Graphene

Abstract
A method to transform carbonate into graphene using shock-wave loading is presented in this paper. Graphene was synthesized using a detonation-driven flyer impacting mixtures of calcium carbonate and magnesium. In addition, by adding ammonium nitrate to the reaction system, nitrogen-doped graphene was formed in a one-step shock wave treatment. The recovered samples were characterized using various techniques such as transmission electron microscopy, Raman spectroscopy,
X-ray diffraction and X-ray photoelectron spectroscopy. The shock synthesis of graphene requires a balance between the growth rate of graphene and the formation rate of carbon atoms. The pressure and temperature are two important factors affecting the synthesis of graphene.

The experimental data (Figure 5) shows indeed that the 2D band can be decomposed into four peaks (2L) and provides strong evidence in favor of multi-layer graphene as the major product.
The ID/IG intensity ratio is widely used to assess the density of defects in graphite materials [29]. The D band of No.5 sample is rather uniform and near the noise level, indicating the NG remains a high crystalline quality. It is noted that the
ID/IG for all samples in this work is much larger than that of CVD-grown graphene
[15]. In addition, a weak disorder-induced feature at 1620 cm-1 can also be observed in Raman spectra of shock-synthesized samples. Based on these results, we can conclude that shock loading can not produce pristine graphene, but graphene with many defects due to its extreme loading process. Shock wave action generates high temperature, high pressure and high strain rate. This extremely nonequilibrium
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process may induce considerable defects in shock-synthesized products. This has also been verified in shock synthesized diamond and graphite [32].
Table 2. Raman data of shock-synthesized graphene and NG.
No ID/IG I2D/IG 2D-FWHM(cm-1)
2 0.6 1.43 41
3 0.5 1.14 54
4 0.35 1 51
5 0.16 1.39 45
1000 1500 2000 2500 3000
2D
G
5

In contrast, high pressure will reduce the formation rate of carbon atoms and the carbon deposition efficiency. In the No. 3 test with a high pressure of 32 GPa and a relatively low shock temperature of 2968 K, only multi-layer graphene was formed without other carbon phases. Appropriate high shock pressures and low shock temperatures are favorable for the synthesis of fewer layer graphene.
4. Conclusion
In this work, a facile shock wave treatment for the synthesis of graphene and NG was developed which provides a simple, energy-saving and novel synthesis route. The shock synthesized graphene/multi-layer graphene and NG were evidenced by TEM,
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Raman, XRD, and XPS measurements. The shock pressure and temperature are two important factors in the synthesis of graphene by affecting the formation rate of carbon.
When the shock pressure and temperature are too low, the shock waves can not generate sufficient energy to produce carbon phase. An increase of pressure and temperature was observed to be favorable for the synthesis of carbon phases.
Appropriate high pressure and low temperature are favorable for the synthesis of