铈掺杂诱导U3O8晶型变化

铈是核反应的重要裂变元素,其氧化物CeO_2容易与UO_2燃料形成U_(1-x)Ce_xO_2固溶体。铀铈固溶体会因为U4+发生氧化而生成(U_(1-x)Ce_x)3O_(8-δ)混合氧化物。Ce在U_3O_8中的存在会改变U_3O_8母体的局域结构,影响着(U_(1-x)Ce_x)3O_(8-δ)产物的物理化学性质。研究铀铈混合氧化物的局域结构,可以帮助理解处于苛刻环境中乏燃料的性状。使用共沉淀方法制备了铈掺杂的U_3O_8混合氧化物样品,即(U_(1-y)Ce_y)3O_(8-δ)(y=0,0.05,0.20),利用粉末X射线衍射(X-ray Diffraction,XRD)获取其物相信息,借助同步辐射X射线吸收精细结构(X-ray Absorption Fine Structure,XAFS)技术来获取(U_(1-y)Ce_y)3O_(8-δ)中铀和铈的局域结构。结果表明:与掺杂前的U_3O_8具有C2mm空间群不同,掺入Ce后的(U_(1-y)Ce_y)3O_(8-δ)转变成了与U_3O_8的P62m空间群一样的晶型,Ce的存在还导致铀的平均价态升高,层内最近邻Ce-U(Ce)的原子距离减小。     

SR-XRD和EXAFS研究Mn掺杂ZnO薄膜的微观结构

用射频磁控溅射技术在蓝宝石衬底上制备了一组不同衬底温度的Mn掺杂ZnO薄膜。质子激发X射线荧光(PIXE)测量表明,薄膜中仅有含量为5 at.%的Mn,未见其它磁性杂质元素(如Fe、Co、Ni等)。同步辐射X射线衍射(SR-XRD)表明,这些Mn掺杂ZnO薄膜具有纤锌矿ZnO结构。SR-XRD和扩展X射线吸收精细结构谱(EXAFS)分析显示,薄膜中未发现Mn团簇或MnO、MnO2、Mn2O3、Mn3O4等二次相,Mn原子是通过替代Zn原子而进入了ZnO晶格。     

纳米复合永磁合金Nd9Fe85-xMnxB6的结构和磁性

利用X射线衍射(XRD)和X射线吸收精细结构(XAFS)技术对淬火速度为20m／s的退火和未退火Nd9Fe85-xMnxB6(x=0，0．5和1．0)样品分别进行了晶体结构和Fe原子局域环境的分析，并用振动样品磁强计分析了样品的磁性。结果表明：退火前，掺杂微量Mn原子对纳米复合Nd-Fe-B磁性材料的晶体结构和近邻配位无序度都有显著影响，随着Mn含量的增加，Nd2Fe14B硬磁相和α-Fe软磁相的结晶度明显增加；在温度为973K、5min退火后，Nd9Fe85-xMnxB6(x=0，0．5和1．0)磁体的主相结构基本相同，但矫顽力由339kA／m增加到398kA／m,我们认为这是由于掺杂的Mn原子影响Nd2Fe14B和α-Fe颗粒晶界的交换耦合作用所致。     

X射线辐照合成金纳米颗粒及其原位表征

X射线辐照合成无机纳米粒子具有简单、清洁、高效等优点,是一种绿色合成方法.X射线技术,如X射线光电子能谱(XPS)、X射线吸收精细结构谱(XAFS)等,特别是同步辐射X射线技术的应用和发展,为人们探索纳米材料的结构信息提供了强大的工具.然而,利用X射线辐照合成金纳米颗粒及利用X射线技术原位探索金纳米颗粒的生长机理的综述...     

Al_2O_3/PI薄膜纳米颗粒形态的SAXS研究

聚酰亚胺(PI)/无机纳米杂化材料具有良好的电绝缘性、优异的机械性能以及高耐热等特性,广泛地应用于电气电子领域.本文利用同步辐射小角X射线散射(SAXS)技术对聚酰亚胺纳米杂化薄膜(Al_2O_3/PI)进行微观结构分析,结合透射电子显微镜(TEM)测试的结果,研究了杂化薄膜中无机纳米颗粒的特性.研究结果表明,无机纳米颗粒尺寸约为4–7 nm,纳米颗粒与基体之间具有明锐的界面,薄膜体系分形维数为2.48.     

