Glassy Carbon Materials Research Articles

Evolution of Glassy Carbon Derived from Pyrolysis of Furan Resin.

Glassy carbon (GC) material derived from pyrolyzed furan resin was modeled by using reactive molecular dynamics (MD) simulations. The MD polymerization simulation protocols to cure the furan resin precursor material are validated via comparison of the predicted density and Young's modulus with experimental values. The MD pyrolysis simulations protocols to pyrolyze the furan resin precursor is validated by comparison of calculated density, Young's modulus, carbon content, sp2 carbon content, the in-plane crystallite size, out-of-plane crystallite stacking height, and interplanar crystallite spacing with experimental results from the literature for furan resin derived GC. The modeling methodology established in this work can provide a powerful tool for the modeling-driven design of next-generation carbon-carbon composite precursor chemistries for thermal protection systems and other high-temperature applications.

Electrophysical Properties and Structure of Natural Disordered sp2 Carbon.

The progress in the practical use of glassy carbon materials has led to a considerable interest in understanding the nature of their physical properties. The electrophysical properties are among the most demanded properties. However, obtaining such materials is associated with expensive and dirty processes. In nature, in the course of geological processes, disordered sp2 carbon substances were formed, the structure of which is in many respects similar to the structure of glassy carbon and black carbon, and the electrical properties are distinguished by a high-energy storage potential and a high efficiency of shielding electromagnetic radiation. Given the huge natural reserves of such carbon (for example, in the shungite rocks of Karelia) and the relative cheapness and ease of producing materials from it, the study of potential technological applications and the disclosure of some unique electrophysical properties are of considerable interest. In this paper, we present an overview of recent studies on the structure, electrophysical properties, and technological applications of natural disordered sp2 carbon with the addition of novel authors' results.

Molecular dynamics simulation of evolution of nanostructures and functional groups in glassy carbon under pyrolysis

With the continued and sustained growth of the field of carbon MEMS (C-MEMS) in several application areas, there is a corresponding increased and renewed interest in understanding the exact molecular structure of the ensuing glassy carbon (GC) material and, therefore, potential to engineer some of its key characteristics. Associated with that interest, the effects of key process parameters like temperature ramping, holding and cooling times on carbonization, the final nanostructures and – importantly – on the nature and distribution of functional groups remain to be of significant research importance to the GC community. While recent in-situ imaging approaches during the synthesis process have opened up opportunities for better understanding of these nanostructures, the 2D nature of the approaches, however, had introduced significant barriers. In this paper, therefore, we present a simulation-based approach using reactive molecular dynamics (MD) where we model the synthesis process and investigate in detail (i) the intermediate and final stages of carbonization with particular focus on GC nanostructures and (ii) formation of functional groups and the processes and parameters that drive their evolution. Our simulation captured the pyrolysis-driven synthesis process where the polymer structure degraded followed by increased carbonization and formation of flakes of 3-, 4-, membered carbon rings that further grew into graphene-type 6-member carbon rings as well as 5- and 7-member rings. These eventually evolved into a complex multi-layer 3D nanostructure consisting of connected but distinct zones of (a) dominant cage-like tubular components and (b) long chains of flat graphene-like parts rich with functional groups. Taken together, the MD simulations demonstrate that (i) holding time at the maximum temperature has the most significant effect in the formation of complex cage-like 3D nanostructures with stacked layers, (ii) the closed cage-like zones have crystallite diameter (La) in the range of 3.2 Å - 9.5 Å with clear and well-defined curved and stacked graphene-like sheets of stacking thickness (Lc) = 3.0 Å - 3.3 Å, (iii) carbonyl, ether, epoxide, hydroxyl, and alkyne groups form predominately on the edges of flat components of GC where abundant non-6 membered rings, dangling bonds, long sp carbon chains, and intermediate structures exist, and to a lesser extent on edges of vacancy defects inside cage-like zones.

