Fission Gas Bubbles Characterisation in Irradiated UO2 Fuel by SEM, EPMA and SIMS

The behaviour of gases produced by fission is of great importance for nuclear fuel operation. Within this context, an experimental method for the characterisation of the fission gas including gas bubbles in an irradiated UO₂ nuclear fuel was developed in our laboratory using SIMS, EPMA and SEM results. SIMS and EPMA have been used to measure the radial distribution of xenon and SEM gives information on bubble formation across the fuel pellet radius. Using SIMS, xenon concentration can be determined in the matrix and in the bubbles. A quantification method, allowing the determination of the total inventory of xenon, is proposed and qualified with EPMA results. It is concluded that the complementary micro-analytical techniques SIMS, EPMA and SEM are very powerful tools for the characterisation of the fission gas bubbles in irradiated nuclear fuel.     

Reaction Mechanisms in Both a CCl2F2/O2/Ar and a CCl2F2/H2/Ar RF Plasma Environment

Decomposition of dichlorodifluoromethane (CCl₂F₂ or CFC-12) in aradiofrequency (RF) plasma system is demonstrated. The CCl₂F₂decomposition fractions _{CCl 2 F 2} and mole fractionsof detected products in the effluent gas stream of CCl₂F₂/O₂/Ar andCCl₂F₂/H₂/Ar plasma, respectively, have been determined. The experimentalparameters including input power wattage, O₂/CCl₂F₂ or H₂/CCl₂F₂ ratio,operational pressure, and CCl₂F₂ feeding concentration wereinvestigated. The main carbonaceous product in the CCl₂F₂/O₂/Arplasma system was CO₂, while that in the CCl₂F₂/H₂/Ar plasma systemwas CH₄ and C₂H₂. Furthermore, the possible reaction pathways werebuilt-up and elucidated in this study. The results of the experimentsshowed that the highly electronegative chlorine and fluorine wouldeasily separate from the CCl₂F₂ molecule and combine with the addedreaction gas. This led to the reactions terminated with the CO₂,CH₄, and C₂H₂ formation, because of their high bonding strength. Theaddition of hydrogen would form a preferential pathway for the HCland HF formations, which were thermodynamically stable diatomicspecies that would limit the production of CCl₃F, CClF₃, CF₄, andCCl₄. In addition, the HCl and HF could be removed by neutral orscrubber method. Hence, a hydrogen-based RF plasma system provideda better alternative to decompose CCl₂F₂.     

Rate Constant for the Reaction of the OH-Radical with CH2F2

The rate constant value of k ₁ = (6.05 ± 0.20)×10⁹ cm³ mol^–1 s^–1 (with ± 1 error) has been determined for the reaction OH + CH₂F₂ (1) by applying the discharge-flow/resonance-fluorescence method at 298 K.     

Spin-spin coupling constant 3 J H,F as a reliable criterion for recognition of individual regioisomeric and tautomeric pairs of H(CF2)2-containing isoxazoles and pyrazoles

The spin-spin coupling constant ³ J _H,F of the H(CF₂)₂ group varies within 1.6—3.5 Hz for 5-R^F- and 3.8—4.5 Hz for 3-R^F-isoxazoles and pyrazoles in CDCl₃ and can serve as a reliable criterion for recognition of regioisomeric and tautomeric structures of H(CF₂)₂-containing heterocyclic compounds.     

A pseudopotential study of the hydrogen bond in H2O·H2S,H2S·H2S and H2O·H2Se systems

Intermolecular potential energy curves for the hydrogen bonded systems H₂O·H₂S, H₂O·H₂Se and H₂S·H₂S were calculated with nonempirical pseudopotentials using optimized-in-molecules basis sets augmented by polarization functions. The H₂O·H₂O interaction energy curve has been also considered as a test case. The present results for H₂O·H₂S and H₂S·H₂S indicate much weaker intermolecular interactions than those found in previous ab initio calculations. The H₂O·H₂Se interaction was found to be quite similar to H₂O·H₂S.This work was partly supported by the Polish Academy of Sciences within the Project PAN-09, 7.1.1.1On leave from Quantum Chemistry Laboratory, Dept. of Chemistry, University of Warsaw, Pasteura 1, 02-093. Warsaw, Poland     

