Catalytic graphitization of electroless Ni-P coated PAN-based carbon fibers

Catalytic graphitization of electroless Ni-P coated PAN-based carbon fibers is reported. PAN-based carbon fibers with and without electroless Ni-P coatings were heat treated and the structural changes were followed by X-ray diffraction and Raman spectroscopy, both of which indicate that the graphitization of PAN-based carbon fibers was enhanced in the presence of the coating. The graphitization was shown to be better for electroless Ni-P coated PAN-based carbon fibers heat treated at 1400 °C than for uncoated fibers heat treated at 2400 °C.     

Catalytic graphitization of templated mesoporous carbons

Graphitic porous carbons with a wide variety of textural properties were obtained by using a silica xerogel as template and a phenolic resin as carbon precursor. The synthetic procedure used to prepare them was as follows: (a) infiltration of the porosity of silica by a solution containing phenolic resin, (b) carbonization of the silica-resin composite, (c) removal of the silica skeleton, (d) impregnation of the templated porous carbon with a metallic salt and (e) catalytic graphitization of the impregnated carbon by heat treatment at 900 °C. The graphitization of the carbons thus prepared varies as a function of the carbonization temperature used and the type of metal employed as catalyst (Fe, Ni or Mn). The porous characteristics of these materials change greatly with the temperatures used during the carbonization step. These graphitized carbons exhibit high electrical conductivities up to two orders larger than those obtained for the non-graphitized samples.     

Catalytic graphitization of novolac resin for refractory applications

This study investigated how to induce graphite generation from the carbonization process of novolac resins using conditions that can be adopted for carbon-containing refractories (CCRs) production. The effect of boron oxide or boric acid (graphitizing agents), cross-linking additive (hexamethylenetetramine) and some processing parameters (mixing technique, vacuum degassing, heating rate and thermal treatments) on carbon graphitization from a commercial novolac resin were evaluated. The X-ray diffraction (XRD) technique was selected to measure the graphitization level and crystal parameters of the prepared samples. Based on the attained results, adding graphitizing agents prior to the pyrolysis of resin resulted in carbon crystallization. The best graphitization level was obtained when the mixtures containing 6 wt% B₂O₃ or 10 wt% H₃BO₃ were fired up to 1000 °C for 5 h using a heating rate of 3 °C/min. Although the reproducibility of the obtained results was ascertained, heterogeneous graphitization could be observed based on the XRD profiles, as well as some discrepancies in the calculated graphitization level values. This phenomenon was attributed to the additives susceptibility to agglomeration, preferential graphitization starting from lower binding energy sites and heat treatment temperature, among others.     

Improving graphitization degree of mesophase pitch-derived carbon fiber by solid-phase annealing of spun fiber

The solid-phase annealing of the mesophase pitch spun fiber was examined between the glass transition (T_g) and softening (T_s) temperatures of the pitch to improve the graphitization degree of the graphitized fiber through recovering or further improving the stacking height of the mesogen molecules in the spun fiber, since the rapid spinning reduced markedly stacking height in the as-spun fiber. A naphthalene mesophase pitch as received carried stacking height of 2.9 nm which was markedly reduced to 1.7 nm by spinning at 230 m/min, giving Lc=40 nm for its graphitized fiber. Annealing at 206 °C improved the stacking height of the spun fiber to 2.4 nm and Lc(002) of the graphitized fiber to 54 nm. Annealing of the methylnaphthalene mesophase pitch fiber at 200 °C was much more effective in improving the stacking height from 3.5 to 5.0 nm and its graphitized fiber to Lc=91 from 40 nm. Such an improved graphitization degree led to improved thermal conductivity and tensile modulus of the graphitized fiber. It must be noted that the annealing of the spun fiber reduced its stabilization rate, indicating densification of molecular stacking in the fiber. The transformation scheme of mesophase pitch into graphite fibers is discussed to clarify the roles of molecular stacking in the clusters and their arrangement in the mesophase pitch fiber during the carbon manufacturing process.     