Bonding effect of liquid magnesium with open-celled carbon foam in interpenetrating phase composite

Abstract The issue of bonding formation in liquid metal/open-celled carbon foam (Cof) systems was examined, taking into account the practical aspects of the synthesis of a new type of Mg-C metal material composite. The problem is complex due to the strong oxidation and intense evaporation of liquid magnesium, as well as the 3D geometry of the carbon component, where metal transport occurred through the foam cells’ windows. Laboratory experiments performed at 700°C in ceramic crucibles showed that spontaneous carbon foam infiltration by liquid metal is impossible under the applied conditions, either in an air atmosphere coupled with flux protection or under argon protection. Comparative tests performed in a UHV chamber filled with static pure Ar by a sessile drop method, coupled with non-contact heating and capillary purification at a test temperature of 700°C directly in the UHV chamber, showed non-wetting behavior of the Mg/Cof couple with a correspondingly high contact angle of about 135°. The graphite capillary was then moved down, the liquid drop being slightly pressed into the foam, but these changes did not induce effective foam penetration. Despite the short contact time for the sessile drop test under an argon atmosphere, SEM+WDS analysis of the solidified Mg/Cof couple revealed the formation of an MgO interlayer at the interface, with a thickness of approx. 1 µm. The experimentally demonstrated presence of oxygen in the carbon foam sample, both before and after its contact with magnesium, points to oxide-type bonding being established between Mg and Cof. This observation is in a good agreement with previous reports on the interface characterization of magnesium matrix composites reinforced with glassy carbon materials and carbon fibers by stir casting and pressure infiltration. Based on the findings of this study, a general structural scheme of the bonding process between carbon foam and liquid magnesium, as an important stage in the syntheses of Mg-C composites, was proposed.

Epi-Intra neural probes with glassy carbon microelectrodes help elucidate neural coding and stimulus encoding in 3D volume of tissue

Objective. In this study, we demonstrate practical applications of a novel 3-dimensional neural probe for simultaneous electrophysiological recordings from the surface of the brain as well as deep intra-cortical tissue. We used this 3D probe to investigate signal propagation mechanisms between neuronal cells and their responses to stimuli in a 3D fashion. Approach. This novel probe leverage 2D thin-film microfabrication technique to combine an epi-cortical (surface) and an intra-cortical (depth) microelectrode arrays (Epi-Intra), that unfold into an origami 3D-like probe during brain implantation. The flexible epi-cortical component conforms to the brain surface while the intra-cortical array is reinforced with stiffer durimide polymer layer for ease of tissue penetration. The microelectrodes are made of glassy carbon material that is biocompatible and has low electrochemical impedance that is important for high fidelity neuronal recordings. These recordings were performed on the auditory region of anesthetized European starling songbirds during playback of conspecific songs as auditory stimuli. Main results. The Epi-Intra probe recorded broadband activity including local field potentials (LFPs) signals as well as single-unit activity and multi-unit activity from both surface and deep brain. The majority of recorded cellular activities were stimulus-locked and exhibited low noise. Notably, while LFPs recorded on surface and depth electrodes did not exhibit strong correlation, composite receptive fields (CRFs)—extracted from individual neuron cells through a non-linear model and that are cell-dependent—were correlated. Significance. These findings demonstrate that CRFs extracted from Epi-Intra recordings are excellent candidates for neural coding and for understanding the relationship between sensory neuronal responses and their stimuli (stimulus encoding). Beyond CRFs, this novel neural probe may enable new spatiotemporal 3D volumetric mapping to address, with cellular resolution, how the brain coordinates function.

