Synthesis of boron-dispersed carbon by pressure pyrolysis of organoborane copolymer

Boron-dispersed carbon was synthesized by pressure pyrolysis of divinylbenzene-tris(allyl)-borane and styrene-tris(allyl)borane at 125 MPa below 650° C. Amorphous boron dispersed in a carbon matrix was oxidized easily to yield boric acid by heat treatment under air at 300° C. The BK image of the product showed that boron was dispersed uniformly in a carbon matrix. Boron-dispersed carbon had the morphology of coalescing spherulite and polyhedra depending upon the concentration of boron in the parent copolymer. The grain size of carbon polyhedra decreased from 2.0m to 0.2m with an increase in the boron concentration from 1.3 to 5.7 wt%. The presence of 0.5 wt% boron in a carbon matrix enhanced the graphitization at 4.0 GPa and 1200° C, decreasing the lattice spacing with an increase in the crystallite size. The crystallite sizes were comparable to each other after heat treatment at 1100° C and 4.0 GPa when the specimen contained boron from 0.5 to 2.5 wt%. The lattice constant (c ₀) and crystallite size (L _c) of boron-dispersed carbon containing 2.5 wt% boron were 677.0 pm and 30 nm, respectively, after heat treatment at 1200° C and 4.0 GPa.     

Synthesis and properties of platinum-dispersed carbon by pressure pyrolysis of organoplatinum copolymer

Platinum-dispersed carbon was synthesized by pressure pyrolysis of divinylbenzenebis (2-allylphenyl)platinum (APPt) and phenylacetylene-APPt at 550 °C and 125 MPa. The crystallinity of platinum dispersed in the carbon matrix synthesized from phenylacetylene(PA)-APPt was higher than that from divinylbenzene(DVB)-APPt. Platinum particles less than 60 nm were dispersed in the carbon matrix synthesized from DVB-APPt at 550 °C and 125 MPa. The carbon matrix formed from PA-APPt contained platinum particles of about 120 nm. The specific area of platinum-dispersed carbon synthesized at 550 °C and 125 MPa increased on subsequent heat treatments in argon, and reached 90 m² g^–1 after heat treatment at 800 °C for 1 h. The activity of platinum-dispersed carbon for the hydrogenation of cyclohexene increased with increasing specific area. Platinum-dispersed carbon formed from DVBAPPt was more active for hydrogenation reaction than that from PA-APPt. The highly active platinum-dispersed carbon could be synthesized from DVB-APPt at 520 °C. The surface area reached 154 m² g^–1 after heat treatment at 800 °C.     

Synthesis of nickel ferrite-dispersed carbon composites by pressure pyrolysis of organometallic polymer

Nickel ferrite-dispersed carbon could be synthesized by pressure pyrolysis of divinylbenzene (DVB)-vinylferrocene (VF)-nickelocene (Cp₂Ni) polymer in the presence of water under 125 MPa and at temperatures below 700°C. By heat treatment at 550°C with water, nickel ferrite particles could be dispersed finely in the carbon matrix, although a small amount of nickel-iron carbide also began to form above 600°C. The morphologies of the carbon particles formed were observed to be polyhedral, coalescing spherulitic and spherulitic. When 30 wt% H₂O, spherulitic carbons a few micrometres in diameter were prepared, in which nickel ferrite particles from 10–30 nm were dispersed in the carbon matrix. The saturation magnetization of carbon composites formed from DVB-3.0 mol% Cp₂Ni-6.0 mol% VF and 20 wt% H₂O at 550°C was about 30 e.m.u.g^–1 and increased with pyrolysis temperature. The coercive force of the carbon composite was 120 Oe and was affected by the amount of added water using pressure pyrolysis. Thermomagnetic measurement shows that the Curie temperature of nickel ferrite-dispersed carbon was about 580 °C.     

