Tin oxide-graphite composite for lithium storage material in lithium-ion batteries

A SnO-graphite composite material, which can deliver high capacities and good cycling stability compared with unsupported SnO, was described. This material prepared via chemical co-precipitation reaction in the presence of graphite consists of high dispersion of SnO with a size of about several hundred nanometers in the graphite. The phase structure was analyzed by X-ray diffraction (XRD). The morphology and the element distribution were examined by scanning electron microscopy (SEM) equipped with energy spectrum. The results show that the SnO-graphite composites produced by slowly hydrolysis have higher rechargeable capacities than pure graphite and better cycling performance than SnO.

GALVANIC CORROSION BETWEEN GRAPHITE EPOXY COMPOSITE MATERIALS AND LY12CZ ALUMINUM ALLOY

The electrochemical approach was used to show the nature of the galvanic corrosion when graphite epoxy composite materials(GECM)were coupled to LY12CZ aluminum alloy. An open circuit potential difference of one volt was obtained in 3.5% NaCl solution between GECM and LY12CZ. Corrosion current data (zero impedance technique) indicated that there was serious corrosion at GECM/LY12CZ couple.When GECM/LY12CZ couples were exposed to ASTM salt spray and alternate immersion condition, fiber glass cloth and H06-2 epoxy primer paint were effective methods for preventing galvanic corrosion.The slow strain rate test (SSRT) showed that GECM increased the LY12CZ stress corrosion crack growth rate.

Preparation and Properties of 1-octadecanol/1,3:2,4-di-(3,4-dimethyl) Benzylidene Sorbitol/Expanded Graphite Form-stable Composite Phase Change Material

A 1-octadecanol（OD）/1,3:2,4-di-（3,4-dimethyl） benzylidene sorbitol（DMDBS）/expander graphite（EG） composite was prepared as a form-stable phase change material（PCM） by vacuum melting method. The results of field emission-scanning electron microscopy（FE-SEM） showed that 1-octadecanol was restricted in the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. X-ray diffraction（XRD） and Fourier transform infrared spectroscopy（FT-IR） results showed that no chemical reaction occurred among the components of composite PCM in the preparation process. The gel-to-sol transition temperature of the composite PCMs containing DMDBS was much higher than the melting point of pure 1-octadecanol. The improvements in preventing leakage and thermal stability limits were mainly attributed to the synergistic effect of the three-dimensional network formed by DMDBS and the honeycomb network formed by EG. Differential scanning calorimeter（DSC） was used to determine the latent heat and phase change temperature of the composite PCMs. During melting and freezing process the latent heat values of the PCM with the composition of 91% OD/3% DMDBS/6% EG were 214.9 and 185.9 kJ·kg-1, respectively. Its degree of supercooling was only 0.1 ℃. Thermal constant analyzer results showed that its thermal conductivity（κ） changed up to roughly 10 times over that of OD/DMDBS matrix.

Microstructure Regulation and Combustion Performance Optimization of PVDF/Al Composite Powder by Non-covalent Functionalized Graphenes

Graphene prepared by non-covalent modification of sulfonated poly(ether-ether-ketone)(SPG)was combined with polyvinylidene fluoride(PVDF)/Al to improve the PVDF/Al thermal conductivity while reducing the effect of the thermal resistance at the graphene-polymer interface.The regulation rule of SPG with different contents on the energy release of fluorine-containing system was studied.When the content of SPG is 4%,the peak pressure and rise rate of SPG/PVDF/Al composite powder during ignition reach the maximum of 4845.28 kPa and 8683.58 kPa/s.When the content of SPG is 5%,the PVDF/Al composite powder is completely coated by SPG,and the calorific value of the material reachs the maximum of 29.094 kJ/g.Through the design and micro-control of the composite powder,the calorific value of the material can be effectively improved,but the improvement of the mass release rate still depends on the graphene content and surface modification state.

Enhanced Thermal Conductivity and Bending Strength of Graphite Flakes/aluminum Composites Via Graphite Surface Modification

The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm^-1·K^-1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3 Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.

Al2_3/Al2O3 Joint Brazed with Al2O3-particulate-contained Composite Ag-Cu-Ti Filler Material

Microstructure and interracial reactions of Al2O3 joints brazed with Al2O3-particulate-contained composite Ag-Cu-Ti filler material were researched by scanning electron microscopy （SEM）, electron probe microscopy analysis （EPMA）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. The interracial reaction layer thickness of joints brazed with conventional active filler metal and active composite filler materials with different volume fraction of Al2O3 particulate was also studied. The experimental results indicated although there were Al2O3 particulates added into active filler metals, the time dependence of interracial layer growth of joints brazed with active composite filler material is t^1/2 as described by Fickian law as the joints brazed with conventional active filler metal.