Lotus Leaf Derived Natural Dye as Sensitizer and Biochar as Counter Electrode for Dye-Sensitized Solar Cells

Natural dyes were obtained from lotus leaf by ethanol extraction, and biochar was prepared by one-step pyrolysis in this study. The UV-Vis spectrum of lotus leaf derived natural dye indicated that it had good light absorption performance. The energy conversion efficiency (PCE) of dye-sensitized solar cell (DSSC) with the natural dye as sensitizer and platinum as counter electrode was 0.36%, and the filling factor was as high as 0.66. Owing to its relatively rich pore structures and glassy carbon materials, the biochar showed its good catalytic performance, which made the PCE of DSSC reach 1.42% when the biochar as counter electrode and N719 as sensitizer. Meanwhile, the PCE achieved 0.15% when lotus leaf derived natural dye as sensitizer and biochar as counter electrode simultaneously. This study has realized the full utilization of biomass in dye-sensitized solar cells, providing the possibility for preparation of low-cost and high-efficiency DSSC.

Оптические свойства отечественного сетчатого стеклоуглерода и его основы

The paper presents the results of experimental studies and mathematical modeling of the optical properties of glassy carbon and domestic reticulated foam materials based on it. Since the optical properties of the surface are studied on dense samples, dense samples were previously created, identical in physical properties to glassy carbon - the basis of highly porous cellular carbon materials. From the experimentally measured the spectral hemispherical reflectivity of the surface of the samples under its normal illumination and by the Kramers-Kronig relations the spectra of optical constants of glassy carbon - the refractive indices and absorption, as well as a number of their derivative characteristics were determined. For them, simple approximating relations are given in the paper. The obtained spectral data was incorporated into the previously developed optical statistical simulation model of ultra-porous reticulated foam materials, which is based on a rigorous electromagnetic theory and allows you to take into account both the features of their microstructure and physical processes that occur in such systems at different spa-tial and temporal scales. The results of the calculation of local spectra, the scattering phase function, and radiation thermal conductivity are presented for the reticulated glassy carbon foam, which has wide prospects for use as a structural and heat-shielding material. Some additional features of the mathematical model are demonstrated also.

In Situ Characterization of Nanostructured Electrode Materials for Energy Conversion and Storage, Using Probe Beam Deflection Techniques

Nanostructured conductive materials of large surface area which are important in many areas of energy conversion and storage, including supercapacitors and fuel cells. While electrochemical techniques (e.g. cyclic voltammetry) assess the charge transfer processes at the electrode interface, the ion exchange process could only be inferred. Techniques of ion exchange determination, such as the electrochemical quartz crystal microbalance (EQCM) are of difficult application to porous electrodes since it requires fixing the porous material to the oscillating crystal. On the other hand, the techniques that monitor ion fluxes outside the electrode surface are able to study the actual ion exchange between a porous electrode and the electrolyte. Among them, Probe Beam Deflection (PBD) is a technique highly suitable to study porous electrodes.[1] The method uses a laser beam travelling parallel to the electrode surface which is refracted by the refractive index gradient associated with the flux of soluble species perpendicular to the electrode, at the center of the laser beam. Since the detection of beam position is optoelectronic, fast (ms) signals can be measured, unlike EQCM, allowing detecting transient phenomena. Since the flux is directly proportional to the surface area (like the current) the ratio of surface area to geometric pathlength (width of the electrode) assures large signal for porous electrodes. In this report, the study of different electrode materials using Probe Beam Deflection techniques is described. After a qualitative exploration using cyclic deflectometry, a continuous mass transport model is used to quantitatively evaluate the chronodeflectometric response.[2] First, the study of different porous glassy carbon materials is described. Then, PBD is applied to study mesoporous ordered Pt materials active in direct methanol fuel cells.[3] Finally, thin films of mesoporous oxides decorated with Au nanoparticles,[4] are investigated. The potential of minimum charge (PMC) can be determined and compared with the value measured by AC Impedance. Besides, transient phenomena like pH changes or effects on the coupled chemical reactions inside the pores can be easily detected. Therefore, a better understanding on the mass transfer in porous electrodes is obtained.

