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watson.fawkes
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Chapter 12 of Strong's Procedures in Experimental Physics has a lovely diagram of a Verneuil process apparatus, detailed enough to build
from, though much less than a measured diagram or a kit. Unfortunately, it doesn't have any commentary on how to operate it, not at least that I could
recall nor quickly locate.
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simba
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I remember seeing this on tv like 10 years ago, so yes its for real. Prices are high but acceptable, at least when I saw it.
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peach
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Quote: Originally posted by Neil  | Browns gas may indeed be wonderful for melting alumina, its oxidizing flame may be useful in the material prep as well as the actual melting. Only
most Browns gas torches I've seen people build have a high rate of self destruction... 
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That's what they get for messing with over-unity and defying the grid assassins.
| Quote: Originally posted by shivas |
I remember seeing this on tv like 10 years ago, so yes its for real. Prices are high but acceptable, at least when I saw it. |
My UK Internet humour has scuppered this situation. I know it's possible (since anything organic will turn to diamond when roasted and crushed at
those values), but it's a bit of an odd thing. In some ways it's very special and personal, in others, it's weird.
[Edited on 1-10-2011 by peach]
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watson.fawkes
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Not nearly as weird as it could be. They
could be making graphite for pencils. "Commemorate your loved one with words: your words, their body."
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Neil
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| Quote: Originally posted by peach | | Quote: Originally posted by Neil | Browns gas may indeed be wonderful for melting alumina, its oxidizing flame may be useful in the material prep as well as the actual melting. Only
most Browns gas torches I've seen people build have a high rate of self destruction...
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That's what they get for messing with over-unity and defying the grid assassins.
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The late distinguished, most excellent Professor Ebelmen made numerous experiments upon the subject of artificially-crystallized alumina. He exhibited
specimens received from him years ago. They are exceedingly small, but remarkably characteristic. Here are some small scales of alumina crystallized
by the operation of fire. The process consists of heating alumina, mixed with about three or four times its weight of borax, in a small platinum
crucible, under certain precautions, in a porcelain furnace—a porcelain furnace where we obtain hard porcelain, and not the so-called porcelain
which we make in this country, and which is made at a low temperature. It must be the true China porcelain furnace, such as was in operation at
Sevres, where he experimented. He exposed the borax and alumina at a high temperature in this furnace. The borax dissolved the alumina, and after a
time off went the boracic acid and the sodium. The crystallized alumina remained at last in brilliant colourless scales. |
From http://books.google.ca/books?pg=PA149&lpg=PA149&dq=c...
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simba
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| Quote: Originally posted by watson.fawkes | | Not nearly as weird as it could be. They
could be making graphite for pencils. "Commemorate your loved one with words: your words, their body." |
Or charcoal also haha...imagine making a barbecue with your parent's ashes, I wonder if it could be considered cannibalism.
[Edited on 2-10-2011 by shivas]
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MeSynth
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| Quote: Originally posted by D4RR3N | How can I grow an aluminium oxide crystal without the need of actually melting aluminium oxide (melts at over 2000C!)
What temperature would aluminium hydroxide decompose into aluminium oxide?
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Chances are your going to have to find something that it's soluble in. I know that a quick way to make it is by mercury aluminum amalgam but then your
working with mercury. This sounds like something I would just give up on..
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Morgan
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I would like to have a large thin sheet or disk about 50 cm in diameter for some electrical experiments.
Sapphire Screen: The Making of A Scratch-Proof Smartphone
https://www.youtube.com/watch?v=vsCER0uwiWI#t=55s
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bfesser
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I'll assume you meant 50 mm and not 50 cm.
<a href="http://www.ebay.com/itm/261388183169" target="_blank">SAPPHIRE WAFER WINDOW for OPTICAL LASER OPTICS APPLICATIONS BIN#5K-10</a>
<img src="../scipics/_ext.png" />
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Morgan
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No, I was dreaming. Maybe in 20 years the costs will come down.
