SiC Graphite Research Articles

Effect of aggregate type on the mechanical properties and slag resistance of Al2O3‐SiC‐C hot metal ladle bricks

AbstractAggregates are important factors that determine the performance of refractory materials. To explore the influence of aggregate types on refractory material properties, Al2O3‐SiC‐C bricks were prepared using bauxite, fused brown corundum, tabular corundum, fused white corundum, and microporous corundum with particle sizes of 5–3, 3–1, and ≤1 mm as aggregates, fused white corundum (≤.075 mm), SiC (≤.075 mm), or flake graphite (≤.15 mm) as the matrix, and a thermoset phenolic resin as the binder. Understanding the effects of the aggregate type on the mechanical properties and slag resistance of Al2O3‐SiC‐C bricks provides a theoretical basis for the selection of different aggregates during production. The results showed that the Al2O3‐SiC‐C brick had good high‐temperature mechanical properties and slag resistance when tabular corundum was used as an aggregate, owing to its high density and low content of cracks and impurity phases. When bauxite was used as an aggregate, its high‐temperature mechanical properties and slag resistance were poor, owing to its high porosity and impurity content.

Influences of WEDM constraints on tribological and micro structural depictions of SiC-Gr strengthened Al2219 composites

The creation of this work is made by mixing various weight percentages of SiC and consistent Graphite with liquefied Al2219. For various mechanical tests including hardness, ductility, flexural, and tensile, are conducted and tested. The broken specimens of composites discovered using a filtered electron magnifying equipment (SEM). The best mechanical properties are identified in composite materials. Additionally, a similar material is focussed on the wear test. The composite with 4% SiC and 0.5% Graphite shown improved mechanical performance among the five different groupings of sic and graphite. The optimized results and the influencing parameters of electrical release WEDM were higher Material Expulsion Rate with less discomfort on the surface and boundary for wear testing also attained with decreased wear rate.

Effects of Er atoms on graphitization process and structural defects for epitaxial graphene

Thermal decomposition of SiC at high temperature usually brings about excessively fast Si sublimation and a very rough surface. In order to fabricate high-quality homogeneous epitaxial graphene on a SiC(0001) substrate, highly reactive erbium atoms are employed in this work. Scanning tunneling microscopy and Raman spectroscopy have been utilized to investigate the modulations of Er atoms on graphitization evolution and structural defects for graphene after annealing durations. Experimental results show that Er atoms pre-deposited on clean substrates can definitely enhance the surface graphitization of SiC and make graphene grow in a controllable way. The existence of Er layer is believed to break Si–C bonds at low temperature and to decrease the Si sublimate rate. It is also demonstrated that Er atoms can modify the type of structural defects in graphene, and the areal density of flower defects increases to 1.22 × 1012 cm−2, quadrupling that in pristine graphene. This work puts forward a fabrication method for epitaxial graphene with flower defects in high density and will enlighten some future applications of graphene in nanoelectronics, electron energy filtering, and chemical catalysis.

Reactive spark plasma sintering of SiC-TiC-diamond composites

SiC-TiC-diamond composites were fabricated via spark plasma sintering at hold temperatures of 1600 °C, 1625 °C, and 1650 °C from a powder blend containing by weight 30 % Si, 30 % Ti, and either 40 % uncoated or TiC-coated diamond. Due to the sintering conditions, sp3-diamond decomposed into thermodynamically favorable sp2‑carbon, reacting with Si and Ti to form SiC and TiC at T ≥ 1600 °C. As the hold temperature increased, the composite density reduced due to excess graphite formation for the uncoated diamond composites. However, at too low of a temperature the porosity fraction increased in the SiC-TiC matrix for the TiC-coated diamond composites. Overall, the results revealed that composites with ~97 % theoretical density and minimal (up to 5 vol%) graphite can be achieved by sintering Si-Ti-uncoated diamond at 1600 °C and Si-Ti-TiC-coated diamond at 1625 °C. X-ray diffraction, electron and x-ray microscopies with imaging analyses were carried out to quantify the volume fractions of each composite phase and used to explain the composite densification behavior. Conventional and energy filtered transmission electron microscopy, in addition to electron energy loss spectroscopy, were conducted to understand the nature of diamond graphitization with respect to the nucleation and growth of SiC, TiC, and nanoscale graphite.

