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1.
Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface. 相似文献
2.
Shivakumar Raman Ph.D. Assistant Professor Kaushal Panchal Graduate Research Assistant P.Simin Pulat Ph.D. Assistant Professor 《Computers & Industrial Engineering》1991,21(1-4):67-71
Tolerances are basic to the production of every part. This is because perfect parts cannot be produced with existing processes and machines. The determination of tolerances for the individual parts of a functional assembly is critical, but not trivial. Numerous approaches are suggested in past literature for (analytical) tolerance allocation. With the advent of total automation, more attempts are being made to computerize manual design tasks. Tolerance design, assignment and allocation can also be fully automated if the assembly function can be estimated by the computer.
In the present paper, an attempt is made to computerize tolerance assignment. A simple example of a two piece assembly, viz., a fit, is used to demonstrate the developed methodology. A feature extraction is first performed from both detail and assembly drawings. Then, probable assembly interfaces are determined using a rule based procedure. Consequently, tolerances are assigned to the basic dimensions of each feature and to the assembly interfaces using a tolerance database and user interaction. More complex analysis for tolerance allocation is also under study. 相似文献
3.
Student O. Z. Rusyn B. P. Kysil' B. V. Kobasyar M. I. Stakhiv T. P. Markov A. D. 《Materials Science》2003,39(1):17-24
We give a quantitative estimate of changes in the structure of 15Kh2MFA steel after its long-term exposure to the combined action of high temperature, tensile stresses, and hydrogen as the factors of degradation of this steel under conditions of oil hydrocracking. Under laboratory conditions, we study the effect of high-temperature hydrogen degradation of 15Kh2MFA heat-resistant steel on changes in the quantitative characteristics of its structural elements, in particular, in the dimension and average distance between carbides as well as in their orientation from one grain to another. Algorithms for the solution of the formulated problems are described, and the possibilities of proposed approaches for the quantitative automatic processing of metallographic images are shown. 相似文献
4.
空冷发电厂的热力设计与分析 总被引:1,自引:1,他引:0
张鸿坚 《中国电机工程学报》1992,12(4):57-61
本文对热力发电厂的汽轮机排汽冷却系统进行了评估。作者编制了计算机程序,并对海勒式空冷系统做了计算,结果显示了塔高、水流速与空气流量、冷却塔与散热器投资以及经济效益的关系。 相似文献
5.
6.
无线数据通信网发展趋势 总被引:1,自引:0,他引:1
无线数据通信具有两大发展趋势,即低速的广域移动数据网及高速的局域无线数据网。本文介绍了其技术特点、应用情况和市场前景,分析了无线数据通信传输技术、网络结构和媒质接入控制等问题。 相似文献
7.
M. Charpentier Ph.D. Student D. Daloz E. Gautier G. Lesoult A. Hazotte M. Grange 《Metallurgical and Materials Transactions A》2003,34(10):2139-2148
One major hindrance to effective implementation of cast gamma TiAl-based intermetallic alloys in aircraft engines lies in
the variability of their mechanical properties resulting from chemical and microstructural heterogeneities. In the present
work, the buildup of microsegregation in a cast Ti-48Al-2Cr-2Nb alloy is investigated through experiments of quenching during
directional solidification (QDS). The solidification process, as well as the partitioning of alloying elements, between the
solid and liquid phases, is investigated. Considering experimental conditions, the α-hcp phase is found to be the primary solidifying phase. A low dendrite tip temperature of 1475 °C was estimated from thermal
recordings. These observations could be explained considering the value of the thermal gradient (around 4 °C/mm). Quantitative
values of partition coefficients are proposed for Al, Cr, and Nb. In addition to Al, Cr is found to segregate in interdendritic
regions, whereas Nb tends to be retained in the Ti-rich inner dendrites. Considering experimental cumulative solute distributions,
the buildup of microsegregation can be satisfactorily represented on the basis of Gulliver-Scheil assumptions. Due to high-temperature
quenching, the QDS experiments are also found to be appropriate to the study of high-temperature phase transformations and
microstructural development of TiAl-based alloys. The results of QDS experiments are discussed with regard to the range of
microstructural and chemical heterogeneities determined within Ti-48Al-2Cr-2Nb investment castings. Finally, regarding solid-state
phase transformations subsequent to solidification, the study attempts to explain the formation of B2 phase particles stabilized
by the ternary additions.
This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented
at the 2002 TMS Annual Meeting, February 17–21, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint
Committee on Mechanical Behavior of Materials. 相似文献
8.
制备轻油蒸汽转化制氢镍催化剂新的共浸法 总被引:2,自引:0,他引:2
用一种新的共浸法制备一批轻油蒸汽转化催化剂样品。运用TG、DTG、DSC和XRD进行的研究发现,与一般共浸法相比,这种着重提高组份间相互作用的新制法有利于提高镍催化剂的活性、抗积炭性、稳定性和金属镍的分散度,并发现用新法制备的催化剂样品,在水热初期约30小时的过程中,出现了镍晶粒先聚集再分散的新现象。 相似文献
9.
WANG Shuncai LI Chunzhi YAN Minggao Institute of Aeronautical Materials Beijing China BIAN Weimin Northeast Institute of Technology Shenyang China WANG Shuncai Graduated Student Institute of Aeronautical Materials Beijing China 《金属学报(英文版)》1990,3(2):104-109
X-ray microanalysis,convergent beam electron diffraction(CBD)and selected area electrondiffraction(SAD)studies on the structures and compositions of the constituent phases in2024 series Al alloys have been conducted.Partial substitution of alloying elements is found tooccur in all the constituent phases,which cause small deviations from the stoichiometric com-positions reported in these ternary compounds.The dominant phase is α-Al_(12)(FeMn)_3Si whichhas a body center cubic crystal structure with the Im■ space group and a=1.25 nm.The nextdominant phase is Cu_2FeAl_7 which has a primitive tetragonal crystal structure with theP4/mnc space group and a=0.6336 nm,c=1.487 nm.The minor phase is α'-Al_(12)Fe_3Si hav-ing α primitive cubic crystal structure with the Pm■ space group and α=1.27 nm. 相似文献
10.
Three-dimensional solid-liquid flow is mathematically formulated by means of the "two-fluid" approach and the two-phase k-ε-Ap turbulence model. The turbulent fluctuation correlations appearing in the Reynolds time averaged governing equations are fully incorporated. The solid-liquid flow field and solid concentration distribution in baffled stirred tanks with a standard Rushton impeller are numerically simulated using an improved "inner-outer" iterative procedure. The flow pattern is identified via the velocity vector plots and a recirculation loop with higher solid concentration is observed in the central vicinity beneath the impeller. Comparison of 相似文献