Synthesis and properties of magnetite-dispersed carbon by pressure pyrolysis of divinylbenzene-vinylferrocene with water

Magnetite-dispersed carbon was synthesized by pressure pyrolysis of the divinylbenzene-vinylferrocene system in the presence of water at 125 MPa below 700°C. Supercritical water influenced the phase separation of oligomers formed during the pyrolysis to give carbons with various morphologies, such as spherulitic, coalescing spherulitic and polyhedral carbon, depending upon the concentration of water. Carbon spherulites from 5 to 10 μm diameter dispersed with magnetite particles (<100 nm) were synthesized by pyrolysis of divinylbenzene-5.1 mol% vinylferrocene and 20.0 wt% water at 550°C and 125 MPa. The specific area of magnetite-dispersed carbon synthesized at 600°C and 125 MPa was 92 m²g⁻¹ after heat treatment at 800°C for 1 h. The specific area of the carbon specimen increased with decreasing pyrolysis temperature of the parent copolymers from 700 to 550°C. The Curie temperature of magnetite-dispersed carbon was 585°C. Magnetite dispersed in the carbon matrix was reduced to wüstite during the further heat treatment in vacuum. The saturation magnetization of magnetite-dispersed carbon was 79% of the theoretical value, and changed in proportion to the concentration of iron in the carbon matrix.     

Multiwall carbon nanotubes from pyrolysis of tetrahydrofuran

Multiwalled carbon nanotubes have been prepared by pyrolysing tetrahydrofuran (THF) in the presence of nickelocene. Pyrolysis of the precursor mixture has been achieved at temperature as low as 600 °C. In this simple approach no carrier gas has been used. The yield of purified carbon nanotubes is found to be more than 65%. Characterization of the as-prepared and purified nanotubes are done by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectra.     

碳纳米管的催化裂解聚苯乙烯法的制备及其表征研究

利用流动催化裂解法以聚苯乙烯为碳源,二茂铁为催化剂前躯体制备出了碳纳米管.用扫描电子显微镜,透射电子显微镜,拉曼光谱和X射线衍射对碳纳米管的结构进行了表征.再者,通过导入噻吩,合成了一种有很多细碳纳米管分支的碳纳米管.该制备过程工艺简单,碳源价格低廉.利用这个方法,通过控制条件,可得到不同结构的碳纳米管.     

Preparation of carbon nanotubes by pyrolysis of dimethyl sulfide

Carbon nanotubes (CNTs) have been synthesized by cobalt-catalyzed pyrolysis of dimethyl sulfide (C₂H₆S). The influences of the experimental conditions on the morphology and microstructure of the product have been quantitatively analyzed. The synthesis temperature of 1000 °C is required for the decomposition of C₂H₆S. Both of the C₂H₆S vapor concentration and flow rate in the reaction chamber determine the quality of the product; the optimum C₂H₆S vapor concentration for CNT growth is around 3.36–5.48%. High flow rate of C₂H₆S vapor promote the formation of branched CNTs (BCNTs). The detailed growth mechanism of BCNTs has been proposed.     

Preparation of carbon coated ceramic foams by pyrolysis of polyurethane

Electronically conducting carbon coatings over alumina foams were prepared by the foams’ impregnation in a polyurethane solution, followed by pyrolysis of the polymer layer. An optimal coating procedure was developed, using a commercial polyurethane lacquer. Pyrolysis was performed by heating the coated foams to 650–1,200 °C in Argon for 2–8 h. Coating characterization included surface area, phase composition, morphological and electrical conductivity measurements. Auger electron spectroscopy (AES) showed the composition was mostly carbon, with trace levels of oxygen impurities. Thickness, microstructure and interface between the alumina foam surface and the carbon film were analyzed using scanning electron microscopy (SEM and HR-SEM).The carbon film’s specific electrical resistivity was 1–10 (Ω m×10⁻²), depending on the pyrolysis time, temperature and number of coatings. The resistivity was found to decrease by a factor of six when the pyrolysis temperature was increased from 750 to 1,200 °C. A second carbon layer, reduced the resistivity further by about a factor of two. These effects are attributed to densification, improved connectivity between the carbon grains and an overall thickening of the carbon layer. Thermal analysis and Raman measurements on the carbon films point to a grain rearrangement that is consistent with the improved conductivity of the films.     