An interconnected and scalable hollow Si-C nanospheres/graphite composite for high-performance lithium-ion batteries

Silicon (Si) anode is the most promising alternative for next generation lithium-ion batteries (LIBs) owing to large theoretical capacity, low working voltage and abundant natural resources. However, tremendous volume change of Si during the (de)lithiation processes causes repetitive formation of solid electrolyte interphase (SEI) layers, loss of electrical contact and electrodes pulverization, limiting its commercial application. Herein, we fabricate an interconnected hollow Si-C nanospheres/graphite composite via a facile and scalable approach. Notably, hollow Si-C nanospheres and graphite are homogeneously combined by using the surfactants as surface modifiers of graphite and introducing carbon dioxide (CO2) into magnesiothermic reduction reaction, resulting in the enhanced compatibility between hollow Si-C nanospheres and graphite, and the well-established electrical conductive network. The resultant Si-C nanospheres/graphite composite anode with carbon content of 59 wt% delivers a large reversible specific capacity of 662 mAh g−1 and a high capacity retention of 65.7% at 0.5 A g−1 after 200 cycles. Such excellent rate performance and superior cycling performance are attributed to high electrical conductivity and buffering effect of graphite, superior compatibility between hollow Si-C spheres and graphite, uniform distribution of both Si-C nanospheres with a unique hollow architecture and graphite flakes inside the composites and well-established interconnected electrical conductive carbon networks, which can effectively alleviate Si volume expansion and maintain good electrical contact during cycling. This strategy provides insights into designing Si-based anodes for practical LIBs.

Effect of silicon/graphite ratio and temperature on oxidation protective properties of SiC/ZrB2–SiC coatings prepared by pack cementation

To investigate the silicon/graphite ratio and temperature on preparation and properties of ZrB2–SiC coatings, ZrB2, silicon, and graphite powders were used as pack powders to prepare ZrB2–SiC coatings on SiC coated graphite samples at different temperatures by pack cementation method. The composition, microstructure, thermal shock, and oxidation resistance of these coatings were characterized and assessed. High silicon/graphite ratio (in this case, 2) did not guarantee higher coating density, instead could be harmful to coating formation and led to the lump of pack powders, especially at temperatures of 2100 and 2200 °C. But residual silicon in the coating is beneficial for high density and oxidation protection ability. The SiC/ZrB2–SiC (ZS50-2) coating prepared at 2000 °C showed excellent oxidation protective ability, owing to the residual silicon in the coating and dense coating structure. The weight loss of ZS50-2 after 15 thermal shocks between 1500 °C and room temperature, and oxidation for 19 h at 1500 °C are 6.5% and 2.9%, respectively.

Optimising the performance of SiC-based varistors through composition and microstructure control

SiC varistors are employed as surge arrestors in high power/high energy niche applications. Using a model formulation based on 50 % SiC and 50 % clay plus graphite, the effects of SiC grain size, composition and graphite content were investigated. Disc and toroidal samples were sintered at 1130 °C under a reducing atmosphere; products were ∼70–75 % dense. The main phases detected by SEM and XRD were SiC, SiO2 (quartz), mullite, graphite and porosity. With increasing graphite content (zero to 11 wt%) the non-linear coefficient (α) decreased from 5.9 to 2.7, the breakdown field Eb decreased from 3346 to 36 V cm−1, and bulk electrical resistivity fell by three orders of magnitude. As SiC grain size reduced from 120 μm to 10 μm, non-linear coefficients (α) almost doubled (3.7–6.3) and breakdown field (Eb) increased by an order of magnitude (226–2656 V cm−1) as a result of increasing numbers of resistive grain boundaries between the device electrodes. The impurity content of SiC grains had a modest impact on electrical properties. The resistance of grain boundary regions was typically one to two orders of magnitude larger than that of grain cores.

