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Author: Subject: aluminium oxide crystal
watson.fawkes
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[*] posted on 30-9-2011 at 07:26


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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[*] posted on 30-9-2011 at 07:38


Quote: Originally posted by peach  

Not so sure about this though, diamonds made from human ashes.

"Made it myself...", "At a jewellery class?", "From my dead cat..."


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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[*] posted on 30-9-2011 at 17:49


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... :(


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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[*] posted on 1-10-2011 at 05:13


Quote: Originally posted by peach  
In some ways it's very special and personal, in others, it's weird.
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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[*] posted on 2-10-2011 at 13:19


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... :(


That's what they get for messing with over-unity and defying the grid assassins.


:D




Quote:

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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[*] posted on 2-10-2011 at 15:13


Quote: Originally posted by watson.fawkes  
Quote: Originally posted by peach  
In some ways it's very special and personal, in others, it's weird.
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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[*] posted on 3-10-2011 at 21:45


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?


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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[*] posted on 2-3-2014 at 16:25


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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[*] posted on 2-3-2014 at 17:04


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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[*] posted on 2-3-2014 at 18:21


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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[*] posted on 3-3-2014 at 04:00


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?


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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[*] posted on 3-3-2014 at 10:41


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?


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.




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[*] posted on 3-3-2014 at 11:28


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?).



Alumina (not the hydroxide) is of course soluble in stuff like molten Na3AlF6 and also CaF2.




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[*] posted on 3-3-2014 at 11:30


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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[*] posted on 3-3-2014 at 12:03


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?).



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.




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[*] posted on 3-3-2014 at 12:12


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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[*] posted on 3-3-2014 at 12:27


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.




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[*] posted on 4-3-2014 at 02:55


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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[*] posted on 29-4-2014 at 14:38


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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[*] posted on 30-4-2014 at 03:33


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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[*] posted on 30-4-2014 at 11:32


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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[*] posted on 30-4-2014 at 12:17


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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[*] posted on 1-5-2014 at 23:22


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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[*] posted on 4-5-2014 at 07:58


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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[*] posted on 4-5-2014 at 09:41


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... :D




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