Amorphous Graphite Research Articles

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.

Amorphous BC5 from first principles calculations

A boron-substituted amorphous graphite (BC5) network is generated using a first principles molecular dynamics simulation and its atomic structure and electrical and mechanical properties are discussed in details. The network has a layered structure with primarily hexagonal (six membered) rings and its average coordination is about 3.0. The material is a solid solution having a minor amount of B-B homopolar bonds. It is structurally different from the BC5 crystal or monolayers proposed in the literature. The model is a semimetal material based on a generalized gradient approximation with the Hubbard correction (GGA+U) calculation. When its mechanical properties are concerned, they are comparable with those of graphite or amorphous graphite.

Highly conductive mesoporous hierarchical carbon hollow fibers fabricated via confinement of TiO2 coating by ALD

AbstractA polysulfone (PSF) hollow fiber composed of interconnected nanofibers within its wall was employed as a template to deposit with a layer of TiO2 by atomic layer deposition. Direct nitridation of the TiO2‐coated PSF hollow fiber at 800 and 1000°C was conducted, and a new hierarchical structure of TiOxN1−x and TiN@nitrogen‐doped carbon hollow fibers, respectively, was formed. The PSF fiber served as the source of carbon and was directly transformed to a nitrogen‐doped carbon fiber because the shape change was confined by the TiO2 coating. In the meantime, TiOxN1−x or TiN was formed after the nitridation of TiO2. X‐ray photoelectron spectrometric analysis indicated that there was no chemical bonding between the nitridized coating and the carbon nanofibers. It implies that the nitridation of TiO2 and carbonization of PSF proceed independently and simultaneously in the nitridation process. Raman spectroscopic analysis also confirmed the formation of graphitic lattice and Ti–N bonding. Electrical measurement indicated that both fibers were highly conductive, with the electrical resistivity in the order of 10−5 Ω m, which is lower than those of amorphous carbon and graphite along the direction perpendicular to the basal plane.

Study on microstructure, mechanical properties and corrosion resistance of NbCN-Cu composite films

In this research, NbCN-Cu films with different Cu contents were prepared by multi-target confocal RF magnetron sputtering. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray Photoelectron Spectroscopy (XPS), Raman spectrometry, Energy Disperse Spectroscopy (EDS), nano-indentation, and electrochemical workstation were used to characterize and analyze the microstructure, mechanical properties and corrosion resistance of the films. The results show that the NbCN-Cu composite films consist of crystalline face-centered cubic(fcc) Cu, face-centered cubic(fcc) NbCN, hexagonal close-packed(hcp) NbCN, and amorphous graphite and CNx phases. When Cu content was 2.6 at.%, a coherent interface was detected between fcc-Cu and fcc-NbCN, hcp-NbCN, and dislocations were detected at the coherent interface when Cu content increased to 9.5 at.%. With the increase of Cu content, the microhardness of the film first increased and then decreased. NbCN-Cu composite film with Cu content of 2.6 at.% had the highest hardness of 32.8 GPa and remarkable corrosion resistance. The self-corrosion potential of the film was 0.18 V and self-corrosion current density was 2.29 × 10−6 A/cm2.

Facile and Green Synthesis of Highly Fluorescent Carbon Quantum Dots from Water Hyacinth for the Detection of Ferric Iron and Cellular Imaging.