Experimental studies on the wear and mechanical properties of Al7075-B4C-Al2O3 composite

In order to deal with the demands of current requirements, traditional metals require changes in some properties. The high strength and light weight application of aluminium is well known. In certain instances, its ductility prevents its application in some environments. In the existing research, Al 7075 is reinforced with materials such as boron carbide (B4C) and aluminum oxide (Al2O3) to achieve low mass, low weight, high power, superior malleability, easy machining and excellent corrosion resistance. Thus, hybrid MMC production is being carried out to enhance these mechanical properties. In this study, Al 7075 is cut into small pieces with 90% wt in the form of a bar and placed in a SiC graphite crucible and the metal matrix is formed by melting it and stirring casting metal to add the reinforcement particles. The quantity of B4C & Al2O3 combined to form the new material was taken at 5% each. The samples were prepared according to ASTM specifications and eventually tested for tensile, compression, hardness, wear and effect measurements, and the findings were compared with those of pure aluminium Al 7075. The test results showed improved properties of Al MMC, which is more efficient than Al 7075.

Strain-inducing photochemical chlorination of graphene nanoribbons on SiC (0001)

As different low-dimensional materials are sought to be incorporated into microelectronic devices, graphene integration is dependent on the development of band gap opening strategies. Amidst the different methods currently investigated, application of strain and use of electronic quantum confinement have shown promising results. In the present work, epitaxial graphene nanoribbons (GNR), formed by surface graphitization of SiC (0001) on crystalline step edges, were submitted to photochemical chlorination. The incorporation of Cl into the buffer layer underlying graphene increased the compressive uniaxial strain in the ribbons. Such method is a promising tool for tuning the band gap of GNRs.

Electrochemical Corrosion of Composite Ceramics and Thermal Spray Coatings in the ZrB2–SiC–AlN System

Polarization studies of the ZrB2–SiC–AlN compact ceramic material and thermal spray coatings of the same composition were conducted in a 3% NaCl solid solution to analyze their cathodic and anodic behavior. The compact ceramic material was produced by hot pressing, the plasma-sprayed coating 240 μm thick was deposited onto a C/C–SiC graphite substrate, and the detonation-sprayed coating 340 μm thick was applied to 12Kh18N9T stainless steel. The microstructure and phase composition of the compact sample and thermal spray coatings were examined. The microstructure was heterophase in all cases. The compact sample and plasma-sprayed coating contained SiC, AlN, and ZrB2 as the main phases, and the detonation-sprayed coating additionally had a small amount of nickel and zirconium oxide. Electron microprobe analysis showed that the plasma-sprayed coating had 20 wt.% oxygen; i.e., the coating contained oxide phases in the amount not revealed by X-rays. The compact ceramic sample showed exceptionally high resistance to electrochemical oxidation: electrochemical potential, Ecorr, at which corrosion current occurs is very high and constitutes +1.51 eV. For the detonation- and plasma-sprayed coatings, Ecorr = –0.25 and –0.05 eV, respectively. The great resistance of the compact ceramic material to electrochemical oxidation correlates with its resistance to high-temperature oxidation above 1700°C. This is due to the formation of an Al2O3–SiO2 mullite film on the surface. The lower resistance of the coatings to electrochemical oxidation compared to the compact material is associated with their increased porosity.

Reversible graphitization of SiC: A route towards high-quality graphene on a minimally step bunched substrate

We show that the thermal decomposition of SiC (0001) surface is reversible, if carried out in near-equilibrium conditions, with an external Si atomic beam applied to the substrate. Taking advantage of this observation we design a novel process, allowing for the growth of uniform, few-layers, ABC-stacked graphene. This process is composed of two phases; the first is a graphene film growth and the second is its reduction to the desired thickness. We find that, when using this scheme instead of the conventional ones the heavy step bunching on the substrate is avoided, and the step heights remain below 2.75 nm.Since the step bunching is one of the most important factors prohibiting the use of epitaxial graphene on SiC in certain application areas, such as analog electronics or sensing, our method has the potential to be applied in future wafer-scale graphene technologies and processes. Moreover, the results obtained in this work exemplify general near-equilibrium phenomena and therefore they may be also relevant for growth methods of other 2D materials.

Influence of secondary phases in A356 MMCs on their mechanical properties at macro- and nanoscale

Metal matrix composites are very inhomogeneous materials, and their properties depend on various parameters (production process, constituents, their interfaces, etc.). The influence of SiC microparticles (40 μm) reinforcement and graphite macroparticles (200–800 μm) addition on the mechanical properties of Al–Si A356 alloy, produced by compocasting, has been assessed using macro- and nanoscale measurements of hardness and modulus of elasticity. The Al makes over 90 wt% of the A356 alloy, so the nanoscale measurements were performed on different α phase regions on each material (core of α phase, eutectic α phase, and α phase near the phase boundaries α phase/secondary phases). The results showed that there is no direct correlation between mechanical properties on macro- and nanoscale. The nanoscale results also showed that the secondary phases (SiC and graphite particles) can have significant effect on the mechanical properties on the atomic level, i.e. in the α phase regions very close to the secondary phases.