Microstructure and properties of high-fraction graphite nanoflakes/6061Al matrix composites fabricated via spark plasma sintering

30-50 wt.%graphite nanoflakes(GNFs)/6061Al matrix composites were fabricated via spark plasma sintering(SPS)at 610℃.The effects of the sintering pressure and GNF content on the microstructure and properties of the composites were investigated.The results indicated that interfacial reactions were inhibited during SPS because no Al4C3 was detected.Moreover,the agglomeration of the GNFs increased,and the distribution orientation of the GNFs decreased with increasing the GNF content.The relative density,bending strength,and coefficient of thermal expansion(CTE)of the composites decreased,while the thermal conductivity(TC)in the X−Y direction increased.As the sintering pressure increased,the GNFs deagglomerated and were distributed preferentially in the X−Y direction,which increased the relative density,bending strength and TC,and decreased the CTE of the composites.The 50wt.%GNFs/6061Al matrix composite sintered at 610℃ under 55 MPa demonstrated the best performance,i.e.,bending strength of 72 MPa,TC and CTE(RT−100℃)of 254 W/(m·K)and 8.5×10^(−6)K^(−1)in the X−Y direction,and 55 W/(m·K)and 9.7×10^(−6)K^(−1)in the Z direction,respectively.

Synthesis and Characterization of Worm-shaped Tubular Lanthanum Aluminum Composite Mesoporous Materials

The lanthanum aluminum mesoporous materials were synthesized using sodium dodecyl sulfate as a template agent by ultrasonic hydrothermal method.The resulting samples were characterized by low angle X-ray diffraction（XRD）,N2 adsorption-desorption studies,transmission electron microscopy（TEM）and surface morphology analysis（SEM）,surface acid（NH3-TPD）,reducibility properties（TPR）,X-ray energy dispersive spectrometer（EDS）and thermogravimetric analysis（TG/DTG）.A l/La composite mesoporous material were synthesized with n（Al）︰n（La）=70︰1.0,80°C of reaction temperature,20 h of reaction time,12 h of crystallization time,650°C of calcination temperature.The specific surface area of the sample is 273.90 m 2 ·g ？1 ,with the average diameter 5.642 nm and pore volume 0.2354 cm 3 ·g ？1 .The samples have mesoporous structure and its particles are similar to a worm-shaped tubular structure.The influence of calcination temperature on the surface physical and chemical properties of Al/La composited mesoporous materials was examined,and the results showed that the acid strength was increased but the amount of acidic sites is decreased as the calcination temperature increased.It was found that the sample calcined at 650°C had appropriate acid content,acid strength and better reducibility.

AN IN SITU SURFACE COMPOSITE AND GRADIENT MATERIAL OF Al-Si ALLOY PRODUCED BY ELECTROMAGNETIC FORCE

Because of the different conductivities between the primary phase (low electric conduc tivity) and the metal melt, electromagnetic force scarcely acts on the primary phase. Thus, an electromagnetic repulsive force applied by the metal melt exerts on the pri mary phase when the movement of the melt in the direction of electromagnetic force is limited. As a result, the repulsive force exerts on the primary phase to push them to move in the direction opposite to that of the electromagnetic force when the metal melt with primary phase solidifies under an electromagnetic force field. Based on this, a new method for production of in situ surface composite and gradient material by electromagnetic force is proposed. An in situ primary Si reinforced surface composite of Al-15wt%Si alloy and gradient material of Al-l9wt%Si alloy were produced by this method. The microhardness of the primary Si is HV1320. The reinforced phase size is in the range from 40μm to 100μm. The wear resistance of Al-Si alloy gradient material can be more greatly increased than that of their matrix material.

Preparation and electrochemical properties of Co_3O_4/graphite composites as anodes of lithium ion batteries

Co3O4/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis （TG/DTA）, X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co3O4/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mA-h/g as the calcination temperature increases from 300 to 500 ℃, and the Co304/graphite composites synthesized at 400 ℃ show the best cycling stability without capacity loss in the initial 20 cycles. peaks, corresponding to the lithium intercalaction/deintercalation for The CV profile of the composite presents two couples of redox graphite and Co3O4, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.

