Graphite Growth Research Articles

Ultrafast Growth of Highly Conductive Graphene Films by a Single Subsecond Pulse of Microwave.

Currently, graphene films are expected to achieve real applications in various fields. However, the conventional synthesis methods still have intrinsic limitations, especially not being applicable on a surface with high curvature. Herein, an ultrafast synthesis method was developed for graphene and turbostratic graphite growth by a single subsecond pulse of microwaves generated by a household magnetron. We succeeded in growing high-quality around 10-layered turbostratic graphite in 0.16 s directly on the surface of an atomic force microscope probe and maintaining a tip curvature radius of less than 30 nm. The thus-produced probes showed high conductivity and tip durability. Moreover, turbostratic graphite film was also demonstrated to grow on the surface of dielectric Si flat substrates in a full coverage. Graphene can also grow on metallic Ni tips by this method. Our microwave ultrafast method can be used to grow high-quality graphene in a facile, efficient, and economical way.

Graphite microcrystals growth in naturally graphitized coal from Hunan, China

The transformation of coal to graphite is a process through which carbon atoms are arranged from amorphous into a crystalline form. However, there is still no study focusing on how the graphite single crystal grow up in graphitized coals during natural graphitization. Herein, a series of naturally graphitized coals were thoroughly studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to uncover the morphological and atomic structural evolution from anthracite to coaly graphite. The anthracite and meta-anthracite samples showed an amorphous carbon structure, whereas the carbon arrangement becomes more and more orderly from semi-graphite to coaly graphite as confirmed by XRD. The crushed particles of anthracite and meta-anthracite show granular and tabular texture with uneven surface under SEM. Small layered graphite flake appears from semi-graphite stage with co-occurrence of dense coal particles, HRTEM data shows the layered graphite flakes are the single graphite crystals. Almost all the dense coal particles change into layered microcrystalline graphite in the most graphitized coals (coaly graphite), and the flaky graphite microcrystals always show up as aggregates. The results will benefit the future applications of the naturally graphitized coals.

Influence of Solute Elements on Graphite Growth During Iron Solidification

Influence of Solute Elements on Graphite Growth During Iron Solidification

Successive steps of growth of compacted graphite in cast irons

Successive steps of growth of compacted graphite in cast irons

Growth mechanisms of vermicular graphite in cast iron

To steadily produce high-quality vermicular graphite cast iron (VGI), it is essential to have a deep understanding of the growth mechanism of vermicular graphite. The morphology and microstructure of graphite in VGI were studied using various techniques, including both experimental and theoretical methods. An abnormal graphite structure with an anomalous layer distance of 6.60 Å was observed by transmission electron microscopy (TEM) imaging, which is approximately two times larger than the normal structure (3.40 Å). The theoretical simulations of possible trace elements added (approximately 34 different elements) to the graphite basal planes were studied and analyzed individually to understand the observed phenomenon and their effects on graphite growth. The theoretical calculations (6.56 Å) show good agreement with the experimental results (6.60 Å), which proves that the lattice anomaly is caused by Mg. The abnormal graphite was believed to be the remains of the transition state during the growth of graphite. Based on the investigation, a mechanism is proposed to describe the influence of Mg during the growth process of vermicular graphite.

Experimental Modeling of Ankerite–Pyrite Interaction under Lithospheric Mantle P–T Parameters: Implications for Graphite Formation as a Result of Ankerite Sulfidation

Experimental modeling of ankerite–pyrite interaction was carried out on a multi-anvil high-pressure apparatus of a “split sphere” type (6.3 GPa, 1050–1550 °C, 20–60 h). At T ≤ 1250 °C, the formation of pyrrhotite, dolomite, magnesite, and metastable graphite was established. At higher temperatures, the generation of two immiscible melts (carbonate and sulfide ones), as well as graphite crystallization and diamond growth on seeds, occurred. It was established that the decrease in iron concentration in ankerite occurs by extraction of iron by sulfide and leads to the formation of pyrrhotite or sulfide melt, with corresponding ankerite breakdown into dolomite and magnesite. Further redox interaction of Ca,Mg,Fe carbonates with pyrrhotite (or between carbonate and sulfide melts) results in the carbonate reduction to C0 and metastable graphite formation (±diamond growth on seeds). It was established that the ankerite–pyrite interaction, which can occur in a downgoing slab, involves ankerite sulfidation that triggers further graphite-forming redox reactions and can be one of the scenarios of the elemental carbon formation under subduction settings.

