Increase In Graphitization Degree Research Articles

Impact of Graphitization Degree on the Electrochemical and Thermal Properties of Coal.

Coal-based cryptocrystalline graphite is an intermediate phase formed during the transformation of highly metamorphic anthracite into crystalline graphite. In order to explore the relationship between the graphitization degree of coal-based cryptocrystalline graphite and its physical properties from macromolecular structure to provide a theoretical basis for industrial application, samples were tested by X-ray diffraction, electrochemistry, and thermal conductivity and compared with standard graphite (SG) and artificial thermal simulation graphitized samples. The results show that with the increase of graphitization degree and the growth of microcrystalline structure, the electrical impedance of cryptocrystalline graphite decreases, the conductivity increases, the specific capacity of initial discharge increases, and the thermal conductivity increases, which gradually approach the electrical and thermal properties of crystalline graphite. The linear equations between impedance and La and Lc are y = -0.42x + 70.44 and y = -1.87x + 70.62, and the correlation coefficients are 0.93 and 0.88. The linear equations between thermal conductivity and the horizontal extension length (La) and vertical stacking thickness (Lc) are y = 0.09x + 1.36 and y = 0.4x + 0.76, the correlation coefficients are 0.82 and 0.84., and the reduction of microcrystalline parameters d002 and the increase of La and Lc lead to a direct improvement of physical properties. Artificial thermal simulation samples also show the same regularity, but their physical properties are lower than those of natural evolution samples. Short-term high-temperature simulation is different from long-term magma heat and pressure, and the growth of graphite microcrystals is more complete under long-term geological conditions, resulting in better physical properties.

Graphitization of anthracite catalyzed by single metal oxides and its enhanced electrical conductivity

ABSTRACT A series of synthetic graphite was fabricated through metal oxide catalytic graphitization using purified anthracite (TYC). The effects of graphitization temperature, catalyst type and its addition methods on structure and properties of graphite products were investigated through the methods of XRD, Raman spectra, SEM, TEM, FTIR and resistivity tester. Increasing graphitization temperature favors the enhancement of order and size of graphite microcrystals, graphitization degree, and conductivity of graphitized products. TiO2 exhibited the best catalytic effects in catalytic graphitization. Compared to directly graphitized TYC at 2800°C (TYC-28), the graphite catalyzed by TiO2 added physically (TYC-28-TiO2) and added chemically (TYC-28-C-TiO2) demonstrated a 13.0 and 16.7% increase in graphitization degree, respectively. Meanwhile, chemical addition method (0.61 × 10−4 Ω·m) outperformed physical addition method (1.21 × 10−4 Ω·m) in improving the electrical conductivity of graphitized products. Moreover, at 2400°C, TYC catalyzed by TiO2 added physically and added chemically presented a graphitization degree of 73.7 and 77.6%, respectively, both exceeding that of TYC-28 (70.7%). Therefore, metallic oxides can enhance the graphitization degree while lowering the required graphitization temperature. This method holds promise for cost-effective and energy-efficient production of high-conductivity graphitized anthracite for batteries, supercapacitors, conductive coatings, and conductive adhesives.

Stripping of carbon coatings in radio-frequency inductively coupled plasma of H2/Ar

This article describes the stripping of amorphous carbon (a-C) coatings in an H 2 /Ar atmosphere using a radio-frequency inductively coupled plasma (RF-ICP) source. The power of the RF-ICP source, atmosphere composition (H 2 /Ar) and bias potential strongly affect the stripping rate (0.7–9.3 μm/h), while the operating pressure has less influence (2.7–3.2 μm/h). The selectivity of stripping of a-C and titanium coatings can be varied from 1 up to ~90 by changing the atmosphere composition. Chemical sputtering plays a key role in the productivity and selectivity of carbon stripping, it should have a higher rate compared to physical sputtering to enable high selectivity of coating stripping. Raman spectroscopy reveals the increase in graphitization degree and decreasing less ordered carbon of a-C coatings under stripping in H 2 /Ar plasma. Phase transformations of sublayer or substrate materials could occur under coating stripping in a reactive atmosphere in the example of hydride formation (TiH 2-x ) in a Ti sublayer. • Stripping of carbon coatings in RF-ICP plasma of H 2 /Ar. • Stripping selectivity of carbon coatings is regulated by H 2 /Ar flow rates. • Graphitization of a-C coatings under stripping in H 2 /Ar plasma.