同步X射线散射技术研究变温及拉伸后聚四氟乙烯的微观结构变化

聚四氟乙烯（PTFE）在变温及拉伸下的微观结构变化研究,对于其服役过程中的失效机制分析具有重要意义。本文采用同步X射线散射技术原位在线研究PTFE在变温处理（25～300℃）以及常温和变温（25～175℃）单轴拉伸下的微观结构变化。结果表明：PTFE的散射强度随温度而增加,不完全晶体逐渐熔融;常温单轴拉伸PTFE在低应变下分子链发生倾斜,片晶沿拉伸方向滑移和转动;在恒定应力的单轴拉伸过程中,随温度升高,PTFE中不完全晶体逐渐熔融,受应力作用片晶被破坏,在其发生α转变之后,其片晶由于非晶部分分子链运动的解冻而被进一步破坏。     

机械合金化Fe0.6Ni0.4体系的结构研究

利用XAFS(X射线吸收精细结构)和XRD(X射线衍射)方法研究了机械合金化Fe0．6Ni0.4系统在制备过程中的晶体结构和Fe原子的局域配位环境。结果表明，球磨5h，样品中Fe、Ni原子开始产生合金化，但仍然为bcc和fcc混合的两种物相；球磨10h后，bcc结构Fe的特征配位峰消失，转化为fcc结构，随着球磨时间的增加，配位无序度逐渐增大；球磨40h后，Fe原子的近邻结构又有新的变化，是由多种物态组成的混合物。     

原位担载型煤直接液化催化剂的表征

通过原位担载法将铁系催化剂担载于煤表面,考察了催化剂前驱体的相态、配位环境以及在载体表面的分散状态。采用X射线吸收精细结构和X射线衍射法对原位担载型铁系催化剂前驱体进行了表征。结果表明,催化剂前驱体在煤表面以非晶态、高分散的形式存在,其化学组成主要为FeOOH,且催化剂前驱体的分散程度与载体煤的物理化学性质有关。     

基于SAXS方法的核石墨微孔结构的温度影响

X射线小角散射(Small Angle X-ray Scattering,SAXS)是研究纳米尺度微观结构的重要手段。本文利用同步辐射SAXS技术测量了25oC、100oC、200oC、300oC和400oC时,IG-110和NBG-18核石墨在纳米尺度范围内孔隙的数量分布及其分形特征的变化。实验结果表明,IG-110和NBG-18核石墨的微观结构中存在微小尺寸上的不均匀区域,且核石墨孔隙的固气结构具有明锐的界面。但随着温度的升高,固气界面的变化并没有呈现出明显的规律性。此外,在纳米尺度上,IG-110和NBG-18核石墨的孔隙数量随温度呈现增加的趋势,且IG-110核石墨孔隙数量的增加幅度大于NBG-18核石墨,其平均孔隙尺寸的减小幅度大于NBG-18核石墨。在核石墨的微孔结构内,其固气界面的分形维数随温度升高逐渐减小,且NBG-18核石墨分形维数的变化幅度小于IG-110核石墨。这表明核石墨的分形结构随温度的升高逐渐光滑。     

同步X射线散射技术研究γ射线辐照后PTFE的结构变化

利用γ射线辐照聚四氟乙烯(PTFE),用差示扫描量热法结合同步辐射小角X射线散射技术和广角散射技术研究辐照PTFE的结构变化.研究了辐照PTFE的颗粒尺寸、结晶度、界面厚度层参数、致密程度随剂量的变化规律.结果表明:室温条件下,7射线辐照的PTFE主要发生裂解.随剂量的增加,试样的熔点及结晶焓增加、颗粒尺寸变小,内部结...     

Ti离子注入SiO_2合成TiO_2纳米颗粒及其光学性质

将105 keV的Ti离子注入到SiO_2玻璃至1×10~(17)、2×10~(17) cm~(-2),并在氧气气氛下进行热处理,借助紫外可见分光光度计、掠入射X射线衍射光谱仪、透射电子显微镜、原子力显微镜等多种测试仪器,详细研究了Ti O2纳米颗粒的形成、结构、分布及其光吸收和催化性能。研究结果表明,高注量Ti离子注入结合氧气气氛热处理可以在SiO_2基底中形成TiO_2纳米颗粒,并以金红石相为主。合成的TiO_2纳米颗粒的形貌明显依赖于离子的注量,随离子注量增加,形状不规则且分散排列的TiO_2纳米颗粒会转变成尺寸较为均匀、分布致密的纳米颗粒,进而形成了TiO_2类颗粒膜结构。另外,光催化降解实验结果表明,合成的纳米颗粒对罗丹明B溶液具有一定的降解作用。     

