高能射线及其屏蔽材料

综述了日常放射性工作中常遇到的几种电离射线,如X射线、γ射线、中子及其他带电粒子的产生机理及其特点,指出了防护这些射线的最有效和最实用的办法是选用适当的屏蔽材料,并详述了这些屏蔽材料的种类和相关的屏蔽原理,提出了屏蔽材料发展方向是研究添加稀土合金的复合材料,并努力提高这些稀土元素在复合材料中所发挥的作用来提高其屏蔽效果。     

大厚度差焊接接头部分屏蔽法射线检测技术

厚度差达到20 mm的焊接接头,同一透照长度内通常要按不同厚度范围分别做几次曝光。设计制作了铅倾斜面屏蔽板,将其固定在射线机射线窗口上,可不同程度地屏蔽射线,使射线在穿过不同厚度焊接接头后,到达胶片上的射线基本一致。试验证明,该方法所摄大厚度差焊接接头底片的黑度和灵敏度均符合标准要求,提高了一次曝光的检测厚度范围,提高了工作效率。     

WC-12Co涂层对中子、γ射线的屏蔽特性及其结合强度的辐照效应

采用常规氧-乙炔焰喷涂技术制备WC-12Co涂层,模拟计算了涂层对中子、γ射线的屏蔽特性.将试样分别置于5#固体镭γ源、Am-Be中子源接受100天辐照,测试辐照前后涂层的结合强度,EDS能谱分析了辐照前后涂层界面元素分布规律.结果表明,γ光子能量小于0.01MeV时,0.5～1 mm厚的WC-12Co涂层可以屏蔽98%以上的射线.1mm厚的WC-12Co涂层可以屏蔽12%的热中子,快中子屏蔽效果欠佳.涂层经中子辐照后强度提高20%～50%,γ射线对涂层强度没有明显影响.中子辐照前后涂层界面元素无扩散现象.初步分析认为,中子辐照后涂层强度提高可能与材料屈服强度、抗拉强度的提高有关.     

碳化钛负载玻璃纤维材料制备与电磁屏蔽性能研究

采用多巴胺对玻璃纤维织物改性处理和原位生成Ti3C2Tx MXene,通过真空抽滤法制备了碳化钛负载玻璃纤维复合材料,研究了碳化钛负载量对电磁屏蔽的影响。结果显示：成功地将Ti3C2Tx纳米片附着在玻璃纤维表面,改善了玻璃纤维的导电网络;刻蚀之后Ti3C2Tx的002衍射峰的位置从9.5 °移动到6.1 °,Ti3AlC2的104衍射峰峰消失不见,表明Ti3C2Tx刻蚀成功;由于碳化钛高导电性和表面的大量电子,电磁波和其发生欧姆损耗,从而降低电磁波能量,达到电磁屏蔽效果。在2~18 GHz频率范围内,碳化钛负载量为2.55 mg/cm2的电磁屏蔽性能达到55.1 dB,其表面电阻为0.95 ?/sq;平均电磁屏蔽表明样品中吸收损耗占主要作用。     

γ射线辐照对316不锈钢在高温水中应力腐蚀破裂的影响

采用经两种剂量γ射线辐照试样的慢应变速率试验(SSRT),结合电化学测试及扫描电子显微镜观察,初步研究了固溶态及敏化态316不锈钢在含5mg/LCl-的300℃高温水中的应力腐蚀破裂行为.结果表明,在试验条件下经辐照的敏化态及固溶态试样的抗应力腐蚀性能均有一定恶化,且随辐照量增大影响也变大.固溶态试样经较高剂量辐照后,SCC敏感性增大较明显,例如经5.07×108radγ射线辐照的试样在200mV控制电位下显示有IGSCC敏感性     

燃料棒X射线照相技术

燃料棒X射线照相是燃料辐照后检验项目之一。主要用于观察包壳管内UO2燃料芯块在堆内辐照后的变化情况。针对燃料棒本身具有很强放射性和细长的特点,从实验室结构、照相装置、工艺参数选择等方面介绍燃料棒X射线照相技术。检验结果表明设计的实验装置完全满足燃料棒X射线检验要求。     

球形储罐^192Ir γ射线检测技术初探

技术改造工程中有照射量率要求的地域 ,其允许辐射范围不足使得运用192 Ｉｒ源对球形储罐进行全景曝光的检测技术受到限制。为拓宽其在实际工程中的应用 ,对球形储罐狭窄范围的192 Ｉｒ源定景透照技术作初步的探讨。1　定景屏蔽透照设计考虑到192 Ｉｒ源对球形储罐全景曝光辐射区距离的确定性与工地实际非射线工作人员在曝光辐射区内的不可避让性之间的矛盾 ,采用光栅对192 Ｉｒ源进行屏蔽控制定景 ,分次对球形储罐透照的方法达到对屏蔽设计区保护的目的。1.1　屏蔽设计现场的环境特点和要求如图 1所示 ,1区和 3区为屏蔽设计区 ,非射线工作…     

