Graphite Matrix Research Articles

Relationship Between Thermal Conductivity and Tensile Strength in Cast Irons

Improved mechanical and thermal properties are important characteristics for enhancing the performance of cast iron components that operate at elevated temperatures. Thermal conductivity defines the temperature distribution within the casting and influences the magnitude of the thermally induced tensile stresses. The microstructural features that increase the thermal conductivity have a negative impact on tensile strength. The results reported in this work show that there is a unique inverse relationship between thermal conductivity and tensile strength, valid for the whole range of cast iron alloys regardless of graphite form, solidification rates, carbon content and matrix constituents. The finding indicates the challenges for the simultaneous improvement of these properties, and it can be utilized as a guideline during the design of cast iron components for high temperature applications.

Simple Construction of Multistage Stable Silicon-Graphite Hybrid Granules for Lithium-Ion Batteries.

Because of its high specific capacity, the silicon-graphite composite (SGC) is regarded as a promising anode for new-generation lithium-ion batteries.However, the frequently employed two-section preparation process, including the modification of silicon seed and followed mixture with graphite, cannot ensure the uniform dispersion of silicon in the graphite matrix, resulting in a stress concentration of aggregated silicon domains and cracks in composite electrodes during cycling. Herein, inspired by powder engineering, the two independent sections are integrated to construct multistage stable silicon-graphite hybrid granules (SGHGs) through wet granulation and carbonization. This method assembles silicon nanoparticles (Si NPs) and graphite and improves compatibility between them, addressing the issue of severe stress concentration caused by uncombined residue of Si NPs. The optimal SGHG prepared with 20% pitch content exhibits a highly reversible specific capacity of 560.0 mAh g-1 at a current density of 200mA g-1 and a considerable stability retention of 86.1% after 1000 cycles at 1 A g-1 . Moreover, as a practical application, the full cell delivers an outstanding capacity retention of 85.7% after 400 cycles at 2 C. The multistage stable structure constructed by simple wet granulation and carbonization provides theoretical guidance for the preparation of commercial SGC anodes.

Metal-organic framework derived core-shell nanoparticles as high performance bifunctional electrocatalysts for HER and OER

Development of an affordable, stable, and efficient electrocatalyst using nonprecious material to generate green H2 and O2 is still a challenging research problem. This research demonstrates the development of an efficient bifunctional electrocatalyst for HER as well as OER. Self-sacrificial nickel-based MOF acted as a precursor in facile pyrolysis carried out at 600, 700, and 800 °C temperatures to yield three bifunctional electrocatalysts viz Ni@NCS-600, Ni@NCS-700, and Ni@NCS-800, respectively. A blend of metallic Ni-nanoparticles and heteroatoms (N, S, & O) doped graphitic matrix has shown a synergistic effect for efficient electrocatalysis. The facile transformation of Ni-MOF into core-shell structure imparts stability to metal electrocatalyst by preventing direct exposure to the electrolytes during water splitting. After systematic characterization by various analytical techniques, their electrocatalytic performances were evaluated for OER and HER in alkaline and acidic medium, respectively. Bifunctional electrocatalytic activity of Ni@NCS-800 was found to be highly efficient, and comparable to precious state-of-the-art catalysts (RuO2 and Pt/C). Ni@NCS-800 exhibits extremely low overpotential, which needs only 330 mV and 366 mV to reach 10 mAcm−2 current density in OER and HER, respectively. The Tafel slope has been derived from the EIS also, imparting the alternating current. Thereby, a superior electrokinetic activity of Ni@NCS-800 has been observed, due to the elimination of non-faradaic current, with a Tafel slope of 32 mV/dec. The stability was evaluated by potentiostatic and potentiodynamic techniques. Therefore, this study explores a suitable pathway for the fabrication of simple, nonprecious, stable, yet catalytically efficient material for HER and OER activity.

