Graphite Nanocrystals Research Articles

Deposition of Wear-Resistant Nanocomposite Coatings from Accelerated С<sub>60</sub> Ions

Hard wear-resistant carbon coatings were deposited from accelerated C60 ions at temperatures of 200 and 300°C. It has been established that the mechanical properties of the coatings are determined by the substrate temperature (Ts) and the energy composition of the beam. The hardness of coatings deposited from C+60 ions with an energy of 7 keV exceeds 50 GPa and is virtually independent of Ts. The presence of C602+ and C603+ with an energy of ~14 and 21 keV, respectively, in the beam leads to a result that is not typical for carbon coatings – the hardness increases by more than 1.3 times with an increase in Ts from 200 to 300°C (from 31.6 GPa to 41.6 GPa). In this case, according to Raman spectroscopy data, the size of graphite nanocrystals in the coating increases with temperature up to almost 2 nm. Coatings obtained under conditions of irradiation with C602+ and C603+ ions are characterized by minimal wear (1.5×10–8 mm3/N∙m, Ts = 200°C) and minimal friction coefficient (µ = 0.05 for Ts = 300°C). We attribute the unusual dependence of hardness on Ts and the improvement in the tribological properties of coatings to the formation of a composite structure based on a diamond-like matrix and graphite nanocrystals in this range of Ts.

Secondary transformations in the structure of grey cast iron

A nanostructural mechanism of secondary transformations in the structure of gray cast iron is proposed. First, structureforming nanocrystals of austenite, ferrite, cementite and graphite are formed from elementary nanocrystals of iron and graphite, free atoms of iron and carbon. The crystallization centers of microcrystals of phases are formed from them. From these centers, structure‑forming nanocrystals of phases, free iron and carbon atoms, microcrystals of austenite, ferrite, cementite and graphite of binary gray cast irons are formed.

Chitin-Derived Hierarchical Meso- and Microporous Carbon Enables High-Rate Sulfur Cathode of Sodium-Sulfur Batteries.

Room temperature Na-S batteries are considered as a promising alternative energy storage system because of their abundant material resources and high theoretical energy density. However, the severe polysulfide shuttle effect and slow reaction kinetics hinder their practical application. Herein, a hierarchical meso- and microporous carbon with nitrogen self-doping (NSPC) is prepared using chitin as the carbon precursor and serves as a novel host to confine the sulfur (S⊂NSPC). An optimized structure of NSPC, including abundant graphite nanocrystals, large pore volume of 1.76 cm3 g-1, and large specific surface area of 2073 m2 g-1 is obtained at the carbonization temperature of 1000 °C. These merits contribute to significantly enhanced charge transfer and ion diffusion of the as-prepared S⊂NSPC-1000 cathode, which exhibits the outstanding sodium storage performance, including high reversible capacities of 1207 mAh g-1 at 0.1 C and 891 mAh g-1 at 2 C and stable cycling with a low capacity decay for 400 cycles at 1 C, among other S⊂NSPC cathodes and previously reported cathodes for Na-S batteries. This cathode can also afford stable cycling at a high sulfur loading.

Effect of N2 reactive gas flow rate on the structural, optical and wettability properties of silicon carbon oxynitride thin films

In the current research, the silicon carbon oxynitride (SiCON) thin film was deposited on the silicon (Si) substrate by radio frequency (RF) reactive magnetron sputtering method. To comprehensively assess the impact of nitrogen flux rate on thin film characteristics, a suite of advanced analytical methods was utilized. The GIXRD analysis confirmed that the SiCON thin film is amorphous in structure. Additionally, Raman spectroscopy detected no graphite nanocrystals within the film. Ellipsometry measurements further showed that the refractive index of the thin films rises with increased nitrogen flux in the reactive gas, indicating a direct correlation between nitrogen concentration during deposition and optical properties. Based on the designs made with McLeod's software, the amount of reflection can be reduced up to 5.7 % at the wavelength of 4 μm and up to 8.5 % in the wavelength range of 3–5 μm for an optimal thickness thin film. The atomic force microscopy (AFM) examination revealed that the surface roughness of the thin films decreases as the nitrogen flux in the reactive gas mixture increases. Additionally, measurements of the water contact angle (WCA) indicated that the SiCON thin films exhibit a hydrophilic state.

