D.Wen 1)
,
Q.K.Cai 2)
,
C.S. Liu 1)
,
Y.J. Guo 1) and Y.H.Zhao 1) 1) School of Materials and Metallurgy
,
Northeastern University
,
Shenyang 110006
,
China 2) Shenyang University
,
Shenyang 110044
,
China
金属学报(英文版)
Laser surface alloying of γ TiAl alloy with nitrogen was studied under the constant protective nitrogen current (20l /min). The experimental results shown that the surface multi layers formed with experimental parameters could be up to 600μm depth; it consists of TiN,Ti 2AlN,α 2 and γ phases, without AlN, and the irregular coarse continuous “flow” line,dendrite,needle and granular nitrides disperse on the fine dendrite casting α 2 and γ phases substrate. The microstructure and compositions in the nitiding layer were determined and analyzed by SEM and EPMA and the mechanism for the formation of microstructure in the nitriding layer was also discussed.
关键词:
laser surface alloying
,
null
,
null
Nanostructured Materials
The Landauer electrical resistivity R of one-dimensional (1D) layered nanostructures is calculated. The analysis of the logarithm of the resistance as a function of grain size reveals that there is a minimum value of resistivity R(min) when the grain size takes a value of d(c), where d(c) depends on the barrier height and excess volume of interface. R increases in the region of d(cl) > d > d(c), where d is the grain size, and d(cl) is another critical value of grain size. The mechanism of the anomalous resistivity behavior is discussed briefly.
关键词:
nanocrystalline;resistance;alloys
Guozhen SHEN
,
Di CHEN
材料科学技术（英文）
One-dimensional (1-D) nanostructures have been attracted much attention as a result of their exceptional properties, which are different from bulk materials. Among 1-D nanostructures, 1-D heterostructures with modulated compositions and interfaces have recently become of particular interest with respect to potential applications in nanoscale building blocks of future optoelectronic devices and systems. Many kinds of methods have been developed for the synthesis of 1-D nanoscale heterostructures. This article reviews the most recent development, with an emphasize on our own recent efforts, on 1-D nanoscale heterostructures, especially those synthesized from the vapor deposition methods, in which all the reactive precursors are mixed together in the reaction chamber. Three types of 1-D nanoscale heterostructures, defined from their morphologies characteristics, are discussed in detail, which include 1-D co-axial core-shell heterostructures, 1-D segmented heterostructures and hierarchical heterostructures. This article begins with a brief survey of various methods that have been developed for synthesizing 1-D nanoscale heterostructures and then mainly focuses on the synthesis, structures and properties of the above three types of nanoscale heterostructures. Finally, this review concludes with personal views towards the topic of 1-D nanoscale heterostructures.
关键词:
Nanostructures
,
Heterostructures
,
One-dime
Xiaosheng FANG
材料科学技术（英文）
One-dimensional (1D) nanomaterials and nanostructures have received much attention due to their potential interest for understanding fundamental physical concepts and for applications in constructing nanoscale electric and optoelectronic devices. Zinc sulfide (ZnS) is an important semiconductor compound of II-VI group, and the synthesis of 1D ZnS nanomaterials and nanostructures has been of growing interest owing to their promising application in nanoscale optoelectronic devices. This paper reviews the recent progress on 1D ZnS nanomaterials and nanostructures, including nanowires, nanowire arrays, nanorods, nanobelts or nanoribbons, nanocables, and hierarchical nanostructures etc. This article begins with a survey of various methods that have been developed for generating 1D nanomaterials and nanostructures, and then mainly focuses on structures, synthesis, characterization, formation mechanisms and optical property tuning, and luminescence mechanisms of 1D ZnS nanomaterials and nanostructures. Finally, this review concludes with personal views towards future research on 1D ZnS nanomaterials and nanostructures.
关键词:
One-dimensional
,
ZnS
,
Nanomaterials
,
Nanost
Zhaoyang ZENG
,
Lide ZHANG
,
Xiaohong YAN
材料科学技术（英文）
Ballistic transport of Q1D electrons through multiple magnetic barriers is investigated. It is shown that ballistic conductance peaks disappear progressively with the increase of the oscillation frequency of the confining parabolic potential.
关键词:
Journal of Physical Chemistry B
Size-controlled gold nanocrystals were conveniently synthesized through direct electroreduction of bulk AuCl4- ions in the presence of poly(N-vinylpyrrolidone) (PVP). PVP greatly enhanced the gold particle formation process and also significantly retarded the gold electrodeposition process, allowing the electrochemical synthesis of gold nanocrystals to be carried out in the form of simple electroreduction. This novel electrochemical method may be extended to synthesis of other noble metal nanoparticles with controllable size on a large scale. The PVPK90-protected gold nanocry.stals spontaneously self-assembled into nearly ordered 2D close-packed arrays and interesting 1D nanostructures. The aggregation of unstable PVPK17-protected gold nanocrystals resulted in the formation of ultrathin single-crystalline films. PVP plays multifunctional roles in controlling the size and shape of gold nanocrystals and in inducing individual gold nanocrystals to construct ID nanostructures. The nanoparticle self-assembling technique based on PVP offers a simple, but effective, path to organize individual gold nanoparticles into various 1D and 2D nanostructured materials.
关键词:
shape-controlled synthesis;uniform silver nanowires;optical-properties;size control;nanoparticles;nanorods;transition;mechanism;nanomaterials;microscopy
Wenhui MA
,
Gang XIE
,
Hua WANG
材料科学技术（英文）
The thermal expansion behavior of La1-xSrxMn1-yCoyO3-d (x=0.2~0.4, y=0.1~0.3) perovskites in air has been investigated. The average linear thermal expansion coefficients increased with increasing Sr content up to 40 mole fraction or Co content up to 30 mole fraction. The expansion is generally attributed to an increase in the average cation radius as some of the cations in the perovskite are reduced in valence when oxygen ions are removed from the structure.
关键词:
Thermal expansion
,
null
,
null
朱杰武
,
柳永宁
,
许雁
,
冯耀荣
机械工程材料
doi:10.3969/j.issn.1000-3738.2005.06.007
在不同温度下测试了X70管线钢动态断裂韧度K1d、J1d和止裂韧度K1a以及夏氏V型缺口冲击韧度Ak,对三者的关系进行了分析.结果表明:温度和加载速率都对断裂韧度产生影响;加载速率变化引起的韧-脆断裂转变具有热激活特征,在热激活分析基础上,在应力强度因子速率K=15 MPa·m1/2s-1条件下,得出断裂韧度、止裂韧度和冲击韧度三者的关系:Ak=4.84×106T-2.8K1d(或K1a).可以用小试样Ak数据计算得到K1d和K1a.
关键词:
管线钢
,
断裂韧度
,
止裂韧度
,
韧-脆断裂转变
田丽丽
,
李中军
,
李辉
应用化学
doi:10.3969/j.issn.1000-0518.2004.01.003
将L-山梨糖的2,3位用异亚丙基保护、在6位上进行选择性苯磺酰化、叠氮化、催化氢化、水解得6-氨基-6-脱氧-L-呋喃山梨糖盐酸盐,再经催化氢化得1-脱氧氮杂-D-葡萄糖(deoxynojirimycin,DNJ)盐酸盐,总收率26%. 采用苄氧羰酰化,将DNJ及其差向异构体进行了分离,得到的N-苄氧羰酰基-1-脱氧氮杂-D-葡萄糖经氢解后生成1-脱氧氮杂-D-葡萄糖.
关键词:
脱氧氮杂-D-葡萄糖
,
糖苷酶
,
合成
,
异构体分离