Microstructure and properties of Cr[sbnd]Nb carbide coatings on graphite via powder immersion reaction assisted coating

Chromium‑niobium (CrNb) carbide coatings were formed on graphite by powder immersion reaction assisted coating (PIRAC) method. In our experiments, a small amount of iodine was added to the mixture of Cr and Nb powder to lower the annealing temperature to as low as 1173 K. The resultant composite coatings comprised Cr7C3 and NbC phases, of which the Cr7C3 phase was found in the graphite's internal gaps and NbC was distributed on the surface of the coatings. The formation of the multilayer structure might be explained by thermodynamics of metal iodides and carbides. The optimal composite coating's hardness was close to that of CrC compounds coatings, and its toughness was close to that of NbC coatings. Thermal expansion coefficient of the coated sample was similar to the graphite matrix within the temperature range of 313-673 K. No cracks were observed even though stress mismatch was expected due to the large temperature change and large difference in mechanical properties between carbides and graphite. These results showed that the multilayer structure of CrNb composite coating synthesized by PIRAC was promising for improving the mechanical properties of the graphite.

A bio‐based compatibilizer for improved interfacial compatibility in thermally conductive and electrically insulating graphite/high density poly(ethylene) composites

AbstractGraphite is a thermally conductive filler. However, when dispersed into high density poly(ethylene) (HDPE) resin, graphite particles tend to agglomerate and requires a compatibilizer to achieve desired thermal/physical properties. In this study, oleic acid (OA), a bio‐based additive and polyethylene‐polyamines (PEPA) were used to synthesize a new compatibilizer, PEPA‐g‐OA, containing numerous NR2 groups. The experimental results showed that PEPA‐g‐OA can significantly improve the compatibility between graphite particles and the HDPE matrix due to uniform dispersion of graphite in the HDPE matrix. When the graphite content was 25 wt%, the thermal conductivity of the composite recorded 1.2 W m−1 K−1 (three times that of neat HDPE) and the volume resistivity was 1.8 × 109 Ω cm, indicating excellent electrical insulation. Compared to the composites with no graphite content, the properties of the composites with 25 wt% graphite content exhibited narrower melting and crystallization peaks, more stable mechanical properties, and higher ultraviolet aging resistance. Synthesized new bio‐based compatibilizer and thermally conductive and electrically insulating composites developed in this study can be useful in different industrial fields for the preparation of the next generation composites.

Self-Assembled Hierarchical Silkworm-Type Bimetallic Sulfide (NiMo3S4) Nanostructures Developed on S-g-C3N4 Sheets: Promising Electrode Material for Supercapacitors

An electrode material composed of bimetallic sulfides on g-C3N4 typically enhances the energy storage capacity of devices due to the merits of each component, but it still suffers from low energy density over long cycles. Although Ni-based bimetallic sulfides have become good electrode materials for supercapacitors, practical applications of these materials are hindered due to unsatisfactory cycling stability. Here, we demonstrate a simple two-step in situ approach to prepare bimetallic sulfide nanobulbs on a sulfur-doped graphitic carbon nitrate matrix for a NiMo3S4@S-g-C3N4 composite, which is further used for supercapacitor devices. A small amount of sulfur doping to g-C3N4 enhances the conducting channels for electron transportation. An NMS@S-gC nanocomposite clearly shows the formation of small nanobulbs that are formed as silk warm-type hierarchical morphology structures and these were wrapped on the surface of S-gC porous nanosheets. The device made up of these composites exhibited a maximum specific capacitance of 142.4 F g–1, a high energy density of 41.4 Wh kg–1, and a power density of 723.5 W kg–1 at a current density of 1 A g–1. Meanwhile, in a three-electrode device configuration, the working electrode demonstrates a specific capacitance of 934.2 F g–1 at 1 A g–1, which is 1.6 times greater than that of bare NiMo3S4. Moreover, the capacitance retention of the device is about 91% even after 5000 cycles at 8 A g–1. The results obtained in this investigation surpassed most reported metallic sulfides on g-C3N4. Hence, this work could give a different pathway for the synthesis of electrode materials for energy storage devices.

