Masayuki Kawaguchi

Growth of regularly coiled carbon filaments by Ni catalyzed pyrolysis of acetylene, and their morphology and extension characteristics

Regularly coiled carbon filaments have been obtained by the catalytic pyrolysis of acetylene at 350–750 °C using Ni plate and powder as a catalyst. Morphology and extension characteristics of the obtained coiled filaments were examined in some detail. The regularly coiled filaments have generally a 0.1–0.3 μm thickness, a 2–8 μm coil diameter, and a 0.1–5 mm coil length. The coiled filaments were always formed by the entwistness of two pair coils which grew in the same direction simultaneously from a diamond‐shaped Ni seed. We have found that the coiled filaments could be elastically extended up to about three times versus the original coil length.

Preparation of coiled carbon fibers by catalytic pyrolysis of acetylene, and its morphology and extension characteristics

Abstract Regularly coiled carbon fibers have been obtained by the catalytic pyrolysis of acetylene at 330 to 750°C using a Ni plate and powders as a catalyst. We have examined the morphology and extension characteristics of the obtained coiled fibers in some detail and discussed the growth mechanism. It has been observed that the coiled fibers were almost formed by the crossing or entwisting of two primary coils which grew in the same (coiling) direction simultaneously from a diamond-shaped nickel seed (combination coils). Other type of the coiled fibers, such as a single coils, double coils, and flat coils were also sometimes observed. The coiled fibers generally have a 0.1 to 0.3 μm thickness, 2 to 8 μm coil diameter, and 0.1 to 5 mm coil length. We have found that the coiled fibers could be extended elastically up to about three times versus the original coil length and semielastically up to about 4.5 times.

A growth mechanism of regularly coiled carbon fibers through acetylene pyrolysis

Abstract Regularly coiled carbon fibers were prepared by Ni catalytic pyrolysis of acetylene. A small amount of H 2 S was indispensable for the growth of the coiled carbon fibers. A Ni compound seed observed on the tip of the pair-coiled carbon fibers is a single crystal. It is suggested that each crystal plane of the Ni compound seed has a different catalytic ability for the growth of the coiled carbon fibers. A growth mechanism for the coiled carbon fibers called the “quasi-VLS mechanism” is proposed, which involves the surface diffusion of carbon species on the Ni compound seed.

Preparation of coiled carbon fibers by pyrolysis of acetylene using a Ni catalyst and sulfur or phosphorus compound impurity

Coiled carbon fibers were prepared by pyrolysis of acetylene activated using a Ni catalyst and a small amount of impurities at 600–800 °C. It was found that the addition of a small amount of sulfur or phosphorus compound impurities in acetylene was indispensable for the growth of coiled carbon fibers. Among the sulfur compounds used, thiophene was the most effective for growing coiled carbon fibers with uniform coil diameter and producing a high yield (about 50% coils). Similar results were obtained with phosphorus trichloride.

Graphite intercalation compound of magnesium fluoride and fluorine

Abstract A graphite intercalation compound of C x F(MgF 2 ) y was prepared under a fluorine atmosphere of 1 atm at temperatures of 20–350°C. The 1st stage compound has the identity period of 9.3–9.4A. ESCA and 19 F NMR spectra indicate that the chemical interaction of intercalated fluorine with carbon is similar to that for graphite fluoride, however, with C x F(MgF 2 ) y having slightly mobile fluorine atoms chemically adsorbed on carbon atoms of graphite layers.

Graphite intercalation compound of fluorine with lithium fluoride

Abstract Graphite intercalation compounds of fluorine and LiF were prepared from several carbon materials. The 1st stage compounds with repeat distances of 9.38–9.44 A were prepared from natural graphite, while graphitized petroleum coke gave a 2nd stage compound with a repeat distance of 12.7 A. A compound of polyacrylonitrile(PAN)-based carbon fiber showed high stability in air, decomposing at 407 °C. The a-axis electrical conductivities were 2.0 × 10 5 Ω −1 cm −1 between 9 and 13 wt.% of intercalant for the compounds of pyrolytic graphite, and (8–9) × 10 3 Ω −1 cm−1 in the 7 – 14 wt.% range for those of PAN-based carbon fiber. Thermogravimetric study revealed that the intercalation reaction occured below 100°C.

