Synthesis of diamond and nanostructures in cavitation
IPGP - Îlot Cuvier
Séminaires de Géochimie-frontières Géosciences
I forwarded the idea of cavitational synthesis of diamond about 40 years ago. In 1973, I published in magazine “Nature” the article entitled “Possibility of natural diamond synthesis under conditions of cavitations occurring in a fast-moving magmatic melt”. The cavitation is known to occur in fluid at abrupt changes of the internal pressure, as example at ship propeller blades, in pipelines, and pumps. The collapse of cavitational bubble is known to generate exclusively high pressures. It has been shown in the cited paper that when a fluid flows through a mantle channel feeding a kimberlite pipe, cavitation can occur. The peak pressure in a collapsing cavitational bubble, when ambient pressure is about several kilobars, easy gets at pressure sufficient for diamond synthesis. The cavitational hypothesis provides explanation to some problems faced by the theory of natural diamond formation, including predominance of volatile elements among chemical impurities in diamond, occurrence of the isotopically light diamonds, and other. It was reasonable to produce the supposed process of cavitational synthesis of diamonds experimentally. It has been implemented recently. The experimental rig was embodied as a gun steel cylinder. It comprises chambers, interconnected by Venturi-shaped channel. Benzene was employed as a working fluid. Ignition of the powder behind a piston in the chamber 1 impels the motion of the fluid. Vapor bubbles originating in the Venturi are propelled to the chamber 2 where additional external pressure was simulated. On completion of the experiment, the working fluid was drained off; suspended particles were precipitated through centrifugation. Microscopic examination, Raman spectra, and electron diffraction pattern of the synthesized particles testifies to the presence of diamond phase. The particles constitute nano-crystallite aggregates. Sizes of diamond nano-crystals are approximately 10 to 30 nm. Among the products of cavitational synthesis there are not only nano-diamonds, but as well another nano-structures, in particular, graphene and nanotubes. Thus possibility of cavitational synthesis of diamond has been experimentally confirmed.