炭化温度对针状焦制锂离子电池负极材料电化学性能的影响

通过循环性能、充放电特性和循环伏安曲线等分析,研究了炭化温度对针状焦制锂离子电池负极材料电化学性能的影响。     

Short residence time graphitization of mesophase pitch-based carbon fibers

The effects of graphitization time and temperature on the properties of three mesophase pitch-based carbon fibers have been characterized. Graphitization temperatures studied were 2400, 2700, and 3000 °C and residence times ranged from 0.7 to 3600 s. Helium pycnometry, measurements of fiber tow resistance, and X-ray diffraction were employed to study fiber properties. As anticipated, substantial variations in fiber properties were noted for the range of graphitization conditions studied and among the three fiber types. Significant structural evolution and property development occurred even at the shortest furnace residence times. For example, for one of the fibers, a furnace residence time of 0.7 s at 3000 °C resulted in a degree of graphitization value of ∼50%, a density of 1.98 g/cm³, and an electrical resistivity of 6.3 μΩ m (corresponding thermal conductivity ∼200 W m⁻¹ K⁻¹). A simple energy consumption analysis suggests that short residence time graphitization at high temperature may result in both lower costs and substantially higher production rates for fibers prepared from mesophase pitch.     

Carbon nanotubes prepared from three-layered copolymer microspheres of acrylonitrile and methylmethacrylate

Carbon nanotubes (CNTs) were synthesized from fine three-layered copolymer microspheres using the polymer blend technique. Diameter of PMMA core/Poly(AN-co-MMA) shell-1/PMMA shell-2 microspheres, prepared by a radical soap-free emulsion polymerization of methylmethacrylate (MMA) and acrylonitrile (AN), was between 400 nm and 500 nm. Microspheres were subjected to melt-spinning at 305 °C, stabilizing in oxygen at 220 °C for 4 h, and finally carbonizing at 1000 °C for 30 min. FE-SEM study of carbonized sample revealed the presence of CNTs arrays on carbon blocks. Similar arrays were observed in a comparative CNTs sample prepared from three-layered microspheres with the pure PAN shells-1 layers. HRTEM showed that the CNTs derived from copolymer microspheres had different structure when compared to the control sample, i.e. CNTs often adhered to each other and contained the internal compartments. The insufficient PMMA shell-2 coating of copolymer microspheres is believed to be a reason for CNTs adhesion. The possible mechanisms of the carbon block formation and the adhesion of CNTs are introduced.     

The graphitization of carbon nanofibers produced by catalytic decomposition of methane: Synergetic effect of the inherent Ni and Si

The catalytic effect of the inherent Ni and Si on the graphitization of carbon nanofibers produced by catalytic decomposition of methane is reported. The participation of the inherent Ni and Si metals as co-catalysts in the graphitization of the carbon nanofibers through the formation of Ni₂Si and SiC was inferred. Taking advantage of this catalytic effect, graphite materials showing structural characteristics comparable to oil-derived graphites which are employed in several industrial applications have been prepared from the carbon nanofibers. Unlike SiC which is further descomposed to graphite, the role of Ni₂Si remains unclear. At the CNFs heat treatment temperatures employed, Ni₂Si is in a liquid state where the carbon can be dissolved to form a supersaturated solution from which the SiC can be produced by segregation, thus being an intermediate stage in the catalytic graphitization of the carbon nanofibers. Further work are currently in progress to go insight this issue.     

Preparation of highly crystalline carbon nanofibers from pitch/polymer blend

High crystalline carbon nanofibers were prepared by using polymer blend technique. Naphthalene-based mesophase pitch (AR pitch) was dispersed finely in polymethylpentene matrix, spun by using a melt-blown spinning machine, stabilized at 160 °C in an oxygen atmosphere and carbonized at 900 °C in a nitrogen atmosphere. Bundles of the carbon nanofibers with ca. 100 nm in diameter were obtained after removal of polymethylpentene at the carbonization process. No impurity carbon was observed. The carbon nanofibers consisted of fine carbon crystallites with preferred orientation along the fiber axis. After heating to 3000 °C, the carbon crystallites grew drastically to have an interlayer spacing of 0.3367 nm and a crystallite thickness of 56.9 nm, respectively, with remarkable improvement of the preferred orientation of the crystallites. Advantages and disadvantages of the present method were discussed briefly.     

石墨化炉用变压器恒功率设计与实践

石墨化炉用变压器后期输出功率不足,是长期困扰石墨化工序的难题。作者于上世纪70年代提出恒功率设计理念,并就石墨化变压器特性设计问题,包括降功率设计及其运行、恒功率设计及其运行、旧设备改进等提出自己的看法,对石墨电极石墨化生产起到了指导作用。