Natural biomass is used for facile synthesis of carbon quantum dots (CQDs) with high fluorescence, owing to its abundance, low cost, and eco-friendliness. In this study, a bottom-up hydrothermal method was used to prepare CQDs from water hyacinth (wh) at a constant temperature of 180 °C for 12 h. The synthesized wh-CQDs had uniform size, amorphous graphite structure, high water solubility (containing multiple hydroxyl and carboxyl groups on the surface), excitation light-dependent characteristics, and high photostability. The results showed that the aqueous solution of CQDs could detect Fe3+ rapidly, sensitively, and highly selectively with a detection limit of 0.084 μM in the linear range of 0–330 μM, which is much lower than the detection limit of 0.77 μM specified by the World Health Organization. More importantly, because the wh-CQDs were synthesized without any additives, they exhibited low toxicity to Klebsiella sp. cells even at high concentrations. Moreover, wh-CQDs emitted bright blue fluorescence in Klebsiella sp. cells, indicating its strong penetrating ability. Correspondingly, the fluorescent cell sorting results also revealed that the proportion of cell internalization reached 41.78%. In this study, wh-CQDs derived from natural biomass were used as high-performance fluorescent probes for Fe3+ detection and Klebsiella sp. imaging. This study is expected to have great significance for the application of biomass carbon spots in the field of cellular imaging and biology.

A viable approach to prepare 3C-SiC coatings by thermal MOCVD using commercial grade precursors

A series of 3 C-SiC coatings were prepared by organometallic chemical vapor deposition (MOCVD) using precursor solution containing a varying proportion of commercial-grade hexamethyldisiloxane (HMDSO) and n-hexane. The phase composition, bonding state, and microstructure of 3 C-SiC coatings were studied in detail by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The microstructure and mechanical properties of the optimal 3 C-SiC coating were characterized by scanning transmission electron microscopy (STEM) and nanoindentation, respectively. Our results revealed that the amount of undesired graphite phase can be significantly reduced in the 3 C-SiC coating by introducing hydrogen gas in the reaction chamber alongside increasing the ratio of HMDSO/n-hexane in the precursor mixture. The STEM results revealed that the optimal coating was predominantly composed of nano-crystalline 3 C-SiC grains alongside a small amount of amorphous graphite. The hardness and elastic modulus of the optimal coating were 38.19 GPa and 363.2 GPa, respectively.

Multiple synergistic losses in the absorption of electromagnetic waves by three-dimensional cross-linked carbon fiber

Carbon fiber with a three-dimensional (3D) cross-linked structure was prepared by electrostatic spinning and heat treatment. The HRTEM images of carbon fiber were used as the basis for determining the types of graphite defects in carbon fiber by combining the intensity ratios of the D and D′ peaks in the Raman spectra, and the contribution of different graphite defects types in carbon fiber to electromagnetic wave absorption was analyzed. Among the three types of graphite defects, sp3 type, vacancy type, and boundary type, the carbon fiber with predominantly boundary type graphite defects showed excellent electromagnetic wave absorption performance. The heat treatment temperature has a significant effect on the conductivity and electromagnetic properties. The broadest effective absorption bandwidth (EAB) is 5.44 GHz at 2.07 mm when the thermal treatment temperature is 650 °C. In carbon fiber with a carbonization temperature of 850°, graphite nanocrystals and large graphite areas coexist and graphite defects are predominantly of the boundary type. Interfacial polarization of amorphous carbon and graphite nanocrystals under the action of electromagnetic waves produces dielectric losses; large graphite areas produce conductive losses and eddy current losses. The dielectric loss, conductive loss, and eddy current loss synergistically achieve a strong absorption of the electromagnetic wave multi-spectrum at 5.08 GHz, −40.55 dB, −43.35 dB, and −44.44 dB at 5.08 GHz, 7.46 GHz, and 14.94 GHz respectively. Without the addition of magnetic materials, the carbon fiber in this study achieves the ability of a dielectric loss type electromagnetic wave absorbing material to possess magnetic loss.

Study on the microstructure and mechanical properties of reactive plasma sprayed TiCxN1−x composite coatings with different Ti/graphite powders

In this present paper, the effects of Ti/graphite mass ratio (4:1, 6:1, 8:1 and 10:1) on the composite, grain size and mechanical properties of TiCN coatings were investigated. Based on the solid-solid reaction of Ti with graphite and solid-gas reaction of Ti with N2 in plasma jet, TiCN phase were in situ synthesized. Results show that all coatings consist of TiCxN1−x(0 ≤ x ≤ 1) main phase, small amount of Ti2O, amorphous graphite and CNx phases. The amount of TiCN phase firstly increases and then decreases along with mass ratio increases, and the content reachs the maximum when the Ti/graphite ratio is 6:1. Besides, the highest sp3C-N fraction (about 36.22%) is detected in the coating, which is benefical to improve hardness and elasticity modulus. Therefore, the value of H/E (0.095) and H3/E2 (0.23 GPa) are higher than other three coatings, which is conductive to improve mechanical and tribological properties. A joint wear mechanism of abrasive wear and adhesive wear is found for TiCN coatings.

