Glass-like Carbon Research Articles

Photon emission during fracture of carbon materials

Photon emission (phE) during fracture was investigated on glass-like carbon, pyrolytic graphite, polycrystalline graphite, and carbon fiber reinforced composites (C∕C composites). The C∕C composites were heat treated at 1000, 1500, and 2000°C. The specimen was fractured by three-point bending and the resulting phE was measured at atmospheric pressure, 10−3 and 10−6Pa. The phE was not observed on any samples at atmospheric pressure, whereas it occurred on the glass-like carbon and C∕C composites at 10−3 and 10−6Pa. The phE intensity at 10−3Pa was higher than that at 10−6Pa. This study revealed that the phE on the carbon materials depended on their crystal structure and surrounding gas pressure. The gas pressure dependence suggests that the phE resulted from gas discharge.

Tannin-based carbon foams

An easily-prepared self-blowing system based on low-cost precursors, mainly tannin and furfuryl alcohol, was pyrolysed at 900 °C. Extremely low-density glass-like carbon foam was obtained, with very high porosity (96.4%, of which 94% is open) and low surface area (below 1 m 2 g −1). The material presents slightly anisotropic properties. The linear cell density is 100 and 190 ppi along two orthogonal directions, and the major physical properties were examined according to these same directions: electrical and thermal conductivities, mechanical strength and elastic modulus, coefficient of thermal expansion, permeability and fire resistance. Since most of these properties compare very correctly with available data from the literature, such a cheap material like the one reported here can compete with commercial vitreous carbon foams, which are all produced from more expensive, non-renewable, resources.

Surface modification behaviors of glass-like carbon by oxygen ion implantation

Surface modification behaviors of glass-like carbon (GLC) by oxygen ion implantation were studied at the ionic doses of 1, 10 and 100×1014ions/cm2. Formation of bank network at the GLC surface, following initial smoothing, was observed with atomic force microscopy (AFM). At the same time, Friction coefficient and surface roughness decreased at the ionic dose of 1×1014ions/cm2, but increased again at higher doses. Increase in surface disorder at lower ionic dose and change to amorphous at higher doses were detected with Raman spectroscopy. As O/C ratio measured with X-ray photoelectron spectroscopy (XPS) increased with the ionic dose, the contact angle of the GLC surface with water decreased. The most biocompatible GLC surface was obtained at the dose of 1×1014ions/cm2.

Graphitization behavior of the implanted furan-resin-derived carbon

Ar or Xe ions were implanted into the fractured-faces or surfaces of as-carbonized glass-like carbon (GC) specimens for modification of the structure of them. Microstructural changes were examined by Raman spectroscopy, by scanning tunneling microscope (STM) and by transmission electron microscopy (TEM). It was found that the as-carbonized surfaces and fractured-faces of the specimens were changed to an amorphous structure by ion implantation. Implanted as-carbonized surfaces of specimens were restored nearly pristine structures after re-heat-treatment at 3000°C. On the other hand, implanted fractured-faces of specimens resulted in well-developed structures after re-heat-treatment at 3000°C. After re-heat-treatment at 3000°C, the degree of graphitization on the implanted fractured-faces was higher than that on the pristine fractured-faces. It can be concluded that mobility of carbon atoms, or free face, seemed to play an important role on surface graphitization.

The effect of nanotube alignment on stress graphitization of carbon/carbon nanotube composites

Carbon nanotubes, when used as filler in a glass-like carbon matrix, has been reported to induce stress graphitization in the matrix. The effects on stress graphitization of the amount of carbon nanotube loading and nanotube orientation in the composite were investigated through microscopy and X-ray diffraction analyses. Results showed that an increase in nanotube content and nanotube alignment could increase the extent of formation of anisotropic regions, thereby hastening stress graphitization. It was shown that the distance between nanotubes could affect the formation of the anisotropic structures, such that they could develop in a circumferential manner around the nanotubes when the nanotubes are situated far from each other or develop continuous regions between nanotubes when they are closer together. The development of these microstructures and its relationship to the residual stresses that accumulate in the material during heat treatment is discussed here.

Analysis of surface oxidation behavior at 500 °C under dry air of glass-like carbon heat-treated from 1200 to 3000 °C

The Surface oxidation behavior at 500 °C under dry air of glass-like carbons heat-treated from 1200 to 3000 °C was investigated by thermogravimetric analysis (TGA), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the oxidation rate of specimens heat-treated above 2000 °C was much slower than the rate of those heat-treated below 1500 °C and varies with the heat treatment temperature of the carbons. Raman spectroscopy revealed that the developed graphite structure of the carbons did not dominate the rates. It was inferred by XPS that the carbon bonded to oxygen in the internal region as well as that on the external surface was easily oxidized. The heat treatment temperature for preventing oxidation was above 2000 °C.

