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Electronic Properties of NdOs4Sb12 NdOs4Sb12的电子性质
4区 材料科学 Q2 Engineering Pub Date : 2007-12-06 DOI: 10.1155/2007/29717
D. Galván
Theoretical calculations on NdOs4Sb12-filled skutterudite are reported. The calculated energy bands yield indication of a semimetallic behavior, while the projected density of states provides support for the existence of hybridization formed by Nd f-, Os d-, and Sb p-states.
本文报道了ndos4sb12填充方角铁矿的理论计算。计算出的能带显示出半金属行为,而预测的态密度支持Nd f-, Os d-和Sb p-形成的杂化存在。
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引用次数: 2
Flow Characteristics of Gas and Liquid through a Cell Porous Disk 气体和液体通过多孔板的流动特性
4区 材料科学 Q2 Engineering Pub Date : 2007-12-05 DOI: 10.1155/2007/52576
Y. Hirano, K. Takeda, Testuya Yano, S. Kumagai, S. Sudo
This paper describes applications of cell porous materials. The authors investigated the flow characteristics of a gas-liquid mixture in a rotating porous disk. For theoretical analyses, the gas is assumed to permeate the entire disk surface. A simple one-dimensional model illustrates that the residence time of the liquid is much greater than that of the gas. Violent interaction in small cells is likely to enhance the chemical reaction between gas and liquid. Cell porous materials might also be exploited for chemical reaction purposes.
本文介绍了细胞多孔材料的应用。研究了气液混合物在旋转多孔圆盘中的流动特性。在理论分析中,假设气体渗透到整个圆盘表面。一个简单的一维模型表明,液体的停留时间比气体的停留时间大得多。小细胞内剧烈的相互作用可能会增强气液之间的化学反应。细胞多孔材料也可用于化学反应。
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引用次数: 1
Strain-Hardening and Fracture Behavior of Die Cast Magnesium Alloy AM50 压铸镁合金AM50的应变硬化及断裂行为
4区 材料科学 Q2 Engineering Pub Date : 2007-11-29 DOI: 10.1155/2007/64195
Zhizhong Sun, Ming Zhou, Henry Hu, Naiyi Li
Understanding tensile and fracture behaviors of die cast magnesium alloys is of importance for proper design of various emerging automotive applications. In the present study, magnesium alloy AM50 was high pressure die cast into rectangular coupons with section thicknesses of 2, 6, and 10 mm. Effect of section thicknesses on strain-hardening and fracture behaviors of the die cast AM50 was investigated. The results of tensile testing indicate that the tensile properties including yield strength (YS), ultimate tensile strength (UTS), and elongation (Ef) decrease with increasing section thicknesses of die cast AM50. The analysis of true stress versus strain curves shows that the straining hardening rates during the plastic deformation of the alloy increase with decreasing section thicknesses. The observation via SEM fractography illustrates that the fracture behavior of die cast AM50 is influenced by section thicknesses. As the section thickness increases, the fracture of AM50 tends to transit from ductile to brittle mode due to increasing porosity content and coarsening microstructure.
了解压铸镁合金的拉伸和断裂行为对各种新兴汽车应用的合理设计具有重要意义。在本研究中,镁合金AM50高压压铸成矩形板,截面厚度分别为2、6和10 mm。研究了断面厚度对压铸AM50的应变硬化和断裂行为的影响。拉伸试验结果表明,AM50压铸件的屈服强度(YS)、极限抗拉强度(UTS)和伸长率(Ef)随截面厚度的增加而降低。真应力应变曲线分析表明,合金塑性变形过程中的应变硬化速率随截面厚度的减小而增大。SEM断口观察表明,AM50压铸件的断裂行为受断面厚度的影响。随着断面厚度的增加,AM50的断裂由延性断裂向脆性断裂过渡,孔隙率增加,显微组织粗化。
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引用次数: 9
Unsteady Growth of BaB2O4 Single Crystal from High-Temperature Solution 高温溶液中BaB2O4单晶的不稳定生长
4区 材料科学 Q2 Engineering Pub Date : 2007-11-25 DOI: 10.1155/2007/61395
X. Pan, W. Jin, Y. Jiang, Y. Liu, F. Ai
Two-dimensional growth of BaB2O4 single crystal from high-temperature solution was performed, and the motion of solid-liquid interface was observed in real time by differential interference microscopy. Results show that the solid-liquid interface exhibits the morphology of a vicinal face where steps with height of several microns are observed. The measurements of growth rate V and step propagating velocity υ show that both V and υ fluctuate by up to 40∼50% of their average values, respectively, under constant external conditions. Such intrinsic fluctuations with time interval of the order of one second is mainly the result of step bunching, which has been confirmed by the gradual decrease of step spacing when approaching the edge of the growing interface. Besides above fluctuations, a longer-period oscillation of V (period interval of 4∼5 seconds) is obtained for relatively rapid growth, which is triggered by the periodical alteration of step propagating directions.