Sapphire sheets
Class400 ha
http://www.crystals.saint-gobain.com/uploadedFiles/SG-Crysta...
Some pretty pictures if you scroll down.
http://arcturus.ligo.caltech.edu/docs/public/P/P030027-00.pd...
http://tech.fortune.cnn.com/2014/02/27/apple-sapphire-arizon...
[Edited on 3-3-2014 by Morgan]
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chornedsnorkack
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| Quote: Originally posted by D4RR3N | How can I grow an aluminium oxide crystal without the need of actually melting aluminium oxide (melts at over 2000C!)
What temperature would aluminium hydroxide decompose into aluminium oxide?
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Under 220 Celsius. Seriously:
http://www.minsocam.org/ammin/AM57/AM57_1375.pdf
But just because corundum is stable over 220 Celsius, and under 220 Celsius at humidity/activity under 1 bar, does not mean diaspore would rapidly
convert to corundum under these conditions. Nor is dry heat in solid conducive to rapid growth of big monocrystals.
You need a solvent. And I wonder about a good one.
Water itself is not liquid under 220 Celsius and 1 bar, and increasing pressure shifts equilibrium towards diaspore, so that corundum can precipitate
from water from 360 degree temperature and 190 bar pressure.
But the problem is, the solubility of alumina in neutral water is poor, and that will hamper crystal growth.
Solvents? Alumina being amphoteric, both bases and acids are good solvents.
But the problem is that they also form salts in solid forms.
For example, you can achieve 330 Celsius in 1 bar sulphuric acid... and the water activity in 98 % sulphuric acid is much below 1 bar, so you could
get out of diaspore stability field in boiling concentrated sulphuric acid. But the problem is, you are then not in stability field of corundum... you
are in stability field of aluminum sulphate, or perhaps aluminum hydrogen sulphates.
If you produce a boiling, saturated solution of aluminum sulphate (note that the solution will have its boiling point raised by solute, and the
heating further increases aluminum sulphate solubility, which again raises boiling point etc.), and boil it with aluminum hydroxide precipitate, will
you be growing diaspore crystals or will aluminum sulphate form solid crystalline basic salts?
What is the boiling point and water activity of saturated boiling aluminum sulphate solution?
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DraconicAcid
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| Quote: Originally posted by chornedsnorkack | | Quote: Originally posted by D4RR3N | How can I grow an aluminium oxide crystal without the need of actually melting aluminium oxide (melts at over 2000C!)
What temperature would aluminium hydroxide decompose into aluminium oxide?
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Under 220 Celsius. Seriously:
http://www.minsocam.org/ammin/AM57/AM57_1375.pdf
But just because corundum is stable over 220 Celsius, and under 220 Celsius at humidity/activity under 1 bar, does not mean diaspore would rapidly
convert to corundum under these conditions. Nor is dry heat in solid conducive to rapid growth of big monocrystals.
You need a solvent. And I wonder about a good one. |
I have spent a long time thinking about this particular project, and it seems to me that a molten salt would probably work. Aluminum hydroxide is not
likely to be soluble even in a melt, but one could conceivably form crystals of alumina by dissolving some other aluminum salt in a melt, along with
some anion that would slowly decompose to give oxide ion (sulphite? carbonate?).
Alternatively, one could melt something like aluminum isopropoxide, and hold it at a temperature where it slowly decomposes to eliminate the organic
parts. It would have to be a slow decomposition, or you'll never get crystals.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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blogfast25
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| Quote: Originally posted by DraconicAcid | I have spent a long time thinking about this particular project, and it seems to me that a molten salt would probably work. Aluminum hydroxide is not
likely to be soluble even in a melt, but one could conceivably form crystals of alumina by dissolving some other aluminum salt in a melt, along with
some anion that would slowly decompose to give oxide ion (sulphite? carbonate?).
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Alumina (not the hydroxide) is of course soluble in stuff like molten Na3AlF6 and also CaF2.
