Advanced Materials Research Vols. 287-290

Abstract: In_xGa_1-xN epilayers have been grown by metalorganic chemical vapor deposition (MOCVD) at different temperatures between 740°C to 830°C. The thickness of InGaN film is 50nm for all samples. The incorporation of indium is found to increase with decreasing grown temperature. The optical properties and film quality of the samples have been investigated by photoluminescence (PL) system and X-ray diffraction (XRD). The Full Width at Half Maximum (FWHM) of PL and XRD decreases with increasing the grown temperature. We also found that the peak emission of PL shifts with changing the grown temperature. The effect of temperature on the film properties was determined. This understanding will lead to better quality control of the optoelectronic devices.

Abstract: The pure phase red phosphor yttrium borate doped with Eu³⁺ was prepared by a new solid state reaction named high temperature ball milling method. The phosphor was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence spectra. The results show that the single phase YBO₃:Eu³⁺ phosphor was obtained at 600°C, which is obviously decreased in contrast to conventional solid state reaction method. The particles are approximately nanometer size with narrow distribution range and spherical morphology. In emission spectra, the strongest peak at 597nm is due to the transition ⁵D₀→7F1 of Eu³⁺ ions under 394nm monitoring wavelength. The luminescent properties of YBO₃:Eu³⁺ phosphor with 25 mol% doping concentration of Eu³⁺ is optimal.

Abstract: For self-manufacture of biodiesel, the purchase cost of the feedstock is around the 70% manufacture cost, so, three kinds of the feedstock were tested & analyzed in this paper for decreasing the feedstock purchase cost for the fully developed technique of the transerification reaction with homogeneous/heterogeneous process. The other hand, the pre-treatment procedure for modulation of both acid number and iodine number is the important step for biodiesel manufacture with the feedstock of waste cooking oil (including extracted fat from cooking residue). And, the relating techniques are also developed actively in Taiwan.

Abstract: High surface area activated carbon (AC) obtained by KOH activation of petroleum coke was leached by HCl aqueous solution and the effects of the ash contents of AC on performance of electric double layer capacitors (ECs) in 3M KOH aqueous electrolyte and 1 M (C2H5)4NBF4/propylene carbonate electrolyte were investigated by cyclic chronopotentiograms and electrochemical impedance spectrometry (EIS). An equivalent circuit model based on a mixed kinetic and charge transfer control was proposed to fit EIS spectra. The model parameters were extracted by Marquardt best fitting. The series solution resistances, polarization resistance and diffusion coefficient related to Warburg impedances were obtained. It is found that the series solution resistances remained constant, polarization resistances decreased and the diffusion coefficients increased after acid leaching for each electrolyte, indicating that acid leaching can remove the electronic inert ash, which decreases contact resistance among particles of activated carbon and opens or widens the blocked pores by ash components. Moreover, the specific capacitances of AC were increased by the acid leaching.

Abstract: The precursors of LiFePO₄ were prepared by a sol-gel method using lithium acetate dehyd- rate, phosphoric acid, ferrous sulfate, and citric acid as raw materials. LiFePO₄/C cathode material was synthesized by microwave method. The effect of different microwave time on the performance of the resulting LiFePO₄/C was investigated. Structural characterization by X-ray diffraction and scann- ing electron microscopy proved that the phase LiFePO₄ was synthesized under the optimal conditions of microwave 10 min(600W), the charge-discharge performance indicated that the LiFePO₄/C had a maximal specific discharge capacity of 122.5 mAh•g^-1 (0.1C) in the first cycle and improve capacity retention. Further AC impendence measurements indicate the sample produced by microwave 10 min shows the low charge transfer resistance.

Abstract: Water lubricated bearings differ from water lubricated bearings in its special choice of material. A novelty material developed with an aim to improve the lubricating performance and bearing capacity, water lubricated bearings BTG plastic alloy is based on latex material, synthesized with different fillings, accelerators and other matters, and displays great mechanical and friction properties. In order to expand its application to the field of water lubrication, a bettered formula was adopted from the aspects of vulcanization, reinforced filling and softened plastification systems to improve its mechanical property. In the experiment, three-leveled orthogonal tests were conducted for the three systems to test the tensile strength, tearing strength, stress at definite elongation, hardness and tensile rate. The impacts of the respective systems were analyzed and the content of each component are determined to get the optimal formula. The modified bearings enjoy some mechanical properties that live up to or even exceed American military standards MIL-B-17901(Vessel).

Abstract: The paper describes a structural stability analysis of fiber reinforced 10kW composite laminate wind turbine blades by using finite element method. The E-glass/epoxy orthotropic materials DB300、DBL850、L900 were employed for construction of a composite laminate shell structure. The composite laminate sheel structures were constructed by two types of lamination method. The rotating effect of wind blade was considered using the linear and the nonlinear static analysis. The results of the nonlinear analysis of displacement and stress show much lower than the linear analysis, because of the geometry nonlinear effect. From the contours of stress and displacement, the maximum stress appeared at the root of the blade, and maximum deformation occurred at the tip of the blade. Finally, the modal properties of the wind blade was investigated, including the natural frequency, modeshaps, and the centrifugal effect.

Abstract: Novel nano-composite powders composed of hard-magnetic Mn₅₄Al₄₆ and soft-magnetic α-Fe were prepared by high-energy ball milling. The effect of α-Fe and preparation conditions on the structure and magnetic properties of the composite powders has been investigated. The ε-MnAl transforms to γ-MnAl, τ-MnAl, and β-phase under ball milling and annealing. The saturation magnetization and coercivity of the two-phase samples decrease with increasing temperature for the τ-phase decomposes at elevated temperatures. With increasing iron content, the coercivity decrease first and then increase up to 0.33 T when the Fe content is 10 wt%. Further addition of the magnetically soft iron phase would result in a decrease of the coercivity.

Abstract: An environmentally benign process was developed for the production of biodiesel from cotton-seed oil using KF loaded with MgO as a heterogeneous solid super base catalyst. The 20 wt% KF/MgO, after desiccated at 120 oC for 4 h, was found to be the optimum catalyst. Hammett indicator method, XRD, SEM and IR were employed for the catalyst characterization. The results showed the activity of the catalysts was correlated with their basicity. The influence of various reaction variables on the conversion, such as the molar ratio of methanol to cotton-seed oil, the catalyst amount, the reaction time and temperature were also discussed. When the transesterification reaction was carried out at reflux of methanol (65 oC), with a molar ratio of methanol to cotton-seed oil 12 : 1, a reaction time 2.5 h and a catalyst amount 2.5 wt%, the highest conversion of cotton-seed oil reached 99.14%.

Abstract: A novel self-powered device based on the aligned carbon nanotube arrays (CNTA) in multi-physics fields has been put forward in this paper. Synthetically utilizing the photic, fluidic and thermic properties of carbon nanotubes, the multi-physical nanogenerators (MPNG) can generate electric currents when the solar irradiation and air flow synchronously effect on the material surface. Various MPNGs are connected in series to construct a unique truncated conus and cylinder shell structure in order to enhance the output voltage for self-powered electronic devices. The multi-physical power mechanism is formed by converting the solar and air flow energy to the thermoelectric effect. By the finite element analysis, the MPNG model including a pair of p-type and n-type CNTA elements is established, and its temperature and potential distribution are simulated. This self-powered device in multi-physics fields can be applied to a more complicated environment and has a fine prospect.