Electrocatalytic CO2 Reduction and H2 Evolution by a Copper (II) Complex with Redox-Active Ligand

The process of electrocatalytic CO₂ reduction and H₂ evolution from water, regarding renewable energy, has become one of the global solutions to problems related to energy consumption and environmental degradation. In order to promote the electrocatalytic reactivity, the study of the role of ligands in catalysis has attracted more and more attention. Herein, we have developed a copper (II) complex with redox-active ligand [Cu(L¹)₂NO₃]NO₃ (1, L¹ = 2-(6-methoxypyridin-2-yl)-6-nitro-1h-benzo [D] imidazole). X-ray crystallography reveals that the Cu ion in cation of complex 1 is coordinated by two redox ligands L¹ and one labile nitrate ligand, which could assist the metal center for catalysis. The longer Cu-O bond between the metal center and the labile nitrate ligand would break to provide an open coordination site for the binding of the substrate during the catalytic process. The electrocatalytic investigation combined with DFT calculations demonstrate that the copper (II) complex could homogeneously catalyze CO₂ reduction towards CO and H₂ evolution, and this could occur with great performance due to the cooperative effect between the central Cu (II) ion and the redox- active ligand L¹. Further, we discovered that the added proton source H₂O and TsOH·H₂O (p-Toluenesulfonic acid) could greatly enhance its electrocatalytic activity for CO₂ reduction and H₂ evolution, respectively.     

Chemical mechanisms in C3F8-H2 radiofrequency discharges

Discharges fed with C₃F₈-H₂ mixtures have been studied by means of mass spectrometry in a tubular reactor operated at 0.5 torr and 50 W. Comparison of the results with those obtained with emission actinometry give additional evidence that emission actinometry and mass spectrometry are powerful diagnostic tools to monitor stable and unstable species in discharges utilized for dry etching and polymer depositions. Mechanisms for end product formation and polymer deposition are also discussed.     

In2O3八面体的碳还原法制备及其发光性能研究

In₂O₃ octahedrons were synthesized by carbothermal reduction using In₂O₃ nanoparticles as the source material. The as-synthesized products were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray(EDX), scanning electron microscopy(SEM), transmission electron microscopy(TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction analysis(SAED) and Room-temperature photoluminescence(PL) spectroscopy. The results show that the products are single-crystalline In₂O₃ octahedrons, the length of the octahedrons is in the range of 400～3 000 nm; the PL patterns display two peaks located at 447nm and 555 nm upon excitation at 380 nm, and the other two peaks located at 444 nm and 550 nm upon excitation at 325 nm; the excitation pattern shows two peaks located at 274 nm and 371 nm, respectively. The growth mechanism of the In₂O₃ octahedrons is discussed, and the high supersaturation ratio is considered as the key factor.     

Comparison of CO2 Reduction Performance with NH3 and H2O between Cu/TiO2 and Pd/TiO2

The aim of this study is to clarify the effect of doped metal type on CO₂ reduction characteristics of TiO₂ with NH₃ and H₂O. Cu and Pd have been selected as dopants for TiO₂. In addition, the impact of molar ratio of CO₂ to reductants NH₃ and H₂O has been investigated. A TiO₂ photocatalyst was prepared by a sol-gel and dip-coating process, and then doped with Cu or Pd fine particles by using the pulse arc plasma gun method. The prepared Cu/TiO₂ film and Pd/TiO₂ film were characterized by SEM, EPMA, TEM, STEM, EDX, EDS and EELS. This study also has investigated the performance of CO₂ reduction under the illumination condition of Xe lamp with or without ultraviolet (UV) light. As a result, it is revealed that the CO₂ reduction performance with Cu/TiO₂ under the illumination condition of Xe lamp with UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:1:1 while that without UV light is the highest when the molar ratio of CO₂/NH₃/H₂O = 1:0.5:0.5. It is revealed that the CO₂ reduction performance of Pd/TiO₂ is the highest for the molar ratio of CO₂/NH₃/H₂O = 1:1:1 no matter the used Xe lamp was with or without UV light. The molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp with UV light was 10.2 μmol/g, while that for Pd/TiO₂ was 5.5 μmol/g. Meanwhile, the molar quantity of CO per unit weight of photocatalyst for Cu/TiO₂ produced under the illumination condition of Xe lamp without UV light was 2.5 μmol/g, while that for Pd/TiO₂ was 3.5 μmol/g. This study has concluded that Cu/TiO₂ is superior to Pd/TiO₂ from the viewpoint of the molar quantity of CO per unit weight of photocatalyst as well as the quantum efficiency.     

