Nucleation, growth, and graphitization of diamond nanocrystals during chlorination of carbides

Abstract

Synthesis of nano- and microcrystalline sp3-bonded carbon (diamond) with cubic and hexagonal structure by extraction of silicon from silicon carbide in chlorine-containing gases has been reported recently. This process is attractive because it can produce diamond at ambient pressure and temperatures below 1000 °C. No plasma or other high-energy activation is required, thus providing an opportunity for large-scale synthesis. However, the mechanism of diamond formation has not been previously analyzed. This work reports on the formation mechanisms of diamond as well as the transformation of diamond to graphite and onionlike carbon upon heating. Study of SiC/carbon interfaces showed that direct epitaxial growth of diamond on SiC is possible, in agreement with previous molecular-dynamics simulation. However, random nucleation of diamond from amorphous sp3-bonded carbon produced as the result of extraction of Si from SiC has also been demonstrated. It has been shown that the presence of hydrogen in the environment is not required for diamond synthesis. However, hydrogen can stabilize the nanocrystals and lead to the growth of thick diamond layers. If no hydrogen is added, diamond nanocrystals transform to graphite, forming carbon onions and other curved graphitic nanostructures.

Diamond synthesis in aluminum matrix in molten alkali-halide at ambient pressure

“…Recently, another significant study [40] was devoted to the synthesis of nanocrystalline sp 3 -bonded carbon (diamond) with cubic and hexagonal structures formed by the extraction of silicon from silicon carbide in chlorine-containing gases 1%-3.5% Cl 2 and 0%-2% H 2 -Ar. This process can also produce diamonds at ambient pressure and at temperatures below 1000°C, without plasma or other highenergy activation.…”

Tribological Behavior of Carbide-derived Carbon Coating on SiC Polycrystal against SAE52100 Steel in Moderately Humid Air

“…The cracks initiated from the subsurface and their propagation were responsible for the high wear of the commercially available graphite. The CDC coating, however, which is composed of nested fullerenic structures [8], described as carbon onions [9][10], had low friction coefficient. Plastic deformation, rather than crack initiation and propagation, were extremely useful for maintaining low wear of the coating (Figs.…”

“…Tribology of carbon (graphite, diamond, diamond-like carbon, and fullerene) nowadays covers a wide range of topics: from additive for oil and grease, solid lubricant for composites, and, in the past decades to low-and super-low-friction carbon coatings [1][2][3][4][5]. Recently, carbide-derived carbon (CDC) has received attention due to its excellent tribological performance [6][7][8][9][10][11][12]. According to the definition, CDC is a pure carbon material produced by selective extraction of metal atoms from a carbide crystal lattice by halogens, supercritical water, oxygen at a low-partial pressure, other etchants, or in vacuum [6].…”

“…CDC coating on top of carbides is found to be versatile as a solid lubricant in various environments, from dry air to high humid air [7,12] and is expected to find many related applications. It should be pointed out that the counterbody used in previous studies was silicon nitride [7][8][9][10][11][12], which is hard, chemically inert, and easily surface finished. Up to now, no attempt has been made to investigate the friction and wear of CDC coating sliding against steel which is widely used and is subject to chemical attack.…”

Nanodiamond: A high impact nanomaterial

“…Since then, numerous other methods of nanodiamond synthesis have been discovered, such as laser ablation [5], high-energy ball milling of diamond microcrystals grown at high static pressure and high-temperature (HPHT) [6], chemical vapor deposition (CVD) [7], microplasma-assisted ND formation from ethanol vapor at atmospheric pressure [8], chlorination of carbides [9], ion irradiation of graphite [10], electron irradiation of carbon onions [11], and ultrasound cavitation [12]. However, detonation synthesis remains a primary source of ND particles at a production level of tons per year.…”