Evaluation of the potential of the Np(VII)/(VI) couple in acid solutions using the reaction Ag(I) + Np(VII) ⇄ Ag(II) + Np(VI)

The reaction of Np(VII) with Ag(I) was studied by spectrophotometry with the aim to evaluate the potential of the Np(VII)/(VI) couple in acid solutions. In perchloric acid solutions with pH 1.5 and 3.05, the potential E is 1.93 and 1.85 V, respectively. Extrapolation to a solution with pH 0 gives 2.20 ± 0.01 V. A close value (E = 2.22 V) is obtained by extrapolating the potential from a 1 M NaOH solution (pH 13.83, E = 0.582 or 0.587 V) to acid solutions (pH 0).     

Incubation of PbSe Thin Films in a Tin(Ⅱ) Salt Aqueous Solution:Modification and Ion-Exchange Reactions

Topochemical ion-exchange reactions between solid micro-and nanostructured metal chalcogenides and aqueous salt solutions are generally used for formation of composite structures based on initial metal chalcogenides and products of their ion-exchange transformation.However,ion exchange has promises as a route to obtaining both composites and solid solutions based on the initial and the end chalcogenide phases.With the help of the ion-exchange technique,single-phase films of Pb_(1-x)Sn_xSe substitutional solid solutions with a tin content up to~2 at.%,which are promising for mid-and long-wavelength infrared radiation(IR)optoelectronics,have been obtained at the interface between PbSe polycrystalline thin films and SnCl_2 aqueous solutions containing sodium citrate.It has been shown that the pH value and temperature of the reaction system play an important role in the ion-exchange process.Incubation of lead selenide(PbSe)films in a tin(Ⅱ)salt aqueous solution also leads to their modification with oxygen-containing tin compounds to a depth of~3 nm.Differences in the film structure,such as changes in the coherent scattering region sizes and orientation of crystallites along the[220]direction,which arise during the contact with citrate-containing SnCl_2 solutions,have also been revealed.For the first time,an idea of the existence of a relatively wide reaction zone of an intragranular topochemical ion-exchange reaction in an aqueous solution,within which substitutional solid solutions can form in micro-and nanostructured systems,has been set forth.     

Phase Composition of Heat-Treatment Products in the ZrO(OH)2–Y(OH)3–FeOOH System

The phase composition of the heat-treatment products in the ZrO(OH)₂–Y(OH)₃–FeOOH system is determined as a function of the precipitation procedure and calcination temperature (620–1570 K) for the compositions 0.97ZrO₂· xY₂O₃· yFe₂O₃(x+ y= 0.03; x= 0, 0.01, 0.015, 0.02, 0.03) and (1 – x– y)ZrO₂· xY₂O₃· yFe₂O₃(x= y= 0.02, 0.025, 0.03, 0.04). At a given ZrO₂: stabilizer ratio, partial substitution of Fe³⁺for Y³⁺increases the degree of ZrO₂stabilization and retards the low-temperature degradation of the material.     

Thermodynamic Analysis of Thermal Decomposition of Al(OH)_3

Thermodynamic analysis of the main reactions in the process of thermal decomposition ofAl(OH)3 was made using Temkin-Schwarzman's method and by means of regression analysis.     

A Simplified Regular Solution Model for Solubility of Nonmetal (2) in Metal(1)-Metal(3) Alloy Systems

A simplifled regular solution model for the solubility of nonmetallic element (2) in metal(1)-metal(3) alloy system has been derived and applied to the Fe-C-j, Ni-C-j and Fe-N-j (j denotes a metal) systems with satisfaction. The exchange energies of concerned systems are evaluated     

Kinetics of α-FeO(OH)Formation in Weak Acidic Medium

The kinetics of α-FeO(OH) formation in weakacidic medium was studied.The effects of the initialconcentration,temperature,pH value,partial pres-sure of oxygen,air flow rate and agitating intensityon the oxidation rate of Fe(OH)_2 suspensions havebeen investigated.It is confirmed that the reactionorder for Fe(Ⅱ) is zero at the stage of α-FeO(OH)seeds formation,and about 0.5 at the stage of theseeds growth,and in the whole process partial pres-sure of oxygen appears in first order.The activationenergy is determined.The dissolution-oxidationequilibrium which exists in the process of seedsformation has been suggested,by which the zeroorder reaction for Fe(Ⅱ) and the plateau in thepH-t curve were explained.Physical process is therate-determining step of the heterogeneousreaction.The study on the kinetics of α-FeO(OH)formation may provide some fundamental informa-tion for the reactor design,the engineering amplifi-cation and the optimization control in the industrialprocess.     

