Fabrication of Onion-like Carbon Using Nanodiamond by Annealing at Lower Temperature and Vacuum

Onion-like carbon （OLC） was fabricated by annealing nanodiamond at 1000 ℃ for 2 hours in low vacuum （1 Pa）. The OLC was characterized by X-ray diffraction （XRD）, high resolution transmission electron microscopy （HRTEM）, Fourier transform infrared spectroscopy （FTIR）, Raman spectroscopy and differential scanning calorimetry （DSC）. The experimental results show that the OLC exhibits similarity to the original nanodiamond particles in shape. The size of the OLC is found to be approximately 5 nm. The transformation mechanism of the OLC from nanodiamond was discussed also.

Fabrication of onion-like carbon from nanodiamond by annealing

Onion-like carbon(OLC)was synthesized by annealing nanodiamond in low vacuum of 1 Pa and at annealing temperatures from 500℃to 1400℃.The high-resolution transmission electron microscope (HRTEM)images,X-ray diffraction(XRD)and Raman spectrum of the OLC showed that there was no OLC when the annealing temperature was lower than 900℃.Moreover,the fragment amorphous carbon existed on the surfaces of the nanodiamond particles.At the annealing temperature of 900℃,the OLC particles began appearing and the size of the OLC particles was smaller than 5 nm.When the annealing temperature was increased from 900℃to 1400℃,the nanodiamond was transformed into OLC gradu- ally.At the annealing temperature of 1400℃,all the nanodiamond particles were transformed into OLC completely.The OLC exhibited similarity to the original nanodiamond particles in shape.A mechanism for the OLC synthesis by annealing was provided.The graphitization started at the surfaces of the nanodiamond particles.The formation process of the OLC includes formation of graphite fragments, connection and curvature of graphite sheets between diamond(111)planes and closure of the graphite layers.

Efficient coating fabrication of onion-like carbon nanoparticles via aerosol deposition

In this work,an onion-like carbon(OLC)nanoparticle coating with a micron-sized thickness was fabricated via aerosol deposition(AD).During the room temperature impact consolidation(RTIC),the OLC nanoparticles(5-10 nm)experienced remarkable deformation along both the perpendicular and parallel directions to the coating-substiate interface.Particle deformation,mechanical interlocking,and van der Waals forces between the OLC particles were revealed as the major regimes for coating formation.The aerosol deposition technique might open new avenues for fabricating carbonaceous nanostructures for various functional applications.

Ultrahigh hardness of carbon steel surface realized by novel solid carburizing with rapid diffusion of carbon nanostructures

In this study, a novel rapid solid carburizing process with a large diffusion depth using nano-diamonds（NDs） was conducted for low carbon steel. Changes of annealed NDs were obtained by Raman spectroscopy and transmission electron microscopy（TEM）, and the results suggested that the NDs experience a stripping process before a special solid-reaction with surface iron atoms from steel substrate. Onionlike carbon（OLC） derived from the annealed NDs provided broken graphitic ribbons as carbon sources that accelerated the rate of adsorption and diffusion. Examination of the surface layer at equilibrium using TEM and X-ray photoelectron spectroscopy（XPS） also revealed the special state of carbon, and an ultrafine mixed phase microstructure was obtained by rapid solid-phase transformation. As a result, a surface hardened layer with ultrahigh hardness and a smooth transition region were realized. We believe that these kinds of diamond or graphitic structures with high activity states have an important influence not only on adsorption and diffusion but also on this special solid-phase transformation.