Graphitization Temperature Research Articles

Self-Assembled Graphene Composites for Flow-Through Filtration.

Spontaneously exfoliated pristine graphene is used as a surfactant to template the formation of electrically conductive filters for the adsorption of an organic dye from water. In contrast to other reported graphene-based adsorption materials, our system provides a continuous approach to water treatment rather than a batch approach, and uses pristine graphene instead of the more costly and environmentally challenging graphene oxide. The use of self-assembled graphene also results in our filters being electrically conductive, providing a convenient route to clean the filters by resistive heating. An investigation of the mechanism of formation and filtration by these filters, templated by self-assembled two-dimensional pristine graphene, is presented. The thermodynamically driven exfoliation of natural flake graphite at a high-energy monomer/water interface produces water-in-oil emulsions stabilized by a thin layer of overlapping graphene sheets. Subsequent polymerization of the continuous monomer phase produces polymer foams with cells lined by graphene. With a combination of acoustic spectroscopy and electron microscopy, the effects of graphite concentration and temperature are studied, as is the correlation between droplet size and the size of the cells in the final polymer foam.

Preparation of Expanded Graphite and Fly Ash Base High Temperature Compound Phase Transition Heat Absorption Material and Its Application in Building Temperature Regulation

In this study, the product substance was pretreated with coal excrement as a raw product substance. Taking expanded graphite and paraffin as phase change product substances, expanded graphite and paraffin or coal excrement base high temperature compound phase transition thermal storage product substance were prepared by mixed sintering method. Firstly, the sintering mechanism of the composite should be deduced. In addition, XRD, TG-DSC and other analytical techniques were used to characterize the morphology and physical character of the product substances. In order to test the temperature regulation ability of the product substance, the composite product substance was fused with cement. The cement block added with composite product substance was taken as the research object, verify the performance of compound phase transition product substance on temperature regulation. In the experimental procedure, when phase change product substances' the proportion was less than 60%, the high temperature compound phase transition thermal storage product substances prepared were well-formed and had good crystallography, and the green body' various tissues were densely distributed. When the paraffin content was above 35 wt%, the external density, compressive strength, and cement blocks' thermal conductivity added with composite product substances increased significantly compared with ordinary expanded perlite cement blocks, which was suitable for building product substances' requirements. When the paraffin content reached 38 wt%, a temperature difference of 19.2 °C to 26.1 °C appeared in the composite product substance' corresponding cube space, indicating that room temperature can be adjusted by adding a certain phase change product substance.

Production of Graphite During the Extinguishing Arc with New SF6 Alternative Gases

Most high voltage circuit breakers in operation use SF6 as the arc interruption medium because of its high dielectric strength and good arc interruption properties. However SF6 also displays a high global warming potential which motivates the investigation of possible alternatives such as CO2–Novec™4710 and N2–Novec™5110 mixtures proposed by different HVCB manufacturers. CB power test comparison between pure CO2 and CO2–Novec™4710 mixture shows that the latter created a large amount of graphite and reduced CB performances after several current breaking shots. Using Gibbs free energy method, a theoretical study has been conducted on SF6 replacement candidates listed above. Aiming to understand graphite formation, several parameters impact were discussed: carrier gas such as CO2 and N2, pressure and O2 initial mixture proportions. The study focuses on graphite condensation temperature and graphite production amount evolutions in respect to the study parameters as well as in respect to CB inter-contacts space condition in terms of pressure and temperature at current-zero. It has been shown that a high percentage of CO2 in the mixture reduces graphite condensation temperature by 2600 K while adding N2 do not make such an impact. Pressure increases graphite condensation temperature and O2 reduces it. The amount of graphite produced is pressure independent but decreases with the increase of O2 proportion in the initial mixture. It has been shown that adding a sufficient O2 amount can prevent graphite production at all.