复合金属层包覆碳纳米管的制备及电磁屏蔽性能

对碳纳米管(CNTs)进行复合金属包覆,可以发挥不同组元间的复合效应,提高在高频范围的电磁屏蔽性能。本文对CNTs进行预处理后,采用超声喷雾化学镀的方法来制备镀镍碳纳米管(Ni-CNTs),在此基础上分别采用化学镀和共沉淀法制备镍银包覆碳纳米管(Ni/Ag-CNTs)和镍铜包覆碳纳米管(Ni/Cu-CNTs)。采用TEM、FESEM和XRD对镀层形态及结构进行表征,结果表明,采用超声喷雾化学镀方法,在改善CNTs分散性的前提下可实现镍层在其表面均匀连续镀覆;并结合化学镀和共沉淀法分别成功制备出Ni/Ag-CNTs和Ni/Cu-CNTs。电磁屏蔽测试表明,Ni/Ag-CNTs和Ni/Cu-CNTs的电磁屏蔽性能显著优于Ni-CNTs (55.62dB),分别达到了89.34 dB和72.21 dB。     

Preparation and characterization of porous magnesium materials

The proper spacer material and the preparation technology for biological compatible porous magnesium materials were explored by the powder metallurgy method, and microstructures, porosity and mechanical properties of sintered porous magnesium were investigated. The results show that compared with spacer materials of NH4CO3, NH3Cl and carbamide, NI-I4CO3 is the best one for preparation of sintered porous magnesium, and the worst one is NH3Cl. The isolated blind pores are formed mainly by the particle interval of the magnesium powders. Adding spacer material favors the formation of open pores, while has little contribution to the formation of blind pores. The overall porosity and porosity of open pore of the sintered porous magnesium increase with the increase of added spacer material, while decrease with the increase of the molding stress. The mechanical properties of sintered porous magnesium increase with decreasing addition of spacer material and increasing molding stress.     

Silicide-matrix materials for high-temperature applications

Intermetallic-matrix composites are attractive alternatives to carbon /carbon and ceramic / ceramic composites for applications up to 1,600°C. Recent work on the intermetallic compounds MoSi₂ and Ti₅Si₃ has included determination of their mechanical properties and deformation behavior, selection of thermodynamically compatible high-strength and ductile reinforcements, and strengthening and toughening mechanisms in silicide-matrix composites for high-temperature service.     

Two-phase materials for high-temperature service

The structures and properties of two families of lattice-coherent composites, those based on γ/γ′ Ni₃Al and those based on TiAl/Ti₃Al, are shown to have strong similarities. The coherent system of cubic/tetragonal Y₂O₃–stabilized ZrO₂ is then described, and shown to have strong similarities to the system TiAl/Ti₃Al. The phases γ TiAℓ (L1_o) and α₂ Ti₃Aℓ (DO₁₉) are not cubic, and their anisotropic thermal expansion may lead to ratcheting creep under conditions of thermal cycling.     

Barriers to applying advanced high-temperature materials

During the past 25 years, aerospace engineers and material scientists have made significant technical progress toward developing next-generation aircraft. However, while advanced high-temperature materials continue to be developed, the outlook for their future application is uncertain and will depend on the ability of these materials to satisfy a more diverse market.     

Joining ODS materials for high-temperature applications

Oxide-dispersion-strengthened (ODS) high-temperature alloys represent a unique class of powder-metallurgy-based engineering materials. They offer combinations of high-temperature strength, oxidation resistance, and hot corrosion resistance that cannot be obtained in other alloys. The alloys were initially developed for the aircraft gas turbine industry; since then, however, applications have expanded to include industrial gas turbines, equipment for handling molten glass, high-temperature furnace assemblies, and a variety of other industrial components. Internationally, the materials are also of interest for nuclear power systems (both breeder and fusion reactors) since ferritic ODS alloys exhibit both excellent swelling resistance and good elevated-temperature creep resistance. Many of these applications require that the ODS alloys be joined to either themselves or to other materials. The purpose of this paper is to review some of the techniques available for making these joints.     

Platinum-group-metal-based intermetallics as high-temperature structural materials

Research on platinum-group-metal (PGM)-based intermetallic compounds, which are candidates as high-temperature structural materials, is reviewed in this article. The research reviewed focuses on PGM-based L1₂ and B2 compounds. Alloys with a face-centered cubic and L1₂ or B2 phase are also reviewed. For more information, contact Y. Yamabe-Mitarai, National Institute for Material Science, High Temperature Materials Group, Sengen 1-2-1, Tsukuba, Ibaraki, 305-0047, Japan; +81-29-859-2525; fax +81-29-859-2501; e-mail mitarai.yoko@nims.go.jp.     

Thin-film shape-memory materials for high-temperature applications

Many applications of shape-memory alloys (SMAs) are likely to require development of alloys having much higher martensite transformation temperatures than are currently available. This article reviews recent reports on a few promising systems, with emphasis on sputtered films in the NiTiX group. NiTiX is a name for the ternary ordered substitutional solutions of Hf, Zr, Au, Pd, or Pt, in the β-NiTi lattice. These have been the most extensively studied compounds and the only high-temperature SMAs yet fabricated as thin films. For films, the exaggerated kinetics of physical vapor deposition and the generous surfaces of the planar form confer economic and technical advantages, especially in cases involving costly additions or troublesome solidification issues. The outlook for technically useful SMAs operating at up to 240°C is quite good. Operation at temperatures above 500°C may be possible, but issues of thermal stability will pose significant challenges. For more information, contact David S. Grummon, Michigan State University, Department of Chemical Engineering and Materials Science, 3525 Engineering Building, East Lansing, MI 48824; (517) 353-4688; e-mail grummon@egr.msu.edu.