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| Robert Clark... |
 Posted: Tue Nov 25, 2008 1:49 pm |
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Very interesting article here reporting on researchers who had
previously announced a rapid means of producing synthetic gem sized
diamonds, now believe their methods will work to produce diamonds of
arbitrary size:
Artificial diamonds - now available in extra large.
18:11 13 November 2008 by Catherine Brahic.
"A team in the US has brought the world one step closer to cheap, mass-
produced, perfect diamonds. The improvement also means there is no
theoretical limit on the size of diamonds that can be grown in the
lab.
"A team led by Russell Hemley, of the Carnegie Institute of
Washington, makes diamonds by chemical vapour deposition (CVD), where
carbon atoms in a gas are deposited on a surface to produce diamond
crystals.
"The CVD process produces rapid diamond growth, but impurities from
the gas are absorbed and the diamonds take on a brownish tint.
"These defects can be purged by a costly high-pressure, high-
temperature treatment called annealing. However, only relatively small
diamonds can be produced this way: the largest so far being a 34-carat
yellow diamond about 1 centimetre wide.
Microwaved gems
"Now Hemley and his team have got around the size limit by using
microwaves to "cook" their diamonds in a hydrogen plasma at 2200 °C
but at low pressure. Diamond size is now limited only by the size of
the microwave chamber used.
"The most exciting aspect of this new annealing process is the
unlimited size of the crystals that can be treated. The breakthrough
will allow us to push to kilocarat diamonds of high optical quality,"
says Hemley's Carnegie Institute colleague Ho-kwang Mao."
http://www.newscientist.com/article/dn16036
Original research article:
Enhanced optical properties of chemical vapor deposited single crystal
diamond by low-pressure/high-temperature annealing.
Yu-fei Meng, Chih-shiue Yan, Joseph Lai, Szczesny Krasnicki, Haiyun
Shu, Thomas Yu, Qi Liang, Ho-kwang Mao, and Russell J. Hemley
Published online before print November 12, 2008, doi: 10.1073/pnas.
0808230105
PNAS November 18, 2008 vol. 105 no. 46 17620-17625
http://www.pnas.org/content/105/46/17620 [abstract]
I had discussed the earlier research that showed they could make
synthetic diamonds of perhaps 50% greater hardness than natural
diamond. From this I suggested this should mean the strength should
also be increased by this amount and could result in ultra large
telescope mirrors, perhaps to 30 meters across, if the process could
be scaled to arbitrary sizes, as now appears likely:
Newsgroups: sci.astro, sci.physics, sci.optics, sci.materials
From: "Robert Clark" <rgregorycl... at (no spam) yahoo.com>
Date: 11 Dec 2004 12:48:10 -0800
Local: Sat, Dec 11 2004 3:48 pm
Subject: Re: Can diamond now be used for telescope mirrors?
http://groups.google.com/group/sci.astro/msg/8d2744a0b5fa94b4?hl=en
Here I suggested that use of ultra high strength microspheres or
microfibers would be able to solve the problem of finding lightweight
storage tanks for the hydrogen fuel on the VentureStar reusable launch
vehicle:
Newsgroups: sci.astro, sci.space.policy, sci.physics, sci.energy
From: Robert Clark <rgregorycl... at (no spam) yahoo.com>
Date: Fri, 5 Sep 2008 20:32:39 -0700 (PDT)
Local: Fri, Sep 5 2008 10:32 pm
Subject: High strength microspheres for hydrogen storage (was: High
strength fibers for hydrogen storage on the VentureStar.)
http://groups.google.com/group/sci.astro/msg/4bddfa864aa04056?hl=en
If the high strength material at the microscale were diamond, the
weight of the propellant tanks could be reduced by a factor of 100,
which would make feasible not only the VentureStar but also the other
competing NASA reusable launch vehicle proposals. With the newly
announced process now being able to make diamond in bulk sizes, the
tanks would not need to consist of numerous microspheres or
microfibers but a single macrosized tank. Note that such lightweight,
high strength tanks would also solve the storage problem for hydrogen
for the hydrogen economy.
Not only could the diamond be used for the propellant tanks but also
for the strength bearing structures of the entire craft since diamond
also has ultra high compressive strength as well as tensile strength.
The weight of the vehicles could conceivable be reduced by a factor of
100: instead of 200,000 lbs., only 2000 lbs.
Metallic hydrogen has been considered an ideal rocket fuel if it
could be produced because it is of high density yet it's energy
content would give it a fuel efficiency of 4 times that of the best
chemical propellants now used. Theoretical modeling also suggests it
could be stable at room temperature once produced and would be a
superconductor.
Experimental and theoretical work suggested metallic hydrogen would be
produced at pressures of 4.5 megabars, 450 GPa:
Apr 10, 2002
Hydrogen metal on the horizon.
"Scientists have long expected solid hydrogen to become a metal when
it is compressed, but so far electrical conductivity has only been
detected in liquid hydrogen. Now an experimental study of solid
hydrogen at pressures up to 320 GPa predicts that it will become
metallic at a pressure of 450 GPa – over four million times
atmospheric pressure. René LeToullec and co-workers at the CEA in
France also found that solid hydrogen becomes opaque – or ‘black’ –
under compression (P Loubeyre et al 2002 Nature 416 613)."
http://physicsworld.com/cws/article/news/5307
Attempts to create ultra high pressures in the megabar range
frequently involve using diamond anvils at the microscale. However,
natural diamond has maximum compressive strength of about 400 GPa. If
it is indeed the case that the 50% increase in hardness of the new
synthetic diamonds over natural diamond also indicates a corresponding
increase in compressive strength, this would put diamond anvils using
these synthetic diamonds within the compressive strength range
required to produce metallic hydrogen.
Bob Clark |
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