Growth of carbon micro-coils by pre-pyrolysis of propane

Carbon micro-coils were obtained by the Ni catalyzed pyrolysis of propane as a carbon source which was pre-heated and pre-pyrolyzed at 1000–1100 °C. The obtained carbon micro-coils were mostly irregular double coils with a larger coil pitch of 1–5 m and larger coil diameter of 5–20 m than that obtained using acetylene.     

Oxidation characteristics of the graphite micro-coils, and growth mechanism of the carbon coils

The oxidation characteristics of the graphite coils obtained by high-temperature heat treatment of the vapor grown carbon micro-coils were examined, and the growth mechanism of the carbon micro-coils is discussed. The ruptured cross section of the graphite coils with a circular cross section (circular graphite coils) exposed in air or an Ar atmosphere at 800–1400°C have generally negative or positive trigonal cone-forms. On the other hand, that of the graphite coils with flat or rectangular cross sections (flat graphite coils) have negative or positive rectangular cone or roof-like forms. The edge between two graphite layers was preferentially oxidized to form three deep striations that extended in the direction of the fiber axis, and then formed six coils from the double circular graphite coils. It is reasonably considered that eight thin coils are formed from the double flat graphite coils. These observations strongly supported the growth mechanism based on the catalytic anisotropy between the catalyst crystal faces.     

Preparation and properties of TiC micro-coils and micro-tubes by the vapour phase titanizing of carbon micro-coils

TiC micro-coils and micro-tubes were prepared by the vapour phase titanizing of the regular carbon micro-coils, and the preparation conditions and some properties were examined. The carbon coils were titanized from the surface of the fiber to the core with full preservation of the coiling morphology to form TiC micro-coils or micro-tubes. The bulk electrical resistivity was 0.1–0.01 ·cm depending on the titanized rate and the bulk density. The specific surface area of the source carbon coils (about 100 m²/g) was significantly decreased with increasing reaction temperature and reaction time. The tensile strength of a TiC micro-tube was 660 MPa. The attenuation ratio against an electromagnetic wave of the TiC micro-tubes (30 wt % in epoxy resin) was about 90% (dB = –10) for 800–900 MHz.     

Vapor-phase formation of single-helix carbon microcoils by using WS2 catalyst and the morphologies

Very regular single-helix carbon microcoils of outer coil diameter 1–;3 m, inner coil diameter 0.5–;2 m, and coil pitch 1–;2 m were prepared by the WS₂-catalyzed pyrolysis of acetylene in the presence of thiophene impurity. The effects of reaction temperature and thiophene gas flow rate on the growth of single-helix carbon microcoils and the morphology were examined in detail. The optimum reaction temperature was 780°C, and optimum gas flow rate of thiophene, acetylene, hydrogen and argon for obtaining regular single-helix carbon coils with a constant coil diameter were 0.2, 40, 90, and 30 sccm, respectively. The formation mechanism of the single-helix carbon microcoils is discussed.     

Various conformations of carbon nanocoils prepared by supported Ni-Fe/molecular sieve catalyst

The carbon nanocoils with various kinds of conformations were prepared by the catalytic pyrolysis of acetylene using the Ni metal catalyst supported on molecular Sieves which was prepared using Fe-containing kaolin as the raw material. There are four kinds of carbon nanocoils conformations produced by this catalyst. The influences of reaction temperature and gas conditions on the conformations of the nanocoils were investigated and the reasons of forming nano-size coils were discussed by comparison with pure Ni metal catalyst.     

碳螺旋纤维的阻抗特性研究

利用化学气相沉积（CVD）法制备微米尺度的碳螺旋纤维, 通过设计的拉伸装置引导试样中的碳螺旋纤维沿拉伸方向有序排列, 使用光学显微镜观察其形貌及排列情况. 具体研究了定向排列碳螺旋纤维的交流阻抗特性, 结果表明：低频时碳螺旋纤维的阻抗和辐角保持不变, 表现为纯电阻行为, 但是高频时（f>10kHz）阻抗和辐角随交流频率升高而迅速减小; 并且碳螺旋纤维对其被拉伸状态很敏感, 阻抗值随拉伸长度增大而增大. 该研究对开发碳螺旋纤维在微电路和微纳米感应器技术中的应用有重要意义.     

