石墨化处理对催化裂解炭球结构的影响

采用催化裂解法制备出炭球,将其分别在2300℃和2800℃进行石墨化处理,用TEM和XRD对微观结构和晶体结构进行了研究。结果表明:未石墨化处理的炭球具有较圆整的球形结构,晶体结构不规整。当氢气流量为3000ml/min和4000ml/min时,获得具有洋葱结构的炭球。球体散布着直径在几个纳米~30nm的铁金属颗粒。经过石墨化处理,炭球的球形结构转变为多面体结构,铁颗粒被除去。2800℃石墨化处理使炭球的石墨层间距降低,石墨化度提高,晶体结构变得非常规整。     

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.     

聚丙烯腈基炭纤维表面电沉积 Ni-Fe合金的催化石墨化性能

在聚丙烯氰基炭纤维上电沉积Ni-Fe合金催化剂,并采用x-射线衍射和拉曼光谱方法考察其对热处理炭纤维石墨化的催化性能.结果表明:Ni-Fe合金在低温条件下对炭纤维石墨化有着优异的催化性能.附有Ni-Fe合金(铁的质量分数为57.91%)的聚丙烯腈基炭纤维经过1250℃热处理后其石墨化度为69.0%,而空白样炭纤维经过2...     

Microstructure transformation of carbon nanofibers during graphitization

The microstructures of vapor-grown carbon nanofibers（CNFs） before and after graphitization process were analyzed by high resolution transmission electron microscopy（HRTEM）, Raman spectroscopy, X-ray diffractometry（XRD）, near-edge-X-ray absorption fine structure spectroscopy（NEXAFS） and thermogravimetric analysis（TGA）. The results indicate that although non-graphitized CNFs have the characteristics of higher disorder, a transformation is found in the inner layer of tube wall where graphite sheets become stiff, which demonstrates the characteristics of higher graphitization of graphitized CNFs. The defects in outer tube wall disappear because the amorphous carbon changes to perfect crystalline carbon after annealing treatment at about 2 800 ℃. TGA analysis in air indicates that graphitized CNFs have excellent oxidation resistance up to 857 ℃. And the graphitization mechanism including four stages was also proposed.     

Silicon/flake graphite/carbon anode materials prepared with different dispersants by spray-drying method for lithium ion batteries

Silicon/flake graphite/carbon (Si/FG/C) composites were synthesized with different dispersants via spray drying and subsequent pyrolysis, and effects of dispersants on the characteristics of the composites were investigated. The structure and properties of the composites were determined by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The results show that samples have silicon/flake graphite/amorphous carbon composite structure, good spherical appearances, and better electrochemical performance than pure nano-Si and FG/C composites. Compared with the Si/FG/C composite using washing powder as dispersant, the Si/FG/C composite using sodium dodecyl benzene sulfonate (SDBS) as dispersant has better electrochemical performance with a reversible capacity of 602.68 mA·h/g, and a capacity retention ratio of 91.58 % after 20 cycles.     

约束弧等离子体制备碳包覆铁纳米颗粒的性能

采用约束弧等离子体技术制备碳包覆铁纳米颗粒,利用X射线衍射、透射电子显微镜、高分辨透射电子显微镜、X射线能量色散分析谱仪和N2吸附等测试手段对样品的化学成分、形貌、微观结构、比表面积和粒度等特征进行表征分析。结果表明：采用约束弧等离子体技术制备的碳包覆纳米金属颗粒具有明显的核？壳结构,内核金属为体心立方结构的铁,外壳为无定形碳。颗粒大多呈球形和椭球形,粒径分布在15～40nm范围内,平均粒径为30nm,内核粒径为18nm,外层碳的厚度为6～8nm,比表面积为24m2/g。     

Carbon nanotube prepared from carbon monoxide by CVD method and its application as electrode materials

Carbon nanotubes with larger inner diameter were synthesized by the chemical vapor deposition of carbon monoxide (CO) on iron catalyst using H2S as promoting agent.It is found that the structure and morphology of carbon nanotubes can be tailored, to some degree, by varying the experimental conditions such as precursor components and process parameters.The results show that the presence of H2S may play key role for growing Y-branched carbon nanotubes.The products were characterized by SEM, TEM, and Raman spectroscopy, respectively.Furthermore, the obtained carbon nanotubes were explored as electrode materials for supercapacitor.     

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。     

炭/炭复合材料石墨化度的XRD均峰位法测定

采用XRD平均峰位法测定了4种C／C复合材料的石墨化度。研究结果表明：用平均峰位法测定C／C复合材料的石墨化度具有简便可靠、区分度高的优点。当C／C复合材料中炭纤维的含量低于基体炭含量时，难石墨化的炭纤维对C／C复合材料XRD谱线低角度一侧的线形有一定影响，但对最终的测量结果影响不大。     

Diffusion saturation of alloy YuNDK24 with carbon

Metal Science and Heat Treatment -     

Microstructure of cobalt dispersed carbon sphere prepared from chelate resin

Carbon spheres containing fine particles of Co metal were prepared by carbonization of the chelate resin complexed with Co(II) ions in pure argon. Diffraction peaks of cubic cobalt were found in XRD patterns from 600°C but the particle size observed by TEM was 10–50 nm in diameter even at 1000°C. Cobalt promoted the decomposition of polyamine functional groups in the resin and the transformation of amorphous carbon to turbostratic structure. The spheres prepared at 700–1000°C had a specific surface area of 170–250 m² g⁻¹.     