Синтез карбида бора электродуговым методом в открытой воздушной среде из углерода различного происхождения

The paper presents the results of experimental studies on the implementation of electric arc synthesis of boron carbide using carbon with different morphology and origin as a feedstock: carbon fibers, flake graphite, carbon obtained by pyrolysis of plant waste, namely, pine sawdust and cedar nuts husks. A feature of the electric arc method used is its implementation using an original plasma reactor using atmospheric air as a working gas medium. Oxidation of feedstock and synthesis products in the working cycle of the reactor is prevented due to the generation of CO and CO2 gases in the reaction zone. The possibility of obtaining a material containing micron and submicron boron carbide crystals in a graphite matrix has been experimentally shown. Also, the paper presents information about the features of the oxidation processes of the obtained materials in comparison with commercial samples of boron carbide.

Synthesis of boron carbide by the electric arc method in open air from carbon of various origins

The paper presents the results of experimental studies on the implementation of electric arc synthesis of boron carbide using carbon with different morphology and origin as a feedstock: carbon fibers, flake graphite, carbon obtained by pyrolysis of plant waste, namely, pine sawdust and cedar nuts husks. A feature of the electric arc method used is its implementation using an original plasma reactor using atmospheric air as a working gas medium. Oxidation of feedstock and synthesis products in the working cycle of the reactor is prevented due to the generation of CO and CO2 gases in the reaction zone. The possibility of obtaining a material containing micron and submicron boron carbide crystals in a graphite matrix has been experimentally shown. Also, the paper presents information about the features of the oxidation processes of the obtained materials in comparison with commercial samples of boron carbide. Keywords: boron carbide, electric arc synthesis, carbon fibers, flake graphite, carbon of plant origin.

Effect of Graphite Size and Matrix Structure on Hydrogen Embrittlement Properties in Ferrite-Pearlite Ductile Cast Iron

Effect of Graphite Size and Matrix Structure on Hydrogen Embrittlement Properties in Ferrite-Pearlite Ductile Cast Iron

Accounting for super-, plateau- and mesa-rate burning by lead and copper-based ballistic modifiers in double-base propellants: a computational study.

We present a first-principles computational study to understand the action of lead and copper-based ballistic modifiers in the combustion of double-base propellants (DBPs). We show that lead oxide clusters are easily broken down upon addition of small amounts of carbon and the resulting graphitic matrix, dispersed with weakly bound and exposed Pb sites, acts as a Lewis acid to bind small molecule Lewis bases such as NO2 and CH2O that form in the combustion flame. This accounts for super-rate burning, where the fuel burn rate is enhanced. We also show how carbon availability accounts for the plateau- and mesa-rate burning effects, where the fuel burn rate is suppressed. In contrast, cluster integrity on binding carbon to copper oxide is retained, and interaction with NO2 and CH2O is essentially negligible. Carbon binds more strongly to copper oxide, however, and we therefore propose that when carbon levels start to fall this results in the lead oxide clusters being starved of carbon, which leads to plateau and mesa burning. Taken together, the calculations support a general model that accounts for the super-, plateau- and mesa-rate ballistic modifier burning effects.

