Stoichiometry of uranyl hydrolysis reaction in acidic aqueous solutions from the evidence of oxygen exchange kinetics

The kinetics of uranyl oxygen exchange with water molecules in aqueous solutions was studied in the pH range 1–4 and uranium concentration range 10^–4–0.1 M. It was confirmed that the exchange is stimulated by hydrolyzed uranyl species. From the evidence of data on the kinetics of uranyl oxygen exchange the reaction stoichiometry of uranyl hydrolysis was determined. The scheme of uranyl hydrolysis involving formation of (UO₂)₂(OH)₂²⁺, (UO₂)₂(OH)₃⁺, and other hydrolyzed species was proposed. To cite this article: L.G. Mashirov et al., C. R. Chimie 336 (2004).

Résumé

Étude de l'hydrolyse de l'uranium hexavalent en milieu acide par échange isotopique de l'oxygène. L'échange isotopique de l'oxygène de l'ion uranyle avec les molécules d'eau a été étudié dans le domaine de pH de 1 à 4 et de concentration en uranium de 10^–4 à 0,1 M. Cet échange a lieu par l'intermédiaire d'espèces hydrolysées de U(VI). La stoechiométrie des formes hydrolysées de U(VI) est déduite des vitesses d'échange isotopique. En particulier, les espèces (UO₂)₂(OH)₂²⁺ et (UO₂)₂(OH)₃⁺ ont été clairement identifiées. Un schéma d'hydrolyse est proposé. Pour citer cet article : L.G. Mashirov et al., C. R. Chimie 336 (2004).     

Stark modulation in the ã A2—X̃,Σg system of CS2

Stark modulation experiments have been carried out on bands of the ã ³A₂—X̃,¹Σ_g⁺ system of ¹²C³²S₂. The most pronounced effects involve nearly degenerate pairs of rotational levels ofthe type J_o,j and J−1_1,J−1 with odd values of J in the 040, 140, 050, 060, 070 and 080 vibrational levels of the upper state. A further effect has been observed in the 090 level but the mechanism has not yet been clarified. Dipole moments have been determined for all vibrational levels except the 080 and 090 which are perturbed. A marked vibrational dependence of the dipole moment is found. ‡|Taken in part from the thesis of M. Larzillière, Doctorat d'Etat, ref : Serie A.O. No. 12772, 1977 Reims, France. †|Laboratoire de Spectrométrie Ionique et Moléculaire, Universités de Lyon I et de St-Etienne, associé au C.N.R.S.     

Tunneled Intergrowth Structures in the Ga2O3–In2O3–SnO2 System

The structures of several Ga₂O₃–In₂O₃–SnO₂ phases were investigated using high-resolution electron microscopy, X-ray diffraction, and Rietveld analysis of time-of-flight neutron diffraction data. The phases, expressed as Ga_4−4xIn_4xSn_n−4O_2n−2 (n=6 and 7–17, odd), are intergrowths between the β-gallia structure of (Ga,In)₂O₃ and the rutile structure of SnO₂. Samples prepared with n≥9 crystallize in C2/m and are isostructural with intergrowths in the Ga₂O₃–TiO₂ system. Samples prepared with n=6 and n=7 are members of an alternative intergrowth series that crystallizes in P2/m. Both intergrowth series are similar in that their members possess 1-D tunnels along the b axis. The difference between the two series is described in terms of different crystallographic shear plane operations (CSP) on the parent rutile structure.     

Application of phosphorus- and nitrogen-containing organic compounds for the isolation of actinides and technetium from acid or basic aqueous solutions

The derivatives of ethers of phosphoric acid, namely O-(2-alkyl) (diethylcarbamoylmethyl) phenylphosphinates (O2ADECMPP), were synthesized and tested for liquid–liquid extraction of transuranium elements, lanthanides and technetium in meta-nitrobenzotrifluoride or 1,2-dichlorethane from acidic solutions. The O-(ethylhexyl) (diethylcarbamoylmethyl) phenylphosphinate (O2EHDECMPP) was used to prepare chelating granulated sorbents. The family of chelating fibrous ‘filled’ sorbents POLYORGS-type shows, according to preliminary experiments, that Pu and Tc at concentrations around 10^–5 M can be recovered almost completely. POLYORGS show fast kinetics for sorption processes. To cite this article: G.V. Myasoedova et al., C. R. Chimie 7 (2004).

