Über die Eigenschaftsänderungen beim Einbau von Tav in Ba2Gd0,67UO6

The Variation of Properties by Incorporation of Ta^v in Ba₂Gd_0.67UO₆ In Ba₂Gd□_0.33U^VIO₆ the complete substitution of U^VI by Ta^V is only possible by filling up the gadolinium vacancies (Ba₂Gd_0.67+0.33xU_1?xTa_xO₆), whereas in the series Ba₂Gd_0.67U_1?yTa_yO_6–0.5y the phase boundary is reached with y = 0.1. Depending on x the variation of the properties is studied by X-ray and spectroscopic methods.     

Über Geordnete Perowskite mit Kationenfehlstellen. II. Der Ersatz von UVI durch NbV in Ba2Gd0,67□0,33UO6

On Ordered Perovskites with Cationic Vacancies. II. The Incorporation of Nb^V in Ba₂Gd_0,67□_0,33UO₆ In Ba₂Gd_0.67□_0.33UO₆ a complete substitution of U^VI by Nb^V is possible by filling the cationic vacancies (x-phase: Ba₂Gd_0.67+0.33xU_1?xNb_xO₆). For the y-Phase (Ba₂Gd_0.67U_1?yNb_yO_6?0.5y) solid solutions are formed only for y ? 0.5. The properties of both phases are studied by x-ray and spectroscopic methods. In Ba₂GdNbO₆ – in contrary to the complete ordered Ba₂GdTaO₆ – the order of gadolinium and niobium id partial.     

An improved gravimetric method for determining oxygen in binary and ternary uranium oxides by addition of alkali or alkaline earth metal nitrate

A known amount of lithium or calcium nitrate solution is added to the sample powder which is then heated in air or oxygen. The oxygen in test samples of UO_2+x, Sr_0.1U_0.9O_{2 + x} and Sr_0.2U_0.5O_{2 + x} was determined with an estimated standard deviation of ± 0.002.     

Uranium oxide clusters by laser desorption ionization during MALDI-TOF MS analysis of uranium(VI)

Laser desorption ionization (LDI) mode of matrix-assisted laser desorptionionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis of uranium(VI)leads to the formation of uranium oxides clusters, as with fast atom bombardment(FAB). Different uranium clusters than those with FAB were observed. Threedifferent families of formula (UO₂)_x O_y ²⁺, and two of formula (UO₂)_x O_y ²⁺ were found.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Magnetic studies on ScyU1−yO2+x solid solutions

Magnetic susceptibilities of Sc_yU_1−yO_2+x solid solutions have been measured from 2.7 K to room temperature. The magnetic moment and Weiss constant have been determined in the temperature range in which the Curie-Weiss law holds. For the solid solutions showing antiferromagnetic transition, the Néel temperature has also been determined. The substitution of Sc³⁺ for U⁴⁺ was found to effect not only magnetic dilution of UO₂, but also oxidation of U⁴⁺ to U⁵⁺. Excess oxygen ions which entered the interstitial sites, weakened the antiferromagnetic interaction between uranium ions and oxidized U⁴⁺ to U⁵⁺. The effect of oxygen vacancies on the antiferromagnetic interaction was small in the concentration range of this experiment (0.8 a/o).     

Determination of Oxygen to Uranium Ratio in Uranium Dioxide Nuclear Fuel by Differential Pulse Polarography

A differential pulse polarographic method for determination of oxygen to uranium ratio in uranium oxides is fully described. An accuracy ?2.62% to +4.35% was achieved by calibrating the method against standard U₃O₃, replicate test runs with UO₂, gave a precision of ±4.59% or better. The method is now successfully used in routine analysis for UO² fuel.     

铁和锰的化学状态对 LaFexMnyAl12-x-yO19 催化剂上 N2O 分解的影响

 以共沉淀法制备了 LaFexMnyAl12-x-yO19 六铝酸盐催化剂, 并用 X 射线衍射、扫描电镜、N2 吸附-脱附、紫外-可见漫反射光谱和穆斯堡尔谱对催化剂进行了表征, 考察了催化剂上高浓度 N2O 分解反应的性能. 结果表明, 在所考察的条件下, Mn 比 Fe 更有利于促进六铝酸盐晶相的形成. LaFexAl12-xO19 (x = 0.5, 1) 中 Fe 以 Fe3+位于六铝酸盐尖晶石结构中的四面体位和镜面层结构中的三角双锥位, 其中后者为 N2O 分解的主要活性中心. LaMnyAl12-yO19 (y = 0.5, 1) 中 Mn 优先以 Mn2+进入四面体位, 然后以 Mn3+进入尖晶石结构中的八面体位, 并成为 N2O 分解的主要活性中心.     