Study on kinetic parameters of pebble bed reactor with TRISO duplex fuel

Thorium, in this case, 232Th has a higher thermal neutron capture cross-section than 238U, which means that more fertile isotopes can be transmuted and could lead to higher fissile isotope 233U. In addition, 233U has a good performance in the thermal spectrum. Theoretically, a nuclear reactor using thorium fuel can also last longer than one using uranium fuel. The use of TRISO duplex fuel is predicted to produce better neutronic behavior in a pebble bed reactor. This work aims to study the kinetic parameters of a pebble bed reactor with TRISO duplex fuel. The configuration of the TRISO duplex fuel pebble consists of an inner region filled with UO2 TRISO particles and an outer region filled with ThO2 TRISO particles surrounded by a graphite matrix of fuel pebble. Three configurations with volume fraction of UO2-ThO2 were considered in this study: 80-20 %, 75-25 %, and 70-30 %. The HTR-10 reactor was chosen as a reactor model because its geometry and material specifications are known. A series of calculations were conducted using the Monte Carlo transport code MCNP6 and ENDF/B-VII.1 nuclear data library. The calculation results were then analyzed to investigate the effect of UO2 and ThO2 compositions in TRISO duplex fuel on the kinetic parameters of the pebble bed reactor with various TRISO packing fractions of 1-50 %. It can be concluded that the utilization of TRISO duplex fuel in a pebble bed reactor could significantly affect the core multiplication factor and kinetic parameters caused by an increase in Th content. On the other hand, the TRISO packing fraction is taking part in neutron moderation since a lower packing fraction means higher moderation for fueled pebble.

Effect on Strength of Different Fiber Orientation Angles of the Composite Plate Under Out of Plane Load

Composite materials obtained by combining two or more materials macroscopically; It is expressed as a new type of material with low specific gravity, high strength and high rigidity properties. Composite materials are materials that are used under different loads and can be produced in various constructions. In this study, the effects of fiber orientation angle degrees on stress and deformation in composite plates with different fiber materials were investigated using the finite element method. Graphite, glass and aramid as fiber materials; Epoxy was chosen as the matrix material. According to the analysis results, while the stress and deformation values increased as the fiber angle increased in the graphite and aramid fiber epoxy matrix composite plates, the stress and deformation values did not change at different fiber angles in the glass fiber epoxy matrix composite plate.

Engineering Energy Level of FeN4 Sites via Dual-Atom Site Construction Toward Efficient Oxygen Reduction.

Single-atom catalysts based on metal-N4 moieties and embedded in a graphite matrix (defined as MNC) are promising for oxygen reduction reaction (ORR). However, the performance of MNC catalysts is still far from satisfactory due to their imperfect adsorption energy to oxygen species. Herein, single-atom FeNC is leveraged as a model system and report an adjacent Ru-N4 moiety modulation effect to optimize the catalyst's electronic configuration and ORR performance. Theoretical simulations and physical characterizations reveal that the incorporation of Ru-N4 sites as the modulator can alter the d-band electronic energy of Fe center to weaken the FeO binding affinity, thus resulting in the lower adsorption energy of ORR intermediates at Fe sites. Thanks to the synergetic effects of neighboring Fe and Ru single-atom pairs, the FeN4 /RuN4 catalyst exhibits a half-wave potential of 0.958V and negligible activity degradation after 10 000 cycles in 0.1m KOH. Metal-air batteries using this catalyst in the cathode side exhibit a high power density of 219.5mWcm-2 and excellent cycling stability for over 2370h, outperforming the state-of-the-art catalysts.

Dual carbon boosts silicon-based anodes for excellent initial coulombic efficiency and cycling stability of lithium-ion batteries

Benefiting from its ultrahigh theoretical capacity and abundant resources, silicon (Si) is considered a prospective anode material. However, Si faces great challenges in practical applications, such as low initial coulombic efficiency (ICE) and rapid capacity decay. Herein, a silicon/graphite/reduced graphene oxide (Si/Gt/RGO) composite was prepared by agitation, freeze-drying, and heat treatment, where Si nanoparticles were embedded in a graphite (Gt) matrix and tightly wrapped by reduced graphene oxide (RGO). Graphite can promote ICE, improve lithium-ion (Li+) transport kinetics, and serve as the matrix to mitigate the swelling of Si. RGO further ensures rapid Li+ diffusion and forms a flexible shell of Si nanoparticles. The flexible shell formed by RGO can relieve internal stress and increase the tolerance of Si swelling. The dual carbon (graphite and RGO) protects Si nanoparticles from pulverization and ensures the electronic contact of Si, thereby rendering superior electrochemical properties. Si/Gt/RGO shows an excellent ICE (81.54 %), a promoted cycling stability (1007.0 mAh g−1 at 0.2 A g−1 after 100 cycles with capacity retentions of 91 % and 686.3 mAh g−1 after 200 cycles at 1 A g−1) and an outstanding rate capability (475.8 mAh g−1 at 3 A g−1). The research provides a methodology for simultaneously enhancing the ICE and cycling properties of silicon-based (Si-based) anodes and provides an idea for the rational design of LIB anodes with high- energy- density.

