended appUcation. Many recipes involving metals that are interesting in terms of catalysis lead to disruption of the balance needed for template-directed pore formation rather than phase separation that produces macroscopic domains of zeoUte and metal oxide without incorporating the metal into the zeohte. When this happens, the benefits of catalysis in confined chambers are lost. Second, hydrothermal synthesis of zeoHtic, silicate based soHds is also currently Hmited to microporous materials. While the wonderfully useful molecular sieving abihty is derived precisely from this property, it also Hmits the sizes of substrates that can access catalyst sites as weU as mass transfer rates of substrates and products to and from internal active sites. 

This acid-catalyzed cleavage of the glycosidic bonds is rather complex and often suffers from a lack of selectivity mainly due to side dehydration or recombination reactions of monosaccharides. In the existing literature, four different classes of solid catalysts are reported (1) cation-exchange resins, (2) siliceous-based materials, (3) metal oxides, and (4) sulfonated amorphous carbons. 

As compared to conventional petrochemicals, the significant hindrance of carbohydrates induces many diffusional limitations and activity of solid catalysts is obviously strictly governed by the accessibility of the catalytic sites. In this context, the porosity of commonly used siliceous-based catalysts or metal oxides is not crucial since, because of the steric hindrance of carbohydrates, the catalytic reaction mainly takes place on the catalyst surface. In the case of organic polymers, utilization of flexible polymeric chains considerably improves the accessibility of the catalytic sites. 

An alternative to silicate-based Portland cement is the calcium aluminate cement, ciment fondu, which originated with the Lafarge company in France in 1908. Ciment fondu is typically made by heating limestone with bauxite, which is mainly AIO(OH) but contains much iron oxide (see Section 17.2). As noted above, calcium aluminate hydrates and hardens much more rapidly than alite, and so ciment fondu, either as such or mixed with Portland cement, can be used whenever a rapidly setting cement is required, for example, for construction at low temperatures. Concretes made from aluminate cements remain serviceable at higher temperatures than Portland cements and so are used to make cast refractories for pyrometal-lurgical applications. 

Figure 1. Isomer shift versus quadrupole splitting data for Fe2+ ions in a variety of coordination environments in silicate and oxide minerals. Calibration of each 295K Mossbauer spectrum from which the parameters are derived is based on reference zero velocity at the midpoint of the a-Fe spectrum. The legend to mineral symbols is contained in Table I.

X-Ray Photoemission Spectroscopy (XPS) Study of Uranium, Neptunium, and Plutonium Oxides in Silicate-Based Glasses... 

The elimination of alcohol from p-alkoxypropionates can also be carried out by passing the alkyl p-alkoxypropionate at 200—400°C over metal phosphates, silicates, metal oxide catalysts (99), or base-treated zeolites (98). In addition to the route via oxidative carbonylation of ethylene, alkyl p-alkoxypropionates can be prepared by reaction of dialkoxy methane and ketene (100). 

Kosova N.V., Avvakumov E.G. Mechanochemical synthesis of calcium silicates based on hydrated oxides. Sib. Khim. Zhum. 1992 2 135-43. 

These areas represent another huge market for oxide based materials. Traditional silicate-based materials are those stable to about 1000-1100 °C and that are used for porcelain chinas, dishware, electric insulators, and other low stress industrial applications. 

Before we examine the structures and properties of metallic classes in further detail, it is useful to consider the natural sources of the metals, generally as oxide and/or silicate-based mineral formations. If the mineral deposit contains an economically recoverable amount of a metal, it is referred to as an ore. The waste material of the rock formation is known as gangue, which must be separated from the desired portion of the ore through a variety of processing steps. 

This chapter deals with silicate and oxide coatings which protect the base material (metal or ceramics) from the effect of ambient environment at elevated temperatures, or improve the mechanical properties of the surface and the appearance of the ware. 

The most important compounds apart from aluminum silicate-based ceramics and clay products are aluminum hydroxide and aluminum oxide, since they are raw materials in the manufacture of aluminum. Other industrially important aluminum compounds are aluminum sulfate, aluminum chloride, sodium aluminate, aluminum fluoride and cryolite (see Section 1.7.1). 

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