Soft mechanochemical synthesis of MgFe2O4 nanoparticles from the mixture of α-Fe2O3 with Mg(OH)2 and Fe(OH)3 with Mg(OH)2

Abstract

The influence of long term soft milling of a mixture of (1) Mg(OH)₂ and α-Fe₂O₃ and (2) Mg(OH)₂ and Fe(OH)₃ powders in a planetary ball mill on the reaction synthesis of nanosized MgFe₂O₄ ferrites was studied. Soft mechanochemical reaction leading to formation of the MgFe₂O₄ spinel phase was followed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and magnetisation measurements. The spinel phase formation was first observed after 5 h of milling and its formation was completed after 15 h in case (2). The synthesised MgFe₂O₄ ferrite had a nanocrystalline structure with a crystallite size of about 10 and 15 nm respectively for cases (1) and (2). Measurements after 15 h of milling show magnetisation values of 15·23 and 10·14 J T^–1 kg^–1 respectively for cases (1) and (2).     

Dissolution Behavior of Undoped and Sn-Doped InAs in HNO3–HBr–CH3CH(OH)COOH

The dissolution of undoped and Sn-doped InAs in HNO₃–HBr–lactic acid solutions is studied. The results demonstrate that doping with Sn markedly reduces the dissolution rate of indium arsenide. Bromine-releasing solutions of the system studied can be used for various treatments of InAs and InAsSn.     

Synthesis and Characteristics of Double Np(VI) Potassium and Pu(VI) Potassium Silicates K[(NpO2)(SiO3OH)]·H2O and K[(PuO2)(SiO3OH)]·H2O

K[(NpO₂)(SiO₃OH)]·H₂O (I) and K[(PuO₂)(SiO₃OH)]·H₂O (II) were prepared by hydrothermal synthesis at 120°C, and their IR and near-IR spectra were measured. The unit cell parameters of the compounds were determined from powder X-ray patterns [a = 7.068(1), b = 7.064(2), c = 6.640(1) Å. = 106.68(1)°, V = 317.6 ų (I); a = 7.102(1), b = 7.100(2), c = 6.637(1) Å, = 107.62(1)°, V = 318.9 ų (II)]. These compounds are isostructural with potassium boltwoodite K[(UO₂)(SiO₃OH)]·H₂O.     

Oxidation of Np(V) and Np(IV) with Fe(CN) 6 3− ions in carbonate solutions

The formal potential of the Fe(CN) ₆ ^3? /Fe(CN) ₆ ^4? couple in 1 M NaHCO₃ and 1–2 M Na₂CO₃ solutions was determined. It is equal to 505 and 510 mV, respectively, exceeding the potentials of the Np(VI)/(V) and Np(V)/(IV) couples in carbonate solutions. The equilibrium of the reaction Np(V) + Fe(CN) ₆ ^3? = Np(VI) + Fe(CN) ₆ ^4? was studied. Fe(CN) ₆ ^3? ions oxidize Np(IV) to Np(V) and then to Np(VI). The arising Np(VI) oxidizes Np(IV). The Np(IV) oxidation accelerates in going from NaHCO₃ to Na₂CO₃. An increase in [Na₂CO₃] or in the ionic strength (by adding neutral salts) decelerates the oxidation. Np(IV) introduced in an HCl solution reacts with Fe(CN) ₆ ^3? or with Np(VI) faster than Np(IV) introduced in a Na₂CO₃ solution. The activation energy of the reaction of Np(IV) with Fe(CN) ₆ ^4? in the range 20–45°C is 107 kJ mol^?1. The reaction mechanism involves formation of the activated complex from ions of Np(IV) hydroxocarbonate and oxidant.     

Synthesis of Co3(OH)2V2O7·1.7H2O nanosheets and its application in lithium ion batteries

Cobalt vanadium oxide hydroxide hydrate (Co₃(OH)₂V₂O₇·nH₂O) nanosheets are successfully synthesized by a simple hydrothermal method. The composition of Co₃(OH)₂V₂O₇·nH₂O is studied by thermal gravity (TG) analysis in N₂ atmosphere and subsequent X-ray powder diffraction (XRD) characterization of the sample obtained via annealing Co₃(OH)₂V₂O₇·nH₂O nanosheets in N₂ atmosphere at 800 °C for 6 h. The results indicate that there are 1.7 water molecules in a Co₃(OH)₂V₂O₇·nH₂O molecular formula. Electrochemical properties of Co₃(OH)₂V₂O₇·1.7H₂O nanosheets as negative electrode of lithium ion batteries are studied by conventional charge/discharge test, which show an initial capacity of 730 mAh g^?1 with steady plateau near 0.9 V at a current density of 0.05 mA cm^?2.     

Chemical Transformations of γ-Al(OH)3during Closed-System Heat Treatment

The chemical transformations of -Al(OH)₃during closed-system heat treatment in a self-generated gaseous atmosphere (water vapor) were studied. At t 200°C, -Al(OH)₃was found to convert into -AlOOH, which, in turn, converts into the equilibrium phase -Al₂O₃at t 400°C. The processes underlying the effect of water vapor on the kinetics and mechanisms of the chemical transformations of -Al(OH)₃and -AlOOH in a closed system are discussed.     