Thermal properties measurement of TRISO particle coatings from room temperature to 900 °C using laser-based thermoreflectance methods

The thermal properties of tristructural isotropic (TRISO) particle coatings have been measured using laser-based thermoreflectance methods from room temperature to 900 °C. At room temperature the pyrocarbon coatings have comparable thermal conductivities below 10 W·m−1·K−1, whereas the SiC coating has a thermal conductivity around 90 W·m−1·K−1. The thermal diffusivities of all coatings display significant reduction with increasing temperature. The thermal conductivity of SiC decreases by more than 25% above 800 °C and the thermal conductivities of pyrocarbons increase moderately with the temperature, displaying similar changes to that of amorphous graphite at elevated temperatures.

The influence of metals on the phase transformations of fullerenes at high pressure and high temperatures

Phase transformations in crystalline fullerenes C60 and C70 with additions of two groups of metals (7 at. % each): carbide-forming (V and nichrome Ni20Cr80) and non-carbide-forming (Ag and Ni) at a high pressure of 8 GPa and high temperatures of 500–1100 °C have been investigated by X-ray diffraction and Raman spectroscopy. The measurements were carried out ex situ after a thermobaric treatment. Two groups of phase transformations were found: crystalline fullerenes into amorphous graphite and the formation of carbides VC, V2C and Cr3C2. The addition of V and nichrome stabilizes fullerene molecules and raises the temperature of transformation of crystalline fullerene into amorphous graphite by hundreds of degrees, while the addition of Ag and Ni does not have such an effect. Thus, the described effect is explained by chemical interaction. Carbides in systems with V and nichrome are formed mainly in the interaction of metal with amorphous graphite, and not with crystalline fullerene. The result is explained on the basis of a comparison of the interaction of metal atoms with fullerene molecules and with individual carbon atoms.

Improved Method for Preparing Nanospheres from Pomelo Peel to Achieve High Graphitization at a Low Temperature

Biomass waste is a valuable resource that can be recovered, reused, and is renewable. However, converting biomass waste to a high degree of order is a bigger challenge, and graphitization at low temperatures is even more difficult. This paper proposes an improved method (Ni element catalysis) for highly graphitizing pomelo peel at low temperatures (750 –900 °C). In this paper, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and high-resolution transmission electron microscopy (HRTEM) were used to study the method and the effect of temperature on structural changes during graphitization. Under the improved method, pomelo peel was transformed into nano-spherical graphitized material. The degree of graphitization reached 80.23% at 900 °C, which was 31.39% higher than that of the traditional method. Furthermore, through HRTEM, the lattice fringe spacing was observed to be 0.337 nm, which is between pure graphite (0.3354 nm) and amorphous graphite (0.3440 nm). In this paper, the improved method can obtain highly graphitized nanospheres at low temperatures, thus reducing energy consumption, reducing environmental pollution, and promoting sustainable development.

Structure and morphology of graphite nanoparticles treated by fiber laser irradiation

The graphite nanoparticles (GNPs) were prepared on the surface of monocrystalline Si by laser irradiation under different laser energy densities (3.3–8.33 kJ/cm2). The effects of laser energy density on structure and surface morphology were systematically investigated. The results show that the morphology of GNPs remained polycrystalline structure under laser irradiation with an energy density of 2.22 kJ/cm2. When the laser energy density was 2.78 kJ/cm2, the GNPs can induce the preset GNPs to transform into amorphous graphite nanofibers. The GNPs under the laser density of 3.33 kJ/cm2 showed a more amorphous structure. With the further increase of the laser energy density to 5.55 kJ/cm2, the main phase composition turned to SiC and Si.

