High-Performance Ceramics III

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Authors: Hong Jie Zhao, Ji Zhou, Zhi Lun Gui, Long Tu Li
Abstract: The low temperature sinterability and magnetic properties of Bi-substituted yttrium iron garnet (YIG) polycrystalline samples were studied in this paper. The results showed that Bi-substitution can lower garnet phase formation temperature from about 1200oC to 900oC and ceramic sintering temperature from over 1300oC to about 1050oC respectively. The Bi-substitution leads to a decrease in initial permeability and an increase in ferromagnetic resonance linewidth (ΔH) of sintered specimens. Saturation magnetization decreases and coercive force increases a few with an increase of Bi content. The mechanism of Bi-substitution on initial permeability and ΔH is discussed. The change in initial permeability of Bi-substituted specimens relative to unsubstituted YIG results from Bismuth volatilization and weakening of superexchange interaction. The lattice dilatation in Bi-substituted YIG gives cause for a decrease of saturation magnetization and an increase of coactivity force.
481
Authors: Yu Hong Zhao, Jia Chen Liu, Shun Li, Yi Rong Liu
Abstract: To meet the need of optical fiber photoreactor designed by mechanism of TiO2 photocatalysis, nanometer TiO2 was coated on the surface of optical fiber by dipping nude fibers into an Al(H2PO4)3-contained TiO2 slurry. Effects of slurry conditions, including content of TiO2 and addition of Al(H2PO4)3 adhesive, on coating thickness and quality were determined. Coating process, especially the effect of coating times, was also concerned. Based on the experimental results, fitting slurry conditions and process parameters were suggested for obtaining high-quality TiO2 coating on optical fiber surface.
485
Authors: Qing Li Ren, Qiang Luo, Wei Chen
Abstract: The highly pure acicular nanosize Mg,Al-hydrotalcite was synthesized by the one-step liquid reaction method at atmospheric pressure. The favorable growth unit in the reaction liquid, the requirements of Al3+ entering the Mg2+-(OH-)6 octahedral and forming the growth unit M-(OH-1)6 (M=Mg2+, Al3+) and growth mechanism that the nanosize Mg,Al-hydrotalcite crystal embryo follows are studied according to the test results of XRD, TEM, SEM and IR. Later, that the nanosize Mg,Alhydrotalcite crystal embryo growth follows the gathering growth theory was deeply investigated.
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Authors: Qiang Luo, Qing Li Ren
Abstract: A prediction model for purity of the artificial synthetic hydrotalcite under varied process parameters based on improved artificial back-propagation (BP) neural networks is developed. And the non-linear relationship between the hydrotalcite purity and the raw material adding amount of NaOH, MgCl2 and AlCl3 was established based on BP learning algorithm analysis and convergence improvement. The hydrotalcite purity can be predicted by means of the trained neural net. Thus, by virtue of the prediction model, the future hydrotalcite purity can be evaluated under random complicated raw material amounts. Moreover, the best processing technology is optimized using the genetic algorithm.
495
Authors: Sung En Lin, Wen Cheng J. Wei
Abstract: Monodispersive and uniform particles have many potential applications. The objectives of this study are trying to synthesize and control the morphology of monodispersive indium oxide (In2O3)particles through hydrothermal process with the help of PVP (polyvinylpyrrolidone) and urea additions. Various cubic, ellipse, or shuttle-like In2O3 particles were synthesized by using hydrothermal conditions (65-85oC). The effects of Sr nitrate were studied. Spherical particles could not be synthesized. The aspect ratio of the In2O3 particle reduced as the concentration of Sr nitrate increased. Crystalline In2O3 phase appeared above 300oC.
499
Authors: Bin Qiao, Zi Long Tang, Zhong Tai Zhang, Rui Long Zong
Abstract: In this article, the anodic aluminum oxide (AAO) was prepared by two-step anodizing process in oxalic acid electrolyte. And a blue-emission of AAO itself attributed to the oxalate was observed. The AAO membrane with ordered nano-sized porous structure was an important membrane to produce nano-materials. And luminescent nano-particles embedded in AAO, such as ZnO in this article, possessed notably special performances which were due to the quantum size effect and the special environment provided by the nano-pores. Since AAO membranes possessed a unique structure, in this paper, an assumption about the application of the membrane in field emission display (FED) and electroluminescence (EL) was proposed.
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Authors: Jun Ping Yan, Zi Long Tang, Shao Hua Luo, Zhong Tai Zhang
Abstract: In order to improve water resistance of phosphors and the stability of particles in aqueous suspensions, the phosphor particles were coated with varying amounts of silica via the hydrolysis of tetraethyl orthosilicate. The composite particles were characterized by transmission electron spectroscopy, BET N2 gas adsorption, sedimentation time studies and fluorescent spectrometer. The specific surface area of the silica-coated phosphor particles showed a non-systematic increase. In comparison to the uncoated phosphor (3.65m2/g), silica coatings of 13, 25, 50, 75wt% yielded specific surface areas of 15.19, 14.29, 37.90 and 226.12 m2/g respectively. This behavior can be explained based on a heterocoagulation coating mechanism in which silica clusters adsorb onto the phosphor particles surface. The sedimentation data display the stability of the coated particles improved as the silica content increased. The excitation and emission spectra show that the luminescent properties of the phosphors are unimpaired or even better. The optimum luminescent properties obtained when coating 50wt% silica after calcining at 400oC.
509
Authors: Ji Yang Chen, Ying Shi, Jian Lin Shi
Abstract: Eu3+ doped Y2O3 nanopowder was prepared by a novel complex precipitation process in which the mixture of ammonium water and ammonium hydrogen carbonate was adopted as complex precipitant. The precipitant precursor and the resultant powder were characterized by FT-IR, XRD, SEM and TEM. The resultant weakly agglomerate and spherical particles have a uniform grain size about 20nm after calcined at 850°C for 2 hours. 3mol% Eu3+ doped Y2O3 nanopowder shows an intense red luminescence at 612nm under UV excitation.
513
Authors: Min Liu, Sheng Wu Wang, Jian Zhang, Li Qiong An, Li Dong Chen
Abstract: Y2.85Er0.15Al5O3 was prepared by combustion process. Phase evolution of the synthesized powders was determined by XRD. Single-phase cubic YAG: Er3+ crystalline powders were obtained by calcining the combusted product at 1000°C and no intermidiate phase was observed. SEM morphology showed that the resultant YAG: Er3+ powders were porous. Upconversion emission spectra were measured on the powder compact pumped by a 980nm continuous wave diode laser. The relationship between pump power and luminescence intensity suggested that a two-photon process is active in this sample. The upconversion machanism of YAG: Er3+ system was also discussed.
517
Authors: Li Qiong An, Jian Zhang, Min Liu, Sheng Wu Wang
Abstract: Yb3+ and Ho3+ co-doped Lu2O3 nanocrystalline powders were synthesized by a reversestrike co-precipitation method. The as-prepared powders were examined by the X-ray diffraction and transmission electron microscopy. The phase composition of the powders was cubic and the particle size was in the range of 30~50 nm. Emission and excitation spectra of the powders were measured by a spectrofluorometer and the possible upconversion luminescence mechanism was also discussed.
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