Résumé

Utilisation de réactifs phosphorés et azotés pour la séparation des actinides et du technétium de milieux acides et basiques. Des dérivés de l’éther de l’acide phosphorique du type O-2-alkyl diéthylcarbamoylméthyl phénylphosphonates ont été préparés et testés pour extraire des éléments transuraniens, des lanthanides et du technétium dans le meta-nitrobenzène ou le 1,2-dichloroéthane, à partir de solutions aqueuses acides. Le dérivé O-éthylhexyl diethylcarbamoylméthyl phénylphosphonate a été utilisé pour préparer des échangeurs solides par effet de chélation. La famille des chélatants fibreux Polyorgs montre, dans des expériences préliminaires, que Pu et Tc, à des concentration de l’ordre de 10^–5 M, peuvent être complètement récupérés à partir de milieux acides contenant d’autres éléments. Ces composés présentent des cinétiques de sorption très rapides. Pour citer cet article : G.V. Myasoedova et al., C. R. Chimie 7 (2004).     

Immobilisation of actinides in phosphate matrices

In the field of the immobilisation of high-activity-level and long-life radwaste (HAVL) for a deep underground repository, several phosphate matrices were already proposed as good candidates to delay the release of actinides in the near-field of such disposal. Among them, thorium phosphate–diphosphate (TPD), monazites/brabantites, britholites, and TPD/monazite composites were extensively studied. The synthesis of samples doped with actinides (Th, U...) through wet and dry chemistry methods then their complete characterisation are reported. Their chemical durability is also examined. These materials appear as promising matrices to immobilise tetravalent and/or trivalent actinides. To cite this article: N. Dacheux et al., C. R. Chimie 7 (2004).

Résumé

Immobilisation des actinides dans des matrices phosphatées. Dans l'optique d'un stockage de déchets radioactifs de haute activité et de vie longue en site géologique profond, plusieurs matrices phosphatées de type céramique ont été proposées afin de retarder le relâchement des actinides dans le champ proche d'un tel stockage. Parmi celles-ci, le phosphate-diphosphate de thorium (PDT), les monazites, les brabantites et les britholites présentent plusieurs des propriétés recherchées pour assurer la rétention de ces éléments sur le long terme. La préparation d'échantillons dopés avec des actinides par voie sèche et/ou humide, leur caractérisation à l'état pulvérulent ou fritté et leur durabilité chimique lors de tests de lixiviation sont examinées ici. Sur la base des propriétés physico-chimiques de ces matrices, des matériaux composites à base de PDT et de monazite ont été préparés puis caractérisés. Tous ces matériaux apparaissent comme des candidats prometteurs pour l'immobilisation des actinides tri- et tétravalents. Pour citer cet article : N. Dacheux et al., C. R. Chimie 7 (2004).     

Sonolysis of actinide(IV) β-diketonates in alkanes

Ultrasonic irradiation with the frequency of 20–22 kHz and absorbed acoustic power about 0.4 W ml^–1 causes degradation of An(IV) tetrakis-β-diketonates, AnL₄, where An(IV) is Th(IV), Np(IV), and Pu(IV), and HL is hexafluoroacetylacetone (HFAA) and dibenzoylmethane (HDBM), in hexadecane solutions in the presence of argon. The rate of the sonochemical process corresponds to a first-order kinetic law with respect to metal β-diketonate concentrations. The first-order rate constant of sonolysis increases with the increase in the volatility of the metal complexes. Solid sonication products consisted of a mixture of actinide carbides and partial degradation products, PDP, of initial metal β-diketonates. It is assumed that metal carbides are formed within the cavitating bubbles as a result of high-temperature process with participation of actinide(IV) β-diketonates and solvent vapours. PDP formation is attributed to the thermolysis of the complexes in a liquid reaction zone surrounding the cavitating bubble. To cite this article: S.I. Nikitenko et al., C. R. Chimie 7 (2004).