Effects of graphite nano-flakes on thermal and microstructural properties of TiB2–SiC composites

In the last decades, the production of ultra-high temperature composites with improved thermo-mechanical properties has attracted much attention. This study focuses on the effect of graphite nano-flakes addition on the microstructure, densification, and thermal characteristics of TiB2–25 vol% SiC composite. The samples were manufactured through spark plasma sintering process under the sintering conditions of 1800 °C/7 min/40 MPa. Scanning electron microscopy images demonstrated a homogenous dispersion of graphite flakes within the TiB2–SiC composite causing a betterment in the densification process. The thermal diffusivity of the specimens was gained via the laser flash technique. The addition of graphite nano-flakes as a dopant in TiB2–SiC did not change the thermal diffusivity. Consequently, the remarkable thermal conductivity of TiB2–SiC remained intact. It seems that the finer grains and more interfaces obstruct the heat flow in TiB2–SiC–graphite composites. Adding a small amount of graphite nano-flakes enhances the densification of the mentioned composite by preventing the grain growth.

Repeated Thermal Shock Behavior of ZrB2-SiC-Graphite Composite under Pre-Stress in Air and Ar Atmospheres.

The thermo–chemo–mechanical coupling on the thermal shock resistance of 20 vol%-ZrB2–15 vol%-SiC–graphite composite is investigated with the use of a self-developed material testing system. In each test, a specimen under prescribed constant tensile pre-stress (σ0 = 0, 10, 20 and 30 MPa) was subjected to 60 cycles of thermal shock. In each cycle, the specimen was heated from room temperature to 2000 °C within 5 s in an air atmosphere or an Ar atmosphere. The residual flexural strength of each specimen was tested, and the fracture morphology was characterized by using scanning electron microscopy (SEM). There were three different regions in the fracture surface of a specimen tested in the air, while no such difference could be observed in the fracture surfaces of the specimens that were tested in Ar. The residual flexural strength of the composite that was tested in Ar generally decreases with the increase of σ0. However, in the range of 0 ≤ σ0 ≤ 10 MPa, the residual flexural strength of the composite that was tested in the air ascended with the increase of σ0 due to the healing effect of oxidation, but it descended thereafter with a further increase of σ0, as the effect pre-stress that became prominent.

Study of Mechanical properties and erosion wear behaviour of novel Al-25Zn alloy/SiC/Graphite hybrid composites

Abstract Plain bearings are extensively used in many engineering application. The erosion of bearing material is one of the major parameter that affects the performance of bearing. In this investigation, four Al-25Zn alloy samples added with silicon carbide and graphite particles were manufactured using stir casting technique. The mechanical properties, surface morphology and solid particle erosion wear characteristics of fabricated specimens were studied. Erosion wear characteristic of specimens was investigated using air jet erosion tester with silica sand particles of irregular shapes of size approximately 150 µm as an erodent at three impact velocities 20, 40 and 60m/s and three different impingement angles 15, 30 and 45 deg. for 25 minute as per Taguchi L9 orthogonal array. The eroded surfaces were characterized by using scanning electron microscope (SEM). The hardness, tensile strength and erosion resistance of Al-25Zn alloy is found to be increased with the addition of hard SiC particles. The reinforcement of graphite in Al-25Zn alloy enhances the erosion resistance, impact strength and tensile strength of composite, in spite of the substantial decrease of hardness. The analysis of variance indicates that the impact velocity is the most important parameter as compared to impingement angle for the erosion of the composites. The existence of hard SiC and soft graphite particles in matrix alloy reduces the erosion of composite due to deflection as well as indentation

Advantages and disadvantages of graphite addition on the characteristics of hot-pressed ZrB2–SiC composites

ZrB2–SiC–graphite composites with 0–35 vol% graphite flakes were densified via hot-pressing route at the temperature of 1800 °C under the uniaxial pressure of 40 MPa for 1 h. Consolidation, mechanical properties, and microstructure of hot-pressed composites were investigated by variation of graphite content. By the addition of graphite, the relative density of composites increased, and at this hot pressing condition, fully densified composites were fabricated. The highest flexural strength of 366 MPa was measured for composite containing 7.5 vol% graphite, while the maximum Vickers hardness resulted in 2.5 vol% graphite doped one, and its value was equal to 20.8 GPa. Phase analysis of hot-pressed samples revealed the formation of the Zr3C2 and B4C phases besides the main existing ZrB2, SiC, and graphite phases. The newly carbide phases formed at the surface of ZrB2 grains. The addition of graphite into the ZrB2–SiC composites improved the sintering process and caused a fine-grained microstructure.

