共查询到20条相似文献,搜索用时 187 毫秒
1.
2.
3.
用差热分析(DTA),结合X射线衍射(XRD)研究了Sm8Fe83Si2C5Cu0.5Nb1.5非晶合金的晶化动力学。结果表明:温度在0 ̄1000℃范围内,该合金的晶化相为α-Fe和Sm2(FeSi)17Cx,α-Fe相的晶化表观激活能力349.53kJ/mol,Sm2(FeSi)17Cx的晶化表观激活能力316.19kJ/mol,两相在晶化初期激活能量小,随晶化量(xc)的增加激活能增大,当α- 相似文献
4.
5.
燃烧还原化合法备氮人钛粉末(Ⅱ)——试验研究 总被引:2,自引:0,他引:2
对用燃烧还原合成法制备氮化钛粉末的过程进行了试验研究,建立了一种无需机械粉磨处理的直接合成工艺。制备的氮化钛粉末粒径分布为0.2 ̄1.0μm,平均粒径为0.5 ̄0.6μm。研究结果表明,副产物氧化镁的机械分割作用是使氮化钛颗粒免于烧结成块的根本原因,恰当地控制合成温度可较好地兼顾产物的氮化率与颗粒形态。 相似文献
6.
7.
旋转喷吹反应自生铝基复合材料的工艺及显微结构 总被引:1,自引:0,他引:1
在大气条件下向铝和铝-镁合金液体内部旋转吹入氧气,氧与铝、镁反应,生成的Al2O3和MgAl2O4陶瓷颗粒分布在基体金属中。自生的Al2O3颗粒尺寸为0.1 ̄3μm,MgAl2O4颗粒尺寸为5 ̄10μm。 相似文献
8.
9.
用线性极化法,极化曲线法和失重法研究了化学镀Ni-Cu-P非晶态合金,纯Ni和A3钢于140℃,pH值5.0、CO2饱和的2W(wt)NaSO4溶液中的腐蚀电化学行为,结果表明,在该介质条件下,Ni-Cu-P合金、纯Ni和A3钢的耐蚀性依次减弱,比值为81.2:23.9:1.0。Ni-Cu-P合金于250 ̄550mV(vs OP)区间发生钝化;纯Ni在50 ̄150mV和高于400mV(vsOP)区 相似文献
10.
11.
The effects of fiber diameter on the mechanical properties of PAN-based carbon fibers have been investigated in a series of processing experiments on fibers with different starting filament diameters. The fiber tows, with similar initial mechanical performance, were stretched at high temperatures to produce a large number of fiber types with a wide range of filament diameters. The three starting carbon fibers tows had nominal filament diameters of 5 μm, 6·5 μm, and 10 μm and contained 12000, 6000, and 3000 filaments respectively. These tows were stretched for 5 minutes at 2600°C with a series of loads of up to 6 kg. For all fiber types and all stretching conditions, substantial increases in Young's moduli were induced, the increases being closely related to the induced extensions. However, it was found that tensile strengths generally decreased if fibers were subjected to high temperatures without significant stretching. On the other hand, the tensile strengths were restored to their original values when greater strains were induced by using higher stresses. Although fibers with a relatively large diameter of 8·3 μm were produced with a modulus of -470GPa and strength of -3·7 GPa, greater improvements in mechanical properties were achieved with smaller diameter fibers. The loads and temperatures involved in these hot stretching experiments were not excessive, and the investigations showed that serious consideration should be given to the feasibility of commercial production of high performance PAN-based carbon fibers by this processing route. 相似文献
12.
13.
《Nanotechnology, IEEE Transactions on》2006,5(5):499-510
This paper proposes a nanorobotic fiber fabrication method which uses proximal probes to draw polymer fibers down to few hundred nanometers in diameter and several hundred micrometers in length. Using proximal probes such as Atomic Force Microscope (AFM) and Scanning Tunneling Microscope (STM) or glass micropipettes, liquid polymers dissolved in a solvent are drawn. During drawing, the solvent evaporates in real-time which solidifies the fiber. Controlling the drawn fibers trajectory and solidification in three-dimensions (3-D), suspended fibers, fiber cantilevers, custom 3-D fibers, and fiber networks, are proposed to be fabricated. Poly(methyl methacrylate) (PMMA) polymer dissolved in chlorobenzene is used to form a variety of suspended polymer fibers with diameters from few microns to 200nm. Fabrication of crossed and linear networks of fibers is also demonstrated. Viscoelastic modeling of polymer fiber drawing is realized using a finite element method to test the significance of the drawing speed and velocity profile on the extensional behavior of the drawn fiber. Since the mechanical properties of the drawn micro/nanofibers could vary from the bulk polymer material significantly, mechanical characterization of suspended fibers using an AFM and a Nanoindenter setup is proposed. Extending this technique to a variety of nonconductive and electroactive polymer fibers, many novel applications in micro/nanoscale sensors, actuators, fibrillar structures, and optical and electronic devices would become possible. 相似文献
14.
Calcium aluminate glass has a refractive index less than 1 at 10.6 μ, and therefore it is a good candidate for a hollow fiber for the transmission of CO(2) laser energy. We have drawn hollow calcium aluminate glass fibers with inner diameters ranging from 380 to 500 μ. The loss for our 500-μm inner-diameter hollow glass fibers measured at 10.6 μm is 8.6 dB/m. 相似文献
15.