Growth Mechanisms and Properties of Coiled Whisker of Silicon Nitride and Carbon

This paper reviews recent studies of regularly coiled whiskers of Si3N4 prepared by the chemical vapor deposition (CVD) method as well as those of carbon by the catalytic pyrolysis method. Coiled Si3N4 whiskers have been obtained from a gas mixture of Si2Cl6 and NH3 at 1200°C on substrates on which metal impurity was painted. The most effective impurity for the growth of the whiskers was Ni for the quartz substrate and Fe for the graphite. A vapor liquid solid (VLS) growth mechanism was suggested from morphology of the whiskers. Coiled carbon whiskers have been grown by the catalytic pyrolysis of acetylene at 300-750°C using Ni powder as a catalyst. A small amount of H2S was indispensable for the growth of the coiled carbon whiskers. A Ni compound seed observed on the tip of the pair-coiled carbon whisker is a single crystal. It is suggested that each crystal plane of the Ni compound seed has a different catalytic ability for the growth of the coiled carbon whiskers. The growth mechanism for the coiled carbon whiskers involves the surface diffusion of carbon atoms on the Ni compound seed. Structure of the coiled whiskers of Si3N4 and carbon was investigated by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Furthermore, extension characteristics of these whiskers were examined.

Photoluminescence characteristics of BN (C,H) prepared by chemical vapour deposition

Hexagonal boron nitride (h-BN) containing carbon and hydrogen, BN(C, H), has been prepared by chemical vapour deposition. It shows wide photoluminescence in the range 300–600 nm. The luminescence is mostly bright and white-blue in colour to the naked eye. The peak position and shape of the luminescence spectra are totally different from those reported on BN(C, H) made by heating BN powder in a graphite crucible in the presence of hydrogen in the atmosphere. A study by electron spectroscopy for chemical analysis on BN(C, H) indicates that impurity carbon substitutes for nitrogen atoms in the h-BN crystal. In other words, impurity carbon can be introduced into h-BN as an acceptor.

Intercalation Chemistry and Electronic Structure of Graphite-Like Layered Material BC2N

A graphite-like layered material of composition BC x N y (x = 2.0-2.4, y = 0.8-0.9), which is called BC 2 N in this paper, was prepared by a chemical vapor deposition method at 1770-2220 K. Lithium (Li) and potassium (K) were intercalated into BC 2 N by an electrochemical method and a vapor-phase reaction, respectively, to make the first-stage compounds with interlayer spacings similar to those of the first-stage graphite intercalation compounds. Sodium (Na) was intercalated into BC 2 N by the electrochemical method as well as the vapor-phase reaction, whereas Na was hardly intercalated into graphite. The X-ray diffraction analysis and an electrochemical capacity suggested that the Na-intercalated BC 2 N was a mixture of the first- and second-stage compounds. X-ray absorption spectroscopy indicated that an unoccupied π* orbital of BC 2 N showed a relatively strong intensity, and the bottom of the orbital was at an energy lower than each bottom of graphite, noncrystalline carbon, and BC 6 N. These results suggested that alkali metals including Na could donate electrons to BC 2 N more efficiently than the other host materials. Thus, the intercalation of alkali metal into BC 2 N proceeds more effectively than the other host materials.

BaTiO3-based positive temperature coefficient of resistivity ceramics with low resistivities prepared by the oxalate method

Positive temperature coefficient of resistivity (PTCR) ceramics with low resistivities at room temperature were obtained by using oxalate-derived barium titanate powders. The average room-temperature resistivity of the PTCR ceramics was 4Ω cm, and the magnitude of their PTCR jump was around four orders with a voltage proof of more than 50 Vmm−1. These PTCR properties are significantly influenced by the calcination temperature of the starting materials and by the resultant properties of the ceramic bodies. The microstructure of such-PTCR ceramics with a low room-temperature resistivity produced in this study was found to be rather heterogeneous. Complex impedance measurements revealed that the resistivity of the present PTCR materials was determined predominantly by the grain-boundary resistance even at room temperature.