Pyrolytic Graphite Research Articles

Solvent Effect for the Structural Control of Molecular Architectures Consisting of Trinuclear Ruthenium Clusters and Ligands at the HOPG Surface.

The molecular architecture of a triruthenium complex and 1,4-di(4-pyridyl)benzene on highly oriented pyrolytic graphite was investigated by drop-casting mixed tetrahydrofuran and methanol solutions. Atomic force microscopy revealed the formation of one-dimensional molecular wires on highly oriented pyrolytic graphite after heating the mixed tetrahydrofuran solution, whereas large ring structures were formed in the methanolic solution. It was found that the molecular architectures composed of triruthenium complexes and 1,4-di(4-pyridyl)benzene strongly depend not only on the temperature of the solution but also on the organic solvents. The formation of the molecular architecture was supported by the ultraviolet-visible absorption spectra of the mixed solution and the electrochemical responses of the deposited film.

Innovative green preparation of activated carbon by combining microwave pyrolysis and self-activation: Pyrolysis behavior, carbon characteristics and arsenic adsorption properties

Self-activation technology offers an eco-friendly strategy to produce activated carbons. This research attempted to enhance the production efficiency of self-activation by introducing microwave heating. Activated carbons were prepared as arsenic adsorbents from bamboo shoot shells (BSS) by combining microwave pyrolysis and self-activation. Microwave pyrolysis showed a faster thermal decomposition rate and lower pyrolysis temperature range than conventional pyrolysis, and H2O and CO2 from pyrolysis acted as activator. Besides, the prediction models of specific surface area (SSA), micropore volume (MPV) and As(V) adsorption capacity (qe) with high accuracy were established using response surface methodology. Based on the qe values, the optimum preparation condition was 1018 °C for 39 min under a microwave power of 1625 W. The activated carbon exhibited satisfactory As(V) adsorption capacity of 4.79 mg/g, with a total pore volume of 0.702 cm3/g and a SSA of 1330 m2/g. This work significantly improved self-activation technology's production efficiency and reduced the arsenic adsorbent's production cost. Furthermore, it also provided a promising strategy for green preparation of activated carbons from biomass resources.

Supercapacitive performance of self-assembled thin film of liquid catocene/basal plane pyrolytic graphite electrode

Reasonable design of electrode material with low cost, lightweight, and excellent electrochemical properties is of great significance for future large-scale energy storage applications. Herein, we report the electrochemical and supercapacitive behaviour of the liquid redox of catocene, 2,2’-bis(ethyl-ferroceneyl) propane, self-assembled on a basal plane pyrolitic graphite electrode in comparison to the solid ferrocene thin film in aqueous sodium sulfate electrolyte. The modified electrode surfaces were evaluated to assess the iron content and the formation of thin film using scanning electron microscopy, laser-induced breakdown spectroscopy, and attenuated total reflectance method. Also, the supercapacitive performances of the related modified electrodes were assessed and compared using cyclic voltammetry and galvanostatic charge-discharge in a three-electrode system and an asymmetric two-electrode supercapacitor system. Electro­chemical results showed that the electrode processes are diffusion-controlled with battery-like behaviour, and the liquid catocene exhibits more effective interaction with the graphite surface in comparison to solid ferrocene. The catocene surface coverage on graphite is nearly 50-75 % higher than ferrocene, leading to improved interaction and charge transfer resistance, observed in electrochemical impedance spectroscopy studies. In galvanostatic charge-discharge evaluations, the supercapacitor based on catocene modified electrode shows a specific capacitance of 141.2 F g-1 at a current density of 1.0 A g-1, with a specific energy density of 56.7 Wh kg-1 at a power density of 2.9 kW kg-1.

Regulation of oxygen vacancies in MnCO3-based catalysts by thermally inducing for efficiently catalytic benzene combustion

Tuning oxygen vacancies through carbon pyrolysis is an effective strategy for fabricating high-performance catalysts to oxidize volatile organic compounds (VOCs). Herein, a series of MnCO3-based catalysts were synthesized by pyrolyzing MnCO3 precursors with different morphologies including dumbbell-like (D), bayberry-like (B) and cubic (C) structures for the benzene oxidation. The catalyst (D-300) derived from dumbbell-like MnCO3 exhibited superior catalytic performance for the benzene oxidation with a T90 of 176 °C and remarkable stability in long-term, cycling and water-resistance tests. Abundant oxygen vacancies in D-300 improved lattice oxygen mobility and redox ability, resulting in superior oxygen uptake and release capabilities. Moreover, oxygen vacancies greatly facilitated the activation and replenishment of gaseous oxygens to generate active oxygen species, thereby dramatically accelerating the cleavage of benzene rings and deep mineralization. In situ DRIFTS analysis demonstrated that benzene preferentially adsorbed onto D-300 due to its abundant acidic sites, and the oxidation of phenolate species was a rate-determining step. H2O may hinder the activation of gaseous oxygen, suppressing the activity of the catalyst.

