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Graphene is the most amazing new material to be identified for
decades. It is the world's thinnest and strongest material, the
best conductor of
heat and electricity, combines brittleness and ductililty as well
acting as
a total barrier to gases but one which still lets water vapour
through
as if
the graphene barrier wasn't there. [links]
The current favoured method to produce graphene is to basically
pull off a single-molecule-thick layer from a block of highly
ordered graphite with a scotch-tape like material then dissolve
the substrate. This works, but is very fiddly and only produces
very tiny samples of this essentially 2-dimensional material.
Others are trying many different methods such as vapour
deposition and chemical growth on substrates but none have really
taken off.
My proposed method is to emulate the technique used to
manufacture float glass. Graphene has a very high melting point
which hasn't even been accurately determined as yet but I've seen
a figure of ~3400 K . I would find a metal with a high, but still
lower than graphene's, melting point such as tantalum ~3290 K
and heat it to around 3350 K then pour it into a tray. A tiny
quantity of melted graphite is then poured onto the liquid
substrate where it disperses into a molecule-thick layer before
slowly cooling to solidity. Bung the whole mechanism into a large
centrifuge if you like to aid the graphene's dispersal to molecular
thickness process then, when the sheets of graphene have
solidified, pick them up carefully (*HOT* - use oven gloves) and
hang'em on the clothesline to cool.
There you go. Sheets of graphene as big as you like with very
little energy cost other than the heat required to melt new
batches of graphite and to maintain the tray at a baking
temperature which is above the melting point of the metal
substrate but below that of graphene. The "half-baking"
temperature in other words.
I shall mention all bun-givers by name during my Nobel acceptance
speech.
Graphene superpermeable to water
http://www.gizmag.c...ble-to-water/21240/
Another amazing property of graphene discovered [AusCan531, Jan 31 2012]
Wikipedia
http://en.wikipedia.org/wiki/Graphene
Good description of many different methodologies being tried to manufacture graphene. [AusCan531, Jan 31 2012]
Czochralski process
http://en.wikipedia...Czochralski_process
I'd try this process to form graphene [xaviergisz, Feb 01 2012]
New use for graphene and carbon nanotube hybrid
http://www.popsci.c...tougher-than-kevlar
[AusCan531, Feb 06 2012]
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You're most likely going to need to run the process in an atmosphere of Argon, which you failed to mention. |
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Yes, but would it work? I can think of two possible
problems: |
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(a) carbon is very soluble in molten iron; what's its
solubility in other metals? Even a trace of
solubility would be very bad. |
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(b) Would the molten graphite form single-
molecule-thick layers? For instance, if you pour
oil on water, it forms relatively thick puddles
rather than a uniform thin layer, because of
surface tension. |
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//run the process in an atmosphere of Argon//.
I'm
embarrassed to say that I don't even know where the planet
Argon is located let alone how to get there. Sorry. |
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[MB] raises good questions to which I don't pretend to know
the
answers. For what it's worth, no one has ever specifically
mentioned to me in my entire lifetime that carbon is
soluble in molten tantalum. Presumably solubility of
metals reaches a saturation point, so does it make sense to
dissolve carbon into the molten substrate to the point of
insolubility then proceed as specified? Would the large
differences in Specific Gravities of carbon and the
saturated substrate be enough to separate the layers or
would one simply end up with a non-
delineated mess? How does the fact that the substrate
metal is kept below the melting point of carbon affect the
whole solubility issue anyway? (I ask a lot of questions for
a potential Nobel Laureate, I know, but that is how one
learns.) |
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Different oils have different viscoscities and I have no idea
as to the viscosity of molten carbon but I'm sure
temperature would be a large factor. The centrifuge would
also play a part in spreading the layers. A tray of 4000
degree molten metal spinning at high speed - what could go
wrong? |
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If the aforementioned difficulties are surmountable I'm
sure large sheets of graphene would be a
valuable enough commodity to make it worthwhile. There
are thousands of potential uses if a viable manufacturing
technique can be found. It is vast project but I've already
got half-vast plans. |
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My second method would be to further pursue the 'drawing'
method mentioned in the Wikipedia article by intercalating
the graphite between sheets of gold then drawing and
pounding them to extreme thinness before melting the gold
away for reuse. I've already got the graphite so would
appreciate as many donations of gold as you can all spare. |
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[pocmloc], you get first mention in Stockhom - subject to
how the gold donations come in, obviously. |
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You could have a problem with the container that is supposed to hold that molten metal. As for possibilities regarding that molten metal, you might consider rhodium. I don't know how it reacts to carbon, but rhodium is able to ignore oxygen at almost 2000 degrees Celsius. |
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Anyway, it seems to me there is probably a simpler way. If they can grow large diamonds from a "seed" in a vacuum-deposition chamber, I assume they can grow sheets of graphene that way, too. |
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Isn't rhodium extremely expensive? |
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It's not used up by this process. |
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Cool links. I like the dry ice method, very mad-scientisty. |
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Graphene mines can be established on demolished grade
schools that have been producing graphene in a systematic
way for a century or more. |
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As a welder and armchair metallurgist, I'm familiar with
innumerable practical properties of carbon (in graphite
form and others) but my scientific understanding, as is
well-known on this forum, is limited, so this may be a
dumb question. Feel free to give me a smart answer, as
long as it doesn't involve too many greek characters. |
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I know that carbon is 'sticky'*; it likes to grab onto other
elements that have open valence electrons, like iron.
