Papers by Author: Zheng Guang Zou

Abstract: Polycrystalline perovskite-type manganite La_0.65Sr_0.2Na_0.15MnO₃ was prepared by sol-gel method. An X-ray diffraction measurement showed that the sample was a single phase. The Curie temperature of the sample was determined to be 350K. The maximum magnetic entropy change |ΔS_M| corresponding to a 1T magnetic field variation was found to be 1.08 J/kg K and about 40.6 J/kg of relative cooling power was obtained near the Curie temperature. The first-order or the second-order on the phase transition of the manganite was distinguished by Banerjee criteria.

Abstract: This work focus on the effects of C vacancy on wetting of Fe to TiC/Fe at the cermet interfaces. We do the whole work using the first-principles density functional theories. The ideal work of adhesion of the pure interface is not big enough, comparing with the expeimental value. Our calculations suggest that the C vacancy at the interface is a very important factor for interface banding of TiC/Fe cermet composite. An adequate quantities of C vacancies at the interface can improve the wetting of TiC/Fe interfaces.

Abstract: First-principles plane-wave pseudopotential calculations of the electron structure and energetics of the interfaces of clean and Ni-doped TiC/Fe are reported. We predicted the atomic structure, bonding, and the interface binding energy of TiC(100)/Fe(100) and TiC(100)/Fe(110). By comparing the interface bonding energy and the total charge density distribution, the interface have priority to combine in TiC(100)/Fe(100) and TiC(100)/Fe(110) ways, where the former’s interface binding energy is higher. So the structure of TiC(100)/Fe(100) is more stable. The doped Ni atoms have preferential access to Fe-based body and form FeNi alloy, and enhance the interface bonding energy, thus effectively reducing the system energy of TiC(100)/Fe(100) and TiC(100)/Fe(110) interfaces, increasing the bonding strength and stability of interfaces of the composite materials.

Abstract: Pyrite nano-powder was synthetized in a high-pressure solvothermal process in the ethanediol solvent, with Fe(NO₃)₃·9H₂O and NH₂CSNH₂ as the raw materials. The sample was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the results show that the product has a pure phase in a typical cubic crystal. The effects of temperature, aging time and surfactant on the shape of the crystallites were investigated systematically. The nano-powder synthetized shows itself in various micro-shapes such as granule, globular and flake, with its diameter ranging from hundreds of nanometers to one micrometer.

Abstract: Selecting Si3N4 as binding agent and Al2O3–Al–Y2O3 as sintering additives, the sintered compact of polycrystalline cubic boron nitride (PcBN) was studied . By modifying the ratio of each component and the parameters of the sintering process, the compact sintered at 4.5 GPa and 1650 °C showed good mechanical properties.The phase constitution, microstructure of the sintered compact were characterized by XRD and SEM respectively. The degree of phase transformation of Si3N4 , the chemical reaction during the sintering process, and the sintering mechanism of the additives were discussed . The best relative density is more than 97 % , the flexural strength is more than 650 MPa, the Vickers hardness Hv is more than 8.7 GPa.

Abstract: In the paper a high-pressure stirring solvothermal method with ethylenediamine as a solvent was used to prepare CIGS powders. The impact factors of reaction temperature and holding time on product-phase and morphology were investigated. The increasing reaction temperature make a important impact on the phase of product and the increasing holding time has much effect on the product morphology. CIGS particles (8-10 μm) were successfully synthesized at reaction temperatures in the range of 200-250 °C for different holding times.

Abstract: To get single-layer of graphene, exfoliating fully intercalated graphite oxide into single- layer graphene oxide is one of the important factors. In this paper, graphite oxide prepared by the Improved Hummers Method, and ultrasound was added to the Low-temperature Reaction of this oxidation process to improve the efficiency of intercalation. Then the obtained graphene oxide was dispersed with surfactant and reduced with Hydrazine Hydrate. XRD patterns indicated that the layer distance of graphite oxide did increased at the aid of the ultrasound, and the obtained reduced products were single- and few-layer. FT-IR analysis further confirmed the preparation of graphite oxide and graphene.

Abstract: It has been demonstrated that V6O13 is a very attractive cathode materials for rechargeable lithium-ion batteries. Cr3+ was doped to improve its electrochemical property. CrxV6O13(x =0.01~0.05) cathode materials were prepared using NH4VO3 and Cr2O3 as raw material by solid phase method in argon atmosphere. The best electrochemical properties of CrxV6O13 were obtained under the optimum conditions as follows: the argon flow rate is 85mL/min, the heating rate is 5°C /min, the holding time 1h at 180°C, 1h at 300°C and 30 min at 450°C. The structural and electrochemical properties were examined by means of X-ray diffraction, SEM and charge–discharge tests. The results demonstrated that the powders maintain double cavity chain structure regardless of the chromium doping. When the Cr doping of x = 0.03, capacity is highest. Maximum initial discharge capacity is 334mA•h/g, 80% of theoretical capacity. During discharge process there is 6.5 Li+ embedded in the Molecules of doping. After discharge cathode became Li6.5Cr0.03V6O13.

Abstract: Steel-bonded cemented carbide GT35 was fabricated from natural ilmenite by in-situ carbothermic reduction and vacuum pressureless sintering. The effects of C content on the mechanical properties and microstructures of GT35 composites were investigated. As an excellent reducer, carbon provides an impetus for a series of reductive process. C content determines the melting point of the steel matrix, and directly affects the mechanism of dissolving and segregating of TiC particles, forming a netlike microstructure. Besides, the liquid steel whose viscosplasticity is determined by C content was coated on the surface of the composite and refrained the release of CO. The results showed that the good mechanical properties of steel-bonded cemented carbide GT35 composite were obtained with 0.9wt.% C at the same sintering conditions and the density reached 6.12g/cm3, the average bending strength was over 1229MPa after heat treatment, the mean hardness HRC was 69.4. It also showed that in-situ reduction of natural limonite was a feasible way to fabricate good performance GT35 composite with a relatively low cost.

Abstract: In the present study, steel-bonded cemented carbide GT35 has been fabricated from natural ilmenite by in-situ carbothermic reduction and vacuum pressureless sintering. The effect of different carbon source on the mechanical properties and microstructure of GT35 composite was studied. The quality of the composite synthesized from natural graphite is higher than those from other carbon source. Some good results were obtained from experiments: the density is about 6.2g/cm3, and the bending strength is 1390MPa, which higher than that of other samples. The structures and ingredient of different carbon source were analyzed to elucidate their different performance in the reactions.