Studies on Spinel LiMn_2O_4 Cathode Material Synthesized from Different Mn Sources

The spinel LiMn2O4 cathode material was synthesized with the solid-state reaction method. Four manganese compounds including electrolytic manganese dioxide (EMD), MnCO3, Mn3O4 and nano-EMD were used as Mn sources while LiOH·H2O was used as the uniform Li source. The crystal structure characteristics of these samples produced were investigated by means of XRD, SEM, particle size distribution analysis and specific surface area testing. Their electrochemical properties were also studied by comparing their specific capacity, charge and discharge efficiency and cycle performance.

Optimization of friction and wear behaviour of Al-Si_3N_4 nano composite and Al-Gr-Si_3N_4 hybrid composite under dry sliding conditions

The tribological behaviour of gravity die stir cast LM6alloy with graphite(Gr)and silicon nitride nanoparticles was investigated.Al?Gr?Si3N4hybrid composite,Al?Si3N4nanocomposite and Al?Gr nanocomposites were separately fabricated to investigate their frictional and wear characteristics under dry sliding conditions.EDS was used to ensure the uniform presence of nano Si3N4and graphite in the cast.L9orthogonal array method was chosen to conduct the experiments to study the effect of different applied loads(20,30and40N)and sliding distances(1,2and3km).The results showed that the respective wear rate and coefficient of friction(COF)decreased by25%and15%for hybrid composite when compared with those of Al?Si3N4nanocomposite whereas the wear rate and COF of Al?Gr was found to be very minimal.The micro Vickers hardness of the hybrid composite was14%more than that of the simple nanocomposite and there was not much notable variation for Al?Gr and Al?Si3N4nanocomposite materials.Scanning electron microscope was used to analyze the worn surface and subsurface,from which it was noted that the predominant wear mechanisms observed were abrasive for nanocomposite and both abrasive and adhesive mechanism for hybrid composite.Analysis of variance(ANOVA)and F-test were used to check the validity model and to determine the significant parameters affecting the wear rates.

Microstructures and wear properties of graphite and Al_2O_3 reinforced AZ91D-Cex composites

The magnesium matrix composites reinforced by graphite particles and Al2O3 short fibers were fabricated by squeeze-infiltration technique.The additions dispersed uniformly and no agglomeration and casting defect were observed.The microstructures and wear properties of the composites with different Ce contents of 0,0.4%,0.8%and 1.0%,respectively,were investigated.Especially,the effect of Ce on the properties was discussed.The results reveal that Ce enriches around the boundaries of graphite particles and forms Al3Ce phase with Al.The addition of Ce refines the microstructures of the composites.With the increase of Ce content,the grain size becomes smaller and the wear resistance of the composite is improved.At low load,the composites have similar worn surface.At high load,the composite with 1.0%Ce has the best wear resistance due to the existence of Al3Ce phase.The Al3Ce phase improves the thermal stability of the matrix so the graphite particles can keep intact,which can still work as lubricant. At low load,the wear mechanism is abrasive wear and oxidation wear.At high load,the wear mechanism changes to delamination wear for all the composites.

Influence of surface roughness on flotation kinetics of quartz

Surface roughness of quartz particles was determined by measuring the specific surface area of particles.The wettability characteristics of particles were determined by measuring the flotation rate using a laboratory flotation cell.Experimental results show that the rod mill product has higher roughness than the ball mill product.For the particles with larger surface roughness,the flotation kinetics constant is also higher.Finally,empirical relationships between surface roughness(r) and the flotation kinetics constant(k) of quartz particles as k=A+Br+Cr0.5lnr+D/lnr+E/r and k=A+Br are presented,in which A,B,C,D and E are constants related to experimental conditions and mineralogical properties of mineral.

Effect of Fe_2O_3/SiO_2 ratio on maghemite-silica particulate nanocomposites

Abstract： Maghemite-silica particulate nanocomposites were prepared by modified 2-step sol-gel process. Superparamagnetic maghemite nanoparticles were successfully produced using Massart＇s procedure. Nanocomposites consisting of synthesized maghemite nanoparticles and silica were produced by dispersing the as-synthesized maghemite nanoparticles into the silica particulate form. The system was then heated at 140 ℃for 3 d. A variety of mass ratios of Fe2O3/SiO2 was investigated. Moreover, no surfactant or other unnecessary precursor was involved. The nanocomposites were characterized using XRD, BET and AGM. The XRD diffraction patterns show the reflection corresponding to maghemite nanoparticles and a visible wide band at 20 from 20° to 35° which are the characteristics of the amorphous phase of the silica gel. The patterns also exhibit the presence of only maghemite and SiO2 amorphous phase, which indicates that there is no chemical reaction between the silica particulate gel and maghemite nanoparticles to form other compounds. The calculated crystallite size for encapsulated maghemite nanoparticles is smaller than the as-synthesized maghemite nanoparticles indicating the dissolution of the nanoparticles. Very high surface area is attained for the produced nanocomposites （360-390 m^2/g）. This enhances the sensitivity and the reactivity of the nanocomposites. The shapes of the magnetization curves for nanocomposites are very similar to the as-synthesized maghemite nanoparticles. Superparamagnetic behaviour is exhibited by all samples, indicating that the size of the maghemite nanoparticles is always within the nanometre range. The increase in iron content gives rise to a small particle growth.

