Key Engineering Materials Vols. 280-283

Abstract: Europium-doped Lu2O3 nanocrystalline powders were prepared via a novel solution combustion route, with glycine as the fuel. The crystalline size and specific surface area of the combustion derived powders are strongly dependent on the glycine-to-nitrate ratio, which can control the combustion flame temperature. XRD, SEM, TEM and BET were used to characterize the phosphors and the photoluminescence was also investigated. Lu2O3:Eu3+exhibits narrow-band red emission extending from 580-700nm with a sharp peak at 611nm, corresponding to 5D0→7F2 transition of the Eu3+ ion.

Abstract: Monodispersed ZrO2 (includes 8mol % Y2O3) precursor nanoparticles, which were well dispersed in aqueous solution, were successfully synthesized. The as-synthesized ZrO2 precursor nanoparticles were homogenously coated on the surface of polystyrene particles. Multilayer coating process was successfully implemented by using polyacrylic acid (PAA) to modify the surface charges of the coated particles, which was characterized by zeta-potential, particles size distribution and scanning electron microscopy (SEM).

Abstract: The three-dimensional (3D) photonic band gap material is a material that there exists a full photonic band gap in which waves are forbidden to propagate whatever the polarization or the direction of propagation. In order to obtain photonic bandgap in lower range, we focus on the fabrication of PBG materials of diamond structure with TiO2 powder mixed with SiO2. The inverse epoxy structure with periodic diamond lattices in millimeter order has been fabricated by stereolithographic rapid prototyping. TiO2 slurry was filled into the epoxy structure and then cold isostatic pressing was applied. After sintering at 700K for 5hrs, the epoxy was burnt out and the designed structure was maintained perfectly. The calculated band diagram shows that there exists an absolute photonic band gap for all wave vectors. The measurement of transmission from 10 to 20 GHz in <100> direction shows that a complete band gap is formed at about 14.7-18.5 GHz. The magnitude of the maximum attenuation is as large as 30 dB at 17 GHz.

Abstract: ZnS and ZnSe for infrared optical windows were fabricated by particular Chemical Vapor Deposition (CVD) process with so-called S method and Se method respectively. Their morphology and defects are reported in this paper. The microstructure, composition and the influence on optical properties of the defects were investigated. The process reasons leading to these defects were discussed as well. Hot isostatic pressing (HIP) treatment was adopted to eliminate some of the defects, and the effect of HIP on optical properties was evaluated.

Abstract: Mn2+-doped Zn2SiO4 inverse opals were synthesized by sol-gel technique combined with the self-assembly of the opal template. Zn2SiO4:Mn2+ precursors were infiltrated into the interstices of the opal template assembled by polystyrene spheres. The polystyrene template was removed by calcining and nanocrystals of Mn2+-doped Zn2SiO4 were obtained in the void of opal template. The inverse opals show photonic crystal behavior and emit yellow light initially with the luminescent peak at 562 nm corresponding with the fact that β-phase is the dominant phase for nanocrystals less than 30nm. As the β-phase transformed to α-phase with the gradual increase of treating temperature and the growth of the crystal, the luminescence from Zn2SiO4:Mn2+ phosphors change from yellow to green.

Abstract: Fully transparent polycrystalline spinel(MgAl2O4)has been prepared by combined vacuum sintering and hot isostatic pressing. This paper investigated transparent polycrystalline spinel optical properties sintered in different atmospheres and discussed the effect of sintered processing parameters on the development of the microstructure and transmission properties. The optical transmittance of the specimen sintered at 1500°C following HIPed at 1800°C was nearly the same as that of single crystal spinel. The transmission properties of spinel can be improved with the increase of temperature and pressure of sintered/HIPed spinel. Specimens sintered in vacuum following HIP have higher transmittance than those sintered in air or in hydrogen.

Abstract: The first experimental work to produce transparent MgAl2O4 nano-ceramics was reported in this paper. The sintering characteristics of transparent nano-ceramics were investigated at relatively low temperature (800 ~ 1100°C) under ultrahigh pressure (2 ~ 5 GPa) using hydrostatic equipment. The morphologies and phases of ceramics were observed by means of SEM and XRD, respectively. The grain sizes of the ceramics are shown to be less than one hundred nanometers, far smaller than the sizes of common transparent ceramics. Furthermore, the higher the sintering temperature and pressure are, the greater the extent of densification is. At the same temperature, the higher the pressure is, the smaller the average grain size is. Under the same pressure, the higher the temperature is, the larger the average grain size is. The optimal sintering condition for preparing transparent nano-ceramics was also determined.

Abstract: The molybdenum powder doped with rare earth oxide was processed by powder metallurgy method and a new style thin film cathode material was firstly processed by Spark Plasma Sintering (SPS) method in this paper. The secondary emission property of such kind of cathode materials were studied, the maxim secondary emission coefficient after the material was activated at 1600°C reached to 3.84 about double that of traditional cathode materials application in magneto. The microstructure, element analysis and phase constitution of materials before and after the secondary emission property was measured were studied through SEM, EDAX and XRD. The results show that a rare earth layer about 5um thickness was created after the material was activated at 1600°C. The material grain size is about 1 um or even smaller and the distribution of elements in such materials is even.

Abstract: Preparing Superconducting Bi-2223 films by dip-coating method is innovative and valuable. The advantages of this technique are low cost and precise stoichiometric. Controlling the evaporation of Pb efficiently can improve the formation of Bi-2223 phase. Textured BSCCO superconductors are studied and a mechanism for alignment of BSCCO grains addressed.

Abstract: In this paper, NiCo2O4 spinel oxide was synthesized by the oxidation of Ni-Co alloy. The variables that affect the formation of spinel oxide include the Ni-Co ratio in the alloy, the oxidation temperature and time. 350°C is the upper oxidation temperature limit. And longer oxidation time is helpful. Surface roughness analysis shows that with the formation of NiCo2O4, the surface shows rougher.