Host effect on the formation of sodium-tetrahydrofuran-graphite intercalation compounds

The formation of sodium-tetrahydrofuran-graphite intercalation compounds (NaTHFGICs) in THF solution with sodium and naphthalene by using various kinds of host carbon materials was investigated and the criteria of the hosts were discussed. Hosts with high crystallinity gave a well-defined stage-1 structure and its formation was very slow. Two phases of stage-1 structure with different I_c values, 1.12 and 0.72 nm, were obtained, the latter being formed after exposure to air. Hosts with low crystallinity, on the other hand, quickly formed undefinable stage structure. A clear criterion for the relation between crystallite thickness L_c(002) and degree of graphitization P₁ was difficult to determine.     

Electrodic characteristics of various carbon materials for lithium rechargeable batteries

Electrodic characteristics of various carbon materials have been investigated to study the correlation between structures of carbon materials and performances of negative electrodes of lithium rechargeable batteries. In the case of highly graphitized carbon materials, the discharge capacity was determined mainly by their crystallinity with no dependence on textures and natural graphite; the highest graphitization at about 360 mAh/g was stage-1 lithium-intercalated graphite, C₆Li (theoretical maximum 372 mAh/g). The coulombic efficiency at the first cycle was strongly dependent on the textures of the carbon materials, and pitch-based carbon fiber of a radial structure showed an excellent coulombic efficiency over 96% by selecting appropriate electrolytes. The performances of the pitch-based carbon fiber were also excellent in the electrolytes consisting of mixed solvents containing propylene carbonate. On the other hand, the pitch coke heat-treated at 550 °C had an initial capacity over 550 mAh/g, which was beyond the theoretically maximum capacity of 372 mAh/g for C₆Li, although the capacity decreased rapidly to less than 250 mAh/g within ten cycles. Polyacrylonitrile (PAN)-based carbon fiber showed a stable capacity with cycling over 350 mAh/g in spite of low graphitization. The initial coulombic efficiency seemed to increase in accordance with decrease of hydrogen and oxygen in the pitch coke, and oxygen and nitrogen in the polyacrylonitrile (PAN) fibers. These phenomena seemed to suggest that carbon materials of disordered structure would have higher capacity than that of the graphitic carbon materials.     

Effect of ether coordination for sodium intercalation into poly(vinyl chloride) cokes with different graphitization degree

Sodium intercalation in three unidentate and three bidentate ether solutions having different molecular sizes was investigated using poly(vinyl chloride) cokes heat-treated at different temperatures. Co-intercalation of ether molecules with sodium cations was found to be governed strongly by the graphitization degree of hosts in contrast with other alkali metals. This tendency is dependent on the strength of bond between sodium and ether molecule, and also the bulk of coordinated molecules; the limit of graphitization degree for co-intercalation of solvent molecules was lower in bidentate solution than in unidentate ones, and the large solvents were prevented from co-intercalation more strongly than small ones.     

Influence of load on sliding tribology of C/C composite with 40Cr steel couple coated by Cr

With the 40Cr steel couple coated by Cr, the sliding tribology behavior of two kinds of C/C composites with different matrix was tested using a M2000 wear tester. The results show that with the increasing of load, the friction coefficients of the composite with resin carbon matrix（RC） decrease quickly from 0.156 under 60 N to 0.123 under 150 N, while those of the composite with rough lamination/smooth lamination/resin carbon （RL/SL/RC） change only between 0.122 and 0.101. The wear volume loss of the two composites increases except for under 100 N. The SEM morphology shows that with the increasing of load, the worn surface of the composite with RC becomes more and more integrated while the size of the debris becomes less and less. The Raman spectrum shows that the graphitization on the worn surface of the fibers draws down after 100 N, the graphitization of the boundary between the fiber and the matrix carbon rises up to 150 N, but the graphitization of the matrix carbon draws down all the while. With the increasing of load, the graphitization on the worn surface of all the worn areas becomes closer and closer, which indicates the worn surface of the different component has the similar friction ability. The composites with RL/SL/RC have better tribological characteristic than the composite with RC.     

