Oxidation states determination

Oxidation state determination, CsPuFe product, thermogravimetric... 

The oxidation state deduced from the DR spectra (open symbols) agrees well with the oxidation state determined by off-line reference titration experiments (full symbols). 

Since crushed basalt has been recommended as a major backfill component (1), experiments were completed to evaluate the rate of dissolved oxygen consumption and the redox conditions that develop in basalt-water systems under conditions similar to those expected in the near-field environment of a waste package. Two approaches to this problem were used in this study (l)the As(III)/As(V) redox couple as an indirect method of monitoring Eh and (2) the measurement of dissolved oxygen levels in solutions from hydrothermal experiments as a function of time. The first approach involves oxidation state determinations on trace levels of arsenic in solution (4-5) and provides an estimate of redox conditions over restricted intervals of time, depending on reaction rates and sensitivities of the analyses. The arsenic oxidation state approach also provides data at conditions that are more reducing than in solutions with detectable levels of dissolved oxygen. 

Analytical. Arsenic oxidation state determinations were per-formed by hydride generation-flame atomic absorption spectroscopy (AAS) at the University of Arizona Analytical Center. The analytical procedures are discussed in Brown, et al. (12). 

XAS can be used in several different ways to determine local structural information about catalysts in reactive atmospheres. This structural information may be static or dynamic it may be geometric or electronic. The depth of information that can be ascertained is often dependent upon the type of catalyst, for example, supported metal nanoclusters versus bulk or surface oxides. It may also be controlled by some property of the catalyst, for example, the concentration of the element in the catalyst that is being investigated. In this section a few examples are provided to highlight the importance and relevance of XAFS in catalyst characterization. The examples are focused on (1) structural information characterizing samples in reactive atmospheres, (2) transformation of one species to another, (3) oxidation state determination, (4) determination of supported metal cluster size and shape, and (5) electronic structure. These examples illustrate the type of information that can be learned about the catalyst from XAFS spectroscopy. 

As mentioned in the introduction, the ability of cerium to switch between the +4 and -h3 oxidation states determines many important applications of ceria-based materials. For this reason, the energy change associated with the bulk reduction in... 

When you are dealing with elements that only show one oxidation state, determining the ratio by which they form can be quite easy. The idea is that the elements will combine in such a ratio that there will be a net charge of zero, for a neutral compound. For example, how would we find the chemical formula for the compound of sodium and chlorine If I told you that sodium (Na) has an oxidation number of +1 and chlorine (Cl) has an oxidation number of -1, they must combine in a 1 1 ratio because (+1) + (-1) = 0. The chemical formula for the compound formed by these elements, in a 1 1 ratio, would be NaCl. No subscripts are needed or used, because they are each understood to be 1. 

H2S interface (Swarzenski etal., 1999b). Such concentration maxima at the redox boundary is also observed for DOC, Sr and Ba. The authors hypothesize that the source of elevated U at the redox boundary must be due to microbial uptake and subsequent release processes. Uranium oxidation state determinations in waters from 1, 22 and 30 m depth reveal that reduced U(IV) is not present in significant abundance, and that the chemical and/or biological reduction of hexavalent uranium is largely inhibited. These results suggest that U, DOC, Sr, Ba, Fe(II), and Mn(II) are greatly modified by direct and indirect microbial transformation reactions which are most concentrated across the redox transition zone in Framvaren Fjord. 

Determination of the oxidation state. Determining the effective charge on the absorbing atom from the chemical shift of the X-ray absorption threshold is a fundamental issue for XANES. However, a direct measure of the "ionization threshold" or "continuum threshold" (i.e., the energy at which the electron is excited in the... 

Oxidation state determination of plutonium aquo ions using X-ray absorption spectroscopy. Polyhedron 17 599-602... 

Figure 7. Synchrotron pXANES spectra of V for glasses produced at different log(/02) = 0 (solid), -6.8 (dash), -9 (dot). The effective oxidation states determined by optical spectrometry (H. Schreiber, VMI) were 4.7, 4.0, and 3.2, respectively. The systematic change in energy and intensity of the preedge peak near 5470 eV is the basis of the oxidation state determination.

The chemical factor, i.e., the chemical nature of metal cations, must be considered first. The nature of metal cations, their electronegativity and oxidation state, determines the ionicity and geometry of the crystalline lattice. 

Kwiatek WM, Galka M, Hanson AL, Paluszkiewicz C, Chichocki T. XANES as a tool for iron oxidation state determination in tissues. J Alloys Compd 2001 325 276-282. 

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