Key Engineering Materials Vols. 609-610

Abstract: The influences of temperature, compounds dosages and water on the size of nanosilica prepared by tetraethyl orthosilicate were discussed, and the transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) were employed to investigate the characteristics of the nanosilica synthesized by the sol-gel method. Moreover, the silane coupling agent was also used to modify the surface characteristic of the nanosilica. Results showed that the influences of temperature, compounds dosages and water on the size of nanosilica had a significant impact. In fact, the optimal synthesis temperature was 45 degrees centigrade, and the stirring time was 2 hours. In this case, the nanosilica can be prepared with the grain size of 100 nm and the narrow particle size distribution. By FTIR analyzing, it can be seen that the combination of the nanosilica and the silane coupling agent was chemical reaction. In addition, the tests showed that the adsorption process finished in 40 minutes.

Abstract: Compared with block and quantum well thin-film materials, nanowire materials can have better thermoelectric properties and higher merit of ZT values. Electro-chemistry method was used to deposit nanowires in the highly ordered holes of AAO (Anodic Aluminum Oxide). Several conditions were discussed and experimented to determine an appropriate condition for the co-deposition of Bi and Te. Some optimization measures are proposed to obtain more stable fabrication results. Analysis demonstrates that the nanowire grew along the pores from the bottom to the top.

Abstract: ZnO and Ag-droped ZnO photocatalysts with different Ag loadings (0.5, 1.0, 1.5, 2.0at%) and different calcination temperature (300, 400, 500, 600, 700°C) were synthesized by a sonochemical method. The morphology and crystal pattern of some prepared catalysts were characterized by XRD and SEM techniques which demonstrated that the prepared catalysts were of hexagonal wurtzite structure. Ag loadings, calcination temperature and other factors, dosage of photocatalyst, reaction time and pH value of seawater, were also taken into consideration in the procedure of photocatalytic degradation reaction under UV light. An orthogonal experiment was carried out to investigate the best combination of factors which can reach the best diesel pollution removal rate and the influence order of factors. Reaction time and dosage of catalyst were the most influential factors in this experiment, and the factor of calcination temperature was the weakest influential factor. The removal rate of diesel can up to 78% when the experiment was undertaken under the very conditions: the dosage of catalyst 2.0g/L, reaction time 2.0h, Ag loading of catalyst 1.0 at%, calcinations temperature 400°C and pH value 8.5.

Abstract: Zinc Oxide (ZnO) is a potential semiconductor as photocatalyst. Nevertheless, its main absorbance wavelength is in the range of UV light, which consist only a small proportion of solar. In order to utilizing the large proportion of solar light, pure ZnO and Li-doped ZnO nanoparticles with different Li loading (1.0, 2.0, 3.0 and 4.0 at%) and various calcination temperature (300, 500, 700, 900°C) were synthesized through a co-precipitation method and characterized by XRD and TEM techniques. The photocatalytic abilities of photocatalysts are evaluated in simulated experiments of removing diesel pollutants in seawater under visible illumination. Six factors, Li loadings, calcination temperature, dosage of photocatalyst, reaction time, diesel initial concentration, and pH value of seawater, were taken into consideration in the process of phtotcatalytic degradation of diesel experiments under visible light. An orthogonal experiment was implemented to investigate the best combination of five factors (the factor of reaction time was excluded) which can lead to the highest diesel removal rate. The characterization of as-prepared nano-particles showed that Li element was doped into ZnO, and all particles were of hexagonal wurtzite structure. The average crystal sizes of Li-doped ZnO with various calcination temperature (300, 500, 700 and 900°C) are 15.03, 25.97, 48.63 and 55.48nm, respectively, and consequently, higher calcination temperature will contribute to the aggregation of particles. Doping Li appropriately can improve the photocatalystic ability of ZnO under visible light, which can deduce from the single-factor experiments. Calcination temperature is also an evident factor to affect the photocatalytic ability of photocatalyst. The influence order of factors in decreasing order can also be obtain through the orthogonal experiment and the result was as follows: calcination temperature > Li loading ≈ pH value > initial concentration of diesel > photocatalyst dosage. The best combination of the five factors is as follows, the dosage of catalyst 2.5g/L, initial concentration of diesel 1.5g/L, Li loading of catalyst 1.0 at%, calcinations temperature 900oC and pH value 8.25, the removal rate of diesel pollutants in seawater is expected to reach 77.31%.

