Low-temperature diffusion in inert-gas bombarded Al2O3

Previous work on diffusion in inert-gas bombarded Al₂O₃ has revealed the presence of four diffusion processes, of which two take place well below the temperatures for self-diffussion, one agrees with self-diffusion, and one occurs at temperatures well above those for self-diffusion. The present work serves to explore in greater detail the two low-temperature processes. It is shown that the first, which is found in -Al₂O₃, Al(OH)₃, and γ-Al₂O₃beginning at about 100° C, is consistent with a range of ΔH's of 28 to 50 kcal/mole. The mechanism of the process is hinted at by the fact that it overlaps the temperatures both for Al(OH)₃decomposition and for point-defect motion in -Al₂O₃; the correlation with point defects is believed, however, to be the more significant. The second process, which is found only in -Al₂O₃ beginning at 500–650° C, implies an essentially single ΔH lying between 69 and 79 kcal/mole. It was suggested previously by Matzke and Whitton on the basis of electron diffraction that the process could be attributed to the amorphous-crystalline transition of -Al₂O₃. Further aspects of low-temperature diffusion in Al₂O₃ were revealed by comparing autoradiographs of specimens of -A₂O₃which were bombarded to various doses and then either heated to 850° C or immersed in unheated 12N NaOH. Thus regions exposed to a high dose and which would be expected to be amorphous, had an increased sticking factor, a greater tendency to lose gas during heating, and an enhanced chemical reactivity.     

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.     

Order–disorder phase transition induced by swift ions in MgAl2O4 and ZnAl2O4 spinels

Grazing X-ray diffraction was used to study in details the behaviour of two spinels, ZnAl₂O₄ and MgAl₂O₄ irradiated by swift ions. Such an irradiation allows to have an important irradiated depth and then accurate diffraction diagrams. Rietveld refinement done on these diagrams clearly show an order–disorder transition due to a melting of cations under irradiation in these two spinels. More especially, these results clearly exhibit that no new phase is created under irradiation in MgAl₂O₄. Raman spectroscopy, sensitive to the crystallographic space group, seems to confirm this analysis.     

Thermodynamic stability of Na2ZrO3 using the solid electrolyte galvanic cell technique

The sodium potential in the test electrode (a) Pt,O₂,Na₂ZrO₃,ZrO₂ was measured by using the emf technique employing Na-β^″-alumina as the solid electrolyte in conjunction with (b) Pt,O₂,Al₂O₃,NaAl₁₁O₁₇, (c) Pt,O₂,Na₂MoO₄,Na₂Mo₂O₇ and (d) Pt,Na₂CO₃,CO₂,O₂ as the reference electrodes over the ranges 880–1045, 700–800 and 850–940 K, respectively. The emf results between electrodes (b) and (c) were utilized for internal consistency checks. From the results on cells formed between (a) and (b) and those on (a) and (c), the standard Gibbs energy of formation, Δ_fG^o (kJ/mol) of Na₂ZrO₃ was determined to be −1699.4+0.3652T (K) valid over the temperature range 700–1045 K. The break in the emf data at 1045 K was corroborated by independent TG/DTA measurements carried out on Na₂ZrO₃ which exhibited an endotherm at 1055 K indicative of a phase transition in Na₂ZrO₃.     

含TBP-HNO3超临界CO2流体静态络合萃取U3O8

建立了一种快速降低萃取系统压力的静态络合萃取实验装置。在此装置上研究了含TBP-HNO₃超临界CO₂静态络合U₃O₈的快速气化测量方法,探索了含TBP-HNO₃超临界CO₂静态络合萃取U₃O₈的行为规律。     

