Papers by Author: Yu Dong Huang

Abstract: Urchinlike Ni particles with different length and quantity spines were successful synthesized. The microstructures and morphologies of the resulting materials were investigated by X-ray diffraction and scanning electron microscopy. The amount of N2H4H₂O plays an important role in the morphology of urchin. The electromagnetic parameters of these urchinlike Ni were measured with vector network analyzer at 2-18 GHz frequency. The results indicate that the microwave absorbing properties are improved by the urchin structure.

Abstract: Si_5.4Al_0.6O_0.6N_7.4 (β-Sialon)/ Y_1.75Si_2.625Al_1.0O_7.5N_1.25 (oxynitride glass) composite solders with different ratio were designed using SiO₂-Al₂O₃-AlN-Y₂O₃-Si₃N₄ mixture powders to join Si₃N₄ ceramic to itself. It was found that both solder composition and bonding temperature have strong influence on the microstructure and strength of the joints. As far as using a pure oxynitride glass solder was concerned, the thickness of the seam turned narrow with the increase of temperature, and the strength had a peak value at 1550 °C. When increasing the designed content of β-Sialon, serious composition separation occurred in the seam at low bonding temperatures, and the strength was also lower than as using pure oxynitride glass. Increasing bonding temperature, the strength of the joints was improved and reached the maximum value of near 80 MPa at 1600 °C for the designed 20%β-Sialon. In this instance, large amounts of fine elongated β-Sialon grains were uniformly distributed in the seam. However, for the 60%β-Sialon containing solder, some pores appeared in the seam and its strength was very low at bonding temperatures.

Abstract: Nd--sialons with the stoichiometric composition of Nd0.333Si10Al¬2ON15 were obtained by hot-press sintering at 1800°C for 1h. The thermal shock behavior of the Nd--sialons was examined by a water-quenching technique. The influence of the thermal shock temperature difference (T) and cycle times on the residual strength was evaluated. Equiaxed -sialon grains formed together with a small amount of intergranular phase M (Nd2Si3-xAl¬xO3+xN4-x) and -sialon phase. The residual strength after a thermal shock tended to decrease gradually with increasing T above 500°C. However, the specimens exhibited an improved residual strength (~94% of the room temperature strength) after a thermal shock of T=1100°C. The residual strength presented a gradual decrease with increasing the thermal shock cycle times at T=1100°C, and was still remained ~55% of the room temperature strength after 11-time cycle. It is contributed to the surface oxidation which may results in the healing of surface cracks and the generation of surface compressive stresses.

Abstract: In the present work, Al2O3 was coated on the quartz fiber by the sol-gel method to improve the high temperature mechanical properties of the quartz fiber/methyl silicon resin composites. The X-ray diffraction results showed that the crystalline property of the Al2O3 coating increased with the processing temperature. Before 500oC treated, the Al2O3 coated fiber reinforced composites have lower flexural strength than the commercial fiber reinforced one. While after 500oC treated, the flexural strength of Al2O3 coated fiber reinforced composites was higher than the uncoated reinforced one. And the flexural strength for the 400oC treated Al2O3 coated fiber reinforced composites was higher than that of the 600oC treated one. The mechanism of the crack propagation in the purchased and Al2O3 coated fiber reinforced composites was also studied through scanning electronic microscopy (SEM).

Abstract: In this paper, a new method based on molecular self-assembly on carbon fiber surface was proposed for the improvement of interfacial properties between fiber and epoxy matrix in a composite system. In order to obtain the controlled interphase, the surface of carbon fibers was first metallized by electroless Ag plating, then was reacted with terminally functionized alkanethiols or aromatic thiols to form Ag-thiolate thin films, which further reacted with epoxy resin to generate a strong adhesion interface. The composition, structure and the morphology of the modified carbon fiber surface were examined by X-ray photoelectron spectroscopy (XPS), surface-enhanced Raman scattering (SERS) and atomic force microscope (AFM), respectively. The results showed that these self-assembly molecules were chemisorbed onto the carbon fiber surface coated with silver via the strong S-Ag bond. In addition, these thiol molecules act as coupling agents between the epoxy matrix and carbon fiber through active functional end-groups, such as –OH, -NH2. The interfacial shear strength (IFSS) of the microcomposites after introduced the controlled interphase using the microbond testing was improved.