Distribution Of Oxidation States Research Articles

Mössbauer and chemical investigations of mudrocks

AbstractThe oxidation state and mineralogical distribution of Fe in two different shale sequences have been studied by Mössbauer spectroscopy and chemical methods. Kimmeridge Clay Formation sediments proved to be richer in total Fe than Gulf Coast shales. In such sediments, Fe may be present in clay minerals (Fe(II) in chlorite, Fe(III) in illite and illite/smectite), pyrite, and ferroan carbonates (siderite, dolomite and ankerite). Pyrite accounts for a much greater proportion of the total Fe in the Kimmeridge Clay samples in which it is difficult to reconcile chemical data with Mössbauer data. There is major doublet overlap of Fe(III) in silicates with Fe(II) in pyrite and spectra cannot be satisfactorily deconvoluted. This would appear to be a fundamental limitation for simple applications. In the pyrite-poor Gulf Coast material, however, chemical and spectroscopic evaluations of overall valence state are much more consistent. Confidence in both determinative techniques is generated, and useful information documenting progressive reduction and redistribution of Fe with burial is obtained.

Distribution of intermediate oxidation states at the silicon/silicon dioxide interface obtained by low-energy ion implantation

This work has been undertaken to understand the morphology of Si/SiO2 interfaces obtained by low-energy ion implantation. The crystallinity of the interface is determined by the observation of tetrahedral configurations [Si–(Si4−x–Ox) with x=0, 1,...,4] of silicon atoms bound to oxygen and/or silicon. The distribution over the whole interface also has been considered and the amorphous dioxide has been characterized by its interfacial depth and compared with the theoretical models such as the random bonding model or the random mixture model.

Microscopic structure of the SiO2/Si interface.

The bonding of Si atoms at the SiO2/Si interface is determined via high-resolution core level spectroscopy with synchrotron radiation. For oxides grown in pure O2, the SiO2/Si interface is found to contain Si atoms in intermediate oxidation states with a density of 1.5 ± 0.5 × 1015 cm−2. From the density and distribution of intermediate oxidation states, models of the interface structure are obtained. The interface is not abrupt, as evidenced by the non-ideal distribution of intermediate oxidation states and their high density (about 2 monolayers of Si). The finite width of the interface is explained by the bond density mismatch between SiO2 and Si. Annealing in H2 is found to influence the electrical parameters by removing the Pb centers that pin the Fermi level. The distribution of intermediate oxidation states is not affected.

A correlated X-ray photoelectron and electron spin resonance spectroscopic study of rhodium-exchanged X and Y zeolites

X-Ray photoelectron (X.p.) and electron spin resonance (e.s.r.) spectroscopies have been employed to study the effect of the location and the Si/Al ratio on the distribution of the various Rh oxidation states in faujasite-type zeolites after various activation processes. The zeolites studied were RhNa-X, RhCa-X, RhNa-Y and RhCa-Y. The samples were activated in flowing oxygen to 200, 400 and 500 °C, activated in vacuum to 500 °C and reduced with H2 at 500 °C after vacuum activation. Strong e.s.r. signals were observed only in the samples activated to 400–500 °C in flowing oxygen, indicating the presence of RhII. The amount of RhI increased with the activation temperature, whereas the amount of RhIII was substantial in the samples activated in flowing oxygen. While no significant effects were attributed to the Si/Al ratio the co-cation had a considerable effect on the distribution of oxidation states, mainly in samples activated in flowing oxygen. The relative amounts of RhIII in RhCa-X and RhCa-Y were larger than in RhNa-X and RhNa-Y; accordingly, the relative amounts of RhI were larger in the latter zeolites.

Speciation patterns of actinides in natural waters: a laboratory investigation

The results of laboratory investigations of actinide speciation in ground waters of varying compositions are summarized, re-evaluated and further interpreted, with the inclusion of additional data. Actinide speciation (solubility, oxidation state distributions) in these water samples exhibits great variability at 10 −10 to 10 −8 M total actinide concentrations. Americium solubility appears to be controlled by the formation of radiocolloids. neptunium is predictably oxidized and soluble in these water samples, with only a few exceptions. Plutonium exhibits widely varying oxidation state distributions—and hence solubility— despite the presence of 6 mg liter −1 dissolved oxygen in all experiments. Plutonium solubility is enhanced by carbonate and fluoride but is diminished by sulfate in reducing waters. In general, these results are compatible with the limited information available for actinide speciation from previous in-situ investigations but they emphasize the paucity of accurate thermodynamic data to describe these systems.

ChemInform Abstract: Solvent Control of Oxidation State Distribution and Electronic Delocalization in an Osmium ‐ Ruthenium, Mixed‐Metal Dimer.

