Papers by Author: Qiong Yu

Abstract: A Method was studied for the determination of Al、Cu、Ni in Zr-based amorphous alloy by inductively coupled plasma atomic emission spectrometry (ICP-AES). Samples were dissolved by hydrochloric acid,nitric acid and hydrofluoric acid,analytical spectral lines for aluminum,copper,nickle are 308.215nm,327.396nm and 231.604nm.Interference of zinc was eliminated by the matrix-matching method, the experiments were done with optimized Operating Parameters. The correlation coefficients of the calibration curve are all 0.999,detection limits are 0.0010%,0.005% and 0.0006% respectively,and the range of recovery is 98%-104%.

Abstract: The template method combined with sol-dipping deposition or sol-electrophoresis was used to prepare titania (TiO₂) nanowires with shape of rod or string of beads. When irradiated under ultraviolet (UV) light for 1 hour, the degradation rate of methyl orange (MO) using nanowire arrays reached 98.5% which was 1.84 times as much as that of the thin film on glass plate, and when irradiated under visible light for 6 hours, the degradation rate reached 96.7% which was 4.17 times as much as that of the thin film.

Abstract: The template method combined with sol-dipping deposition or sol-electrophoresis was used to prepare titania (TiO₂) nanowires with shape of rod or string of beads. The SEM was used to characterize the surface and cross section of the TiO₂ nanowire arrays. With parallel orientation, the nanowires were uniformly distributed.

Abstract: Cadmium Selenide/Cadmium Sulfide (CdSe/CdS) core/shell quantum dots (QDs) in aqueous solution were prepared by solve-separate method using CdSe as core and mercapto-acetate acid as stabilizer and surfactants. The results of experiments indicate that the size of the CdSe/CdS QDs was about 5nm estimated by FE-TEM, which is accordant with that calculated from the XRD data by the Scherer equation after emendation. The QDs belong to the cubic structure (zinc blende) by XRD analysis. The intensity of luminescence of the quantum dots was greatly improved after the surface was coated with CdS shell. With increasing the time of refluence, the intensity of photoluminescence was promoted correspondingly. The excitation wavelength was 350nm, two emission peaks were clearly observed, the first high-energy peak was at 600nm and the second one located in 700nm. The first high-energy band was attributed to electron–hole recombination after relaxation and the second energy band was to deep traps in quantum-confined systems.

Abstract: Si₃N₄ based nanocomposites were prepared with nano-sized amorphous SiO₂ and Si₃N₄ powders by pressureless sintering method. The microstructures, phase composition, mechanical and dielectric properties of the nanocomposites were investigated. The scanning electrical microscope (SEM) photographs reveal that the grains are big and elongated. The X-ray diffraction (XRD) analysis shows that the main crystalline phase in the composites is Si₂N₂O formed during the sintering process. More β-Si₃N₄ phases were retained in the nanocomposites with the increase amount of the amorphous Si₃N₄ powders and no phase of SiO₂ were observed. The densities and the strength of the nanocomposites decreased with the increase of amorphous SiO₂ content. Despite low density, the flexural strengths of the composites reaches 220MPa and the ceramic has excellent dielectric properties with dielectric constant as low as 3.2-4.7 and dielectric loss in the range 2.6-3.9×10^-3.

Abstract: A new preparation method was developed to produce Si₃N₄-SiO₂-Si₂N₂O composites for broad band radome applications. The three-dimensional cross-linked polyphenylsiloxane (PPS) was used as an organic precursor. The composites obtained through react bonding between Si and the precursor powders in the stream of N₂ were examined. The conversion of the PPS polymer to the ceramic was examined by TG analysis and conventional X-ray diffraction (XRD) techniques. It was found that the ceramics contained a primary Si₂N₂O phase, some β-Si₃N₄ phase and a minor α-SiO₂ phase. Despite low density (1.7-2.0g•cm^-3), the flexural strengths of the composites reaches 195Mpa at room temperature. The ceramic has excellent dielectric properties with dielectric constants as low as 3.2-5.5.

Abstract: Barium strontium titanate (Ba_0.6Sr_0.4TiO₃: BST) powders were prepared by the oxalate co-precipitation method. The ceramics from thus obtained BST powders with B₂O₃-Li₂CO₃ addition were prepared by conventional oxide mixing method. The powders and the ceramics were observed and analyzed by SEM and X-ray diffraction. The effects of B₂O₃-Li₂CO₃ addition and powder properties on the sintering behavior and the dielectric properties of BST-based ceramics were investigated. SEM results revealed that the BST powders are micron-sized with cauliflower-shaped rough surface leading the specific surface area reaches 18.52m²/g. In dilatometric studies, the ceramics without B₂O₃-Li₂CO₃ addition didn’t produce the desired shrinkage and dense microstructure at relative low temperatures (<1000°C). However, the sintering temperature is decreased to 850°C by addition of small amount (≤3wt %) of B₂O₃ and Li₂CO₃. This was also verified in sintered microstructures. The XRD results showed that the main phase of the ceramics was BST without any other crystalline phases of remarkable extent. With increasing of B₂O₃-Li₂CO₃ content, the permittivity and the tunability of the ceramics were decreased.

Abstract: The preparation and characterization of silver powders with spheric shape and different sizes by chemical reduction of silver ions in the presence of ethanol amine using hydrochinone (C6H6O2) as the reducing agent are described. The size distribution, microstructure, and the phase composition of the obtained Ag Powders were characterized by the Laser Particle Size Analyzer, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and the X-ray diffraction (XRD). The Ag powder was in face-centered cubic crystal structure with spheric morphology. The average tap density of silver powders is up to 4.0g/cm3. It was also found that the size of the Ag particles can be adjusted conveniently to a certain degree by varying the silver ions content, the addition amount of dispersing agent, the aging time, the temperature of the reaction, and the concentration ratio of hydrochinone to Ag+.