Preparation of semiconducting carbon fibre by pyrolysis of polyacrylonitrile precursor

Semiconducting carbon fibres were prepared from polyacrylonitrile precursor by pyrolysis in an inert atmosphere in temperature range 550–800 °C. The obtained fibres have an electrical resistivity between 10⁴ and 10^–2 cm^–1 and showed negative temperature coefficients. Electrical resistivity was mainly governed by the pyrolysis temperature and both electrical resistivity, , and thermistor constant,B, decreased with increasing pyrolysis temperature and duration. A linear relation between log and thermistor constantB was observed. Chemical analysis and infrared spectra indicated that the concentration of nitrogen and hydrogen decreased and basal plane structure developed accompanying an increase in carbon content as the pyrolysis temperature increased.     

Preparation of carbon spheres by low-temperature pyrolysis of cyclic hydrocarbons

Low-temperature pyrolytic decomposition of xylene, benzene, toluene, and naphthalene was investigated as a low-cost method for synthesis of a large quantity of perfectly shaped pure carbon spheres. The reaction occurred in a closed iron container at temperatures in the range of 500–700 °C and under pressure of 20 MPa. Some of the experiments were carried out in the presence of distilled water in vapor state near to its critical point, under which conditions it reacted as a very strong oxidant. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analysis were used to investigate the properties of the material obtained. The results demonstrated that synthesis had proceeded in the following sequence: vaporization of hydrocarbon, hydrocarbon transformation to condensing drops of heavy hydrocarbons, then drop growth accompanied by continuous alteration of the heavy carbon compounds until their final carbonization. Synthesis in a closed space stimulated particle growth, and particle diameters reached 1 to 12 μm. Continuous condensation of vapor onto the resulting drops caused agglomeration of some of the spheres to form pearl-necklace-like chains when the spheres docked to one another in the course of growth. Carbon atoms in the spheres were arranged in concentric, incompletely closed graphitic shells, which made them stable up to 600 °C in air. Above this temperature, rapid sphere degeneration occurred. Oxygen reacted with carbon atoms situated at the shell edges during heating in air, with some remaining in the spheres; oxygen penetration increased with treatment temperature.     

乙醇热解制备C／C复合材料探索研究

以可再生的资源无水乙醇为前驱体,在负压条件下,沉积温度为900℃～1200℃,采用压力梯度CVI工艺制备C/C复合材料.考察了沉积时间与密度的变化规律,采用偏光显微镜和扫描电镜观察了材料的组织结构和断口形貌,利用三点弯曲测定了材料的弯曲强度.结果表明:采用乙醇为前驱体,可大幅度提高致密化效率,96h制备出密度为1.47g/cm3的C/C复合材料;易于获得高织构的组织,制备试样的热解炭组织以粗糙层为主,断裂方式为假塑性断裂.乙醇是一种很有应用前景的制备C/C复合材料的前驱体.     

Formation of carbon nanotubes without iron inclusion and their alignment through ferrocene and ferrocene-ethylene pyrolysis

So far carbon nanotubes grown from the method most common method at present, that is, pyrolysis of ferrocene, invariably contains Fe inclusion. In addition, they are generally grown in random configurations. In the present investigations CNTs without Fe inclusion and in aligned configurations have been prepared by the pyrolysis of ferrocene (C10H10Fe) as well as pyrolysis of ferrocene in the presence of ethylene (C2H4). This has been achieved through optimization of growth parameters, for example, heating rate of ferrocene, pyrolysis temperature, and flow rates of carrier gas argon (Ar) and ethylene (C2H4). The as-synthesized samples have been characterized by transmission and scanning electron microscopic techniques. The optimum results relating to synthesis of carbon nanotubes without Fe inclusion and in aligned configurations have been obtained at 1000 degrees C pyrolysis temperature under flow rates of Ar of approximately 1000 sccm and of C2H4 of approximately 100 sccm. These carbon nanotubes have been found to have an outer diameter between approximately 20 and 60 nm and lengths between approximately 15 and 20 microns.     

