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Papers by Author: X. Zhang

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Synthesis of Ordered Mesoporous Carbon Using MCM-41 Mesoporous Silica as Template

Authors: Chun Fu Lin, X. Zhang, Hong Lin, Ning Wang, Jian Bao Li, Xiao Zhan Yang

Abstract: Mesoporous carbon with high surface area and ordered structure was synthesized via a nanocasting process using mesoprous MCM-41 silica as a template and sucrose as a carbon precursor. Sample was characterized by XRD, SEM, TEM and nitrogen adsorption. The results show that the templated carbon has a BTE surface area ∼1200 m2/g, a pore volume ∼1.0 cm3/g, and a bimodal porosity centered at around 4 nm and 46 nm.

543

Study of Bonding of Grain Boundaries in Steels Using EELS

Authors: X. Zhang, Lina Zhang, Jun Jie Qi, Yue Ma

Abstract: A novel EELS technique was developed to study bonding of grain boundary in many kinds of steels. We measured the normalized intensities of Fe white lines and calculated the occupancies of 3d states of iron, and then analyzed the relationship of the occupancies of 3d states of iron and the fracture property of the steels. We found that if the grain boundary has a different occupancy of 3d state of iron from that of the bulk, the steel tends to have an intergranular fracture, whereas if the grain boundary has almost the same occupancy of 3d state as the bulk, the steel tends to have a transgranular fracture. Our result shows that the difference in the occupancy of 3d state between bulk and grain boundary can be used to study the fracture mode at grain boundary in steel.

4063

Synthesis and Characterization of ZnO Nanowires Using a Simple PVD Approach without Catalysts

Authors: Long Shan Wang, X. Zhang, Fan Hao Zeng

Abstract: Two kinds of ZnO nanowires with different morphologies and characters were produced on Si (100) using a new PVD approach by heating and oxidizing Zn powders directly without any catalysts. The nanowires have an average diameter of 80nm (deposited at the evaporation source) and 30nm (deposited downstream of the evaporation source) respectively, and are evenly distributed over an area of > 20mm2. The two nanowires have complete different photoluminescence properties. One has a strong green emission (510nm) with a weak UV emission (380nm). The other has a strong and sharp UV emission (385nm), showing the capability for UV laser emitters.

3535

Large-Scale Synthesis of In₂O₃ Nanowires and Their Characterization

Authors: Fan Hao Zeng, X. Zhang

Abstract: Large-scale single-crystalline In2O3 nanowires were successfully synthesized by simply evaporating the pure indium at 950ı. The as-synthesized products, characterized by XRD, SEM, and TEM, were pure, structurally uniform, and single crystalline with typical diameters of 10 to 100 nanometers and lengths of up to a few hundreds of micrometers. The growth mechanism of the nanowires also was discussed.

3513

Simulation of Structural Parameters and Superconducting Transition Temperature of MgB₂ under Pressure

Authors: Yang Shao, X. Zhang, Fu Ling Tang

Abstract: We successfully developed the potential parameters for simulation of MgB2. With these potential parameters, we calculate the lattice parameters and volume variations with pressure up to 240GPa. All these results agree well with experimental data under 40GPa and provide reasonable tendencies from 40GPa to 240GPa. By employing the McMillan expression, it is found that the lattice stiffening dominants the behavior of Tc under pressure in the scope of BCS theory. Using our calculated Grüneisen parameter G g , the simulated pressure effect on Tc accords well with experimental results. Our result shows that the Tc of MgB2 can be destroyed by high pressure.

3319

Magnetotransport Behaviors in Electron-Doped Manganese Oxide La_0.9Te_0.1MnO₃

Authors: Guotai Tan, X. Zhang, Zhao Hui Chen

Abstract: The magnetotransport behaviors of electron-doped colossal magnetoresistance (CMR) manganites La0.9Te0.1MnO3 have been investigated in external magnetic fields up to 4 T. The temperature dependence of the resistivity shows that the transport mechanisms of the sample below the metal-insulator transition temperature are attributed to the electron-phonon and magnon scattering behaviors. While the resistivity above Curie temperature (Tc=240 K) can be fitted with either polaron transport or variable-range hopping, and the fitting results are affected significantly by the magnetic fields. The electron spin resonance investigation indicated that there exist the ferromagnetic clusters up to 280 K in the paramagnetic phase of the sample. As a result, a possible correlation between the resistivty and phase separation is considered.

2259

Magnetoresistance and Current-Controlled Electric Transport Properties of Fe-C Film on Si Substrate

Authors: Q.Z. Xue, X. Zhang

Abstract: Using pulsed laser deposition we prepared Fex-C1-x films on Si (100) substrates. We show that the lightly Fe-doped amorphous carbon films on Si substrate have large MR at room temperature. At T=300K and B=5T a large positive MR of 138% was found in Fe0.011-C0.989 film. Furthermore, we find that when temperature T<258K, the MR of Fe0.011-C0.989 film on Si substrate is negative and when 258K

2207

Distribution of Mo at Grain Boundary of 1300MPa CrMo Steel

Authors: W.G. Yang, L.N. Zhang, X. Zhang, W.J. Hui

Abstract: TEM, EDS and STEM were used to investigate distribution of Mo element in new CrMo steel ADF1 which is applied to 1300MPa high strength bolts with superior delayed fracture resistance. Research results reveal that Mo easily concentrates at grain boundaries. According to refined EDS point and mapping analysis, the region of Mo segregation at grain boundary is about several nanometers wide, and distribution of Mo along the grain boundary is not uniform. The average content of Mo at grain boundary is about double of that in grain area. Concentration of Mo can increase the bonding force of grain boundary, and this is of advantage to the improvement of strength and delayed fracture resistance of the new CrMo steel.

109

TEM Observation on Nano-Precipitation of Plain Low Carbon Steel by CSP

Authors: L.N. Zhang, X. Zhang, Y. Ma, D.L. Liu

Abstract: Plain low carbon steel produced by compact strip production (CSP) process was analyzed using TEM, EELS and XEDS. Nano-sized oxides and sulfides were observed in the steel. The nano-oxides are mainly ferrospinel of <20nm in size, and the nano-sulfides are MnS and FeS particles with size of 20-100 nm. They distributed both in grains and at grain boundaries. These nano precipitates could form in cast slab before heavy deformation by rolling process. It is proposed that besides the grain refinement, the nano-pricipitation plays an important role in yield strength enhancement. This mechanism may provide a new approach to strengthen plain low carbon steels.

101

Characterization of Kinetics of Deformation-Enhanced Transformation in a Low Carbon Steel

Authors: Jun Jie Qi, Wang Yue Yang, Zu Qing Sun, X. Zhang

Abstract: Quantitative characterization of microstructural development during deformation enhanced transformation in a low carbon steel was investigated on a Gleeble 1500 machine. General conclusions of the features of austenite transformation kinetics during deformation-enhanced transformation were formulated. It was shown that the process of deformation-enhanced transformation can be divided into three stages according to the characteristics of transformation kinetics: The kinetics equations of two early stages fitted well in J-M-A equation. The kinetics of the first stage obeys Cahn’s site saturation mechanism, with the value of kinetics parameter n of 4. Ferrite nucleates at austenite grain boundaries and triple points during the first stage. Kinetics of the second stage doesn’t obey Cahn’s theory, with the value of kinetics parameter n of 1-1.5, corresponding to ferrite nucleation repeatedly at areas with high stored energy in front of the ferrite/austenite interface. The kinetics doesn’t obey the law of J-M-A equation any more in the final stage, and only few nucleation sites left at this moment.