Glass-Like Carbon Spheres — Activation, Porosity and Application Possibilities

A brief review on spherical carbons, including fullerenes and related spherical particles, is first provided, followed by a review of the results on air activation, porosity and applications focused on glass-like carbon spheres derived from phenolic resin spheres. Kinetic studies of the oxidation in air provide a fundamental understanding of activation process of glass-like carbon spheres. On the basis of the results, a new activation procedure, viz. two-step activation, is proposed, which provides ca. 10% higher oxidation yield in obtaining a comparative pore structure. Some possibilities for applications of these glass-like carbon spheres are also described, such as the adsorption/desorption of CO2 gas and chlorinated methanes, the adsorption of organic molecules from their aqueous solutions, and the provision of electrodes for electric double layer capacitors and lithium ion rechargeable batteries.

A Truing Technique of Flattening Diamond Grains for Fabricating Microstructures with Fine Surfaces

A truing technique that can be used to shape the tip of an electroformed diamond tool into a hemisphere and flatten diamond grains on the tool working surface at the same level as the bond face was developed. A polycrystalline diamond disk whose top surface roughened by electrical discharge machining was partially flattened by grinding was used as a truer. Diamond grains on the tool working surface were successfully flattened along the hemispherical tool profile when the grains mesh size of #1000 was employed. In addition, a grinding test using glasslike carbon as a work material revealed that a surface roughness of less than 50 nm Rz could be obtained in both cases when moving the tool on contour and scanning paths.

Glass-like carbon

Glass-like carbon

Micro lens imprinted on Pyrex glass by using amorphous Ni–P alloy mold

We fabricated micro lenses on a Pyrex glass using thermal nanoimprint technology. The mold material employed to imprint on the Pyrex glass was a Ni/Ti/Si substrate electroless-plated with an amorphous Ni–P alloy. The fabrication of the mold involved high precision FIB processing. In this technique we used a newly developed low-cost mold for imprinting on Pyrex glass rather than using the commonly employed more expensive mold made of glass-like carbon material. Micro lens shaped concave curvatures of radii 12μm and 20μm were created on mold by an FIB system equipped with three-dimensional CAD software. The mold was then used for thermal imprinting on Pyrex glass substrate to fabricate lenses. The accuracy of Ni–P mold proved to be far superior to that of pure Ni mold.

The Study of the Imprint Mold Materials Suited for B2O3-La2O3 Based Glass

Reactivity between nanoimprint mold material and optical glass has been investigated by measuring the contact angle between these materials in a nitrogen atmosphere at high temperature up to 1000°C. Since the low softening temperature optical glass was chosen in this study, the thermal upper limit of the contact angle measurement was set 800°C on. As the mold materials, electrodeposits Ni-W alloy containing 40 wt% W and the glass like carbon (GC) were chose. In the case of the GC, the contact angle did not changed largely at the temperatures up to 800°C, while obvious reactant phase in the interface layer between GC and the molten glass was observed. In the case of the Ni-W alloy, the contact angle decreased with increasing the temperature while, no reactant phase was observed at the interface. This indicated that indicating the Ni-W alloy is suitable as the mold materials for the B2O3-La2O3 based optical glass.

C07 バインダレスPCDならびにcBN製マイクロボールエンドミルの試作と加工特性(OS-12 ナノ加工と表面機能(2))

Micro ball endmill with a tool tip radius of 50 μm was formed using binderless poiy crystalline diamond (PCD) and binderless cBN as tool materials. Which is similar to that of single crystal diamond tool, smooth and sharp cutting edges without micro chips could be formed. Cutting test revealed that binderless PCD was effective for the interrupted cutting of hard and brittle materials such as glass-like carbon and cemented carbide.

A method for origin correction of Raman band frequencies in the first order Raman spectrum for carbon materials and Raman frequency of G band versus d002 plots

A method was developed to correct the Raman frequencies of the D, G and D, bands in the first order Raman spectrum for carbon materials with an incident excitation beam of 514.5 nm. It was demonstrated that the lighting of the Ne lamp set at a proper position in the Raman spectrometer during the measurement of the first order spectrum causes superposition of the 556.28nm line from Ne lamp at 1458.52cm-1 in Raman shift scale on the first order Raman spectrum, being of use as a standard. There could be a practical application on the plots of the Raman frequency of the G band (G-RF) vs. interlayer spacing don for carbon materials in assessing quality. The method is demonstrated for determination of G-RF for a cleaved surface of a kish graphite, an HOPG edge plane, PC basal planes, a polished surface of commercially available isotropic graphite, a buffed surface of glass-like carbon and side surfaces of benzene-derived vapor-grown carbon fibers.