Graphitization of a diamond surface upon high-dose ion bombardment

Results from structural and morphological studies, measurements of the sheet electrical resistance, and estimating resistivity ρm of a graphite-like conducting surface layer formed upon high-dose irradiation of the (111) face of a synthetic diamond with Ar+ ions at an energy of 30 keV and a target temperature of 400°C are presented. It is found that the orienting effect of the diamond lattice is visible in the suppression of the formation of graphite crystallites with axis c perpendicular to the surface. The thickness of the modified layer is 40–50 nm, and its sheet resistance is 0.5 kΩ/sq. Resistivity ρm = 20–25 μΩ m of the modified layer lies within the range of ρ values of graphite and glassy carbon materials.

Wettability and work of adhesion of liquid sulfur on carbon materials for electrical energy storage applications

The wettability of glassy, microcrystalline and nanocrystalline carbon materials by liquid sulfur is studied by the sessile-drop technique applying the contact heating and drop-dispension procedures. Liquid sulfur shows a good wetting on all examined substrates just after melting, although the contact angle depends on the type and structure of the carbon material. Sulfur drops remain on the surfaces of glassy carbon and electrographite, whereas the liquid infiltrates into the substrates pressed from carbon micro- or nanoparticles. In the latter case, the infiltration rate increases along with decreasing size of particles used for preparation of the substrates, indicating a role of capillarity. The wetting and adhesion in the sulfur-carbon material systems are determined by the van der Waals interactions.

Structure and adsorption properties of microporous glassy-carbon materials

Products of the calcination of polymer based on furan resin modified by surface-active agent and diluter are studied. Microporous glassy-carbon materials with specific areas of up to 1350 m2/g are obtained. The materials are studied by means of electron microscopy, and their specific surface areas are compared to their structures. The range of solution compositions in which bicontinual structures are formed as three-dimensional networks from polymer drops is determined; the drop size varies from 0.3 to 1.5 μm.

Trapping State of Hydrogen Isotopes in Carbon and Graphite Investigated by Thermal Desorption Spectrometry

Thermal desorption spectrometry (TDS) has been investigated to obtain fundamental information of tritium behavior in graphite and carbon materials especially at high temperatures. 29 brands of graphite, HOPG, glassy carbon and CFC materials charged with deuterium gas are tested up to the temperature of 1735 K with a heating rate of 0.1 K/s. TDS spectra have five peaks at 600–700 K, around 900 K, 1200 K, 1300–1450 K and 1600–1650 K. The amounts of released deuterium have been compared with crystallographic parameters derived from XRD analysis. Reduction of tritium retention and inventories are discussed.

Mechanical Properties for Reliability Analysis of Structures in Glassy Carbon

Despite its good physical properties, the glassy carbon material is not widely used, especially for structural applications. Nevertheless, its transparency to particles and temperature resistance are interesting properties for the applications to vacuum chambers and components in high energy physics. For example, it has been proposed for fast shutter valve in particle accelerator [1] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000005F005200650066003300380032003500380030003900310035000000 [2] 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000005F005200650066003300380032003500380030003900320030000000 . The mechanical properties have to be carefully determined to assess the reliability of structures in such a material. In this paper, mechanical tests have been carried out to determine the elastic parameters, the strength and toughness on commercial grades. A statistical approach, based on the Weibull’s distribution, is used to characterize the material both in tension and compression. The results are compared to the literature and the difference of properties for these two loading cases is shown. Based on a Finite Element analysis, a statistical approach is applied to define the reliability of a structural component in glassy carbon. In this paper, the determination of the mechanical properties of glassy carbon allows the analysis of reliability of structures in glassy carbon.