A Coral‐Like FeP@NC Anode with Increasing Cycle Capacity for Sodium‐Ion and Lithium‐Ion Batteries Induced by Particle Refinement

AbstractWe present a coral‐like FeP composite with FeP nanoparticles anchored and dispersed on a nitrogen‐doped 3D carbon framework (FeP@NC). Due to the highly continuous N‐doped carbon framework and a spring‐buffering graphitized carbon layer around the FeP nanoparticle, a sodium‐ion battery with the FeP@NC composite exhibits an ultra‐stable cycling performance at 10 A g−1 with a capacity retention of 82.0 % in 10 000 cycles. Also, particle refinement leads to a capacity increase during cycling. The FeP nanoparticles go through a refining–recombination process during the first cycle and present a global refining trend after dozens of cycles, which results in a gradually increase in graphitization degree and interface magnetization, and further provides more active sites for Na+ storage and contributes to a rising capacity with cycling. The capacity ascending phenomenon can also extend to lithium‐ion batteries.

A Coral-Like FeP@NC Anode with Increasing Cycle Capacity for Sodium-Ion and Lithium-Ion Batteries Induced by Particle Refinement.

We present a coral-like FeP composite with FeP nanoparticles anchored and dispersed on a nitrogen-doped 3D carbon framework (FeP@NC). Due to the highly continuous N-doped carbon framework and a spring-buffering graphitized carbon layer around the FeP nanoparticle, a sodium-ion battery with the FeP@NC composite exhibits an ultra-stable cycling performance at 10 A g-1 with a capacity retention of 82.0 % in 10 000 cycles. Also, particle refinement leads to a capacity increase during cycling. The FeP nanoparticles go through a refining-recombination process during the first cycle and present a global refining trend after dozens of cycles, which results in a gradually increase in graphitization degree and interface magnetization, and further provides more active sites for Na+ storage and contributes to a rising capacity with cycling. The capacity ascending phenomenon can also extend to lithium-ion batteries.

An electrically conductive SiBCN film prepared via polymer-derived ceramic and chemical vapor deposition methods

High-temperature surface acoustic wave (SAW) sensors for multi-parameter simultaneous measurement are widely needed in the fields of aerospace and energy. For the SAW sensors that can be operated up to 1200 °C, high temperature conductive coatings are required to match with the YCa4O(BO3)3 (YCOB) single crystal, which is the only available piezoelectric ceramics now for use at 1200 °C. Promising high temperature conductive films comprised of SiBCN ceramics were coated via chemical vapor deposition (CVD), polymer-derived ceramic (PDC) route and PDC plus CVD method, respectively. The microstructure, morphology and electrical properties of the films were characterized in detail. It was found that a film with few defects and good conductive performance can be obtained at 1000 °C by PDC plus CVD route. However, a BN film has to be deposited on YCOB wafer first to suppress its decomposition in inert atmospheres around 1000 °C in the case of using CVD method. The overall conductivity change is primarily due to the increase in graphitization degree of free carbon in PDC-SiBCN.

Char reactivity and kinetics based on the dynamic char structure during gasification by CO2

Coal char reactivity is the essential for gasifier design and operation. Char structure and reactivity are dynamic with reaction during gasification. To obtain the relationship between dynamic structure and reactivity, char samples at different carbon conversion were prepared at 1223 K by a rapid heating thermogravimetric analyzer (R-TGA). The ex-situ char reactivity was investigated in TGA between 1073 and 1223 K, and was correlated with the dynamic structure. Besides of XRD and SEM results, nano-computed tomography (nano-CT) revealed the morphology of carbon matrix and minerals during gasification. Results showed that reaction rate of in-situ char significantly increased firstly and then decreased, which was attributed to the gas switch step, the increase of graphitization degree and inhibition effect of minerals. In contrast, the reactivity of ex-situ char was initially controlled by chemical structure and later by the abundant catalytic activity of minerals. The reactivity decreased slightly and then increased with increasing carbon conversion. The unreaction core model (URCM) was more suitable to interpret the gasification kinetics based on the dynamic char structure and fitting coefficient. Meanwhile, the results by iso-conversional method also supported the validity of URCM, but also indicated that the activation energy of char gasification gradually increased during in-situ gasification.