Densifying (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C high‐entropy ceramics by two‐step pressureless sintering

AbstractA pressureless two‐step sintering method was used to densify high‐entropy carbide (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C, with high density and good mechanical performance. The material was heated up to 2200°C and subsequently soaked at 1900°C for 2–8 h with the incorporation of 2–4 wt.% phenolic resin. With increasing resin content, the large‐sized pores disappeared, and the average grain size decreased. However, with increased holding time from 2 to 8 h, the average grain and pore size did not change significantly, the density increased up to 96.2%, and evident grain growth of graphite was observed. The mechanical properties of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C with 4 wt.% phenolic resin addition and 8 h soaking at 1900°C were measured as follows: flexural strength 361±28 MPa, Vickers hardness 16.0±0.3 GPa, and elastic modulus 426±2 GPa.

Catalytic graphitization of single-crystal diamond

Diamond and graphene are carbon allotropes with starkly different physical characteristics. Their combination into graphene-on-diamond heterostructures could benefit from the complementary properties of both components. Graphitization of single-crystalline diamond surfaces is a promising synthesis route, but a clear understanding of the growth of graphene or graphite from solid carbon sources is so far missing. Using aberration-corrected transmission electron microscopy, Raman spectroscopy, and electrical transport measurements, we provide detailed insight in the mechanisms of structural changes of nickel-catalyzed graphitization of diamond. We propose competing atomistic processes occurring at contact sites of diamond and Ni, depending on diamond surface terminations. One-dimensional etching process dominates on (111) diamond surfaces that remain almost atomically flat during graphitization. Two-dimensional etching of (110) and (100) diamond surfaces results in Ni drilling into the diamond substrate. Our findings also provide evidence on the reaction rates of the catalysis. The most reactive diamond surface in the (100) orientation is covered with the largest amount of well-crystallized graphite, whereas the (111) surface shows the highest stability against catalytic etching. In the latter case, only a thin disordered graphite layer is formed, yielding the lowest electric conductance. By clarifying these etching mechanisms, our results can improve the synthesis of graphene-on-diamond heterostructures.

Bifilm Inclusions in High Alloyed Cast Iron.

Continuous improvement in the quality of castings is especially important since a cast without defects is a more competitive product due to its longer lifecycle and cheaper operation. Producing quality castings requires comprehensive knowledge of their production, crystallization process, and chemical composition. The crystallization of alloyed ductile iron (without the addition of magnesium) with oxide bifilm inclusions is discussed. These inclusions reduce the quality of the castings, but they are a catalyst for the growth of spheroidal graphite that crystallizes in their vicinity. The research was carried out for cast iron with a highly hyper-eutectic composition. Scanning electron microscopy and EDS analysis were used in the research. A detailed analysis of the chemical composition was also carried out based on the spectrometric method, weight method, etc. Based on the obtained results, a model of spheroidal graphite crystallization near bifilm inclusions was proposed. The surface of the analyzed graphite particles was smooth, which suggests a primary crystallization process. The phenomenon of simple graphite and bifilm segregation towards the heat center of the castings was also documented.

When is a Cast Iron Eutectic?

The literature often mentions that cast irons that appear eutectic by thermal analysis are hypereutectic if one refers to the equilibrium phase diagram. This is a source of ambiguity and confusion. The analysis of experimental results on hypereutectic cast irons has previously shown that taking into account the solidification path during the primary precipitation of graphite makes it possible to differentiate slightly hypereutectic cast irons from very hypereutectic cast irons. This approach is applied here to a cast iron which appears eutectic when inoculated and hypoeutectic when not. Thus, it is confirmed that graphite growth only becomes effective when a minimal undercooling is reached, independently of inoculation. However, only an alloy with a carbon equivalent at the boundary between mildly and strongly hypereutectic alloys and which is inoculated can appear eutectic by thermal analysis.

Effects of Cu on the Morphology and Growth Mode of Graphite in Compacted Graphite Iron

In this article, Cu is found to have a great influence on the graphite morphology and growth mode in compacted graphite iron (CGI). Metallographic pictures show that the number of vermicular graphite of the surface of CGI casting is significantly higher than that of the core, and there is more spheroidal graphite in the core of casting. In addition, a special form of graphite, which is defined as distorted graphite appears in the matrix. From the EPMA results, it can be concluded that the segregation of Cu promotes the distortion of graphite, and part of distorted graphite is transformed into vermicular graphite under the action of vermicular elements (Mg, La, and Ce). The increase in the number of spheroidal graphite improves the strength of casting, but it reduces the thermal conductivity.