Résumé

L’irradiation ultrasonore avec une fréquence de 20–22 kHz et une intensité acoustique de 0,4 W ml^–1 conduit à la décomposition de An(IV) tétrakis-β-dicétones, AnL₄, où An(IV) est Th(IV), Np(IV) et Pu(IV), et HL est l’hexafluoroacétylacétone (HFAA) et le dibenzoylméthane (HDBM) en milieu hexadécane sous argon. La cinétique de décomposition sonochimique est d’ordre 1 par rapport à la concentration du complexe et la cinétique augmente avec la volatilité du complexe métallique. Les produits solides de décomposition sont un mélange de carbure d’actinides et de produits de décomposition partielle PDP. Il a été observé que les carbures d’actinide sont formés dans la bulle de cavitation compte tenu des fortes températures et de la présence simultanée du complexe métallique volatil et du solvant (hexadécane). La formation des PDP est attribuée à la thermolyse du complexe à l’interface de la bulle de cavitation. Pour citer cet article : S.I. Nikitenko et al., C. R. Chimie 7 (2004).     

Dissolution and extraction of actinide oxides in supercritical carbon dioxide containing the complex of tri-n-butylphosphate with nitric acid

Dissolution of individual actinide oxides (Th, U, Pu, Np), or their mechanical mixtures, as well as of solid solutions U–Pu, U–Np, U–Am and U-Pu-Eu oxides in supercritical fluid carbon dioxide (SF-CO₂) containing the complex of tri-n-butyl phosphate (TBP) with nitric acid (TBP–HNO₃) has been investigated. The effect of the calcination temperature of solid solutions of dioxides on the separation of actinides during supercritical fluid extraction (SFE) has been studied as well. It was shown for the first time that milligram amounts of uranium dioxide could be quantitatively dissolved in (SF-CO₂) containing the TBP–HNO₃ complex and efficiently separated from Pu, Np, and Th during SFE of mechanical mixture of these oxides. On the contrary, both U and Pu are quantitatively dissolved in SF-CO₂–TBP–HNO₃ during SFE from solid solutions of U–Pu dioxide. An increase of the calcination temperature of the mixed U(IV)–Pu(IV) dioxide from 850 to 1200 °C has no influence on the relative extraction yield of these actinides during SFE. To cite this article: T. Trofimov et al., C. R. Chimie 7 (2004).

Résumé

Dissolution d’oxides d'actinides et extraction d’éléments dans le dioxide de carbone supercritique contenant le complexe tri-n-butylphosphate–acide nitrique. La dissolution d’oxydes de Th, U, Pu et Np, de leurs mélanges et de solutions solides U–Pu, U–Np, U–Am et U–Pu–Eu dans le dioxyde de carbone supercritique (CO₂-SC) contenant le complexe tri-n-butyl phosphate–acide nitrique (TBP–HNO₃) a été étudiée, et notamment l’effet de la température de calcination des solutions solides. On montre que quelques milligrammes de UO₂ peuvent être dissous dans le système CO₂-SC–TBP–HNO₃ et être séparés de Pu, Np et Th en traitant un mélange d’oxydes. En revanche, U et Pu sont dissous dans la phase CO₂-SC–TBP–HNO₃ durant le traitement des solutions solides U(IV)–Pu(IV). Une augmentation de la température de calcination de 850 à 1200 °C de ces solutions solides n’a pas d’effet sur le rendement d’extraction des actinides. Pour citer cet article : T. Trofimov et al., C. R. Chimie 7 (2004).     

Effect of gleysation on remobilization of radionuclides in waterlogged soils

Joint leaching of iron and other macro- and microelements including radionuclides from radioactively contaminated floodplain soil of the Yenisei River is studied on miniecosystems. In developing anaerobic conditions, the redox potential E_h decreased to +140 mV, causing partial reduction of iron and solubilisation of iron hydrous oxide and organomineral films of the soil. Leaching of stable elements and radionuclides with water proceeds parallel to that of iron. To accelerate reductive mobilization of iron, 0.4% aqueous ascorbic acid was used instead of water as the leaching liquid phase. In this case, E_h approached –60 mV, and the leaching of stable and radioactive elements considerably increased, the effect being most pronounced for plutonium. To cite this article: E.K. Legin et al., C. R. Chimie 7 (2004).