Microstructure, wear and corrosion characteristics of Cu matrix reinforced SiC–graphite hybrid composites

The aim of the present study is to investigate the effect of SiC-graphite reinforcement on the properties of pure copper. Copper matrix composites with SiC-graphite reinforcement (0, 2.5,5, 7.5 and 10 wt.%) were prepared by stir casting process. Microstructure, phase, density, hardness and wear rate of prepared samples have been investigated. X-ray diffraction revealed that there is no intermediate phase formation between the reinforcement and matrix as a result of interfacial bonding between them. Microstructure study shows the uniform distribution of SiC-graphite particles in the Cu-matrix. Mechanical and corrosion properties of these Cu matrix MMCs were found to be dependent on the reinforcement content. Hardness was found to decrease with the addition of graphite due to its soft nature. Composite containing 5 wt.% reinforcement has shown minimum wear rate and maximum corrosion resistance. It is expected that the present composite will be useful for thermal management applications especially in heat exchangers.

Self-assembled triangular graphene nanostructures: Evidence of dual electronic response

Structural and electronic properties of bilayer graphene films and nanostructures obtained through the graphitization of SiC(0001) were investigated in this work using scanning tunneling microscopy and spectroscopy. We report on the observation of triangular nanostructures which result from extended stacking faults in the SiC substrate and their effects on graphene layers that are formed on top of them. Spectroscopic measurements revealed distinct electronic responses as a function of the local hydrogen intercalation. Spectroscopic signatures ranging from single- to double-layer graphene, as well as intermediate states were observed as a consequence of the (in)complete hydrogen intercalation process. High resolution topographic scanning tunneling microscopy images at resonant bias voltages inside triangular nanostructures reveal that the bottom layer of the bilayer graphene film is still bonded to the substrate. Therefore, the triangular nanostructures present edges and facets with the coexistence of carbon atoms in sp3 and sp2 hybridizations. Using atomistic calculations we have modeled the local density of states of these objects reproducing their electronic response. The generation of regions with distinct electronic responses is potentially interesting for high-density data storage with hidden bit capabilities.

Tribological characterisation in dry sliding conditions of compocasted hybrid A356/SiCp/Grp composites with graphite macroparticles

The influence of SiC microparticles reinforcement and graphite macroparticles addition on the friction and wear characteristics of A356 Al-Si alloys, produced by compocasting, has been assessed using a pin-on-disc tribometer. The incorporation of SiC reinforcement increased the coefficient of friction and reduced the wear. The addition of graphite did not reduce the coefficient of friction. In the case of hybrid composite with 1 wt% graphite, wear was more or less the same as with SiC reinforced composite, while in the case of hybrid composite with 3 wt% graphite, wear was further reduced. On the worn surfaces of hybrid composites, the presence of the discontinuous mixed surface layer, containing graphite and transferred counter-body material, was noticed.

Si beam-assisted graphitization of SiC (0001)

We have performed a study of thermal graphitization of SiC (0001) surface in the high-purity molecular beam of Si atoms obtained from a controllable source. With the aid of Si beam, we have been able to achieve the semi-equilibrium reaction conditions and to control the growth rate of graphene film freely until complete stop of the graphitization, at the test temperature of 1350 °C. Samples treated in Si beam are characterized by larger and homogeneous areas of graphene having uniform thickness, and much improved crystallographic ordering. This is attributed mainly to the improved buffer layer structure. The buffer layer shows neither disordered regions, nor point defects, which are prevalent in UHV-annealed samples. Significantly smaller concentrations of other surface defects are also observed. The used approach is a promising alternative to more commonly used buffer gas graphitization methods. Apart from the precise control for process parameters and very high process purity, it also allows for a co-deposition of other atoms at the growth stage.