Controllable fabrication of graphitic nanocarbon encapsulating FexNiy hybrids for efficient splitting of water

The hybridized electrocatalysts constituted by binary 3d transition nanoparticles with a varied ratio of Fe to Ni were successfully synthesized through a two-step fabrication procedure, a homogeneous precipitation process, and a successive graphitization process. A superior oxygen evolution reaction (OER) efficiency with a yielded remarkable low overpotential of ∼0.26 V and a Tafel slope of ∼56 mV/decade is achieved for the heterostructured Fe1Ni2 nanoparticles coated by graphitic nanocarbon in a 1 mol/L KOH solution. The influencing factors for synthesizing the electrocatalysts, such as the graphitization temperature, the content of iron and the thickness of the carbon shells are also carefully investigated, and improved electrocatalytic efficiency is achieved with appropriate fabrication parameters for the hybridized catalysts. It is considered that the synergistic effect of the defects and electrochemical conductivity of the graphitic carbon shells shows great influences on the electrocatalytic activity. In addition, the detailed electrochemically active surface area and the electrochemical impedance suggest that the FexNiy hybrids coated by graphitic nanocarbon have improved the mass transport and electron transfer rate, resulting in an enhanced electrocatalytic water splitting efficiency. This work opens up a new way to fabricate promising oxygen-evolving catalysts with high-efficiency and low-cost.

Graphite creep negation during flash spark plasma sintering under temperatures close to 2000 °C

Graphite creep has high importance for applications using high pressures (100 MPa) and temperatures close to 2000 °C. In particular, the new flash spark plasma sintering process (FSPS) is highly sensitive to graphite creep when applied to ultra-high temperature materials such as silicon carbide. In this flash process taking only a few seconds, the graphite tooling reaches temperatures higher than 2000 °C resulting in its irreversible deformation. The graphite tooling creep prevents the flash spark plasma sintering process from progressing further. In this study, a finite element model is used to determine FSPS tooling temperatures. In this context, we explore the graphite creep onset for temperatures above 2000 °C and for high pressures. Knowing the graphite high temperature limit, we modify the FSPS process so that the sintering occurs outside the graphite creep range of temperatures/pressures. 95% dense silicon carbide compacts are obtained in about 30 s using the optimized FSPS.

Preparation and Characterization of Anatine TiO2/Expanded Graphite with High Expansion Volume

Element of Ti was introduced to expandable graphite surface by Sol-gel method; TiO2/expanded graphite was prepared after expansion of high temperatures. Detection by scanning electron microscope(SEM), X-ray diffraction(XRD), energy disperse spectroscopy(EDS) and differential scanning calorimetry(DSC) to semples, the results were founded: The better process conditions with high expansion volume are as follows: graphite that particle size is more than 180μm, expansion temperature is about 650°C-750°C. The contents of Ti in compounds of anatine TiO2/expanded graphite can be reached 3.16%; the volume of compounds can be reached 234ml/g. The results showed that the lower temperature and smaller particle size of graphite is benefit for anatine type of TiO2, but higher temperature is good to high expansion volume. The preparation condition should be balanced with crystal type, heat loss and expansion volume.

THERMAL BEHAVIOUR CORRELATION FOR THERMAL COLUMN IN THE NATIONAL RESEARCH UNIVERSAL (NRU) REACTOR

The National Research Universal (NRU) reactor is a major research facility that provides a beam of slow neutrons with a minimum of gamma rays and other types of radiation for experimental purposes. The thermal column consists of 5 graphite radial sections separated with an air gap for cooling. The graphite components require continuous monitoring to ascertain that temperatures are controlled within safe margins. Wall temperatures of the graphite sections are obtained via thermocouples affixed to the column walls. The safety margins for operation of the thermal column are driven by the temperatures of the closest radial section to the reactor core (HG1). Although, most of the thermocouples in HG1 are no longer functional, the thermocouples are functional in the adjacent graphite section (HG2). This study relied on the historical data of the graphite temperatures over a few years to develop an empirical correlation that relates temperatures in HG1 to those of HG2. The correlation sets limits on the functional thermocouples in HG2 to ensure HG1 remains within the prescribed limits (149–232 °C). Correlations were developed using statistical analysis of the historical data. A control band of approximately 40 °C for HG2 with confidence levels of 68% and 95%, respectively, were established.

