Materials Science Forum Vols. 809-810

Abstract: Mesoporous ZnO thin film is an important part of dye-sensitized solar cells (DSSCs) due to it determines the amount of adsorbed dyes. However, small specific surface area of ZnO thin film prepared by ordinary methods restricts the increase of conversion efficiency of DSSCs. In this work we adopted two-step electrodeposition method to fabricate ZnO thin film, which increase the roughness and dyes adsorption. ZnO nanosheets with many adsorbing nanoparticles were observed by scanning electron microscope (SEM). It is noteworthy that DSSC based on two-step electrodeposition method exhibit more outstanding photoelectric performance than those based on one-step electrodeposition method, which demonstrates that two-step electrodeposition method is in favor of increasing specific surface area and adding dyes adsorption, which eventually contributes to improvement the conversion efficiency of DSSCs.

Abstract: Thermal insulation exterior wall coating has been successfully prepared, using styrene-acrylic emulsion as film former, and xonotlite as heat-insulating filler, which produced by hydrothermal reaction. The insulation mechanism of xonotlite is explored, through analyzing the microstructure of homemade xonotlite thermal insulation exterior wall coating. The results show that xonotlite is a kind of compound type heat-insulating filler that can effectively weakened the heat transfer in the coating, like heat conduction, thermal convection and thermal radiation.

Abstract: Ni-P-β-SiC was prepared using different granularity β-SiC and rolling electroless plating technology. The test results show that β-SiC particles in composite coating are uniform, and the thickness and hardness of composite coating are 17~25μm and 520~620HV, respectively. At the same time, the friction and wear behavior of Ni-P-β-SiC composition coating have been studied. The results show that the wear weight loss decrease and the friction coefficient increase with the increase of β-SiC granularity.

Abstract: A facial method to prepare zeolite LTA membrane via microwave-assisted heating method was reported. The A-type zeolite seeds were prepared by hydrothermal method from a precursor solution composed of A₂O₃:SiO_2:Na₂O:H₂O with molar ratio of 1:5:40:1000. The optimized process parameters for synthesizing the zeolite seeds are reaction for 10 min, microwave power of 135 W, and the ratio of H₂O/Na₂O is 25. Zeolite LTA membrane was prepared via secondary growth method by microwave heating on the silicane and zeolite seed modified ceramic supports. The prepared zeolite seeds and membrane were characterized with X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR) and scanning electron microscopy (SEM). The results show that the size of the zeolite seeds are in the range of 100-400 nm with regular cubic morphology, and the zeolite membrane have homogeneous thickness of 1.5 μm and perfect morphology without defects and pinholes. The easy operation and controllable process make the zeolite membrane by this method properly have wide application for the gas sensor and devices.

Abstract: Single and multilayer of Al₂O₃ and TiO₂ were fabricated on anodized aluminum by atomic layer deposition. The effect of processing parameters on pore sealing and anti-corrosion property was studied. It is concluded that the micropores on anodized aluminum could be sealed by atomic layer deposition oxide films through SEM and staining experiments. The anti-corrosive property is affected mainly by the film thickness and process temperature. The acidic drip and salt spray test shows that the anti-corrosion property is enhanced as the film thickness increase. With the similar thickness, Al₂O₃/TiO₂ multilayer film has the best anti-corrosion property, while the single Al2O3 layer appears the poorest. The complementary roles between two basic materials result in the enhanced application property.

Abstract: Rare-earth doped β-NaYbF₄ upconversion phosphors were synthesized using a simple hydrothermal procedure. It is found that under 980 nm excitation β-NaYbF₄:0.1%Tm are more efficient than β-NaYF₄:20%Yb,0.1% that is known as one of the most effective upconversion materials. The unusual result may be related to the particles size. After introducing 0.1%Er³⁺ into the NaYbF₄:0.1%Tm lattice, the upconversion white emission with color coordinate of (0.3016,0.3748) is obtained. The investigation of achieving mechanism indicates that besides the energy transfer from Yb³⁺ to Tm³⁺ and Er³⁺, respectively, there exists a new energy transfer process: ³F_2,3 (Tm³⁺) + ⁴I_11/2 (Er³⁺) → ³F₄ (Tm³⁺) + ²H_11/2/⁴S_3/2 (Er³⁺).