Graphite Dendrites in Cast Iron and Their Fundamental Role in the Control of Morphology to Obtain Aero-Eutectic Graphite

This work analyzes the growth of graphite in the eutectic system of gray cast iron, focusing on laminar type A and undercooled type D morphology, and a modified morphology, such as vermicular or compact graphite. The objective of the study is to find an optimal graphite structure, from which a new class of lightweight materials results that has been called aero-eutectic graphite (AEG). The method to obtain AEG consists of dissolving the gray iron ferrous matrix by means of a chemical attack. From experiences of unidirectional solidification, it has been found that laminar graphite grows in a non-faceted way, coupled to austenite, while in vermicular the growth is through foliated dendrites. This characteristic allows vermicular graphite to have a higher specific intrinsic surface area. According to the Brunauer-Emmett-Teller (BET) analysis, the surface of the vermicular was 106.27 m2 g−1, while those corresponding to type A and D were 83.390 m2 g−1 and 89.670 m2 g−1, respectively. AEG with graphite type D was used as a cathode in Li-O2 batteries with satisfactory results, reaching more than 70 charge and discharge cycles, and 150 cycles at this time and still cycling, using Ru(bpy)3(ClO4)2 as redox mediator.

Desiccation drives the growth of crystalline graphite in the cold mantle wedge: Evidence from the Achankovil Suture Zone, southern India

Carbon is constantly released from subducting slabs back to the atmosphere in the form of gases such as CO2 and CH4. This constitutes a source of greenhouse gases that can regulate atmospheric chemistry over geological timescales. However, the carbon carried by hydrothermal fluids released from slabs may be locked along their ascending paths for variably long periods of time. The processes involved in this chromatographic pathway remain unclear. Here we report the co‐occurrence of graphite and phlogopite in highly metasomatized rocks derived from the mantle wedge of a Late Neoproterozoic subduction zone in the Achankovil Suture Zone in southern India. Petrographic, isotopic, and fluid inclusion evidence suggests these rocks formed in an environment soaked in C‐bearing fluids derived from the subducting slabs. We propose that desiccation of slab‐derived fluids in contact with a dry mantle wedge is the main driver for this phenomenon, while redox change only plays a marginal role. Our work provides a perspective on the diversity of non‐traditional carbon graphitization pathways in the lithosphere. It shows that refractory forms of elemental carbon of abiotic origin may be ubiquitous in the cold mantle wedge.

An Integrated Multi-scale Model for Graphite Growth Mechanism in Industrial Cast Iron

An Integrated Multi-scale Model for Graphite Growth Mechanism in Industrial Cast Iron

Growth of nanocrystalline graphite on sapphire by implantation of large carbon clusters from SNICS source

Nano-crystalline graphite (NCG) structures on insulating layers have been grown via implantation of kilo-electron-volt (keV) energetic carbon clusters (Cn) on sapphire (Al2O3) and post-implantation thermal annealing conditions. The clusters were produced using a source of negative ion using Cesium sputtering (SNICS) with graphite and carbon nanotubes (CNT) as cathode materials. The Graphite cathode exhibited high currents for most of the cluster sizes. However, the CNT cathodes showed higher yields for relative heavy clusters (n = 16, 18, and 20). Also, carbon clusters as large as n ~ 56 were observed from the SNICS source. The Sapphire substrates were implanted with carbon cluster (Cn, n = 18) ions at 11 keV (~611 eV per carbon atom) with fluences of 1.1 × 1015 C18-clusters/cm2 (~2 × 1016 carbon atoms/cm2). Ion impact craters and surface build-ups were observed. Further, we have studied the carbon bonding characteristics by Raman Spectroscopy (RS) on as-implanted and annealed implanted samples. We have observed well-developed disorder (D), graphite (G), and 2D peaks from the optimized samples, indicating the formation of nano-crystalline graphite (NCG) structures on the surface. The ratio of D and G peaks in the RS spectra suggests that the nano-crystalline cluster diameter or in-plane correlation length is about 10–16.5 nm. The Crystal size approaches a maximum value with increasing post-implantation thermal annealing temperature. We have studied the growth of NCG by X-ray Photoelectron Spectroscopy (XPS) for the chemical bonding and distribution. The average sizes of crystalline NCGs were also estimated using Grazing Angle X-ray Diffraction (GAXRD) Spectrometry. The surface morphology of the implanted samples was investigated using Atomic Force Microscopy (AFM).

Epitaxial synthesis of graphene on 4H-SiC by microwave plasma chemical vapor deposition

Epitaxial graphene (EG) on semi-insulating SiC prepared by a thermal decomposition method is the most promising strategy for graphene application in large-scale integrated circuits due to compatibility with current semiconductor processes. In this study, high-quality few-layer graphene (FLG) was epitaxially grown on the semi-insulating on-axis 4H-SiC by microwave plasma chemical vapor deposition (MPCVD). Both sides of the SiC substrate were etched with H2 plasma at ∼1000 °C to promote the nucleation and the growth of graphite before epitaxial growth. The surface morphology and properties of EG on SiC (0001) were measured by energy-dispersive x-ray (EDX), x-ray photoelectron spectrogram (XPS), and atomic force microscope (AFM). The qualities of EG grown on the two surfaces of SiC at various temperatures were checked by Raman spectroscopy. Furthermore, the EG growth was controlled by the effect of Ar plasma in the MPCVD and the few-layer (1–3 layers) high-quality EG films were formed on SiC (000). The room temperature Hall mobility of EGs up to 2790 cm2 V−1 s−1 on SiC(000) was realized.

