Micro-coiled Carbon Fibers Research Articles

Effect of high temperature treatment on the topological microstructure of micro-coil carbon fibers

The topological microstructure of micro-coiled carbon fibers (MCFs) before and after high temperature treatment (HTT) was explored and characterized. Results suggested that as-grown MCFs had an annular ring-like structure in the cross section and a herringbone-like structure in the longitudinal section, but the orientation range of graphitic domains was wide. After HTT, the coiled fibers consisted of stacked pyramidal prisms of ordered graphitic domains. The apparent morphology of the coiled fibers is a uniform spiral prism. The evolvement of the microstructure of MCFs after HTT was also confirmed by X-ray diffraction and Raman spectroscopy. The topological microstructure provides a reliable reference for the prediction of properties and projected applications of the MCFs. [New Carbon Materials 2012, 27(6): 448–454]

Electrically conductive adhesive based on bismaleimide‐triazine resin filled with microcoiled carbon fibers

AbstractElectrically conductive adhesive (ECA) was prepared with cyanate ester resin and bismaleimide resin formed bismaleimide‐triazine resin as the matrix, a γ‐glycidoxy propyl trimethoxy silane (KH‐560) as the coupling agent, and the carbon microcoils (CMCs) as the conducting filler. CMCs were synthesized by the catalytic decomposition of acetylene using nickel sulfide particles as the catalyst, which prepared by solvothermal method. The morphology and microstructure of CMCs were examined by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. The electrical conductivity of the ECA increased to 3.16 × 10−2 S/cm. When the content of CMCs was 1.5 wt %, the shear strength between 25 and 200°C remained at a high value of 22.8 and 21.4 MPa, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Preparation and Characterization of Micro-coiled Carbon Fibers

Carbon microcoils (CMCs) were synthesized by the catalytic decomposition of acetylene using nickel sulfide particles as the catalyst which prepared by solvothermal method. The morphology and microstructure of the catalyst and micro-coiled carbon fibers were examined by SEM, FT-IR and XRD. The results showed that the catalyst was regular hexagonal phase nickel sulfide with its diameter of 1−2 μm and a smooth surface. CMCs have double helix structure, rectangular cross-section and identical coil diameter. The molecular structure of CMCs contained both unsaturated -C=C- and saturated -CH2- and -CH3 groups. The microstructure of CMCs was of poor degree of order with a low graphitization degree, containing a certain amount of amorphous carbon and crystal defects.

Helical nanocoiled and microcoiled carbon fibers as effective catalyst supports for electrooxidation of methanol

We have demonstrated a new synthesis of twist-shaped nanocoiled and herringbone-type double microcoiled carbon fibers via catalytic chemical vapor deposition of acetylene over NiCuMgAl-layered double hydroxides. The materials were characterized by power X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and N 2 adsorption–desorption experiments. For the first time, the use of electrodes modified with platinum particles supported on as-grown helical carbon fibers was studied for electrocatalytic oxidation of methanol. Especially, the electrode supported on herringbone-type double microcoiled carbon fiber showed much larger Pt active surface area than that supported on commercial carbon black. Furthermore, such electrocatalyst has exhibited about fourfold enhancement of activity and excellent anti-poisoning ability, which is believed to be attributed to the combined beneficial effects of novel microstructure and special composition of as-grown helical carbon fibers.

Research on the Impedance Characteristic of Carbon Coils

Micro-coiled carbon fibers were prepared by chemical vapor deposition method(CVD),and aligned via a device designed for executing action with mechanical drawing.Optical microscope was performed to characterize the morphology and aligned state of the fibers.The AC impedance characteristics(impedance |Z| and phase angle θ) of the aligned carbon coils were studied.The results show that impedance and phase angle of the carbon coils keep stable at low frequency,but decrease rapidly with the frequency increasing at high frequency area(f10kHz).Furthermore,the aligned fibers are sensitive to their extending states,and their impedance increases with the extending length prolonging.The study is useful to develop the technique of micro-circuits and micro-sensor based on carbon micro-coils.

Effect of Graphitization on the Morphologies and Microstructures of Micro-coiled Carbon Fibers

Micro-coiled carbon fibers were prepared by a catalytic chemical vapor deposition method, and treated in an argon atmosphere at 2500℃.Scanning electron microscope(SEM),Raman spectro- scope and X-ray diffraction(XRD)were performed to characterize morphologies and microstructures of the non-graphitizated and graphitizated micro-coiled carbon fibers,and graphitization mechanism was discussed preliminarily.The results reveal that micro-coiled carbon fibers are purified prominently, morphologies of micro-coiled carbon fibers is similiar to the original fibers,and microstructures of micro- coiled carbon fibers are more regular after the graphitization treatment.The interlayer spacing d_(002) (0.3626-0.3378nm)decreases,graphitization degree,L_c,mean size of crystal in the c-direction(1.6404- 3.8590nm)and L_a,mean size of crystal in the a-direction(2.04-7.21nm)increase.

