Synthesis of carbon-encapsulated metal nanoparticles by a detonation method

1. Synthesis of carbon-encapsulated metal nanoparticles by a detonation method Pengwan Chen*, Hao Yin State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, Beijing, 100081, China *E-mail address:pwchen@bit.edu.cn

2. Introduction • Carbon-based materials play a major role in today’s science and technology. • In the following years, carbon encapsulated metal nanoparticles have become an active research area around the world due to their possibility for catalysts, magnetic resonance imaging, high density magnetic data storage, magnetic inks, electrode in batteries, photo-catalytic activity. • Moreover, the carbon coatings can endow these magnetic particles with the biocompatibility and stability in many organic and inorganic media.

3. Introduction • Over the past decades, many approaches have been developed to prepare nanoparticles, mainly including modified arc discharge, CVD, ion-beam co-sputtering, RF plasma technique, high-temperature heat treatment, the laser vaporization technique, high pressure synthesis, combustion and detonation. • Detonation technology is an effective, convenient and cost-efficient technology for producing diamond, carbon nanotube, graphene and carbon encapsulated metal nanoparticles according to its unique characteristics: quickness, self-heating and easy fabrication of carbon clusters.

4. .The starting reactants were prepared in the form of a 20mm in diameter cylindrical grain made of the mixture of fine uniform powders and the cold pressed under pressure of 11 MPa (110 bar). Experimental conditions • RDX was used as explosive. • Iron tristearate can provide both iron catalyst and carbon sources for assembling carbon-encapsulated iron nanoparticles. • Cobalt/Iron/ Nickel powders were used as catalytic and nano-metal particles sources. • Dicyandiamide(DCD) provides additional carbon source for shell assembling. • The starting reactants were made of the mixture of fine uniform powders in the form a cylindrical grain. • The detonation of explosive was initiated by a non-electric detonator or heating . • XRD, HRTEM, Raman, magnetic properties measured

5. Apparatus Explosion vessel Stainless steel pressure vessel

6. Li Xiaojie. Composites science and technology 2009.

8. Results and discussion

9. Raman Investigation

10. HRTEM JEM-2010 Initiated by non-electric detonator

13. 3:1

14. Mr/Ms<0.25 show superparamagnetism behavior

15. Initiated by heating

16. 3:1

19. RDX+DCD+Co RDX+DCD+Ni

20. Conclusion • The carbon-encapsulated metal nano-particles with a well core–shell structure were produced by the detonation method. • The results show that the diameters of nano-particles are 5-100nm, and metal/metal carbide cores and graphitic/amorphous shells are formed in these nano-particles. The thickness of the carbon shells are 2-10nm with 4-30 layers. The spacing of the carbon shell is about 0.34nm, which is approximately equal to the spacing of graphite layers. • It is found that carbon-encapsulated iron nano-particles can be formed while RDX/ precursor mass ration is from 1:1 to 3:1 and exhibits certain superparamagnetic behavior.

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