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71.
在Ag38.5Cu33.4Ge28.1三元共晶合金的深过冷实验中,获得的最大过冷度为175 K(0.22TE). XRD分析表明,不同过冷条件下其共晶组织均由(Ag),(Ge)和η(Cu3Ge)三相组成. 在小过冷条件下,三个共晶相协同生长,凝固组织粗大.随着过冷度的增大,共晶组织明显细化,(Ge)相与其他两相分离,以初生相方式生长,而(Ag)相与η相始终呈二相层片共晶方式共生生长. 当过冷度超过80 K时,初生相(Ge)由小过冷时的块状转变为具有小面相特征的枝晶方式生长. 部分小面相(Ge)枝晶出现规则的花状,花瓣数介于5—8之间,并且过冷度越大(Ge)相越容易分瓣. 花状(Ge)枝晶的晶体表面为{111}晶面簇,择优生长方向为〈100〉晶向族.
关键词:
三元共晶
晶体形核
深过冷
快速凝固 相似文献
72.
通过对二值无稳态触发器设计原理的重新归纳,本文从三值单稳态触发器的设计出发,提出了基于集成门电路的三值无稳态触发器的设计方案, 并用PSPICE程序进行计算机验证. 结果表明所设计的三值无稳态触发器具有正确的逻辑功能. 本文还进一步提出了三值等宽的三值无稳态触发器的设计方案. 相似文献
73.
Ren-Min Wu Na Qi Yu-Wen Jia Zhu Guan Liang-Ren Zhang Li-He Zhang Zhen-Jun Yang 《中国化学快报》2014,25(12):1583-1585
A facile and efficient protocol for the synthesis of sulfur substituted-cyclopyrophosphate of cIDPRE(P_S~1-cIDPRE) was developed.The key step was the cyclization process which was completed by the sulfur substituted cyclization precursor 1b via the one-pot phosphoramidite strategy. 相似文献
74.
S.V. Ivanov M.Yu. Chernov V.A. Solovev P.N. Brunkov D.D. Firsov O.S. Komkov 《Progress in Crystal Growth and Characterization of Materials》2019,65(1):20-35
High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5?μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1?Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ~8?μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic InxAl1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded InxAl1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6?μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T?=?10–300?K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As4/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3?×?107 cm?2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300?nm, the extremely low surface roughness with the RMS value of 1.6–2.4?nm, measured by AFM, as well as rather high 3.5?μm-PL intensity at temperatures up to 300?K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform. 相似文献
75.
I. M. J. J. van de Ven-Lucassen M. F. Kemmere P. J. A. M. Kerkhof 《Journal of solution chemistry》1997,26(12):1145-1167
The Taylor dispersion technique is used to measure the ternary mutual diffusion coefficients of aqueous nonelectrolyte solutions at 25°C. The dispersion of the injected solutes is recorded by a differential refractometer and an ultraviolet-visible detector. The diffusion coefficients are calculated directly by fitting the theoretical dispersion equations to about six experimental curves simultaneously. If the ternary diffusion effects in the measured dispersion profiles are not confused by the inaccuracy of the experimental method or an unfavorable relative detector sensitivity, the diffusion coefficients are precise. For the system methanol + acetone + water, it is shown that the Taylor dispersion method is unsuitable for the determination of all the diffusion coefficients if the methanol mole fraction is less than 0.45 or the acetone mole fraction if more than 0.001. 相似文献
76.
Fereshteh K. Yousefi Ali Jannesari Shahla Pazokifard Mohammad Reza Saeb Alison J. Scott Alexander Penlidis 《大分子反应工程》2019,13(4)
Ternary monomer reactivity ratios of triisopropylsilyl acrylate (SiA), methyl methacrylate (MMA), and n‐butyl acrylate (BA), as common monomers in self‐polishing coatings (SPCs) binders are obtained using experimental data collected from free radical bulk polymerization at 70 °C. Different terpolymerizations at low and medium‐high conversions are performed at optimized feed compositions. Estimations are made using the error‐in‐variables model (EVM) framework, applying the recast form of the Alfrey–Goldfinger (AG) model and a direct numerical integration (DNI) approach to the collected data. Estimations from individual low and medium‐high conversion data are compared to those found with the combined data (full conversion range data). The highest certainty in point estimates are obtained with analysis of the full conversion range data. Furthermore, the reactivity ratios determined from the combined data fall between those found with analysis of individual low and medium‐high conversion data, another corroboration of reliable data collection. Reactivity ratios determined from analysis of the combined data (rSiA/MMA = 0.4185, rMMA/SiA = 1.3754, rSiA/BA = 0.8739, rBA/SiA = 0.5736, rBA/MMA = 0.3692, rMMA/BA = 1.7919) are used in the recast AG model to predict cumulative terpolymer composition as a function of conversion. The experimental data and model prediction show satisfactory agreement. 相似文献
77.
Ling Wang 《Applied mathematics and computation》2005,170(2):760-1343
Simulation optimization aims at determining the best values of input parameters, while the analytical objective function and constraints are not explicitly known in terms of design variables and their values only can be estimated by complicated analysis or time-consuming simulation. In this paper, a hybrid genetic algorithm–neural network strategy (GA–NN) is proposed for such kind of optimization problems. The good approximation performance of neural network (NN) and the effective and robust evolutionary searching ability of genetic algorithm (GA) are applied in hybrid sense, where NNs are employed in predicting the objective value, and GA is adopted in searching optimal designs based on the predicted fitness values. Numerical simulation results and comparisons based on a well-known pressure vessel design problem demonstrate the feasibility and effectiveness of the framework, and much better results are achieved than some existed literature results. 相似文献
78.
Yichun Chi 《Insurance: Mathematics and Economics》2011,48(3):326-337
In this paper, we generalize the Cramér-Lundberg risk model perturbed by diffusion to incorporate jumps due to surplus fluctuation and to relax the positive loading condition. Assuming that the surplus process has exponential upward and arbitrary downward jumps, we analyze the expected discounted penalty (EDP) function of Gerber and Shiu (1998) under the threshold dividend strategy. An integral equation for the EDP function is derived using the Wiener-Hopf factorization. As a result, an explicit analytical expression is obtained for the EDP function by solving the integral equation. Finally, phase-type downward jumps are considered and a matrix representation of the EDP function is presented. 相似文献
79.
A simple and rapid method for the simultaneous analysis of a ternary mixture containing trimethoprim, sulphamethoxazole and phenazopyridine hydrochloride is reported. The procedure consists of extraction in 0.1 M hydrochloric acid, filteration and measurement of the amplitudes of the third-derivative spectra at 242 and 276 nm and the absorbance at 450 nm for the determination of trimethoprim, sulphamethoxazole and phenazopyridine hydrochloride, respectively. Good linearity, accuracy, precision and selectivity were found, and the method is proposed for routine quality control purposes, even for the uniformity of contents test. 相似文献
80.
Abstract Glasses with composition × CoO.(0.25-x) CaO.0.75 B2O3 have been prepared over the range 0 ≤ x ≤ 0.25 containing 2 mol% of V2O5. Electron paramagnetic Resonance spectra of VO2+ of these glasses has been measured at X-band (ν ≈ 9.15 GHz) at room temperature and at liquid nitrogen temperature. Spin Hamiltonian parameters of the VO2+ ions have been calculated. It is found that for x ≤ 0.12 the octahedral symmetry of the V4+ site is improved. A part of these glasses were annealed at 473 K for 24 hours and EPR spectra were recorded and analysed. 相似文献