Materials Science Forum Vols. 620-622

Abstract: Titanate nanotubes have been directly prepared by hydrothermally treating P25 powders in NaOH aqueous solution. Effect of calcination temperature on crystal phase, morphologies and specific surface area of the as-synthesized nanotubes has been investigated in detail. The Na2Ti3O7 tubular structure could be kept well even after calcination at 600 °C and began to transform to Na2Ti6O13 nanorods at around 645 °C. The specific surface area of the as-synthesized nanotubes was 200.6 m2/g and reached to the maximum of 347.9 m2/g after calcination at 300 °C and then decreased sharply with the further increase of the calcination temperature.

Abstract: To obtain porous and thick TiO2 film, the precursor sol was prepared by hydrolysis of Ti isopropoxide and then complexed with trehalose dihydrate. The porous TiO2 film was fabricated by dip-coating technique on quartz glass substrates using this sol. The TiO2 films were calcined at 500-700 °C. The photocatalytic activity of the films was evaluated by examining decomposition of methylene blue in aqueous solution under UV light irradiation. The TiO2 film prepared from the sol with trehalose was more active than TiO2 film prepared from the sol without trehalose. The trehalose addition to the dip-coating solution was effective in improving the photocatalytic activity of the TiO2 film.

Abstract: TiO2 thin film was prepared on soda lime glass by hydrolysis of Ti(OC4H9)4 in alcoholic solutions by sol-gel method combined with spin-coating and calcination different temperatures. Prepared samples were characterized by XRD, FESEM, and measurement of contact angles and transmittance. XRD identification reveals that the films are composed of anatase TiO2 when the annealing temperature was set at 450~550 oC. SiO2 layer was coated on the surface of the glass firstly to barrier the diffusing of sodium ions from the substrate. Light-induced superhydrophilicity of the TiO2 thin film has been investigated. To increase the illumination light intensity will decrease the water contact angle. The superhydrophilicity of the TiO2 thin film will disappear more slowly in the dark than that in the field of ultrasound.

Abstract: A unique method, so called, hydro-thermal synthetic method was applied to produce nano-sized inorganic blue (Y2SiO5:Ce) and red (Y2O2S:Eu+3) emitting phosphors. Electron microscopy revealed that the nano-sized emitting phosphor particles have spherical shape with 23-50nm in size. The particles can effectively change ultraviolet rays of 1-390 nm to infrared rays of 750nm -1mm, which are suitable to promote the growth of plants. The principle excitation and emitting spectrum of the red phosphor in 590-700 nm emitting spectrum were in the region of 308nm and 617nm, respectively, whereas, those of the blue phosphor in 420-470nm emitting spectrum were in the region of 254nm and 464nm, respectively. The addition of 0.1-0.2 wt% of the 2:1 mixed red and blue powders to a film showed the maximum emitting intensity of 537x1000 count/sec.

Abstract: The binding energy of anatase TiO2, in which the Ti was substituted by other transition metals in the 4th, 5th and 6th periods of the periodic system of the elements, has been calculated by using first principles method. The doping limits of V, Cr, Zr, Nb, Mo and W are 61.5%, 39.7%, 88.2%, 100.0%, 65.0%, and 63.2%, respectively predicted by the calculated binding energy, while the doping limits of other transition metals are much lower. So, these transition metals can easily be doped into the anatase structure theoretically while it is difficult for the others. And the band structure and density of states (DOS) of V, Cr, Zr, Nb, Mo and W doped anatase TiO2 have also been calculated and analyzed.

Abstract: AZO/TiO2 double-layered semiconductor coupled films were prepared through sequentially depositing AZO and TiO2 films on glass substrates by radio frequency (RF) magnetron sputtering. PVP-pretreatment and post-annealing were performed on these double-layers to achieve an exposure of the AZO buried-layer in different baring conditions. The photocatalytic efficiencies of these buried-layer bared structures were measured through dye decomposition under ultraviolet irradiation. Silver mirror reactions were operated to explore a possible photocatalytic mechanism associated with these buried-layer bared conditions. The buried-layer bared AZO/TiO2 coupled films present 2 ~3 times of photocatalytic activity comparing to the normal AZO/TiO2 double-layered or single layered ones. It suggested that the self-built electrical field formed from coupling semiconductors reduces the recombination of electron-hole pairs, increases the yield of surface photogenerated charges, and enhances the photocatalysis.

Abstract: Sintered NdFeB permanent magnet is widely used in many areas because of its excellent magnet property. In this study, the machining parameters of electrical discharge machining (EDM) are varied to study the effects of electrical discharge energy on material removal rate and surface roughness of NdFeB magnet. Moreover, the micro-cracks on the machined surface induced by EDM are also examined. The experimental results reveal that the MRR increases with the electrical discharge energy. The number of surface cracks on the machined surface increases with the enhancement of discharge energy Thus, using EDM process to machine sintered NdFeB magnet depends on setting the machining parameters to prevent surface crack.

Abstract: Machines for manufacturing large scale flat displays are enlarging as the size of glasses increases. This work develops porous materials with a low thermal expansion coefficient and a high Young’s modulus. SiC and LiAlSiO4 were used for a positive and a negative thermal expansion materials, respectively. Compositions of powders for porous materials were determined to obtain a desirable Young’s modulus and thermal expansion coefficient by using SiC-VBM-LiAlSiO4 phase diagram at 20 % of porosity. The empirical values of Young’s modulus and a thermal expansion coefficient are close to the theoretical values by using the diagram. Fabricated porous material had high enough Young’s modulus of 87 GPa, and low enough thermal expansion coefficient of 2 x 10-6 K-1 at temperatures ranging from -17 °C to 190 °C with 22 % of porosity.

Abstract: Flexible pavement-asphalt mixture plays an important role in structures of the primary road and bridge at present. However, the mixture is a type of viscoelstic material and is sensitive to environment temperature, especially a high temperature. The permanent deformation due to high temperature and the material’s viscoelastic shorten the service life of the road and even lead to traffic accident. Therefore it is necessary to analyze the pavement’s mechanical performance. In the study, the viscoelastic constitutive equation of the mixture is transformed to Prony Series. The objective of this study is to characterize the stability of asphalt pavement at high temperatures with a three-dimensional finite element and accurately predict the pavement’s strain and stress in vehicle load.

Abstract: The principle and process of producing molybdenum powder via reduction reaction of molybdenum trioxide at lower temperature in a N2-H2 system were researched. The effects of hydrogen concentration, temperature, and volatilization rate of molybdenum trioxide on particle size were analyzed. The experimental results showed that the optimal process parameters were 770°C-790°C in 60min when the hydrogen flow rate was 700mL/min. Particle size of superfine molybdenum powder was less than 4μm. The concentrations of hydrogen, temperature and volatilization rate of molybdenum trioxide have great effect on the particle size of superfine molybdenum powder.