Oxygen composition

The oxygen composition of doped brownmillerite structure materials is not always exactly 5.0 and depends upon a number of factors, especially the surrounding oxygen partial pressure. Thus, the oxide formed when Fe is replaced by Co has a broad... 

To be investigated are the influences of gassing rate and stirrer speed on an oxidation reaction in an aerated batch reactor. The outlet gas is assumed to be of normal air composition, which eliminates the need of a balance for the well-mixed gas phase, since the gas oxygen composition does then not change. 

The most studied non-stoichiometric system in actinide CaF2-structured compounds is the An-0 system all actinide dioxides (with the exception of Th02) present large departures from stoichiometry. Since uranium and plutonium dioxides (and their solid solutions) are employed as fuels in nuclear reactors, a very large effort has been dedicated to the study of their physical and physico-chemical properties. All these properties are affected by the oxygen composition of the compound. 

Each meteorite class has a unique oxygen composition. The origin of these unique compositions is not fully understood, but is known to reflect two types of isotopic variations. Mass-dependent isotope variations, introduced in Chapter 2, result from physical and chemical processes that slightly favor one isotope over another due to the difference in mass. Mass-independent variations probably reflect mixing of components with isotopic compositions that originated either through nucleosynthesis or through processes that do not depend on mass. We will discuss these processes in more detail in Chapter 7. 

Magnetic materials—control of oxygen composition and physical properties of Mn-Zn ferrites... 

In a typical furnace control system the fuel flow is manipulated to hold temperature or pressure in the process. The air is ratioed to the fuel. This ratio is adjusted to maintain a reasonable oxygen composition in the stack gas. 

When Srinivasan and Noyes116 photooxidized diethyl ketone in the presence of 98% oxygen-18, they found the quantum yield of diethyl ketone-18 was 0.7 and, as in the case of the acetone-oxygen-18 photooxidation, no isotopic change was detected in the oxygen composition. 

OXYGEN COMPOSITION VERSUS FRACTION OF STOICHIOMETRIC OXYGEN... 

In fact, the observed values of the silicate oxygen are depleted with respect to the initial oxygen (with a slope of 0.65) and do not fall over the mixing line of ozone and silicate (100 and 10%o as two end-members, respectively, see Fig. 4.9). This implies that the relevant oxidation step may involve OH (or HO2) when H2 is present as a reactant and generate the mass-independent oxygen composition by SiO + OH —> Si02 + H SiO + H02 - Si02 + OH. 

The third part (175 A) of the A1 oxide represents a diffusion layer with deficient oxygen composition AlxOy (y smaller than x). ... 

The overriding safety constraint in this process involves oxygen concentration in the gas loop, which must remain below 8 mole % to remain outside the explosivity envelope for ethylene mixtures at process conditions. The most direct manipulated variable to control oxygen composition at the reactor feed is the fresh oxygen feed flow. ... 

The rocksalt structure consists in two interpenetrating fee lattices of anions and cations, in which all atoms are in an octahedral environment. It is met in alkaline-earth oxides (MgO, CaO, SrO, BaO) and in some transition metal oxides like TiO, VO, MnO, FeO, CoO, NiO, etc, with cations in a 4-2 oxidation state. The non-polar surfaces of lowest Miller indices are the (100) and (110) surfaces they have neutral layers, with as many cations as oxygen ions, and their outermost atoms are 5- and 4-fold coordinated, respectively. Actually, planar surfaces can only be produced along the (100) orientation. The polar direction of lowest indices is (111) it has an hexagonal 2D unit cell, three-fold coordinated surface atoms and equidistant layers of either metal or oxygen composition. 

To achieve the required oxygen composition, the calculated amounts of iron and uranium oxides (Equation 1,2)... 

All the deductions proceed from the assumption that the catalyst surface is uniform relative to the isotopic exchange. If the surface is non-uniform, then the constants for exchange K, and as well as the isotopic oxygen composition of catalyst surface ocg, will be different for... 

Cross comparisons between the collated structural data, however, indicate generally excellent consistency, apart from minor differences that can now be ascribed largely to small differences in oxygen composition. Such differences are indicated by the unit cell constants (Table I, Figure 3), by coordinates such as Cul z, or 04 z (Table II), and by certain separations such as Cul-04 (Table III). 

In addition to pseudocubic structures, ABO3 compounds form an extraordinary number of structures based on mixed cubic (c) and hexagonal (h) close-packed AO3 layers (14). Some of this polytypism has been shown to be associated with the oxygen composition (15.16). The combination of mixed sequences (c,h), cation composition, and oxygen stoichiometry can give rise to a large number of complex structures and a range in properties (17). 

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