Chemical composition binary oxide

The binary systems we have discussed so far have mainly included phases that are solid or liquid solutions of the two components or end members constituting the binary system. Intermediate phases, which generally have a chemical composition corresponding to stoichiometric combinations of the end members of the system, are evidently formed in a large number of real systems. Intermediate phases are in most cases formed due to an enthalpic stabilization with respect to the end members. Here the chemical and physical properties of the components are different, and the new intermediate phases are formed due to the more optimal conditions for bonding found for some specific ratios of the components. The stability of a ternary compound like BaCC>3 from the binary ones (BaO and CC>2(g)) may for example be interpreted in terms of factors related to electron transfer between the two binary oxides see Chapter 7. Entropy-stabilized intermediate phases are also frequently reported, although they are far less common than enthalpy-stabilized phases. Entropy-stabilized phases are only stable above a certain temperature,... 

For auother possible reactiou mechauism for the formatiou of mixed oxides, binary alkoxide (glycoxide) may be formed prior to the formation of the mixed oxide. In fact, various binary glycoxides have been prepared and their crystal structures have been elucidated. Formation of BaTiOj by the glycothermal reaction may be explained by this mechanism, because Ba-Ti binary alkoxide is well established. However, formation of garnet phases (Sections III.C.l through III.C.3) cannot be explained by this mechanism because addition of seed crystals, in some cases, gives a product with a chemical composition completely different from that of the product obtained without the addition of the seed crystals. 

Schindler and Hawthorne [29] presented novel insights into the chemical composition and occurrence of uranyl oxide hydrates using a combined binary representation and bond-valence approach. In essence, this approach looks for conditions of overlap of the bonding requirements emanating from the stmctural unit and interstitial components. The outcome is a series of predicted compositions and mineral stabilities. 

Table 1 shows the target phase, calculated and measured molar ratios, the starting chemicals, hydrolysis rado, and initial surface area for each of the aerogel powders. The target phase is the major crystalline phase expected to be found in the samples when they are used as catalyst support materials in a combustion environment. The molar ratio of the two metal elements in the binary oxide powders was calculated using the known weights of the starting materials. However, since the composition of some of the commercial solutions and chemicals... 

Using the self-formation phenomenon to fabricate hierarchically meso-mac-roporous binary mixed oxides, the mesoporosity and macroporosity can be tailored by tuning contents of the chemical components. Furthermore, the use of mixed alkoxide solutions and surfactants allows for the formation of binary metal oxide materials with structural properties of large multiporosity and high specific siuface area. Such modulable monolithic materials with multiscaled pore sizes and a wide variety of chemical compositions should be promising for multiple apphcations in catalysis and separation technology. 

Quantitative and qualitative changes in chemisorption of the reactants in methanol synthesis occur as a consequence of the chemical and physical interactions of the components of the copper-zinc oxide binary catalysts. Parris and Klier (43) have found that irreversible chemisorption of carbon monoxide is induced in the copper-zinc oxide catalysts, while pure copper chemisorbs CO only reversibly and pure zinc oxide does not chemisorb this gas at all at ambient temperature. The CO chemisorption isotherms are shown in Fig. 12, and the variations of total CO adsorption at saturation and its irreversible portion with the Cu/ZnO ratio are displayed in Fig. 13. The irreversible portion was defined as one which could not be removed by 10 min pumping at 10"6 Torr at room temperature. The weakly adsorbed CO, given by the difference between the total and irreversible CO adsorption, correlated linearly with the amount of irreversibly chemisorbed oxygen, as demonstrated in Fig. 14. The most straightforward interpretation of this correlation is that both irreversible oxygen and reversible CO adsorb on the copper metal surface. The stoichiometry is approximately C0 0 = 1 2, a ratio obtained for pure copper, over the whole compositional range of the... 

The immense number of chemical compounds formed by the halogens provides chemists with an extraordinary database from which numerous chemical and physical phenomena can be correlated with respect to various periodic trends. From databases like Inorganic Crystal Structure Data (ICSD, http //www.fiz-karlsruhe.de ) and International Centre for Diffraction Data (ICDD, http //www.icdd.com) with 67 000 and 25 000 entries, respectively, one can easily make out that halides are one of the dominant classes of compounds besides oxides. Even within the subset of inorganic solids, there is tremendous diversity of composition, stracture, and properties and to summarize this would create its own encyclopedia. Therefore, the discussion in this article is limited primarily to binary halides, their structures, and some of their properties, except halides of elements which are nonmetals. Binary actinide hahdes are discnssed elsewhere see Actinides Inorganic Coordination Chemistry). Complex hahdes (sohd phases containing two or more kinds of metal ions), ... 

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