Properties of Co-doped N-type FeSi2 processed by mechanical alloying

Iron-silicide was produced with a mechanical alloying process and consolidated through vacuum hot pressing. The as-milled powders were of metastable state and fully transformed into the ß-FeSi₂ phase through subsequent isothermal annealing. The as-consolidated iron silicides consisted of an untransformed mixture of α-Fe₂Si₅ and ?-FeSi phases and a partially transformed β-FeSi₂ phase was found in the low density compact. Isothermal annealing was carried out to induce transformation into a thermoelectric semiconducting β-FeSi₂ phase. The transformation behavior of the β-FeSi₂ was investigated utilizing DTA, SEM, and XRD analyses. Isothermal annealing at 830°C in vacuum led to a thermoelectric semiconducting β-FeSi₂ phase transformation, but some residual metallic α and ?-phases were unavoidable even after 96 hours of annealing. The iron silicide microstructures were investigated using SEM and TEM. The mechanical and thermoelectric properties of the β-FeSi₂ materials before and after isothermal annealing are characterized in this study.     

Catalytic composites based on yttria stabilized zirconia for oxidative dehydrogenation of ethane

LiCl/YSZ is found to be a very effective catalyst for the oxidative dehydrogenation of ethane. LiCl supported on YSZ-MgO composite shows increase in catalytic activity and ethylene selectivity. Addition of Mn and Sn as promoters to this system leads to 85% ethane conversion, 77% ethylene selectivity and 65% ethylene yield at 662 °C. Use of Li₂O in the place of LiCl results in lower ethylene yields. Further modification is needed to improve the catalyst stability.     

Formation of gold nanoparticles within a liquid crystalline polymeric matrix

We could prepare a novel composite consisting of a liquid crystalline polyester matrix and gold nanoparticles (7-14 nm). The polymer bears methoxy-terminated, hydrophilic, low molecular weight (350) PEG pendants on the rigid, hydrophobic aromatic polyester backbone. The polymers from a layered, sematic-like morphology at room temperature, where the interlayer is occupied by the PEG pendants. An aqueous solution of HAuCl4 was allowed to diffuse into the hydrophilic domains and the gold ions were reduced by hydrazine to gold nanoparticles. Our findings combine the concepts of self-assembly and nanoparticles, which can lead to formation of many interesting new nanocomposites.     

Direct Numerical Simulation of Turbulent Flow in a Square Duct: Analysis of Secondary Flows

A direct numerical simulation of turbulent flow in a square duct was performed for a Reynolds number based on bulk streamwise velocity and duct height equal to 4,440. The mechanism by which secondary flows are generated in a square duct was investigated. Two counterrotating secondary flows occur around the duct corner. These secondary flows were found to play a key role in momentum transfer between the corner and center of the duct. A conditional quadrant analysis was performed in the local maximum and minimum regions of the wall shear stress in order to characterize the pattern of the mean secondary flows.     

微波辐射辅助柠檬酸络合法制备的Ho3+/Tm3+/Yb3+共掺杂CaWO4的白光性能（英文）

采用微波辐射辅助柠檬酸络合法制备Ho3+/Tm3+/Yb3+共掺杂CaWO4纳米晶升频转换荧光粉。将柠檬酸络合物前驱体在300~700°C热处理3 h。Ho3+/Tm3+/Yb3+共掺杂CaWO4C在400°C时开始结晶,在600°C时结晶完成。经600°C热处理的Ho3+/Tm3+/Yb3+共掺杂CaWO4主要呈球形,且形态均匀。在980 nm的激光激发下,Ho3+/Tm3+/Yb3+共掺杂CaWO4纳米晶出现肉眼可见的明亮的白色升频转换发射,这种现象来自Tm3+的475 nm蓝光发射以及Ho3+的543 nm绿光和651 nm红光发射。通过调整Tm3+和Ho3+的浓度可以控制Ho3+/Tm3+/Yb3+共掺杂CaWO4的CIE色度图从冷到暖白色之间变化。讨论了Tm3+和Ho3+浓度对升频转换光性能的影响以及与激光泵功率相关的影响机制。     

Fabrication of Mg−Ni hydrogen storage alloys by rotation-cylinder method

For many years, the Mg−Ni alloys have been studied as good lightweight hydrogen storage materials, however, the alloys present strong difficulties in the fabrication process of mass products. The rotation-cylinder method (RCM) has been developed for magnesium based composites with moderate rotation under a normal atmosphere. In this study, the Mg-3, 6, 9, 12 mass% Ni alloys were easily manufactured by RCM and their hydrogenation properties were evaluated with a Sieverts-type automatic pressure-composition-isotherm (PCI) apparatus at 523, 573 and 623K. The evolution of the microstructure of as-cast specimens appeared to be a typical hypoeutectic structure. From the results of the backscattered electron image (BEI) and energy dispersive spectrometry (EDS), the difference between the composition of the α-Mg and Ni-rich eutectic regions was distinguished clearly. The hydrogenation properties of Mg−Ni alloys depended on the behavior of the nickel compositions. Especially, the hydrogen kinetics of Mg-9 mass% Ni was more excellent than the others.     

Structure of PPTA fibers derived directly from a liquid crystalline prepolymer dope in an organic solvent

The structure and properties of the pulp-like aromatic polyamide PPTA fibers prepared directly from a polymerization medium were studied by scanning electron microscopy (SEM), X-ray diffractometry, and polarizing light microscopy. The morphology of the fiber appears significantly different from that of Kevlar and does not reveal a skin-core structure. Regular defect bands and, thus, the regular clustering of the chain ends also could not be observed.     

Balancing charge carrier mobility by constructing chemical structures to contain both hole- and electron-transporting moieties in electroluminescent organic compounds

For the purpose of balancing charge carriers’ transport, we designed and synthesized two new compounds that are composed of both electron- and hole-transporting structural moieties: electron-transporting moieties are diaryl-1,3,4-oxadizole (Oxa) groups and hole transport moieties carbazole (Cz), or triphenylamine (TPA) moieties. The compounds formed amorphous glassy films when vacuum deposited and their glass transition temperature (T_g) was close to or higher than 150 °C. Their electronic structures (the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and E_g values) and hole and electron mobilities in the compounds were studied. A couple of compounds bearing oxadiazole moieties revealed the electron mobility greater than 1.0 × 10⁻⁴ cm²/(V s) at the electric field of 7.5 × 10⁵ V/cm. The single layer light-emitting electroluminescence (EL) devices show that the external quantum efficiencies of the devices fabricated with those compounds having balanced carrier mobilities are much higher than those of the compounds composed of predominantly hole- or electron-transporting moieties.