Experimental research on semi-coke for blast furnace injection

The combustion properties and grindability of Shenmu low-rank coal (SM) and its four different semi-cokes were studied by the self-designed equipment and Hardgrove method. The four semi-cokes were obtained under the pyrolysis temperature of 400, 500, 600 and 700 °C, named as SM-400, SM-500, SM-600 and SM-700, respectively. The analyses of nitrogen adsorption, Fourier-transform infrared spectroscopy (FTIR) spectra and Raman spectra were carried out to explain the change in combustion ratio and grindability. The result showed that the specific surface area of samples had an essential effect on the combustion ratio of SM-400 and SM-500. Meanwhile, the grindability depended on the strength of coal matrix, and the augment of pore amounts would increase the grindability. The functional groups and graphitization degree of the same sample were identical with the combustion ratio. With the pyrolysis upgrading temperature increasing, the combustion ratio of sample decreased, corresponding to the decrease in the benzene ring and the increase in graphitization degree. In addition, the thermogravimetric analysis was carried out, and the result was compared against what was shown in the data of combustion ratio. For pulverized coal injection, the combustion ratio was more intuitive and more accurate than combustibility.

One-Step Pyrolytic Synthesis of Multiwalled Carbon Nanotubes: The Role of Resupply of Carbon Species on the Quality Control.

An investigation on varying experimental parameters such as solution quantity (2.5, 5 and 7.5 mL) and reaction time (15, 30, 45 and 60 min) was carried out for the production of high-quality multiwalled carbon nanotubes (MWCNTs) in one step pyrolysis. Structural analysis revealed the uniform diameter distribution and the length of nanotubes in the range of 60-80 nm and 0.4-2 μm, respectively. Raman and X-ray diffraction analysis showed a remarkable reduction in defect density with increase in graphitization degree, upon increasing the solution volume and reaction time. MWCNTs prepared at higher solution quantity (7.5 mL) with higher reaction time (60 min) showed higher crystallinity (70% graphitization) and lower defect density (ID/IG: 0.56). The attainment in equilibrium of evaporation cum precipitation in formation of high quality nanotubes structure is evaluated. An effective resupplying of condensed precursors by re-evaporation leads for the achievement of low defect density nanotubes with higher product yield is achieved.

Creep Deformation of Carbon-Based Cathode Materials for Low-Temperature Aluminum Electrolysis

The uniaxial-compression creep behavior of semi-graphitic carbon products was investigated using modified Rapoport equipment in a K3AlF6–Na3AlF6–AlF3 and a Na3AlF6–AlF3 system. The stress exponent is low for the K3AlF6–Na3AlF6–AlF3 system in the steady-state creep stage. With an increase in graphitization degree and grain size, the interlayer space and porosity of the tested samples decrease after aluminum electrolysis. A low temperature can suppress carbon-cathode damage. Based on these stress exponents and a microstructural investigation using transmission electron microscopy, it is proposed that dislocation glide is the dominant creep mechanism for the carbon cathode during aluminum electrolysis in the steady-state creep stage.

The Study of the Role of Fullerene Black Additive during the Modification of Ductile Cast Iron

The use of fullerene black (FB) as effective modifying additive to cast iron is substantiated by its high potential. Research of nanoadditives to modifier has shown an increase in graphitization degree and the forming of favorable morphology of globular graphite. The results of microstructural analysis and tribological trials have confirmed an improvement of ductile cast iron’s structure and properties when treated with FB-additive.

Polyvinylidene Fluoride-Based Carbon Supercapacitors: Notable Capacitive Improvement of Nanoporous Carbon by the Redox Additive Electrolyte of 4-(4-Nitrophenylazo)-1-naphthol

The nanoporous graphitic carbon materials (NGCM) have been prepared by a synchronous carbonization and graphitization process, using waste polyvinylidene fluoride (PVDF) as carbon precursor and Ni(NO3)2·6H2O as the graphitic catalyst. It reveals that the carbonization temperature plays a crucial role in determining the pore structures as well as their electrochemical performances. Increasing the carbonization temperature from 800 to 1200 °C, the corresponding porosity has slightly decreased, accompanied by an increase of graphitization degree. Next, to further improve the electrochemical performance of the sample prepared at 800 °C, a novel redox additive of 4-(4-nitrophenylazo)-1-naphthol (NPN) with different amounts has been introduced in 2 mol L–1 KOH electrolyte. Therein, the specific capacitance by adding 4 mmol L–1 of NPN can reach 2.98 times higher than the pristine value. Apparently, the mixed electrolytes have largely enhanced the electrochemical performance, which is expected to be applied in th...

Hot corrosion resistance of four graphite material in molten Solar Salt

Solar Salt is the best hot transfer medium molten salt of solar thermal power generation.In order to study the hot corrosion behavior of four graphite is in the molten Solar Salt.The graphite immersed equipped with molten salt crucible placed in a muffle furnace,each period of time remove the sample and weight the weight gain until the sample is completely destroyed.The destruction forming of graphite is analyzed by XRD, SEM and OP.The study found that the order of hot resistant corrosion of molten Solar Salt of four graphite materials are the fine structuregraphite,isostatic graphite,9# graphite and cold pressing graphite.The principal factors can affect hot corrosion resistant of graphite is the graphitization degree. The hot corrosion resistance of the graphite can be enhanced with the increase of graphitization degree.