Revisiting Thermal Analysis of Hypereutectic Spheroidal Graphite Cast Irons

This study deals with early solidification of hypereutectic cast irons at varying carbon content and roughly constant alloying additions. Thermal analysis of such alloys shows that the start of the eutectic reaction occurs at a nearly constant temperature for mildly hypereutectic compositions. A similar trend is observed with more hypereutectic compositions but at a higher starting temperature. This jump in the start temperature of the eutectic reaction has not been previously evidenced and is here addressed by considering primary precipitation of graphite. Limiting the analysis to spheroidal graphite cast irons, it is demonstrated that simulation of primary graphite precipitation based on a 2D nucleation/lateral growth model allows substantiating the experimental distinction found between mildly and highly hypereutectic cast irons. This modeling explains that highly hypereutectic alloys start eutectic solidification in a limited temperature range that is nearly insensitive to the initial carbon equivalent of the alloy and to inoculation. This approach also suggests that the start of the eutectic solidification of mildly hypereutectic cast irons is shifted to lower temperature until growth of austenite enriches the liquid in carbon to such an extent that growth of graphite becomes possible.

Fast, wafer-scale growth of a nanometer-thick graphite film on Ni foil and its structural analysis

The growth of graphite on polycrystalline Ni by chemical vapor deposition (CVD) and the microstructural relation of the graphitic films and the metallic substrate continues to puzzle the scientific community. Here, we report the wafer-scale growth of a nanometer-thick graphite film (∼100 nm, NGF) on Ni foil via a fast-thermal CVD approach (5 min growth). Moreover, we shed light on how localized thickness variations of the NGF relate to the Ni surface topography and grain characteristics. While on a macro-scale (mm2), the NGF film looks uniform—with a few hundred highly ordered graphene layers (d0002 = 0.335 nm), when studied at the micro- and nano-scales, few-layer graphene sections can be identified. These are present at a density of 0.1%–3% areas in 100 µ m2, can be as thin as two layers, and follow an epitaxial relation with the {111} fcc-Ni planes. Throughout the 50 cm2 NGF, the sharp graphite/substrate interfaces are either composed of a couple of NiCx layers or a graphene layer. Moreover, the NGF was successfully transferred on SiO2/Si substrate by a wet chemical etching method. The as-produced NGFs could complement or offer an alternative to the mm-thick films produced from natural graphite flakes or polymer sheets.

Layer-controlled single-crystalline graphene film with stacking order via Cu-Si alloy formation.

Multilayer graphene and its stacking order provide both fundamentally intriguing properties and technological engineering applications. Several approaches to control the stacking order have been demonstrated, but a method of precisely controlling the number of layers with desired stacking sequences is still lacking. Here, we propose an approach for controlling the layer thickness and crystallographic stacking sequence of multilayer graphene films at the wafer scale via Cu-Si alloy formation using direct chemical vapour deposition. C atoms are introduced by tuning the ultra-low-limit CH4 concentration to form a SiC layer, reaching one to four graphene layers at the wafer scale after Si sublimation. The crystallographic structure of single-crystalline or uniformly oriented bilayer (AB), trilayer (ABA) and tetralayer (ABCA) graphene are determined via nano-angle-resolved photoemission spectroscopy, which agrees with theoretical calculations, Raman spectroscopy and transport measurements. The present study takes a step towards the layer-controlled growth of graphite and other two-dimensional materials.

Catalytic graphitization of coke carbon by iron: Understanding the evolution of carbon Structure, morphology and lattice fringes

The catalytic graphitization process of coke carbon with iron was investigated in the temperature range of 1100 °C–1500 °C using X-ray diffraction, scanning electron microcopy, high-resolution transmission electron microscopy (HRTEM). The evolution of micro-crystal graphite lattice fringes was carefully analyzed by image processing of the HRTEM micrographs. A strong catalytic effect of iron on graphitization was observed at temperature above 1200 °C with an obvious increase of carbon structural orders. Iron was found to promote the decrease of d002 value and increase of Lc values of the turbostratic carbon, while the d002 value of the newly formed graphitic carbon is quite below that of the commercial graphite when it just forms at 1200 °C. The melting point of iron particles were decreased due to the significant carbon dissolution into iron, leading to the melting and aggregation of iron. The lattice fringe length and the stacking number of micro-crystal graphite were found to increase obviously, while no clear change of crystal orientation was observed. This indicates that the growth of micro-crystal graphite was along its original orientation. The carbon dissolution – graphite precipitation mechanism can be used to explain the catalytic graphitization process very well.