Propagation and mode coupling within relatively short (~1-10?m) large core, nominally multimode, fibers are of interest in a number of applications. In this research, we have studied the output beam quality and mode coupling in various fibers with core diameters of 100-400?μm and lengths of 2?m. Output beam quality (M2) and mode-coupling coefficients (D) have been studied for different clad dimensions, numerical apertures, and wavelengths. The mode-coupling coefficients have been determined based on modal power diffusion considerations. The results show that D scales approximately as the inverse square of the clad dimension and inverse square root of the wavelength. Output from a 2?m length fiber of 100?μm core and 660?μm clad fiber is close to single mode (M2=1.6), while output from a 200?μm core and 745?μm clad fiber also has high beam quality. 相似文献
16.
Applegate RA Donnelly WJ Marsack JD Koenig DE Pesudovs K 《Journal of the Optical Society of America. A, Optics, image science, and vision》2007,24(3):578-587
We report root-mean-square (RMS) wavefront error (WFE) for individual aberrations and cumulative high-order (HO) RMS WFE for the normal human eye as a function of age by decade and pupil diameter in 1 mm steps from 3 to 7 mm and determine the relationship among HO RMS WFE, mean age for each decade of life, and luminance for physiologic pupil diameters. Subjects included 146 healthy individuals from 20 to 80 years of age. Ocular aberration was measured on the preferred eye of each subject (for a total of 146 eyes through dilated pupils; computed for 3, 4, 5, 6, and 7 mm pupils; and described with a tenth-radial-order normalized Zernike expansion. We found that HO RMS WFE increases faster with increasing pupil diameter for any given age and pupil diameter than it does with increasing age alone. A planar function accounts for 99% of the variance in the 3-D space defined by mean log HO RMS WFE, mean age for each decade of life, and pupil diameter. When physiologic pupil diameters are used to estimate HO RMS WFE as a function of luminance and age, at low luminance (9 cd/m2) HO RMS WFE decreases with increasing age. This normative data set details (1) the 3-D relationship between HO RMS WFE and age for fixed pupil diameters and (2) the 3-D relationship among HO RMS WFE, age, and luminance for physiologic pupil diameters. 相似文献
17.
The Faraday effect provides a mechanism for achieving unidirectional light propagation in optical isolators; however, miniaturization requires large Verdet constants. High rare-earth content glasses produce suitably large Verdet values, but intrinsic fabrication problems remain. The novel powder-intube method, or a single-draw rod-in-tube method, obviates these difficulties. The powder-in-tube method was used to make silica-clad optical fibers with a high terbium oxide content aluminosilicate core. Core diameters of 2.4 μm were achieved in 125-μm-diameter fibers, with a numerical aperture of 0.35 and a Verdet constant of -20.0 rad/(T m) at 1.06 μm. This value is greater than 50% for crystals found in current isolator systems. This development could lead to all-fiber isolators of dramatically lower cost and ease of fabrication compared with their crystalline competitors. 相似文献
18.
Self-assembly of one-dimensional nanoscale building blocks into functional 2-D or 3-D complex superstructures has stimulated a great deal of interest. We report the synthesis and characterization of nanopolyhedrons assembled from ultrathin SnO(2) nanowires based on the sodium dodecyl sulfate (SDS)-assisted hydrothermal process. As-synthesized SnO(2) nanopolyhedrons have uniform diameters around 300 nm and are self-assembled by numerous ultrathin SnO(2) nanowires with diameters of 5-10 nm. The growth mechanism was also studied by investigating the samples synthesized at different reaction time. Thin films of the assembled SnO(2) nanopolyhedrons were configured as high performance sensors to detect methanol, ethanol, and acetone, which exhibited 1 ppm sensitivity, very fast response and recovery times (several seconds for different gases with concentrations of 1-200 ppm) to all the target gases and highly selective detection to acetone. 相似文献
19.
An assessment of the science and technology of carbon nanotube-based fibers and composites 总被引:1,自引:0,他引:1
Tsu-Wei Chou Limin Gao Erik T. Thostenson Zuoguang Zhang Joon-Hyung Byun 《Composites Science and Technology》2010
This paper examines the recent advancements in the science and technology of carbon nanotube (CNT)-based fibers and composites. The assessment is made according to the hierarchical structural levels of CNTs used in composites, ranging from 1-D to 2-D to 3-D. At the 1-D level, fibers composed of pure CNTs or CNTs embedded in a polymeric matrix produced by various techniques are reviewed. At the 2-D level, the focuses are on CNT-modified advanced fibers, CNT-modified interlaminar surfaces and highly oriented CNTs in planar form. At the 3-D level, we examine the mechanical and physical properties CNT/polymer composites, CNT-based damage sensing, and textile assemblies of CNTs. The opportunities and challenges in basic research at these hierarchical levels have been discussed. 相似文献
20.
The effect of temperature on the bend radius that a c-axis-oriented sapphire fiber can withstand was determined for fibers of various diameter. Bend stress rupture tests were performed for times of 1–100 h and temperatures of 300–1700 °C. Fibers would survive the bend test undeformed, would fracture or would deform. The bend survival radius was determined to be the radius above which no fibers fractured or deformed for a given time-temperature treatment. It was found that the ability of fibers to withstand curvature decreases substantially with time and increasing temperature and that fibers of smaller diameter (40–83 μm) withstood smaller bend radii than would be expected from just a difference in fiber diameter when compared with the bend results of the fibers of large diameter (144 μm). This was probably due to different flaw populations, causing high temperature bend failure for the tested sapphire fibers of different diameters. 相似文献