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Boffis
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I think you are all missing the obvious answer. The OP wanted to know how to grow Al2O3 crystals; answer from a suitable solvent.
"Suitable solvents" for are a bit thin on the ground but it dissolves in molten cryolite Na3AlF6 and also PbF2 (Mp c 820 C) and PbO (Mp c 900 C) and
there may be other, eutectic, mixture with lower melting points. The vapour pressure of molt lead fluoride is high so it evaporates fairly quickly at
>1000 C and this method is also used for crystal growing. Cryolite has a higher melting point but you may be able to reduce this by adding other
alkali metal fluorides like lithium.
All you need then is a high temperature furnace with a good temperature control unit that allows controlled slow cooling and one of those
platinum-iridium crucibles.
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DraconicAcid
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by DraconicAcid | I have spent a long time thinking about this particular project, and it seems to me that a molten salt would probably work. Aluminum hydroxide is not
likely to be soluble even in a melt, but one could conceivably form crystals of alumina by dissolving some other aluminum salt in a melt, along with
some anion that would slowly decompose to give oxide ion (sulphite? carbonate?).
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Alumina (not the hydroxide) is of course soluble in stuff like molten Na3AlF6 and also CaF2. |
True, but I was thinking of lower-temperature melts that would be easier to work with at home. I've actually worked with cryolite melts, and they
weren't fun.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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blogfast25
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Considering the Standard Enthalpy of Formation (and that most of that is actually lattice energy) finding a low temp. ionic solvent that can rip that
lattice apart will always be a challenge. Never say 'never', though (ooops!)
[Edited on 3-3-2014 by blogfast25]
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DraconicAcid
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| Quote: Originally posted by blogfast25 | | Considering the Standard Enthalpy of Formation (and that most of that is actually lattice energy) finding a low temp. ionic solvent that can rip that
lattice apart will always be a challenge. Never say 'never', though (ooops!) |
Yes....which is why I was suggesting forming it from an aluminum salt and a source of oxide ion in the melt, rather than dissolving alumina in the
melt.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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chornedsnorkack
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As I pointed out, aqueous solutions have the problem of boiling in diaspore stability field.
Cryolite/fluoride melts melt over 900 Celsius, which is much more than the needed temperature of 200...400 Celsius.
Common salts which do melt under 400 Celsius include alkali. But alkali would not precipitate alumina seeing that the stable solid phase would be
solid aluminates.
However, salts that also are low melting include nitrates of alkali metals.
Is alumina soluble in alkali metal nitrate melts?
If aluminum nitrate were decomposed in alkali metal nitrate/nitrite melts, would it be a good condition to crystallize alumina, or would alumina form
aluminates?
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rskennymore
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Has anyone had any luck attempting this?
I read an ACS publication from some folks from japan a few months back and gave it a shot with some cheaper equipment...
link: https://www.jstage.jst.go.jp/article/jcersj/113/1323/113_132...
The gist of it is they're using Molybdenum Trioxide as a flux to dissolve the alumina/chromium, which then slowly evaporates off leaving nice
tetragonal crystals.
The experiment: 28.5 grams of Molybdenum Trixoide was mixed with 1.5 grams of Aluminum Oxide doped with about 0.5%wt Cr2O3. All reagents were ACS
Reagent grade 99.5% or higher.
Since Platinum crucibles are out of my budget range for a random project, I decided to attempt this experiment using a cheaper zirconia crucible I
found on ebay.
The crucible, with lid slightly offset to facilitate vapor escape, was placed in a small test kiln with NiChrome heating elements and heated to 300C
for 2 hours and then slowly raised to 1100C over the next 3 hours. After reaching 1100C it was held there for 5 hours and then the kiln was powered
off and allowed to cool overnight.
