Key Engineering Materials Vols. 368-372

Abstract: A refined coal tar pitch with softening point of 33oC was obtained by a mixed solvent extraction method. The pitch was carbonized at 500oC to get micrometer carbon material with needlelike structure. The carbonized produce was further calcined at 1500oC for 30h. The resultant product was characterized by SEM, OM, EDS and XRD. Experimental results indicated that a mixed solvent extraction method could effectively get rid of primary quinoline insoluble (QI). SEM and OM examinations showed that there were more than 70% fibrous structures and a small amount mosaic structures. The size of the fibrous structure was greater than 150μm in length and less than 30μm in width. The result of EDS exhibited that the material mainly consisted of carbon. XRD analysis revealed that there was a sharp diffraction peaks at 26.5oC, which was corresponded to the (002) plane of graphite structure.

Abstract: In this paper, the sintering behavior of Ni/YSZ anode and YSZ electrolytes fabricated by aqueous tape casting were studied. This study involved tape casing of Ni/YSZ (8 mol% Y2O3 stabilized ZrO2) anode, and co-sintering of anode supports and electrolytes. At last, thickness of 140 mm (after sintering) with uniform microstructure and ~30% porosity anode and thickness of ~10 0m (after sintering) with high density (> 95%) and electrolyte were achieved.

Abstract: The manufacture of the electrolyte film is crucial for the fabrication of solid oxide fuel cells (SOFCs). This paper reviews the main methods for fabricating the electrolyte film, which are generally classified as chemical methods, physical methods and ceramic molding methods. The characteristics of each method and its application are discussed.

Abstract: The rate capability of 18650 lithium-ion cells was studied in the paper. The experimental results showed that the reversible capacity declined to 89.5, 85.8 and 81.2% of the initial capacity after 300 cycles at discharge rate of 0.5, 1 and 2C, respectively. The XRD and SAED analysis indicated that at a high current density partial positive electrode material LiCoO2 transformed gradually from well-layered structure to rock salt cubic crystal. Upon the cycling, the degradation of cathode materials’ structure and much thicker negative film on anode electrode surface contributed to the rate capability fade.

Abstract: Spinel LiMn2O4 powders were prepared by solution combustion synthesis using nitrate and acetate salts as raw materials and urea as fuel. The phase composition of as-synthesized powders was identified by XRD and the microscopic structure was examined by SEM. Single-phase spinel LiMn2O4 was prepared when acetate salts were used, and the incorporation of nitrate salts resulted in the formation of Mn2O3. The products consisted of slight agglomerations of fine particles with the size of 50-200nm. It was found that the addition of nitrate salts increased the reaction rate and the yield of LiMn2O4 was depressed when more nitrate salts were used as a reactant.

Abstract: Spinel LiMn2O4 was prepared by solution combustion synthesis. The effect of fuel content and calcination procedure on phase composition and microscopic structure of LiMn2O4 was studied. X-ray diffraction patterns showed that fuel content had no obvious influence on the grain size and phase purity of LiMn2O4. Higher calcination temperature led to higher phase purity, lager grain size, and better crystallization of resultant LiMn2O4. Below 600°C the effect of calcination time was inconspicuous, which became notable above 700°C. Scanning electron microscope images showed that nanocrystalline LiMn2O4 was obtained when the calcination temperature was lower than 600°C and the grain size increased at higher temperatures.

Abstract: Well-crystallized LiFePO4 cathode materials were synthesized by NaCl-KCl molten salt method. The effect of heating time on the structure, morphology and electrochemical properties of the materials were studied in detail. Single olivine-type LiFePO4 phase was obtained, and the morphology and particle size of the powders could be controlled by changing the synthesis conditions. It was shown that LiFePO4 cathode material synthesized at 680°C for 3h with the salt content N=2 (defining the molar ratio of NaCl-KCl/LiFePO4 as N) had a narrow particle-size distribution and spherical or quasi-spherical shape. Meanwhile, the tap density of the cathode material reached the maximum of 1.501gcm-3. The charge-discharge test indicated that the initial charge and discharge specific capacity reached 138mAhg-1 and 125mAhg-1 respectively at the current density of 0.3mAcm-2.

Abstract: In this study, K3Li2-xNb5+xO15+2x (KLN) thin films were prepared by laser-ablated a sintered ceramic target. For an optimum deposition condition, in-situ post annealing method was employed on as-deposited films. XRD measurements showed that KLN films with (310) preferred orientation were obtained on fused quartz substrate. Surface morphology studies indicated that in-situ post annealing could improve the surface quality of KLN thin films. The average transmittance of as-deposited and annealed films in the visible range was nearly 80% to 90%.

Abstract: SrBi2Nb2O9 (SBN) thin films were prepared on fused quartz substrates at room temperature by pulsed laser deposition. The crystallization behavior and surface morphology were studied at various oxygen pressures by XRD and AFM. The results indicated that the films had polycrystalline structure with a single layered perovskite phase, and exhibited higher crystalline quality, less rough surface morphology, and larger grain size with increasing oxygen pressure. The optical transmittance of the samples was measured in the wavelength range 200-900 nm, and the dispersion relation of refractive indices and wavelength was found to follow the single electron oscillation model. The energy gap of SBN films grown at oxygen pressure of 5 Pa was estimated to be around 3.88 eV by assuming a direct transition between valence and conduction bands.

Abstract: High-quality In2O3 powder and ZnO powder had been used to make the ceramic target and the atomic ratio of 1 to 1 of indium and zinc had been prepared in this study. The alloyed thin films had been deposited on sapphire (001) substrates at different temperatures (100–600°C) by using pulsed laser deposition (PLD) technique. An x-ray diffractometer and an atomic force microscope were used to investigate the structural and morphological properties of the alloyed thin films. It was observed that the alloyed thin films deposited at the temperatures lower than 300°C were amorphous, and the alloyed thin films deposited at high temperatures were crystallized. A spectrophotometer was used to investigate the transmittances of the alloyed thin films. It was found that the alloyed thin films were of high quality. The band gap energies of the alloys were calculated by linear fitting the sharp absorption edges of the transmittance spectra. The Hall measurements were also carried out to identify the electrical properties of the thin films.