Advanced Materials Research Vols. 391-392

Abstract: The effect of single pulse, electromagnetic stirring plus single pulse on the microstructures and properties of high strength Al-Cu alloy welds is investigated. The results show that the grain structure of weld under conventional MIG welding are coarse, oriented columnar grains, the ultimate tensile strength of weld joint is 286.5 MPa, the elongation rate of joint is 2.4%. The thermal gradient at the solid-liquid interface in the welding pool is decreased and the density of heterogeneous nucleation is enhanced by electromagnetical stirring plus single pulse, which resulted in the coarse and oriented columnar grains transforming to fine equiaxed grains; morphology and distribution of α(Al)-CuAl2 eutectic along the grain boundaries are improved, so it significantly improves the mechanical property of weld joint, the ultimate tensile strength of weld joint is up to 326.0 MPa, the elongation rate of joint reaches 7.8%.

Abstract: The thermal behavior and thermal decomposition kinetic parameters of podophyllic acid and picropodophyllic acid in a temperature-programmed mode have been investigated by means of DSC and TG-DTG. The kinetic model functions in differential and integral forms of the thermal decomposition reactions mentioned above for leading stage were established. The kinetic parameters of the apparent activation energy Ea and per-exponential factor A were obtained from analysis of the TG-DTG curves by integral and differential methods. The most probable kinetic model function of the decomposition reaction in differential form was 2/3•α-1/2 for podophyllic acid and 1/2• (1-α)-1 for picropodophyllic acid. The values of Ea indicated that the reactivity of picropodophyllic acid was highter than that of podophyllic acid in the thermal decomposition reaction. The values of the entropy of activation ΔS≠, enthalpy of activation ΔH≠ and free energy of activation ΔG≠ of the reactions were estimated.

Abstract: SiO₂-TiO₂ mixed oxides was prepared by the homogeneous precipitation method using tetraethoxysilane and tetrabutyl titanate as precursors. Zinc catalyst supported on SiO₂-TiO₂ was prepared by the incipient wetness impregnation method and employed as effective catalyst for the direct synthesis of diphenyl carbonate from carbon dioxide and phenol. The stability of the heterogeneous catalyst was also studied in detail. No significant loss of activity was observed during the 5 runs except for the first recycle.

Abstract: Hexagonal prismatic hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAP) was successfully prepared by a homogeneous precipitation method. The products were characterized by X-ray diffraction, Fourier transform infrared spectrum, and scanning electron microscope. The growth process of the hexagonal prism was surveyed in detail based on the effects of the reaction time on the phase composition and the crystal morphology.

Abstract: This article will present using chemical reduction to prepare silver nano-particles, which is a certain improvement base on the traditional hydrogen peroxide (H₂O₂) Silver ammonia by using a new reductant urea peroxide (CO (NH₂) ₂•H₂O₂) to replace hydrogen peroxide. Hydrogen Peroxide silver ammonia is widely used in the nano-silver particles Preparation, however, the nano-silver particles prepared in traditional ways is not homogeneous and very easy agglomerated, therefore, in this experimental by using of urea peroxide as a reductant, under condition of temperature 30°C, 45 nm homogeneous nano-silver particles is successfully prepared. The detection instrument used in the experimental is transmission electron microscopy and laser particle size analyzer.

Abstract: The nanocrystalline MgAl₂O₄ powder was prepared by thermal explosion mode of low-temperature combustion synthesis (LCS) using urea as fuel and nitrates as oxidizers. The molar ratio of nitrates to urea and the adiabatic flame temperature was calculated according to the propellant chemistry and combustion thermodynamics theory respectively, and the effect of thermal explosion temperature on the properties of powder was investigated. The phase and morphology of the synthesized powder were investigated by X-ray diffraction and scanning electron microscopy. The results showed that the combustion process completed in very shortly time, and the cauliflower-like powder with porous structure was obtained. The crystalline size of MgAl₂O₄ increased with the increasing of thermal explosion temperature, and the powder had good crystalline shape and purity. The average crystalline size of MgAl₂O₄ prepared at 400 was approximately 40nm.

Abstract: Nine types of active carbon’s adsorption isotherm of nitrogen and methane at 298K, 308K and 318K were measured, and their selectivity factor and PSA sorption selection parameters were calculated. The results show the nine active carbons have desirable selective adsorption characters on methane to nitrogen. AC3 has the highest selectivity factor. It reaches to 5.11 at 298K. And AC3 is the optimal adsorbent in 9 different adsorbents. Its PSA sorption selection parameter is higher than others with the methane concentration of 0.2% at the operating pressure between 50kPa to 150kPa abs. In above conditions the higher the selectivity factor is, the higher the PSA sorption selection parameter will be.

Abstract: Ternary composites of polyamide 6 (PA6), mixed with unmaleated ethylene propylene diene terpolymer rubber (named as EPDM-M) and calcium carbonate (CaCO₃, with three different kinds of surface morphology) were prepared via two-step melt blending process. The influence of surface morphology of CaCO₃ on the impact toughness of PA6/EPDM-M/CaCO₃ was investigated. It was found that the Izod impact strength of the composites improved with increasing of the surface area of CaCO3. The characterization of CaCO₃ by BET tester and scanning electron microscope (SEM) obviously showed that both needle-shaped CaCO₃ and spherical CaCO₃ were have a bigger specific surface area and rougher morphology than ground CaCO3. So they have a better toughen effect, which was well explained the results of impact test. Morphology observed on the impact fracture revealed that the formation of voids by the debonding of CaCO₃, which could trigger the matrix emerged obvious plastic deformation in the composites that included needle-shaped CaCO₃ or spherical CaCO3. This phenomenon also can be demonstrated that needle-shaped CaCO₃ and spherical CaCO₃ had superior toughen effective. Consequently, the surface morphology of CaCO₃ had a distinctive effect on the toughness of PA6/EPDM-M/CaCO₃ Composites.

Abstract: Three Fe-Y alloy coatings with differernt kinds of Y contents were prepared on stainless steel by magnetron sputtering. The hot corrosion behavior of sputtered alloy coatings with Na2SO4 deposits at 800 °C was investigated by discontinuous weigh measurement. Results show that the sputtered Fe-Y alloy coatings exhibit good adhesion with the matrix of stainless steel, and the hot corrosion kinetic curves of the specimens approximately follow the parabolic rate law. The Fe oxides are the main substances in the corrosion scale, and the hot corrosion rate of the three Fe-Y alloy coatings increases as the Y content increases. Therefore, the hot corrosion resistance of Fe-15Y alloy coating is better than that of Fe-20Y or Fe-30Y alloy coating.

Abstract: To consider the effective utilization of agricultural wastes, rice straw/Poly (lactic acid) (PLA) composites were prepared by the mechanically compounding and injection molding. The water contents were increased with increasing the rice straw content. After natural weathering or burial in soil, more microcracks were observed on the surface of the PLA composites rather than the pure PLA. Moreover the tensile strength and the fracture strain of PLA composites were obviously decreased with increasing the weathering and burial testing term.