在高温溶液中进行了BaB2O4单晶的二维生长,并用差示干涉显微镜实时观察了固液界面的运动。结果表明,固液界面呈邻面形态,存在高度为几微米的台阶;生长速率V和阶跃传播速度υ的测量表明,在恒定的外部条件下,V和υ分别波动高达其平均值的40 ~ 50%。这种时间间隔为1秒数量级的本征波动主要是阶跃聚束的结果,在接近生长界面边缘时阶跃间距逐渐减小证实了这一点。除了上述波动外,由于阶跃传播方向的周期性变化,在相对较快的生长条件下,还会产生较长周期的V振荡(周期间隔为4 ~ 5秒)。
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引用次数: 2
Some Material Characteristics of Cold-Sprayed Structures 冷喷涂结构的一些材料特性
4区 材料科学 Q2 Engineering Pub Date : 2007-11-22 DOI: 10.1155/2007/27347
V. Champagne, D. Helfritch, M. Trexler
The deposition and consolidation of metal powders by means of cold spray are methods whereby powder particles are accelerated to high velocity through entrainment in a gas undergoing expansion in a rocket nozzle and are subsequently impacted upon a surface. The impacted powder particles form a consolidated structure which can be several centimeters thick. The characteristics of this structure depend on the initial characteristics of the metal powder and upon impact velocity. The influence of impact velocity on strain hardening and porosity are examined. A materials model is proposed for these phenomena, and model calculation is compared with experiment for the cold spraying of aluminum.
金属粉末的冷喷涂沉积和固结是一种方法,通过在火箭喷嘴中膨胀的气体中夹带粉末颗粒加速到高速并随后撞击到表面。受冲击的粉末颗粒形成固结结构,可达几厘米厚。这种结构的特性取决于金属粉末的初始特性和冲击速度。研究了冲击速度对应变硬化和孔隙率的影响。针对这些现象提出了一种材料模型,并将模型计算与铝冷喷涂实验进行了比较。
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引用次数: 14
RF Power and Thermal Annealing Effect on the Properties of Zinc Oxide Films Prepared by Radio Frequency Magnetron Sputtering 射频功率和热退火对射频磁控溅射制备氧化锌薄膜性能的影响
4区 材料科学 Q2 Engineering Pub Date : 2007-11-20 DOI: 10.1155/2007/26459
Chaoyang Li, M. Furuta, T. Matsuda, T. Hiramatsu, H. Furuta, T. Hirao
Polycrystalline zinc oxide (ZnO) films were prepared by radio frequency (RF) magnetron sputtering under different powers. The XRD results showed that ZnO crystallite size along c-axis decreased by 43% with deposition power increased from 60 W to 300 W, increased 36% with annealing temperature rising to 400 ∘ C . TDS measurement revealed that the desorption peaks of both atomic Zn (60 W-deposited) and oxygen molecule (180 W and 300 W-deposited) obtained from ZnO films were originated from 300 ∘ C . When annealing temperature was higher than 300 ∘ C , the sheet resistance dramatically decreased, and compressive stress in the (002) plane changed to tensile stress as well. The comparison measurements of ZnO films crystallinity strongly suggested that both lower deposition power and certain thermal annealing temperature over 300 ∘ C would contribute to the formation of high quality ZnO films.