That's essentially what makes it so useful to people like me
(an experienced fabricator has 101 uses for a #2 pencil
that don't involve writing). So wouldn't your proposed
liquid metal substrate have to be treated in such a way as
to eliminate every single vacancy (difficult) and also kept
100% pure (nigh impossible on a mass-production scale,
even in a clean-room) throughout the process? Every time
you bring a metal, any metal as far as I know, to a molten
state and then
cool it again, a tiny amount of molecular breakdown is
inevitable as the crystalline structure passes through
multiple configurations. |
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*[Alterother] terminology |
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I am definitely not a metallurgist of armchairs or anything
else but fools rush in and all that. I was actually very
tempted to say "Carbon?, why mention that when I'm using
graphite? Sheesh guys, you're embarrassing yourselves
here." |
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The contamination issue
you mention is basically the
same as the one [MB] raised and may well be a fatal flaw. I
do know, however, that if I use pure elemental tantalum or
rhodium or gold or whatever and pure carbon there won't
be any
'molecular
breakdown' as long as the elements can indeed be kept
from combining. |
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As to what form the carbon takes when it cools, who
knows. "Damn! Another sheet of pure diamond when I
wanted graphene." In reality, and based upon my personal
history, I would probably
just end up
with a very awkwardly shaped pencil lead and some nasty
burns. (BTW, the only relevant Greek character I know of
is
Hephaestus who was the crippled god of fire and
metalworking.) |
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I don't know how to melt graphite, but it practically
vaporizes under a welding arc. When I need to weld cast
iron and don't have any Nirod, I scribble a pencil up and
down my weldment until the root is loaded with graphite,
then use 7018 (an electrode made for welding mild steel)
and peen the hell out of the weld while it cools. The
graphite burns white on the leading edge of the puddle,
brighter than magnesium. Somehow I can't picture it just
calmly melting. |
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[8th] hit the nail on the head by pointing out the need to conduct the process in an inert atmosphere. No oxygen = no burning. |
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There's no oxygen in a weld puddle either; the solid flux
burning off of the electrode (or the flux gas introduced
by a wire-feed gun) creates an artificial atmosphere
around
the arc and puddle. If any oxygen gets in there, it means I
screwed up and will spend the next few minutes grinding it
out and starting over. Much profanity is typically involved,
as well. |
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I guess that must mean that the graphite isn't actually
combusting, but having seen it dozens of times, I'm hard
pressed to come up with a better description of what it
looks like. It definitely doesn't melt in the same way
common metals
melt. |
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Anything at temperatures over 3000K will be glowing brightly whether it's oxidising or not. |
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My idea for creating large sheets of graphene would be using the Czochralski process. |
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I'd start with a long diamond blade that is single atom thickness at the blade's edge. The blade would initially rest on a carbon substrate. A laser would be fired in a line directly below the blade's edge, heating the carbon to 5000ºK and thus melting it. The blade would slowly be lifted, and a graphene sheet would (hopefully) form on and hang from the blade. |
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At atmospheric pressure I believe carbon vaporizes,
not melts. In order to get liquid, you need to keep
it up around a hundred atmospheres, plus or minus. |
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Ignoring that, I suspect even if you could find a
liquid substrate that won't preferentially absorb the
carbon, at best you're going to end up with
unordered graphite, including some small graphene
sheets. |
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Yeah OK, you'd need to do the whole thing in 100 atmospheres of inert gas. That shouldn't be impossible since that it's less than the pressure inside a scuba tank. |
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(c) There's no such thing as "melted graphite". |
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(d) Carbon cannot exist as a liquid below 10800 kPa (about 100 atmospheres). |
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//Is tantalum expensive? // |
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Not really. The best I could find on the net after a short search is $100+/lb or $300/lb for capacitor-grade tantalum powder. You'd only need a few millimetres thickness just as long as you provide enough thermal mass to keep it from cooling. It would last indefinitely as it isn't consumed in the process. Even gold would be financially viable over the short-to-medium term due to the value of the end product. |
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As the more learned HB'ers chime in, I think it is becoming obvious that the technical difficulties outweigh the financial ones. We need to ensure that the graphene doesn't combine with the substrate after we somehow 'melt' the carbon in over 100 atmospheres pressure of an inert gas in a crucible that retains integrity at over 4000K whilst spinning rapidly in a centrifuge. If guys like [MaxwellBuchanan] and [spidermother] solve those little issues, I'll be happy to pony up $3k for 10 pounds of tantalum. |
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The engineering obstacles can all be overcome, but it is the solubility/contamination issues which worry me. I'm not saying it can't be done but p'raps it needs to be a 'shared' Nobel Prize. |
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//It would last indefinitely as it isn't consumed in the process.// Heated liquid metal evaporates just like anything else. The rate of consumption may be low, but it's non-zero. |
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Just guessing, but I'd think the simple Brownian motion of an extremely hot substrate would interfere with getting a 1-atom thick deposition layer on top of it. |