γ-Cu2(OH)3Cl as precursor in the preparation of copper (I) and (II) oxides and copper powder

When-Cu₂(OH)₃Cl is decomposed in air or nitrogen flow, different amounts of cuprous oxide are obtained as final product depending on both the heating rate and the ambient atmospheres. However, the temperature of formation of cuprous oxide only appears to depend on the partial pressure of oxygen. When thermal decomposition is carried out under dynamic vacuum in the X-ray high-temperature diffraction chamber, using a tantalum strip as the heating element, copper is obtained as final product at a comparatively low temperature.     

Synthesis and structure of actinide(VII) compounds Rb3NpO4(OH)2·3H2O and Rb3PuO4(OH)2·3H2O

Actinide(VII) salts Rb₃[NpO₄(OH)₂]·3H₂O (I) and Rb₃[PuO₄(OH)₂]·3H₂O (II) were prepared as single crystals and examined by X-ray diffraction. The compounds are isostructural and crystallize in the monoclinic system, space group C2/c, Z = 4; unit cell parameters: a = 12.1544(3), b = 10.9942(2), c = 7.789(2) ?, ?? = 91.0930(11)° for I and a = 12.1254(3), b = 10.9506(2), c = 7.7699(2) ?, ?? = 90.8253(12)° for II. The main structural elements of I and II are centrosymmetrical anions [AnO₄(OH)₂]^3? forming together with water molecules, owing to strong hydrogen bonding, chains oriented along [101]. In [AnO₄(OH)₂]^3? anions, the central An(VII) atom has a tetragonal-bipyramidal oxygen surrounding. The An-O(OH) interatomic distances decrease in going from I to II owing to actinide contraction by a factor of ??2 more strongly than the An-O bond lengths in the equatorial planes of the bipyramids. The previously studied structure of Cs₃[NpO₄(OH)₂]·3H₂O (III) was refined.     

An XPS study of interaction of neptunyl(V) in aqueous solution with goethite (α-FeOOH)

Sorption and physicochemical state of Np on the goethite (-FeOOH) surface were studied. The oxidation state of Np on the -FeOOH surface was studied by the liquid extraction. The neptunium complexes formed on the surface were studied by X-ray photoelectron spectroscopy. The ionic and elemental composition of the goethite surface and NpO ₂ ⁺ complexes with -FeOOH were determined from the XPS data. No Np(IV) and Np(VI) compounds were detected. Neptunyl(V) Np(V)O ₂ ⁺ forms complexes with the surface groups of -FeOOH. The equatorial plane of these complexes is occupied by the oxygen atoms of -FeOOH and water and/or carbonate group CO ₃ ^2– .Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 503–506.Original Russian Text Copyright © 2004 by Yu. Teterin, Kalmykov, Novikov, Sapozhnikov, Vukcevic, A. Teterin, Maslakov, Utkin, Khasanova, Shcherbina.     

Formation of a sol of mixed U(IV) · U(VI) hydroxide in aqueous solutions with pH 1.5–4

containing U(IV) polymer start to form. With an increase in pH from 1.5 to 4 or in temperature, the induction period becomes shorter. Under anaerobic conditions, the colloidal solution is stable for more than a month. Centrifugation at 8000 rpm (5500g) allows separation of the colloidal particles from the liquid phase. The colloid slowly dissolves in mineral acids saturated with argon or in a K₂CO₃ solution, whereas precipitates of individual freshly prepared U(IV) and U(VI) hydroxides dissolve rapidly. Short UV irradia-of a UO₂(ClO₄)₂ solution saturated with argon and containing ethanol (pH 2.5) results in the appearance of U(V) which then disproportionates, and U(IV) forms with U(VI) a black colloid similar to that arising on mixing U(IV) and U(VI) solutions.     

First-principles Investigation on Solution Hardening of Interstitial Impurity Elements (O,N) inγ-TiAl

1. Introduction7-titanium aluminides (7-TiAl) are considered asthe top candidate materials for structural applica-nons with high operational temperature[1]. However,similarly to the most illtermetallic compounds, thepromising applications of 7-TiAl are limited by theproblem of poor ductility at ambient condition. Dueto this reason, many researches have been carried outin recent years to overcome such a demerit[2]. As themost conventional and effective way in altering the microstructure of ma…     

Synthesis and study of hydrated uranium(VI) oxides, UO3·nH2O

A procedure was developed for preparing synthetic schoepite [(UO₂)₈O₂(OH)₁₂](H₂O)₁₂ (UO₃·2.25H₂O). The dehydration and thermal decomposition of this compound were studied by X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. The relationship between schoepite and other hydrated forms of uranium(VI) oxide was found.