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Now showing items 129 - 144 of 1311

  • α-Fe layer formation during metal dusting of iron in CO-H2-H2O gas mixtures

    J. Zhang   A. Schneider   G. Inden  

    Abstract The formation of an α-Fe layer between cementite and graphite was observed and investigated during metal dusting of iron in CO-H2-H2O gas mixtures at both 600°C and 700°C. The condition to form this phenomenon is determined by the gas composition which depends on temperature. The iron layer formation was observed for CO content less than 1 % at 600°C and less than 5 % at 700°C. With increasing CO contents, no α-Fe layer was detected at the cementite/graphite interface by optical microscopy. In this case cementite directly contacts with the coke layer. The morphologies of the coke formed in the gas mixtures with low CO contents were also analysed. Three morphologies of graphite have been identified with 1 % CO at 600°C: filamentous carbon, bulk dense graphite with columnar structure, and graphite particle clusters with many fine iron containing particles embedded inside. At 700°C with 5 % CO the coke mainly consists of graphite particle clusters with some filamentous carbon at the early stage of reaction. Coke analysis by X-ray diffraction shows that both α-Fe and Fe3C are present in the coke. The mechanism of α-Fe accumulation between cementite and graphite is discussed in this paper.
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  • Parameter and Return-value Analysis of Binary Executables

    J. Zhang   R. Zhao   J. Pang  

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  • Microstructures and magnetic property in Mn-rich off-stoichiometric Mn2NiGa Heusler alloys

    J. Zhang   W. Cai   Z.Y. Gao   J.H. Sui  

    Microstructure and magnetic properties were investigated in Mn 50+xNi 25Ga 25-x ferromagnetic shape memory alloys. Some Mn-rich precipitates were observed in polycrystalline samples after being annealed at 1073 K for 24 h, and 1123 K for 24 h is required for a single martensitic phase. The saturation magnetization substantially decreases with higher Mn content and higher annealing temperature at which no precipitates were found in a field up to 50 KOe.[All rights reserved Elsevier].
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  • Ion irradiation-induced phase transformations in δ–γ–β phases of Sc2O3–ZrO2 mixtures

    J. Zhang   Y.Q. Wang   J.A. Valdez   M. Tang   J. Won   K.E. Sickafus  

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  • Polyvinylpyrrolidone-Directed Crystallization of ZnO with Tunable Morphology and Bandgap

    J. Zhang   H. Liu   Z. Wang   N. Ming   Z. Li   A.?S. Biris  

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  • Kugel patch repair of superior lumbar hernias

    X. Zhou   J. Zhang   H. Hu  

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  • Spatiochromatic Context Modeling for Color Saliency Analysis

    J. Zhang   M. Wang   S. Zhang   X. Li   X. Wu  

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  • Growth characteristics of SiC in a hot-wall CVD reactor with rotation

    J. Zhang   U. Forsberg   M. Isacson   A. Ellison   A. Henry   O. Kordina   E. Janzén  

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  • Coke formation during metal dusting of iron in CO-H2-H2O gas with high CO content

    J. Zhang   A. Schneider   G. Inden  

    Abstract Iron carburisation and coke formation during metal dusting of iron have been investigated in the gas mixture of 75%CO-24.8%H2-0.2%H2O at 600°C and 700°C. In all cases, cementite is formed at the surface, together with a coke layer on the top. In the coke layer, two morphologies of graphite are identified: compact bulk graphite with a uniform thickness and a columnar structure, and filamentous carbon with iron-containing phases at the tip or along its length. The examination of coke formation in different stages of reaction at 700°C reveals that the coke contains two layers. The inner layer is composed of filaments, while the outer layer consists of the compact columnar graphite. After 2 h reaction the top compact graphite layer has suffered a serious deformation and has formed fractures because of the growth of catalytic filamentous carbon underneath. These filaments grow outside from these fractures and finally cover the whole surface after 4 h reaction. At 600°C, however, the coke contains a thick bulk graphite layer and non-uniformly distributed filaments on the top. The bulk graphite layer is composed of many graphite columns which are loosely piled and are vertical to the surface. Each graphite column consists of many fine graphite fibres in parallel with the columnar axis. Filaments grow outside preferably from the gaps among these graphite columns and along the grinding scratches. TEM analysis of the coke detects very convoluted filaments with iron-containing particles at the tip or along their length. XRD and TEM analyses show that these particles are Fe3C rather than metallic iron.
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  • Trusting advice from other buyers in e-marketplaces

    J. Zhang   R. Cohen  

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  • Thermal decomposition kinetics of the synthetic complex Pb(1,4-BDC)·(DMF)(H2O)