Abstract: Since the Appearance of Hollow-Core Photonic Bandgap Fiber (HC-PBF), it was Widely Concerned for its Excellent Characteristics. in Order to Study the Characteristics of the HC-PBF that can be Used in Resonator Fiber Optic Gyros (R-Fogs), the Model Structure of a Polarization-Maintaining HC-PBF was Built and its Performance was Simulated by Using the Finite Element Method (FEM). its Mode Field Distribution and Birefringence Characteristics were Obtained. the Influences of the Air Core and Cladding Structures on the Mode Field Distribution and Birefringence were Simulated and Analyzed Further. the Result Showed that there are both Core Mode and Surface Mode in the Structure we Built. by Adding Scattering Points into the Fiber Core, the Surface Mode can be Significantly Suppressed. by Matching the Size of Core and Air Holes around the Core, a Birefringence up to 8*10^-4 were Obtained.

Abstract: This paper introduces the principle and manufacture process of a film-taped metallic mesh, and the influence of the parameters of metallic mesh film on optical and electromagnetic features has also been analyzed. By using the flexographic printing technology, the metal mesh film with the line widthes of 15, 203040μm and the period of 300μm on PET substrates have been made, and the maximal electromagnetic shield effectiveness is more than 15dB. The results indicate that the optical and electrical performance of the metallic mesh film is inconsistent, and it is better to select a thinner line width and smaller period to obtain optimal shielding effectiveness.

Abstract: In this study, spherical and cubic Ag₃PO₄ microcrystals were prepared by a facile liquid chemical method and characterized by the XRD, SEM and UV-visible spectrometry. It was found that the as-prepared Ag₃PO₄ cubes showed the higher photocatalytic activity and stability than the sphere under visible-light irradiation in degrading Rhodamine B (RhB). The enhanced photocatalytic activity of the Ag₃PO₄ polyhedron might be attributed to a higher active surface energy of the former one.

Abstract: Silicon micro-nanostructures were directly produced by femtosecond laser in air. By varying the laser power, we can tune the surface morphology, the wetting property. As-prepared silicon micro-nanostructures show superhydrophilicity, but with removal of native SiOx, superhydrophobicity is observed without surface modification. And a reversible switch between superhydrophilicity and superhydrophobicity can be realized by immersing samples in hydrofluoric acid and hydrogen peroxide, respectively, for many times.

Abstract: Europium-doped lutetium (Lu2O3:Eu3+ ) powders were prepared by micro-emulsion method. A small amount of an aqueous solution of Lu(NO3)3, Eu(NO3)3 and aqueous ammonia was slowly dropped into the water-in-oil micro-emulsion system (water / cetyl trimethyl ammonium bromide (CTAB) / n-butyl alcohol and cyclohexane) under vigorous stirring at 80 °C. The precipitates were obtained by Ostwald’s ripening at 250 °C for 6 h, which were then heated at 400 °C, 600 °C and 800 °C. The SEM morphology showed that the powders were rods of about few hundred nanometers in length and 40 nm in diameter. The spectrograms of X-ray diffraction (XRD) demonstrated that the Lu2O3:Eu3+ crystallinity was enhanced with the increasing of temperature. The photoluminescence results revealed that the intense emission bands centered at 612 nm. This method provides a new way to obtain different morphology and luminescent properties of Lu2O3:Eu3+ powder.

Abstract: Based on molecular mechanics and the stick-spiral model, this paper first presents the analytical analysis of the effective in-plane mechanical properties of both zigzag and armchair monolayer graphene sheets. We find that the equivalent in-plane elastic constants of monolayer graphene sheets are the same in the two principal directions of graphene. The effective in-plane mechanical properties of graphene are then evaluated numerically using an improved molecular structural mechanics (MSM) model, in which the flexible connections are used to characterize the bond angle variations of graphene. Furthermore, the effective bending rigidity of the beam representing a C-C bond in this improved MSM model is determined from the energy equivalence over the basic cell of graphene and the force constants given by molecular mechanics. A rigidly connected frame model with the bending stiffness of the equivalent beams for C-C bonds different from the existing structural mechanics model is also used to evaluate the mechanical properties of graphene. The flexibly connected frame model gives very good results of Youngs modulus and Poisson ratio of monolayer graphene sheet. The new rigidly connected frame model presented here also gives improved results than the existing rigidly connected frame model of graphene.