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。     

掺杂Cr2O3对UO2芯块烧结行为的影响

提高燃料燃耗的一个有效手段是通过增大UO₂晶粒尺寸来减少元件内部气体压力，在大晶粒UO₂芯块中，裂变气体到达晶界表面的距离增加，因而裂变气体的释放速率降低，元件内部气体压力的增高缓慢。本文研究了添加Cr₂O₃对UO₂晶粒尺寸的影响。对纯UO₂、添加0.5% Cr₂O₃及5% Cr₂O₃ 3种配方的芯块进行了试验，在5%H₂Ar保护下，以10 ℃/min和5 ℃/min的升温速率升温至1 700 ℃，然后烧结2 h或4 h，对比纯UO₂芯块与添加Cr₂O₃的芯块发现，添加Cr₂O₃可有效增大晶粒尺寸；较长的烧结时间可促进晶粒长大；较低的升温速率也使晶粒长大。烧结过程产生液相烧结，液相浸润晶粒边界，促进晶粒长大。     

UO2?-Er2O3燃料芯块制备技术初步研究

对Er₂O₃质量分数为4.32%的UO₂-Er₂O₃可燃毒物燃料芯块的制备技术进行了初步研究。通过对比不同工艺条件（混料、成型、烧结）下，芯块的外观完整度、密度、晶粒度等性能，初步得到了UO₂-Er₂O₃燃料芯块的制备技术。试验表明:干法球磨混合6?h，添加5‰的聚乙烯醇（PVA），300~350?MPa压力下冷压成型，1700~1750℃、H₂气氛中烧结2~3?h，可得到外观完整、密度大于等于95%理论密度（T.D.）、晶粒尺寸大于8?μm的UO₂?-Er₂O₃燃料芯块。      

Micro-PIXE and channeling PIXE analysis of Ag-doped YBa2Cu3O7−δ thin films

Nuclear Microscopy, utilizing a 2 MeV He⁺ beam for channeling Rutherford Backscattering (RBS) and PIXE analysis, was used to characterise Ag-doped YBa₂Cu₃O_7−δ thin films and measure the lateral distribution of the Ag. The samples were prepared by in situ two-beam pulsed laser deposition in order to investigate the effects of such dopings on critical current densities [1 and 2]. Films deposited at temperatures above 650°C form needle-like surface structures with a length of up to 100 μm; these tend to align with in-plane a–b axis. Results for a sample prepared at a substrate temperature of 730°C and a maximum Ag concentration of 5 at.% are discussed. The needle-like structures were found to be rich in Ag and Cu, and the YBa₂Cu₃O_7−δ film contained 0.02 at.% Ag. Broad beam PIXE-channeling results indicate that 19% of the Ag is substitutional.     

高温结晶合成Mn2O3@MoS2复合材料及其对铀的吸附性能

采用高温熔盐电解法合成了MoS₂,为了提高MoS₂对铀的吸附性能,以MoS₂为基底复合Mn₂O₃。MoS₂的片层结构有效地分散了Mn₂O₃的团聚,同时引进了亲铀氧基团。采用电子扫描显微镜及能谱(SEM & EDS)、X射线衍射仪(XRD)、Zeta电位仪等对Mn₂O₃@MoS₂复合材料进行了表征,表征结果表明,高温结晶合成的Mn₂O₃@MoS₂复合材料具有完整的微观形貌和稳定的晶体结构。通过静态吸附批实验探究了在不同变量下Mn₂O₃、MoS₂和Mn₂O₃@MoS₂三个材料对溶液中铀的吸附效果,结果表明,Mn₂O₃@MoS₂的吸附性能优于Mn₂O₃和MoS₂,在pH=5.5时,吸附平衡时间为90 min,吸附动力学遵循准二级动力学模型,吸附等温线符合Langmuir模型。Mn₂O₃@MoS₂的单层饱和吸附容量为117.5 mg/g,在293.15~318.15 K的温度梯度中,升温有利于吸附进行。     

Surface modification of MgAl2O4 and oxides with heavy ions of fission fragments energy