Résumé

Effet du passage en milieu anaérobie sur la mobilisation des radionucléides dans les sols humides. La lixiviation simultanée du fer et d’autres éléments de sols contaminés de la vallée de la rivière Yénései a été étudiée. En imposant des conditions anaérobies, le potentiel redox chute à 140 mV, causant une réduction partielle du fer trivalent et la solubilisation de l’hydroxyde de fer et du film organominéral du sol. Les lixiviations du fer, des autres éléments et, par conséquent, des radionucléides contaminant le sol vont de pair. Pour accélérer la mobilisation réductive du fer, une solution d’acide ascorbique à 0,4% a été utilisée à la place de l’eau. Dans ces conditions, la valeur de E_h approche –60 mV et la lixiviation des éléments augmente considérablement, cet effet étant plus prononcé pour le plutonium. Pour citer cet article : E.K. Legin et al., C. R. Chimie 7 (2004).     

Structural and magnetic properties of the solid solution () YMn1−x(Cu3/4Mo1/4)xO3

Recently, the ferroelectromagnet YMnO₃ has been the focus of interest because it exhibits both antiferromagnetism (Néel temperature 80 K) and ferroelectricity (Curie temperature 914 K). There have been no reports of complete YMn_1−xM_xO₃ solid solutions in which substitution of the foreign M cation preserves the hexagonal P6₃cm structure. In contrast there exist several homeotypic phases with the general formula, Ln_1+nCu_nMO_3+3n (n=1 (M=Ti), 2 (M=V) and 3 (M=Mo); Ln: lanthanide). Several YMn_1−x(Cu_3/4Mo_1/4)_xO₃ compounds have been synthesized. The solid solution, from YMnO₃ (x=0) to YCu_3/4Mo_1/4O₃ (x=1) has been characterized by X-ray diffraction and transmission electron microscopy study. For 0<x<0.9, the compounds are found to crystallize in the non-centrosymmetric structure, space group P6₃cm, of YMnO₃. The Mn-free end member, x=1, crystallizes in a complex multiple cell, the superstructure being associated to Cu³⁺/Mo⁶⁺ cationic ordering. Dilution of the Mn³⁺ magnetic array by the paramagnetic (Cu²⁺) and diamagnetic (Mo⁶⁺) cations is found to decrease the antiferromagnetic ordering temperature and it becomes undetectable for x0.5 compositions.     

In situ high temperature NMR and EXAFS experiments in rare-earth fluoride molten salts

The local structure in molten YF₃–LiF and LaF₃–LiF binaries has been investigated by NMR and EXAFS spectroscopy. For YF₃–LiF, the high-temperature ¹⁹F and ⁷Li NMR spectra have been recorded in situ in the molten state for compositions ranging from pure LiF to pure YF₃. The LaF₃–LiF system has been studied by ¹⁹F and ¹³⁹La NMR and EXAFS spectroscopy at the LIII edge of La. The local environment around the La³⁺ in the molten state does not depend on the composition, while ¹⁹F chemical shift evolution confirms the progressive formation of bridged species. To cite this article: A.-L. Rollet et al., C. R. Chimie 7 (2004).

Résumé

Étude in situ par spectroscopies RMN et EXAFS à haute température de fluorures de terres rares fondus. La structure locale des mélanges fondus YF₃–LiF et LaF₃–LiF a été étudiée par spectroscopies RMN et EXAFS à haute température. Pour le système YF₃–LiF, les spectres RMN à haute température de ¹⁹F et ⁷Li ont été enregistrés in situ dans le liquide pour différentes compositions variant de LiF pur à YF₃ pur. Le système LaF₃–LiF a été étudié par RMN de ¹⁹F et ¹³⁹La, et par EXAFS au seuil LIII du lanthane. L’environnement autour du La³⁺ à l’état fondu ne dépend pas de la composition, alors que les évolutions du déplacement chimique du fluor confirment la formation progressive d’espèces pontantes. Pour citer cet article : A.-L. Rollet et al., C. R. Chimie 7 (2004).     

