Papers by Author: Wei Min Wang

Abstract: Co-doped ZnO nanorods membrane was deposited at glass substrate in a simple chemical water bath. The morphology and crystal structure of the samples were characterized by SEM, TEM and XRD. It is shown that the ZnO rods membrane exhibits an excellent orientation along the c axis. X-ray diffraction study also indicates decrease in the lattice parameter after Co doping. The results of EDS and XPS verify that Co²⁺ is successfully doped into the lattice of nano ZnO rods. 2at% and 5at% Co doped ZnO rods behave stronger UV emission and weaker visible emission.

Abstract: A new type of ZnO/Ag micro hybrid material has been fabricated by a facile wet chemical method using citrate as a crystal growth modifier. The morphology and component of ZnO/Ag hybrid material were characterized by SEM and XRD. It is shown that the platelike crystals connect together by means of embedding. The sample is composed of wurtzite ZnO and face-centered cubic Ag. The results of XPS, UV-Vis and PL spectra verify the electron transfer from Ag to ZnO. The photocatalytic test with Rhodamine B (RhB) as a representative dye pollutant shows that the ZnO/Ag hybrid material exhibits an improved photocatalytic activity.

Abstract: Pulse Current Heating (PCH) process is a new method characteristic with shorter time and lower temperature to the fabrication of materials. In the present paper, the PCH was used to join Cu/Fe. The microstructures of the joined samples were observed by optical microscope, the diffusions of elements near the interfaces were made qualitative and quantitative analyses by Electron Probe Mechanism. Diffusion coefficients of Cu and Fe at PCH and Radiation Heating (RH) joining methods were compared. The results showed that, the transition layer widths were from 5 to 8 μm when the Cu/Fe joined at 750 to 850°C under 5 MPa pressure with holding times 5 or 10 or 15min. Width of the transition layer increase with the increasing of joining temperature and the extension of holding time. The initial interface will move from the Cu side to the Fe one due to the Kirkendall effect. The diffusion coefficients both of Cu and Fe to PCH joining were larger by three orders of magnitude than those of RH joining. The differences between the two methods were analyzed from dynamics and thermodynamics.

Abstract: Self-propagating high-temperature synthesis with reduction process was used to fabricate LaB6 ceramic powder from La2O3-B2O3-Mg system. The combustion reaction carried out in inert atmosphere (Ar) and the combustion temperature was about 1600°C. The products were washed with dilute hydrochloric acid and distilled water, respectively, to remove LaBO3, Mg3B2O6, MgO and other impurities. The influence of compact pressure and addition of SHS diluent on the grain size was studied. The result indicates that as the compact pressure increased, the mean size of powder decreased gradually. The addition of diluents reduced the synthesis temperature, and as the amount of diluent increased, the grain size of LaB6 powder was found to reduce continuously. Microstructure analyses show that the mean grain size of LaB6 powder prepared by SHS with reduction process is less than 500 nm, which is finer compared with the grain size prepared by traditional process.

Abstract: Two different kinds of mullite precursors with composition 3Al2O3•2SiO2 (3:2) were prepared by conventional drying ethanol solution and spray-drying aqueous solution of aluminum nitrate nanohydrate and tetraethoxysilane, respectively. The results of scanning electron microscope (SEM) indicate that one powder consists of irregular particles with size of 1-10μm, the other powder is made of inhomogeneously sized hollow spherical particles with mean size of 0.5-5μm. The TG-DTA curves indicate the hollow spherical particles are unfavorable to eliminate the decomposed products. After the precursors were sintered by Spark Plasma Sintering at 1450°C for 10min, the microstructures of the former are made of fine equiaxed grains with sizes of around 0.5μm, the latter consist of elongated grains distributed in the matrix of fine grains with imhomogenous size of 0.5~10μm due to the liquid phase forming. The different microstructures lead to the former sintered body is transparent, while, the sample from spray-drying is opaque.

Abstract: Carbon nanotubes reinforced alumina was fabricated by spark plasma sintering method. When adding 0.2wt% nanotubes, the fracture toughness of the composites prepared increases 19% compared with the pure alumina ceramics. The effect of sintering schedule on microstructure and mechanical properties is investigated systematically. Microstructure studies reveal that at high sintering temperature, the nanotubes tend to gather in the gaps surrounded by three or more grains in a flocculent state, which leads to poor mechanical properties. Raman spectrum indicates that long sintering duration may cause serious nanotubes destruction and lower the mechanical properties.

Abstract: In this text, 5083 aluminum alloy was prepared with the method of the liquid nitrogen cryogenic milling (cryomilling). The microstructure,microstructural evolution and thermal stability of sample powder was investigated by XRD,SEM and DSC. The experimental results show that the particles size of 5083 aluminum alloy power during cryomilling was gradually reduced; milling time and milling speed are the main factors of affected alloy structure and performance, and high speed cryomilling could result in more uniform nanometer grains. The microstructure of the cryomilling 5083 aluminum alloy for 5 hours is micron-sized agglomerates with an average grain size of 45 nm.

Abstract: Within a very short heating period, fine mullite powder with practicle size below 1µm was obtained in a novel synthesis system, a self-propagating high-temperature synthesis (SHS) chemical furnace, from which the tremendous heating derived. The combustion reactants consisting of Ni, Al and TiC were chosen as a chemical furnace in this system to supply the heat, calcining temperature was increased at a heating rate of 1350K/min in the heating process, till the maximum temperature (1350°C). The rapid mullitization process was performed within 1 min, microstructure analysis indicated that small mullite grains (<50nm) were crystallized, fine mullite particles (<1µm) with narrow particle size distribution, favorable activity for sintering were derived. And significant grain growth was observed in mullite powder, when the combustion reactants consisting of Ni, Al and <30 mol.% TiC.

Abstract: Dense nanocrystalline Y2O3 ceramics without grain growth have been successfully obtained by a new method, which is based on the self-propagating high temperature synthesis and quick pressing. A suitable self-propagating system with a maximum combustion temperature of 1350 °C and a heating rate of 1300 °C/min was chosen as a chemical furnace to supply the heat to densify nanocrystalline Y2O3. Dense samples without grain growth were obtained when the applied pressure was 120 MPa.

Abstract: The Indium Tin Oxide(ITO) is known as a poorly sinterable material. The Spark Plasma Sintering(SPS) and the hot-pressing sintering(HP) were used to fabricate Indium Tin Oxide Ceramics from ITO nanoparticles. The maximum bulk density of 7.02 g/cm2(relative density; 98.2% TD)was obtained when sintered in Ar at 1000oC for 1min by SPS sintering. While the bulk density of 7.08 g/cm2(relative density; 99% TD) was obtained when sintered in Ar at 1050 oC for 4h by HP sintering.