Facile flame synthesis and electrochemical properties of carbon nanocoils

Abstract Carbon nanocoils (CNCs) were in situ synthesized by using tin oxide nanoparticle catalyst from stannic chloride precursor in an ethanol flame. The anisotropic deposition rate of carbon among tin dioxide crystal planes provides the driving force for the coiling of carbon fibers. The obtained CNCs have tight coil pitches and average fiber and coil diameter of approximately 50–80 nm and 80–100 nm, respectively. BET measurement and BJH method reveal that the CNCs possess a mesoporous character. The CNCs present excellent specific capacitance as ca. 40 F/g using as polarized electrodes, which is considerably higher than that of the micro-coiled carbon fibers or carbon nanofibers, maybe the ideal candidate using as supercapacitor.

Direct synthesis of micro-coiled carbon fibers on graphite substrate using co-electrodeposition of nickel and sulfur as catalysts

Micro-coiled carbon fibers were directly prepared on the graphite substrate using co-electrodeposition of nickel and sulfur as catalysts, in this paper. The diameter of coil and that of micro-coiled carbon fiber are about 800 nm and 400 nm, respectively. Compared with the current preparation methods of catalysts, electrochemical deposition is an effective, cheap and simple technique. Especially, this method is suitable for preparation of ally catalyst. The parameters of electrochemical deposition (deposition time and current density) have little influence on helix of growth and growth mechanism of carbon fibers. By adjusting the electrolyte solution, the amount of sulfur in catalyst are easily carried out, and it is found that sulfur content in catalyst plays an important role on morphological characteristics of carbon fibers.

Electromagnetism and Absorptivity of the Modified Micro-coiled Chiral Carbon Fibers

Micro-coiled chiral carbon fibers are modified by nano-Ni. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to compare the composition and morphology of the unmodified and the modified fibers. The results show that electromagnetism parameters of the modified are different from those of the unmodified. After modification by nano-Ni, the micro-coiled chiral carbon fibers have decreased permittivity and electrical loss. The permeability and magnetic loss of the modified carbon fibers become larger than those of the unmodified ones. Moreover, the modification of unmodified chiral carbon fibers into the modified is much like changing hollow electric windings into those with magnetic cores inside. The modifier intensifies the cross polarization of the chiral carbon fibers and makes the permittivity and the permeability get closer to each other which improves the matching performance and enhances absorbability of coatings. In the range of 6-18 GHz, the reflectivity of the coating is 6-8 dB and the bandwidth is 12 GHz. The area density of the coating is below 3 kg/m2.

Electrical properties of a single microcoiled carbon fiber

Regular microcoiled carbon fibers with a double helix structure have been synthesized by the catalytic pyrolysis of acetylene at 750–790°C using Ni powder as a catalyst and thiophene as a promotor. The measurements by a standard four-probe technique of resistance, I-V curves, and magnetoresistance of a single microcoiled fiber are presented. I-V curves and the temperature dependence of the resistance are in accordance with Mott-David [Electronic Processes in Noncrystalline Materials (Oxford University Press, Oxford, 1979), 2nd ed., p. 32] variable range hopping above 13K and Shklovskii-Efros [Electronic Properites of Doped Semiconductors (Springer, Berlin, 1984), p. 202]; Pollak-Shklovshii [Hopping Transport in Solids, (North-Holland, Amsterdam, 1991), 273] variable range hopping below 13K. In addition, a positive magnetoresistance with H2-dependence behavior is observed at low temperature.

Microwave Electromagnetic Characteristics of a Microcoiled Carbon Fibers/paraffin Wax Composite in Ku Band

The complex relative permittivity ∈γ and permeability μγ of microcoiled carbon fibers (MCCFs) imbedded in paraffin wax were measured at Ku band frequencies (12.4–18 GHz). Both the real and imaginary parts of the complex relative permittivity of the MCCFs/paraffin wax composite decreased with increase of the frequency. The real part of the complex relative permeability of the composite increases with increase of the frequency, and the imaginary part is nonzero and nearly constant over the measured frequency range. The dielectric loss tangent (tan δ∈), the magnetic loss tangent (tan δm), and amplitude attenuation factor (α) were determined as well. On the basis of the experimental results, the MCCFs/paraffin wax composite is mainly a kind of dielectric lossy material with small magnetic loss and diamagnetism in the Ku band.