Controllable synthesis of carbon microcoils/nanocoils by catalysts supported on ceramics using catalyzed chemical vapor deposition process

Carbon microcoils (CMCs) and carbon nanocoils (CNCs) were prepared by the catalytic pyrolysis of acetylene using Ni-based or Fe-based catalysts supported on molecular sieves by the catalyzed chemical vapor deposition (CCVD) process. The growth pattern, morphology and structure of the CMCs and CNCs (to be called by a joint name ‘carbon coils’) were examined in detail. By using a ceramic supporter, the anisotropy of the catalysts could be utilized and carbon coils could be more effectively obtained compared to non-supported alloy catalysts. Furthermore, the morphologies of the carbon coils could be controlled. The Raman spectra indicated that the structures of all these carbon coils were nanocrystalline phases in amorphous networks in spite of the different catalysts and preparation conditions.     

新型催化剂制备微螺旋碳纤维的研究

利用溶剂热法制备了硫化镍,并以它为催化剂通过化学气相沉积法催化制备了微螺旋碳纤维。采用扫描电子显微镜对微螺旋碳纤维的微观形貌进行了表征,发现产物几乎全部为双螺旋碳纤维,同时通过研究影响微螺旋碳纤维生长的因素,发现微螺旋碳纤维的最佳生长条件为:反应温度750℃,气体流量110sccm,噻吩温度30～35℃,反应时间90min。FT-IR结果表明,微螺旋碳纤维分子结构中既含有不饱和的C=C双键,又含有饱和的-CH2-和-CH3基团。     

The phenomenon of changing coiling-chirality in carbon nanocoils obtained by catalytic pyrolysis of acetylene with various catalysts

Carbon nanocoils were prepared by the chemical vapor deposition process of the catalytic pyrolysis of acetylene at 700-800 degrees C with various catalysts. Twisting or coiling-formed carbon nanocoils with changing coiling-chirality and zigzag-formed carbon nanofibers were obtained with SUS 304, WS2, Pt-Pd, TiN, and Ni as the catalysts. Their morphologies and microstructures were examined in detail, and then the changing mechanism of the coiling-chirality was discussed. No apparent difference in the microstructure between the part of a nanocoil with changing coiling-chirality and the part of a zigzag nanofiber with changing zigzag-chirality, or between a bulk right-clockwise coil and a bulk left-clockwise coil was observed. It was supposed that changing coiling-chirality was mainly caused by the gradual or successive change in chemical composition on the thin layers present on the surface of catalyst grains during the chemical vapor deposition process.     

Preparation of single-helix carbon microcoils by catalytic CVD process

Three-dimensional (3D) single-helix spring-like carbon microcoils (SH-CMCs) were obtained by the catalytic pyrolysis of acetylene at 800-820 °C over the Fe-Ni alloy catalysts; their growth morphologies and microstructure were examined. The diameter of carbon fiber, from which the carbon nanocoils was formed, was about 0.5 μm, the coil diameter was about 1-2 μm, and the coil pitch was about the same with the coil diameter. The SH-CMCs were generally grown by a double-directional growth mode.     