AbstractUV/VIS spectra of the mixed oxidation state dimer (IIIB)/(IIIC), the reduced dimer (IIIA), and related monomers, and near IR spectroscopic studies show that variations in solvent can be used to control the oxidation state distribution within the Os ‐ Ru dimer (IIIB)/(IIIC) and, thus, to induce intramolecular electron transfer.

Solvent control of oxidation state distribution and electronic delocalization in an osmium-ruthenium, mixed-metal dimer

Solvent control of oxidation state distribution and electronic delocalization in an osmium-ruthenium, mixed-metal dimer

Plutonium oxidation state distributions in the Pacific Ocean during 1980–1981

The concentration of plutonium and its oxidation state distribution have been measured as a function of depth at three locations in the North Pacific Ocean. Concentration profiles were similar to those observed in the same area during 1974 with primary maxima at depths of a few hundred meters below the surface and secondary maxima near the bottom. Oxidation state distribution profiles were similar at the three locations with plutonium about equally divided between the reduced and oxidized forms except near the bottom. There the oxidized form was more abundant and comprised ∼ 90% of the total plutonium. No major change in oxidation state occurred at the depths of the shallow concentration maxima suggesting that their formation and persistence were not dependent upon a redox change. The concentration maxima near the bottom coincided with the enhanced abundance of the poorly sorbed oxidized form suggesting that they resulted from the loss of oxidized plutonium from the sediments.

Probing the transition layer at the SiO2-Si interface using core level photoemission

High resolution Si 2p photoelectron spectra obtained with synchrotron radiation are used to determine the distribution of oxidation states in the intermediary layer at the SiO2-Si interface. A ratio of 0.4:0.3:0.3 is found for the Si3+:Si2+:Si1+ intensities independent of Si surface orientation and oxide thickness. The interface is not completely abrupt (5±1 Å width).

Comment on the evaluation of the chemical forms of plutonium in seawater and other aqueous solutions

A method for estimating equilibrium oxidation state distributions of plutonium dissolved in seawater is presented. Application of the method contradicts a previous report that computational methods predict a predominance of hexavalent plutonium in seawater.

Determination of oxidation states of uranium dioxide pellets by two-step flow-coulometry

A chemical method for analysis of distribution of oxidation states of metals in solids has been developed as a reference to other methods based on physical measurements. A solid is dissolved with a continuous flow of strong phosphoric acid from surface to bulk, and oxidation states of the dissolved ions are determined consecutively by two-step flow-coulometry. Strong phosphoric acid dissolves such solids as uranium or iron oxides to ions whose oxidation states are the same as those in solids. The oxidized surface of about 20 A on a UO/sub 2/ pellet which had stood for about 10 years at room temperature in air was estimated to be UO/sub 2/ /sub 05/, and the O/U ratio decreased toward the bulk until 0.1 ..mu..m. After the pellet was heated for 10 h at 300 or 430 /sup 0/C in air, the oxidized surface layer increased to about 8 ..mu..m (400 A of powdered U/sub 3/O/sub 8/ + UO/sub 2+x/, 0.66 > x > 0.01) or about 820 ..mu..m of U/sub 38/ + 450 ..mu..m of UO/sub 2+x/, 0.66 > x > 0.01), respectively.

Ion exchange separation of different oxidation states of sulphur formed by35Cl(n, p)35S reaction in alkali halides

Studies on the distribution of various oxidation states of recoil sulphur formed by35Cl(n, p)35S reaction in the alkali halides, namely, NaCl, KCl and RbCl have been made. A suitable anion exchange method using Amberlite IRA-410 in the chloride form has been described for rapid separation of the various radiosulphur species. The elution was carried out by means of nitrate solutions. The observed results on the effect of cation environment in affecting the distribution of radioactive sulphur amongst its various oxidation states were discussed on the basis of electron affinity and ionic size of the metal ion in question.

XPS Studies of Structure-Induced Radiation Effects at the Si/SiO2 Interface

The interfacial structures of radiation hard and soft oxides grown by both dry and wet processes on silicon substrates are examined using high resolution x-ray photoelectron spectroscopy (XPS). Substantial differences are observed in the relative concentration of strained Si-O-Si bridging bonds in the interfacial region and in the distribution of intermediate oxidation states of silicon at the abrupt Si/SiO2 chemical interface. Thin thermal SiO2 films ( substrates are irradiated with electrons having kinetic energies of 0 to 20 eV during in situ XPS measurements. Straightforward field-effect behavior is observed for electron kinetic energies below 6 eV. Both oxide/vacuum surface states and Si(+3) species at the Si/SiO2 interface are generated and allowed to relax during the course of the measurements. These results are correlated with the presence of a strained layer of SiO2 (~20 A) at the interface that we had previously reported. A structural model for hole and electron trap generation by ionizing radiation is developed to interpret these results and our previous observations.

