Gd2O3-Nd2O3-ZrO2-CeO2体系的高温固相反应研究

为研究Gd₂O₃-Nd₂O₃-ZrO₂-CeO₂四元氧化物体系的高温固相反应,以Gd₂O₃、Nd₂O₃、ZrO₂、CeO₂混合粉体为原材料,在1 673 K和1 773 K温度下煅烧24、48、72 h,分别制备了系列样品,并对合成样品进行了XRD和SEM分析。结果表明,合成产物为具有缺陷萤石相且伴有少量烧绿石相的Gd_2-xNd_xZr_2-xCe_xO₇（0≤x≤2）晶体化合物。随着煅烧温度的升高和煅烧时间的延长,产物中立方烧绿石相的化合物增多,晶粒尺寸变大,且有少量未知相生成。进而探讨了锆基陶瓷固化多核素的潜在应用,并提出了未来研究的相关热点问题。     

Radiation effects on PbO-Al2O3-B2O3-SiO2 glasses by FTIR spectroscopy

The infrared absorption spectra of PbO-Al₂O₃-B₂O₃-SiO₂ glasses have been measured in the spectral range 600-4000 cm⁻¹ before and after absorbed dose of 50 Gy, 4 kGy and 50 kGy to investigate the structural change due to irradiation. The structural change due to composition has also been discussed. The experimental results clearly indicate that after irradiation, a significant change in structure of lead alumino borosilicate glass network is observed. It was shown that BO₄ groups decreases and BO₃ groups increases with the increase of Al₂O_3.     

Phasengleichgewichte in den systemen UO2-UO2,67-ThO2 und UO2 + x-NPO2

Solid-state chemical investigations have established that in the compositional range UO₂-UO_2.67-ThO₃ of the U-Th-O ternary system, the following single-phase domains exist: U₃O₈, which does not dissolve any ThO₂ in the solid state; an ordered M₄O₉ phase on the section between U₄O₉ and U₂Th₂O₉, below ≈ 1150 °C; and a phase with fluorite structure which occupies a large part of the system and which at 1250 °C is bounded by the compositions UO₂-UO_2.25 (U_0.43, ThO_0.57)O_0.25-ThO₃. The maximum O/M ratio of the “fluorite” phase is O:(U + Th) = 2.25. The highest oxidation valency of uranium is 5.30; this value falls as more thorium oxide is incorporated in the (U.Th)O_{2 + x} “fluorite” phase.     

Electrical properties of annealed, fully metamict REE2FeBe2Si2O10

The electrical properties of annealed, fully metamict gadolinite REEFe²⁺Be₂Si₂O₁₀ are studied as a function of annealing temperature. Changes due to annealing are also probed by ⁵⁷Fe Mössbauer spectroscopy and X-ray diffraction. The electrical conductivity measured at f = 100 Hz between 110 and 750 K varies markedly, ranging from 10⁻¹⁰ to 10⁻⁶ S m⁻¹ for untreated samples and 10⁻⁹ to 10⁻³ S m⁻¹ for sample annealed in argon at 1373 K. Average measured activation energies for electrical conduction are 0.47 and 0.63 eV for ranges of 400-450 K and 500-600 K, respectively. The dielectric permittivity shows strong dispersion effects above 235 K. After high temperature annealing, the electrical conductivity shows a marked dispersion below 604 K. The combination of polaron hopping and hydroxyl anion migration is proposed for the electrical conduction mechanism.     

HfO2 and Ta2O5 as grain growth inhibitors in Eu2O3

Because of the high neutron capture cross section for five consecutive europium isotopes, Eu₂O₃ is of interest as a control material for nuclear reactors. A tendency toward excessive grain growth degrades its mechanical properties. Small amounts of HfO₂ and Ta₂O₅ were added to the Eu₂O₃ in attempts to suppress this grain growth. Three at % substitution of Hf for     

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.     