碳界面层制备工艺对SiC_f/SiC材料力学性能的影响

用低压化学气相沉积(LPCVD)法,以丙烯(C_3H_6)为碳源,氮气(N_2)为稀释气制备了2.5维连续碳化硅纤维增韧碳化硅(SiC_f/SiC)复合材料的碳界面层,其厚度为～0.1 mm.研究了不同丙烯含量(体积分数,下同)(60%,50%,45%)对碳层形貌、微观结构及SiC_f/SiC力学性能的影响.结果表明:当C_3H_6含量为60%时,热解碳层表面光滑,石磨化度高;当C_3H_6为50%和45%时,碳层粗糙,有很多较大颗粒存在,石磨化度低.3种复合材料的弯曲强度差别不大,分别为303,311和320 MPa.然而,当C_3H_6含量为60%时,材料韧性断裂,断裂功高;为50%和45%时,材料脆性断裂,断裂功低.不同的纤维拔出滑移阻力是SiC_f/SiC断裂行为不同的原因.     

Effect of fiber characteristics on fracture behavior of C_f/SiC composites

Cf/SiC composites were prepared by precursor pyrolysis-hot pressing, and the effect of fiber characteristics on the fracture behavior of the composites was investigated. Because the heat treatment temperature of fiber T300 (below 1500℃) was much lower than that of fiber M40JB (over 2000℃), fiber T300 had lower degree of graphitization and consisted of more impurities compared with fiber M40JB, suggesting that T300 exhibits higher chemical activity. As a result, the composite with T300 showed a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface as well as the degradation of fibers during the preparation of the composite. However, the composite with M40JB exhibits a tough fracture behavior, which is primarily attributed to a weakly bonded fiber/matrix interface and higher strength retention of the fibers.     

THF insertion in n-doped polyacetylene

The residual coinsertion of THF in polyacetylene (PA), n-doped by THF solutions of organo lithium, sodium and potassium, has been quantitatively analysed after cryogenic pumping (at −80 °C and −196 °C) of samples kept at room temperature.

It is found that the amount of coinserted THF per CH increases with the doping level y up to a maximum of y = 8–10% and then decreases. This maximum increases when the size of the cation decreases, from K to Li. With Na and K, and for any doping level, the THF content is higher in cis-doped than in trans-doped samples, while with Li no difference is observed between the two isomers. The influence of solvation on properties is discussed.

A synergic effect was observed during solvation by a THF/toluene mixture.     

Assessing metal transfer stability and spatter severity in flux cored arc welding

Abstract

Five experimental basic type flux cored arc welding consumable wire electrodes were manufactured from the same base formulation. The composition of these electrodes was adjusted in an attempt to improve the operating performance. This involved additions of various ratios of alkali oxides, namely, lithium, magnesium, sodium, and potassium containing ingredients, in the flux formulations. The operating behaviours of these experimental electrodes and two reference products (i.e. one commercial basic T–5 and one commercial rutile T–1 electrode) were thoroughly investigated by recording welding arc signals using a high speed data acquisition system. By comparing these electrodes among themselves, the experimental electrodes were reported to exhibit extremely stable arcs, some showing electrical arc signals even smoother than those for the reference rutile grade electrode. Despite their improved metal transfer consistency, however, basic electrodes were characterised by somewhat higher spatter levels.     

Zinksilicatanstriche

Zinc silicate coatings Zinc dust is increasingly used as a pigment for highly pigmented coatings for anti-corrosive and heat resistant coatings in a variety of applications were confined to a number of organic binders on a single-component or two-component basis and to organic-binders, recent developments have led to an increasing application of inorganic binders, viz. alkali silicates. These are special sodium, potassium and lithium silicates (waterglass). The film is formed by the reaction of zinc with alkali silicates when an alkali-zinc complex is formed. The base must be pre-treated by Graden 3 sand blasting. The film thickness amounts to 100–120 microns. The coating may be applied with or without top coat. The best way of applying the coating is by spray gun. The coating has a high resistance to wear, solvents, and temperature.     

MoCl5 intercalation into carbon fibers

The host effect on the intercalation of MoCl₅ was studied using vapor-grown (VGCFs), mesophase-pitch-based (MPCFs) and PAN-based carbon fibers (PANCFs) heat-treated to different temperatures. MoCl₅ successfully intercalated into VGCFs, but MPCFs and PANCFs showed no intercalation. MoCl₅ intercalated into 2000°C- and 2200°C-treated VGCFs having larger interlayer spacing than 2900°C-treated MPCFs where no intercalation was observed. The use of MoO₃ or MoOCl₃ with MoCl₅ found to affect the stage structure in VGCFs but was not able to perform intercalation in MPCFs and PANCFs. In VGCFs, the intercalation of MoCl₅ depends on the heat treatment temperature. Stage-1 structure in single phase was formed from 3000°C-treated VGCF with MoCl₅ and MoO₃ in the molar ratio of 1:1:0.37. SEM studies of stage-1 VGCF 3000°C-treated fiber showed the peeling of thin layers from the fiber surface and cleavage along the fiber axis of the fiber. Apparent diameter of fibers increased to roughly 3 times after intercalation.     