The effect of deformation temperature on the microstructure evolution of Inconel 625 superalloy

Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900 °C and 1200 °C with different true strains and a strain rate of 0.1 s⁻¹. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of deformation temperature on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found that the relationship between the DRX grain size and the peak stress can be expressed by a power law function. Significant influence of deformation temperatures on the nucleation mechanisms of DRX are observed at different deformation stages. At lower deformation temperatures, continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation is considered as the main mechanism of DRX at the early deformation stage. However, discontinuous dynamic recrystallization (DDRX) with bulging of the original grain boundaries becomes the operating mechanism of DRX at the later deformation stage. At higher deformation temperatures, DDRX is the primary mechanism of DRX, while CDRX can only be considered as an assistant mechanism at the early deformation stage. Nucleation of DRX can also be activated by the twinning formation. With increasing the deformation temperature, the effect of DDRX accompanied with twinning formation grows stronger, while the effect of CDRX grows weaker. Meanwhile, the position of subgrain formation shifts gradually from the interior of original grains to the vicinity of the original boundaries.     

Zn离子注入增强TiO_2纳米管光电效应

用阳极氧化法在钛金属表面制备出致密有序的TiO_2纳米管阵列,用MEVVA源离子束技术在其上进行金属Zn离子的掺杂注入。用电镜观察离子束轰击对TiO_2纳米管阵列结构的影响。研究了掺杂前后TiO_2纳米管阵列在紫外光和可见光区域的光电效应。用全势线性缀加平面波(FP-LAPW)法讨论了TiO_2纳米管对可见光响应的机理。     

The effect of irradiation and post-irradiation annealing on the yield stress and microstructure of vanadium-carbon alloys

Vanadium and vanadium-carbon alloys containing 0.15, 0.3 and 1 at% carbon were irradiated in JMTR with fast neutrons (E_n > 1 MeV) at 773 K to a dose of 5 × 10²⁴n/m². Tensile test and microstructural observations were carried out after irradiation and post-irradiation annealing. All of the. specimens showed radiation hardening. The irradiation produced voids, dislocations and radiation-induced quasi-carbides, which were formed by the agglomeration of vacancies and carbon atoms. The radiation anneal hardening in the alloys occurred at 873 K. The void number densities in the alloys had a peak at 873 K while the quasi-carbides decomposed at the same temperature. Therefore, invisible voids existing in the as-irradiated condition would grow by absorbing the vacancies, which were released in the process of decomposition of the quasicarbides during annealing, and the increase of the visible voids would effectively contribute to the radiation anneal hardening of these alloys.     

Post-annealing effect on the microstructure and photoluminescence properties of the ion beam synthesized FeSi2 precipitates in Si

FeSi₂ precipitates with various structural properties embedded within silicon matrix were formed by iron ion implantation using a metal vapor vacuum arc ion source followed by thermal annealing at various conditions. The microstructure and phase properties of the implanted samples were studied by transmission electron microscopy. The orientation relationships and thus the interfacial coherence between the FeSi₂ precipitates and the Si matrix were observed to change with the annealing conditions. A good correlation is identified in-between the structural properties and the photoluminescence properties of these samples.     

The dependence of in-reactor UO2 densification on temperature and microstructure

The in-reactor changes in size of sintered UO₂ are analyzed by superposing matrix swelling and pore shrinkage. At first pore shrinkage dominates and results in densification, an effect which has been known for a few years. With regard to shrinkage mechanisms one should distinguish between very fine pores and coarser pores, the latter being responsible for the majority of total porosity in well sintered UO₂. For this coarser porosity a two-step mechanism is postulated: first, the generation of vacancies by the fission fragments traversing the pores, second, the migration of these vacancies to effective sinks (grain boundaries) producing densification. Based on this assumption the dependence of densification on fission rate, temperature, pore size distribution and grain size is evaluated. There is a transient temperature above which the generation of vacancies is rate controlling and below which the vacancy migration becomes the rate controlling mechanism. At temperatures much lower than the transient temperature no densification should be observed.     

The effect of temperature and microstructure of sintered beryllium oxide on the scattering cross section of thermal neutrons

The total effective neutron cross section _t for sintered beryllium oxide in the 0.0025–10 ev neutron energy range was measured by means of a mechanical selector at four temperatures of the scattering sample: 290, 800, 1300 and 1500 °K. Measurements of _t for beryllium oxide samples of different microstructure were also carried out at room temperature. Slight anisotropy of scattering, due to texture, and a marked influence of the size of the crystal grain on _t, due to the extinction effect, were noted.