Defect chemistry of uranium oxides

Uranium oxides are known as nonstoichiometric compounds whose composition changes according to external conditions such as temperature and oxygen partial pressure. The change of composition caused by the formation of defect structure results in a change of their properties. In this paper, the compositional changes of UO₂ and doped UO₂ [(U, M)O₂; M=La, Ti, Pu, Th, Nb, Cr, etc.] and also those of other uranium oxides (U₄O₉, U₃O₈) are shown against oxygen partial pressure. From the results of doped UO₂, it is concluded that the valence control rule holds to a first approximation. The defect structures are estimated both from log x vs. log Po₂ (x: deviation from the stoichiometric composition and Po₂: oxygen partial pressure) and log vs. log Po₂ (: electrical conductivity) relations. The defect structures of UO₂ and doped UO₂ are derived based on the Willis model for UO_2+x. The detect structure of U₄O₉ phase is similar to that of UO_2+x, but the defect structures of U₃O₈ phase are complicated due to the existence of many higher-order phase transitions. The thermodynamic data such as the partial molar enthalpy and entropy and the heat capacity are important to characterize the defect structure. The high temperature heat capacities of UO₂ doped with Gd show pronounced increases at high temperatures the onset temperature decreases as the dopant content increases. The increase of heat capacity is interpreted to be due to the formation of lattice defects. The heat capacity measurements on U₄O₉ and U₃O₈ clucidate the presence of the phase transition. The mechanisms of these phase transitions are discussed.     

Über Perowskitphasen in den Systemen BaO–SE2O3–UO2,x mit SE = Seltene Erden,La und Y. II. Verbindungen der Zusammensetzung Ba2(SE0,67U0,33)UO6,17

In the BaO–SE₂O₃–UO_2.x system the formation of the compounds Ba₂(SE_0,67U_0.33)UO_6.17 is observed. They crystallize in a pseudocubic ordered perovskite lattice, and contain tetravalent and pentavalent uranium in the ratio 1:3. Their magnetic and spectroscopic properties are reported.     

Gibt es „Wolframylgruppierungen”︁? Über Perowskitphasen im System Ba2Y0,67UO6?Ba2CaWO6

Do ? Wolframyl Groups ”? Exist? On Perovskite Phases in the System Ba₂Y_0,67UO₆ ? Ba₂CaWO₆ In the system Ba₂Y_{0.67(1? x)}Ca_xU_{1? x}W_xO₆ a solid solution series is formed up to x ? 0.85. The properties are studied by x-ray and spectroscopic methods.     

Electronic absorption spectroscopy of alkaline earth metal uranate compounds

Summary Electronic absorption spectra have been measured by diffuse reflectance for MgUO_4–x, MgU₃O₉, CaUo)_4–x, Ca₂UO₅, Ca₃UO₆, Ca₂U₃O₁₁, CaU₂O₇, CaU₄O₁₂, SrUO₃, SrUO₄, SrUO_3.67, Sr₂U₃O₁₁, SrU₄O_12.8, Sr₂UO₅, Sr₃UO₆, BaUO₄, Ba₃UO₆, BaU₂O₇, Ba₂U₂O₇ and Ba₂U₃O₁₁.Measurements in the near i.r. region of the spectrum have identified transitions arising within the manifold of the 5f electronic levels which indicate the presence of uranium(V) in certain compounds. The portion of the spectrum between 20 000 and 30 000 cm^–1 is shown to contain charge-transfer transitions and, in certain instances, vibrational progressions which are characteristic of the symmetry of the UO₆ octahedron in the solid state structure.     

Magnetic studies on (U,La)O2+x solid solutions

Magnetic susceptibilities of La_yU_1−yO_2+x solid solutions with fluorite structure were measured from 4.2 K to room temperature. An antiferromagnetic transition was observed for the solid solutions with lanthanum concentration0 ≤ y ≤ 0.3 in both stoichiometric (x = 0) and hypostoichiometric oxygen range (x < 0). From comparison of the magnetic properties of solid solutions with different oxygen amounts (x < 0, x = 0, x > 0), both oxygen vacancies and interstitial oxygens were found to weaken the magnetic exchange interactions between uranium ions. The Ne´el temperature decreased with decreasing uranium concentration. The variation of the Ne´el temperature of (U, La)O₂ solid solutions with uranium concentration was different from that of (U, Th)O₂ solid solutions. The magnetic moment decreased with decreasing uranium concentration. Its rate was larger than that of (U, Th)O₂ solid solutions and was comparable with that of (U, Y)O₂ solid solutions. The oxidation state of uranium in the solid solutions was examined from the magnetic susceptibility data. The uranium ions were found to be in either the tetravalent or the pentavalent state. The effect of magnetic dilution was larger with La₂O₃ than with Y₂O₃ and/or Sc₂O₃.     