At some point through the cooling process the crucible cracked due to the large amount of residue present in the bottom with an obviously different
thermal expansion ratio. The Japanese experimenters indicated that after 5 hours ~99% of the flux had evaporated so this was not anticipated and
leaves me wondering what kind of ventilation their furnace had. Upon further inspection it became apparent that the zirconia had been attacked by the
flux, diffused into the melt, and possibly prevented the flux from evaporating.
However, after removing the solid mass from what was left of the crucible and grinding it up in a mortar and pestle, tiny red sand-grain sized
crystals were found and separated from the gravel via tweezers. They aren't big, but they scratch glass and are red, so I am calling this a success.
Pictures to prove it: http://imgur.com/a/KXLAg#0
I can say definitively that zirconia is the wrong material to use for this process. Iridium is most likely the correct material. I have attempted it
since this experiment using a chemically bonded silicon carbide crucible, and it appears to also be attacked by Molybdenum Trioxide flux. I'd like to
give Boron Nitride a try but haven't got the budget this month...
Cheaper materials that I think *might* work would be tantalum, niobium, and maybe a nickel-chromium crucible if you could somehow plate it with
iridium or something. I aim to try the latter at some point in the near future.
Working on a source for Iridium Chloride if anyone has any leads 
Cheers
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deltaH
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Well done rskennymore! Your ruby grains are beautiful.
I wonder if zirconium crucibles might be an alternative. I used to use them for sodium peroxide fusions at red heat to oxidise mineral samples for
metal assays. They were tough as nails.
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rskennymore
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| Quote: Originally posted by deltaH | Well done rskennymore! Your ruby grains are beautiful.
I wonder if zirconium crucibles might be an alternative. I used to use them for sodium peroxide fusions at red heat to oxidise mineral samples for
metal assays. They were tough as nails. |
Not a bad idea. Zirconium is pretty reactive with oxygen at higher temps from what I gather. I wonder how long it would last in atmosphere at those
temps? It *shouldn't* pull oxygen out of the flux...
I guess if i was going with an inert gas i could probably get away with some kind of nickel-chromium alloy... That's what the heating elements are
made of after all.
Any material scientists or metallurgists have any ideas?
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blogfast25
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Nice crystals. Grow bigger ones and a fortune could be in the making, even though they wouldn't fetch the same as natural ones.
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deltaH
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Yeah on second thoughts rskennylmore, I doubt zirconium will stand your extreme temperatures in an oxidising environment and while
they are far less costly than platinum crucibles, the gamble probably ain't worth it considering that they are, nevertheless, not cheap!
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rskennymore
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I think I might try plumbing nitrogen into the furnace with a zirconium crucible. I found a source of 45ml Zirconium crucibles for around 50 bucks
each and ordered one. If it doesn't work then it'll just go in the element collection.
Also, I've been doing some reading... It seems adding a layer of iridium to refractory metals has been studied to some extent by NASA: https://archive.org/details/nasa_techdoc_19680019183
According to their results section (page 43 of the pdf) Niobium plated with Iridium showed no measurable amount of loss due to diffusion after 30
hours at 1300C. Since the experiment for aluminium oxide crystal growth requires 1100C, I think an Iridium plated Niobium crucible would probably last
quite a while and still come in a lot cheaper than a platinum crucible.
They mention a lot of difficulties in achieving a coherent plating on the more reactive metals (niobium/tantalum). I don't think I have the resources
to attempt the pressure-bonding method they employ, or the molten salt electrolyte. However this patent: US20120073980 gives some promise for a
diy-er.
At one point, the NASA document mentions that Iridium electroplates easily onto nickel and that a intermediary layer of nickel enabled them to plate a
coherent layer onto tantalum and niobium.
Zirconium isn't mentioned in any of these documents.
Much experimentation to come.
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deltaH
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Wow, 50 bucks... that doesn't sound too bad. I guess it is worth the gamble if you can get nitrogen in there. Best of luck with the trial!
As for iridium plating, I have a sneaky suspicion that it might just be one of those things that doesn't sound too complicated in principle...
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