Solid-phase transformation of glass-like carbon nanoparticles into nanotubes and the related mechanism

Multi-walled carbon nanotubes have been synthesized through the solid-phase transformation of metal-containing glass-like carbon nanoparticles by heating at temperatures of 800–1000 °C. From microscopic observations on the morphologies and structures of the nanotubes and various intermediate objects, it is shown that the transformation occurs by nanoparticles first assembling into wire-like nanostructures, and then transforming into nanotubes via particle–particle coalescence and structural crystallization.

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

A carbon-rich black layer, dating to approximately 12.9 ka, has been previously identified at approximately 50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at approximately equal 12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at approximately 12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.

Frictional property of glass-like carbon heat-treated at 1000–3000 °C

Frictional coefficient ‘ f’ was measured in the air and in water at glass-like carbon (GLC) surfaces heat-treated between 1000 and 3000 °C. GLCs heat-treated at higher temperature had smoother and more hydrophobic faces, and lower f. The f was smaller than 0.10 for GLCs heat-treated at and above 2000 °C, which indicates their applicability as a solid lubricant or a self-lubricating material. The f = 0.06 observed for GLC heat-treated at 3000 °C was nearly the same as that of pyrolytic graphite (PG). Slightly lower f's were obtained in water than in the air.

Controlled Synthesis of Ordered Mesoporous C−TiO2 Nanocomposites with Crystalline Titania Frameworks from Organic−Inorganic−Amphiphilic Coassembly

Highly ordered mesoporous carbon−titania nanocomposites with nanocrystal-glass frameworks have been synthesized via the organic−inorganic−amphiphilic coassembly followed by the in situ crystallization technology. A soluble resol polymer was used as a carbon precursor, prehydrolyzed TiCl4 as an inorganic precursor, and triblock copolymer F127 as a template. The carbon−titania nanocomposites with controllable texture properties and composition can be obtained in a wide range from 20 to 80 wt% TiO2 by adjusting the initial mass ratios. The C−TiO2 nanocomposites with “bricked-mortar”frameworks exhibit highly ordered 2D hexagonal mesostructure and high thermal stability up to 700 °C. The nanocomposites have high surface area (465 m2 g−1) and large pore size (∼4.1 nm). Additionally, the nanocomposites show good performance in degradation of Rhodamine B due to the photocatalytic activity of the titania nanocrystals and the strong adsorptive capacity of the glasslike carbon.

Two-step activation of glass-like carbon spheres – An approach to high yield activation

Two-step activation of glass-like carbon spheres – An approach to high yield activation

Glass nanoimprint using amorphous Ni–P mold etched by focused-ion beam

The authors succeeded in glass-nanoimprint lithography of micropatterns and nanopatterns using an amorphous Ni–P alloy mold. Glasslike carbon has been used as a mold material to mold not only Pyrex glass but also quartz, because it is still stable at a temperature of 1650°C. However, it is difficult to process glasslike carbon substrates into arbitrary shapes by machining. They thought that amorphous Ni–P alloy could be used as a mold material for industrial glass molding. If Ni is electroless plated when mixed with suitable amount of P on a Si wafer, the Ni–P alloy layer becomes amorphous. An appropriate ratio of Ni and P was determined by the results of x-ray-diffraction measurements. The optimized composition ratio of Ni–P was Ni:P=92:8wt%. Moreover, line and space patterns and dot arrays with linewidths of as little as 500nm were etched on the mold using focused-ion beam (FIB) and the processing accuracy for the amorphous Ni–P layer was compared with that for the pure Ni layer. The result was that patterns of 500nm width were etched to a depth of 2μm on an amorphous Ni–P alloy mold and the processed surfaces were smooth. In contrast, in the case of the pure Ni layer, the processing line was notched and the sidewalls were very rough. The crystal grain seems to hinder the processing of the nanopattern. After FIB etching, the amorphous Ni–P alloy was thermally treated at 400°C to improve the hardness. Finally, line and space patterns and dot arrays on the amorphous Ni–P alloy mold were nanoimprinted on Pyrex glass using a glass-nanoimprint system (ASHE0201) that National Institute of Advanced Industrial Science and Technology developed.

Glass-like carbon derived from a polymer consisting of furfuryl alcohol and tetraethylene glycol

Glass-like carbon derived from a polymer consisting of furfuryl alcohol and tetraethylene glycol