In this paper we report on results of surface modification in several candidate materials for inert matrix fuel hosts (MgAl₂O₄, MgO and Al₂O₃) induced by (0.5–5) MeV/amu Kr, Xe and Bi ion bombardment in the fluence range of 2 × 10¹⁰–10¹² ions/cm². The size and shape of nanoscale hillock-like defects, each of which was created by the impact of a single ion, have been studied by using atomic force microscopy (AFM) technique. It was found that mean hillock height on sapphire and spinel surfaces depends linearly on the incident electronic stopping power. The hillocks are highest in MgAl₂O₄, having a lower threshold for the lattice disorder in the bulk material via relaxation of electronic excitations. As a possible reason for the hillocks formation, the plastic deformation due to the defects created by the Coulomb explosion mechanism in the target subsurface layer is suggested.     

Investigation of Stable Al2O3 Scale on Fe-Al Aluminized Coating for Tritium Barrier

It is well known that α-Al₂O₃ phase has stablility performance, high permeation reduction factor and good resistance performance in liquid LiPb, which is considered as the reference tritium barrier coating in future fusion reactor. In order to study the formation mechanism of stable α-Al₂O₃ scales on fusion structure material, the oxidation behavior of Fe-Al aluminized coating on China Low Activated Martensitic （CLAM） steel was investigated under the oxygen partial pressure from 1 Pa to 20 kPa at the temperature of 940-980 ℃. The Al₂O₃ scales were analyzed by thermogravimetric analysis meter, grazing angle X-ray diffractometer, glow discharge spectrometer, focused ion beam and transmission electron microscope. A single continuous Al₂O₃ scales with the maximum thickness of about 2 000 nm was formed on the diffusion Fe-Al aluminized layer. Thermogravimetric analysis results show that the higher oxidation rate constant is achieved while increasing the oxygen partial pressure, and then oxidation rate constant decreases. The phase transformation of Al₂O₃ scales on the surface of Fe-Al aluminized coating was studied during different oxidation time ranges from 3 min to 180 min. The metastable γ-Al₂O₃ and α-（Al0.948Cr0.052）₂O₃ phases is formed in the earlier oxidation process and finally transformed to stable α-Al₂O₃ phase. The features of the transient α-（Al0.948Cr0.052）₂O₃（113） and α-Al₂O₃（113） were detected by GXRD and then confirmed by focused ion beam and transmission electron microscope.     

Threshold oxygen levels in sodium necessary for the formation of NaCrO2 in sodium-steel systems

A knowledge of the threshold oxygen level in liquid sodium necessary for the formation of NaCrO₂ in sodium-steel systems is useful in the operation of fast breeder reactors. There is considerable discrepancy in the data reported in the literature. In order to resolve this, the problem was approached from two sides. Direct measurement of oxygen potential in the Na(l)-Cr(s)-NaCrO₂(s) phase field using the galvanic cell In, In₂O₃/YDT/Na, Cr, NaCrO₂ yielded: _o2 = −800847 + 147.85 T J/mol O₂ (657–825 K). Knudsen cell-mass spectrometric measurements were carried out in the phase field NaCrO₂(s)-Cr₂O₃(s)-Cr(s) to obtain the Gibbs energy of formation of NaCrO₂ as: ΔG^o_f,T(NaCrO₂) = −870773 + 193.171 T J/mol (825–1025 K). The threshold oxygen levels deduced from G^o_f,T (NaCrO₂) data were an order of magnitude lower than the directly measured values. The difference between the two sets of data as well as differing experimental observations from operating liquid sodium systems are explained on the basis of the influence of dissolved carbon.     

RBS investigations of buffer layers between YBa2Cu3O7−x and silicon

The deposition of high-quality high-T_c superconducting films on silicon wafers for future hybrid electronic devices is strongly hampered by the interdiffusion between films and substrate. This effect degrades the superconducting properties seriously and is a strong function of temperature. Since high processing temperatures are inevitable for good films, suitable buffer layers are needed to reduce the interdiffusion. We have investigated the combinations ZrO₂/Si(100), BaF₂/Si(100), and noble-metal/TiN/Si(100) at temperatures up to 780°C in oxidizing ambient. YBa₂Cu₃O_7−x films have been deposited onto the buffer layers by laser ablation. Thereafter the interfaces have been analyzed by Rutherford backscattering. So far only ZrO₂ has demonstrated sufficient stability to serve as a buffer layer for the laser-ablated YBa₂Cu₃O_7−x films. All other combinations suffer from interdiffusion or oxidation.     