OS2001 第3成分を添加した天然素材由来C/Cコンポジットの摺動特性

In recent years, we have a problem that the depletion of natural resources caused by large consumption of energy, and global warming caused by greenhouse gases. Therefore, effective utilization of biomass resources friendly to natural environment is attracting wide attention. We have prepared the C/C composite using bacterial cellulose and the third ingredient of Bamboo in this study. The C/C composite developed is a kind of glassy carbon material having excellent sliding properties. This can be used as the sliding parts of robots and soon. So, sliding experiments this material, to clarity the friction and wear characteristics. From the results, it data was possible to obtain a better than diamond-like carbon (DLC). At the same time we have also observed effects on materials to be sliding. As a result, we have found that the influence of the materials to be sliding is changes with sintering temperatures of C/C composite and the third ingredient.

Fabrication of a new electrochemiluminescent sensor for fentanyl citrate based on glassy carbon microspheres and ionic liquid composite paste electrode

Due to the high performance of glassy carbon in the aspects of mechanical strength, electrical conductivity and high corrosion resistance, etc., glassy carbon has been widely used in the electrochemistry. A new form of glassy carbon, glassy carbon microsphere, was utilized to couple with ionic liquid in preparing a new electrochemiluminescent platform for Ru(bpy) 3Cl 2. Room temperature ionic liquid has been proposed to be very interesting and efficient pasting binder to replace the non conductive organic binders for the fabrication of composite paste electrode. Attributed to the special characteristics of glassy carbon microspheres and room temperature ionic liquid [N-octylpyridium tetrafluoroborate (OPFP)], this new electrochemiluminescent sensor exhibited excellent electrochemiluminescent performance in Ru(bpy) 3 2+ solution. We first found that fentanyl citrate could increase the ECL of Ru(bpy) 3 2+, hence an ECL approach was developed for the determination of fentanyl citrate based on this glassy carbon microspheres based electrochemiluminescent platform with high sensitivity. Under the optimized conditions, the enhanced electrochemiluminescent intensity versus fentanyl citrate concentration was linear in the range of 1.0 × 10 −8 to 1.0 × 10 −4 mol L −1 with a detection limit of 8.5 × 10 −9 mol L −1, and the relative standard deviation for 1.0 × 10 −6 mol L −1 fentanyl citrate was 1.90% ( n = 10). This protocol has extended the application scopes of glassy carbon material and promoted the application of glassy carbon microspheres in electroanalysis.

A study on the recovery of actinide elements from molten LiCl–KCl eutectic salt by an electrochemical separation

Pyroprocessing is a prominent way for the recovery of the long-lived elements from the spent nuclear fuel. Electrorefining is a key technology for pyroprocessing and generally composed of two recovery steps—deposition of uranium onto a solid cathode and the recovery of TRU (TRansUranic) elements. In this study, it was investigated on electrochemical separation of actinides to develop an actinide recovery system in a molten LiCl–KCl eutectic salt. In the electrorefining experiment, uranium was successfully separated from cerium. The effects of the anode material and the surface area were investigated during the electrolysis experiments for a more efficient electrorefining system. Anode potential decreased with an increasing anode surface area, however, an anode effect was observed in case of a complicated anode structure for high surface area. Glassy carbon was found to be the best anode material among the molybdenum, graphite, glassy carbon, and oxide materials. It was found that the solid cathode with a perforated ceramic container could be one of the candidates for a salt clean-up process to remove residual actinide elements in the salt after the recovery step.

Molecular dynamics simulation on diffusion of lithium atom pair in C 150H 30 cluster model for glassy carbon at very low temperatures

As the preliminary step to elucidate the ion transfer mechanism of lithium (Li) species in the cathode electrode of glassy carbon material, molecular dynamics (MD) simulation was taken place describing the initial thermal movement of two Li atoms in the simulation time range of 10 ps maximally in the hydrogen terminated cluster model, C 150H 30, at molecular mechanics 2 (MM2) level. The formation of Li 2 atom pair is specified in the central area of the cluster model as the result of the structural optimization. In the low temperature range from 4 to 10 K, accompanied by the rotational and stretching vibrational motions, it goes around the central area of the cluster model. Diffusion process of the atom pair is simulated dynamically for the first time in the present study. Decomposition of the atom pair occurred at 50 K and it produces two Li atoms which go and back independently from the center to the edge of the cluster model crossing the CC bonds orthogonally. Formation and diffusion processes of Li 2 atom pair may be responsible for the charge–discharge cycles in the glassy carbon electrode in the lithium secondary battery.