Participation of Surface Oxygen in the Stabilization of the Rh/HOPG System with Respect to NO₂

In this work, using the method of X-ray photoelectron spectroscopy (XPS), a comparative study of the nature of the interaction of NO₂ at room temperature and a pressure of 10⁻⁵ mbar with two samples of highly oriented pyrolytic graphite (HOPG), on the surface of which rhodium was preliminarily deposited by vacuum deposition, was carried out. Before metal deposition, one of the HOPG samples was annealed in vacuum at 600°C, and the other was subjected to bombardment with argon ions, followed by exposure to air at room temperature for an hour in order to introduce strongly bound oxygen atoms into the surface composition. After deposition of rhodium on two samples of HOPG prepared, two model catalysts were obtained, designated as Rh/C and Rh/C(A)-O. It was found that the interaction of NO₂ with Rh/C led to the oxidation of graphite with the destruction of the surface layer. The Rh particles remained in the metallic state, but at the same time they were introduced into the near-surface layer of the carbon support. On the contrary, when the Rh/C(A)-O sample was treated with NO₂, the deposited rhodium was partially converted into RH₂O₃, while the graphite was oxidized to an insignificant degree and retained its original structure. The role of surface oxygen in the stabilization of graphite with respect to oxidation to NO₂ was discussed.

Sustainable Utilization of Waste Biomass: Pyrolysis Kinetics of Jujube Pits and Lithium Storage Behavior of Pyrolytic Carbon

Sustainable Utilization of Waste Biomass: Pyrolysis Kinetics of Jujube Pits and Lithium Storage Behavior of Pyrolytic Carbon

Impact of process parameter on the behavior of pyrocarbon deposition in chemical vapour infiltration (CVI) process

Carbon-carbon composite manufactured by deposition of pyrocarbon (PyC) through chemical vapor infiltration (CVI) has the key issue of being process parametric sensitive which necessitates the detailed study of the effect of process parameters on the rate of PyC deposition. Conventional method of studying the parametric effect by changing one variable at a time keeping the other variables constant has a limitation of more number of experiments and missing the interaction effect among the variables. Here, the effect of process parameters including temperature, pressure, methane gas flow rate, and nitrogen gas flow rate on the mass gain and PyC deposition was studied by Taguchi method, a statistical optimization method, which has the advantage of very few experiments performed at specific pairs of process parameters only. The experiments were performed at three levels of the process parameters. Carbon-Carbon composite material is processed through the CVI process where PyC was deposited on porous carbon fiber preforms at various process conditions as per the Taguchi method. The impact of gas residence time, Reynolds number, Prandtl number, and Peclet number were also investigated. It was observed that the CVI process parameters significantly affect the rate of PyC deposition. Optimized CVI process parameters are essential for achieving a high rate of PyC deposition to reduce the processing time. The findings have revealed that a higher PyC deposition rate arises under high temperatures, pressure, methane gas flow rate, and optimal nitrogen gas flow rate. The effect of the critical interaction of the CVI process parameters on the rate of PyC deposition was also obtained. Based on the experimental studies, process guidelines are proposed for the densification of carbon fibers preform to realize C/C composite products.

Algal-based biochar and hydrochar: A holistic and sustainable approach to wastewater treatment

Biochar and hydrochar are carbon-rich solid products of algal and terrestrial biomass obtained through various thermochemical processes, mainly hydrothermal liquefaction, pyrolysis, and hydrothermal carbonization. Both are regarded as economical, potent, and environmentally friendly adsorbents for wastewater remediation. The versatile applicability of biochar and hydrochar, which is due to their enhanced surface physicochemical properties, includes efficient metal biosorption, soil fertility enhancement, and carbon sequestration. Consequently, there has been an increase in research for producing and exploiting biochar and hydrochar from algae. Both micro- and macro-algal biomass have strong potential due to their sustainability footprint and distinct properties. This review focuses on a comprehensive account of the synthesis of algal biochar and hydrochar and use in wastewater treatment to develop innovative solutions for efficient mitigation of several aqueous pollutants and heavy metal ions. The review discusses the various thermochemical production routes, biophysical characterization techniques, and modes of mechanism for wastewater bioremediation. Algal-based biochar and hydrochar are reported to have higher porosity and more diverse functional groups such as amines, hydroxyl, and carboxyl compared to their cellulosic and waste-derived counterparts, demonstrating an increased wastewater remediation efficiency. In addition, presence of inorganic metal including sodium, potassium, magnesium, and phosphorus in algal chars facilitates the formation of mesopores and graphite structures, improving their cation exchange capacity. Moreover, algal chars may exhibit pH buffering capacity, which could help stabilize the pH during wastewater treatment processes. Notably, the low O/C content of algal hydrochars enhances the binding and removal of organic pollutants including toxic dyes and antibiotics. The review highlights the development of modified algal chars to enhance the porosity, surface area, structural integrity, and adsorption capacity enabling a higher bioremediation potential.

