Amorphous Graphite Research Articles

Mechanistic Insights into the Evolution of Graphitic Carbon from Sulfur Containing Polar Aromatic Feedstock.

In the realm of carbon fiber research, a variety of structural configurations is noted, comprising crystalline, noncrystalline, and semicrystalline forms. Recent investigations into this domain have revealed an array of intriguing phases of carbon, among which amorphous graphite is the most notable for its unique mechanical, thermal, and electrical properties that arise from its inherent topological disorders. In this study, we utilized the ReaxFF molecular dynamics (MD) simulations to investigate the carbonization and graphitization processes involved in the production of amorphous graphite from benzothiophene, a sulfur-containing polar aromatic precursor. We developed C/H/S ReaxFF force field parameters to describe the high-temperature chemistry of benzothiophene. Our investigation reveals the reaction mechanisms, providing critical insights into the underlying chemical processes toward the formation of amorphous graphite and the structural characteristics of the end products. The formation of volatile gaseous molecules and their continuous elimination led to the development of noncontinuous layered graphite structures analogous to amorphous graphite consisting of pentagons, hexagons, and heptagons. These findings offer unprecedented insights into the carbonization and graphitization processes of sulfur-containing heavy-end aromatic feedstock. This knowledge lays the groundwork for advancing synthesis methods and developing amorphous graphite materials with specific properties.

Microstructure and tribological properties of Al-30Si-5Cu composite coating reinforced with ceramic phases synthesized in situ by plasma spraying

For improving the wear resistance of Al-30Si-5Cu coating, in this study, the composite coating in-situ synthesized TiC-TiN-TiN0.8C0.2/Al-30Si-5Cu (TiCN/Al-30Si-5Cu) was prepared used TiH2-graphite aggregates as raw materials and plasma spraying technology. The effect of in-situ synthesized ceramic reinforcements on the coating was researched in detail. The results showed that during the plasma spraying process, TiH2 decomposed and chemically reacted with graphite to form TiC. Additionally, some Ti also reacted with N2 and O2 in the air to form TiN and TiO2. The phases composition of TiCN/Al-30Si-5Cu composite coating were α-Al, β-Si, θ-Al2Cu, β-Ti, TiC, TiN, TiN0.8C0.2, TiO2, as well as amorphous CNX and residual graphite. The TiC-dominated ceramic phases and β-Si were uniformly distributed in the coating, which were tightly bound to the α-Al matrix. Because of the exceptionally rapid cooling rate during the coating preparation, a minor amount of submicron Si particles were also generated. The microhardness, elasticity modulus, and fracture toughness of TiCN/Al-30Si-5Cu composite coating appeared improvements compared to those of Al-30Si-5Cu coating. The TiCN/Al-30Si-5Cu composite coating exhibited smoother friction coefficient curve, along with lower friction coefficient and wear volume in comparison to the Al-30Si-5Cu coating. This suggested that the ceramic reinforcing phases in-situ synthesized led to a notable advancement in the wear resistance of the TiCN/Al-30Si-5Cu composite coating. The wear resistance of TiCN/Al-30Si-5Cu composite coating demonstrated an increasement of 78.3 % over the substrate and 28.2 % over the Al-30Si-5Cu coating. Under the dry friction test conditions outlined in this study, the wear mechanism of the TiCN/Al-30Si-5Cu composite coating included abrasive wear and fatigue wear, coupling with a minimal amount of oxidative wear.