Oxidized Graphite Nanocrystals for White Light Emission

We investigated the formation of graphite nanocrystals covered with graphite oxide for white light generation. The nanoparticles were formed using cost-efficient oxidation of a carbon-based dye pigment at different temperatures and verified using X-ray diffraction and Raman measurements. Formation of the graphite nanoparticles via thermal annealing was observed, while their light emission increased at higher oxidation temperatures. This was associated with a higher amount of oxygen defect groups. The time-resolved photoluminescence measurements showed linearly faster decays at shorter wavelengths and similar decays at different annealing temperatures. Broadband and linear vs. excitation emission spectra of the particles were found to be suitable for white-light-emitting devices and phosphor markers. The fast photoluminescence decay opens the possibility for the application of nanoparticles in optical wireless communication technology.

In-situ construction of functional carbon layer on the plasma electrolytic oxidation-pretreated Ti-6Al-4V alloy to enhance anti-static properties

Thermal control coatings prepared by plasma electrolytic oxidation (PEO) have shown broad application potential, especially in the aerospace field. However, the high insulation nature results in charge accumulation during the real application in spacecraft, aggravating the risk of electrostatic discharges and endangering equipment's safety. Herein, a functional anti-static thermal control composite coating on the surface of Ti-6Al-4V alloys was constructed by preparation route involving in-situ polymerization and carbonization of polydopamine (PDA) on the PEO layer. After the introduction of carbonized PDA, the composite coating retained the pristine porous structure of the PEO coating with improved crystallinity. Notably, the consecutive functional carbon layer ingrates the graphite nanocrystals and N-doped graphite to achieve high conductivity and then renders the composite coating with the lowest volume resistivity (6.04 × 104 Ω m) and surface resistance (9.0 × 107 Ω/□). Moreover, the two-step prepared coating showed high absorption (200–2500 nm, 0.929) and emission (2–16.6 μm, 0.921) along with excellent stability at high temperature (∼200 ℃) and low temperature (∼−200 ℃) even over 48 h. This contribution reveals a promising direction to widen the practical application of the PEO thermal control coating.

About solid solutions of alloys

It is shown that the open pores of the crystal lattices of iron, manganese, titanium, cobalt cannot contain hydrogen, oxygen, nitrogen and carbon atoms. In solid solutions of alloys, hydrogen and oxygen atoms are present in the adsorbed state. Nitrogen atoms are mainly included in metal nitrides. Carbon atoms are found in elementary graphite nanocrystals. In solid solutions of alloys consisting of metals, their atoms are part of nanocrystals. They mainly consist of metal alloys. The formation of solid solutions of alloys is a nanostructural process.

Long-term stability of lithium–sulfur batteries via synergistic integration of nitrogen-doped graphitic carbon-coated cobalt selenide nanocrystals within porous three-dimensional graphene-carbon nanotube microspheres