A comparison study on the burnup of HTR-10 fuels using radiometric and mass spectrometric methods

Online burnup measurement of a single irradiated spherical fuel element using gamma spectrometry has been applied for years on HTR-10. This reactor has a complex operation history for varies experiments, which raises the uncertainty over the non-destructive measured burnup. In this research, three irradiated spherical fuel elements with different burnup were deconsolidated, and their coated particles were analysed by both radiometric methods based on Cs-137 activity and mass spectrometric methods based on neodymium and actinide mass. The burnup distribution in each spherical fuel element was indicated by fractional U-235 burnup of particles from various radii and relatively uniform. The inventory of Cs-137 in one spherical fuel element was measured by on- and off-line gamma spectrometry and results showed tiny differences. Destructively measured Cs-137 activities from particles indicate negligible portion of Cs-137 in the graphite matrix. Burnup calculated from Cs-137 by radiometric method and Nd-148 by mass spectrometric method were compared. Results showed that the two values were not significantly different for fuels with a clear radiation history, but differences were observed in the fuel with a complex radiation history.

Coral-like porous microspheres comprising polydopamine-derived N-doped C-coated MoSe2 nanosheets composited with graphitic carbon as anodes for high-rate sodium- and potassium-ion batteries

Here, an innovative strategy for the synthesis of coral-like porous microspheres comprising polydopamine-derived N-doped C-coated MoSe2 composited with graphitic carbon (Coral MoSe2-GC@NC) for use as advanced anode materials for sodium- and potassium-ion batteries (SIBs and PIBs) is introduced. The prepared composite is comprised of few-layered MoSe2 particles with enlarged interlayer spacing, which are encapsulated within the graphitic carbon matrix, which acts as an efficient transport pathway for electrons. It is also characterized by the 3D interconnected pores derived from decomposition of polystyrene nanobeads, which ensure high contact area between the electrode and electrolyte and shortened sodium- and potassium-ion diffusion length. N-doped C with high electrical conductivity is coated uniformly on the surface, which plays the role of reinforcing the structural integrity as well as providing additional conductive pathway for facile electron transport. When applied as anodes for both SIBs and PIBs, the microspheres show good structural robustness and high rate capability. The anode exhibits high structural integrity, where stable cycle performance up to 200 cycles at 2.0 A/g for SIBs and 150 cycles at 1.0 A/g for PIBs was observed. In terms of rate performance, the anode exhibited high discharge capacities of 82 mA h g−1 (at 25 A/g, SIBs) and 152 mA h g−1 (at 10 A/g, PIBs), which clearly demonstrates the structural merits of the prepared microspheres.

Adsorption of Sr on electrochemical deconsolidation products of matrix graphite

With the development of high-temperature gas-cooled reactor (HTGR), the disposal of its spent fuel elements will become an important factor that affects its industrialization. As one of alternative routes for head-end process of HTGR spent fuels’ reprocessing, electrochemical deconsolidation method separates TRISO fuel particles from matrix graphite (MG) and produces electrochemical deconsolidation product (EDP) with larger surface area than MG and abundant functional groups. In this paper, the chemical composition and structure of EDPs obtained in HNO3 with concentrations of 4%, 34% and 68% were studied, and the application of EDPs on strontium ions (Sr2+) adsorption was investigated. The results showed that EDP-4% with more carbonyl groups on the surface possessed the largest Sr2+ capacity of 44.8 mg/g at pH 5, while EDP-34% containing more hydroxyl and epoxy groups had the smallest capacity of 9.6 mg/g. The capacity for EDP-68% lay in the mid value of 19.5 mg/g. Density functional theory (DFT) calculations and adsorption experiments jointly evidenced that the type and amount of functional groups both significantly impacted the Sr2+ adsorption. The proposed adsorption mechanism provides theoretical foundation to evaluate the distribution of 90Sr during HTGR spent fuels’ electrochemical deconsolidating.

