In Situ Study of Nanostructure and Electrical Resistance of Nanocluster Films Irradiated with Ion Beams

An in situ study is reported on the structural evolution in nanocluster films under He⁺ ion irradiation using an advanced helium ion microscope. The films consist of loosely interconnected nanoclusters of magnetite or iron‐magnetite (Fe‐Fe₃O₄) core‐shells. The nanostructure is observed to undergo dramatic changes under ion‐beam irradiation, featuring grain growth, phase transition, particle aggregation, and formation of nanowire‐like network and nanopores. Studies based on ion irradiation, thermal annealing and electron irradiation have indicated that the major structural evolution is activated by elastic nuclear collisions, while both electronic and thermal processes can play a significant role once the evolution starts. The electrical resistance of the Fe‐Fe₃O₄ films measured in situ exhibits a super‐exponential decay with dose. The behavior suggests that the nanocluster films possess an intrinsic merit for development of an advanced online monitor for fast neutron radiation with both high detection sensitivity and long‐term applicability, which can enhance safety measures in many nuclear operations.     

纳米γ-Fe2O3/SiO2复合氧化物的制备及气敏性质

Nanostructured γ-Fe2O3/SiO2 complex oxide was prepared by sol-gel method with tetraethoxysilane and iron nitrate as precursors. The particle size distribution, thermal and phase stabilities and gas sensing properties were systematically characterized by TEM, granularity distribution, TG-DTA, XRD and gas sensitivity measurements. The particle size is about 10 nm and size distribution is very narrow. The sensitivity of the sensing element to CO, H2, C2H4, C6H6 and the effects of zalcination temperature on the sensitivity and conductance of gases were examined. The combination of excellent thermal stability and tunable gas sensing properties through careful control of the preparation and judicious selection of material compositions gives rise to novel nanocomposites, which is attractive for the sensitive and selective detection of reducing gases and some hydrocarbon gases.     

Magnetic properties of nanostructural γ-Ni-28Fe alloy

1Introduction The nickel-iron alloys in the permalloy system,with about10%to65%(mass fraction)iron,are probably important soft magnetic alloys[1],which have been widely used in industry,such as recording heads,transformers or magnetic shielding materials.…     

电导率对纳米磁性金属膜微波吸收性能的影响

基于纳米金属膜电导率和介电性的理论基础,采用0．05—5GHz宽频带扫频测量所得的复磁导率,计算分析电导率对具有不同微波磁谱特性的纳米磁性金属膜吸波性能的影响。研究结果表明：具有较高磁导率的纳米磁性膜,当其电导率低于100S／m时,该薄膜材料在微米级厚度时就具有良好的吸波性能,即在0．05—5GHz的宽频段反射率小于-4dB;降低薄膜电导率可以显著改善薄膜吸波材料的电磁匹配性能,从而提高其吸波性能。     

HVOF-Sprayed Coatings Engineered from Mixtures of Nanostructured and Submicron Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> Powders: An Enhanced Wear Performance

In previous studies, it has been demonstrated that nanostructured Al₂O₃-13 wt.%TiO₂ coatings deposited via air plasma spray (APS) exhibit higher wear resistance when compared to that of conventional coatings. This study aimed to verify if high-velocity oxy-fuel (HVOF)-sprayed Al₂O₃-13 wt.%TiO₂ coatings produced using hybrid (nano + submicron) powders could improve even further the already recognized good wear properties of the APS nanostructured coatings. According to the abrasion test results (ASTM G 64), there was an improvement in wear performance by a factor of 8 for the HVOF-sprayed hybrid coating as compared to the best performing APS conventional coating. When comparing both hybrid and conventional HVOF-sprayed coatings, there was an improvement in wear performance by a factor of 4 when using the hybrid material. The results show a significant antiwear improvement provided by the hybrid material. Scanning electron microscopy (SEM) at low/high magnifications showed the distinctive microstructure of the HVOF-sprayed hybrid coating, which helps to explain its excellent wear performance. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Magnetic properties of nanostructural γ-Ni-28Fe alloy

Nanostructural γ-Ni-28Fe alloy (nano γ-Ni-28Fe) was successfully prepared by mechanochemical alloying(MCA). The relationship between the microstructure and the synthesis conditions was investigated by using XRD, TEM, SEM as well as BET analyzer. The results show that nano γ-Ni-28Fe alloy is composed of a gamma phase (FCC structure). Its grain size is about 20 nm at reduction temperature below 600 °C. The magnetic measurements indicate that the saturation magnetization of nano γ-Ni-28Fe alloy is 102.4 A·m²/kg, and the coercivity is much higher than that of conventional coarse-grained counterpart. The result may be attributed to its decrease of the grain size and chemical composition in nano γ-Ni-28Fe alloy.     

高能球磨合成W—Ni—Fe纳米复合粉末特性

采用X衍射、BET氮吸附法和DTA差热分析方法对球磨后的90W-7Ni-3Fe(质量百分数）纳米复合粉的组织结构变化、表面特性和热稳定性进行了系统的研究。XRD和DTA的分析结果表明：球磨可以生成纳米复合粉,晶粒内部产生很大的晶格畸变,同时球磨产生的密度和缺陷使原子扩散加快,形成超饱和固溶体、非晶和扩大W在粘结相中的溶解度,BET氮吸附结果证明了球磨使粉末产生微孔,比表面、中孔表面和孔径降低。     

塑性变形过程中微观结构分析理论的最新进展

多晶金属塑性变形时会产生大量微结构,具有这种特征的单元称为变形结构单元.实际上所有的变形结构单元均由位错组成,而根据单个位错间的相互作用来描述大范围单元的位错产生与扩展的理论还没有形成.本文主要阐述微观结构的产生和演化,以及位错、位错界、介观结构对塑性变形过程的影响,并介绍了通过塑性变形制备纳米结构金属的基本原理及提高材料韧性的途径.     

Hydrogen Storage in Carbon-Based Nanostructured Materials

Carbon nanostructures represent a revolution in science and hold the potential for a large range of applications because of their interesting electrical, mechanical, and optical properties. Multiwall carbon nanotubes and carbon nanofibers of herringbone formation were grown by chemical vapor deposition on different catalysts from a number of hydrocarbon sources. After the total or particle removal of the catalyst system, the carbon nanostructures were analyzed for hydrogen uptake. Six samples of nanofibers grown on a Pd-based catalyst system (with a surface area of 425–455 m²/g) were controlled oxidized in air, such that they had different ratios of Pd/C varying from 0.05 to 0.9 mole ratio. The hydrogen uptake experiments were performed volumetrically in a Sievert-type installation and showed that the quantity of desorbed hydrogen (for pressure intervals ranging from 1 to 100 bars) by the carbon nanostructures free of any metal catalyst particles was between 0.04 and 0.33% by weight. For the samples of nanofibers that contained Pd in various Pd/C ratios, palladium revealed catalytic properties and supplied atomic hydrogen at the Pd/C interface by dissociating the H₂ molecules. The results show a direct correlation between the Pd/C ratio and the quantity of hydrogen absorbed by these samples. A saturation value of about 1.5 wt.% was reached for a high ratio of about 1:1 of Pd/C. The multiwall carbon nanotubes grown on a Fe:Co:CaCO₃ catalytic system and purified by acid cleaning and air oxidation showed a hydrogen uptake value of 0.1 to 0.2 wt.%.