Synthesis of iron-dispersed carbons by pressure pyrolysis of divinylbenzene-vinylferrocene copolymer

Versatile carbons with finely dispersed iron were synthesized by pressure pyrolysis of a copolymer prepared from divinylbenzene and vinylferrocene at temperatures below 680? C and pressures of 125 MPa. The pyrolysis conditions of the copolymer were found to influence the final morphology of carbons to give fibrils, spheres and polyhedra. The resulting carbons contained uniformly fine particles of cementite (Fe₃C) which were less than 30 nm in size, whereas the magnetite was dispersed in the carbon matrix by pressure pyrolysis in the presence of water. Highly dispersed cementite in carbon was found to decompose into metallic iron by further heat treatment above 850? C. Porous spherulitic carbons were also synthesized by heat treatment of magnetite containing carbon spherulites.     

酞菁铁固态热裂解制备新型炭纳米材料

研究了酞菁铁在密封体系中固态热裂解制备新型炭纳米材料的方法。通过这种方法，可以大量制备排列整齐又很直的碳纳米管。实验发现，升高热裂解温度，尤其温度高于800℃时，有利于碳管的生长。同时，这种方法还是一种非常有效的制备特殊结构纳米炭材料的方法。如用这种方法可以得到很长的具有电缆型结构的纳米炭，在其中具有单晶结构的炭化铁形成了电缆的金属芯。其他一些特殊炭结构，如项链型炭结构、管中管炭结构等也可以用这种方法制备出来。     

Synthesis of cementite-dispersed carbons by pressure pyrolysis of organoiron copolymers

Cementite-dispersed carbons were synthesized by pressure pyrolysis of divinylbenzene-vinylferrocene and styrene-vinylferrocene copolymer at temperatures below 600° C and the pressure of 125 MPa. The pyrolysis process of both copolymers was analysed by infrared spectra and magnetization of the pyrolysed substances. The absorption band of iron-carbon bond of divinylbenzene-vinylferrocene copolymer decreased on increasing its pyrolysis temperature from 300 to 450° C and finally disappeared at 500° C. The carbonization of divinylbenzene-vinylferrocene proceeded more rapidly than styrene-vinylferrocene at temperatures between 450 and 500° C. Styrene-vinylferrocene was heat-treated at 250° C for 2 h under 100 MPa affording a paramagnetic product, whereas the paramagnetic character of divinylbenzene-vinylferrocene was revealed after heat-treatment at 380° C. The saturation magnetization of cementite-dispersed carbon synthesized from both kinds of copolymers was comparable when the pressure pyrolysis was carried out at temperatures between 520 to 600° C at 125 MPa. The saturation magnetization of cementite-dispersed carbon formed at 550° C under 125 MPa was correlated linearly with the iron content in carbon. Threedimensional cross-linked divinylbenzene-vinylferrocene copolymer gave the highly dispersed cementite particles less than 50 nm with the coercive force of 950 Oe. On the other hand, the larger particle size of cementite up to 120 nm and the lower coercive force about 400 Oe were obtained in carbon matrix prepared by the pressure pyrolysis of styrene-vinylferrocene copolymer.     

Formation of fractal carbon structures in barrier-discharge plasma under atmospheric pressure

Conditions in which fractal carbon structures are formed in barrier-discharge plasma under atmospheric pressure to obtain submicrometer carbon particles have been studied.     

Formation of dense and non-agglomerated lead oxide particles by spray pyrolysis

Submicrometre, highly pure and dense PbO particles were synthesized by pyrolysis of a spray of a lead nitrate, Pb(NO₃)₂ solution generated by an ultrasonic transducer in a tubular-flow reactor at 300–800 °C and at various carrier gas flow rates. The produced particles were non-agglomerated, non-porous, and mainly tetragonal PbO above 500 °C. Below this temperature, the conversion could not be completed. The high purity, completely densified particles could be obtained at high gas flow rates. The observed particle yields higher than 90%, indicated the high efficiency of this process. Preheating of the mist before the pyrolysis stage was found to be necessary for densification of the particles. Experiments indicated that the spray was dried at the end of the preheating stage forming dense and non-porous Pb(NO₃)₂ particles. These non-porous particles decomposed and shrunk to PbO particles without any particle bursting into pieceS. Therefore, it was concluded that the decomposition occurred through the liquid phase allowing the evolution of gaseous reaction products by bubbling.