Solid catalytic growth mechanism of micro-coiled carbon fibers

Micro-coiled carbon fibers were prepared by catalytic pyrolysis of acetylene with nanosized nickel powder catalyst using the substrate method. The morphology of micro-coiled carbon fibers was observed through field emission scanning electron microscopy. It was found that the fiber and coil diameter of the obtained micro-coiled carbon fibers is about 500–600 nm and 4–5 μm, respectively. Most of the micro-coiled carbon fibers obtained were regular double carbon coils, but a few irregular ones were also observed. On the basis of the experimental observation, a solid catalytic growth mechanism of micro-coiled carbon fibers was proposed.

Development and characterization of micro-coil carbon fibers by amicrowave CVD system

Nano- and micro-coiled carbon fibers find applications in electronicdevices, electromagnetic absorbers and filters. Smart devices can be conceivedusing tunable films on these fibers and tunable host materials. A new methodof producing helical carbon fibers with dimensions in the order of less than amicrometer has been developed using microwaves. The microwave CVD systempresented here eliminates the use of the toxic impurity gas, which is requiredin the conventional method. Both methods involve gas phase reactions over asubstrate seeded with an appropriate catalyst. Micro-coiled carbon fiber(MCCF) was grown by the catalytic pyrolysis of acetylene on a silicon carbidesubstrate on which nickel metal powder was dispersed as a catalyst. Variousfactors, for example flow rate of the gas, particle size of the catalyst,effect of reaction temperature and time, were studied in order to understandthe growth of the microwave synthesis of MCCF. MCCFs were also synthesized bya conventional method in the presence of thiophene as an impurity gas so thata comparison can be made with the materials obtained by the microwave system.The morphology of the final products were investigated by scanning electronmicroscopy. The carbon products obtained by traditional and microwave methodswere investigated with the help of x-ray diffraction. The effect of variousreaction conditions on the morphological development of a MCCF were examinedin detail. Furthermore, a brief study was made on the microwave absorbingproperty of the MCCF.

Vapor growth of micro-coiled carbon fibers and the properties

Vapor growth of micro-coiled carbon fibers and the properties

Catalytic effects of metal carbides, oxides and Ni single crystal on the vapor growth of micro-coiled carbon fibers

Micro-coiled carbon fibers were prepared by the impurity-activated chemical vapor deposition using the powders of metal carbides, metal oxides, and a Ni single crystal. The catalytic effect of these impurities on the coil yield and morphology were examined, and the growth mechanism is discussed. The pre-oxidized Ti plate, Ti 2O 3 and TiC powders, and a Ni single crystal as well as various metal powders provided the micro-coiled carbon fibers. For the Ni single crystal, the Ni(100) crystal gave the highest coil yield followed by Ni(111)and then Ni(110). It is considered that the anisotropic deposition rate of a carbon among the Ni single crystal planes is the driving force of the coiling of carbon fibers to form the coiled fibers.

Vapor Growth of Micro-coiled Carbon Fibers and the Properties

Micro-coiled carbon fibers (coils) were prepared by catalytic pyrolysis of acetylene at 650-850°C, and growth conditions, morphology, growth mechanism and some properties were examined. The key points for obtaining coils with high coil yield were strict control of (1) kind of catalyst, (2) kind and flow rate of impurity gas, (3) reaction temperature, and (4) separation between source gas inlet and substrate. The most effective catalysts were Ni, Ti, and W. The coils show an excellent electromagnetic shielding effect. TiC coils were obtained by vapor phase titanizing of the coils.

Vapor phase preparation of micro-coiled carbon fibers by metal powder catalyzed pyrolysis of acetylene containing a small amount of phosphorus impurity

Micro-coiled carbon libers were vapor phase prepared using the catalytic pyrolysis of acetylene in the presence of a metal powder catalyst and a small amount of phosphorus impurity. Growth conditions and morphology of the obtained coiled carbon Obers were examined. Among the transition metal powders used, nickel was the most effective lor the growth of the coiled carbon fibers and the maximum coil yield of about 45V was obtained using PH3 as the impurity. The optimum reaction temperature and PH3 impurity How rate was 650 C and 0.01 seem, respectively.

Preparation and properties of coiled carbon fibers by the catalitic pyrolysis of acetylene

Microcoiled carbon fibers were obtained by the Ni catalyzed pyrolysis of acetylene at 600-800°C. The presence of small amounts of a sulfur compound impurity was indispensable for the growth of the coiled carbon fibers in high yield with good reproducibility. The optimum growth temperature was 750°C irrespective of the kind of sulfur compounds used as the impurity. The optimum impurity gas flow rate was restricted to a very narrow range depending on the impurity type. The maximum yield (about 50%) of the coiled carbon fibers was obtained using thiophene. Some properties of the coiled carbon fibers were examined. A new growth mechanism for the coiled carbon fibers will be presented