Graphite powder is a very versatile material that can be used for many purposes. For instance, it can be used as a lubricant and magnetorheological elastomer.
Graphene nanoflakes are small, flake-like particles of graphite powder. Their average length is five nanometers (nm), ranging from 100 to 200 nm. They can be produced by various solvents, including ionic liquids, surfactants, and hummers. They are used to make transparent conductive electrodes. They are also used in the manufacturing of magnetic elastomers, batteries, brake linings, and crucibles. They have excellent thermal conductivity. These properties make graphene highly interesting for applications in high-performance nanoelectronics and sensors.
The synthesis of graphene involves two methods. One method is epitaxial growth, which produces a high-crystalline graphene film. The other method is chemical vapor deposition. These processes have different advantages and disadvantages.
Epitaxial growth is a costly process. Its yield varies by the thickness of the substrate and the quality of the precursors. However, the process is scalable. A recent study demonstrated the transfer printing of macroscopic graphene patterns from patterned HOPG.
The electrochemical method of producing graphene is simple and environmentally friendly. It does not require hazardous oxidizing materials and can be scaled up easily. It also produces high-quality graphene. The three main advantages of this method are listed in Table 1.
The process of exfoliation is based on a weak Van der Waals attraction. In order to break the attraction, an external force of 300 nN/mm2 is required. It is also important to keep the graphite layers stable in the medium. A good solvent is important. These solvents should minimize interfacial tension and increase graphene concentration. In addition, ionic liquids can be used as a stable solvent for the graphene. They can be used for green chemistry.
The electronic properties of graphene are not fully investigated. The reason for this is the difficulty in transfer. The electronic properties of graphene are also limited by the large system sizes. Some researchers have conducted experiments using molecular dynamics to investigate the microscopic origin of friction. The results are promising.
In addition to the above-mentioned production methods, there are other ways to prepare graphene. Graphene flakes can be made by mechanical exfoliation. It is the cheapest method to produce high-quality graphene. The process is done by a cold wall system, which never heats the walls. This produces a defect-free graphene.
Graphite is one of the main components of magnetorheological elastomers (MREs). Various studies have been performed to improve the mechanical and electrical properties of MREs. Graphite is known to enhance the electrical conductivity, increase the initial mechanical properties, and provide a better structure to MREs.
MREs are mainly fabricated from a polymer matrix. The types of matrix materials used include silicone, natural rubber, and synthetic elastomers. Carbonyl iron particles are usually used as magnetic filler particles. In some cases, these particles are mixed with graphite or graphene particles. These additives can also improve the rheological performance of MR materials.
Some researchers have developed a coating on the surface of the magnetic particles to improve the interaction between the particles and the matrix medium. This can increase the sedimentation stability of the material. The main deformations of MREs with graphite microparticles are determined by the intensity of the magnetic field. It is important to note that the magnitude of the magnetic field will change the rheological and electric conductivity of the MRE.
Some of the additives can increase the plasticity of the matrix. In addition to that, these additives can average the distribution of internal stresses in the material. Using silicone oil in the SR matrix can help to create a more homogeneous distribution of CIPs. This can increase the gap between the matrix molecules and reduce the conglutination of the molecules. This results in a better bonding of the CIPs with the rubber matrix.
In order to produce a more pronounced and dynamic mechanical performance of MR elastomers, graphite particles were introduced into the conventional MREs. In addition to this, carbon black was added to the elastomers. Lastly, a graphite/room temperature vulcanized silicon rubber (Gr-MRE) was fabricated. The properties of the GR/RTV-MRE were analyzed under different magnetic flux densities. The piezoresistive coefficient was also studied.
The dynamic shear modulus of the isotropic MR elastomers was investigated. This research demonstrated that the storage modulus changes in over 50 percent with the magnetic flux density. Compared to MRE, the relative magnetorheology of the isotropic MR elastomers decreased. In some cases, the zero-field modulus was higher for the hard matrix materials.
Lithium-graphite intercalation compounds
Various studies have been carried out to explore the intercalation of alkali metal ions into graphite. However, the mechanisms of insertion are still not well understood.
A new model of lithium intercalation into graphite is proposed in this work. This model is based on the Daumas-Herold intercalation model. In this model, Li+ ions are inserted into graphite through a series of intermediate stages. The driving force for insertion depends on the mutual distribution of Li atoms. In addition, the model has been predicted for a novel carbon.
This model is in accordance with the experimental results. The electronic structures of pristine graphites and AB-stacked graphites are shown. The formation energy of a Li-GIC can be estimated from this model. The structure of a graphite electrode was also studied. It was found that a LiC6 compound has a simple hexagonal planar structure. This structure was confirmed by spectroscopic observations.
The electronic structures of a LiC12 compound show a new ab initio self-consistent-field energy-band structure. The new structure is related to the polarization of the valence orbitals of the graphite atoms. It is also in agreement with the observation of local dislocations in an aged graphite electrode. The crystal structure is a close reflection of the hexagonal mesh of C6. The ionic radius of the Na+ ions in the graphite is large. The ionization energy of the alkali metals decreases with increasing the number of atoms. This favors the electrostatic coupling between the positive ion and the negatively charged graphene.
In this study, the effect of lithium concentration on the free energy of intercalation was investigated in the graphite structure of a randomly oriented high graphene (ROHG). The effect of Li on the OCV was modeled in a half-cell. The theoretical model was based on the Monte Carlo approach. The enthalpy contribution to the free energy of intercalation was also calculated. This was done in an UB3LYP/6-311G(d) level of theory. The interlayer binding energy and the van der Waals interactions in the graphite lattice are also in good agreement with the experiment.
This study demonstrates that entropy is associated with the free energy of lithium intercalation in the structure of an experimental carbon. The effects of different lithium compounds on the enthalpy are also seen.
Graphene powder can be used as a lubricant
Graphene powder is one of the most promising lubricants. It enjoys exceptional chemical stability. Graphene can be used as a solid lubricant and as a lubricant additive in conventional lubricants. It has unique tribological properties and has potential applications in the field of nano-composite materials. Several studies have been conducted on the anti-wear and antifriction properties of graphene.
Graphene has superior tribological properties to graphite oxide. It can be used as an additive in lubricants to improve lubrication and antiwear performance. Graphene particles can be produced by supercritical CO2 stripping of graphite. They are stable, crystalline, and do not require continuous heating.
Chemical modification of graphene can also improve its dispersibility. The modification reduces the out-of-plane flexibility of the molecules. The resulting reduction in adhesive force results in a reduction in the friction coefficient. This is achieved through an increased normal stiffness and bending stiffness.
The tribological behavior of graphene on steel has been studied at micro-scale. However, recent macro-scale tribological investigations have opened up new avenues for graphene use. These experiments confirmed previous predictions about the tribological properties of graphene.
In addition to reducing wear, graphene can improve the lubrication of steel. Graphene platelets can be chemically modified to decrease the adhesive force between steel and lubricant. These plates can then be uniformly dispersed in the base oil. The additive concentration is an important factor in reducing the friction and wear of a lubricant. It has been found that 0.075 wt.% of chemically modified graphene provides improved load-carrying capacity. Moreover, it reduced the wear scar diameter of the steel balls by 33%.
In a study on the lubrication performance of graphene in water, Xie et al. reported that the average wear scar diameter decreased with an increase in the graphene concentration. They also reported that the coefficient of friction (COF) in water is lower than that of the same graphite at room temperature. The friction coefficient is relatively stable when less than 0.15 wt.% is added to a lubricant.
Despite its low friction, graphite does not provide protection from corrosion. Unlike graphene, graphite does not produce a good thin film coverage.
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