The effect of Np concentration on the preparation of Np(III) by hydrogen reduction

To establish the effect of neptunium concentration on the fraction of trivalent neptunium produced by hydrogen reduction, various concentrations of neptunium in 1 M HClO 4 were treated by H 2 in the presence of a Pt catalyst and extracted by 0.5 M TTA/xylene to determine the oxidation-state distribution of the element. Although neptunium was quantitatively reduced to the trivalent state at concentrations higher than 10 −3 M, the fraction reduced decreased with decreasing concentration of neptunium to 10 −8 M, when no trivalent neptunium was produced. Tracer concentrations of neptunium were quantitatively reduced to the trivalent state in the presence of more than 10 −3 M Sn(IV).

Determination of the oxidation states of neptunium at tracer concentrations by adsorption on silica gel and barium sulfate

The adsorption method for determination of the distribution of neptunium among its oxidation states at tracer concentrations by use of silica gel and barium sulfate as adsorbents is described. In the pH range 6–7, Np(VI) was quantitatively adsorbed on silica gel, while Np(V) remained in the supernatant solution. In acid solutions, the precipitate of barium sulfate adsorbed Np(IV) selectively, leaving Np(V) and Np(VI) in solution. By means of these adsorption methods combined with the use of TBP extractions, the oxidation-state distribution of neptunium in acid or neutral solution in the presence of various redox reagents was determined and shown to be consistent with the expectation from the oxidation potential of the solution.

The Distribution of Oxidation States of Iodine Isotopes in the Fission by Protons of Natural Uranium

Oxidation states of iodine, produced in the fission of uranium by protons of energies 30 and 80 MeV in solid matrices of UO2(NO3)2.6H2O and UO2SO4.3H2O, have been studied. No proton energy dependence was found. The percentage distribution of I7+ as (IO4)− is independent of the matrix. However I5+ (as IO3−) is enriched at the expense of the reduced state (I2° + I−) due to oxidation by the (NO3)− formed by the radiation decomposition of UO2(NO3)2.6H2O. Formation of the nuclide by isomeric decay does not perturb the distribution. The result of β−decay is to increase the I7+ component. Iodine isotopes formed independently in fission have the same distribution of oxidation states, but not unique enough to serve as a measure of this mode of formation.

The effect of vitamin E on the intracellular distribution of the different oxidation states of selenium in rat liver.

1. The liver intracellular distribution of (75)Se, (75)Se(2-) and (75)SeO(3) (2-) formed from orally administered Na(2) (75)SeO(3) was studied in rats given four different dietary treatments. 2. Subcellular fractionation was done by using sucrose density gradients in a B XIV zonal centrifuge rotor, and conditions were established so that separation of lysosomal, mitochondrial, smooth- and rough-surfaced endoplasmic reticulum, and soluble fractions was achieved. 3. Marker enzymes acid phosphatase, succinate-2 - p - iodophenyl - 3 - p -nitrophenyl - 5 - phenyltetrazolium reductase and glucose 6-phosphatase were used, together with electron microscopy, to establish the identity of the fractions. 4. The dietary treatments investigated were: (a) vitamin E-deficient diet for 3 months, re-fed with vitamin E during the terminal 5 days; (b) vitamin E-deficient diet; (c) adequate diet; (d) vitamin E- and selenium-deficient diet, re-fed with vitamin E during the terminal 5 days. 5. In adequately fed rats, selenide was particularly associated with the mitochondrial fractions; in vitamin E-deficient rats, little selenide was found and the buoyant density of the mitochondria was increased, whereas re-feeding with vitamin E showed a restoration of the normal pattern. In vitamin E- and selenium-deficient rats, re-fed with vitamin E, there was no tendency for selenide to be localized in the mitochondria. 6. In the microsomal regions of the gradients, adequately fed rats showed a concentration of selenide, particularly in the smooth endoplasmic reticulum fractions, and to a lesser extent in the rough endoplasmic reticulum fractions. This was not observed in vitamin E-deficient rats, and the normal pattern was restored on re-feeding with vitamin E, both in rats given the vitamin E-deficient diet and the vitamin E- and selenium-deficient diet. 7. Some selenide was also found in the soluble fractions, when vitamin E was present, and a substantial proportion of this selenide was found to pass through a dialysis membrane. 8. These results are taken to support our hypothesis that the active form of selenium may be selenide located in non-haem iron-containing proteins, and that the function of vitamin E may be to protect the selenide from oxidation.

The determination of the oxidation states of tracer uranium, neptunium and plutonium in aqueous media

This report describes the development, testing and application of a chemical procedure for determining the distributions of uranium, neptunium and plutonium among their respective oxidation states in various aqueous media at tracer concentrations. The separations achieved are of the order of 95% clean. Results are presented which show the per cent extraction of uranium, neptunium and plutonium oxidation states by 0.4 M2-thenoyltrifluoracetone at various values of pH, and per cent carried by lanthanum fluoride from distilled water and sea water under various conditions. Radiochemical analysis of the separated fractions can then be used to determine the required oxidation state distributions.