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And my guess for [Alterother] - I think that bright emission you mentioned would be like the light from a carbon arc lamp, maybe? |
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Maybe one could use glass instead of tantalum. Avoid oxidation, miscibility problems. |
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If one could use two different substances (maybe glass and tantalum) chosen such that the density of the apparently semilegendary liquid graphite was right between them, and if liquid graphite did not love itself in such a way as to form blobs in the manner of hydrophobic liquids in water (which I think it would as Max noted above), then one could have a self-assembling sandwich in which you lift the cool top layer of glass (which is several meters thick, heavy and made of salvaged cathode ray tubes, and so serves to keep the graphene below under adequate pressure) and see the vast expanse of pristine graphine lying atop the bed of tantalum, all in one enormous sentence. |
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What are the limitations of the current method
using adhesive tape? |
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I asked because the stickytape method seems
inherently good and amenable to improvement. If
it can, indeed, only produce small patches of
graphene then the
problem must be: |
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1) The graphite itself is uneven, with single-
molecule "steps" on its surface, leading to a
patchwork on the adhesive film. |
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2) The monolayer is broken during or after the
peeling and dissolving of the adhesive film or |
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3) The adhesive is not good enough, such that
only patches of graphene are pulled off the
graphite. |
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All of these ought to be soluble problems, shirley? |
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Another option would be to find a way to
reassemble large graphene sheets from small
ones, perhaps by cutting them into tiny uniform
triangles and floating them on a liquid so that
they form a continuous raft (the right surface
energies would encourage them to sit next to
eachother), then doing some chemical magic to
form new carbon-carbon bonds at the joins. |
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// like the light from a carbon arc lamp, maybe? // |
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Very much so, I think. It's not uncomfortable to view
through a shade 11 or 12 faceplate, but it's definitely
brighter than the arc itself. |
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One thing I do know is that the graphite won't 'float' on
molten steel or iron; that's why my little tricks work. By
introducing graphite to a white-iron weldment when using
a mild steel rod, it's absorbed directly into the matrix and
raises the carbon content to the requisite ratio. |
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Interestingly enough, graphite can also be used to
_prevent_ weld adhesion in other processes. For example,
if I need to extract a bolt that has sheared off deep inside
a threaded well, coating the threads with graphite will
keep spatter and slag from sticking to them when I
carefully fuse the end of an electrode to the broken bolt,
allowing me to remove it by twisting the rod with pliers. I
have no idea why this trick works, but it's never failed me. |
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Another idea for forming graphene would be to float a thin film of coronene on a substrate and then heat in the absense of oxygen. |
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All the great annotations showing up on this posting make
me happy. Not Nobel Prize happy, but happy nonetheless.
Thanks guys. |
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/an experienced fabricator has 101 uses for a #2 pencil that don't involve writing/ |
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I was ruminating on this. I wonder how many uses are left after excluding those that involve poking/prodding other less experienced fabricators, and those that involve personal hygiene. |
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/coating the threads with graphite will keep spatter and slag from sticking to them/
Pretty much anything coated with graphite will have less stuff stick to it, I would guess. |
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// I wonder how many uses are left after excluding those
that involve poking/prodding other less experienced
fabricators, and those that involve personal hygiene. // |
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[Alterother] must have bought that new translation
of the _Kama Sutra_ |
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//Pretty much anything coated with graphite will have less stuff stick to it, I would guess.// Unless "anything" is a piece of cast iron, and "stuff" is white-hot molten low-carbon steel surrounded by plasma, is the point [Alterother] was making. |
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(Even further off topic, it's annoying that in terms of carbon content, it goes iron < steel < cast iron.) |
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//those uses (for graphite) that involve personal hygiene// |
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Do they put lead in your pencil? |
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[spidermother], also there is 'liquid iron' from blast furnaces
which is cast into 'pig iron'. At 4.5% carbon, this is to the right of
your list. |
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Then of course there are the virtually innumerable
stainless steels, which in terms of carbon content typically
fall between Iron (no carbon) and mild (or low-carbon)
steel (.05%-.3% carbon), but can contain up to .5% carbon.
It's all really quite simple and straightforward once you
accept that almost every grade and/or permutation of iron
and/or steel has at least three or four different names
dependant on origin, end-purpose, specific industry, etc.
Sometimes I wonder why, with so many different types of
this incredibly useful material, we even bother with trying
to come up with something newer and better.* |
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