Investigation of the Effect of Different Glassy Carbon Materials on the Performance of Prussian Blue Based Sensors for Hydrogen Peroxide

AbstractThree different kinds of glassy carbon (GC‐R, GC‐K, GC‐G) were equally pretreated, further modified with electrochemically deposited Prussian Blue and used as sensors for hydrogen peroxide at an applied potential of −50 mV (vs. Ag|AgCl). Their performance was evaluated with respect to the following parameters: the coverage and electrochemistry of the electrodeposited Prussian Blue, the sensitivity and the lower limit of detection for hydrogen peroxide, and the operational stability of the sensors. GC‐R showed the best behavior concerning the surface coverage and the operational stability of the electrodeposited Prussian Blue. For this electrode the sensitivity for hydrogen peroxide (10 μM) was 0.25 A/M cm2 and the detection limit was 0.1 μM. Scanning electron microscopy was used to study the surfaces of the three electrodes before and after the electrodeposition of Prussian Blue and to search for the reason for the three different behaviors between the different glassy carbon materials. The Prussian Blue modified GC‐R was also used for the construction of a glucose biosensor based on immobilizing glucose oxidase in Nafion membranes on top of electrodeposited Prussian Blue layer. The operational stability of the glucose biosensors was studied in the flow injection mode at an applied potential of −50 mV (vs. Ag|AgCl) and alternatively injecting standard solutions of hydrogen peroxide (10 μM) and glucose (1 mM) for 3 h. For the GC‐R based biosensor a 2.8% decrease of the initial glucose response was observed.

Indentation hysteresis of glassy carbon materials

Abstract Indentation hysteresis during both pointed and spherical indentation is a common feature of the observed force-displacement response of glassy carbon materials. Field and Swain proposed a method of analysis of this behaviour with spherical indenters in the form of classic indentation stress-strain curves. They also proposed that the response resulted from limited reversible slip of the graphite-like nanocrystalline structure of these so-called glassy carbon materials. The present work extends the previous study by investigating the influence of the nanocrystalline grain size and the hysteretic response with indenters of sharper apical angle. It is found that the extent of the hysteresis is dependent upon the grain size as is the contact stress for the initiation of yielding. The critical strain for the onset of non-recoverable hysteretic response is clearly identified with sharper-apical-angle indenters. This irreversibility of the hysteretic response is discussed in terms of an analysis proposed...

Microstructural changes of phenolic resin during pyrolysis

AbstractAfter curing, phenol‐formaldehyde resins were postcured at 230°C in air for 32 h and then carbonized and graphitized from 300 to 2400°C. Thermal fragmentation and condensation of the polymer structure occurred above 300°C. The crystal size of the cured phenolic resins decreased with the temperature increase. Above 600°C the original resin structures disappeared completely. Below 1000°C the stack size (Lc) and crystal size (La) were small. Above 1000°C the Lc increased with the increasing treatment temperature. The carbonized and graphitized resins were characterized using Raman spectroscopy. Below 400°C there were no carbon structures in the Raman spectra analysis. Above 500°C the G and D bands appeared. The frequency of the G band of all carbonized and graphitized samples shifted to 1600 cm−1 from the 1582 cm−1 of graphite. The D band shifted to 1330 cm−1 from the 1357 cm−1 of the imperfect carbon. The carbonized and graphitized phenolic resins could not be considered as truly glassy or amorphous carbon materials because they had some degree of order in the basal plane. However, the crystal size was very small even at 2400°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1084–1089, 2001