采用不同功率的射频磁控溅射法制备了多晶氧化锌(ZnO)薄膜。XRD结果表明,当沉积功率从60 W增加到300 W时,ZnO沿C轴晶粒尺寸减小43%,退火温度上升到400°C时晶粒尺寸增大36%。TDS测量结果显示,ZnO薄膜中原子Zn (60w沉积)和氧分子(180w和300w沉积)的解吸峰均来自300°C。当退火温度大于300°C时,片材的电阻急剧下降,(002)平面的压应力也转变为拉应力。氧化锌薄膜结晶度的对比测量强烈表明,较低的沉积功率和超过300°C的一定的热退火温度都有助于形成高质量的氧化锌薄膜。
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引用次数: 9
Low Dark Current Mesa-Type AlGaN Flame Detectors 低暗电流台面型海藻火焰探测器
4区 材料科学 Q2 Engineering Pub Date : 2007-11-18 DOI: 10.1155/2007/62825
Lung-Chien Chen
This study characterizes and reports on the fabrication process of AlGaN flame photodetectors with an Al0.1Ga0.9N/GaN superlattice structure. The AlGaN flame photodetectors exhibited a low dark current (∼1.17×10−10 A at bias of −5 V) and large rejection ratio of photocurrent (∼2.14×10−5 A at bias of -5 V) to dark current, which is greater than five orders of magnitude. Responsivity at 350 nm at a bias of -5 V was 0.194 A/W. Quantum efficiency, η, was 0.687 at a reverse bias of 5 V.
本文研究并报道了Al0.1Ga0.9N/GaN超晶格结构的AlGaN火焰光电探测器的制备过程。AlGaN火焰光电探测器具有较低的暗电流(−1.17×10−10 a,偏置为−5 V)和较大的光电流(−2.14×10−5 a,偏置为-5 V)对暗电流的抑制比,大于5个数量级。在-5 V偏置下,350 nm处的响应度为0.194 a /W。在反向偏置5 V时,量子效率η为0.687。
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引用次数: 0
Characterizations of Polystyrene-Based Hybrid Particles Containing Hydrophobic Mg(OH)2 Powder and Composites Fabricated by Employing Resultant Hybrid Particles 含疏水性Mg(OH)2粉末的聚苯乙烯基杂化颗粒及其复合材料的表征
4区 材料科学 Q2 Engineering Pub Date : 2007-10-30 DOI: 10.1155/2007/19232
S. Kimura, T. Hyodo, Y. Shimizu, M. Egashira
Polystyrene (PS)-based hybrid particles containing a large amount of Mg(OH)2 powder treated with methylhydrogen polysiloxane (MHS) were fabricated by a bulk and subsequent suspension two-step polymerization method. All the particles fabricated showed spherical shape and their particle sizes were about 500 μm, irrespective of the additive amount of the Mg(OH)2 powder modified with MHS (ST-1). The actual content of ST-1 powder incorporated inside each kind of hybrid particle was almost the same as that in the raw mixture, and agglomeration of ST-1 powder was hardly observed inside the hybrid particles. The compressive strength of the hybrid particles remained almost unchanged, even when the ST-1 powder content increased from 10 to 50 phr. Furthermore, a composite fabricated by employing the hybrid particles achieved homogenous distribution of ST-1 powder and showed a higher oxygen index than that of a composite fabricated by directly mixing of PS pellets and ST-1 powder.