Nanostructured P-doped activated carbon with improved mesoporous texture derived from biomass for enhanced adsorption of industrial cationic dye contaminants

Developing of high-performance carbonaceous materials from biomass is a significant contemporary research subject to meet the increasing demand for functional adsorbents with low price, high available and sustainability for adsorptive removal processes of industrial pollutants. The present work investigates formation of nanostructured surface modified P-doped activated carbon (ACP) materials via thermochemical activation of orange peel (OP) biomass residual materials, by phosphoric acid, H3PO4. Different impregnation ratios of phosphoric acid to OP (w/w) were investigated at different activation temperatures (400–800 °C). The formed ACP materials were characterized by TGA−DTA, FTIR−ATR, Raman spectroscopy, XRD, N2 gas adsorption/desorption, HR−TEM microscopy, EDX and elemental surface mapping. The results indicated that ACP materials were structured in the form of plate-like nanoparticles of amorphous graphite that composed of few graphene layers. The ACP materials exhibited high surface area (up to 1700 m2/g) with high contribution from mesoporosity (up to 94%) of slit-like pore shape. The point of zero charge was found at pH of 6.3, which permits application at neutral adsorption conditions. The formed ACP adsorbents exhibited distinguished adsorption capacities, qads, for methylene blue (MB) with successful recyclability. The adsorption capacities were enhanced (up to qads = 452 mg/g) for the materials formed at high acid impregnation ration and activated at high temperatures. The adsorption process of MB was spontaneous, fits with the Langmuir adsorption isotherm and pseudo-second-order kinetic. The high adsorption capacities for the ACP adsorbents were correlated with their micro/nano-structures, which were dominated by nano plate−like amorphous graphite particles composed of few graphene−like layers.

Biomass derived P−doped activated carbon as nanostructured mesoporous adsorbent for chromium(VI) pollutants with pronounced functional efficiency and recyclability

The removal of heavy metals pollutants from contaminated water by adsorption is one of the most effective physicochemical techniques. The recycling approach of residual biomass into adsorbent materials, has received increasing attention for biomass valorization. In effort for Orange peel (OP) biomass valorization, the conversion of OP into phosphorous (P)−doped activated carbons (ACP) materials was investigated via phosphoric acid thermochemical activation at 400–800 ºC. Thus, two groups of ACP materials were derived from OP, with a low and a high (acid: OP) ratios termed as ACPL and ACPH, respectively. The materials were characterized by many standard techniques including: XRD, Raman spectroscopy, XPS, FTIR-ATR, HRTEM, EDX and elemental mapping. The materials were structured in nanosized (2–3 nm) amorphous graphite plate−like nanoparticles composed of few graphene layers, showed high specific surface area, SBET, and slit-shaped mesoporosity. The application of the ACPL and ACPH materials as adsorbents were investigated for Cr(VI) ions, batch adsorption from solutions, by atomic absorption spectroscopy. Generally, the adsorbents showed pronounced adsorption capacity (up to 100.4 mg/g), which was for ACPH > ACPL, and was increased with increasing of the activation temperature. Therefore, different adsorption isotherms, thermodynamic and kinetic models were investigated. Accordingly, the adsorption isotherms of ACPH adsorbents were best fit the Langmuir isotherm model, whereas ACPL adsorbents were best fit the Freundlich isotherm model. The adsorption process for the most active sample was exothermic, followed the pseudo-second-order kinetics and showed recyclability of the adsorbents. This indicates that orange peel biomass can be valorized and converted into very valuable efficient adsorbent for Cr(VI) removal.

