HRTEM and Raman characterisation of the onion-like carbon synthesised by annealing detonation nanodiamond at lower temperature and vacuum

Abstract

Onion-like carbon (OLC) was synthesised by annealing detonation nanodiamond for 1.5 h at temperatures from 500 to 1400 C and at a vacuum of 1 Pa. The results showed that the nanodiamond was transformed into the amorphous carbon (a-C) at first and then the a-C was transformed into the OLC gradually with the increase in annealing temperature. Moreover, at the annealing temperature of 600 C, the nanodiamond started transforming into a-C from the edge of the nanodiamond particle (1 1 1) crystal plane. At the annealing temperature of 750 C, the nanodiamond was transformed into the a-C completely. At the annealing temperature of 850 C, the a-C began transforming into the OLC at the edge area. At the annealing temperature of 1000 C, the OLC particle with a size smaller than 5 nm was synthesised. However, in the centre of the OLC particle, untransformed a-C coexisted. At the annealing temperature of 1100 C, the microstructure of the OLC particle with a size smaller than 5 nm became optimised. At the annealing temperature of 1200 C, the OLC particle with a size larger than 5 nm was fabricated. There was also untransformed a-C coexisting in the centre of the OLC particle. At the annealing temperature of 1350 C, all the a-C was transformed into the OLC. The average size of the OLC was approximately 5 nm, which was the same as that of the nanodiamond. The layers of the OLC were varied from several to 12.

Vacuum or flowing argon: What is the best synthesis atmosphere for nanodiamond-derived carbon onions for supercapacitor electrodes?

“…It was shown that nanodiamond first transforms into amorphous carbon before graphitization from the outside to the inside starts. Additionally, particle-particle connections are established and an amorphous carbon phase at the interface between graphitic shells and diamond core exists [70]. Therefore, besides a non-Raman visible diamond core and the actual carbon onion material, we have to consider amorphous carbon when fitting the spectra.…”

Carbon Nano‐Onions: A Review of Recent Progress in Synthesis and Applications

“…[56] Briefly, the graphitization process of NDs starts at 600°C on the surface and progressively extends into the bulk of the particle. [57] The transformation of sp 3 to sp 2 starts by amorphous carbon, which graphitizes at temperatures between 900 and 1,100°C. [58] The complete transformation of the diamond core occurs at temperatures above 1,600°C.…”

Understanding structure and porosity of nanodiamond-derived carbon onions

“…Studies on the synthesis of carbon onions from nanodiamonds indicate that the sp 3 -to-sp 2 transformation starts at around 600°C by forming amorphous carbon [35]. At temperatures between 900 and 1100°C, this amorphous layer progressively graphitizes and continuing sp 3 -to-sp 2 transformation protrudes from the outside to the core of the particles [36].…”