Abstract: Sr₄Al₁₄O₂₅:Eu²⁺, Dy³⁺ luminescent phosphor was synthesized for the first time from using cyclodextrin as chelating agent by sol-gel method. The structural characterization, surface morphology and properties of the phosphor were studied. The results revealed that the target phosphor with relatively regular morphology, smaller grain size, pure phase and high crystallinity can be achieved at 1200°C for 4 h in a reducing atmosphere. The average grain size of the Sr₄Al₁₄O₂₅:Eu²⁺, Dy³⁺ phosphor nanoparticles ranges from 50 to 100 nm . And the phosphorescence in blue-green (483 nm) by Eu²⁺.

Abstract: Acetylene (C₂H₂) was used as carbon source gas, nitrogen (N₂) as dilution gas. The electric properties of carbon fibers was briefly discussed by energizing the carbon fibers in vacuum condition which were applied for the preparation of carbon/carbon composites by the method of chemical vapor deposition. The deposition mechanism and microstructure of pyrolytic carbons in carbon fibers under different deposition crafts were also discussed. Results indicate that the greater the initial voltage, the higher the temperature, we can change the deposition temperature by changing the initial voltage according to the relationship between the brightness and the surface temperature of carbon fibers. The surface of carbon fibers will be etched in the process of electrifying which would make the pyrolytic carbons preferred deposition on the etching point which became the growth center in the early deposition process. The pyrolytic carbons deposited with a spherical microcrystalline structure under the gas flow of C₃H₆/N₂=2:3, When the rate of gas flow is C₃H₆/N₂=1:2, The pyrolytic carbons deposited with a spherical microcrystalline structure after deposited for 0.5h, but after deposited for 1h, the deposition of large patches of molecular is dominant which lead to that: from a macro perspective, the pyrolytic carbons were a layered structure, From a microscopic perspective, they were a spherical microcrystalline structure with different size.

Abstract: The CaCO₃ and CaCO₃:Eu³⁺ phosphors have been synthesized by solid state reaction at room temperature without further sintering treatment. The morphology, crystalline structure, and fluorescent properties of the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), spectrofluorometer, respectively. Also, the influences of Eu³⁺-doping concentration on the photoluminescence (PL) properties were investigated in detail. The results indicate that the morphology of as-prepared CaCO₃ particles are irregular cubic in shape and about 200-400nm in size, while the CaCO₃:Eu³⁺ particles are the aggregates of many small nanoparticles with nearly 30nm in size, indicating that Eu³⁺ ions have a great influence on the CaCO₃ particle morphology and size. The lines around 392nm in luminescence excitation spectrum is the most noticeable. Upon excitation at 392nm, the PL emission spectrum is composed of two band and strong peaks at 589nm and at 613nm. The peaks at 589nm is attributed to magnetic dipole transition ⁵D₀–⁷F₁ and with the increase of the Eu³⁺-doped concentration, the intensity decreases gradually; but it shows the opposite trend for the peak at 613nm which is attributed to the hyper sensitively forced electric dipole transition⁵D₀–⁷F₂.

Abstract: A copolymer liquid crystal with a coumarin side group is synthesized and investigated. Under different exposure energy, the thin film of copolymer is irradiated by linearly polarized ultraviolet light (LPUV). Moreover, through changing exposure temperature and annealing temperature to investigate its photoreaction properties and reorientation performance. It is made clear that the value of optical anisotropy appears maximum with the increase of exposure energy. However, with the exposure temperature increasing, the Photo-Fries rearrangement tend to be occurred and the degree of the cyclo-addition reaction is reduced. Finally, dealing the exposed film with the liquid crystal temperature, the optical anisotropy of the film has cyclical change, but the maximum anisotropy remains nearly unchanged.