Estimating price elasticity of demand for mineral commodities used in Lithium-ion batteries in the face of surging demand

The accelerating adoption of clean energy technologies is driving demand for certain mineral commodities like lithium, essential for electric vehicle batteries. Understanding the influence of the energy transition on each market requires examining their supply and demand price elasticities. However, there have only been a limited number of studies that have estimated mineral demand price elasticities in emerging technologies. We empirically estimate the price elasticity demand (PEDs) for mineral commodities used in lithium-ion battery cathodes and anodes—cobalt, graphite, lithium, manganese, and nickel. We also test whether the price elasticities of these mineral commodities have changed due to any structural changes in recent years, given the recent expansion in the sales of electric vehicles. Using Two Stage Least Squared (2SLS) econometric techniques, we find that demand has become less elastic for lithium (-0.11), cobalt (-0.45), nickel (-0.09), and manganese (-0.04) after structural breaks in 2020, 2013, 2009, and 2014, respectively. In contrast, demand for natural amorphous graphite (-0.36), and natural flake graphite (-0.58) remains relatively stable over the time period assessed.

Continuously compressing crushing towards a dry processing method, a testing for graphite ore

In this study the comminution methods of graphite bearing ore were compared by using five different crushing methods, namely a jaw crusher, a roll crusher, uniaxial compression tests, and a new type of continuously compressing crushers. These new continuously compressing crushers were available in laboratory and pilot scales. The particles in the + 1700 µm size class produced by continuously compressing crushing were coarser and rougher in texture compared to the rounded particles produced traditionally by a jaw crusher. In the size class −100 µm, most of the graphite flakes were observed independently in the products of each of these crushing methods. The liberation of ultra-coarse-grained graphite flakes in size class + 300 µm was most observed after pilot-scale continuously compressing crusher. The shape and enrichment of the graphite flakes were very similar after both laboratory and pilot scale continuously compressing crushers. In contrast, the graphite flakes produced by jaw crusher appeared as broken particles in the form of accumulation of several layered and non-independent graphite flake structures. The results of this study demonstrate that the new innovative continuously compressing crushing method enables the enrichment of coarser and cleaner graphite, which has a much higher value and wider industrial applications compared to amorphous and fine-grained graphite.

The influence of boron and silicon on the phase transformations of fullerene C60 at high temperatures and pressure

The effect of doping with two carbide-forming nonmetals - Si or B - (7 at. % each) on the phase transformations of crystalline C60 fullerene at a pressure of 8 GPa in the temperature range of 400–950 °C was studied using the X-ray diffraction method. Samples were synthesized from powders in a high pressure toroidal chamber, and X-ray examination was carried out at room temperature after rapid cooling. It has been shown that doping does not change the sequence of phase transformations of C60 fullerene as the temperature increases, the following phases are still observed: fcc phase - rhombohedral phase – disordered (amorphous) graphite. Boron reduces the formation temperature of disordered graphite, but silicon does not. This influence of carbide-forming non-metallic elements is fundamentally different from the influence of carbide-forming metals – Al and Fe, the addition of which increases the stability of fullerene molecules and increases the temperature of its transformation into disordered (amorphous) graphite by hundreds of degrees (P. A. Borisova, M. S. Blanter, V. V. Brazhkin, and V. P. Filonenko, Phase Transformations in C60 Fullerene with Iron and Aluminum at High Pressures and Temperatures, Bulletin of the Russian Academy of Sciences: Physics, 84 (2020) 851–856).

Stable cycling and low-temperature operation utilizing amorphous carbon-coated graphite anodes for lithium-ion batteries.

With the continuous expansion of the lithium-ion battery market, addressing the critical issues of stable cycling and low-temperature operation of lithium-ion batteries (LIBs) has become an urgent necessity. The high anisotropy and poor kinetics of pristine graphite in LIBs contribute to the formation of precipitated lithium dendrites, especially during rapid charging or low-temperature operation. In this study, we design a graphite coated with amorphous carbon (GC) through the Chemical Vapor Deposition (CVD) method. The coated carbon layer at the graphite interface exhibits enhanced reaction kinetics and expanded lithium-ion diffusion pathways, thereby reduction in polarization effectively alleviates the risk of lithium precipitation during rapid charging and low-temperature operation. The pouch cell incorporating GC‖LiCoO2 exhibits exceptional durability, retaining 87% of its capacity even after 1200 cycles at a high charge/discharge rate of 5C/5C. Remarkably, at -20 °C, the GC-2 maintains a specific capacity of 163 mA h g-1 at 0.5C, higher than that of pristine graphite (65 mA h g-1). Even at -40 °C, the GC-2‖LiCoO2 pouch cell still shows excellent capacity retention. This design realizes the practical application of graphite anode in extreme environments, and have a promising prospect of application.

