Preparation and characterisation of Tl2Pu(MoO4)3 and Tl4Pu(MoO4)4 in Tl-Pu-Mo-O system by X-ray and thermal methods

The quaternary Tl-Pu-Mo-O system was investigated for the first time and two new quaternary compounds Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ were synthesized by solid state reactions of Tl₂MoO₄ with Pu(MoO₄)₂ in 1:1 and 2:1 molar proportions at 773 K and 823 K, respectively. X-ray powder diffraction data of these compounds were indexed on orthorhombic system. Thermogravimetric (TG) curves of Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ were recorded in air and no significant weight changes were observed up to 973 K and 1033 K, respectively. Differential thermal analysis (DTA) curves of Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ showed endothermic peaks due to the melting of the compounds at 838 K and 1013 K, respectively. Non-isothermal kinetics of decomposition of Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ in air was studied using thermogravimetric technique. Tl₂Pu(MoO₄)₃ and Tl₄Pu(MoO₄)₄ when heated up to 1673 K decomposed to Tl₂O and MoO₃ in the gaseous form, giving solid PuO₂ as an end product. The reactions followed unimolecular nucleation and growth mechanism with activation energies of 106 kJ/mol and 157 kJ/mol, respectively.     

Thermophysical studies on the binary system UO2(NO3)2·6H2O - Sr(NO3)2

Thermoanalytical (TG-DTA-EGA) and X-ray diffraction measurements have been used to study the reaction between uranyl nitrate hexahydrate and strontium nitrate. The results confirmed the absence of a direct interaction between the two compounds. The presence of strontium nitrate, however, ensured that the extent of hydrolysis and polymerisation of uranyl nitrate hexahydrate during its dehydration and decomposition to UO₃ is significantly reduced. DTA curves recorded in both heating and cooling modes gave evidence to the occurrence of a reaction between molten strontium nitrate and uranium trioxide to form nitrato-complexes of uranium and strontium. X-ray diffraction data on reaction residues obtained at different temperatures and cooled to room temperature also showed evidence for the formation of such complexes. The results obtained indicated an increase in thermal stability of these nitrato-complexes with increase in Sr/U ratio. The complex with an Sr/U ratio of 2.0 is stable up to 660 °C and the complex with Sr/U ratio of 4.0 is stable up to 680 °C. These complexes decompose at higher temperatures to give strontium uranates.     

Decomposition and multiphase reactions in the system UO2(NO3)2·6H2O-Ni(NO3)2·6H2O at elevated temperatures

Solid state reactions between uranyl nitrate hexahydrate and nickel nitrate hexahydrate in mixtures of various ratios have been studied at elevated temperatures. The binary system of uranyl nitrate hexahydrate and nickel nitrate hexahydrate was found to form a eutectic of composition 53 mol% uranyl nitrate hexahydrate and 47 mol% nickel nitrate hexahydrate at 40 °C. The overlap of evolution of nitric oxide (NO) and water vapour above 230 °C confirmed the presence of hydroxynitrates of uranium and nickel as intermediate products. These hydroxynitrates began to react above 280 °C to form nickel uranate, NiU₃O₁₀, in the case of mixtures containing 75 mol% uranyl nitrate hexahydrate. When the proportion of uranyl nitrate hexahydrate in the mixture was higher than 75 mol%, U₃O₈ formed along with nickel uranate. For the mixtures containing uranyl nitrate hexahydrate lower than 75 mol%, NiO was observed to form along with NiU₃O₁₀.     

The pre-dose effect in natural white mica (H2KAl3(SiO4)3)

A comprehensive study of the pre-dose effect was carried out for natural white mica. A pre-dose of 1 kGy of γ-radiation followed by thermal activation to 550 °C of fired mica (heated at 800 °C for 10 h) leads to a large increase in the TL sensitivity. The TL response to γ-rays of sensitized aliquots was found to be linear-sublinear while that of unsensitized aliquots was linear-superlinear referring specifically to graphs drawn on a linear-linear scale. The change in the TL sensitivity of mica was explained by using the recombination during heating model. This study is of importance in dating and retrospective dosimetry.     