    J. Zhang   J. L. Zeng   Y. Y. Liu   L. X. Sun   F. Xu   W. S. You and Y. Sawada  

    Pb(1,4-BDC)路(DMF)(H2O) (1,4-BDC=1,4-benzenedicarboxylate; DMF=dimethylformamide) has been synthesized and investigated by elemental analysis, FTIR spectroscopy, thermogravimetry (TG), derivative thermogravimetry (DTG). TG-DTG curves show that the thermal decomposition occurs in four stages and the corresponding apparent activation energies were calculated with the Ozawa-Flynn-Wall (OFW) and the Friedman methods. The most probable kinetic model function of the dehydration reaction of the compound has been estimated by the Coats-Redfern integral and the Achar-Bridly-Sharp differential methods in this study.
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  • Structure stability of Ti3AlC2 in Cu and microstructure evolution of Cu–Ti3AlC2 composites

    J. Zhang   J.Y. Wang   Y.C. Zhou  

    The structural stability of Ti 3AlC 2 in Cu and the microstructure evolution of Cu-Ti 3AlC 2 composites prepared at different temperatures were investigated by high-resolution transmission electron microscopy and X-ray diffraction. A mild reaction between Ti 3AlC 2 and Cu occurred at 850-950degC, and strong reactions occurred above 950degC. The reaction was identified as diffusion of Al from Ti 3AlC 2 into Cu to form Cu(Al) solid solution. Ti 3AlC 2 retained its structure under the partial loss of Al. Further depletion of Al resulted in highly defective Ti 3AlC 2 accompanied by the inner diffusion of Cu into Ti 3AlC 2 along the passway left by the Al vacancies. When Al was removed, Ti 3AlC 2 decomposed and transformed into cubic TiC x. In addition, TiC twins formed by the aggregation of C vacancies at twin boundaries. With the help of first-principles calculation and image simulation, an ordered hexagonal TiC x was identified as a transition phase linking Ti 3AlC 2 and c-TiC x. The effect of the reaction and phase transformation on the microstructure and properties of Cu-Ti 3AlC 2 composites was also discussed.
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  • Broadband and Precise Microwave Time Reversal Using a Single Linearly Chirped Fiber Bragg Grating

    J. Zhang   J. Yao  

    We propose and experimentally demonstrate a novel technique to achieve broadband and precise microwave time reversal using a single linearly chirped fiber Bragg grating (LCFBG). In the proposed approach, the time reversal is realized by the LCFBG that is operating in conjunction with a polarization beam splitter (PBS) to enable a triple use of the LCFBG with the microwave waveform entering the LCFBG from either the long or the short wavelength end. Since the LCFBG has a wide bandwidth and is used three times with exactly complementary and identical dispersion, broadband and precise microwave time reversal is ensured. A theoretical analysis is performed which is validated by simulations and an experiment. The time reversal of three different microwave waveforms with a bandwidth over 4 GHz and a time duration of approximately 10 ns is demonstrated.
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  • Systematics of the Freshwater Amphipod Genus Crangonyx (Crangonyctidae) in North Americaby J. Zhang; J. R. Holsinger

    Review by: G. van der Velde  

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  • The effect of Y on glass forming ability

    J. Zhang   H. Tan   Y.P. Feng   Y. Li  

    We have discovered a new glass forming region (GFR) defined by melt-spinning at a speed of 30m/s in a ternary Fe-Fe 2B-Fe 4B 4Y eutectic in the Fe-B-Y alloy system. This GFR is remarkably wide, within the compositional range 19-40 at.% B, 3 to ~10 at.% Y and 76-50 at.% Fe, with the best glass former being Fe 71.2B 24Y 4.8 for a 1mm fully amorphous rod. The effect of Y content on the glass forming ability (GFA) is perhaps primarily due to the characteristic of the ternary triangle, and Y in the case of Fe-B-Y system should be treated as a base element. [All rights reserved Elsevier]
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  • Oxidation Mechanism of Steels in Liquid–Lead Alloys

    J. Zhang   N. Li  

    The oxidation mechanism of steels in liquid-lead alloys (lead or lead-bismuth) was studied. Parametric dependencies of oxidation, including oxygen-concentration effects, oxidation-rate constant and corrosion-rate effects, are analyzed. An oxidation model is developed based on the assumptions that the chemical reactions are at equilibrium locally, and scale removal is due to mass-transfer corrosion. The model shows that outward-iron diffusion in the solid phase (oxide layer) controls the oxide growth and mass-transfer rate in the flowing-boundary layer determines the corrosion-product transport in the liquid phase (liquid-lead alloy). The oxide thickness depends on both the parabolic oxide-growth-rate constant and the mass-transfer-corrosion rate. For long-term operation, the outer layer of a duplex-oxide layer can be completely removed by flowing lead alloys and it is expected that a pure-chromium-oxide layer forms underneath the Fe-Cr spinel if iron is heavily depleted. The oxide thickness and steel weight change are very different from those of the pure parabolic law and they are classified into distinct and universal categories. The model is validated partially by application to interpreting the measured oxide behavior of several steels in a lead-bismuth eutectic-test loop
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