Graphene production with stirred media mills
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Graphene production with stirred media mills C. Knieke, A. Berger, W. Peukert Institute of Particle Technology, Friedrich-Alexander University Erlangen-Nuremberg Cauerstr. 4, 91058 Erlangen, Germany
Introduction Since the discovery of stable graphene sheets by Novoselov und Geim in 2004 [1] the one atom thick carbon material has been attracted great interest because of its outstanding physical, mechanical and chemical properties [2]. Although there had been intensive research to find new ways in the preparation of single-layer graphene sheets in the last few years, especially the large-scale production of graphene still remains challenging. In this paper we present a new approach, which allows the high-yield production of graphene sheets in a simple stirred media milling process. Under mild milling conditions single- and multilayer graphene sheets have been successfully produced from commercial graphite powder in a liquid medium. Stirred media milling is known as a scalable technique for the production of highly concentrated nanoparticle suspensions by real breakage of the particles down to a range of 10 nm [3].
Experimental Synthetic graphite (GS 6, RMC Remacon, Bad Säckingen, Germany) with a mean particle size of 4 µm was used in the delamination experiments. The feed material was dispersed in a surfactant-solution. The particles were stressed in a vertical laboratory stirred media mill (PE 075, Netzsch Feinmahltechnik GmbH, Selb, Germany) in batch mode. As grinding media yttria stabilized zirconia milling beads (Tosoh Corporation, Tokyo, Japan) were used.
Results and Discussion During the delamination procedure in the stirred media mill, the graphite particles were stressed between the milling beads. Shear and compressive normal forces can lead under mild milling conditions, i.e. low stress energies, to a continuous mechanical peeling of graphene sheets from the graphite surface. This selective size reduction is enabled by the strong anisotropy of the bond forces in the graphite crystal. To reach delamination of thin layers with high aspect ratio the weak van der Waals forces between the graphene sheets
have to be overcome by the shear forces, whereas the much stronger in-plane covalent bonds have to withstand the acting forces to prevent a fracture of the flakes. Agglomeration or restacking of the delaminated sheets could be avoided by using a surfactant, which acts as stabilizer. Hence, free-standing and highly dispersed single- and multi-layer graphene sheets can be produced in a simple wet grinding process. By means of Atomic Force Microscopy and Raman spectroscopy the presence of singlelayer graphene sheets was verified. A thickness distribution of delaminated sheets was generated by measuring 300 flakes with the AFM technique. The resulting thickness
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Figure 1: Thickness distribution of graph
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