Enthalpy measurements of La2Te3O9 and La2Te4O11

Enthalpy increment measurements on La₂Te₃O₉(s) and La₂Te₄O₁₁(s) were carried out using a Calvet micro-calorimeter. The enthalpy values were analyzed using the non-linear curve fitting method. The dependence of enthalpy increments with temperature was given as: H°(T) − H°(298.15 K) (J mol⁻¹) = 360.70T + 0.00409T² + 133.568 × 10⁵/T − 149 923 (373 ? T (K) ? 936) for La₂Te₃O₉ and H°(T) − H°(298.15 K) (J mol⁻¹) = 331.927T + 0.0549T² + 29.3623 × 10⁵/T − 114 587 (373 ? T (K) ? 936) for La₂Te₄O₁₁.     

Thermophysical properties of NpO2, AmO2 and CmO2

The information on thermal and mechanical properties of the minor actinide dioxides: NpO₂, AmO₂ and CmO₂, is still very scarce, and a large uncertainty exists because of difficulties related to their fabrication and manipulation. Prognosis based on a set of the sound physical models and the similarity principle can be useful in this situation. Using the combination of the macroscopic and microscopic approaches developed earlier for thermodynamic properties of actinide dioxides, and the Klemmens model for their thermal conductivity, a few relationships bounding the main thermophysical properties of the actinide dioxides were deduced. These relationships were applied for the calculation of the isochoric and isobaric heat capacity, the isobaric thermal expansion coefficient, the isothermal bulk elastic modulus and the thermal conductivity of NpO₂, AmO₂ and CmO₂ in a large temperature range. A rather satisfactory agreement with the available experimental data and recommendations was demonstrated.     

Formation of U2C3 in the reaction of UC2 with UO2

The formation of U₂C₃ by the reaction of UC₂ with UO₂ has been studied by chemical and X-ray analyses at temperatures between 1400 and 1700 °C in vacuo. The reaction is represented by 7 UC₂ + UO₂ → 4 U₂C₃ + 2 CO.     

Phase studies in the UO2-Gd2O3 system

The incorporation of gadolinium directly into nuclear fuel is important regarding reactivity compensation, which enables longer fuel cycles. The incorporation of Gd₂O₃ powder directly into the UO₂ powder by dry mechanical blending is the most attractive process, because of its simplicity. Nevertheless, processing by this method leads to difficulties while obtaining sintered pellets with the minimum required density. This is due to the bad sintering behavior of the UO₂-Gd₂O₃ mixed fuel, which shows a blockage in the sintering process that hinder the densification process. Minimal information exists regarding the possible mechanisms for this blockage and this is restricted to the hypothesis based on the formation of a low diffusivity Gd rich (U,Gd)O₂ phase. The objective of this investigation was to study the phase formation in this system, thus contributing to clarifying the causes of the blockage. Experimental evidence indicated the existence of phases in the (U,Gd)O₂ system that revealed structures different from the fluorite-type UO₂ structure. These phases appear to be isostructural to the phases observed in the rare earth-oxygen system.     

UO_2C_2O_4·TRPO配合物中有机磷的测定

以H     

NHO3氧化去除Np—Pu反萃液中的H2C2O4

研究了用ＮＨＯ３氧化去除ＴＲＰＯ流程反萃Ｎｐ－Ｐｕ的Ｈ２Ｃ２Ｏ４反萃液中Ｈ２Ｃ２Ｏ４的条件。７．５ｍｏｌ．Ｌ＾－１ＨＮＯ３－０．３ｍｏｌ．Ｌ＾－１Ｈ２Ｃ２Ｏ４混合液于９０℃下蒸发１３０ｈ和１００℃下蒸馏回流６ｈ，Ｈ２Ｃ２Ｏ４可完全分解去除；混合液中添加适量催化剂ＭｎＣＯ３，于１００℃下蒸发或蒸馏回流，Ｈ２Ｃ２Ｏ４分解加速，１－１．５ｈ内Ｈ２Ｃ２Ｏ４完全分解。蒸发或蒸馏回流过程中产生的ＨＮＯ２把Ｎｐ     

Er2Fe17—xAlx（x=2,5）化合物的中子衍射研究

利用Rietveld分析方法对Er2Fe17-xAlx(x=2,5)在室温下的中子衍射数据进行了精修。Er2Fe15Al2化合物具有Th2Ni17型六角结构,空间群为P63／mmc,Al原子分别占据12j(占位数0．21）和12k(占位数0.13)位;Er2Fe12Al5化合物具有Th2Zn17型三角结构,空间群为R3m,Al原子分别占据18f(占位数0．35）、18h(占位数0．36）和6c(占位数0．37）位。所有的Fe原子磁矩间为铁磁性耦合。Er原子磁矩与Fe原子磁矩间为亚铁磁耦合。在2个样品中,磁矩均位于垂直于六重轴的平面内,呈面磁晶各向异性。给出了居里温度Tc,并对磁性能和结构之间的关系进行了简单的讨论。     