层次孔结构双功能碳负极材料的制备及性能

在500～900℃的活化温度下,以酚醛树脂为碳源,采用模板-物理活化联合法制备系列超级电容电池用层次孔结构双功能碳负极材料。借助扫描电镜、透射电镜及比表面积测试仪分析材料的物理结构,组装模拟电容器和对锂半电池,利用恒流充放电法及循环伏安法考察其电化学行为。结果表明:制备的层次孔结构碳材料具有较大的中微孔结构和局域石墨微晶结构;在LiPF6/EC+DMC和Et4NBF4/AN两种电解液中均表现出良好的电化学性能;其中以活化温度为600℃时制备的碳材料性能最优,其锂离子半电池可逆容量达到611.2 mA.h/g(0.2C),50次循环效率为74%,6C倍率下稳定可逆容量仍高达223 mA.h/g,模拟电容器比电容高达143 F/g(0.1 A/g),且倍率性能优异。     

碳纳米管表面处理技术的研究

对催化裂解法制备的碳纳米管（CNTs)分别进行了酸处理，高温石墨化及酸处理结合高温石墨化的综合处理。利用透射电镜，拉曼光谱仪，红外光谱仪等手段对处理前后的CNTs进行了分析。结果表明，石墨化和酸煮对CNTs表面的去除非晶碳，提高晶态化程度的作用都具有明显的效果，而2种方法相结合则对碳纳米管晶化程度的提高作用效果更加显著。     

Preparation and mechanical properties of carbon/carbon composites with high textured pyrolytic carbon matrix

Short carbon fiber felts with an initial porosity of 89.5% were deposited by isobaric, isothermal chemical vapor infiltration using natural gas as carbon source. The bulk density of the deposited carbon/carbon (C/C) composites was 1.89 g/cm³ after depositing for 150 h. The microstructure and mechanical properties of the C/C composites were studied by polarized light microscopy, X-ray diffraction, scanning electron microscopy and three-point bending test. The results reveal that high textured pyrolytic carbon is deposited as the matrix of the composites, whose crystalline thickness and graphitization degree highly increase after heat treatment. A distinct decrease of the flexural strength and modulus accompanied by the increase of the toughness of the C/C composites is found to be correlated with the structural changes in the composites during the heat treatment process.     

Evaluation of the Effect of the Concentration of Sodium Hydroxide with and without Potassium Oleate on the Behavior of Lead by Cyclic Voltammetry

The effect of the concentration of sodium hydroxide with and without potassium oleate on electrochemical behavior of lead has been investigated using cyclic voltammetry. It has been shown that the number of anode and cathode peaks on the curve depends on the potential scan rate and the concentration of alkali. Anode peaks are related to the formation of lead compounds (PbO and PbO₂), the presence of which has been confirmed by X-ray phase analysis. It has been determined that the dissolution of lead in sodiumhydroxide solution with and without potassium oleate proceeds under diffusion-kinetic control. Potassium oleate facilitates lead passivation in the solutions with lower concentration of alkali decreasing the potential and current of active–passive transition and does not affect or restricts it in more concentrated solutions.     

Interaction of π-bonds of the silicon–silicon triple bond with alkali metals: An isolable anion radical upon reduction of a disilyne

The reduction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with an equivalent amount of alkali metal (Li, Na, K, KC₈) in THF produced the corresponding disilyne anion radicals 2a–c. Their EPR spectra are independent of the metals used in THF, indicating that the disilyne anion radical species exists as solvent-separated ion pairs in polar solvents. The one-electron reduction also occurred with potassium in toluene to produce the potassium salt of the anion radical 3, which was isolated as extremely air- and moisture-sensitive dark brown crystals. The molecular structure of 3 was established by X-ray crystallography, which showed that the potassium ion is solvated by one toluene molecule. The EPR spectrum of 3 in toluene showed the interaction of the anionic silicon atom with the K⁺ ion.     