Substrate-induced strain in molybdenum disulfide grown by aerosol-assisted chemical vapor deposition

Transition metal dichalcogenides have been extensively studied in recent years because of their fascinating optical, electrical, and catalytic properties. However, low-cost, scalable production remains a challenge. Aerosol-assisted chemical vapor deposition (AACVD) provides a new method for scalable thin film growth. In this study, we demonstrate the growth of molybdenum disulfide (MoS2) thin films using AACVD method. This method proves its suitability for low-temperature growth of MoS2 thin films on various substrates, such as glass, silicon dioxide, quartz, silicon, hexagonal boron nitride, and highly ordered pyrolytic graphite. The as-grown MoS2 shows evidence of substrate-induced strain. The type of strain and the morphology of the as-grown MoS2 highly depend on the growth substrate’s surface roughness, crystallinity, and chemical reactivity. Moreover, the as-grown MoS2 shows the presence of both direct and indirect band gaps, suitable for exploitation in future electronics and optoelectronics.

In situ loading of ZnO on hierarchical porous carbon derived from banana-peel waste to enrich mechanism for microwave absorption

Biomass has received widespread attention due to its easy availability, low cost, and environmental friendliness as an electromagnetic wave absorber candidate. Inspired by the natural porosity of biomass, the three-dimensional (3D) porous carbon materials derived from banana peels were prepared via coordination and pyrolysis carbonization. A conductive network of biomass-zinc complexes was constructed by introducing Zn2+ to coordinate with organic polymers. Hierarchical porous carbon/ZnO composites with a 3D skeleton network were obtained, which demonstrated outstanding electromagnetic wave absorption performance with an effective absorption bandwidth (EAB) of 6.72 GHz and the reflection loss (RL) of −44.18 dB. The banana peel-derived porous carbon (BPC) embedded with ZnO particles brings about conductive loss and interface polarization, further enriching the microwave loss mechanisms. This work offers a fresh idea for creating a green, sustainable, and high-value functional carbon-based composite material.

Electrochemical exfoliation of graphene from pencil lead

Addressing an ever-increasing demand for graphene in recent years, simple, accessible, and effective graphene synthesis methods are essential. One of such methods is to use a highly oriented pyrolytic graphite (HOPG) to perform an electrochemical exfoliation. While this is one of the simplest and most cost-effective methods, the limited availability and price of HOPG hinders its usage. Our study proposed a simple and economical electrochemical exfoliation of pencil lead, producing graphene with properties comparable to that produced from HOPG. The electrical properties are determined by depositing graphene onto a screen-printed electrode. Graphene from pencil leads can achieve an electrical resistance as low as 1.86 kΩ, marking over 80% improvement in electrical performance compared to bare electrodes. This finding provides an alternative for the synthesis of graphene, increasing its availability and the cost-effectiveness as well as contributing towards a potential commercialization of the method in the future.

Microscopic growth of pyridinium oxime based amphipathic on graphite: Effect of relative position of substituents

AbstractAmphipathic molecules with surfactant like properties have several applications ranging from healthcare to the chemical industry. Their ability to form thin films on surfaces with ordered and controllable patterns determines their applicability. Here, we report two pyridinium oxime‐based surfactants, which possess similar aggregation properties in solution, but exhibit substantially different assembly on highly oriented pyrolytic graphite (HOPG) surface. The two compounds are regioisomers with the oxime unit placed either in meta or para position of the pyridinium ring. While the para isomer assembled to anisotropic one‐dimensional (1D) islands and long rod‐like structures, the meta isomer formed two‐dimensional (2D) islands on the HOPG surface. This difference is rationalized through molecular level force‐field calculations that show anisotropy in the growth of the para isomer resulting from an effective overlap of the alkyl chains and oxime groups, which is distinctly not feasible in the assembly of the meta isomer. The assembly of these compounds is compared with another oxime‐containing compound of similar structure, but without the charged pyridinium unit. The charged unit seems to be crucial for the preferential formation of multilayer islands even at low coverage.

