Papers by Author: Qiang Shen

Abstract: In this paper, the raw SiC powder is oxidized at high temperature (1000 °C for 4h), and a layer of SiO₂ oxide film is formed on the surface of SiC particles. By adding phosphoric acid, phosphoric acid reacts with SiO₂ at lower temperatures to form phosphate. Phosphate decomposition produces gas to create pores. At 1200 °C, the phosphate is completely decomposed into SiO₂, and a large amount of gas is produced to prepare porous SiC ceramic with high porosity and high strength. The effects of H₃PO₄ content on the phase composition, microstructure, porosity and mechanical properties of the prepared porous SiC ceramic were investigated. With the increase of H₃PO₄ content, the porosity increased and the bending strength decreased. The results suggest that at the sintering temperature of 1200 °C, the porosity of the samples can reach 58.3%~71.2%, while the bending strength of them can reach 8.72~31.09 MPa.

Abstract: The thermal reaction and phase evolution of APP/Al (OH)₃/α-SiO₂ with different mass ratios during heating were studied by TG, FTIR, XRD and SEM, respectively. When the temperature is not higher than 300 ^oC, mass ratio of m_APP:m_{Al (OH)3}:m_SiO2 has no effect on the phase evolution of APP/Al (OH)₃/α-SiO₂ and the main interaction product is AlNH₄HP₃O₁₀. APP/Al (OH)₃/α-SiO₂ with lower content of APP, appears larger weight loss rate due to the thermal decomposition of Al (OH)₃. The thermal reaction of APP/Al (OH)₃/α-SiO₂ is significantly influenced by the APP content as temperature rises to higher than 300 ^oC. The decomposition products of APP can chemically interact with Al (OH)₃ to generate Al₂P₆O₁₈ and Al (PO₃)₃ during 600 ^oC ~900 °C. When the content of APP increases, much more APP can chemically react with Al (OH)₃ and also with part of α-SiO₂ to generate SiP₂O₇. SEM shows the relatively dense microstructure due to micro-bridges of liquid phase with phosphate content increasing.

Abstract: In this paper, full-density Al-Zn-Mg-Cu-Zr powder metallurgy (P/M) alloy is prepared by hot-press sintering in vacuum at 600°C. Experiments are conducted to evaluate the effects of Zn additive in the range of 7.2-8.4 wt.% on the microstructure and mechanical properties of Al-Zn-Mg-Cu-Zr alloys. X-ray diffraction (XRD), scanning electron microstructure (SEM) and electron probe micro-analyzer (EPMA), and mechanical properties such as tensile strength are measured. The porosity decreases gradually with increasing of Zn and it achieves 0.01% with a density of 2.95 g/cm³ at 8.4% Zn. The tensile strength reaches the maximal value of 436 MPa at 8.4% Zn.

Abstract: Three-dimensional (3D) flowerlike CuO structures were prepared successfully by reducing copper chloride (CuCl₂·2H₂O) aqueous solution in the presence of cetyltrimethylammonium bromide (CTAB). The as-prepared CuO structures were characterized by UV-Vis, X-ray powder diffraction (XRD), FESEM and EDS techniques. The flowerlike CuO structures consisted of Salix leaf-like nanostructures. A possible growth mechanism for the formation of 3D flowerlike CuO structure was proposed. The processes of ripening and directed growing of nanoparticles were most important factors to obtain the 3D flowerlike CuO structures.

Abstract: The RGO/Ag nanocomposite with a homogeneous dispersion of Ag on the surface of RGO has been successfully prepared via situ chemical reduction method using DMF (dimethylformamide) as solvent and reducing agent. The RGO/Ag nanocomposite was characterized by X-ray diffractometer (XRD), Fourier transform-infrared (FTIR) spectra, Fieldemission scanning electron microscope (FESEM) and transmission electron microscope (TEM). It is suggested that in the presence of the PVP (polyvinylpyrrolidone), the electrostatic attraction of Ag⁺ ions with negative GO sheets lead to the decoration of Ag nanoparticles on the surface of RGO sheets in RGO/Ag nanocomposite.