Effects of Plasma Power and Plasma Sheath on Field Emission Properties of Carbon Nanotubes

With a nickel catalyst, carbon nanotubes (CNTs) were prepared by microwave plasma-enhanced chemical vapor deposition (MPCVD). Transmission electron microscopy (TEM) images reveal the center hollowness and multiwall structure of CNTs. The tip-growth mechanism of the CNTs prepared by MPCVD is confirmed by the Ni particles enclosed at the tips of the CNTs. The degree of CNT graphitization increases with plasma power up to about 1000 W and then reaches the upper limit. This is attributed to an insufficient carbon feedstock for CNT growth. The field emission (FE) efficiency of the CNTs increases with plasma power. For plasma powers not greater than 1000 W, the increase in graphitization degree and the decrease in the number of defects in a CNT emitter array enhance FE performance. The defects produced by the large split catalysts remaining in the CNTs at low plasma powers (700 and 800 W) also result in a low FE efficiency. Although the CNTs grown at moderate to high plasma powers (1000 to 1200 W) have similar graphitization degrees, a low plasma power results in split catalysts and hence defects, as evidenced by TEM observation. These defects accumulate electrons, block electronic transport, and hence reduce the FE efficiency of the CNTs. The effect of kinked CNTs produced by the a plasma sheath on FE efficiency is negligible.

Characterization of heat-treated porous carbons using argon adsorption

The microstructural variation of Norit R1 Extra activated carbon, progressively heated at 1373 K, was explored in terms of pore size and pore wall thickness distributions, for various periods of heating time, determined by argon adsorption at 87 K, both using an infinite as well as and finite wall thickness model. The latter approach has recently been developed in our laboratory and has been applied to several virgin carbons. The current results show significant variations in small pore size regions (<7 Å) in association with strong growth of thick walls having at least three carbon sheets, as a result of heat treatment. In particular, shrinkage of the smallest pores due to strong interaction between their opposite walls as well as smoothening of carbon wall surfaces due to an increase in graphitization degree under thermal treatment have been found. Further, the results of pore wall thickness distribution are well corroborated by X-ray diffraction. The results of pore size and pore wall thickness distributions are also shown to be consistent with transmission electron microscopy analyses.

Effect of discharging energy on electric-spark discharge graphitization of carbon

The effect of discharging energy on graphitization of carbon caused by spark shock was investigated. Three different types of heat treated carbons, petroleum coke carbon, pitch-bonded petroleum coke carbon and Akabira coal carbon were used for this purpose. The change in the graphitization degree was investigated by X-ray diffraction by determining the interlayer spacing fd, and the crystallite thickness L c . The X-ray diffraction profiles of lines showed for specimens shocked by electric spark discharge of the highest discharging energy a sharp and strong (002) peak, although for those shocked by lower discharging energy showed a composite (002) peak. The interlayer spacing d(002) for the specimens shocked with the discharging energy as high as 4600 J decreased to about 3·36Å. It was found that the increase in degree of graphitization by electric spark discharge was greater when the discharging energy increased. Electron micrographs of the specimens shocked by the discharge of highest energy show some laminar crystals having similar appearance to natural graphite.

The effect of electric spark discharge on graphitization of carbon

The effect of electric spark discharge on graphitization of carbon was investigated using three different types of heat treated carbon such as petroleum coke, pitch-bonded petroleum coke, and Akabira coal carbon. Each cylindrical specimen of 6 mm dia. by 6 mm length was shocked by electric spark discharge between iron electrodes in an iron capsule. The capacity of condenser was 20,000 μF and the charging voltage was 680 V. The pulse duration of spark discharge recorded by synchroscope was 1–2 millisec. The change of the graphitization degree was investigated by determining the inter-layer spacing d and crystallite thickness L c by X-ray diffraction. The interlayer spacing d of petroleum coke and pitch-bonded petroleum coke pre-heat-treated over the range from 1000° to 2800°C decreases to 3·56–3·57 Å, and their crystallite thickness L c increases to 400–1000 Å as a result of the electric spark shock. It was found that the increase in degree of graphitization was more remarkable when the carbon is heat treated to lower temperature. X-ray diffraction profiles for Akabira coal carbon also showed an increase in degree of graphitization resulting from the electric spark shock