Three-dimensional porous microspheres consist of highly conductive reduced graphene oxide-carbon nanotube (rGO‒CNT) framework with well-embedded cobalt selenide (CoSe2) nanocrystals coated with N-doped graphitic carbon (NGC) were synthesized (referred as “P–CoSe2@NGC/rGO‒CNT” microspheres) and utilized as an electrocatalytic interlayer to enhance the performance of lithium-sulfur (Li–S) batteries. The incorporation of the NGC layer and rGO‒CNT framework not only enhances the electronic conductivity significantly but also offers numerous conductive pathways (primary and secondary) for efficient electron transport. Macropores (φ = 100 nm) formed by the decomposition of PS nanobeads (φ = 200 nm) guarantee effective electrolyte penetration and short diffusion pathways. Moreover, the CoSe2 nanocrystals offer a multitude of polar active sites that effectively anchor polysulfide intermediates, reducing the loss of active material. Benefiting from the nanostructure merits, Li–S cells featuring a P–CoSe2@NGC/rGO‒CNT-coated separator and a conventional sulfur electrode demonstrated outstanding rate capability (up to 2.0 C) and remarkable cycling stability (1000 cycles at 2.0 C). Even under more demanding cell conditions, such as high sulfur content (71 %), high sulfur loading (4.6 mg cm−2), and low E/S (5.6 μL mg−1) ratio, the cell exhibits impressive cycling stability with 420 cycles at 0.1 C, along with feasible rate performance up to 0.3 C.

Investigation of silicon carbon oxynitride thin film deposited by RF magnetron sputtering

In this research, silicon carbon oxynitride (SiCON) thin films were deposited on silicon substrate by a radio frequency magnetron sputtering method. The effect of methane reactive gas flow rate on the structural, morphological, optical, and mechanical properties of the thin films was evaluated by using of grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) , field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR), ellipsometry and nano-indentation methods. The results of the GIXRD proved the formation of an amorphous structure in the thin films. Also, the Raman spectroscopy results determined the absence of graphite nanocrystals in the thin film structure. FE-SEM revealed the formation of a thin film with a smooth, dense and crack-free surface. AFM results showed that SiCON thin film is formed with very low surface roughness in the RMS range of 0.73 nm to 4.39 nm. The results of the ellipsometry analysis indicated that the refractive index of the thin film was changed during increase of the CH4 reactive gas flow rate in the of 1.4 to 1.61 at 4 µm. According to the nano-indentation results, sample N10-C20-R1 has the highest hardness and Young's modulus equals 22.7 GPa and 231.6 GPa, respectively.

Corrosion-resistant nanostructured carbon-based coatings for applications in fuel cells based on bipolar plates

The paper reports on carbon coatings deposited by accelerated C60 ion beam irradiation onto the VT1-0 titanium alloy surface at different substrate temperatures, considering potential applications in fuel-cell bipolar plates. We identified the temperature range for forming a conductive carbon nanocomposite coating (CNC) at different accelerating voltages (Ua). The obtained CNC consists of graphite nanocrystals embedded in an amorphous diamond-like matrix. The nanocomposite containing ∼40% of sp3 bonds is formed at Ts = 300–400 °C under Ua = 6 kV. The increase in accelerating voltage to 8 kV reduces the temperature of the nanocomposite formation to Ts = 200 °C. Interface contact resistance (ICR) of a CNC coated titanium plate decreases to 2.6 ± 0.7 mOhm⋅cm2 at a sealing pressure of 1.5 MPa, which is close to carbon paper – graphite contact resistance. This low ICR value persists after prolonged corrosion tests. Tribological studies established high wear resistance and high adhesion of CNC to titanium substrate, showing potential for stable operation of coated bipolar plates in mobile applications. CNC allows to overcome the limitation of corrosion-caused ICR increase, which makes CNC-coated titanium a promising candidate to substitute gold-coated stainless steel as a raw material for bipolar plates of proton-exchange membrane fuel cells.