The reaction of MgCl2·4H2O with CCl2F2

A new reaction of MgCl₂·4H₂O with CCl₂F₂ is investigated by DTA and TG from room temperature to 350 °C. It is observed that MgF₂ was obtained between 252 and 350 °C, Below the temperature, MgCl₂·4H₂O dehydrates and hydrolyzes to MgCl₂ and Mg(OH)Cl, which are the real reactants of the reaction with CCl₂F₂. The formation of MgF₂ is ascribed to the reaction of MgCl₂ and Mg(OH)Cl with HF, which forms by decomposition of CCl₂F₂ with the taking part in of H₂O released from dehydration of hydrated magnesium chloride on the surface of MgCl₂ and Mg(OH)Cl, which catalyzes the decomposition of CCl₂F₂ in this case. Consequently, the reactions are tested in the fluid-bed condition. It is found that MgF₂ formed at temperatures down to 200 °C in a fluid-bed reactor. This reaction may be used as a method of disposing of the environmentally sensitive CCl₂F₂ (rather than release into the atmosphere). It is also a method for the preparation of MgF₂.     

Gram-Scale Synthesis of an Ultrastable Microporous Metal-Organic Framework for Efficient Adsorptive Separation of C2H2/CO2 and C2H2/CH4

A highly water and thermally stable metal-organic framework (MOF) Zn₂(Pydc)(Ata)₂ (1, H₂Pydc = 3,5-pyridinedicarboxylic acid; HAta = 3-amino-1,2,4-triazole) was synthesized on a large scale using inexpensive commercially available ligands for efficient separation of C₂H₂ from CH₄ and CO₂. Compound 1 could take up 47.2 mL/g of C₂H₂ under ambient conditions but only 33.0 mL/g of CO₂ and 19.1 mL/g of CH₄. The calculated ideal absorbed solution theory (IAST) selectivities for equimolar C₂H₂/CO₂ and C₂H₂/CH₄ were 5.1 and 21.5, respectively, comparable to those many popular MOFs. The Q_st values for C₂H₂, CO₂, and CH₄ at a near-zero loading in 1 were 43.1, 32.1, and 22.5 kJ mol⁻¹, respectively. The practical separation performance for C₂H₂/CO₂ mixtures was further confirmed by column breakthrough experiments.     

Ab initio and density functional theory study of the enthalpies of formation of F2SOx and FClSOx (x=1, 2)

Enthalpies of formation of F₂SO, F₂SO₂, FClSO and FClSO₂ molecules have been determined using ab initio molecular orbital theory and density functional theory (DFT) calculations. Different DFT approaches and levels of the Gaussian-3 and the complete basis set (CBS) ab initio model chemistries have been employed to calculate enthalpies of formation from both total atomization energies and isodesmic reaction schemes. The best values at 298 K for F₂SO, F₂SO₂, FClSO and FClSO₂ as derived from an average of G3, G3B3, CBS-Q and CBS-QB3 isodesmic energies are −140.6, −181.1, −92.6 and −132.3 kcal mol⁻¹, respectively. The results obtained suggest that the accumulated small component errors found in the DFT-based methods are significantly reduced at the ab initio levels employed. Structural properties, harmonic vibrational frequencies, mode assignations and infrared intensities derived from B3LYP and mPW1PW91 functional with the 6-311+G(3df) basis set are presented.     