变截面形状螺旋形炭纤维的制备和生长机理

以镍为催化剂,通过控制碳源气体乙炔的流速,在1 013 K-1 053 K温度下,制备了纤维截面形状在生长过程中由扁平形变为圆形的螺旋炭纤维,同时螺旋直径也相应的由4.2 μm变化为6.0 μm,这种变截面螺旋炭纤维的发现,为微机械系统提供了一种新型弹簧.提出了变截面螺旋炭纤维的生长机理,认为催化剂颗粒的各向异性不仅影响螺旋炭纤维螺径的大小,还影响纤维的截面形状.随着生长过程中反应条件的改变,催化剂各向异性也发生改变,长方形催化剂既可以生长扁平形也可以生长圆形截面螺旋形炭纤维,但是立方形催化剂只能生长圆形截面螺旋形炭纤维.该机制的提出不仅有助于加深对双螺旋炭纤维生长本质的认识,还对指导螺旋形炭纤维的控制生长具有重要意义.     

Two opposite growth modes of carbon nanofibers prepared by catalytic decomposition of acetylene at low temperature

Helical carbon fibers were synthesized by the catalytic decomposition of acetylene as carbon source at low temperature of 240–260 °C with two nanocopper catalysts prepared by the hydrogen-arc plasma method and thermal decomposition of copper tartrate. Two growth modes for helical carbon fibers were obtained. One is mirror-symmetric growth mode, and the other is asymmetric growth mode. In the two growth modes, there were always only two helical fibers in regular shapes that were grown over a single copper nanoparticle. The two helical fibers had identical coil diameter, coil length, fiber diameter, cycle number, tight coil pitch, and cross section. In mirror-symmetric growth mode, the two helical fibers had absolutely opposite helical senses. The catalyst particle size was less than 50 nm and the coil diameter was <100 nm. Whereas in asymmetric growth mode, the two helical fibers had absolutely identical helical senses. The catalyst particle size was larger than 200 nm and their coil diameters reached 1 μm. The catalyst particle size had considerable effect on the growth mode for helical carbon fibers.     

Study on cross section of high temperature superconducting coil

It is in particular of importance for HTS coils to secure a larger central magnetic field and/or a large stored energy with shorter length of HTS tapes. The critical current of an HTS tape depends on both the flux density and the flux angle against tapes. From this point, the performance improvement of HTS coils is taken into account with an analytical model. The minimum volume coil derived from the Fabry Factor constant curve is taken concerning the original coil shape, which is often employed in low temperature superconducting coils. The coil critical current was analyzed in consideration of the anisotropic properties of the tape.The electric field of HTS tapes in the coil was calculated at the coil critical current and the high electric field portion were cut out. The optimal coil cross section is obtained by iterating this calculation process. As a result, the critical current and the stored energy density of the coil were improved. The stored energy density increased about 17% and the central magnetic field was almost kept constant regardless of 19% reduction of HTS tapes, as compared with the original coil with the rectangular cross section.     

全pH范围内超疏水大面积的微米螺旋炭丝

通过控制催化前驱体(酒石酸铜)的电化学氧化在金属表面形成了铜催化剂,并通过铜催化裂解乙炔在金属表面制备了大面积的微米螺旋炭丝。用SEM, FT-IR,XPS和测接触角对所制制螺旋炭丝进行了表征。发现螺旋炭丝具有非常好的化学稳定性和全PH范围的超疏水性质。这种炭丝被期待用做特殊的界面功能材料。     

Catalytic synthesis of carbon nanofibers and nanotubes by the pyrolysis of acetylene with iron nanoparticles prepared using a hydrogen-arc plasma method

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were synthesized at different temperatures by the catalytic pyrolysis of acetylene with iron nanoparticles prepared using a hydrogen-arc plasma method. The obtained carbon nanomaterials were characterized by transmission electron microscopy and field-emission scanning electron microscopy. An iron nanoparticle was always located at the tip of CNFs or CNTs, whose diameter was approximately identical with the diameter of the iron nanoparticle. The structures of the products were closely related to the reaction temperature, and could be changed from fibers to tubes by simply increasing the temperature. CNFs were obtained at the reaction temperature of 550-650 °C. When the reaction temperature was increased to 710-800 °C, CNTs were obtained.     

