Advanced Materials Research Vols. 622-623

Abstract: Thin films thermoelectric module fabricated by pulsed-dc magnetron sputtering system using Ca₃Co₄O₉ (p-type) and ZnO (n-type) targets of 60 mm diameter and 2.5 mm thickness, which were made from powder precursor, and obtained by solid state reaction. Thin films of p-Ca-Co-O (Seebeck coefficient = 143.85 µV/K, electrical resistivity = 4.80 mΩm, power factor = 4.31 µW/m K²) and n-ZnO (Seebeck coefficient =229.24 µV/K, electrical resistivity = 5.93 mΩm, power factor = 8.86 µW/m K²) were used to make a thermoelectric module, which consist of four pairs of legs connected by copper electrodes (0.5 mm thickness, 3.0 mm width, and 3.0-8.0 mm length). Each leg is 3.0 mm width, 20.0 mm length, and 0.44 µm thickness on a glass substrate of 1.0 mm thickness in dimension 25.0x50.0 mm². For preliminary test, a module was used to thermoelectric power generation. It was found that the open circuit voltage increased with increasing temperature difference from 3 mV at 5 K up to 20 mV at 78 K. The internal resistance of a module reached a value of 14.52 MΩ. This test indicated that a module can be generated the electrical power. Therefore, it can be used as an important platform for further thin films thermoelectric module research.

Abstract: The equilibrium structures of orthorhombic LaCrO₃ (O-LaCrO₃) and rhombohedral LaCrO₃ (R-LaCrO₃) crystals were investigated by using the plane-wave self consistent field (PWSCF) method based on density functional theory (DFT). The optimized lattice parameters for both phases are in accordance with experimental results reported in literature, confirming the reliability of LSDA+U scheme used in the calculations. We have quantificationally investigated the binding energies and electronic properties of these two types of LaCrO₃ crystals. The negative total energy and binding energies indicate the ground state property and the good structrual stability of O-LaCrO₃ crystal, which is important for the preparation of nano materials, the synthesis of ceramic materials made of doped O-LaCrO₃ crytals, as well as their applications in high technology fields, and predict the metastable property of R-LaCrO₃ crystal. Furthermore, the band structures show that O-LaCrO₃ is a direct semiconductor with wide energy gap, while R-LaCrO₃ is an indirect semiconductor with narrow energy gap. The interaction between Cr and O atoms in O-LaCrO₃ crystal possesses the character of covalent bonding.

Abstract: The present investigation deals with the damage behavior of composite tube with pinned-joint holes made by filament winding technique. The pin-loaded holes are tailored to fail mainly with bearing mode. The main objective of the paper is to investigate the stress state and damage behavior of pin-loaded holes made by filament winding. The failure load and the failure mode are analyzed numerically and experimentally. A good agreement between experimental results and numerical predictions is obtained.

Abstract: The paper first introduced the method of analyzing the micro-structural morphology, then with assistance of image processing techniques and a second-order intensity function, simulated the two-phase composite micro-structure and selected its RVE. By an object function based on the second-order intensity function and using genetic algorithm, the RVE of original composite microstructure was created and its elastic moduli were analyzed. Numerical calculations showed that the represent volume element can well represent the original composite microstructure.

Abstract: This paper investigates the interaction between the convective flow induced by the straining flow and the interface morphology of a particle growing in the convective undercooled melt. The resulting approximate solution of the particle shape shows that the convection makes the growing particle enhance its growth velocity and protrude near the surface where the flow is incoming, but decreases its growth near the surface where the flow is outgoing, and both the incoming flow and the anisotropic surface tension make the velocity of the particle have a superposition effect along the favorite crystalline direction. The convection makes the particles growing in the undercooled melt evolve into various shapes of the interface morphology which have high strength/weight ratio and specific surface fraction and then help to form the final material of excellent mechanical and physical properties.

Abstract: Pure and doped Zinc Sulfide (ZnS) quantum dots have attracted increasing interest from researchers working on various scientific and engineering applications in electronics, nonlinear optical devices for communication, and optical computers. In this study, ZnS nanoparticles doped with lanthanum (ZnS:La) with approximately 11 nm size was produced at 150°C by chemical precipitation route. Zinc Sulphide is an extensively studied group II-VI semiconductor with wide application in field of Photo Luminescence (PL),Electro Luminescence(EL) and Cathodo Luminescence (CL). It is an excellent light transmission material with high refractive index 2.27. XRD, SEM, FTIR UV-Vis and EDS characterize the samples.In this study, the UV–Visible absorption spectra of ZnS:La showed a red shift in the absorption shoulder compared with the spectra of undoped samples. ZnS nanoparticles could be doped with lanthanum ions during synthesis without altering the X-ray diffraction (XRD) patterns of ZnS. Also, the XRD pattern of the powders showed cubic crystal structures for ZnS:La. The Optical band gap has been found to be 2.7 eV. It was found that energy Band gap Eg decreases with doping of La.

Abstract: A supported Pd(II)/biguanide complex on ordered mesoporous SBA-15 material (Pd@SBA-15/Met) exhibited catalytic activity in the cross-coupling reaction. The structural and surface characteristics of the prepared catalysts were investigated by various techniques (XRD, SEM, FT-IR and AAS). The catalytic performance of the catalysts was evaluated in Suzuki-Miyaura coupling reaction and it was proved to act as a recoverable catalyst in green media with excellent reactivity combined with recyclability.

Abstract: The mechanical properties of hydroxyapatite ceramics was improved by adding 5 wt% of Ca-P-Na-based-glass to be as sintering aid and were made their powder to submicron sized. The powders are uniaxially compact and then sintering at 1300°C in air.Microstructure and mechanical properties of the ceramic composite products were investigated. It was found that the strength of hydroxyapatite composite was increased about 42% that of the sample which fabricated by micron sized HA composite powder having the same porosity and this values are in rang of values of the strength of the cortical human bone. Moreover, Young modulus values of 16.4 1.8 GPa matched well with the Young modulus values of human bone, so it will not cause interfacial stress between implant and bone leading to good fixation of the materials.

Abstract: La-doped Pb(Mg1/3Nb2/3)0.67Ti0.33O3 ceramics were fabricated by a two-stage sintering method from conventional raw materials. The effects of La doping on the phase structure and electrical properties of ceramics were investigated. X-ray diffraction analysis showed that the pyrochlore phase increased with the increase of La-doping level. The effects of La doping on the dielectric, ferroelectric and piezoelectric properties of the ceramics were also investigated. The results showed that La doping seriously weakened the electrical properties of the ceramics. The ceramics possess optimum properties (d33=239pC/N, Pr=10.6μC/cm2, Ec=8.5kV/cm, tanδ=0.029, εr = 2250) when the doping level is low (x = 0.02).

Abstract: In this paper, the early hydration procedure of standard cement materials is tested and analysized with electrodeless resistivity method. The experimental results show that for standard cement material, the early hydration procedure can be divided into 4 stages: dissolution period, setting period, acceleration period and deceleration period, respectively. Moreover, the characteristic point according the experimental data can be defined to determined stage in the hydration procedure, and be related with the key parameters for cement materials in hydration procedure, such as water/cement ratio. The electrodeless resistivity method can be used to predict the hydration behavior, especially early hydration behavior of cement as a new measurement technology.