Structure and Magnetism of Pr1−xSrxFeO3−δ

Crystal structure, redox, and magnetic properties for the Pr_1−xSr_xFeO_3−δ solid-solution phase have been studied. Oxidized samples (prepared in air at 900°C) crystallize in the GdFeO₃-type structure for 0≤x≤0.80, and probably in the Sr₈Fe₈O₂₃-type (unpublished) structure for x=0.90. Reduced samples (containing virtually only Fe³⁺) crystallize as the perovskite aristotype for x=0.50 and 0.67 with randomly distributed vacancies. The Fe⁴⁺ content increases linearly in the oxidized samples up to x≈0.70, whereupon it stabilizes at around 55%. Antiferromagnetic ordering of the G type is observed for oxidized samples (0≤x≤0.90) which show decreasing Néel temperature and ordered magnetic moment with increasing x, while the Néel temperature is nearly constant at 700 K for reduced samples. Electronic transitions for iron from an average-valence state via charge-separated to disproportionated states are proposed from anomalies in magnetic susceptibility curves in the temperature ranges 500–600 K and 150–185 K.     

Mössbauer study of the FeV2O4---Fe3O4 system

Mössbauer spectra of the Fe_1+xV_2−xO₄ spinel solid solutions are taken to investigate the cation distribution. Room temperature spectra can be interpreted by assuming that the cation distribution is represented approximately as Fe²⁺[Fe³⁺_xV³⁺_2−x]O₄ for 0 x 0.35 and Fe³⁺[Fe²⁺Fe³⁺_x−1V³⁺_2−x]O₄ for 1 x 2 and the ionic valence arrangement changes from the 2-3-3 type (Fe²⁺[Fe³⁺_xV³⁺_2−x]O₄) to the 3-2-3 one (Fe³⁺[Fe²⁺V³⁺]O₄) in the range 0.35 x 1. Fe₂VO₄ is found to be 3-2-3 spinel, Fe³⁺[Fe²⁺V³⁺]O₄. Its paramagnetic spectrum at 473°K is, however, composed of a broad single line with isomer shift value of 0.61 mm/sec relative to stainless steel, in which the line splitting due to the ferric and ferrous ions is rendered indistinguishable.     

Thermodynamique de composes azotes III. Etude Thermochimique de la glycine et de la l-α-alanine

The enthalpies of formation of glycine and L-α-alanine are determined by two complementary techniques: combustion calorimetry and change of state (sublimation) calorimetry.

Full-size image (2K)

Full-size image (2K)

The values of the experimental and theoretical energy of conjugation of these two molecules (partially conjugated) and the energetical value of the C---N bond in Laidler's scheme, derived from the experimental enthalpy of atomization, are also given.

Full-size image (3K)

Full-size image (3K)

Résumé

Les enthalpies de combustion à létat condensé de la glycine et de la L-α-alanine ont été déterminées à d'un calorìmetre isopéribolique à bombe rotative. Leurs valeurs à l'état standard à 298,15 K sont: δH°_c = −(972,98±0,19) kJ mol⁻¹ pour la glycine et ΔHδ_c = −(1621,45 − 0,48) kJ mol^-1 pour la L-α-alanine. Les enthalpies de sublimation à l'état standard à 298,15 K ont été obtenues par calori-     

Pillaring of Layered Perovskites, K1−xLaxCa2−xNb3O10, with Nanosized Fe2O3 Particles

