Papers by Author: Gang Qin Shao

Abstract: For over 1400 years, Dapu county, under the jurisdiction of Meizhou city, Guangdong province, one cradleland of the Hakka traditional culture, is renowned for the blue and white porcelain in China. In this work, the mechanism and technics to produce Dapu geographical indication products of blue-and-white porcelains with high quality were studied, based on the distinct characteristics of local resources.

Abstract: The Bi2MnxV1-xO5.5- powders were synthesized by high temperature melting method. The effect of Mn dopant concentration on the crystal structure and chemical composition was studied. The crystal structure was determined by X-ray powder diffraction. The chemical composition was tested by X-ray fluorescence (XRF) and Energy Disperse Spectroscopy (EDS). When x < 0.2 the Aurivillius structure solid solution coexisted with few BiVO4. When 0.2 ≤ x ≤ 0.3 the γ-phase Bi2MnxV1-xO5.5- solid solution with tetragonal structure formed and the maximum Mn atomic content was 2.14%. When x ≥ 0.4 the manganese oxide secondary phase appeared. And when x = 0.8 the Bi7VO13 structure solid solution formed while the Aurivillius structure disappeared.

Abstract: NiO-YSZ (NiO-yttria stabilized zirconia, 3:2, wt.%) and samaria doped ceria (SDC) tapes were prepared by aqueous tape casting. NiO-YSZ anode-supported SDC film electrolyte half-cell was fabricated by laminating and co-sintering at 1400°C for 2 h. The single cell was prepared after LSCF-SDC (lanthanum strontium cobalt ferrite-SDC, 1:1, wt.%) cathode was coated on the electrolyte surface and sintered at 1300 °C for 2 h. The discharge performance of the single cell was tested from 500 °C to 800 °C at different H2 flow rate. Results showed that the relationship between current (I) of and H2 flow rate (ν) was I = 8 × 106 ν. Before reaching the threshold value of H2 flow rate, the current density of single cell increased with the increasing of H2 flow rate. However, the current density did not change with increasing of H2 flow rate over the threshold value. The open circuit voltage (OCV) of single cell at 500°C, 600°C, 700°C, 800°C was 0.978, 0.921, 0.861, 0.803 V, respectively. The maximum power density reached 93.03 mW/cm2 at 800°C. The resistance of interface layer between Ni-YSZ anode and SDC electrolyte was the key impact on the power density.

Abstract: BiFeO3-based single-phase multiferroics have been widely studied in both ceramics and films. However, the macroscopic magnetic properties of BiFeO3 ceramics were now most very weak. In this work, MnO2 and Co2O3 were used as B-site substitutes in BiFeO3 ceramics in order to the enhancement of magnetic properties. The change of magnetization was analyzed based on the phase composition and the microstructure of ceramics.

Abstract: The effect of Nd2O3 and Sm2O3 on the microstructure, nonlinear electrical properties, and dielectric properties of WO3-based ceramics was investigated. The dopant Nd2O3 and Sm2O3 can promote the grain growth of WO3 grains. It was also found that Nd2O3 and Sm2O3 can reduce the breakdown voltages values of WO3-based ceramics effectively, but do not strongly influence the nonlinear values. The nonlinear coefficient of doped samples was 2-3 and the barrier voltage was very low with the value of 0.04-0.08 V. Through impedance analysis, it can be found that those rare earth ions have a great influence on the dielectric properties. The dielectric constant of doped samples was higher than that of undoped samples, and the high dielectric constant makes them suitable as capacitor-varistor materials. The theory of defects in the crystal lattice was introduced to explain the nonlinear electrical behavior of the WO3-based varistor ceramics.

Abstract: The 5-axis milling processes were conducted with several uncoated WC-Co tools, which are with taper ball end mills with four flutes. There is a severe problem of high rate of tool failure, which has led to the high cost and low productivity of the milling process. In order to find out the real reason, some former work, which included the tool geometry analysis, tool path and tool posture analysis, as well as the cutting force calculating, had been done. It has been found that most of the tool failures are resulted from cutting edge chipping or the workpiece material of titanium alloys attached to the tool. Meanwhile, a suddenly applied load or an abrupt unloading of the tool at the end of a cut is another important factor. Moreover, the tool materials had been analyzed, which included the element composition analysis with XRD, the microstructure analysis with SEM. XRD results indicate the cobalt at the tip of tool is less than at the shank of tool. SEM results indicate there are micro-cracks concentrated in the cutting edge area. The tool material failure mechanism will be set up based on the tool material analysis in this study.

Abstract: The transition-metal carbide cemented by metal has excellent combined properties. In this study, cermets were prepared by vacuum sintering from carbide-metal composite powders. The transition- metal oxides (Cr2O3, MoO3, V2O5, Nb2O5 and TiO2), cementing-metal oxides (Co3O4 and NiO), and carbon black were used as raw materials to pre-synthesize composite powders such as Cr3C2-Co, Mo2C-Co, VC-Co, NbC-Co and TiC-Ni, by a direct reduction and carburization process in vacuum. Results show that the participation of Co3O4 and NiO as well as the vacuum circumstance were greatly propitious to the carburization of transition-metal oxides into carbides. The carbothermal condition was greatly improved by the direct reduction and carburization process.

Abstract: Tungsten carbide (WC) targets with low cobalt (Co) content (0.1 - 0.2 wt.%) were prepared by hot-press sintering at 1700°C for 60 minutes in argon, from element starting powders of tungsten, cobalt and carbon. Results show that the as-fabricated targets yield relatively high relative density above 99% and high HRA above 92. WC with low Co content is formed easily than pure WC. The hot-press sintering process, while element starting powders are used, is an in-situ reaction technique for accelerating the WC’s diffusion rate to obtain a dense sintered body.

Abstract: YSZ-NiCr powder was synthesized by gel-reduction process at 850°C for 2 h. YSZ-NiCr cermet was fabricated by hot-press sintering at 1350°C for 1 h. The powder has a mean particle size of 42 nm and the sintered specimen has a fine and homogeneous microstructure with a mean crystalline size of 0.2 &m. The conductivity has a tendency to decrease with increasing temperature. This behavior can be accounted for that there are two conduction paths through the cermet, an electronic path through the Ni/Cr metal phase and an ionic path through the ZrO2-Y2O3 phase. The objective of this work is to give a possible improvement in the cermet anode of SOFC.

Abstract: Nanocomposite WC-10Co powder produced by spray pyrolysis-continuous reduction & carbonization technology and cubic boron nitride (CBN) plated with titanium by vacuum vapor deposit were used, and this paper adopted spark plasma sintering (SPS) process to prepare CBN enhanced ultrafine WC-10Co cemented carbide cermets composite material. The microstructure and mechanical properties of CBN-WC-10Co composites were investigated. The results show that CBN-WC-10Co composites consolidated by spark plasma sintering can reach 95.0 % relative density, and transverse rupture strength (TRS) is 1050 MPa, the average grain size of cermets matrix is less than 420 nm, and CBN-WC-10Co composites with excellent properties are achieved. The CBN still remains very good crystal shape after 1240°C spark plasma sintering, and there is not obvious clearance between CBN plated with titanium and the cermets matrix, the coated titanium layer can not only improve the thermal stability of CBN, but also increase the properties of CBN-WC-10Co composites.