Composites of graphene and encapsulated silicon for practically viable high-performance lithium-ion batteries

A facile and scalable approach to synthesize silicon composite anodes has been developed by encapsulating Si particles via in situ polymerization and carbonization of phloroglucinol-formaldehyde gel, followed by incorporation of graphene nanoplatelets. As a result of its structural integrity, high packing density and an intimate electrical contact consolidated by the conductive networks, the composite anode yielded excellent electrochemical performance in terms of charge storage capability, cycling life and coulombic efficiency. A half cell achieved reversible capacities of 1,600 mAh·g-1 and 1,000 mAh·g-1 at 0.5 A·g-1 and 2.1 A·g-1, respectively, while retaining more than 70% of the initial capacities over 1,000 cycles. Complete lithium-ion pouch cells coupling the anode with a lithium metal oxide cathode demonstrated excellent cycling performance and energy output, representing significant advance in developing Si-based electrode for practical application in high-performance lithium-ion batteries.

Cell responses and hemocompatibility of g-HA/PLA composites

The objective of this study was to investigate the hemocompatibility and cell responses to some novel poly（L-lactide） （PLA） composites containing surface modified hydroxyapatite particles for potential applications as a bone substitute material. The surface of hydroxyapatite （HA） particles was first grafted with L-lactic acid oligomers to form grafted HA （g-HA） particles. The g-HA particles were further blended with PLA to prepare g-HA/PLA composites. Our previous study has shown signifi- cant improvement in tensile properties of these materials due to the enhanced interracial adhesion between the polymer matrix and HA particles. To further investigate the potential applications of these composites in bone repair and other orthopedic sur- geries, a series of in vitro and in vivo experiments were conducted to examine the cell responses and hemocompatibility of the materials. In vitro experiments showed that the g-HA/PLA composites were well tolerated by the L-929 cells. Hemolysis of the composites was lower than that of pure PLA. Subcutaneous implantation demonstrated that the g-HA/PLA composites were more favorable than the control materials for soft tissue responses. The results suggested that the g-HA/PLA composites are promising and safe materials with potential applications in tissue engineering.

Ionic Liquid-Assisted One-Step Hydrothermal Synthesis of TiO2-Reduced Graphene Oxide Composites

We have demonstrated a facile and efficient strategy for the fabrication of soluble reduced graphene oxide sheets （RGO） and the preparation of titanium oxide （TiO2） nanoparticle-RGO composites using a modified one-step hydrothermal method. It was found that graphene oxide could be easily reduced under solvothermal conditions with ascorbic acid as reductant, with concomitant growth of TiO2 particles on the RGO surface. The TiO2-RGO composite has been thoroughly characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Microscopy techniques （scanning electron microscopy, atomic force microscopy, and transmission electron microscopy） have been employed to probe the morphological characteristics as well as to investigate the exfoliation of RGO sheets. The TiOR-RGO composite exhibited excellent photocatalysis of hydrogen evolution.

A novel hydrogen peroxide biosensor based on the BPT/AuNPs/graphene/HRP composite

A novel hydrogen peroxide biosensor based on the BPT/AuNPs/graphene/HRP composite was developed. Firstly, graphene was prepared under the protection of polyvinylpyrrolidone (PVP), and then the AuNPs/graphene composite was synthesized via in situ decoration. Using biphenyldimethanethiol (BPT) as a connector, the AuNPs/graphene composite was immobilized on the surface of the Au electrode, and whereafter the horseradish peroxidase (HRP) was decorated on the surface of the composite by adsorption. The morphology and structure of the products were characterized by XRD, SEM, TEM and UV-visible spectroscopy. The electrocatalytic performance of the resulting BPT/AuNPs/grapheme/HRP composite (namely, biosensor) was studied by electrochemical instrument. The results show that the biosensor has high sensitivity and fast response to H2O2. In the solution of pH 7.4 with potential -0.2V, the linear response of the biosensor to H2O2 ranges from 5.0×10-6 to 2.5×10-3M with the detection limit of 1.5×10-6M.