Nanosized Fe₂O₃ clusters are pillared in the interlayer spaces of layered perovskites, H_1−xLa_xCa_2−xNb₃O₁₀ (0≤x≤0.75) by a guest-exchange reaction using the trinuclear acetato-hydroxo iron cation, [Fe₃(OCOCH₃)₇ OH·2H₂O]⁺. The interlayer spaces of niobate layers are pre-expanded with n-butylammonium cations (n-C₄H₉NH⁺₃), which are subsequently replaced by bulky iron pillaring species to form Fe(III) complex intercalated layer niobates. Upon heating at 380°C, the interlayered acetato-hydroxo iron complexes are converted into Fe₂O₃ nanoclusters with a thickness of ca. 3.5 Å irrespective of the interlayer charge density (x). The band-gap energy of the Fe₂O₃ pillars (E_g2.25 eV) is slightly larger than that of bulk Fe₂O₃ (E_g2.20 eV) but is smaller than that expected for such a small-sized semiconductor, which can be assigned to the pancake-shaped Fe₂O₃ pillars of 3.5 Å in height with comparatively large lateral dimension. X-ray absorption spectroscopic measurements at the Fe K-edge are carried out in order to obtain structural information on the Fe₂O₃ pillars stabilized between the niobate layers. XANES analysis reveals that the interlayer FeO₆ octahedra have coordination environments similar to that of bulk α-Fe₂O₃, but noncentrosymmetric distortion of interlayered FeO₆ is enhanced due to the asymmetric electric potential exerted by the negatively charged niobate layers. Scanning electron microscopic observation and nitrogen adsorption–desorption isotherm measurement suggest that the pillared derivatives are nanoporous materials with the highest BET specific surface area of ca. 116 m²/g.     

Titanate-based ceramics for separated long-lived radionuclides

Studies have been conducted in France to minimize the potential long-term impact of nuclear waste by enhanced chemical separation of the minor actinides (Np, Am, Cm) and some long-lived fission products (I, Cs, Tc). Two options may be considered following this work: (i) the initial reference option is transmutation by neutron bombardment in nuclear facilities, (ii) the second option would be to incorporate the separated elements into an inorganic matrix ensuring long-term stability. In the case of specific conditioning, zirconolite and hollandite are the potential host phases for the minor actinides and caesium, respectively. Both of these matrices have shown strong potential: (i) for incorporating the respective radioelement in the crystalline structure, (ii) for fabricating the ceramic by natural sintering in air, (iii) for chemical durability with a very low initial alteration rate (about 10^–2 g m^–2 d^–1 at 100 °C), then very rapidly reach alteration rates more than four orders of magnitude lower. In the case of zirconolite ceramics, the high chemical durability is conserved even after amorphization of the crystalline structure by external irradiation with heavy ions or by self-irradiation in natural zirconolites 550 million years old. To cite this article: C. Fillet et al., C. R. Chimie 7 (2004).

Résumé

Pour réduire l'impact potentiel à long terme des déchets nucléaires, des études sont conduites en France sur la séparation chimique poussée des actinides mineurs (Np, Am, Cm) et de certains produits de fission à vie longue (I, Cs, Tc). À l'issue de cette étape, deux options sont envisageables : (i) la transmutation par bombardement neutronique dans des systèmes nucléaires est la première option de référence, (ii) la seconde option consisterait à incorporer les éléments séparés des autres déchets nucléaires dans une matrice minérale stable à long terme. Dans le cadre d'un conditionnement spécifique, la zirconolite et la hollandite sont des phases hôtes potentielles respectivement pour les actinides mineurs et le césium. Ces deux matrices ont montré une potentialité élevée (i) d'incorporation du radioélément considéré dans la structure cristalline, (ii) d'élaboration de la céramique par des procédés de frittage naturel sous air, (iii) de durabilité chimique, avec une vitesse initiale d'altération très faible (de l'ordre de 10^–2 g m^–2 j^–1 à 100 °C), puis très rapidement des diminutions des vitesses d'altération de plus de quatre ordres de grandeur. Pour la céramique zirconolite, cette propriété de durabilité chimique élevée reste conservée, même après amorphisation de la structure cristalline par irradiation externe aux ions lourds ou par auto-irradiation sur des zirconolite naturelles âgées de 550 millions d'années. Pour citer cet article : C. Fillet et al., C. R. Chimie 7 (2004).     