Effect of different acid corrosion reagents on de-cobalt effect and performance of PDC at room temperature

In this study, we investigated the effects of four different acid reagents, sulfuric acid, compound acid, phosphoric acid and Lewis acid-FeCl3, on the depth of Co depletion layer, thermal stability and bending strength of polycrystalline diamond compacts (PDC) at room temperature. The results show that the thermal stability and bending strength of PDC after soaking in different acid corrosion reagents are closely related to the acid-etching effect, especially the depth of Co depletion layer. Sulfuric acid has the best effect of removing cobalt at room temperature. After soaking for 48 h, the depth of Co depletion layer reached 140 um from the surface. Its initial graphitization temperature was 850 °C, and then increased 130 °C with treatment. The bending strength of the PDC was significantly reduced after removing Co from PDC. The larger the depth of Co depletion layer, the lower the bending strength.

Simple construction of ruthenium single atoms on electrospun nanofibers for superior alkaline hydrogen evolution: A dynamic transformation from clusters to single atoms

Abstract The challenges for preparing metal single atoms (MSAs) catalysts are facile synthesis approaches and the suitable supports with strong coordination to stabilize MSAs. Herein, we reported a facile strategy to synthesize the Ru single atoms (Ru SAs) through the dynamic transformation from clusters to single atoms by combining the electrospun technology and NH3-assisted graphitization process. The small Ru nanoclusters (NCs) supported on carbon nanofibers (CNFs) were in situ converted into Ru SAs in N-doped CNFs under the NH3 treatment. Through controlling the NH3 treatment time and graphitization temperatures, the Ru nanocrystals exhibit a dynamic transformation from nanoclusters to single atoms. The results indicate that the Ru NCs with larger amounts of Ru SAs exhibit superior HER activity in alkaline media with low overpotential of 34 mV at 20 mA cm−2, which is even significantly better than commercial Pt/C catalysts. The mass activity of Ru SAs/NCNFs is about 390 A g−1Ru at an overpotential of 100 mV, which is ~3.5 times higher than that of commercial Pt/C (110 A g−1Pt). This strategy will provide a new way for the large-scale production of MSAs transformed from different metal nanoparticles or nanoclusters.

Nanodiamond graphitization at heating and irradiation

In this work the graphitization and thermal stability of detonation nanodiamonds were studied. Received data showed that the temperature of graphitization of nanodiamond particles lies in wide range and the temperature of graphitization beginning depend on the particle size. It is established the influence of heating rate on the size of nanodiamond conglomerates. The analysis of literature shows that the graphitization processes take place at irradiation. Depending on the type and irradiation dose the point defects, amorphous and graphite phases can form in the diamond structure. Annealing of irradiation samples showed the defect structure restore to ideal lattice and the release of stored energy.

Comparative study of melting of graphite and graphene

Abstract The melting lines of graphite and liquid carbon have been studied for a long time. However, numerous controversies still remain in this field; for instance, different experiments give different melting temperatures. In this work, we explore the melting lines of graphite and graphene by means of classical and ab-initio molecular dynamics. We show that the empirical models developed on the basis of experimental data (AIREBO potential, Tersoff potential and some others) fail to reproduce the properties of liquid carbon properly. The models fitted to ab-initio data (LCBOPII and GAP) give much better results. However, both types of empirical models and ab-initio simulations evidence the presence of smooth structural crossover in liquid carbon. We also show that the “melting” of graphene discussed in previous works on computer simulation is indeed sublimation and propose a novel method to simulate the melting of graphene: simulation of graphene sheet in argon atmosphere. The melting temperature of graphene in argon atmosphere appears to be close to the melting temperature of graphite.

