The tests at the ESRF have demonstrated the unique properties of a new material,
the Aggregated Diamond Nanorods (ADNR). Synthesized recently by a team from
the University of Bayreuth, this material has been identified as the hardest
and least compressible material in the world. It could potentially replace diamonds
in industry.
Nanorods of many materials are proving very successful, and their properties
often exceed that of nanotubes, making them excellent candidates for industrial
applications. Theoretical calculations predicted that diamond nanorods too would
have properties superior to that of carbon nanotubes. But, so far, nobody had
been able to actually synthesize diamond nanorods. This is no longer true. A
team from the Bayerisches Geoinstitut (Universität Bayreuth) has just reported
the synthesis of these aggregated diamond nanorods (ADNR) and their remarkable
properties, after having measured them at the ESRF.
The Bayreuth team tested the compressibility and density of this new material.
Experiments conducted at the ESRF on the High-Pressure beamline confirmed that
the X-ray density of the ADNR material is higher than that of diamond by 0.2 –0.4%;
thus making it the densest form of carbon. Subsequent experiments, carried out
by loading a diamond anvil cell with both single crystal diamond and ADNR material,
in order to directly compare their behaviour under static load, identifies that
ADNR is also 11% less compressible than diamond.
The combination of the hardness of the ADNR and its chemical stability makes
it a potentially excellent material for machining ferrous materials. “The fact
that diamond nanorods are very dense and non-compressible has not only strengthened
theoretical predictions, but also given a positive sign that they have very interesting
unique properties“, explains Leonid Dubrovinsky, one of the authors of the paper.
At the ESRF, researchers tested the “Vickers microhardness”, using a diamond
indenter. They showed directly that the probe tip failed to make an indentation
on the surface of the ADNR. Moreover ADNR can scratch (111) faces of type-IIa
natural diamonds, thus ADNR is harder than natural diamond and consequently more
resistant against abrasion. The random arrangement of the nanorods most probably
gives rise to the increased hardness of ADNR and the reduction in C-C bond length
in outer layers of nanorods gives rise to the increased density.
Mechanical testing has also shown that under the same conditions, due to the
increased resistance against graphitisation, ADNR material is a much more effective
grinding piece than synthetic or natural diamond. This makes it a potentially
valuable material in machining ferrous metals and ceramics and, due to its nanocrystalline
nature, for precision machining and polishing.
The invention of the team (Natalia Dubrovinskaia, Leonid Dubrovinsky, and Falko
Langenhorst) describing the method of synthesis of superhard, wear resistant,
and thermally stable aggregated diamond nanorods and their applications has been
patented.
References:
(Ref. 1) Natalia Dubrovinskaia, Leonid Dubrovinsky, Wilson Crichton, Falko Langenhorst,
Asta Richter. Aggregated diamond nanorods, the densest and least compressible
form of carbon. Applied Physics Letters, 22 August 2005.
(Ref. 2) N.A. Dubrovinskaia, L.S. Dubrovinsky, F. Langenhorst. Verfahren zur
Herstellung von nanokristallinem stäbchenförmigem Diamant und Anwendungen
dafür. Deutsche Patentanmeldung: 10 2004 026 976.9, 2. Juni 2004.
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