Materials Science Forum Vols. 544-545

Abstract: The cycle behavior and rate performance of C-LiFePO4/SPE/Li cell have been investigated at 25 °C. Carbon coated LiFePO4 (C-LiFePO4) was employed as cathode and 25PVDFLiClO4EC10PC10 was used as solid polymer electrolyte (SPE). The C-LiFePO4/SPE/Li cell exhibited above 140 mAh/g of discharge capacity at 0.1 mA/cm2 and excellent reversible cyclability with a stable capacity on cycling. In addition, the discharge capacity of C-LiFePO4/SPE/Li cell was 150 mAh/g at 0.1 C (0.02 mA/cm2) and 130 mAh/g at 1 C (0.2 mA/cm2), respectively.

Abstract: Al2O3 and TiO2 were sintered with three types (lead, zinc, bismuth) of borosilicate glass. Their microwave dielectric properties and sintering behavior were investigated as functions of glass type, glass addition (10~50 vol%) and sintering temperature (600~950°C for 2 hrs). Sintering characteristics were well described in terms of softening temperature, second phase, and excessive liquid. In particular, Bi2O3 addition to the glass enhanced reaction with Al2O3 and TiO2 to form liquid phase and second phase. In terms of dielectric properties glass/Al2O3 composites for application to substrates while glass/TiO2 composites for filters were shown to be appropriate.

Abstract: The proper control of total impurities and oxygen contents of oxygen-free high conductivity (OFHC) copper prepared by vacuum high-frequency melting technique was studied using Mahalanobis-Distance (MD) outlier detection method as functions of raw material purities, vacuum pressure, melting temperature and holding time. The properties of vacuum-melted OFHC copper was examined by thermo-gravimetric analysis, differential scanning calorimetry, hardness test, macro and optical microstructure analyses and ultimate tensile test. In multivariate systems, the existence of outlier makes it difficult to analyze the system and oultier detection belongs to the most important tasks in experimental data analysis. Mahalanobis Distance is most commonly used as a diagnosis of existance of outlier in multivariate system. The relationship between experiment conditions and total impurities and oxygen contents can be defined with the regression analysis results. At this research, our desirable manufacturing conditions is to obtain the total impurities under 40 ppm and oxygen contents under 5 ppm. After this statistical approach, the suggested minimum maufacturing conditions are the purity of raw material was 4N, vacuum pressure was 10-1 torr, melting temperature was 1150°C and melt holding time was 20 minutes.

Abstract: La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) -based honeycomb cell was first time successfully built and operated in the case of single-wall used condition and the full 4-walls cell one. Power generation characteristic of this honeycomb cell was measured from 700°C to 900°C by using various electrochemical techniques including polarization, current interruption and impedance spectrometry. The LSGM honeycomb cell shows the exact high power density compared with the ZrO2 based cell at the operating temperature range, and its value is 394 and 252 mW/cm2 at 800°C and 700°C, respectively. Thermal stability of this honeycomb cell is also studied and it is seen that the good performance through several times thermal cycling is observed. The 4-walls’s cell stack is successfully working at 800°C, and the volumetric power density is achieved to a value of about 700 mW/cm3.

Abstract: Iron, sulfur and transition metal powders were used as the starting materials to prepare iron disulfide (FeS2) cathode material at room temperature by high energy mechanical alloying. Modified FeS2 were also prepared by incorporation of transition metals like Co and Ni. Li/FeS2 cells with the prepared iron disulfides as cathodes were studied for discharge properties at room temperature using the 0.5M LiTFSI in tetra(ethylene glycol) dimethyl ether (TEGDME). The first discharge capacities of Li/composite FeS2 cell with 5 wt.% Co and 3 wt.% Ni were 571 and 844 mAh/g, respectively, compared to 389 mAh/g for the cell without any additive. The enhanced properties resulted from the better electronic conductivity of the material containing the metallic additive. The initial capacity and cyclic performance were improved when nickel and cobalt were added to prepare the modified iron disulfide.

Abstract: Electrorheological (ER) particles were obtained by the adsorption of multiwalled carbon nanotubes (MWCNT) on the surface of silk fibroin microspheres. The resulting spherical polymeric microspheres consist of a silk fibroin core and an MWCNT shell, which is electrically conducting. The silk fibroin microspheres were prepared by the phase separation of the silk fibroin and poly(ethylene oxide) (PEO) blend solution, and the MWCNT dispersion was prepared by ultrasonication with cetyltrimethylammonium bromide (CTAB) surfactant. The ER particles were prepared using a simple process involving the blending of the silk fibroin microsphere suspension and aqueous MWCNT dispersion. The morphology of the ER particles was examined by field emission scanning electron microscopy (FESEM) and their electrical conductivity measured by the four-probe method was 4.8×10-4 S/cm. The prepared composite microspheres suspended in silicone oil showed typical ER characteristics, including the formation of a chain-like structure under an applied electric field (1.9 kV/mm). This phenomenon can be explained by the interfacial polarizability of the MWCNTs adsorbed on the surface of the polymeric microspheres.

Abstract: Bone healing and growth are controlled by the rate of deposition of hidroxiapatite (HA). This process have been so far accredited to the work of osteoblasts, which are attracted by the electrical dipoles produced either by piezoelectricity, due to deformation of the bone, specially the collagen in it, or due to outside electrical stimuli. The present work shows that even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen, can produce the precipitation of HA by electrochemical means, without catalyzer as in biomimetic deposition. These findings could clarify the contribution of osteoblasts in bone growth as compared to the electrochemical action by itself. Further studies ascertaining the osteoblastic activity due to the electric field are being advanced.

Abstract: Gd-doped ceria electrolyte (Ce0.8Gd0.2O1.9, GDC, 700 μm thick), 30 vol% Ni-GDC cermet anode and perovskite cathode La0.6Sr0.4CoO3 (LSC) or La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) were used to evaluate the electric power of the cell using 3 vol%-H2O containing H2 fuel at 873 and 1073 K. Terminal voltage, ohmic resistance and overpotential were analyzed during the operation of the cell. The maximum power density with LSC and LSCF cathode was 53 and 113 mW/cm2 at 1073 K, respectively. The ohmic resistance and overpotential at the cathode was smaller for LSCF than for LSC.

Abstract: Five oxidized metallic alloys, namely, Crofer22, equivalent ZMG232, stainless steel SS430, SS304 and Inconel718 were subjected to oxidation treatment in hot air environment for various period of time. Then the resulted oxide scale was analyzed by scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and X-ray diffraction (XRD). All the five alloys contain comparable amount of Cr, Mn, Fe, and their surface oxides as analyzed indicate to be Cr2O3 and (Mn, Fe)Cr2O4 spinel compound.

Abstract: An experimental study is carried out to investigate the performance and the practical application of polymer electrolyte membrane fuel cell(PEMFC) with the double-tied catalyst layers in a Membrane Electrolyte Assembly (MEA). Characteristics of PEMFC depend highly on the conditions such as gas pressure, temperature, thickness, supplied oxidant type (Oxygen/Air) as well as humidification. They are controlled under the same condition for the comparison of the simulation. Testing condition is fixed at 60sccm and 70°C in anode and cathode, respectively. The humidification about 15% the performance is improved no humidification rather. The current density is increased around 20% significantly when pure oxygen gas is provided as an oxidant. It is found that measured values of unit cell voltage and current are influenced strongly by the type and amount of oxidant, which give more enhanced values in case of oxygen compared to the ambient air as oxidant.