Sciencemadness Discussion Board

Hydrothermal synthesis of rubies from chromium-doped AlCl3.6H2O

Admagistr - 14-11-2021 at 16:34

I've had a mixture of AlCl3.6H2O, spiked with CrCl3 hydrate, sealed into a vial of borosilicate glass. I'm going to grill this mixture on charcoal, wrapped in Al foil. If it holds up and doesn't explode in the course of the reaction, I look forward to finding a tiny Cr-diaspore and rubies, If the temperature is low I only get a Cr-diaspore, at a temperature of over 350 C I should only get a rubies, and at a lower temperature a mixture of diaspore and rubies...Has anyone tried to make a hydrothermal ruby;-)?

SWIM - 14-11-2021 at 18:30

So this mixture is going to become rubies and HCl??

How long do you plan to heat it?

[Edited on 15-11-2021 by SWIM]

high pressure vessel.jpg - 192kB

Admagistr - 14-11-2021 at 19:00

Quote: Originally posted by SWIM  
So this mixture is going to become rubies and HCl??

How long do you plan to heat it?

[Edited on 15-11-2021 by SWIM]


Yes, the reaction looks like this: 2AlCl3.6H2O = Al2O3+ 9H2O+ 6HCl, unfortunately I don't know exactly how much time it takes for the reaction to pass successfully, but longer time is a better option, I suppose it will take at least a few hours. I'll grill until I've consumed a whole pack of charcoal. Then I'll look at the result;-)




[Edited on 15-11-2021 by Admagistr]

SWIM - 14-11-2021 at 19:25

I hope it works out for you.

Sounds like a lot of pressure for hot glass.

Admagistr - 14-11-2021 at 19:55

Quote: Originally posted by SWIM  
I hope it works out for you.

Sounds like a lot of pressure for hot glass.


Thank you! I'll let you know how the experiment went, it's quite possible that the borosilicate ampoules won't last and will explode... Of course, autoclave is a much better choice, but it would have to be made of tantalum, because that's the metal of choice in the extremely corrosive environment of hot hydrochloric acid...I don't have an autoclave yet, I may get one soon...And what temperature and pressure will your autoclave take? Good thing you sent the autoclave photo, it matches the post:-)

Panache - 14-11-2021 at 23:30

Quote: Originally posted by Admagistr  
Quote: Originally posted by SWIM  
I hope it works out for you.

Sounds like a lot of pressure for hot glass.


Thank you! I'll let you know how the experiment went, it's quite possible that the borosilicate ampoules won't last and will explode... Of course, autoclave is a much better choice, but it would have to be made of tantalum, because that's the metal of choice in the extremely corrosive environment of hot hydrochloric acid...I don't have an autoclave yet, I may get one soon...And what temperature and pressure will your autoclave take? Good thing you sent the autoclave photo, it matches the post:-)



Is tantalum really that resistant to HCL, hmmm, i didnt believe any metal other than iridium perhaps would survive hcl at those temperatures and pressures. coiuldnt you simply place your sealed ampule inside a regular autoclave with i dont know some water, then charcoal the lot?

Admagistr - 15-11-2021 at 04:44

Quote: Originally posted by Panache  
Quote: Originally posted by Admagistr  
Quote: Originally posted by SWIM  
I hope it works out for you.

Sounds like a lot of pressure for hot glass.


Thank you! I'll let you know how the experiment went, it's quite possible that the borosilicate ampoules won't last and will explode... Of course, autoclave is a much better choice, but it would have to be made of tantalum, because that's the metal of choice in the extremely corrosive environment of hot hydrochloric acid...I don't have an autoclave yet, I may get one soon...And what temperature and pressure will your autoclave take? Good thing you sent the autoclave photo, it matches the post:-)



Is tantalum really that resistant to HCL, hmmm, i didnt believe any metal other than iridium perhaps would survive hcl at those temperatures and pressures. coiuldnt you simply place your sealed ampule inside a regular autoclave with i dont know some water, then charcoal the lot?


I'll take another look at the resistance of tantalum to HCl. For iridium, it is reported to dissolve in concentrated HCl under high pressure, in the presence of NaClO4. Thanks for the idea of putting the sealed glass ampoule in the autoclave along with some water! If tantalum could withstand hot HCl under these pressures, that would be great, because getting tantalum autoclave would be much more real than the iridium...Can anyone give us some advice?

unionised - 15-11-2021 at 04:52

The trick of putting a sealed ampoule in an autoclave along with some water is only valid if the vapour pressure of the stuff in the ampoule will be more or less the same as that of water.

