Advanced Materials Research Vol. 412

Abstract: Porous alumina insulation materials were prepared by the combination method of gelcasting and foaming. The effects of the amount of blowing agent, the solid volume, and the sintering temperature on porosity of aluminum oxide ceramic were studied. The result showed that, when the amount of blowing agent is 1wt %, the solid volume is 45vol % and the sintering temperature is 1500°C, the porous alumina ceramics with high porosity, small pore diameters, evenly distributed, high bending strength and low heat conductance can prepared.

Abstract: Uniform rod-like Bi₂S₃ nanostructures were successfully synthesized by a simple hydrothermal process in a high yield. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and UV-vis absorption spectroscopy were used to characterize the obtained products. It was found that the morphologies of the as-obtained Bi₂S₃ were highly dependent on the experimental parameters, including the pH value and the solvent. The adjustments of two parameters could lead to an obvious shape evolution of products. Then based on the discussion of the experimental parameters and the captive intermediate, the possible growth mechanism was proposed.

Abstract: Using gas-solid reaction method, the non-crystalline alumina nanofibers with different morphology and aspect ratios could exuberantly grow by feeding air into one closed box or bubbling air into several organic liquids which contained the thin aluminum amalgam sheet at room temperature. Their diameters were about 2-10nm, whereas the length-diameter ratios were distributed widely. The diameters and length could be controlled by adjusting the kinds of the organic reagent. The as-grown nanofibers were then heat-treated at temperatures range from 300 to 1000°C. The results of X-ray diffraction and thermo-gravimetric analysis indicated the γ-Al₂O₃ nanofibers would be produced at 500°C and the α-Al₂O₃ particles could be obtained at about 1000°C. The electron micrographs suggested the nanofibers growth direction was randomly in the air or organic solutions, except for growing regular naonofibers in polyoxyalklene-400. The growth mechanics of alumina nanofibers were briefly discussed.

Abstract: Electrolyte containing F^– was employed to conduct two-step anodic oxidation. Through adjustment of the composition of electrolyte, TiO₂ nanotube array with high aspect ratio was grown in situ on Ti matrix, and meanwhile the binary doping with non-metallic elements, namely, F and S, was achieved. Using FSEM, XRD and EDS, the characterization on the topography, structure and doped elements of TiO₂ nanotubes were performed. Taking methyl orange as the target degradation substance and using xenon lamp to simulate natural lighting, the comparison between the doped non-high-aspect-ratio nanotube and the doped high-aspect-ratio nanotube was made to investigate the related photoelectrocatalytic property. The results showed that the photoelectrocatalytic property of doped nanotube with high aspect ratio was significantly superior to that with non-high aspect ratio. The mixed crystal ratio of anatase and rutile obtained after calcination for 2h at 500°C enabled higher photoelectrocatalytic activity of TiO₂ nanotube array.

Abstract: ron-zircon pigment has been synthesized by non-hydrolytic sol-gel method using zirconium chloride and tetraethoxysilane as precursors, anhydrous ferric chloride as colorant, lithium fluoride as mineralizer and anhydrous ethanol as solvent. Iron-zircon pigment has been characterized by means of DTA-TG, XRD, Colorimeter and TEM. The results show that only a small fraction of iron is incorporated in the zircon crystal structure while the remaining iron cations are trapped within the zircon matrix. The iron-zircon with the red value (a*) of 20.64 can be synthesized at 700°C with the optimum Fe/Zr molar ratio of 0.2.

Abstract: Effects of V-Ti-Zr-Re containing modification powders on the mechanical properties and microstructure of low alloy steel castings by conventional normalizing, hardening and tempering processes and normalizing-free heat treatment were investigated. The results showed that for the as-modified casting, martensite and carbides were the main phases after direct quenching and low-temperature tempering but skipping normalizing. The mechanical properties were almost the same or even higher in impact toughness than the same material but bearing also normalizing treatment. Both samples modified by alloy powders, whether normalizing treated or not, possessed superior mechanical properties to those castings without being modified. The modification technique can be applied in low alloy steel production to eliminate the time and energy consuming normalization process, so that the cheap, energy saving and environment friendly materials are thus expected.

Abstract: Nickel nanoparticles were synthesized from liquid precursor via H-plasma reduction route. XRD patterns revealed that pure metallic nickel powders could be obtained when nickel ammine complex aqueous solution was used as precursor. FESEM showed that the products are composed of well-dispersed nanospheres with an average diameter less than 100 nm. The tap density is about 3.85g/cm³, and the sheet resistance of the conductive film prepared using the nickel particles is about 58mΩ.

Abstract: Au/C catalyst used for the liquid phase selective oxidation of glucose to gluconate was prepared by gold sol method that includes the preparation of metallic colloid by citrate reduction and subsequent immersion by carbon support. The influence of gold particles of different size on the activity of Au/C catalyst was studied. The results show that the catalyst with good dispersed spherical gold particles has higher catalytic activity. After 16 runs, the conversion of glucose selective oxidation can still achieve over 96% under mild reaction conditions.

Abstract: nanosilver powder has high surface activity, catalysis property and wide usage, so it is important to study its preparation method. In this paper, nanosilver powder was prepared with industrial AgNO₃ as raw materials, hydrazine hydrate as the reducing agent, polyvinylpyrrolidone (PVP) as the polymeric protective agent, polyethylene glycol as the dispersing agent by solution chemical reduction method. The effects of AgNO₃ concentration on the preparation of nanosilver were studied, and the final product was examined with TEM testing. The test results show that it can be obtained flake nanosilver with good performance by controlling the reaction conditions, such as dispersion, stability and crystal properties.

Abstract: Using the high-energy ball milling craft, the case that the silver powders’ changes along the condition of ball milling is researched by the orthogonal experiment methods, the laser particle analyzer and the scanning electronic microscope. The influences of the milling times, the dispersant agents, speed and ratio of ball to powder on the distribution of particle size, the shape of grain and the specific surface are studied. The results show that, by using the composite dispersant agent, milling for 20h,ethanol as grinding aids and calcium stearate as dispersing agent, powders of average diameter is 8.55μm and specific surface area is 0.67(m2/g), with higher laminarization and less reunion of ultrafine flake silver powders.