Th(NO_3)_4-UO_2(NO_3)_2-HNO_3-H_2O/30%TBP-正十二烷萃取体系主要组分分配比模型

利用文献报道的Th(NO3)4-UO2(NO3)2-HNO3-H2O/30%TBP-正十二烷体系各组分的分配比实验数据对现有的分配比模型进行分析和比对,提出了一个计算该体系各组分分配比的新模型。利用34组实验数据对新模型进行了验证,符合情况良好。计算结果表明,本文提出的模型明显优于原模型,可作为Th(NO3)4-UO2(NO3)2-HNO3-H2O/30%TBP-正十二烷萃取体系中Th(Ⅳ)、U(Ⅵ)和HNO3萃取行为计算机模拟的基础。模型建立的条件为:温度,25℃;U(Ⅵ)浓度,0~100g/L;Th(Ⅳ)浓度,0~232g/L;硝酸浓度,0~4.5mol/L。     

An experimental study on linear differential scattering coefficients of the radioactive compounds UO2(C2H3O2)2 · 2H2O and Th(NO3)4 · 5H2O at 60 keV

The linear differential scattering coefficients at 60 keV have been measured for UO₂(C₂H₃O₂)₂ · 2H₂O (uranyl-acetate) and Th(NO₃)₄ · 5H₂O (thorium-nitrate) radioactive compounds at seven angles ranging from 60° to 120° at intervals 10°. The obtained results have been compared with relativistic and non-relativistic theoretical values.     

离子液体中UO2(CMPO)3(NO3)2的组装及CMPO萃取铀的机理

离子液体具有独特的物理化学性质,可以参与或影响两亲分子自组装。离子液体介质中的自组装研究所涉及的两亲分子多为有机化合物,而金属配合物在离子液体中的组装鲜有报道。另外,萃取剂正辛基苯基-N,N-二异丁基胺基甲酰基甲基氧化膦(CMPO)在1-乙基-3-甲基咪唑双三氟甲基磺酰亚胺盐(C₂mimNTf²)中萃取UO₂⁺²时形成的萃合物结构组成有待深入研究。本工作探究了UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²中的组装行为。原位透射电镜(原位TEM)研究表明:UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²(含70μL水)中形成聚集体,冷冻刻蚀电镜(FF-TEM)显示该聚集体是胶束。此外,研究了CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成。离子色谱结果表明:萃取前后水相中NO^-₃浓度变化不大,电喷雾质谱(ESI-MS)上均为UO₂(CMPO)₃(NTf₂)₂的碎片离子峰,这些结果说明:CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成为UO₂(CMPO)₃(NTf₂)₂而非UO₂(CMPO)₃(NO₃)₂。这有助于深入了解金属配合物在离子液体中的组装行为,并对理解CMPO-C₂mimNTf²体系萃取UO₂⁺²的机理提供了重要参考。     

Rapid synthesis of Pb5(VO4)3I, for the immobilisation of iodine radioisotopes, by microwave dielectric heating

Rapid synthesis of Pb₅(VO₄)₃I, a potential immobilisation host for iodine radioisotopes, was achieved in an open container by microwave dielectric heating of a mixture of PbO, PbI₂, and V₂O₅ at a power of 800 W for 180 s (at 2.45 GHz). The resulting ceramic bodies exhibited a zoned microstructure, differentiated by inter-granular porosity and phase assemblage, as a consequence of the inverse temperature gradient characteristic of microwave dielectric heating. Liquid PbI₂ within the interior of microwave processed ceramics assisted formation of Pb₅(VO₄)₃I, and reduced inter-granular porosity. In contrast, the exterior of microwave processed ceramics comprised poorly sintered Pb₅(VO₄)₃I with the presence of minor reagent relics. Quantitative microanalysis, electron diffraction and Rietveld analysis, confirmed the synthesis of stoichiometric Pb₅(VO₄)₃I within precision. The crystal structure of Pb₅(VO₄)₃I was found to adopt space group P6₃/m with a = 10.4429(3) Å and c = 7.4865(2) Å.     

Thermoluminescence properties of nanocrystalline K2Ca2(SO4)3:Eu irradiated with gamma rays and proton beam

Thermoluminescence properties of nanocrystalline K₂Ca₂(SO₄)₃:Eu prepared by ball milling technique have been studied and the nanophosphor’s suitability as an effective gamma radiation and proton beam dosimeter material has been examined. It is found that the nanophosphor is suitable for dosimetry over a very wide range of doses ∼1 Gy to 1 kGy for gamma radiation. And for proton beam the same nanophosphor shows a more or less linear response for the dose range 0.1-100 Gy. A comparative study of this nanophosphor with its corresponding microcrystalline form (prepared by solid-state diffusion method) as well as the nanocrystalline form prepared by (the more conventional) co-precipitation technique has shown that the nanophosphor prepared by the ball milling technique is in almost all respects better than the other two forms reported earlier.     