In-situ preparation, modulation and mechanism of refractory metal carbide gradient coating

TiC, ZrC and TaC modified layers were in-situ prepared on graphite matrix by chemical vapor infiltration method with metal salts as the activator. Taking the TiC modified layer as an example, through thermodynamic calculation and experiment, the thermal decomposition process of raw materials (Ti/K2TiF6) was analyzed, the formation mechanism of TiC was determined, and the distribution of TiC modified layer was modulated. The results show that activator K2TiF6 has higher decomposition temperature than NH4Cl, which is conducive to improving the utilization rate of raw materials in the gas infiltration process. Increasing the content of Ti powder can increase the concentration of reaction gas and contribute to the formation of TiC modified layer. When the molar ratio of Ti to K2TiF6 is 3:1, the surface thickness and infiltration depth of TiC are 5.42 and 136.24 μm, respectively. Increasing the reaction temperature can improve the rate of in-situ reaction and the thickness of TiC surface layer. When the experimental temperature rises to 1600 °C, the TiC surface layer thickness increases to 20.27 μm.

Improving dispersion and delamination of graphite in biodegradable starch materials via constructing cation-π interaction: Towards microwave shielding enhancement

• Biodegradable graphite/starch materials with high EM shielding were prepared. • Cation-π interaction improved delamination and dispersion of graphite in starch. • Orientation of graphite was also very important to EM shielding performance. • Cation-π interaction could enhance interfacial polarization of microwaves. • Orientation of graphite endowed the Salisbury screen effect. Herein, a low-cost, biodegradable, and high-performance microwave shielding graphite/starch material was fabricated via constructing a cation-π interaction between ammonium ions and graphite. The graphite flakes and starch were firstly mixed with distilled water containing ammonium hydroxide to form graphite/starch slurry under an ultrasonic assistant. The cation-π interaction could improve delamination degree and dispersion of graphite in starch matrix. The slurry was first used as a coating material on the surface of wood and paper to develop shielding packages. The effect of coating thickness and coating layers on EM shielding property of the materials was investigated. Second, the composites with a high orientation of graphite were fabricated by compression at high pressures. The electrical conductivity and EM shielding effectiveness (SE T ) of the materials were greatly enhanced by construction of cation-π interaction and orientation of graphite. Specifically, the EM SE T values increased from 56.9 to 66.8 dB for the composites with 50 wt.% graphite and 2.0 mm in thickness by constructing cation-π interaction. The EM SE T values raised from 17.4 to 66.8 dB via the graphite orientation in the materials with the same components and thickness. The shielding mechanism of the compressed composites with orientation dispersion of graphite was also discussed in comparison to the coating layer with random dispersion of graphite.

Forming and heat resistance study of NiAl‒ZrO<sub>2</sub> gradient thermal barrier material for superalloys

In this work the spark plasma sintering (SPS) technique was used to forming a functionally gradient thermal barrier material based on nickel aluminide (VKNA) and zirconium oxide (YSZ). Layer-by-layer powders of VKNA / mixtures VKNA + 15 (30) % YSZ / YSZ were consolidated in a graphite matrix at 1070°C in a vacuum atmosphere for 5 minutes and at a pressure of 30 MPa. It is determined that the sintered material has good adhesion of layers, there are no interlayer boundaries. To check the functionality of the material, thermocyclic tests were carried out at 1100°C in the air. The results showed that the material containing the sublayer VKNA + 30 % YSZ has better heat resistance. Ill. 5. Ref. 28. Tab. 2.