Advanced Materials Research Vols. 532-533

Abstract: The flaws in a heavy bridge-making steel plate (Q370qE) were detected by ultrasonic test, the types and formation reasons of which were studied by metallographic examination, scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectrometer. The results showed that the types of the flaws were mainly crack, micropore and inclusion. The formation of crack and micropore was attributed to the center segregation, porosity, as well as the role of structural stress and thermal stress. Moreover, the inclusions were mainly composite oxides (MgO, Al₂O₃, CaO, etc.) and MnS, the former came from the raw materials and impurity oxides, however, the latter came from the center segregation of the alloying elements. Besides, some improvement measures to reduce detecting flaws were also proposed.

Abstract: Polylactide(PLA)-based wood plastic composites(WPCs) modified with SBS were manufactured by extrusion blending followed by injection molding. The fracture surfaces created from the impact test were recorded with SEM. Fractal analysis has been used to calculate the fractal dimension of the fracture surfaces with four different techniques. Then, the relationship between the fractal dimension of the fracture surfaces and its impact strength of the PLA-based WPCs was investigated with the linear regression nethod. The results showed that there is a positive correlation between the impact strength and the fractal dimension for each calculation method.

Abstract: Si₃N₄ based nanocomposites were prepared with nano-sized amorphous SiO₂ and Si₃N₄ powders by pressureless sintering method. The microstructures, phase composition, mechanical and dielectric properties of the nanocomposites were investigated. The scanning electrical microscope (SEM) photographs reveal that the grains are big and elongated. The X-ray diffraction (XRD) analysis shows that the main crystalline phase in the composites is Si₂N₂O formed during the sintering process. More β-Si₃N₄ phases were retained in the nanocomposites with the increase amount of the amorphous Si₃N₄ powders and no phase of SiO₂ were observed. The densities and the strength of the nanocomposites decreased with the increase of amorphous SiO₂ content. Despite low density, the flexural strengths of the composites reaches 220MPa and the ceramic has excellent dielectric properties with dielectric constant as low as 3.2-4.7 and dielectric loss in the range 2.6-3.9×10^-3.

Abstract: A new preparation method was developed to produce Si₃N₄-SiO₂-Si₂N₂O composites for broad band radome applications. The three-dimensional cross-linked polyphenylsiloxane (PPS) was used as an organic precursor. The composites obtained through react bonding between Si and the precursor powders in the stream of N₂ were examined. The conversion of the PPS polymer to the ceramic was examined by TG analysis and conventional X-ray diffraction (XRD) techniques. It was found that the ceramics contained a primary Si₂N₂O phase, some β-Si₃N₄ phase and a minor α-SiO₂ phase. Despite low density (1.7-2.0g•cm^-3), the flexural strengths of the composites reaches 195Mpa at room temperature. The ceramic has excellent dielectric properties with dielectric constants as low as 3.2-5.5.

Abstract: With 2,2',5',2''-Terthiophene as starting material, two liquid crystalline compounds containing Schiff’s base unit were synthesized in this paper. The structure of the compounds was confirmed by FTIR and ¹H NMR. The thermally induced phase transition behaviors were investigated by POM and DSC, and the temperature ranges of liquid crystal phase of the two compounds were compared. Results showed that the symmetric compound exhibited a lower clearing point temperature and broader temperature range of liquid crystal phase.

Abstract: According to Cr-Ni stainless steel, three different welding technology and the appropriate welding process parameters were selected. Three welded joints of Cr-Ni stainless steel were prepared. The microstructure in weld metal zone of Cr-Ni stainless steel under different welding methods was studied by X-fluorescent chemical composition analysis and microstructure analysis. The results show that alloy composition of the weld metal are different and distribute unequally under different welding methods, microstructure morphology and grain size of the weld layer are quite different. the structure of bottom is small amount of γ phase and a little δ phase are combined together and cover is γ phase and Cu-wealthy phases in the welds under TIG-MAG welding. the structure of bottom is coarse columnar crystal and cover is typical cellular dendrite in the welds under TIG- TIG welding. the structure of bottom is tiny equiaxial dendrites and columnar crystal and cover is some γ phase and a little δ phase are combined together in the welds under TIG-SMAW welding.

Abstract: We demonstrate the synthesis of a three-layer-coaxial SnO₂/ZnSn₂O₄/ZnO core–shell nanocable heterostructures with diameters 80-150 nm via thermal oxidation of Zn and Sn mixture powders. The products are characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and field emission transmission electron microscopy (TEM). The structural analysis shows the formation of ZnSnO₄ in the interface region between the SnO₂ core and ZnO shell, which is resulted from inter－diffusion of Sn and Zn ions during thermal evaporation. The selected area electron diffraction (SAED) pattern was composed of two series of overlapped polycrystalline rings attributed to SnO₂ and Zn₂SnO₄, one set of hexahedron diffraction spots that can be indexed to the hexagonal ZnO. On the basis of investigation of the microstructures, the possible formation mechanism of Zn₂SnO₄ is discussed.

Abstract: We have successfully synthesized iron base composites reinforced with SiC particles by a dynamic hot-pressing sintering process heating directly by electrical current. The corresponding equipment was improved and the best processing parameters was achieved after a systematically investigation. It was found that the novel sintering process, heating using continuous electrical current and then followed by dynamic temperature preservation using cyclic current, could effectively reduce the sintering time to 300 seconds and greatly improve the properties of the composites. The ultimate tensile strength of the as-prepared SiC_p/Fe composite reaches 918Mpa, with a relative density of 99.8% and a hardness of 480HB.

Abstract: Steel sheet/aluminum foam/steel sheet sandwich structure have higher stiffness than aluminum sheet/aluminum foam/aluminum sheet sandwich. So in this study the aim is to manufacture steel/Al-foam core/steel sandwich panels by rolling of two steel-face sheet and Al-Si powders. The deformation of the rolled-piece, powder grains and the joining deformation of the composite interface are discussed and analyzed in this paper. SEM and EDS of the compound interface are investigated. It was concluded that a metallurgy bonding interface was formed by diffusion reaction and a brittle compound generated.

Abstract: In this paper, we shall first briefly introduce fuzzy sets and related concepts of the reaction principle of Cu-ZSM-5 catalyst with the NO, and the preparation of Cu-ZSM-5 catalyst is also investigated. And the NOx conversion efficiency of Cu-ZSM-5 catalyst is analyzed with the experiment. Compared to V₂O₅/WO₃/TiO₂ catalyst, the reaction activity of Cu-ZSM-5 catalyst at low temperature is much better, while the range of reaction activity temperature of V₂O₅/WO₃/TiO₂ catalyst is relatively wide. Finally, with the diesel engine ESC test, the Cu-ZSM-5 Catalyst for SCR system can effectively reduce the NOx emissions, and the diesel engine which is installed the SCR is able to achieve the requirements of Euro Ⅳ for NOx limits.