Abstract: Ammonia borane (AB) hydrides have been employed as disposable hydrogen (H2) sources for fuel cell applications, due to their high hydrogen capacity. In this paper, ammonia borane (AB) complex with high purity was synthesized by chemical method, using the low cost raw materials of NaBH4, CO2, and NH3. The thermal dynamic for the synthesis process is analyzed. The phase composition for the obtained ammonia borane (AB) complex powders was detected by X-ray diffraction (XRD) characterization. The results suggest that, very high purity ammonia borane (AB) complex powders were obtained, which was quite in agreement with the standard index of ammonia borane.

Abstract: Transparent conducting antimony doped tin oxide (ATO) films have been prepared on quartz glass substrate by pulsed laser deposition (PLD) method which is distinctive to maintain the elemental components between the targets and the obtained thin films under optimal conditions. The effect of annealing temperature on the electrical and optical properties of the ATO thin films has been discussed. The annealing treatments have been often employed to reduce the defects and enlarge the grain size for more desirable crystalline structure. As the annealing temperature increases, the ATO thin films exhibited a slightly enhanced crystallinity. Furthermore, annealing treatment can promote both conductivity and transmittance significantly, especially for conductivity. The X-ray photoelectron spectroscopy is used to explore the variation of Sb5+/Sb3+ ratio against the annealing temperature. The optimal resistivity is 2.7×10-3 Ω cm and the average transmittance is about 92% at annealing temperature of 550 oC.

Abstract: Tape casting play a significant role in industrial area, such as multilayered ceramic (MLC) packages, functionally graded materials (FGM), low temperature co-fired ceramics (LTCC) and so on. For the complexity of the rheology for slurry during tape casing process, the control of tape thickness by experience was unstable. Although few numerical and analytical studies on predicting the tape thickness have been done, but these efforts have focused on Newtonian, Bingham, Power law, respectively. There is no unified equation to calculate the tape thickness among different rheological models. In this paper, the calculation results are characterized by wide adaptability; the blade gap, the casting speed and the slurry rheological property are incorporated into calculation; the effect of parameters in the result is studied; Parameter P_nd can be used as a guide to check which mark patterns of the flow velocity profiles in the channel. The results proposed and the experimental measurements from existing publications are in close agreement. Compared with the prediction of the existing models, the calculation results proposed has good agreement with them.

Abstract: The sinterability of ZrB₂-20vol.% SiC ceramics by high-energy ball milling as well as introduction of Zr and Al as sintering additives. Densification process and microstructure of ZrB₂-SiC ceramics were investigated. After high-energy ball milling, the average particle size decreased to about 500 nm-2 μm, and ZrB₂-SiC powder can be sintered to 98.92% theoretical density at 1800 °C, but a trace of amount of oxidation (ZrO₂) were detected in sintered sample. Introduction of Zr, Al and C combined with high-energy ball milling enhanced the densification of ZrB₂-SiC ceramics and reduced the particle sizes, and the relative density of obtained ceramic reached up to 99.49% at 1800 °C. The additions of Zr, Al and C can remove the oxide impurities of the surface of ZrB₂ particles and form a reaction between oxide impurities. The fracture toughness increased of the 40% when ZrB₂ powders were milled by high-energy ball milling, and increased to 4.77±0.18 MPa•m^1/2. However, the attrition-milled composites had lower hardness and Young’s modulus, which was attributed to the presence of a second phase in the grain boundaries.

Abstract: In this paper, silicon nitride porous ceramics with high porosity and bimodal pore structure were prepared using pressureless sintering at 900~1100°C. In these porous ceramics, zirconium phosphate (ZrP2O7) was used as a binder and starch and naphthalene powders were used as pore forming agents. The obtained results showed that the porosity could be controlled in the range of 34 % to 70 % by changing the content of pore forming agents. The pores were formed by the continuous reaction of ZrP2O7 at ~250 °C and burnout of starch at ~550 °C (when starch was used as a pore forming agent), or sublimation of naphthalene at 80°C (when naphthalene was used as a pore forming agent). The bimodal pore structure was produced with pore size of less than 0.5m and ~10 m when using starch as a pore forming agent and the pore size of less than 0.5m and ~30μm when using naphthalene as a pore forming agent.