Advanced Materials Research Vols. 295-297

Abstract: Cyclic plasticity and viscoplasticity of directionally solified superalloy, DZ125, have been described using the Chaboche unified constitutive model. A set of initial material parameters has been determined utilizing the monotonic, cyclic, relaxation and creep test data of DZ125 at 980°C, while an optimum set of material parameters has been obtained by means of least-square procedure.

Abstract: NaY_1-xTb_x(WO₄)₂ green phosphors have been synthesized by a facile combustion method. The structure, morphology and luminescence properties of as-synthesized phosphors were characterized via X-ray powder diffraction (XRD), photoluminescence spectra, and decay curve. The XRD results indicate that as-synthesized phosphors exhibit sheelite-type structure without any impurity phase. The as-obtained phosphors emit strong green light centered at 546 nm under ultraviolet light excitation. The lifetimes are about 0.57 ms. The excellent luminescence properties make it a new promising green phosphor for fluorescent lamps application.

Abstract: The wavelength of 1550nm has broad application prospect in the field of laser communications. A kind of Er-Y-Ba-Na quaternary fluoride sensitive to 1550nm was synthesized by high-temperature solid state reaction method and the synthesis conditions were optimized with orthogonal experiments. The samples present the green and red characteristic emission of Er³⁺ while the ratio of red to green emission intensity shows higher obviously compared with the representative fluoride upconversion material NaYF₄: Er,Yb. The possible physical mechanism was discussed.

Abstract: Six-ring Rock is widely used as containers of water and additives to produce health care products. In this paper, the composition and microstructure of Six-ring Rock have been investigated by using scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy, x-ray diffraction and other technologies. Results show that Six-ring Rock is composed of CaMg(CO₃)₂, SiO₂ and KAlSi₃O₈. Fe atoms exist in CaMg(CO₃)2 by replacing Mg atoms. Six-ring Rock shows nano-size lamellar and acerose microstructures on the surface, and nano-size monocrystals in the body. Six-ring Rock is a natural nano structure mineral.

Abstract: One of the most important characteristics of porous concrete is the ability to capture and transport water. The permeability of porous concrete is therefore needs to be evaluated. This paper will investigate various methods for testing the permeability of porous concrete and compares the different results from falling head and constant head tests. The hydraulic theories were then applied into the analysis to determine the permeability of the porous concrete samples.

Abstract: Interfacial behaviors of SiC fiber reinforced titanium matrix composites during thermal exposure were investigated by SEM, EDS and XRD. The effect of C coating was mainly analyzed. The results showed that C coating can be an effective barrier of the diffusion of Si element. And the C coating of SCS-6 SiC reinforced Ti6Al4V will be almost completely consumed after thermal exposure for 25 hours at 925°C. TiC will be found in the interface when the C coating exists. After C coating is completely consumed, there is Ti₃SiC₂ occurring besides TiC and the interfacial debonding strength is high. However, without the protection of C coating, the fibers will be consumed and their longitudinal tensile strength will be decreased, and this will affect the service performance of the composites.

Abstract: The infrared normal spectral emissivity of microstructured silicon prepared by femtosecond laser was measured for the middle infrared waveband at temperature range 100 to 200°C. Compared to that of flat silicon, emissivity was enhanced over the entire wavelength range. For a sample with different spike height, the minimum emissivity at a temperature of 100°C is more than 0.6. Although the average emissivity is less than Nextel- Velvet-811-21 Coating , it can be used stably at more wide temperature ranges. These results show the potential for microstructured silicon to be used as a flat blackbody source or silicon-based devices.

Abstract: Mg doped BaAl₁₂O₁₉:Mn²⁺ phosphor is one of the most efficient green phosphors for PDP. It is difficult to prepare the phosphor both have small particle size (< 3μm) and high luminescence. In the present work, a BaAl₁₂O₁₉:Mn²⁺ phosphor with small particle size was synthesized by the chemical co-precipitation method. Phase transformation and particle growth process during calcining process were investigated. The nucleation process was also discussed. The results show that, the phase transformation is complicated, the transition phases include BaCO₃, γ-Al₂O₃, BaF₂, BaAl₂O₄ and two phases contain Mn; The BaAl₁₂O₁₉ phase is formed from the reaction between BaAl₂O₄ phase and γ-Al₂O₃ phase, no a-Al₂O₃ phase appears during the entire process; The formation temperature of pure BaAl₁₂O₁₉ phase is 1200°C, which is lower than that in the high-temperature solid state reaction method. High efficiency BaAl₁₂O₁₉:Mn²⁺ phosphor with small particle size (< 2μm) and hexagonal flaky shape can be prepared by this method.

Abstract: The corrosion resistance of bainitic steel was compared with a weathering steel 09CuPCrNi through accelerated corrosion tests. The results indicated that the corrosion resistance was better for bainitic steel than 09CuPCrNi based on the weight loss. The characteristics of the rust layers indicated the rust layers on two steels are composed of two parts: the loose outer rust layer and the dense inner rust layer. The rust layers are mainly composed of goethite (α-FeOOH) with a few of lepidocrocite (γ-FeOOH). The factors including homogeneous microstructure and lower carbon content played important roles in enhancing the corrosion resistance of bainitic steel.

Abstract: Uniform and well-dispersed photoluminescent semiconductor CdSe(Cadmium selenium) QDs(Quantum dots) were in-situ prepared stabilized by G4.0-NH₂ PAMAM dendrimers in water and effects of metallic ions such as Zn²⁺, Cd²⁺, Cu²⁺, Ag⁺, Pb²⁺, K⁺, Na⁺ on the photoluminescence(PL) properties of CdSe QDs were studied using spectrophotometric titration. The results show that Zn²⁺ and Cd²⁺ ions enhance the PL intensity of CdSe QDs, Cu²⁺, Ag⁺ and Pb²⁺ ions quench the PL intensity, while K⁺ and Na⁺ ions have no obvious effects. Those are attributed to the surface modification of CdSe QDs. Excess Cd²⁺ ions can reduce the non-combination centers, increase the passivation of PAMAM on the surface of CdSe QDs, and form a Schottky-like barrier which enhanced the PL efficiency. Excess Zn²⁺ ions can also increase the PL intensity of CdSe QDs in the same way as Cd²⁺ ions because of the much similar lattice parameters of CdSe and ZnSe. However, a CuSe, Ag₂Se or PbSe shell on CdSe QDs emerges due to the substitution of Cd²⁺ ions, which leads to the decrease of band-edge emmiting of CdSe QDs. And the quenching effect of Ag⁺ is stonger than Cu²⁺ and Pb²⁺ because of the lower solubility of Ag₂Se formed on the surface of CdSe QDs. Oil latent fingerprints deposited on tinfoil surface treated with CdSe/dendrimer NCs(Nanocomposites)、Cd²⁺-CdSe/ PAMAM NCs and Zn²⁺-CdSe /PAMAM NCs emitted bright yellow photoluminescence under ultraviolet excitation of 365nm from an UV LED in the dark., among, fingerprint treated with Cd²⁺-CdSe/dendrimer NCs and Zn²⁺-CdSe /PAMAM NCs was detected with better resolving rate.