Computer simulation of carbonization and graphitization of coal

This study describes computer simulations of carbonization and graphite formation, including the effects of hydrogen, nitrogen, oxygen, and sulfur. We introduce a novel technique to simulate carbonization, ‘Simulation of Thermal Emission of Atoms and Molecules (STEAM)’, designed to elucidate volatile outgassing and density variations in the intermediate material during carbonization. The investigation analyzes the functional groups that endure through high-temperature carbonization and examines the graphitization processes in carbon-rich materials containing non-carbon impurity elements. The physical, vibrational, and electronic attributes of impure amorphous graphite are analyzed, and the impact of nitrogen on electronic conduction is investigated.

Valorization of olive stones for the synthesis of phosphorus-modified porous carbons and their use as support of Pd particles for the oxidative condensation of furfural with ethanol

Activated carbons have been synthesized by a pyrolytic treatment and a chemical activation with H3PO4 to give rise to amorphous graphite, with high micro-mesoporosity and Brönsted acid sites. These materials have been employed as supports to incorporate Pd species to be used as catalysts in the oxidative condensation of furfural with ethanol to obtain furan-2-acrolein (F2A), as main product. The catalytic results show that F2A is obtained at shorter reaction times, with a maximum yield of 45 % after 180 min at 150 °C. The catalytic studies at longer reaction time worsen the F2A yield due to undesired and uncontrolled condensation reactions, which lead to the formation of humins. On the other hand, it is demonstrated that the amount of oxidant (H2O2) and base (Na2CO3) must be modulated to attain an optimum F2A yield.

Natural radioactivity level in graphite samples from the Cătălinul deposit, Parâng Mountains, Romania: sources identification and radiological risk assessment

Twenty graphite samples (amorphous and crystalline flake types of graphite) were collected from the ore storage of the Catalinul deposit and, the 238U, 232Th, 40K naturally occurring radionuclides have been investigated by gamma-ray spectrometry. The mineral contents of selected graphite samples were examined using a scanning electron microscope (SEM). The radiological hazard parameters: radium equivalent activity (Raeq), absorbed gamma dose rates in air (DR), and external hazard index (Hex) were calculated and compared with international safety limits. Radiometric data showed average specific activities for 238U, 232Th and, 40K of 80.40, 49.69 and, 124.21 Bq kg–1 for amorphous graphite respectively, 38.53, 76.25 and, 241.12 Bq kg–1 for flake graphite. Zircon, rutile, uraninite, coffinite, urano-thorite, and monazite are the main radioactive element bearing minerals. The mean of the radiological hazard parameters: Raeq – 262.22 (Bq kg–1), DR – 123.72 (nGy/h), and 0.7 – Hex do not exceed the recommended values by UNSCEAR.

Revealing Mechanistic Insights into Amorphous Graphite Formation from Oxygenated Polar Heavy-End Aromatic Feedstock

Revealing Mechanistic Insights into Amorphous Graphite Formation from Oxygenated Polar Heavy-End Aromatic Feedstock

Carbonization of Zr-Loaded Thiourea-Functionalized Styrene-Divinylbenzene Copolymers: An Easy Way to Synthesize Nano-ZrO2@C and Nano-(ZrC, ZrO2)@C Composites