Layered Metal Composites: Newest Generation of Radiation-Protective Materials

The expediency of development of one of the newest highly effective radiation-protective materials—layered composites of “light metal/heavy metal” type is substantiated. The characteristics of the internal architecture of composites of Al/Pb type made by consecutive application of vacuum and normal atmospheric rolling are adduced. The differences between the radioisotope and accelerating techniques of experimental testing of radiation-protective properties of materials are described. The results of the testing of composites and the influence of their structure on radiation-protective properties of the investigated materials are characterized. It is shown that the radiation-protective efficiency of composites certain structures may be 30% - 40% higher than the aluminum. This gives the opportunity to reduce the weight of radiation-protective structure at preservation of effectiveness of protection at aluminum level, or to increase the effectiveness of protection at constant weight of this structure.

Electroless nickel plated graphite fibers and surface behavior in G_(r(Ni))/6061Al composite

The electroless nickel plated graphite fibers reinforced aluminum matrix composites (Gr(Ni))/Al) were produced by squeeze casting, and the microstructure of Gr(Ni)/Al composite and surface behavior of Ni-P coating were studied. The optimum process of electroless Ni-P plating included: burning to get rid of glue→degreasing→neutralization→acidulating→sensitizing→activation→electroless plating. The surface analysis results show that the electroless nickel plating can diffuse into the graphite fiber surface during the squeeze casting, and the Ni-P coating and aluminum alloys can produce brittle phase NiAl3 or NiAl. The X-ray diffraction(XRD) results indicate that Al4C3 is so little that no Al4C3 peaks are found, and the harmful Al4C3 can be decreased by the electroless plating Ni-P coating. The coating improves the interfacial bonding of continuous graphite fibers reinforced aluminum matrix composites.

Piezoresistivity of Carbon Fiber Graphite Cement-based Composites with CCCW

The electrical conductivity and piezoresistivity of carbon fiber graphite cement-matrix composites（CFGCC） with carbon fiber content（1% by the weight of cement）,graphite powder contents （0%-50% by the weight of cement） and CCCW（cementitious capillary crystalline waterproofing materials,4% by the weight of cement） were studied.The experimental results showed that the relationship between the resistivity of CFGCC and the concentration of graphite powders had typical features of percolation phenomena.The percolation threshold was about 20%.A clear piezoresistive effect was observed in CFGCC with 1wt% of carbon fibers,20wt% or 30wt% of graphite powders under uniaxial compressive tests,indicating that this type of smart composites was a promising candidate for strain sensing.The measured gage factor （defined as the fractional change in resistance per unit strain） of CFGCC with graphite content of 20wt% and 30wt% were 37 and 22,respectively.With the addition of CCCW,the mechanical properties of CFGCC were improved,which benefited CFGCC piezoresistivity of stability.

Effects of graphite on the microstructure and properties of ultrafine WC-11Co composites by spark plasma sintering

Ultrafine WC-11Co hard metals added with different proportions of graphite were prepared by spark plasma sintering at 40 MPa/1200°C for 5 min,and the influence of graphite as free carbon on the microstructure and mechanical properties were investigated.The XRD analysis showed that decarbonization could be prevented by adding graphite.Compact hard metals composed of finer and more homogeneous WC grains with little flaws can be achieved after 0 wt.% to 1.5 wt.% graphite was added.The hardness and fracture toughness increase initially with increasing graphite content,and with over 1.5 wt.% they descend due to coarse grains and more defects.Therefore,1.5 wt.% graphite is the optimal addition content in view of the hardness and transverse rupture toughness.Furthermore,the coercive force decreases while the saturated magnetic intensity increases with the increase of graphite content.

Influence of graphite particle size and its shape on performance of carbon composite bipolar plate

Bipolar plates for proton exchange membrane fuel cell (PEMFC) where polymer is used as binder and graphite is used as electric filler were prepared by means of compression molding technology. Study on the effects of graphite particle size and shape on the bipolar plate performance, such as electrical conductivity, strength, etc. showed that with decrease of graphite particle size, bulk electrical conductivity and thermometric conductivity decreased, but that flexural strength was enhanced. After spherical graphite occurrence in flake-like form, the flexural strength of the bipolar plate was enhanced, electrical conductivity increased but thermal conductivity decreased in direction paralleling pressure direction, and both electrical conductivity and thermometric conductivity reduced in direction perpendicular to pressure direction.

