Bing She Xu

Green Synthesis of Starch-Stabilized Silver Nanoparticles and their Antibacterial Properties

Stable silver nanoparticles were synthesized from AgNO3 through a simple green route using biodegradable and renewable starch as stabilizing agent. Nanoparticles have been studied for their formation, structure, morphology and size using UV–vis spectroscopy, X-ray diffraction (XRD) and HRTEM analysis. XRD showed that the nanoparticles were of face centered cubic structure. UV–Vis and HRTEM revealed that the spherical particles having radius 5-20 nm are mostly stabilized by starch. Further, antibacterial properties of these starch-stabilized nanoparticles show promising results for S.aureus in growth inhibition ring test.

Effects of La on the Microstructures and Mechanical Properties of AZ91 Magnesium Alloy and its Mechanism

Microstructure changes brought by the addition of La element to AZ91 magnesium alloy are studied, also, the precipitating phases were identified and their influence on the mechanical properties of alloys was investigated. Results show La makes refinement of microstructure of the AZ91 alloy, and decrease the size of Mg17Al12 phase. La element takes a priority to react with Al element over Mg, forming binary phase Al11La3 with high melting point. Certain amount of La increases tensile strength, yield strength and elongation. With more addition, La would combine more Al in matrix and decrease strengthening effect, because Al11La3 phase would become coarsening. The mechanical poroerties tests indicate that AZ91+0.16%La alloy has the best properties. Maximum tensile strength, maximum yield strength and elongation are 245MPa, 178MPa and 14.5% respective, increased by 21%, 19% and 48% respectively. The mechanism of La strenthing mechanical properties is proposed that Al11La3 phase enriched on solid-liquid interface, increased the degree of supercooling, refined the grain size and changed the crystal style.

Thermal Stability of Nanocrystallized Surface Layer in Al-Zn-Mg Alloy by Surface Mechanical Attrition Treatment

After surface mechanical attrition treatment (SMAT) for Al-Zn-Mg alloy, a gradient structure with average grain size increased from 20nm in surface layer to about 100nm at a depth of 20μm was formed. The thermal stability of surface nanostructured layer in Al-Zn-Mg alloy samples was investigated by vacuum annealing at 100°C, 150°C, 200°C and 250°C for 1h, respectively. The microstructural evolution as well as the microhardness along the depth from top surface layer to matrix of SMATed samples was analyzed. Experimental results showed that the grain size of surface nanocrystallites remains in submicro-scale, ranging from 300nm to 400nm, when annealed at a temperature of 250°C, and the microhardness of surface nanostructured layer was still high compared with that of matrix, indicating satisfying thermal stability of nanocrystallized layer. This might be attributed to the presence of substantive trident grain boundaries and pinning effect of dispersive precipitated phases in nanocrystalline materials, which hindered the grain boundary migration that leading to grain growth.

Fabrication of Zr55Al10Ni5Cu30 Amorphous Composite Coating on Plain Carbon Steel by Laser Cladding and Remelting

A Zr-based amorphous composite coating was fabricated by laser cladding and remelting on plain carbon steel. The amorphous phase contents of coatings were tailored by controlling the power density. The effect of amorphous phase content along the depth direction on the microhardness and corrosion resistance of the coating was studied. The results showed that the content of amorphous phase significantly decreased from the remelted layer to the cladded layer. In addition, it was found that the maximum microhardness of the coating were about 1061 HV0.1, observed 200 μm beneath the surface. Potentiodynamic polarization studies in 3.56 wt.% NaCl solution indicated that the remelted layer exhibited excellent corrosion resistance due to the high amount of amorphous phase.

Synthesis and Characterization of Carbon-Encapsulated Nickel Nanoparticles from De-Oiled Asphalt

Carbon-encapsulated Ni nanoparticles with the size of 5 to 30 nm were synthesized from de-oiled asphalt (DOA) by heat-treatment at 1800 °C with nickel powder. The nanoparticles exhibited well-constructed core-shell structures, with Ni cores and graphitic shells. High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) examinations confirmed that the carbon-encapsulated Ni nanoparticles were uniformly dispersed in carbon matrix and the Ni nanoparticles were surrounded by several carbon layers with well ordered arrangement. The formation of the core-shell nanoparticles was selectively controlled by adjusting the ratio of de-oiled asphalt to nickel powders. The possible growth model for the carbon-encapsulated Ni nanoparticles was discussed briefly. This result presents a simple and controllable way to synthesize carbon-encapsulated nickel nanoparticles.