Thermal processing of Zr-loaded ion-exchangers is a facile route to synthetize (ZrO2, ZrC)@C composites. In the present paper, furnace and RF-thermal plasma processing of ZrOCl2 loaded thiourea-functionalized styrene-divinylbenzene copolymer was investigated and led to composites containing ZrO2 and ZrC. Different ZrO2@C composites were formed between 1000 and 1400 °C in 2 h, whereas the composite containing ZrC was created at 1400 °C in 8 h. The ratio of ZrO2/ZrC, the prevailing ZrO2 modifications, and the crystallite sizes strongly depend on the synthesis conditions. The ZrC-containing composites formed only at 1400 °C in 8 h and by the plasma treatment of the ZrO2@C sample prepared in the furnace, resulting in 8 and 16% ZrC content, with 44 and 41 nm ZrC crystallite sizes, respectively. The ZrO2-containing composites (tetragonal, monoclinic, and cubic modifications with 65–88 nm ZrO2 crystallite sizes and 15–43 m2/g BET surface areas) formed in a tube furnace between 1000 and 1400 °C in 2 h. All ZrO2@C composites had both amorphous carbon and graphite, and their ratio is temperature dependent. The carbonaceous compounds were characterized by Raman spectroscopy with analysis of the G and D band intensities. XPS studies showed the surface oxidation of ZrC.

The Etching Mechanisms of Diamond, Graphite, and Amorphous Carbon by Hydrogen Plasma: A Reactive Molecular Dynamics Study

AbstractUnderstanding how hydrogen plasma etches various potential products during the diamond growth process can contribute to improving the knowledge of diamond growth. However, due to the absence of an in situ characterization technique during the etching process, the complex chemical reactions involved in the process obscure the atomic‐scale etching mechanisms. In this paper, the etching mechanisms of diamond (001), graphite (0001), and amorphous carbon substrates irradiated by hydrogen plasmas are investigated and compared using molecular dynamics simulations based on ReaxFF. When the incident energy of H atoms is 1 eV, the rate of carbon loss from graphite and amorphous carbon are far higher than that from diamond. As the incident energy of H atoms increases, the etching rate of diamond shows a slow increase, while the etching rates of amorphous carbon and graphite exhibit more significant increases. It can be concluded that the etching rate of diamond is significantly lower than that of graphite and amorphous carbon under H plasma. In the Chemical Vapor Deposition (CVD) process of diamond growth, the generated graphite and amorphous carbon are rapidly etched, leaving only diamond. This offers a plausible explanation for the growth mechanism of diamond through CVD.

The influence of mercury vapor on the electrical resistance of chalcogenide amorphous films

Using the planar structures "Ni layer - chalcogenide amorphous film - Ni layer" and "graphite probe - chalcogenide amorphous film graphite probe" samples, the influence of mercury vapor on the electrical resistance of amorphous films of the Se-Te, Se-Sb and Se-As systems was investigated. It was established that exposure of samples in mercury vapor leads to a decrease in their electrical resistance by 4-7 orders of magnitude. As the temperature and mercury concentration increase, the transition time from a high-resistance state to a low-resistance state decreases. When introducing Te, Sb, and As into amorphous selenium and increasing their concentration in the composition of the films, the transition time increases, and the value of the change in resistance decreases. It was established that the change in resistance is mainly determined by the change in surface conductivity of chalcogenide films. A decrease in the electrical resistance of selenium-containing amorphous films modified with mercury is caused by the formation of HgSe crystalline inclusions in their matrix.

Preparation of thermally stable organic-inorganic hybrid nanocomposites from chemically functionalized oxidized graphite by in situ catalytic oxidative decarboxylation

