Papers by Author: Cheng Biao Wang

Abstract: Novel multipods-branched Cd-Se-S micro-/nanostructures (MNSs) were successfully prepared in a tube furnace by thermal evaporation under atmospheric pressure through using high-purity CdS and CdSe mixture powder with a molar ratio of 1:1 as evaporation source, high-purity Ar gas as carrier and protective gas, and mica wafer as substrate. Under the optimum condition, the evaporation temperature was 1100 °C, Ar gas flow rate was 200 sccm, and the distance between the evaporation source and substrate was 22 cm. The microstructure examination revealed that the length of the obtained branches was up to tens of microns and the diameter of the branches was of a few microns. The composition and crystal structure analyses indicated that, the chemical composition of the multipods-branched Cd-Se-S MNSs was CdSe_0.86S_0.14, which had a hexagonal structure and good crystallinity. The photoluminescence spectrum at room temperature displays an intrinsic emission peak around 620 nm. In addition, their growth might be controlled by a vapor-solid mechanism.

Abstract: TiCN-based cermets were prepared by hot-press sintering through adding various amounts of AlN nanopowder (0-20 wt.%) into a 64 wt.% TiC_0.5N_0.5-10 wt.% WC-8.5 wt.% Mo-12.5 wt.% Ni-5 wt.% Co system. The microstructure and mechanical properties of the prepared cermets were investigated. For the prepared cermets, samples with 5 wt.% AlN nanopowder exhibited optimum mechanical properties of Vickers hardness 2191 HV₁₀, bending strength 601 MPa, and fracture toughness 6.03 MPa.m^1/2, respectively.

Abstract: In this work, we fabricated ZrB₂-SiC-ZrSi₂ composites containing different fractions (0.5-5 vol.%) of ZrSi₂ by spark plasma sintering at 1600 °C under a uniaxial pressure of 30 MPa. The addition effect of ZrSi₂ on the composition, microstructure and mechanical properties of the composites were investigated. The results indicated that the densification of ZrB₂-SiC-ZrSi₂ composites could be enhanced along with the increase of the added fraction of ZrSi₂, with its relative density reaching the maximum of about 85.6% when 3 vol.% of ZrSi₂ was added. The hardness of the composites would decrease after the addition of ZrSi₂ in the range of 960-1200 HV₅. The flexural strength initially increased and then decreased with the addition of ZrSi₂, reaching a maximum of about 330 MPa when 3 vol.% of ZrSi₂ was added.

Abstract: In order to investigate the influence of (Bi_0.5M_0.5)TiO₃ (M=Li, Na, K, Rb) addition on the Curie temperature (T_c) and positive temperature coefficient (PTC) effect of BaTiO₃-based ceramics, BaTiO₃-(Bi_0.5M_0.5)TiO₃ (M=Li, Na, K, Rb) solid solutions were prepared by a conventional solid sintering reaction using high-purity reagents. It was found that the T_c of the samples would vary with (Bi_0.5M_0.5)TiO₃ of different alkali ions, in which BT-BKT ceramics had the highest value (about 148 °C). Moreover, the incorporation of alkali ions would influence the PTC effect of the sample, which can be defined by the resistivity jump with the ratio of maximum to minimum resistivity (ρ_max/ρ_min). Under the present conditions, the ρ_max/ρ_min of BT-BRT and BT-BLT ceramics were almost equal and higher than those of BT-BNT and BT-BKT ceramics.

Abstract: Cordierite samples were prepared using quartz sand tailings, industrial alumina and magnesite tailings as raw materials by high-temperature reaction. The influence of mineral composition and sintering temperature on the final phase composition and physical properties of cordierite were studied. The results shown that a large number of cordierite generated at 1300 °C. When the ratio of Al₂O₃/SiO₂ equals to 1.08, the flexural strength of samples increased to 27.66 MPa.

Abstract: Mullite material was prepared from quartz (SiO₂) and industrial alumina (γ-Al₂O₃). The effects of mineral composition and sintering temperature on the final phase composition and physical properties of mullite were investigated. The results shown that a large number of mullite phase was emerged in samples when the ratio of alumina to silica (A/S) was 2.55. At 1500 ^oC and 1600 ^oC, the flexural strength of the samples reached to 87.13 MPa and 89.50 MPa, respectively. Consider the environmental protection and energy saving, the optimal sintering temperature was 1500 °C.

Abstract: The stability of SiC and SiO₂ in helium with little water vapor is studied in this paper in order to confirm whether they can service as anti-oxidation layers on the surface of fuel elements of high temperature gas-cooled reactor (HTR) under water-ingress accident. Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC in He-H₂O is the partial pressure of H₂O; the critical temperature of passive oxidation for SiC increases with the partial pressure of H₂O. The influence factors controlling the critical temperature of decomposition for SiO₂ are the partial pressure of H₂O and the amount of H₂O in gas for 1 mol SiO₂, the critical temperature of decomposition for SiO₂ increases with the partial pressure of H₂O while it decreases with the amount of H₂O in gas for 1 mol SiO₂. SiO₂/SiC composite coating is more suitable than SiC coating in He-H₂O with little H₂O.

Abstract: The development of environment-friendly water-based lubricants has been paid more and more attention in modern manufacturing due to environmental concern and human health. In this paper, several water-soluble molybdenum-containing additives (WMCAs) were synthesized, and characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The tribological properties of WMCAs in water were evaluated by a four-ball tester. The results indicated that WMCAs exhibited beneficial effect on the anti-wear and friction-reducing properties of water under all tested concentrations, which could be attributed to organic nitrogen compound, iron oxides and MoO3 in WMCAs tribofilm.

Abstract: Mn-Zn ferrites with different doping contents of W⁶⁺ ions were prepared by using standard ceramic technique. The microstructure and magnetic properties of the as-prepared Mn-Zn ferrites were investigated. It was found that all the samples with different contents of W⁶⁺ ions consisted of ferrite phase of typical spinel cubic structure. With increasing doping content of W⁶⁺ ions, the lattice constant of the ferrites decreased but the grain size increased. Through the measurement of magnetic properties, it was revealed that the saturation magnetization and initial permeability of the samples increased with small doping content of W⁶⁺ ions but decreased with additional doping, and the Curie temperature decreased monotonously with W6+ ion doping.

Abstract: B2O3-doped ZnO-Pr6O11 based varistor ceramics were fabricated by sintering samples at 1350 °Cfor 2h with conventional ceramic processing method. The microstructure and electrical properties of the as-prepared samples were investigated. X-ray diffraction analysis showed that after the addition of B2O3 with the amount designed in this study, no new phase was examined in the detection limit. Through scanning electron microscopy it was found that the doping of B2O3 can promote the growth of ZnO grains, and the sintering of the samples. The result of electrical properties indicated that the nonlinear coefficient and varistor voltage of the samples could be improved to some extent with appropriate doping amount of B2O3, resulting in the highest nonlinear coefficient 6.7, lowest leakage current 329 μA/cm2, and highest varistor voltage 92.4 V/mm, respectively.