Thermodynamic studies on Cs4U5O17(s) and Cs2U2O7(s) by emf and calorimetric measurements

The oxygen potentials over the phase field: Cs₄U₅O₁₇(s)+Cs₂U₂O₇(s)+Cs₂U₄O₁₂(s) was determined by measuring the emf values between 1048 and 1206 K using a solid oxide electrolyte galvanic cell. The oxygen potential existing over the phase field for a given temperature can be represented by: Δμ(O₂) (kJ/mol) (±0.5)=−272.0+0.207T (K). The differential thermal analysis showed that Cs₄U₅O₁₇(s) is stable in air up to 1273 K. The molar Gibbs energy formation of Cs₄U₅O₁₇(s) was calculated from the above oxygen potentials and can be given by, Δ_fG⁰ (kJ/mol)±6=−7729+1.681T (K). The enthalpy measurements on Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were carried out from 368.3 to 905 K and 430 to 852 K respectively, using a high temperature Calvet calorimeter. The enthalpy increments, (H⁰_T−H⁰₂₉₈), in J/mol for Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) can be represented by, H⁰_T−H⁰_298.15 (Cs₄U₅O₁₇) kJ/mol±0.9=−188.221+0.518T (K)+0.433×10⁻³T² (K)−2.052×10⁻⁵T³ (K) (368 to 905 K) and H⁰_T−H⁰_298.15 (Cs₂U₂O₇) kJ/mol±0.5=−164.210+0.390T (K)+0.104×10⁻⁴T² (K)+0.140×10⁵(1/T (K)) (411 to 860 K). The thermal properties of Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were derived from the experimental values. The enthalpy of formation of (Cs₄U₅O₁₇, s) at 298.15 K was calculated by the second law method and is: Δ_fH⁰_298.15=−7645.0±4.2 kJ/mol.     

Unimolecular isomerization from (CH3)3CNC to (CH3)3CCN induced by infrared free electron laser

Irradiation of IR Free Electron Laser at Tokyo University of Science (FEL-TUS) to t-butyl isonitrile ((CH₃)₃CNC) in the gas phase induced the isomerization reaction to trimethylacetonitrile ((CH₃)₃CCN). From the kinetic analyses, the isomerization reaction was attributed to the IR multiphoton activated unimolecular process. The wide frequency tunability of FEL-TUS enabled us to reveal that the excitation of the NC as well as the CN stretching motion efficiently drove the isomerization.     

Heats of formation of (U,Mo)Al3 and U(Al,Si)3

The heats of formation of (U,Mo)Al₃ intermetallic compounds were obtained by measuring the reaction heats of U-Mo/Al dispersion samples by differential scanning calorimetry. Based on literature data for the reaction heats of U₃Si/Al and U₃Si₂/Al dispersion samples, the heats of formation of U(Al,Si)₃ as a function of the Si content were calculated. The heat of formation of (U,Mo)Al₃ becomes less negative as the Mo content increases. Conversely, the heat of formation of U(Al,Si)₃ becomes more negative with increasing Si content.     

High-temperature specific heat of UO2 ThO2, and A12O3

The high-temperature specific heat of solid UO₂, ThO₂, and Al₂O₃ can be represented by an equation of the form $\text{C}{}_{\mathrm{p(s)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) + dT}{}^3$, (1) where ?_D is the Debye temperature, F(?_D/T) is the Debye function, $\text{d}$ represents contributions of the anharmonic vibrations within the lattice, and $\text{n}$ denotes the number of atoms per molecule. In the liquid the corresponding equation is $\text{C}{}_{\mathrm{p(1)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) +}\text{h}\text{T}{}^2$, (2) where h is the anharmonic term. It is shown that for Al₂O₃ and UO₂, where experimental data for the liquid phase are also available, $\text{d}\text{h}$ has the same value, Indicating that both materials behave identically. If we compare the thermodynamic relationship $\text{C}{}_{\mathrm{p}}\text{? C}{}_{\mathrm{v}}\text{= Vα}{}^2\text{KT}$, (3) where V is the volume, $\text{α}$ the volume expansion coefficient, and $\text{K}$ the bulk modulus, with equation (1), It follows that d must be equal to $\text{Vα}{}^2\text{K}\text{T}{}^2$; the value of $\text{Vα}{}^2\text{K}\text{T}{}^2$ is calculated in the temperature region where d was obtained; within experimental error they are equal.     