Effects of Different Factors on Antibacterial Properties of Crosslinked Chitosan-Coated Ag-Loading Nano-SiO2 Composites

Chitosan (CTS) and Ag-loading nano-SiO2 (SLS) are excellent antibacterial materials. However, when used alone, these monocomponent antibacterial agents are sometimes far from meeting requirements in special conditions. In this study, crosslinked chitosan-coated Ag-loading nano-SiO2 composites (CCTS-SLS) were synthesized by adsorption crosslinking reaction. Then Escherichia coil (ATCC 8099) was taken as the experimental bacteria for antibacterial tests. The experimental results indicate that the mass ratio of SLS to chitosan had the greatest influences on the value of MIC (minimal inhibitory concentration) for CCTS-SLS composite. However, the heating temperature had a weak influence on the antibacterial performance of CCTS-SLS composite.

Effect of Surface Grafting-Modified on Structure and Property of Cellulose Fibers

Cellulose fibers were chemically modified on surface by acrylamide polymerization and glutaraldehyde crosslinking. The chemical and morphological structures of modified cellulose fibers were investigated with X-ray diffraction, FTIR spectra, and scanning electron microscopy (SEM). The crystalline conformations of the cellulose fibers were slightly changed in polymerization and crosslinking process. The wet strength of modified cellulose fibers was improved. Appreciable difference between the surfaces of native and modified cellulose fibers was observed from SEM images.

Effects of Sr Addition on Mechanical Properties and Microstructure of Mg-6Al Magnesium Alloy

The effects of Sr addition on the mechanical properties and microstructure of Mg-6Al mag- nesium alloy both at 25 °C and at 175 °C were investigated by means of OM, SEM and EDS and XRD. Upon the Sr addition of 2%, the tensile strength was increased by 7.2% to 184.4MPa at 25 °C, while it was increased by 30% to 155.4MPa at 175 °C. The strengthening mechanism of Mg-6Al-xSr at lower temperature (25 °C) was different from that at higher temperature (175°C). The results show that the addition of strontium effectively improved the microstructure and mechanical properties of magnesium alloy.

Synthesis, Electronic States, and Electroluminescent Properties of Aluminum Complex Based on Mixed Ligands with 8-Hydroxyquinolinate and Acetylacetone

We report the synthesis, photophysical investigation, computational studies and electroluminescent(EL) properties of an organic electroluminescent material-Bis(8-hydroxyQuino line) acetylacetone aluminum (Alq2A). It is characterized by 1H NMR, IR and elemental analysis techniques. The absorption and fluorescence spectra of various Alq2A systems including solution in ethanol, powder and thin film on quartz (thickness of 50nm) have also been systematically evaluated. Analysis of the electronic structure of Alq2A calculated by quantum chemical calculations reveals a localization of orbital and the distribution of orbital energy. The results from EL experiments indicate that Alq2A has good electron transport properties as compared with tris(8-hydroxyquinolinato) aluminum (Alq3). Thus, Alq2A is considered to be a superior emitter and electron transporting material for display application compared with Alq3.

Effect of Siro-Spun Processing Parameters on Properties of 55/45 Flax/Cotton Blended Yarn

Limited studies exist related to the siro-spun spinning of flax ( Linum usitatissimum L.) and cotton (Gossypium hirsutum) blends. The purpose of this study was to determine the influence of various siro-spun processing parameters, including twist factor, space between two rovings and specification of traveler, on yarn qualities, such as yarn hairiness, tenacity and evenness. Results show that both specification of traveler and space between two rovings significantly influenced yarn hairiness and evenness, and heavier traveler and greater space led to decreased hairiness, but bad evenness. Twist factor influenced yarn evenness highly significantly, and smaller twist factor led to worse yarn evenness. Results also indicate the optimum levels of siro-spun process parameters as follows: twist factor αm = 150, space between two rovings 8 mm, traveler Fo 5/0. In relation to the general ring-spinning yarn, the siro-spun spinning yarns had decreased hairiness, little increased tenacity and similar evenness.