Processing and performance of ultra high temperature ceramic matrix composite (UHTCMCs) using radio frequency assisted chemical vapour infiltration (RF-CVI)

Ultra-high temperature ceramic matrix composites (UHTCMCs) have been produced using a radio frequency assisted chemical vapour infiltration (RF-CVI) process. The composites were based on 2.5D carbon fibre preforms with a 0 / 90° (out of plane) fibre orientation and containing 23 % fibre volume fraction. These were initially impregnated with zirconium diboride (ZrB2) powder in the form of a slurry and then, after solvent removal, the majority of the porosity filled with pyrolytic carbon (PyC) using the RF-CVI process at 1273 K and 0.5 kPa chamber pressure. The latter resulted in a uniform rough laminar texture with good interfacial bonding. As intended, an inverse temperature profile was achieved using the RF heating, enabling uniform densification of the preform from the inside out, with no entrapped porosity and achieving 90 % of theoretical density in only 24 h, at least a tenfold reduction in processing time compared to the conventional CVI process and a fivefold reduction compared to other modified CVI processes such as forced flow or pressure gradient CVI. The resulting UHTCMCs displayed good mechanical strength and thermo-ablative behaviour.

Dispersion effect of nano-structure pyrolytic carbon on mechanical, electrical, and microstructural characteristics of cement mortar composite

ABSTRACT In material science, converting waste into nanomaterials by green technologies highlights the interest in producing sustainable carbon nanomaterial (SCN). This study first-ever utilized tyre-char as a Nano-Structure Pyrolytic Carbon (NSPC) to develop electrically conductive composites. Unlike other carbon nanomaterials, the efficiency of NSPC particle as an SCN in developing electrically conductive composites was investigated in terms of dispersion, mechanical, water absorption, electrical resistivity, and microstructure. The results of sedimentation and zeta potential (−19 mV) showed the excellent dispersion of NSPC particle in water with the combined effect of superplasticizer and ultrasonication. The compressive (40.37%) and flexural strength (10.76%) than that of plain cement mortar composite (CMC) is achieved with 2 wt.% and 1.5 wt.% of NSPC particle, respectively. The water absorption rate and volume of permeable voids were reduced, exhibiting less agglomerations. The percolation zone of AC and DC resistivity of NSPC composite ranges between 1 and 2 wt.%, and the established percolation threshold is at 2 wt.%. XRD analysis showed C-S-H formation consistently increased with curing age, and HR-SEM with EDAX analysis exhibits the dense microstructure and well-distributed NSPC particle at the nanoscale. These experimental outcomes significantly enhanced the reliability and provided a framework for tailoring NSPC particle as SCN for developing electrically conductive composite.

Verification of lifetime and mechanical load aspects for ITER diagnostic pressure gauges based on ZrC emitter.

Hot cathode ionization gauges will measure the neutral gas pressure in the vacuum vessel of ITER. Overall, 52 gauge heads based on the concept of the ASDEX pressure gauge but using novel ZrC emitters are located in the divertor, in equatorial ports and in pumping ducts. The initial lifetime tests of the novel gauge design have raised the concern that the pyrolytic graphite used to indirectly heat the ceramic ZrC emitter erodes too fast during operation. This effect might limit the lifetime of the gauges below the limits acceptable according to the inherent availability (ignoring operational delays) requirement of 99.8% for the diagnostic system over the lifetime of ITER. Long term operation tests have been performed using 0.1mm thick W, Ir, and Mo foils as an interlayer between the pyrolytic graphite and the ZrC within a constant atmosphere of 20Pa H2. The longest lifetime of 860h has been achieved with the Ir foil. Subsequent vibration tests applying accelerations on a shaker with magnitudes typical for seismic and ITER disruption loads demonstrated that the emitter can survive such demanding loads even after far-progressed erosion of the pyrolytic graphite. Additional ON/OFF cycle tests demonstrated that the gauge is still fully operational. In combination with a revision and consolidation of the operational plan and the reliability, accessibility, maintainability, and inspectability (RAMI) analysis, ITER's inherent availability requirement for the diagnostic system could be demonstrated successfully.