ABSTRACT In this study, the preparation of thermally stable organic-inorganic hybrid nanocomposites from chemically functionalized oxidized graphite is carried out by in-situ catalytic oxidative decarboxylation of 3,5-dinitrobenzoic acid (reactant) in the presence of potassium persulfate (oxidant), silver nitrate (catalyst) and graphite (support) under thermal or microwave conditions. The effects of heat transfer and dosages of reactant, catalyst and oxidant on the crystalline structure and the morphology of nanocomposites are studied in detail. The prepared nanocomposites are characterized by EDS, elemental mapping, FE-SEM, FT-IR and XRD. The thermal stability of nanocomposites is examined by TGA and DSC. EDS shows that nanocomposites are composed of C, O, N, S, K and Ag elements. FT-IR exhibits that the graphitic layers in nanocomposites are mainly oxidized and functionalized with carboxyl, carbonyl, hydroxyl, epoxy, sulfate, nitrate and nitroaryl groups. Addition of nitroaryl groups to nanocomposites is also supported by an increase found in their C and N contents. XRD demonstrates the coexistence of both oxidized amorphous carbon and graphite in combination with different levels of organic and inorganic phases. The prepared nanocomposites show good thermal stability. The total area of the DSC curve in these nanocomposites compared to graphite is enhanced.

Atomistic nature of amorphous graphite

This paper focuses on the structural, electronic, and vibrational features of amorphous graphite [R. Thapa et al, Phys. Rev. Lett., 2022, 128, 236402]. The structural order in amorphous graphite is discussed and compared with graphite and amorphous carbon. The electronic density of states and localization in these phases were analyzed. Spatial projection of charge densities in the π bands showed a high charge concentration on participating atoms in connecting hexagons. A vibrational density of states was computed and is potentially an experimentally testable fingerprint of the material. An analysis of the vibrational modes was carried out using the phase quotient, and the mode stretching character. The average thermal conductivity calculated for aG was 0·85 and 0·96 W/cmK at room temperature and 1000 K, respectively.

Structure Evolution and Properties Modification for Reaction-Bonded Silicon Carbide.

Complex structure reaction-bonded silicon carbide (RB-SiC) can be prepared by reactive melt infiltration (RMI) and digital light processing (DLP). However, the strength and modulus of RB-SiC prepared by DLP are not sufficient, due to its low solid content (around 40 vol.%), compared with the traditional fabrication techniques (solid content > 60 vol.%). With this understanding, a new method to improve the properties of RB-SiC was proposed, by the impregnation of composite precursor into the porous preform. The composite precursor was composed of phenolic (PF) resin and furfuryl alcohol (FA). PF and FA were pyrolyzed at 1850 °C to obtain amorphous carbon and graphite into the porous preform, respectively. The effects of multiphase carbon on the microstructure and performance of RB-SiC was studied. When the mass ratio of PF to FA was 1/4, the solid content of RB-SiC increased from 40 vol.% to 68.6 vol.%. The strength, bulk density and modulus were 323.12 MPa, 2.94 g/cm3 and 348.83 Gpa, respectively. This method demonstrated that the reaction process between liquid Si and carbon could be controlled by the introduction of multiphase carbon into the porous preforms, which has the potential to regulate the microstructure and properties of RB-SiC prepared by additive manufacturing or other forming methods.

Cost-efficient clean flotation of amorphous graphite using water-in-oil kerosene emulsion as a novel collector

• A water-in-oil kerosene emulsion was prepared using non-ionic surfactants Span-80 and Tween-80 as the emulsifiers. • The emulsified kerosene outperformed pristine kerosene as a collector in amorphous graphite flotation. • The emulsified kerosene increased the flotation recovery of amorphous graphite by 5.96%, with 52% lesser total kerosene consumption. • Cryo-SEM was employed to visualize the in-situ microstructure of the kerosene emulsion. Kerosene is one of the most used collectors in graphite flotation, while its consumption undergoes an enormous increase, especially in amorphous graphite flotation, imposing heavy economic burdens and raising environmental concerns. In this work, a novel water-in-oil type kerosene emulsion was prepared, and its flotation performance as a collector on an amorphous graphite ore was examined and compared to pristine kerosene. An optimized emulsification process was developed based on the roughing flotation test. Particle size distribution analysis, optical microscope, and Cryo-SEM studies indicated homogenous and fine emulsified kerosene droplets in aqueous. More importantly, the open circuit flotation test proved emulsified kerosene as a superior collector to pristine kerosene in terms of enhancing the clean flotation efficiency of amorphous graphite.

