Advanced Materials Research Vols. 287-290

Abstract: The effect of the pulse electric discharging (PED) on the solidification structure of pure aluminum during the directional solidification was investigated. Experimental results showed that fine microstructures were generated by exerting PED, and the cellular spacing decreased greatly with increasing current density. The effect of pulse electric discharge on the temperature gradient in front of the solid-liquid interface was analyzed, the cellular spacing was measured and expressed as the function of solidification processing parameter by using a nonlinear regression analysis, and the refinement mechanism using the PED treatment was also discussed.

Abstract: The orthotropic mechanical behaviors of weft-knitted flax fiber fabric reinforced polypropylene (PP) composites, which were produced by hot pressing of knit layers composed of a commingled yarn with a flax fiber content of 50vol.%, are investigated in both meso- and macro-scales. In meso-scale, the repeating unit cell (RUC) finite element (FE) model is developed, in which impregnated yarns are assumed to be isotropic elastic while the matrix is modeled as an elastoplastic, isotropic solid. Then, stress-strain curves of the RUC are simulated for its elastoplastic orthotropic parameters. Finally, in macro-scale of its specimen, the tensile behavior of the composite laminates with six parallel plies is simulated by means of 3D elastoplastic FE method. The applicability and limitation of this model have been discussed.

Abstract: Two 0.17C-3Mn-1.5Al-0.2Si-0.2Mo steels with and without Nb microaddition were melted in a vacuum induction furnace. The steels are characterized by bainitic-martensitic structures with large fraction of retained austenite. To design a thermomechanical treatment for steels with required multiphase structures a knowledge of their hot deformation resistance and softening kinetics is of primary importance. The paper presents the results of the compression tests carried out at various temperatures and strain rates using the Gleeble simulator. A softening kinetics was determined in a double-hit compression test. It was found that the dynamic recrystallization was a process controlling work hardening of steels except for hot deformation conditions characterized by the highest Zener-Hollomon parameter values. Nb microalloyed steel has higher flow stresses and peak strains than the steel without Nb. A solute drag effect of niobium results also in a slower recrystallization kinetics for the Nb containing steel.

Abstract: To prepare molecularly imprinted polymers (MIPs) with good recognition properties，the effect on the MIPs adsorption performance were investigated from the different functional monomers. The MIPs were synthesized by using andrographolide as template, and α-methyl acrylic acid (MAA), acrylamide (AM) and 1 - vinylimidazole were used as functional monomer. Before polymerization, the interaction between the template molecule and the two functional monomers was studied by UV spectrum. After polymerization the different adsorption properties of MIPs prepared by the three types of functional monomers were compared by equilibrium binding. The results showed that the adsorption properties of the MIPs by 1-vinyl imidazole as functional monomer were similar to the MIPs by AM as functional, which the former is slightly higher than the latter and significantly higher than that of the one by MAA as functional monomer.

Abstract: Nano metal Ag nanoparticles were synthesized by pulse electron beam (e-beam) irradiation at room temperature and the atmospheric pressure. The staring materials were AgNO₃, toluene, ethanol and ethylene glycol. The ethanol and ethylene glycol plays a role of prohibiting agglomeration of metal ions. Energy dispersive X-ray spectrometer (EDX) was used to characterize the elements. Transmission electron microscopy (TEM) images were used to determine the shape and diameter. The time of e-beam irradiation affect to the particle size and aggregation. The average particle size was 10 nm and 30 nm for the dose time of 1 and 5 min, respectively. The shape of particles were changed from spherical to disk-like to coral-like, with increasing the irradiation time from 1 to 5 to 10 min.

Abstract: The microstructure and tensile properties at room temperature of as-cast, solution-treated and aged samples of a Mg-5Sn-4Al (wt%) alloy are investigated. The microstructure of the as-cast sample consists of a-Mg primary, Mg2Sn and Mg₁₇Al₁₂ divorced eutectic, secondary precipitations Mg₁₇Al₁₂ and Mg₂Sn. After solution treatment, all the Mg₁₇Al₁₂ particles and the majority of Mg2Sn phases are dissolved into the matrix and the tensile strength and the elongation of the alloy increase obviously. During aging process many fine particles of Mg₂Sn precipitate which result in the improvement of the yield strength.

Abstract: CdTe/CdS/ZnS core-shell-shell (CSS) quantum dots (QDs) were synthesized in aqueous solution via water-bathing combined hydrothermal method using L-cysteine (L-Cys) as a stabilizer. This method possesses both the advantages of water-bathing and hydrothermal methods, and thus can prepare CSS QDs with markedly reduced synthesis time than previously reported methods. The as-prepared QDs display a higher fluorescent intensity than bare CdTe or CdTe/CdS. After co-cultured with yeast at different growth phase, the as-prepared L-Cys capped CdTe/CdS/ZnS QDs showed much less toxicity than the other CdTe or CdTe/CdS QDs. Our results demonstrate that the CSS QD would have a promising potential in fields of bio-labeling and cell imaging.

Abstract: The effect of deformation conditions on dynamic recrystallization of U75V、RE-Ⅱwas studied by high temperature compression tests on Gleeble-1500D thermomechanical simulator. The models of activation energy Q and dynamic recrystallization were obtained by linear regression method to provide basic data for prediction and control of microstructure and properties of U75V、RE-Ⅱproducts.

Abstract: The curing monitoring of the polymeric composite materials has attracted wide interests recently. In order to improve the performance of Gr/Epoxy composites, monitoring the curing process is a demand, especially for the characterization of residual stress after manufacture. The main objective of current research is to explore the application potential of embedded fiber Bragg grating (FBG) to monitor the characterization of the curing process in a Graphite/Epoxy composite. The changes in the shape of the optical spectra, intensity attenuation as well as wavelength shifts in the optical fiber sensors were utilized to assess the curing development and residual stress measurement. The residual stress yielding during curing process was analyzed and presented systematically in this paper.

Abstract: The surface microstructured silicon prepared by femtosecond laser pulses irradiation in SF₆ shows significantly enhanced light absorption over a wide wavelength range. Absorptance of microstructured silicon is measured from 2 to 16μm, and the absorptance can up to 0.8 in the measured wavelength range. The absorptance of microstructured silicon increases as the height of spikes increases. Emissivity of microstructured silicon at different temperatures(100°C-400°C) is measured from 2.5μm to 25μm. Greatly enhanced emissivity compared to that of flat silicon was observed. At a certain temperature, with increasing the height of the spikes, the emissivity increases. For a sample with 13–14μm high spikes, the emissivity at a temperature of 100°C is approximately 0.96. A tentative explanation for the high absorptance of microstructured silicon has been carried out from three aspects: impurity states, structure defects and multiple reflection of light between spikes. The excellent properties of microstructured silicon make it a promising candidate for applications of infrared detectors, silicon solar cells, flat blackbody source and so on.