Toward Carbon-Negative and Emission-Curbing Roads to Drive Environmental Health

Roadway infrastructures are exposed to solar ultraviolet (UV) radiation during their service life. UV rays generate free radicals that diffuse deep into bitumen layers, accelerating the aging and degradation of bituminous composites. Here, we hypothesize that carbonaceous particles grafted by bioderived molecules such as amines and amides can serve as scavengers of free radicals, delaying aging in bituminous composites. To test this hypothesis, we use laboratory experiments and molecular dynamics simulations to compare the efficacy of biochars made from woody biomass and algal biomass in delaying the aging of bituminous composites. We further examine the underlying molecular mechanisms that delay aging by computing the extent of diffusion of free radicals through an amorphous graphite film in the pristine form and in amine- and amide-functionalized forms. The laboratory results indicate that algal biochar is considerably more effective than woody biochar in delaying aging. The simulation results corroborate laboratory findings showing that even at low concentrations, surface functionals such as amines and amides considerably enhance the efficacy of pristine carbon in shielding the underlying layers against the diffusion of free radicals such as hydrogen peroxide (H2O2). At high concentrations (e.g., 10 wt %), amines were found to be more effective than amides in reducing the diffusion rate of H2O2. This indicates that the scavenging efficacy of carbonaceous particles can be optimized by proper biografting. The algae that were used to make functionalized carbonaceous particles in this study are a means to capture CO2 from air. Therefore, our findings contribute to extending the sustainability of highway infrastructures while moving toward carbon-negative and emission-curbing roads to promote environmental health.

Mechanochemical remediation of fluoranthene contaminated soil and biotoxicity evaluation

ABSTRACT A mechanochemical (MC) method was employed for the remediation of soil contaminated with fluoranthene (C16H10, FL) a four-ringed polycyclic aromatic hydrocarbon (PAH) containing three benzene rings and a central five-membered heterocyclic ring, with the effects of soil inorganic components, milling conditions, and the degradation mechanism investigated. Results showed that the addition of SiO2 and kaolin to soil resulted in a greater increase in the effectiveness of FL removal than other inorganic additives. After 3 hours of milling at 500 rpm, the FL removal rate from SiO2 containing soil, reached 99.26%, with the removal efficiency increasing in accordance with an increase in milling duration and speed. The milled samples were characterized by FT-IR, Raman spectroscopy, and GC-MS analysis, revealing the mechanism of FL degradation, including destruction of the aromatic skeleton structure and the formation of amorphous carbon and graphite. The MC remediation method was applied to FL contaminated soil, showing that FL was efficiently degraded in soil without any soil additives, resulting in a significant reduction in the biotoxicity of the remediated soil. The organic matter, moisture content and pH of the actual soil changed slightly after mechanical ball milling. Thus, the MC method has high potential in the remediation of PAH-contaminated soils. HIGHLIGHTS A mechanochemical (MC) method for the degradation of fluoranthene was assessed. The use of silica and kaolin as soil additives enhances fluoranthene remediation. Fluoranthene can be efficiently removed from contaminated soil by milling alone. The degradation mechanism was skeleton structure destruction and carbonization. The biotoxicity of soil was significantly reduced by milling.

Study on the Tribological Properties of F-T DS/ZnFe-LDH Composite Lubricating Material

The homemade soot capture device was used to burn Fischer-Tropsch synthetic diesel (F-T diesel) in order to simulate the combustion of F-T diesel in the engine and collect its soot (F-T DS, FS). The zinc-iron hydrotalcite (ZnFe-LDH) and the composite materials of FS and ZnFe-LDH (F-T DS/ZnFe-LDH, FS/ZnFe-LDH) were prepared by hydrothermal synthesis, and the similarities and differences in tribological characteristics of the above three lubricating materials such as 10# white oil (10# WO) lubricant additives were investigated. FS is an aggregation composed of amorphous carbon and graphite microcrystals. ZnFe-LDH is mainly composed of nanosheets, Zn, and Fe hydroxide particles, with a high degree of crystallization, while FS/ZnFe-LDH is a “sandwich layer” composed of nanosheets and soot particles. Because of the addition of cetyltrimethylammonium bromide and the grafting of a long carbon chain lipophilic group in the preparation process, FS/ZnFe-LDH has better anti-wear properties than the FS and ZnFe-LDH Effect. When FS/ZnFe-LDH is added at 0.2 wt.%, the average friction coefficient (AFC) and average wears scar diameter (AWSD) are at their lowest. Compared with pure 10# WO, the minimum values of AFC and AWSD have dropped by 36.84% and 22.58%, respectively. XPS analysis of the wear scar surface shows that when ZnFe-LDH and FS/ZnFe-LDH are used as lubricating additives of 10# WO, together with the organic matter in the white oil and the iron element in the friction pair, tribochemistry occurs under the combined action of the adsorption force and the tribochemical reaction, a friction protection film containing four elements of C, O, Fe, and Zn is formed on the surface of the wear scar, which effectively reduces the wear and reduces the friction coefficient.