Rate Coefficient for Self-Association Reaction of CF2 Radicals Determined in the Afterglowof Low-Pressure C4F8 Plasmas

We have analyzed decay kinetics of CF₂ radicals in the afterglow of low-pressure, high-density C₄F₈ plasmas. The decay curve of CF₂ density has been approximated by the combination of first- and second-order kinetics. The surface loss probability evaluated from the frequency of the first-order decay process has been on the order of 10^–4. This small surface loss probability has enabled us to observe the second-order decay process. The mechanism of the second-order decay is self-association reaction between CF₂ radicals (CF₂+CF₂C₂F₄). The rate coefficient for this reaction has been evaluated as (2.6–5.3)×10^–14 cm³/s under gas pressures of 2 to 100 mTorr. The rate coefficient was found to be almost independent of the gas pressure and has been in close agreement with known values, which are determined in high gas pressures above 1 Torr.     

Molybdovanadophosphoric Acid Catalyzed Oxidation of Hydrocarbons by H2O2 to Oxygenates

Heteropoly acids of the general formula H_3+x[PMo_12-xV_xO₄₀] (where x = 1,2,3) catalyzed the oxidation of aromatic hydrocarbons at 65°C with H₂O₂ to give oxygenated products. Among the catalysts, H₄[PMo₁₁VO₄₀] was found to be a more active catalyst and its activities have been reported in the oxidation of cyclohexane, methyl cyclohexane, naphthalene, 1-methyl naphthalene and biphenyl.     

Studies on the reaction of salicylidenebenzoic-hydrazide (SBH) with Ce3+, Th4+ and UO2 2+

The stoichiometry and structure of salicylidenebenzoic-hydrazine (SBH) chelates with UO₂(II), Ce(III) and Th(IV) in buffer-ethanol mixtures and in pure ethanol is studied applying conductometric titration, visible spectrophotometry and ir-spectrophotometry. The ir-spectra revealed that coordination takes place through the C=O and C=N groups.Deceased December 1977.     

Tetracyanonickelate compounds as sorptive materials and the substitution of their H2O content by D2O

The compounds NiNi(CN)₄·3,5H₂O and Ni(NH₃)₂Ni(CN)₄·H₂O have been studied to examine the possibility of substituting their H₂O or NH₃ content by D₂O. Contact with D₂O was performed after heating the compounds to several temperatures. Depending on the degree of decomposition of the original compounds different ranges of substitution were possible. In such manner the compounds NiNi(CN)₄·3,5D₂O, NiNi(CN)₄·5D₂O, Ni(NH₃)₂Ni(CN)₄·D₂O, and Ni(D₂O)₂Ni(CN)₄·D₂O were prepared and thermally they were less stable than the original ones. The substitution by D₂O is in agreement with the sorptive properties of the original tetracyanonickelate against different organic compounds using GC, since these could substitute the guest component and sometimes also the ligands during their decomposition.     

An ab initio investigation into the SN2 reaction: Frontside attack versus backside attack in the reaction of F− with CH3F

The energy hypersurface for the attack of fluoride ion on methyl fluoride has been explored with ab initio LCAO-SCF calculations at a split-valence basis set level. Transition states for frontside and backside attack have been located. In addition to transition states, two possible F^–-CH₃F clusters have been identified. The transition state for the substitution of fluoride with retention of configuration is found to be 56 kcal/mol higher than the transition state for inversion of configuration. The transition state for hydride displacement with inversion is 62 kcal/mol above the transition state for fluoride substitution with inversion.     

RuO_2/TiO_2纳米薄膜的新构建及对CO_2的电催化还原

在旋涂有球状纳米TiO2薄膜的导电玻璃(ITO)基底上采用循环伏安法(CV)电沉积RuO2作为电催化还原CO2的阴极.采用场发射扫描电子显微镜(FE-SEM)表征了RuO2/TiO2纳米薄膜的形貌,并应用近稳态电位扫描法和计时电流法(i～t)研究了薄膜的电催化CO2性能.结果表明所构建的RuO2/TiO2薄膜中纳米粒子大小均匀、排列致密,且较传统热分解法所得催化剂有更好的电催化性能.