Elsevier

Ceramics International

Volume 47, Issue 15, 1 August 2021, Pages 21934-21942
Ceramics International

Synthesis of graphene nanosheets by the electrical explosion of graphite powder confined in a tube

https://doi.org/10.1016/j.ceramint.2021.04.211Get rights and content

Abstract

The electrical explosion method, due to its simplicity and high efficiency, has attracted significant attention in graphene synthesis. Generally, graphite rods and carbon fibers are used to form graphene by electrical explosions in a liquid medium. In the present work, the preparation of graphene from graphite powder in a tube by electrical explosions was proposed. A certain amount of graphite powder was confined in a tube and electrically exploded in an argon atmosphere. The diameter of the constraint tube affected the microstructure of the as-prepared products (graphite nanosheets and few-layer graphene) under the charging voltage of 14 kV. When the diameter of the constraint tube was 3 mm, explosive products were mainly composed of few-layer graphene. The collision degree between graphite powder particles and the diameter of the constraint tube were the key factors to form graphene by electrical explosions. The underlying mechanism governing the generation of graphene was carefully illustrated. Moreover, a self-designed device for electrical explosions was developed.

Introduction

Graphene has good application prospects in supercapacitors and secondary batteries [1], various film materials for heat dissipation [2], corrosion prevention [3], seawater desalination [4], and wave absorption [5], and composite materials [6,7]; thus, these promising applications have stimulated the large-scale production of graphene [8]. Synthesis methods of graphene can be divided into two categories: (i) Bottom-up approach — In this method, graphene is formed by the recombination of carbon atoms. Chemical vapor deposition, arc discharge, and epitaxial growth are the main bottom-up approaches [[9], [10], [11], [12], [13]]. Although these techniques have been commercialized, the cost of high-quality graphene is still very high. (ii) Top-down exfoliation method — In this process, graphite is exfoliated into graphene by an external force. High-quality graphene sheets can be obtained by overcoming van der wall force interactions between graphite layers [14]. The exfoliation of graphite is one of the most promising ways to synthesis graphene at an extremely low cost [15,16].

Among different exfoliation techniques, the micromechanical exfoliation of graphite by adhesive tape is an initially explored and effective approach to produce high-quality, large-area graphene sheets [[17], [18], [19]]. In addition, The sonication-assisted liquid-phase exfoliation of graphite [[20], [21], [22]], fluid dynamics-based [[23], [24], [25], [26], [27]] and electrochemical exfoliation approaches also have been adopted to produce graphene [[28], [29], [30]]. Although the above-discussed mechanical exfoliation methods are extremely promising, several issues still require constant attention. First, graphite stripping efficiency is low due to insufficient energy injection, leading to a low yield of graphene. Second, most graphite remains non-exfoliated; thus, centrifugation is required [31]. Therefore, it is necessary to find a new method to synthesize graphene simply and quickly by applying enormous instantaneous energy to graphite.

Electrical wire explosion can apply enormous instantaneous energy to a conductor for a few microseconds, and it is a promising low-cost method to produce various nanometer powders because of its simplicity and efficiency. Electrical wire explosion is generally carried out in a vacuum or a medium. A strong current generated by a pulse capacitor passes through a wire, and the wire melts due to Joule heating under the action of the pulsed current. The molten metal was further heated by an increase in the resistance and the current density, causing the material to evaporate [32]. After the vaporization of wire, it forms a mixture of vapor and droplets. Shock wave was generated by the expansion, The products spread out rapidly with a shock wave in the subsequent explosion. After cooling, the gas and droplets nucleate and grow to form nanoparticles and quickly disperse into the surrounding medium at a very high speed [33].

Bakina et al. [34]synthesized Al nanopowder and Al/AlN composite nanoparticles by exploding Al wires in nitrogen and argon. Lee et al. [35]prepared NiO/Ni/graphene nanocomposites by exploding nickel wires in oleic acid-containing commercial graphene. Kurlyandskaya et al. [36] produced FeNi magnetic nanoparticles by the electrical explosion of iron-nickel wires. Wada et al. [37]synthesized nanosized Ti–O particles by exploding Ti wires in distilled water. In addition, Numerous attempts have been made to prepare carbon materials (graphene, amorphous carbon, nanoclusters, composites) by electrical wire explosion. Rud et al. [38]prepared carbon nanotubes and fullerene by the electrical wire explosion and spark erosion of graphite in an organic medium. Baklar et al. [39]obtained necessary conditions for the synthesis of fullerene and nano-diamond by electrical explosions in cylindrical graphite conductors through theoretical derivations. Furthermore, fullerene [40,41] and carbon nanotubes [42,43] have been synthesized by the electrical explosion of carbon fibers. Gao et al. [44] successfully prepared a monolayer and few layers of graphene in distilled water by electrical wire explosion using high-purity graphite rods as raw materials.

However, existing research on the electrical explosion of graphite has mainly focused on filamentous conductors (graphite rods and carbon fibers), which are operated in liquid medium. Liquid media have a certain compression effect on shock waves generated by electrical explosions, enhancing the mechanical effect of shock waves on graphite materials. Compared to graphite rods and carbon fibers, graphite powder is cheap, abundant in nature, and an excellent conductor. But graphite powder is made up of a large number of discrete particles in clusters, which are not as dense as filamentous conductors, so it is difficult to explode in the liquid medium. Similar to a liquid-phase environment, the tube can also exert great pressure on the explosive product for electrical explosion in gaseous medium, making the electrical explosion of graphite powder possible.

In this study, a self-designed device for electrical explosions was developed. Graphene was successfully prepared by the electrical explosion of graphite powder confined in a tube. The obtained graphene was uniformly suspended in a argon atmosphere to form an aerosol. A certain concentration of graphene aerosol was obtained by controlling the number or frequency of electrical explosions. The effect of tube diameter on graphene formation was investigated. Finally, the formation mechanism of graphene in the constraint tube by electrical explosions was discussed.

Section snippets

Principle

On the basis of previous research on the preparation of nanometer powders by the electrical explosion of metal wires, a new method for the electrical explosion of graphite powder confined in a tube was proposed (Fig. 1). Natural graphite powder was first placed in a constraint tube made of polyethylene. One end of the tube was closed, and its other end was open. Graphene was sprayed out along the open end. A large current generated by a high-voltage system formed a breakdown channel between two

Results and discussion

The typical scanning electron microscopy (SEM) images of the synthesized products at the energy of 864 J with different constraint tube diameters are exhibited in Fig. 3. It is noticeable that two types of synthesized products were formed for different constraint tube diameters — agglomerated graphite flakes (each flake had a size of 2–20 μm) and microscopic flocculent graphite (irregular wrinkled flakes pressed on each other). The SEM images of explosive products obtained for the tube diameter

Conclusions

Few-layer graphene was produced by the electrical explosion of graphite confined in a tube at an argon medium. The diameter of the confinement tube influenced the collision degree of explosive products during electrical explosions, leading to the formation of different types of carbon structures, such as graphite nanosheets and few-layer graphene. The optimal diameter of the confinement tube to prepare few-layer graphene under the charging voltage of 14 kV was found to be 3 mm. Graphene

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

We acknowledge the financial support from the National Natural Science Foundation of China (Grant No.51765038), the National Natural Science Foundation of China (Grant No. 61866021) and Open Foundation of State Key Laboratory of Synthetical Automation for Process Industries, China(Grant No. PAL-N201808); We thank LetPub (www.letpub.com) for its linguistic assistance during the preparation of this manuscript.

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