Insulator–metal transition in Nd0.8Na0.2Mn(1−x)CoxO3 perovskites

The electric and magnetic properties of the perovskites Nd_0.8Na_0.2Mn_(1−x)Co_xO₃ (0x0.2) prepared by the usual ceramic procedure were investigated. The insulator-to-metal-like (IM) transition, closely related to a ferromagnetic arrangement, was revealed for the composition of x=0.04 and a similar tendency was detected for x=0. The insulating behavior persists down to low temperatures for higher contents of cobalt ions in spite of the transition to the bulk ferromagnetism. The properties are interpreted in terms of the steric distortion, tilting of the Mn(Co)O₆ octahedra and the double-exchange interactions of the type Mn³⁺–O²⁻–Mn⁴⁺and Mn^3.5+δ–O²⁻–Co²⁺, respectively. Presence of antiferromagnetic domains in the ferromagnetic matrix for the most of cobalt-substituted samples is supposed.     

Crystal structure and magnetic properties of Sr4Mn2NiO9

The crystal structure of Sr₄Mn₂NiO₉ has been refined on single crystal. This phase belongs to the series A_1+x(A^′_xB_1–x)O₃ (x=1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with ≈80% in the pseudo square faces of the prism and ≈20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr₄Mn₂NiO₉ is antiferromagnetic with a Néel temperature at T=3 K. The Curie constant measured at high temperature is in good agreement with ≈80% of the Ni²⁺ ions in the spin state configuration S=0.     

Synthesis and Properties of the Mixed Hydrated Oxides V2?yWyO5 + δ < eqid2 > nH2O

Compounds of the general formula V_{2 − y}W_yO_{5 + δ} < eqid3 > nH₂O (0 < y ≤ 0.25) with the layered structure of polyvanadic acid V₂O₅ < eqid4 > nH₂O (H₂V₁₂O_{31 − δ} < eqid5 > nH₂O) have been prepared from peroxide solutions using the sol–gel process. The samples contain up to 5–8 wt% vanadium (IV). The water content changes within the range of 0.7 ≤ n ≤ 1.5 in depending on tungsten concentration. The V_{2 − y}W_yO_{5 + δ} < eqid6 > nH₂O (y ≤ 0.125) form the thin films described an interlayer distance of 11.60 ± 0.05 Å. The thermal properties, IR, and X-ray photoelectron spectra of the compounds synthesized have been studied. The thermal stability of the phases increases with the rising of tungsten content. The dehydration finishes with the forming solid solution V_2−yW_yO₅ and WO₃. The electrical conductivity of V_2−yW_yO_{5 + δ} < eqid7 > nH₂O (0 < y ≤ 0.25) powders was measured between 293 and 473 K at a relative humidity of 12%. The activation energy of conduction is independent upon the W content and equals 0.22–0.24 eV. Partial substitution of vanadium for tungsten was found to reduce the conductivity of the phases. The conductivity of the films increases with the increasing of relative air humidity and is governed by proton diffusion across the V-O-W layers.     

Research and application of inorganic selective sorbents at Mayak PA

This work has been performed in order to identify selective inorganic sorbents for caesium and strontium. Thin-layer sorbents with nickel ferrocyanide embedded in an inert matrix were found to be the best for caesium. Sorbents including non-stoichiometric manganese dioxide were selected for strontium. Bench tests have been carried out on the purification of desalted water of SNF storage-pool from ¹³⁷Cs, and on the purification of contaminated natural water from ⁹⁰Sr. The facility for synthesizing the ferrocyanide sorbent with the registered mark ‘Seleks-CFN’ has been brought into operation. The sorbent ISM-S seems promising for ⁹⁰Sr decontamination. To cite this article: M.V. Logunov et al., C. R. Chimie 7 (2004).

Résumé

Recherches et applications sur l’utilisation de sorbants spécifiques à Mayak. Des sorbants sélectifs du césium et du strontium ont été identifiés. Pour le césium, le meilleur s’avère être le ferrocyanure de nickel, s’il est utilisé sous forme de couche mince. Pour le strontium, on a sélectionné des composés non stœchiométriques de dioxyde de manganèse. On a mené des tests visant à épurer en césium l’eau des piscines d’entreposage des combustibles nucléaires usagés, et en strontium des eaux contaminées. Une installation industrielle permettant de préparer le sorbant à base de ferrocyanure de marque « Seleks-CFN » a été réalisée. Le sorbant ISM-S semble prometteur pour la décontamination en strontium. Pour citer cet article : M.V. Logunov et al., C. R. Chimie 7 (2004).