Large-scale synthesis of the controlled-geometry carbon coils by the manipulation of the SF6 gas flow injection time

Carbon coils could be synthesized using C2H2/H2 as source gases and SF6 as an incorporated additive gas under thermal chemical vapor deposition system. Nickel catalyst layer deposition and then hydrogen plasma pretreatment were performed prior to the carbon coils deposition reaction. According to the different reaction processes, the injection time of SF6 gas flow was varied. The characteristics (formation density, morphology, and geometry) of the deposited carbon coils on the substrates were investigated according to the different reaction processes. Finally, the large-scale synthesis of carbon coils and their geometry control could be achieved merely by manipulating SF6 gas flow injection time. Three cases growth aspects were proposed according to SF6 gas flow injection time in association with the fluorine's characteristics for etching the materials or enhancing the nucleation sites.     

Effects of the size of nano-copper catalysts and reaction temperature on the morphology of carbon fibers

In this study, carbon fibers with different morphologies, including coiled carbon nanofibers and straight carbon fibers, were obtained by the chemical vapor deposition using a Cu-catalytic pyrolysis of acetylene at 250 °C. The influences of nano-copper catalyst particle size and the reaction temperature on the morphology of carbon fibers were investigated. Under the same reaction condition, coiled carbon nanofibers generally were synthesized using nano-copper catalyst with smaller particles size, and bigger copper particles are apt to produce straight carbon fibers. With decreasing of reaction temperature to 200 °C, straight carbon fibers were obtained, instead of coiled carbon nanofibers at 250 °C. The product was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD).     

利用层间化合物制备载Pt催化剂

通过利用Pt(IV)-GICs和Pt(IV)乙炔黑层间化合物来制备应用于甲醇电氧化石墨和乙炔黑载铂催化剂。具体过程如下在惰性气氛下,利用H     

Surface characterization and nanomechanical properties of diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films were synthesized by RF plasma enhanced chemical vapor deposition using acetylene as the carbon source and the effects of acetylene/nitrogen ratio in the reaction atmosphere, deposition pressure, and plasma post-treatment using different atmospheres on the surface roughness and mechanical properties of DLC films were investigated. Although the surface roughness, characterized by AFM, decreased as the acetylene/nitrogen ratio in the reaction atmosphere decreased, the hardness of DLC films measured by nanoindentation also decreased with the decrease of the acetylene/nitrogen ratio, which is consistent with the Raman results of the I_D/I_G ratio. Rougher films with higher residual stress were obtained when using a deposition pressure higher than 40.0 Pa (0.3 torr). For the effect of plasma post-treatment using different atmospheres, surface smoothing was found for the hydrogen plasma post-treatment, whereas nitrogen and argon plasma post-treatments resulted in surface roughening. Hydrogen plasma post-treatment was found to lower the surface roughness without significantly sacrificing the hardness.     

Mutual Inductance and Force Calculations Between Coaxial Bitter Coils and Superconducting Coils with Rectangular Cross Section

Mutual inductance and force calculations between coaxial Bitter coils and superconducting coils with rectangular cross section in a hybrid magnet system using derived semi-analytical expressions based on two integrations were performed. The mutual inductance and force calculations are based on the assumption of the uniform current density distribution in superconducting coils. The current density distribution of a Bitter coil in radial direction, however, is inversely proportional to the radius of the Bitter coil. The influence of the current density redistribution caused by a cooling hole and an inhomogeneous temperature distribution of Bitter coil of a water-cooled magnet was not considered. The obtained expressions can be implemented by Simpson’s integration with FORTRAN programming. We confirm the validity of mutual inductance calculation by comparing it with a filament method, and give the accuracy of two methods. The mutual inductance values computed by two methods are in excellent agreement. The derived semi-analytical expressions of mutual inductance allow a low computational time compared with filament method to a specific accuracy. The force is derived by multiplying the currents of the two coils by their mutual inductance gradient.