基于铌酸银的耐高温放射性碘吸附剂的制备及性能

通过机械混合法制备了一种基于铌酸银(AgNbO_3)的耐高温放射性碘吸附剂(AgNbO_3/Al_2O_3)。和常规载银吸附剂(Ag/Al_2O_3)相比,AgNbO_3/Al_2O_3吸附剂的吸附性能更为稳定;特别是在650℃以上时,其对放射性碘的去污因子远高于常规载银吸附剂。表征测试结果表明,该吸附剂结构稳定性良好,可耐受较长时间的高温。热重测试和高温脱附试验等结果表明,碘化银在AgNbO_3/Al_2O_3吸附剂表面稳定性的提高是该吸附剂在高温时吸附性能更佳的主要原因,其将来有望用于核事故中的应急处置。     

阳离子有序相Ce2Zr2O7.97的石墨还原制备及其结构表征

采用石墨还原法探索了CeO₂-ZrO₂二元体系在不同还原温度、还原时间条件下的物相组成及结构,借助X射线衍射、红外振动光谱等手段对还原样品进行了物相表征及结构分析。实验结果表明：通过石墨还原能在较低温度（T_red＝1050 ℃）、较短时间（t＝24 h）内合成纯相Ce₂Zr₂O_7.97,较传统先还原（95%Ar+5%H₂,T_red≥1400℃,t＞48 h）后氧化（O₂或空气气氛）工艺更简单经济;Ce₂Zr₂O_7.97相能在1050～1300 ℃、24～72 h还原条件下稳定存在并保留至室温而不发生相分解,其机制可能归因于石墨所形成的弱还原环境;Ce₂Zr₂O_7.97相拥有与烧绿石Ce₂Zr₂O₇相近的有序阳离子亚晶胞结构,但由于其氧空位（O3、O4、O11）被大部分氧离子所填充,导致该相结构对称性降低。本文提出的石墨还原法制备富氧相Ce₂Zr₂O_7.97有望成为一种较传统制备工艺更简单经济的新方法,而Ce₂Zr₂O_7.97相能在还原气氛中稳定存在,可为An₂Zr₂O_7+x固化体的存放环境提供借鉴和参考。     

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.     

Heavy ion irradiation effects in the rare-earth sesquioxide Dy2O3

Polycrystalline pellets of the rare-earth sesquioxide Dy₂O₃ with cubic C-type rare-earth structure were irradiated with 300 keV Kr²⁺ ions at fluences up to 5 × 10²⁰ Kr/m² at cryogenic temperature. Irradiation-induced microstructural evolution is characterized using grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). In previous work, we found a phase transformation from a cubic, C-type to a monoclinic, B-type (C2/m) rare-earth structure in Dy₂O₃ during Kr²⁺ ion irradiation at a fluence of less than 1 × 10²⁰ Kr/m². In this study, we find that the crystal structure of the top and middle regions of the implanted layer transform to a hexagonal, H-type (P6₃/mmc) rare-earth structure when the irradiation fluence is increased to 5 × 10²⁰ Kr/m²; the bottom of the implanted layer, on the other hand, remains in a monoclinic phase. The irradiation dose dependence of the C-to-B-to-H phase transformation observed in Dy₂O₃ appears to be closely related to the temperature and pressure dependence of the phases observed in the phase diagram. These transformations are also accompanied by a decrease in molecular volume (or density increase) of approximately 9% and 8%, respectively, which is an unusual radiation damage behavior.