Transformation of onion-like carbon from nanodiamond by annealing

Understanding structure and porosity of nanodiamond-derived carbon onions

“…On a single particle level, the transformation causes a significant increase in volume because of the much larger (0 0 2)-plane spacing of graphitic carbon (0.344 nm; extending radially from the center of the onions) compared to the initial CAC bonding distance of diamond (0.154 nm). This strain-buildup also results in the occurrence of d-spacings much smaller than 0.344 nm near the core of carbon onions [39]. The expansion depends on the sp 3 -to-sp 2 ratio and an increase in diameter from around 5 nm up to 10 nm has been observed experimentally by TEM [39] and calculated with reactive force field modeling [37].…”

“…Nitrogen gas sorption was performed at À196°C in the relative pressure range from 5 AE 10 À7 to 1.0 in 68 steps. The pore size distribution (PSD) between 0.56 and 37.5 nm was derived using the quenched-solid density functional theory (QSDFT) [39,40] supplied by Quantachrome assuming a slit shape pore geometry. The latter has recently been shown to be the most appropriate model for carbon onions [49].…”

“…Thus, along with the increase in particle diameter during the sp 3 -to-sp 2 transition, there is also a severe decrease in density, and consequently the SSA increases significantly [15]. Yet, at high temperatures (>1800°C), carbon onions start sintering which ultimately gives raise to the formation of tight agglomerates [39]. This process is promoted by the evolution of reactive gases originating from surface functional groups leading ultimately to the formation of large polyhedral crystals [43].…”

“…This strain-buildup also results in the occurrence of d-spacings much smaller than 0.344 nm near the core of carbon onions [39]. The expansion depends on the sp 3 -to-sp 2 ratio and an increase in diameter from around 5 nm up to 10 nm has been observed experimentally by TEM [39] and calculated with reactive force field modeling [37]. A broad overview about the mechanism of phase transition from nanodiamond to carbon onions, as well as the kinetics and the influence of the precursor, is given in Ref.…”

“…As shown by X-ray diffraction (XRD) and Raman spectroscopy studies, the degree of graphitization increases with higher temperatures due to the higher ordering of the carbon shells into graphitic carbon [17,[39][40][41]]. On a single particle level, the transformation causes a significant increase in volume because of the much larger (0 0 2)-plane spacing of graphitic carbon (0.344 nm; extending radially from the center of the onions) compared to the initial CAC bonding distance of diamond (0.154 nm).…”