Molecular dynamics simulations of C2, C2H, C2H2, C2H3, C2H4, C2H5, and C2H6 bombardment of diamond (1 1 1) surfaces

The sticking and erosion of C₂H_x molecules (where x=0-6), at 300 and 2100 K onto hydrogenated diamond (1 1 1) surfaces was investigated by means of molecular dynamics simulations. We employed both quantum-mechanical and empirical force models. Generally, the sticking probability is observed to somewhat increase when the radical temperature increases and strongly decrease with increasing number of H atoms in the molecule.     

Nd（Fe,Si）11C1．5永磁合金的中子与X射线衍射研究

用中子衍射和X射线衍射技术对配比成分为NdF10.5Si1.5C1.5的永磁合金样品的晶体结构和磁结构进行了研究。测定其为四方的BaCd11型结构,Si元素择优占据8d替代晶位,C原子进入间隙的8c晶位。中子衍射结果表明其磁结构为易面结构。     

Carbon deposition from a γ-irradiated CO2/CO/CH4/C2H6 gas mixture on the manganese oxides MnO, Mn3O4 and Mn2O3

The composition of oxides formed on steel surfaces within power reactors may influence heat transfer efficiency. Previous studies have indicated that carbon is deposited on spinal-type oxides containing manganese, iron, cobalt, nickel and chromium. In this investigation, characterised manganese oxides have been subjected to γ-irradiation under conditions similar to those experienced in reactors in an effort to understand the catalytic processes involved in deposit initiation and growth. Mn₃O₄ and Mn₂O₃, under the conditions present in the γ-cell, were reduced to MnO during the time of exposure. Relative carbon deposition rates were observed to follow the trend MnO>Mn₃O₄≈Mn₂O₃.     

Thermodynamic studies on SrThO3(s)

The Gibbs energy of formation of SrThO₃(s) has been determined using e.m.f. and manometric techniques. In the e.m.f. method, two fluoride cells have been constructed to determine Δ_fG⁰_m(SrThO₃,s,T) using CaF₂(s) as a solid electrolyte. The cells used are:

     

Reactivity of hydrogen peroxide towards Fe3O4, Fe2CoO4 and Fe2NiO4

The kinetics of CRUD oxidation by H₂O₂ has been studied using aqueous suspensions of metal oxide powder. Fe₃O₄, Fe₂CoO₄ and Fe₂NiO₄ were used as model compounds for CRUD. In addition, the activation energies for the reaction between H₂O₂ and the three CRUD models were determined. The rate constants at room temperature were determined to 6.6 (±0.4) × 10⁻⁹, 3.4 (±0.4) × 10⁻⁸ and 1.6 × 10⁻¹⁰ m min⁻¹ for Fe₃O₄, Fe₂CoO₄ and Fe₂NiO₄, respectively. The corresponding activation energies are 52 ± 4, 44 ± 5 and 57 ± 7 kJ mol⁻¹, respectively. The mechanism of the reaction is briefly discussed indicating that the final solid product in all three cases is Fe₂O₃. In addition to the experimental studies, the theoretical grounds for kinetics of reactions in particle suspensions are discussed. The theoretical discussion is also used to explain the somewhat unexpected trends in reactivity observed experimentally.     

Thermoelectric power studies of ferromagnet U2ScB6C3

The thermoelectric power (TEP) of a ferromagnet U₂ScB₆C₃ (T_C = 61 K) has been measured in the temperature range 5-300 K. The TEP is positive over the whole measured temperature range and reaches a relatively large value at room temperature of 29 μV/K. Below 30 K and above 200 K the TEP follows a straight line S(T) ∼AT, with slope of 0.23 and 0.085 μV/K², respectively. The change in the slope can be explained by the electron-phonon interaction renormalization effects or spin-reorientation associated with a change in the electronic structure. Analysing the temperature dependence of the ratio [S(T)/T]/[S_300 K/300] and taking into account the specific heat data, we suggest that spin fluctuations are another important factor in determining the thermoelectric power behaviour of U₂ScB₆C₃.