Low Cost Gas Diffusion Layer Materials and Treatments for Durable High-Performance PEM Fuel Cells

The gas diffusion layer (GDL) is a critical component of proton exchange membrane fuel cells (PEMFC). It serves as the primary mediator in electrical and thermal conductivity as well as gas and water transport within the cell. Currently, the production of GDLs is dependent on the use of high-cost materials and manufacturing methods. The most common base material for GDLs is polyacrylonitrile (PAN). PAN, in addition to its high base cost ($15 - 20/kg), requires high graphitization temperatures (> 1700°C) in order attain sufficient conductivity and post-carbonization treatment with Teflon to increase the hydrophobicity for improved water transport. The high strength of PAN based GDLs has been required to prevent fiber intrusion into the channel of the flow field. Some state-of-the-art flow fields no longer utilize the land/channel design, and as such may not require the use of high strength materials like PAN in order to be functional. This presents the opportunity to create novel GDLs with equivalent or superior performance at lower cost. We are investigating methods to significantly reduce the cost of GDL production while maintaining durability and performance characteristics necessary to PEM fuel cells. First, we are developing the use of inexpensive, natural fiber materials, such as cotton, jute, and bamboo. Second, we are developing methods to reduce the carbonization temperatures and eliminate manufacturing steps, such as the need for a microporous layer. Figure. SEM images of commercial (A) (without microporous layer), cotton (B), and jute (C) based GDLs. The cotton and jute GDLs had been carbonized at 1100°C in N2 atmosphere. Figure 1

On the difference of graphitization behavior between vitrinite- and inertinite-rich anthracites during heat treatment

ABSTRACTTwo vitrinite- and inertinite-rich anthracites from Daliuta and Hujiahe, Shannxi, China, were heated to temperatures to 2900°C. The aim of this study was to investigate the difference of graphitization behavior between vitrinite and inertinite. X-ray diffraction, Raman spectroscopy, and HRTEM analysis were applied to characterize the graphitized products. Graphitization behaves as two aspects, namely crystallization and reorganization of structures. The results show that graphitization temperature for vitrinite is lower than inertinite. Besides, the graphitization of vitrinite is characterized by homogenous crystallization and reorganization of structures. The two processes are likely simultaneous during graphitization. However, the graphitization of inertinite is described by a heterogenous process. A mutation appears both in crystallization and reorganization process and the two processes are non-synchronous during graphitization.

Impact of the volume heat source on the RANS-based CFD analysis of Molten Salt Reactors

Several efforts have been spent in recent years to address the simulation challenges posed by the non-conventional design of Molten Salt Reactors (MSRs). One of the design specificities of MSRs is the volume heat source in the liquid fuel, which has been proven by various authors to significantly alter the heat transfer processes in these reactors. This paper focuses on the impact of a volume heat source on the wall treatment of the standard high-Reynolds Reynolds-Averaged Navier Stokes (RANS) turbulence models. A modified thermal wall function is derived and its impact is discussed for typical MSR calculations. The results show a non-negligible impact on graphite temperatures, both at steady state and during transients.

Temperature dependence of catalytic activity in graphene synthesis for Sn nanoparticles

Graphene synthesis at lower temperatures is quite important for a wider range of practical applications. Sn, which is recently found as a promising catalyst for the low-temperature graphene growth, is taken as the study material in this work. Based on the detailed transmission electron microscopy (TEM) observation, we found that catalytic activity of Sn nano-particles is highly temperature dependent which was observed during graphitization of amorphous carbon. For this study, C–Sn composite nanofibers were prepared on an edge of a carbon foil by the Ar+ ion irradiation with simultaneous supply of Sn. As-fabricated C–Sn composite nanofibers were observed to be the amorphous C nanofibers (CNFs) in which the Sn nanoparticles dispersed. The as-prepared samples were annealed at 180–250 °C in a vacuum and were characterized using Raman spectra and high-resolution TEM to study the graphitization process. The graphitization started to occur at an annealing temperature of 180 °C, which is much lower than the graphitization temperature for bulky Sn. Based on the detailed TEM observation of annealed samples, a model to explain the graphitization mechanism at such a low temperature was proposed.