Boosting redox kinetics using rationally engineered cathodic interlayers comprising porous rGO–CNT framework microspheres with NiSe2-core@N-doped graphitic carbon shell nanocrystals for stable Li–S batteries

Here, we propose the synthesis of a three-dimensional (3D) nanostructure comprising NiSe2-core@N–doped graphitic carbon (NGC) shell nanocrystals securely implanted within a highly conductive and porous reduced graphene oxide–carbon nanotube (rGO–CNT) framework (3D P-NiSe2@NGC/rGO–CNT), using spray pyrolysis technique followed by selenization and utilized as multifunctional cathodic interlayers in lithium–sulfur (Li–S) cells. The uniformly distributed arrays of macropores (ϕ = 100 nm) were formed by thermal decomposition of polystyrene nanobeads (ϕ = 200 nm). The porous structure shortens the charge diffusion length, allowing rapid charge transport and efficient electrolyte percolation besides accommodating unwanted volume perturbations. The NGC shell surrounding the NiSe2 nanocrystals acted as the primary conduction conduit for electron transport, while the self-supporting rGO–CNT framework served as a secondary pathway for consecutive electron transfer besides enhancing the structural robustness. Further, the polar NiSe2 nanocrystals offered numerous chemisorption sites for effectively capturing polysulfides, thus minimizing the shuttling effect and increasing active material utilization. The Li–S cell exhibited improved rate performance (till 4.0C) and excellent cycling stability (1000 cycles at 2.0C, average capacity decay rate of 0.04% per cycle). Even at severe cell parameters (effective S content = 74%, S loading = 4.5 mg cm−2, and electrolyte/sulfur = 5.7 µL mg−1), the cells delivered a stable rate performance and long-term cycling (400 cycles at 0.1C, average decay rate of 0.10% per cycle). We believe the nanostructure design strategy that we developed for this study could spur the development of more enduring and practical Li–S battery technology.

Deposition of graphenic nanomaterials from elevated temperature premixed stagnation flames

The work examines the unique nanostructure of carbon nanoparticles deposited from sooting premixed flames with flame temperatures exceeding 2200 K. This flame temperature regime has previously been shown to transition from typical soot formation conditions to a regime whereby the flame-form carbon adopts a nanostructure considerably more ordered than soot. Graphenic carbon deposits observed by High-resolution TEM (HRTEM) are reported here corroborating previous Raman spectroscopy evidence. The use of premixed stretch-stabilized flames enables particle production in the high-temperature regime under a flow field amenable to low-dimensional flame modeling. Although the flame flow configuration is relatively simple, three sample preparation methods are used to assess the representation of true carbon properties as they exist in the flame. HRTEM imaging is carried out on carbon particle samples prepared by rapid-insertion deposition, aerosol dilution probe deposition and carbon particle film deposition. Images from rapid-insertion samples show amorphous particles in the lightly sooting flame and turbostratic particles in the heavy sooting flame. There is trace evidence of graphenic structure in rapid-insertion samples but the most striking particles on the TEM grid are graphite nanocrystals presumably formed by a new artificial crystallization process. HRTEM images of particles collected over time by diluted aerosol deposition and film deposition show clear graphenic structures. Overall, the carbon nanostructure observed by HRTEM is a mixture of amorphous, turbostratic and graphenic carbon lattices depending on the flame condition and sampling method. The current work highlights potential impacts of higher flame temperatures and higher equivalence ratio on deposited flame-formed carbon. Namely, graphenic particle structure is observed in rapid-insertion deposition samples but graphene portions are most abundant in aerosol dilution and carbon particle film deposition samples. This may indicate that graphene structures grow on the deposition surface over time.

On modification of eutectic cast iron graphite

It has been shown that elementary crystalline cells of graphite and basic products of iron modification do not correspond to the principle of structural and dimensional correspondence of Dankov –Konobeevsky. Modifying elements Al, Ca, Mg, Ba, Ce increase the phase tension melt‑graphite by binding surface‑active oxygen and sulfur. Modifying cast iron eutectic graphite is a nanostructured process in which modifying elements refine elemental graphite nanocrystals from adsorbed oxygen and sulfur atoms. This contributes to an increase in the concentration of graphite nuclei upon solidification of the cast iron melt. The modification reduces the concentration of dissolved hydrogen, which increases the effectiveness of the modifying effect. Reduced concentrations of demodifying surface‑active elements, melt degassing, increased heat removal contribute to increasing the degree of branching and compactness of graphite dendrites during iron crystallization. The strongest modifying element of eutectic cast iron graphite is magnesium.