Microstructural transformation impact on mechanical and tribological performance of different temperature heat-treated carbon/carbon composites

Due to the harsher application environments of C/C composites, optimizing the internal structure of C/C materials through high-temperature treatments (HTT), specifically above 2300 °C, has become an effective method to enhance their properties. The current study investigates the influence of microstructural evolution on the mechanical and tribological behavior of carbon/carbon composites after heat treatments at 2300 °C and 2700 °C. The C/C composites experience a reduction in mechanical properties as the heat treatment temperature is raised. This may be due to the rearrangement of carbon atomic layers at high temperatures, resulting in increased orientation in pyrolytic carbon. However, fibers parallel to the friction surface are relatively less affected, while fibers perpendicular to the friction surface and PyC are more significantly affected. The average coefficient of friction increases from 0.19 to 0.42 as heat treatment temperature from 2300 °C to 2700 °C under the brake pressure of 1 MPa with 25 m/s brake speeds. This phenomenon is attributed to the samples with high graphitization degree (2700 °C) producing a large number of flaky chips under shear stress during friction, which can be easily ground and compacted to form a complete friction film. Additionally, the more easily deformable z-axis fiber asperities increase the contact area, resulting in an increase in the coefficient of friction and friction stability.

Conversion of Chicken Rice Waste into Char via Hydrothermal, Pyrolysis, and Microwave Carbonization Processes: A Comparative Study

Conversion of Chicken Rice Waste into Char via Hydrothermal, Pyrolysis, and Microwave Carbonization Processes: A Comparative Study

The evolution of clay mineral and its indication of hydrocarbons under overpressure: An example from the shale of the Qingshankou Formation in the Gulong Sag

The enrichment and development of shale oil are significantly influenced by the evolution of clay minerals. In this paper, the mineralogy and clay mineral crystallinity of shale samples from Wells X1, X2 and X3 in the Gulong Sag are characterized by X-ray diffraction analysis (XRD) and field emission scanning electron microscopy (FE-SEM). Geochemical parameters, including total organic carbon (TOC) and rock-eval pyrolysis, were also evaluated. The results reveal that illite in the shale primarily exists in the matrix, originating mainly from the transformation of smectite and I/S mixed layer. Chlorite in pores is predominantly formed through fluid precipitation and crystallization. The study area exhibits abnormal evolution of illite and I/S mixed layers, as well as the phenomenon of rapid chlorite growth under overpressure condition. The abnormal evolution of illite and I/S mixed layer may attribute to the inhibition of the conversion reaction from I/S mixed layer to illite. Chlorite's rapid growth occurs through the nucleation mechanism. Furthermore, through the analysis of clay and organic matter correlation, coupled with overpressure and hydrocarbon-rich section considerations, it is observed that chlorite may play a significant role in the storage and generation of S1. This study contributes to a better understanding of the relationship between clay mineral evolution and shale reservoir overpressure, offering valuable insights for the accurate assessment of shale oil.

High repetition-rate dual-channel X-ray spectrometer for high-intensity laser-plasma experiments.

We describe the development and demonstration of a high-repetition-rate-capable dual-channel (DC) x-ray spectrometer designed for high-intensity laser-plasma experiments (≥1×1021 W/cm2). The spectrometer, which operates at high repetition rates, is limited only by the refresh rate of targets and the camera's frame rate. It features two channels, each equipped with a flat highly oriented pyrolytic graphite (HOPG) crystal and a unique detector plane, allowing it to resolve two distinct x-ray bands: approximately 7-10 and 10-13keV. Each detector plate carrier holds two slots for active (scintillators) or passive (imaging plates) x-ray detectors. We present the design and testing of the HR-DC-HOPG using both the COMET laser (10J, 0.5ps shot/4min) at LLNL's Jupiter Laser Facility and the SCARLET laser (10J, 30fs shot/min) at Ohio State University. The results demonstrate the spectrometer's performance across various laser energies, target materials, pulse shapes, and detector types.

Time- and angle-resolved photoemission spectroscopy with wavelength-tunable pump and extreme ultraviolet probe enabled by twin synchronized amplifiers.

We describe a setup for time- and angle-resolved photoemission spectroscopy with wavelength-tunable excitation and an extreme ultraviolet probe. It is enabled by using the 10kHz twin Ti:sapphire amplifiers seeded by the common Ti:sapphire oscillator. The typical probe energy is 21.7eV, and the wavelength of the pump excitation is tuned between 2400 and 1200nm by using the optical parametric amplifier. The spectral width of the extreme ultraviolet probe is 53meV, and the time resolution is dependent on the wavelength for the pump, better than 60fs for the pump energy >0.7eV. This system enables the pump energy to be matched with a specific interband transition and to probe a wider energy-momentum space. We present the results for the prototypical materials of highly oriented pyrolytic graphite and Bi2Se3 to show the performance of our system.