Effect of Ag and Li ion irradiation on superconducting Tl2Ca2Ba2Cu3O10 single crystals

The effect of irradiation by 50 MeV Li³⁺ and 200 MeV Ag¹⁵⁺ ions on single crystals of Tl₂Ca₂Ba₂Cu₃O₁₀ (Tl2223) superconductor has been investigated at different fluences. Isothermal magnetization hysteresis loops have been recorded at different temperatures using a SQUID magnetometer and the effect of irradiation on the critical current density, irreversible field, second magnetization peak and pinning force has been studied. Irradiation by 200 MeV Ag¹⁵⁺ ions resulted in increased hysteresis and irreversibility field while no change in second magnetization peak position and critical temperature was observed. A broadening in the hysteresis loop before the second magnetization peak was also observed for the crystals irradiated by Li³⁺ ions. Annealing of irradiated crystals at 500 °C resulted in reduction of point defects created by Li³⁺ ions.     

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.     

Reduction of UO2 by H2

The reactivity of H₂ towards UO₂²⁺ has been studied experimentally using a PEEK coated autoclave where the UO₂²⁺ concentration in aqueous solution containing 2 mM carbonate was measured as a function of time at p_H2∼40 bar. The experiments were performed in the temperature interval 74-100 °C. In addition, the suggested catalytic activity of UO₂ on the reduction of UO₂²⁺ by H₂ was investigated. The results clearly show that H₂ is capable of reducing UO₂²⁺ to UO₂ without the presence of a catalyst. The reaction is of first order with respect to UO₂²⁺. The activation energy for the process is 130 ± 24 kJ mol⁻¹ and the rate constant is k_298K=3.6×10⁻⁹ l mol⁻¹ s⁻¹. The activation enthalpy and entropy for the process was determined to 126 kJ mol⁻¹ and 16.5 J mol⁻¹ K⁻¹, respectively. Traces of oxygen were shown to inhibit the reduction process. Hence, the suggested catalytic activity of freshly precipitated UO₂ on the reduction of UO₂²⁺ by H₂ could not be confirmed.     

Characterization and densification studies on ThO2-UO2 pellets derived from ThO2 and U3O8 powders

ThO₂ containing around 2-3% ²³³UO₂ is the proposed fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). This fuel is prepared by powder metallurgy technique using ThO₂ and U₃O₈ powders as the starting material. The densification behaviour of the fuel was evaluated using a high temperature dilatometer in four different atmospheres Ar, Ar-8%H₂, CO₂ and air. Air was found to be the best medium for sintering among them. For Ar and Ar-8%H₂ atmospheres, the former gave a slightly higher densification. Thermogravimetric studies carried out on ThO₂-2%U₃O₈ granules in air showed a continuous decrease in weight up to 1500 °C. The effectiveness of U₃O₈ in enhancing the sintering of ThO₂ has been established.     

Damage evolution in Au-implanted Ho2Ti2O7 titanate pyrochlore

Damage evolution at room temperature in Ho₂Ti₂O₇ single crystals is studied under 1 MeV Au²⁺ ion irradiation by Rutherford backscattering spectroscopy along the 〈0 0 1〉 direction. For a better determination of ion-induced disorder profile, an iterative procedure and a Monte Carlo code (McChasy) were used to analyze ion channeling spectra. A disorder accumulation model, with contributions from the amorphous fraction and the crystalline disorder, is fit to the Ho damage accumulation data. The damage evolution behavior indicates that the relative disorder on the Ho sublattice follows a nonlinear dependence on dose and that defect-stimulated amorphization is the primary amorphization mechanism. Similar irradiation behavior previously was observed in Sm₂Ti₂O₇. A slower damage accumulation rate for Ho₂Ti₂O₇, as compared with damage evolution in Sm₂Ti₂O₇, is mainly attributed to a lower effective cross section for defect-stimulated amorphization.