Advanced Materials Research Vols. 287-290

Abstract: Unburned carbon is an industrial waste product of oil-fired fly ash. Recycled ground unburned carbon with an average particle size of 5 μm after heat treatment at 2500°C displayed an first coulombic efficiency of approximately 89.8% at a charge and discharge rate of 0.1 C. The discharging capacity of this type of carbon was 293.7 mAhg^-1, and its capacity retention was approximately 94.7% after 50 cycles. However, the first coulombic efficiency of ground unburned carbon receiving nitric acid treatment after heat treatment increased to 91.1%, its discharging capacity increased to 318.6 mAhg^-1, and its capacity retention increased to 98.5% after 50 cycles. Rate capability tests show that the unburned carbon after heat treatment exhibited a higher capacity in the lower C-rate region (0.2~3 C) at a 0.2 C rate charge and variable C-rates discharge. However, unburned carbon with nitric acid treatment is a suitable material for the higher C-rate region (5~10 C). Unburned carbon after heat treatment exhibited a higher capacity in the lower C-rate region (0.2~0.5 C) at the same C-rate charge and discharge.

Abstract: LiFePO₄/C was synthesized from a gel precursor with ferric iron and an organic chelating agent as carbon source. Reductive atmosphere of N₂ + H₂ with H₂ content of 0-20 vol % was used in the sintering process of LiFePO₄/C composites. The microstructures of the obtained LiFePO₄/C particles were characterized by X-ray diffraction, field emission scanning electron microscopy, element analysis and particle size analysis. The results showed that suitable reductive sintering atmosphere was needed to get pure LiFePO₄/C phase, but too strong reducibility led to the formation of iron phosphides, most of which was Fe₂P. The amount of Fe₂P increased with the increase of H₂ content in the sintering atmosphere. The rate capability of LiFePO₄/C was improved when the sintering atmosphere became more reductive, while the discharge capacity of 0.1C decreased, which was probably due to the appearance of Fe₂P phase.

Abstract: The Mn-Cl co-doped LiFePO₄ was succefully synthetized by two-step solid-state reaction. After doping, the Lattice constants shifted while the morphology changed only little, revealing that the properties may not be improved by the slight changed grain size but the crystal structure. The co-doped sample presented a high discharge capacity of 161.1mAhg−1 at 0.1C, 157.7mAhg−1 at 0.5C, 149.1mAhg−1 at 1C, nearly 30mAhg−1 higher than that of the pristine LiFePO₄/C respectively. The electrochemical reversibility and cycle stability of co-doped LiFePO₄/C were enhanced. Moreover, the Li⁺ diffusion and exchange current density of that was increased after doped with Mn²⁺ and Cl^- .

Abstract: LiFePO₄/C cathode material with different carbon sources was synthesized by using a two-step carbothermal reduction method. The structure and electrochemical properties of the samples were characterized by XRD, SEM and galvano-static charge-discharge method. The effect of different carbon sources on the structure, morphology and its electrochemical properties of the LiFePO₄/C composite materials were investigated. The results showed that the properties of the samples depended on carbon sources, significantly. The sample synthesized by citric acid as carbon source had the best electrochemical performance. The reason of performance difference of the LiFePO₄/C composite materials caused by carbon source was discussed.

Abstract: Pyrite nano-powder was synthetized in a high-pressure solvothermal process in the ethanediol solvent, with Fe(NO₃)₃·9H₂O and NH₂CSNH₂ as the raw materials. The sample was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the results show that the product has a pure phase in a typical cubic crystal. The effects of temperature, aging time and surfactant on the shape of the crystallites were investigated systematically. The nano-powder synthetized shows itself in various micro-shapes such as granule, globular and flake, with its diameter ranging from hundreds of nanometers to one micrometer.

Abstract: The aqueous solution polymerization methods were used for the synthesis of superabsorbent resin. The effects of different experimental factors on synthetic resin water absorbency were investigated in this paper. The variables examined in this study included monomer concentration, neutralization degree, initiator and crosslinker concentration, reaction temperature and time, etc. The maximum absorbencies of distilled and 0.9% saline water are 919 times and 92 times respectively under optimum condition. Analysis from FTIR and SEM shown the polymer molecules can be firmly fixed with kaolin, the bonding of kaolin and polymer is good in CSR.

Abstract: To enhance the mechanical strength of hydroxyapatite (HAP), a nano-HAP/β-sheet fibroin (nano-HAP/SF) composite was synthesized by mixing nano-HAP sols with SF sols. A β-sheet structural SF was prepared by a salt-resolving method. The nano-HAP sols was prepared by a co-precipitation method. The phase composition of HAP and nano-HAP/SF composites were investigated by X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). Their morphologies were observed by scanning electron microscopy. The mechanical strength of the nano-HAP/SF composite was measured by a universal material detector. The bioactivity and biocompatibility of the obtained composites were confirmed by tests in simulated body fluid (SBF) and by a culture of rat osteoblasts cell. Results showed that the obtained SF is a typical silk II with β-sheet conformation. The FTIR spectra analysis indicated that the chemical bonds were formed between SF and HAP in the nano-HAP/SF. The result of SBF test demonstrated that the needle-like crystals of HAP were formed on the surface of the sample and the result of cell culture showed that the rat osteoblasts grown and reproduced well on the surface of the composite. The compression strength of SP/HAP reached 63 MPa.

Abstract: A new type of chemically cross-linked polymer blend membranes consisting of poly(vinyl alcohol) (PVA) and quaterized hydroxyethylcellulose ethoxylate (QHECE) have been prepared and evaluated as OH^--conducting polymer electrolytes. The OH^--conductivity (s) of the membranes was investigated as a function of cross-linking time, blending composition and water uptake. Membrane swelling decreased with cross-linking time, accompanied by an improvement in mechanical properties and a small decrease in OH^--conductivity due to the reduced water absorption. The OH^--conductivities in the range of 2.7 ×10^-4－1.52 ×10^-3 S cm^-1 were obtained at room temperature (19±2°C), depending on the polymer composition and the content of cross-linking agent. TG analysis showed that the membranes exhibited the thermal stability high up to 350°C when incorporating 75% QHECE. In addition, the membranes displayed a high alkaline stability without losing their integrity and OH^--conductivity after conditioning in 6M KOH at 60°C for one week.

Abstract: In this paper, the crystal structure and hydrogen storage properties of the sodium hydride at different x value (NaH_xD_1-x, NaH_xT_1-x, NaD_xT_1-x; x=0, 0.25, 0.5, 0.75, 1.0) are investigated by using density functional theory within the generalized gradient approximation (GGA). The calculated results of NaH (D, T) are in good agreement with the other theoretical results. It has been found that, densities decreased with the increase of x value, while lattice parameters stay constant. The hydrogen storage properties of sodium hydride were predicted. The density-value x (ρ-x) relationship, the variations of the hydrogen storage properties with different crystal structure were obtained systematically.

Abstract: Porous silicon were prepared by electrochemical corrosion. Undoped and boron doped silicon films were deposited on quartz substrate、porous silicon and silicon substrate by PECVD,and were solid phase crystallized at different temperature and different hours. The microstructure of films before and after annealing were studied by Raman and XRD. The results show that:the crystallization of films deposited on porous silicon and monocrystalline silicon substrate are better than quartz substrate; The substrate which has silicon crystal lattice play an important role of seed crystal in the solid phase crystallization, the same grain orientation film can be grown on certain condition.