Tribological Suitability of aluminium hybrid composite above atmospheric temperature

Industries are facing problems with light weight alloys due to tribological impediments in which utmost complicated problem is wear. As a consequence, endeavour has been made to fabricate increased wear resistance materials. In 2014, 2.87 million tons of aluminium was used by the global automotive industry (excluding China). By 2020, an annual demand of 4.49 million tons of aluminium is projected. Key factors of this growth include both increased production of automobiles and broader use of aluminium alloys in modern automobiles.The main advantage of spacecraft aluminum alloys is their ability to withstand hi gh and low temperatures, vibration loads, and radiation. Additionally, aluminium alloys exhibit outstanding strength and durability in cryogenic environments as the temperature drops. In the present investigation Al2618 is used as a Matrix and hard ceramic boron carbide, with amorphous graphite is used as reinforcement. Stir casting is used to synthesis the hybrid composite. Statistical model taguchi is used to assess the dry sliding wear properties of the hybrid Metal matrix composite at different temperature (50°C, 100°C, 150°C). Evaluation of particle distribution of reinforcement in the matrix and worn surface morphology is studied by SEM. Wear resistance of the hybrid composite (reinforced with B4C & Gr) is enhanced at 150°C than conventional alloy. Glazed layer formation in Al2168 matrix is less than glazing layer formation formed on hybrid composites Adhesive wear is observed during test.

The Production of Carbon Nanofiber on Rubber Fruit Shell-Derived Activated Carbon by Chemical Activation and Hydrothermal Process with Low Temperature.

Recently, the conversion of biomass into carbon nanofibers has been extensively studied. In this study, carbon nanofibers (CNFs) were prepared from rubber fruit shell (RFS) by chemical activation with H3PO4, followed by a simple hydrothermal process at low temperature and without a vacuum and gas catalyst. XRD and Raman studies show that the structure formed is an amorphous graphite formation. From the thermal analysis, it is shown that CNFs have a high thermal stability. Furthermore, an SEM/TEM analysis showed that CNFs’ morphology varied in size and thickness. The obtained results reveal that by converting RFS into an amorphous carbon through chemical activation and hydrothermal processes, RFS is considered a potential biomass source material to produce carbon nanofibers.

Energy storage in carbon materials synthesized from fir bark modified with graphite and zinc chlorine

The purpose of this study is to investigate the synthesis process of composite materials based on fir bark for thermochemical transformation and to determine the influence of additives such as zinc chloride, natural graphite of various origins on the structural and electrochemical characteristics of the carbonized products. Modification of fir bark sawdust with amorphous and/or crystalline graphite and zinc chloride allowed for the synthesis of products with a specific surface area of up to 780 m2/g and an apparent specific electrical capacity up to 540 F/g. It was revealed that carbonization of samples containing zinc chloride leads to the formation of porous carbon/zinc oxide composites. The solid residue obtained from the mixture of three components (fir bark, crystalline graphite, and zinc chloride) has the highest apparent specific electrical capacity. It is assumed that the combination of the structures of amorphous, crystalline carbon, and zinc oxide promotes the diffusion of electrolyte and the accumulation of electric charge in carbon composite.