Molecular Dynamics Simulation for Temperature and Graphite-Like Structure Effects on Amorphous Carbon Graphitization

The effects of temperature and graphite-like structure additive on the graphitization process of amorphous carbon were investigated through molecular dynamics simulation. The molecular models of amorphous carbon and graphite-like structure-amorphous carbon were constructed with the initial density of 1.62 g/cm3 and carbon atoms number of 4096 by rapid quenching method. After annealing treatment at 3200 K, 3600 K and 4000 K respectively, the evolution rules of sp2 C atoms and the instantaneous conformations of the graphite-like structure-amorphous carbon system were analyzed to investigate the effects of temperature and graphite-like structure on the graphitization process. It could be found that increasing graphitization temperature properly could improve graphitization degree of amorphous carbon. Addition of graphite-like structure could promote recrystallization of the irregular carbon atoms in amorphous carbon materials, thus accelerating graphitization process and promoting graphitization of the system.

Experimental Investigation of Natural Circulation During Air-Ingress Scenario in a Very High Temperature Reactor

In order to investigate air-ingress phenomena in a gas-cooled very high temperature reactor (VHTR), natural circulation experiments have been conducted in a helium flow loop after the injection of nitrogen into the lower plenum. A pair of helium analyzers were used to measure the nitrogen and helium concentrations in the lower plenum and upper plenum. The changes in the nitrogen concentration in the upper plenum were used to calculate the time required for the transport of nitrogen from the lower plenum to upper plenum through a riser flow channel made of graphite. The effect of system temperature and pressure on the rate of nitrogen transport has been studied extensively. Furthermore, a close examination of the graphite flow channel wall temperatures at different elevations showed small but sudden drops indicating the arrival of nitrogen at each elevation. From these data, the upward transport of nitrogen injected into the lower plenum under natural circulation conditions could be quantitatively investigated. The experimental findings indicate that the driving mechanisms for air transport through the reactor core of VHTR would result from both molecular diffusion and natural circulation. At low graphite temperatures in the riser, molecular diffusion is the dominating mechanism; however, as the riser temperature increases, natural circulation becomes dominant and the rate of nitrogen transport increases. Further, the time constants for these mechanisms have been calculated using a simplified species transport equation.

Production of Aluminum-Graphite Composite by Spark Plasma Sintering

An aluminum-graphite composite was obtained by spark plasma sintering. The graphite particle size, compaction temperature, and soaking time were shown to influence the aluminum carbide formation process. It is demonstrated that the use of larger graphite plates decreases Al4C3 formation by almost a factor of two. The influence of the graphite content on the density, CLTE, and thermal conductivity of the composite was studied. It was found that for graphite weight content above 70% the thermophysical properties of compacts degrade significantly because large numbers of pores are formed.

The Effect of Graphitization Temperature on the Composition and the Electrical Conductivity of Carbon Nanotube

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Separation of Phosphorus and Manganese from Steelmaking Slag by Selective Reduction

Steelmaking slag contains considerable amount of manganese (Mn) and phosphorus (P), and recycling them is an important issue. Since Mn is an alloy added to enhance the steel quality, while P is a harmful impurity in the steel product, they need to be separated for recycling. We have already found the possibility of separating Mn and P from steelmaking slag by selectively reducing P2O5 and FeO while suppressing the reduction of MnO. As a fundamental study for the selective reduction of P from steelmaking slag, in this study, we vary the slag basicity, graphite mixing ratio, temperature, and crucible type to find the optimum condition. Artificial steelmaking slag with various compositions is synthesized and mixed with graphite powder in an Al2O3 or a MgO crucible. The reduction is conducted at 1673 K, 1773 K, and 1873 K for 20 to 80 minutes. As a result, carbon saturated metal is formed from the slag, and the reduced metal and slag were separated easily. We find that a decrease in slag basicity suppressed the reduction rate of Mn while enhancing that of P. The activation energy for the reduction rate constant of P is found to be close to that of the diffusion of P in slag.