Thermodynamics and phase relationships of the ternary lanthanum-uranium-oxygen system

In the selected regions La:(La + U) = 0.05 and O:(La + U) = 2.00 of the ternary system lanthanum-uranium-oxygen emf measurements on solid state galvanic cells, coulometric titrations, and X-ray diffraction techniques were used to obtain phase boundaries and thermodynamic data in the temperature range from 600 to 1000°C. For the first time order disorder transformations of La_1−yU_yO_2+x up to 15 mole% lanthanum are reported. The transformation temperature is 1415°K for UO_2.23; 1397°K for La_0.05U_0.95O_2.23, and 1449°K for La_0.15U_0.85O_2.23. The vibrational entropy component of excess oxygen in M_1−yU_yO_2+x is estimated.     

Über Perowskitphasen des Systems Ba2Y0,67U1−xWxO6

On Perovskite Phases of the System Ba₂Y_0,67U_1?xW_xO₆ A solid solution series is formed between the polymorphic perovskites Ba₂Y_0.67UO₆ and Ba₂Y_0.67WO₆ (cubic: a = 8.37₂ Å; hexagonal: a = 4× 5.88₁ Å and c = 4× 7.77₈ Å). The structure is cubic between x = 0.1 and 0.99 and for x > 0.95 hexagonal as well. Strong deviations from the ideal behaviour are detectabel with spectroscopic methods. The shape of the UO₆ and WO₆ octahedrons experiences only minor changes within the series.     

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba_1-xSr_xM_yTi_1-yO₃ (M = Zr, Sn, 0?x?0.4, 0?y?0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr²+and Zr⁴⁺ or Sn⁴⁺ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO₃ phase at room temperature.     

A gravimetric method for the determination of oxygen in uranium oxides and ternary uranium oxides by addition of alkaline earth compounds

A simple gravimetric determination of oxygen in uranium oxides and ternary uranium oxides is described. In alkaline earth uranates which are formed by heating in air at 800–1100°C, uranium is in the hexavalent state over certain continuous ranges of alkaline earth-to-uranium ratios. Thus, if an alkaline earth uranate or a compound containing an alkaline earth element, e.g. MgO, is mixed with the oxide sample and heated in air under suitable conditions, oxygen can be determined from the weight change before and after the reaction. The standard deviation of the O:U ratio for a UO_2+x test sample is ±0.0008–0.001, if a correction is applied for atmospheric moisture absorbed during mixing.     

Über Das System Ba2Sm0,67U1−xWxO6

On the System Ba₂Sm _0.67U_1?xW_xO₆ The ordered perovskites Ba₂Sm_0.67UO₆ and Ba₂Sm_0.67 WO₆ are forming a complete serie of solid solutions with 4 formula units Ba₂Sm_0.67U_1?xW_xO₆ in the unit cell. By diffuse reflectance and i.r.-spectroscopic measurements the relations between color and constitution are shown.     

Phase Equilibria and Crystal Structure of Complex Oxides in the La–Sr–Co–Ni– System

Phase equilibria in the La–Sr–Co–Ni–O system were studied in air at 1100°. The samples for the study were synthesized by the standard ceramic and citrate processes. The limiting solubility and structure of La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were determined by Xray powder diffraction analysis. La_1-xSr_xCo_1-yNi_yO₃- solid solutions with 0 x 0.5 have a distorted rhombohedral perovskitelike structure (R c space group). An increase in the strontium concentration reduces the rhombohedral distortions, and the compounds with x < 0.5 have an ideal cubic structure (Pm3m space group). (La_1-xSr_x)₂Co_1-yNi_yO₄ crystals have a tetragonal K₂NiF₄ type unit cell (I4/mmm space group). The relationships between unit cell parameters and compositions were obtained for singlephase La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ samples. The existence regions of La_1-xSr_xCo_1-yNi_yO₃- and La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were distinguished on P–T phase diagrams.     

Oxidative leaching of uranium from SIMFUEL using Na<Subscript>2</Subscript>CO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O<Subscript>2</Subscript> solution

A feasibility and basic study to find a possibility to develop such a process for recovering U alone from spent fuel by using the methods of an oxidative leaching and a precipitation of U in high alkaline carbonate media was newly suggested with the characteristics of a highly enhanced proliferation-resistance and more environmental friendliness. This study has focused on the examination of an oxidative leaching of uranium from SIMFUEL powders contained 16 elements (U, Ce, Gd, La, Nd, Pr, Sm, Eu, Y, Mo, Pd, Ru, Zr, Ba, Sr, and Te) using a Na₂CO₃ solution with hydrogen peroxide. U₃O₈ was dissolved more rapidly than UO₂ in a carbonate solution. However, in the presence of H₂O₂, we can find out that the leaching rates of the reduced SIMFUEL powder are faster than the oxidized SIMFUEL powder. In carbonate solutions with hydrogen peroxide, uranium oxides were dissolved in the form of uranyl peroxo-carbonato complexes. UO₂(O₂) _x (CO₃) _y ^2−2x−2y , where x/y has 1/2, 2/1.