Additive manufacturing of recyclable, highly conductive, and structurally robust graphite structures

• Complex, electrically conductive structures with relatively high compressive strength. • Printable aqueous pastes made from graphite and cellulose nanocrystals. • Additively manufactured from sustainable and recyclable materials. • Structures made via direct ink writing (DIW) and dried at room temperature. • Minimal and controllable shrinkage of printed structures. This study investigates the design and use of a printable, sustainable, aqueous paste for room-temperature low-energy material extrusion (ME) additive manufacturing (AM) of complex structures. To this end, pastes with controlled rheology and a total solid content of ∼42% are formulated. Constituents of the pastes are commercial graphite and cellulose nanocrystal (CNC) powder, as a dispersing additive, with 91:09 and 88:12 graphite:cellulose wt.% compositions. The AM structures are dried in air at three rates (slow, medium, and fast). The structure of printed parts is characterized using electron microscopy, X-ray diffraction, Infrared/X-ray photoelectron spectroscopy, X-ray micro-computed tomography, and thermogravimetric analysis. The compressive strength of AM graphite structures reached 5.8±0.6 MPa with almost no effect from drying rates. However, samples containing more cellulose were ∼30% stronger in compression. Carbonization of the AM parts increased their electrical conductivity by more than an order of magnitude to ∼2400 S.m −1 . In addition, it enabled the fabrication of nearly pure graphite structures. The mechanical and electrical properties of samples fabricated in this study exceed the performance of previously reported AM graphite structures. Moreover, the recyclability of the printed parts was demonstrated by regenerating pastes via mixing printed parts in water and re-printing new parts with the paste. The AM graphite structures can be used in numerous applications, including but not limited to electrical discharge machining (EDM), electrochemical machining (ECM), high-temperature customized sealing, high-temperature composite tooling, and energy conversion and storage.

A sensing strategy based on aptamers alkylated with melphalan and graphite nanocrystals in a bed of tetrahedral amorphous carbon for electrochemical detection of lead ions in human urine

We report a voltammetric aptasensor based on the graphite nanocrystals in a bed of tetrahedral amorphous carbon (GNC-TAC) and guanine (G)-rich aptamers alkylated with melphalan anticancer for determination of ultratrace Pb2+ in the clinical samples. In this work, an adhesive and stable layer of GNC-TAC was formed on the cellulose paper by the ion beam sputtering deposition (IBSD) method. This porous conductive nanographite film plays a key role in providing a large area for adsorption of ferrocene carboxylic acid (FC-COOH) anticancer as a redox indicator. Then, melphalan that attaches the alkyl groups to the guanine bases of DNA aptamer was bonded covalently to the carboxylic groups of FC-COOH via the aid of EDC/NHS. The introduction of Pb2+ ions to the aptamer/melphalan/FC-COOH/GNC-TAC/paper electrode leads to the formation of a G-quadruplex (G4)/Pb2+ complex and dissociation of this complex from the modified electrode surface. The target-induced aptamer release from melphalan/FC-COOH/GNC-TAC/paper electrode makes the sensing interface smaller which results in an increase in the current signal. Based on this signal-on mechanism, the sensitive detection of Pb2+ ions in the dynamic linear range (DLR) of 0.5–700.0 μg L−1 is realized (limit of detection (LOD): 0.15 μg L−1). The present strategy shows remarkable advantages including high selectivity and wide detectable range. More importantly, the good consistency of the results obtained with the aptasensor and those by the quality control material (QCM) analysis and atomic absorption spectroscopy equipped with graphite furnace (GF-AAS) technique showed that the proposed strategy has a high potential for Pb2+ detection in the clinical samples.