Preparation and Thermal Properties of a Novel Modified Ammonium Alum/Expanded Graphite Composite Phase Change Material

Thermal energy storage(TES)using phase change materials(PCMs)is a powerful solution to the improvement of energy efficiency.The application of Ammonium alum(A-alum,NH4Al(SO_(4))_(2)·12H_(2)O)in the latent thermal energy storage(LTES)systems is hampered due to its high supercooling and low thermal conductivity.In this work,modified A-alum(M-PCM)containing different nucleating agents was prepared and further adsorbed in expanded graphite(EG)to obtain composite phase change material(CPCM)to overcome the disadvantages of A-alum.Thermal properties,thermal cycle stability,microstructure and chemical compatibility of CPCM were characterized by differential scanning calorimetry,thermal constant analysis,scanning electron microscopy,X-ray diffraction and Fourier transform infrared spectroscopy.The cold rewarming phenomenon of CPCM was established and explained.Results showed that the latent heat and melting point of CPCM were 187.22 J/g and 91.54℃,respectively.The supercooling of CPCM decreased by 9.61℃,and thermal conductivity increased by 27 times compared with pure A-alum.Heat storage and release tests indicated that 2 wt%calcium chloride dihydrate(CCD,CaCl_(2)·2H_(2)O)was the optimum nucleating agent for A-alum.The result of TG and 30 thermal cycles revealed that CPCM exhibited favorable thermal stability and reliability during the operating temperature.The prepared modified A-alum/EG CPCM has a promising application prospect for LTES.

Processing Compressed Expanded Natural Graphite for Phase Change Material Composites

Phase change materials(PCMs)are used in various thermal energy storage applications but are limited by their low thermal conductivity.One method to increase conductivity involves impregnating organic PCMs into highly porous conductive matrix materials.Of these materials,compressed expanded natural graphite(CENG)matrices have received the most attention.Despite this attention,the effect that CENG processing has on PCM saturation and overall matrix thermal conductivity has not been fully investigated.Therefore,the effect of the heat treatment process used to expand intercalated graphite flakes is evaluated here.Higher heat treatment temperatures yielded higher saturation rates and overall saturation at similar matrix porosities.For example,increasing temperature from 300℃to 700℃resulted in approximately 60%-70%increase in pore saturation after 100 minutes of soaking.The exposure time to heat treatment had less of an effect on PCM saturation.The exposure time had negligible effect above 30 min and above 500℃heating temperatures.However,because the expanded graphite was found to oxidize around 700℃,the use of longer exposure time in manufacturing applications can be beneficial if a shortened impregnation time is needed.Heat treatment conditions did not impact thermal conductivity.The composite latent heat of fusion was also reduced approximately proportionally to the PCM mass fraction.A local maximum in axial thermal conductivity was observed at around 83%porosity,which is similar to previous studies.The observed conductivity at this maximum was a factor of 81 times greater than the conductivity of the PCM.

纵扭超声辅助铣削SiCp/Al复合材料表面质量研究

高体积分数SiCp/Al复合材料具有高比强度、高比模数和良好的耐磨性等优异性能。然而,它们的高硬度和脆性会导致精密制造过程中应力分布更为复杂,这会使材料中产生过大的力和过多的热,从而影响加工精度和工件耐久极限寿命。目的通过分析切削过程中颗粒的去除机理和表面缺陷类型,利用纵扭超声辅助铣削(longitudinal-torsional ultrasonic assisted milling,LTUAM)技术,改善高体积分数SiCp/Al复合材料的加工表面质量。方法利用ABAQUS和PYTHON软件,建立考虑颗粒断裂过程的两相随机分布颗粒SiCp/Al复合材料模型,并采用Johnson-Cook模型和Brittle Cracking模型对SiCp/Al复合材料纵扭超声辅助铣削过程进行有限元模拟仿真。针对不同加工参数,进行SiCp/Al复合材料纵扭超声辅助铣削和常规铣削(conventional milling,CM)试验,评估有限元仿真模拟与试验结果的一致性。结果模拟结果表明,损伤和裂纹主要产生在SiC颗粒(SiCp)中上部的切削线上,凹坑缺陷主要产生在颗粒下部的切削线上。试验结果显示,表面缺陷的类型主要包括颗粒的损伤和拔出、颗粒的损伤和断裂形成凹坑、未损伤的颗粒形成凸起、破损颗粒与刀具在已加工表面上挤压摩擦形成犁沟、铝基体涂覆、表面微裂纹和表面空穴等,并且当加工速度120 m/min,超声振幅3μm时,最大裂纹深度最小,表面缺陷最小,表面质量最好。结论对比有限元仿真结果与试验结果发现,二者的表面质量变化趋势基本具有一致性。纵扭超声辅助铣削技术的应用对提高SiCp/Al复合材料的表面质量有较好效果。