采用本体-后悬浮两步聚合法制备了含有大量Mg(OH)2粉末的聚苯乙烯(PS)基杂化颗粒,并用甲基氢聚硅氧烷(MHS)处理。与MHS (ST-1)改性Mg(OH)2粉末的添加量无关,制备的颗粒均呈球形,粒径均在500 μm左右。每种杂化颗粒内部实际掺入的ST-1粉末含量与原混合料中的含量基本相同,杂化颗粒内部几乎没有ST-1粉末的结块现象。当ST-1粉末含量从10 phr增加到50 phr时,杂化颗粒的抗压强度几乎保持不变。此外,采用混合颗粒制备的复合材料实现了ST-1粉末的均匀分布,并且比直接将PS颗粒与ST-1粉末混合制备的复合材料具有更高的氧指数。
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引用次数: 0
Ultralight-Weight Cellulose Aerogels from NBnMO-Stabilized Lyocell Dopes 由nbnmo稳定Lyocell Dopes制备的超轻质纤维素气凝胶
4区 材料科学 Q2 Engineering Pub Date : 2007-10-29 DOI: 10.1155/2007/73724
F. Liebner, A. Potthast, T. Rosenau, E. Haimer, M. Wendland
Cellulose aerogels are intriguing new materials produced by supercritical drying of regenerated cellulose obtained by solvent exchange of solid Lyocell moldings. From N-methylmorpholine-N-oxide solutions with cellulose contents between 1 and 12%, dimensionally stable cellulose bodies are produced, in which the solution structure of the cellulose is largely preserved and transferred into the solid state. The specific density and surface of the obtained aerogels range from 0.05 to 0.26 g/cm3 and from 172 to 284 m2/g, respectively, depending on the cellulose content of the Lyocell dopes and regeneration procedure. A reliable extraction and drying procedure using supercritical carbon dioxide, the advantageous use of NBnMO as stabilizer for the Lyocell dopes, and selected physical properties of the materials is communicated.
纤维素气凝胶是一种新型材料,它是对固体Lyocell模塑的溶剂交换得到的再生纤维素进行超临界干燥而制成的。从纤维素含量在1 - 12%之间的n -甲基morpholine- n -oxide溶液中产生尺寸稳定的纤维素体,其中纤维素的溶液结构在很大程度上被保留并转移到固体状态。所获得的气凝胶的比密度和表面分别在0.05至0.26 g/cm3和172至284 m2/g之间,这取决于Lyocell dopes的纤维素含量和再生程序。介绍了一种可靠的超临界二氧化碳萃取和干燥工艺,利用NBnMO作为Lyocell掺杂剂的稳定剂,以及材料的选定物理性质。
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引用次数: 29
Processability of Pultrusion Using Natural Fiber and Thermoplastic Matrix 天然纤维和热塑性塑料基体拉挤的可加工性
4区 材料科学 Q2 Engineering Pub Date : 2007-10-25 DOI: 10.1155/2007/37123
T. Nguyen-Chung, K. Friedrich, G. Mennig
Fundamental mechanisms of the pultrusion process using commingled yarns of polypropylene matrix and discontinuous flax fiber to produce thermoplastic profiles were investigated in numerical and experimental manners. Essential issue is the fact that all natural fibers are discontinuous by nature, which may negatively influence the processability. The pultrusion process will be only successful if the pulling force exerted on the solidified pultrudates can be transmitted to the regions of unmelted commingled yarns by “bridging over” those melted regions within the die. This can be realized by applying a sufficient number of small yarn bundles of high compactness rather than a thicker single bundle of lower compactness as the raw material. Furthermore, the possibility of adding extra melt into the yarn bundles by side-fed extrusion has been investigated showing that the impregnation can be improved only for the outer layers of yarns, which is owed to the high viscosity of the thermoplastic melt and the limited length of the die.
采用数值和实验方法研究了聚丙烯基混纺纱与亚麻纤维混纺纱生产热塑性型材的基本机理。关键问题是所有天然纤维本质上都是不连续的,这可能会对加工性能产生负面影响。只有当施加在固化拉挤料上的拉力能够通过“桥接”在模具内熔化的区域传递到未熔化的混纺纱区域时,拉挤过程才会成功。这可以通过使用足够数量的高紧致度的小纱束来实现,而不是使用较粗的低紧致度的单纱束作为原料。此外,研究了通过侧送挤压向纱束中添加额外熔体的可能性,结果表明,由于热塑性熔体的高粘度和模具长度有限,只能改善纱线外层的浸渍。
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引用次数: 10
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Advances in Materials Science and Engineering
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