Structural properties of carbon prepared from aligned polyacetylene thin films

Aligned polyacetylene (PA) thin films consisting of fibrils of about 100 nm in diameter were carbonized at 1000 °C in a vacuum or in an argon gas. Structures and morphologies of the carbons prepared from the aligned PA thin films were investigated using Raman spectroscopy, X-ray measurements, and scanning and transmission electron microscopes. The carbonization gave rise to a char of amount of 20% in weight of the PA film. The char was found to contain nanorods of about 10 nm in width. Morphology of the carbon nanorod reflected that of the aligned PA thin film. Subsequently, the char was graphitized by further heating at 2600 °C.     

Characterization of cobalt oxide nanocatalysts prepared by microemulsion with different surfactants, reduction by hydrazine and mechanochemical method

Cobalt oxide (Co₃O₄) nanoparticles were prepared by different techniques (i) by microemulsion with different surfactants, (ii) by reduction as nanometal with hydrazine hydrates and (iii) by thermal treatment of precursor obtained from mechanochemical reaction of Co(NO₃)·H₂O with NH₄HCO₃. The products were calcined at 400 °C to give crystalline Co₃O₄. The obtained different samples of Co₃O₄ were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) from which the particle size was calculated. The results revealed that all samples obtained from different methods were nanosized particles.     

A study on carbon concentration distribution and microstructure of P/M materials prepared by carbusintering

Carbusintering (CBS) process was used to produce powder metallurgy (P/M) parts (Fe–2Ni–1.5Cu–xC). Influence of sintering parameters such as temperature on diffusion coefficient of carbon was investigated. The specimen with the porosity of 6–13% got the carbon content of the surface ranged from 1.23 to 1.32 wt.%. After heat treatment, the hardness and impact energy were enhanced to 48 HRC (484 HV) and 13 J, respectively. The change in carbon concentration along the case depth was determined quantitatively by means of chemical analysis. The carbon concentration profile was satisfactorily modeled by classical solution derived from Fick’s second law. An undesired acicular structure was observed in the specimen with low green compact density due to the high carbon content. CBS process can provide outstanding performance in surface hardening of P/M materials. The use of CBS process was able to make process simple by taking sintering and carburizing as one step. The higher carbon content of the surface in P/M parts can be easily achieved compared to conventional carburizing.     

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.     

Physical and electromagnetic shielding properties of green carbon foam prepared from biomaterials

100% green carbon foam from the fibrous fruits of Platanus Orientalis-L (Plane) along with the tar oil as binder has been prepared using a powder molding technique. The objective was to develop a porous monolithic carbon from biomaterials with a considerable strength necessary for various physical, thermal and electromagnetic shielding applications. Fast carbonization was carried out at 1000 °C under the cover of Plane tree pyrolyzed seeds without using any external protective gas. For comparative analysis, some samples were mixed with 5% (mass fraction) iron chloride during the molding process. Iron chloride being a graphitization catalyst and activating agent helped in increasing the specific surface area from 88 to 294 m²/g with a 25% decrease in flexural strength. Thermal stability was improved due to the incorporation of more graphitic phases in the sample resulting in a little higher thermal conductivity from 0.22 to 0.67 W/(m·K). The catalytic carbon foam exhibited shielding effectiveness of more than 20 dB over the X-band frequency. Absorption was dominant with only 8.26%–10.33% reflectance, indicating an absorption dominant shielding mechanism. The new material is quite suitable for high temperature thermal insulation being lightweight, highly porous with interconnected porous morphology most of which is preserved from the original biomaterial.     

Air oxidation of SiC fibers prepared from carbon fibers and SiO vapor

Activated carbon fiber composite (ACFC) was reacted with SiO vapor to prepare SiC fibers containing nanopores. The SiC fibers obtained were not oxidation resistant, showing nearly complete oxidation at 1000°C after about 25 hr in air, though the oxidation product was amorphous silica which was generally considered to be oxidation resistant. The poor oxidation resistance was attributed to highly porous, amorphous SiO₂ formation on the inherently highly porous SiC fibers. Interconnected micropores inside the fibers rendered the fibers easily oxidizable.     

Characterization of thermal flame sprayed coatings prepared from FeCr mechanically milled powder

This paper discusses augmenting a thermal flame spray process with a mechanically milled feedstock to deposit low porosity FeCr coatings onto a steel substrate. A variety of tests were performed to assess the quality of the coatings obtained: microstructural and chemical analyses using X-ray diffraction (XRD) and optical and scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDS). The microscopy studies showed that the coatings displayed a lamellar structure with two distinct darker phases and contained unmelted particles; moreover, oxides and micro-cracks were observed at the surface. A lower level of porosity was observed compared to that reported in the literature, and the chromium concentration was found to increase with decreasing coating thickness. The mechanical properties of the coatings were characterized using micro-hardness, adhesion and residual stress tests. The results show a cohesive fracture mode for all samples, whatever the coating thickness. Electrochemical tests were carried out using open circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. The best electrochemical properties were observed for coatings in which the voids were sealed with a polymeric substance and those fabricated with a Ni-based bond coating. However, the thinner coatings show higher chromium concentrations, lower porosity, and better mechanical and electrochemical properties than the thicker coatings.