Studies of mechanical and technological parameters and evaluation of the role of lustrous carbon carriers in green moulding sands with hybrid bentonite

Green moulding sands containing special carbonaceous additives, which are the source of lustrous carbon (LC), are discussed in this paper. Five potential lustrous carbon carriers, i.e., two types of hard coal dust (No.1 and No.2), amorphous graphite (No.3) and two hydrocarbon resins (No.4 and No.5), were selected for tests as carbonaceous additives to conventional moulding sands. To better emphasize the differences in the additives used, reference green moulding sand (GMS1) was prepared and subjected to a wide range of basic tests focussed on technological parameters, such as permeability (Pw), friability (Fw), Dietert mouldability test (PD) and compactability (Z) and mechanical parameters, such as compressive strength (Rcw), tensile strength (Rmw), strength in the transformation zone (Rkw). The proposed comprehensive spectrum of tests was repeated on sands with five carbonaceous additives. The most important for the use of additives as carbon carriers was to interrelate the content of lustrous carbon (LC), loss on ignition (LOI) and the obtained results of mechanical and technological tests carried out on conventional moulding sands with the surface quality of iron castings. For this purpose, a series of iron castings was made in the prepared moulding sands and used for the assessment of surface quality based on a number of roughness parameters (Ra, Rz, Rp, Rq, Rv, Rlr, RSm). As a result of the studies it was found that the carbonaceous additives proposed for use help to obtain high-quality surfaces in iron castings.

Controllable Fabrication of Flexible and Foldable Carbon Nanofiber Films

AbstractCarbon nanofibers (CNFs) fabricated through traditional methods are generally composed of amorphous carbon and graphite sheets, which usually endow CNFs with high modulus and brittleness. Here, a strategy of controlling graphite sheet structures in CNFs for the scalable fabrication of silk‐like flexible CNF films that can be arbitrarily folded in any shape and can undergo thousands of dynamic bending deformation cycles is reported. In detail, the carbon precursor of polyacrylonitrile (PAN) is first electrospun into NFs and then by controlling the pre‐oxidation reaction and carbonization process to design CNFs with different graphitization degrees, flexible CNF films with tunable mechanical properties from the traditional bending resilience flexibility to truly foldable flexibility can be fabricated. Meanwhile, a correlation mechanism between microstructure and the foldable flexibility of CNFs is proposed. Importantly, it is found that manipulating the pre‐oxidation temperatures of precursor PAN NFs can effectively reduce the structural stiffness of CNFs due to the appropriate number of graphene sheets. This study provides a theoretical basis for designing truly foldable CNF films for multiple applications.

Origin of multiple principal slip zones in a fault gouge zone within granitoids

Fault zones in crystalline rocks generally possess a relatively narrow (<50-cm-thick) fault core (i.e., a fault gouge layer/zone). However, the Geumwang Fault, a major strike-slip fault developed in granitic rocks in Korea, has a wider (∼24-m-thick) fault core with several gouge layers. Here we conduct detailed field and microanalytical investigations on the fault core of the Geumwang Fault. Results showed that some of the gouges are primary gouges in which seismic slip was localized as the principal slip zones (PSZs), whereas others are secondary gouges that formed by the injection of fluidized gouge material into fractures. Within the PSZs, the presence of amorphous carbon and graphite implies that frictional heat generated by coseismic slip triggered siderite decomposition. It was likely the consequence of gouge fluidization induced by thermal pressurization under fluid drained conditions. In addition, the gouge fluidization seems to neutralize the foliation of the PSZ. This process, together with weakening of the damage zone by long-term alteration, may facilitate subsequent seismic slip occurred along foliated breccia or the fault core boundary rather than the former neutralized PSZs, thereby widening the Geumwang Fault. We propose that coseismic fluidization of PSZ by thermal pressurization can act as a potential mechanism to widen the fault core and generate multiple gouge layers in crystalline rocks.