Catalytic graphitization of polyacrylonitrile (PAN)-based carbon fibers with Fe-Cr2O3 composite coating

The process of electrodepositing Fe-Cr2O3 composite coating on polyacrylonitrile(PAN)-based carbon fibers and its catalytic graphitization were studied.Carbon fibers with and without electrodeposited Fe-Cr2O3 composite coating were heat treated at different temperatures and the structural changes were characterized by XRD,Raman spectroscopy and SEM.The results indicate that Fe-Cr2O3 composite coating exhibits a significant catalytic effect on graphitization of carbon fibers at low temperatures.When the Fe-Cr2O3-coated carbon fibers were heat treated at 1 300°C,the interlayer spacing(d002) and ratio of relative peak area(AD/AG) reach 3.364-and 0.34,respectively.Whereas,the extent of graphitization of pristine carbon fibers is comparatively low even after heat treatment at 2 800°C and the values of d002 and AD/AG are 3.414  and 0.68,respectively.The extent of graphitization of carbon fibers increases not only with the increase of the catalyst gross but also the Cr2O3 content in Fe-Cr2O3 coating.The catalytic effect of Fe-Cr2O3 composite coating accords with the dissolution  precipitation mechanism.     

Use of polymeric ionic liquids as stabilizers in the synthesis of polypyrrole organic dispersions

Polypyrrole dispersions in several organic media were synthesized by using polymeric ionic liquids (PILs) both as steric stabilizers and as phase transfer agents. Firstly, PPy aqueous dispersions were prepared by polymerizing pyrrole in the presence of poly(1-vinyl-3-ethylimidazolium bromide) as steric stabilizer. By addition of different salts: lithium triflate, bis(trifluoromethane)sulfonimide lithium salt, bis(pentafluoroethane)sulfonimide lithium salt, dodecylbenzenesulfonic acid sodium salt and p-toluene-4-sulfonic acid monohydrate, the polymeric stabilizer becomes hydrophobic, precipitating in water and trapping the PPy dispersed microparticles inside. Polypyrrole organic dispersions were obtained by dispersion of the corresponding powders in a variety of organic solvents such as methanol, N,N-dimethylformamide (DMF), acetone, tetrahydrofurane (THF), butanone and toluene. The dispersability or non-dispersability of the PPy powders in each of the organic solvents depended on the nature of the added coagulating salt. Characterization of the PPy organic dispersions by photon correlation spectroscopy and atomic force microscopy (AFM) showed individual particles with sizes between 100 and 400 nm. After casting the organic dispersions, the films showed a granular nanostructured surface and electrical conductivity values as high as 10⁻¹ S/cm.     

Protective ceramic multilayer coatings for carbon fibers

Uniform, adherent, crack-free and non-bridging HfC and HfC/SiC coatings on carbon fibers have been synthesized by a reactive CVD (RCVD) process at low temperatures. To fabricate SiC coating on HfC-coated carbon fiber, an alternative approach using unsaturated organosilicon polymer solution was also proposed. The schemes describing the formation of carbide coatings on carbon fibers by RCVD and transformation of unsaturated organosilicon polymers into silicon carbide are discussed. The HfC and HfC/SiC coatings were studied by SEM, EDS and XPS techniques. Coatings are composed of hafnium, silicon and carbon as the main constituents and oxygen and fluorine as contaminants. As was proposed, the composition of the coatings is affected by several factors, among them a chemical attack of coated fibers by gaseous oxygen- and fluorine-containing by-products can be considered as dominant ones. The duplex HfC/SiC-coated carbon fibers exhibit more oxidation resistance at elevated temperatures than the initial and HfC-coated carbon fibers.     

In Situ Embedment of ZnS Nanocrystals in High Porosity Carbon Fibers as an Advanced Anode Material for Efficient Lithium Storage

ZnS is a promising material for lithium-ion battery anodes due to its abundant natural resources, simplicity of synthesis, and high theoretical lithium storage capacity. However, it needs to be optimized for its low conductivity and volume effect during the charge-discharge process. The traditional method of combining with carbonaceous materials is usually laborious, and the required sulfuration process may possibly result in the destruction of materials morphology. In this study, hybrid materials formed by the combination of ZnS nanocrystals and high porosity carbon fibers were synthesized by one-step electrospinning using zinc diethyldithiocarbamate and polyacrylonitrile as raw materials and poly (ethylene glycol)—block-poly (propylene glycol)—block-poly (ethylene glycol) as template. The method is simple and avoids the influence of sulfuration process on the morphology of materials. The composite presents a specific capacity of 592.2 mAh g⁻¹ under a current density of 1 A g⁻¹ after 1000 cycles. The porous structure significantly decreases the diffusion mean-free path of Li⁺ and inhibits the volume effect associated with the lithium storage process of ZnS. In addition, the 3D cross-linked carbon fibers improve the conductivity of materials. This study can serve as an inspiration for the development of other lithium storage composites.