Nanostructured recrystallization of iron‑carbon alloys

Recrystallization of iron-carbon alloys has been shown to be a nanostructured process. Microcrystals of secondary cementite of steels and cast iron are formed from elementary nanocrystals of iron and graphite, free atoms of graphite and iron-carbon complexes. Microcrystals of primary α-ferrita steels are formed from elementary nanocrystals of iron and graphite, free iron atoms. Microcrystals of cast iron secondary graphite are formed from elementary nanocrystals and free graphite atoms. Eutectoid microcrystals are formed from elementary nanocrystals of iron and carbon, free atoms of iron and carbon, iron-carbon complexes.

Nanostructured crystallization of casting alloys

Crystallization of casting alloys has been shown to be a nanostructured process. Microcrystals of phases in the temperature range of liquidus and solidus, during eutectic and peritectic reactions, are formed from nanocrystals of components A and B of alloys, their free atoms and atomic complexes. Microcrystals of primary austenite and austenite-graphite eutectics during crystallization of cast iron, microcrystals of austenite and δ-ferrite during crystallization of steel are formed as a result of nanostructural reactions from elementary nanocrystals of iron and graphite, free atoms of iron and graphite, iron-carbon complexes. Primary and eutectic microcrystals of silumin are formed from elementary nanocrystals of aluminum and silicon, free atoms of aluminum and silicon, aluminum-silicon complexes.

Facile synthesis of core-shell structured C/Fe3O4 composite fiber electromagnetic wave absorbing materials with multiple loss mechanisms.

The use of heterostructures in electromagnetic wave absorption applications has been limited by the problem of homogeneous dispersion in composites. In this study, three-dimensional (3D) cross-linked electromagnetic wave absorbing composites with the carbon nanofiber/Fe3O4 (CNF/Fe3O4) core-shell structure were synthesized by expanding the interface of the heterogeneous structure with Fe3O4 nanocrystals uniformly modified on the surface of the carbon nanofiber. The 3D cross-linked structure of the composites contributes to the generation of conductive loss and macroscopic eddy current loss. The heterogeneous interface formed by graphite nanocrystals and amorphous carbon in the carbon nanofiber is identified by high-resolution transmission electron microscopy and Raman spectroscopy as having a strong electromagnetic wave absorption capacity for boundary-type defects. The Fe3O4 nanocrystal particles on the surface of the carbon nanofiber not only have the strong magnetic loss capability of magnetic materials but also form a new heterogeneous interface with the carbon nanofiber surface, which further enhances the interfacial polarization of the composite and improves the electromagnetic wave absorption properties. With the synergistic effects of interfacial polarization, macroscopic and microscopic eddy current losses, conductive losses, and magnetic losses, the electromagnetic wave absorption performance of the composites is further enhanced based on the carbon nanofiber. The reflection loss reaches -51.11, -42.99, and -55.98 dB at 9, 12 (X-band), and 17GHz (Ku-band), respectively, corresponding to the thicknesses of 2.0, 1.5, and 1.0mm. In addition, the widest effective absorption bandwidth is 3.3GHz at 14.7-18GHz (only 1.09mm).

Nanostructured steel crystallization

Steel crystallization has been shown to be a nanostructured process. Austenite microcrystals in liquid steel with a carbon concentration of 2.5 to 9 atomic percent, δ‑ferrite microcrystals in melt with a carbon concentration of up to 2.5 atomic percent, austenite microcrystals in peritectic reaction are formed from elementary nanocrystals of iron and graphite, free iron atoms and iron‑carbon complexes.

On carbon distribution in austenite Fe‑C alloys

Based on the calculations of the model of the elementary crystal cell γ‑iron, it is shown that carbon ions cannot be present in its open pores. Carbon in Fe‑C alloys dissolves and distributes mainly as elementary graphite nanocrystals. In steel austenite, carbon is found in elementary graphite nanocrystals and in iron‑carbon complexes. In cast iron austenite, carbon is found in elementary graphite nanocrystals.