Admagistr - 15-11-2021 at 05:02

Quote: Originally posted by unionised  
The trick of putting a sealed ampoule in an autoclave along with some water is only valid if the vapour pressure of the stuff in the ampoule will be more or less the same as that of water.


Thank you very much for that important note!

Bezaleel - 17-11-2021 at 04:10

Shouldn't you go to temperatures where Al2O3 actually fuses in order to get rubies? From what I know of artificial gemstone creation, you always need to get to the liquid state, or at least to the temperature where you will get a solution.

E.g. some metal fluorides can be crystallised from their solutions in molten NaF or a eutectic of alkaline(earth) fluorides.

Admagistr - 17-11-2021 at 09:08

Quote: Originally posted by Bezaleel  
Shouldn't you go to temperatures where Al2O3 actually fuses in order to get rubies? From what I know of artificial gemstone creation, you always need to get to the liquid state, or at least to the temperature where you will get a solution.

E.g. some metal fluorides can be crystallised from their solutions in molten NaF or a eutectic of alkaline(earth) fluorides.


It's a good idea. In nature, gems are made in a similar way. I often use the trick of using a mineralizer, most often MoO3, which lowers the melting temperature of Al2O3 by more than 1000 C! But this mineralizer is very volatile, so I'm helping myself to alkaline carbonate to limit its volatility. Al2O3 reacts with MoO3 to produce Al2(MoO4)3, but at high temperatures it breaks down again into Al2O3 and MoO3 and, by breaking down this compound, the Al2O3 crystallises and leaves a sapphire, or a ruby and MoO3 displaces and, when cooled, leaves beautiful needles of MoO3...

Bezaleel - 19-11-2021 at 16:02

Interesting. MoO3 MP 802 °C, BP 1,155 °C. That's relatively low for a metal oxide. Al2O3 MP 2,072 °C, BP 2,977 °C.

Do you say that Al2O3 would actually dissolve in molten MoO3, forming Al2(MoO4)3 dissolved in MoO3?

I once tried something somewhat similar - dissolving copper wire in molten tellurium. What happened was that the copper did initially dissolve, but the melting point of copper telluride is much higher than the melting point of tellurium, so a few seconds later I was left with a hard black lump, which would not melt in my test tube.

Admagistr - 19-11-2021 at 21:53

Quote: Originally posted by Bezaleel  
Interesting. MoO3 MP 802 °C, BP 1,155 °C. That's relatively low for a metal oxide. Al2O3 MP 2,072 °C, BP 2,977 °C.

Do you say that Al2O3 would actually dissolve in molten MoO3, forming Al2(MoO4)3 dissolved in MoO3?

I once tried something somewhat similar - dissolving copper wire in molten tellurium. What happened was that the copper did initially dissolve, but the melting point of copper telluride is much higher than the melting point of tellurium, so a few seconds later I was left with a hard black lump, which would not melt in my test tube.


Interesting experiment with tellurium;-). Al2O3 reacts with MoO3 to produce Al2(MoO4)3, which with another MoO3 molecule also reacts to produce Al2(Mo2O7)3 and possibly other higher polymolybdates if MoO3 is really a lot. But at a temperature above the melting point of MoO3, this one gradually evaporates, leaving simpler molybdate until finally pure crystalline Al2O3! The method works similarly for SiO2,BeO,ZrO2,HfO2, also probably for GeO2,Ga2O3.

draculic acid69 - 19-11-2021 at 22:06

Quote: Originally posted by Admagistr  
Quote: Originally posted by Panache  
Quote: Originally posted by Admagistr  
Quote: Originally posted by SWIM  
I hope it works out for you.

Sounds like a lot of pressure for hot glass.


Thank you! I'll let you know how the experiment went, it's quite possible that the borosilicate ampoules won't last and will explode... Of course, autoclave is a much better choice, but it would have to be made of tantalum, because that's the metal of choice in the extremely corrosive environment of hot hydrochloric acid...I don't have an autoclave yet, I may get one soon...And what temperature and pressure will your autoclave take? Good thing you sent the autoclave photo, it matches the post:-)



Is tantalum really that resistant to HCL, hmmm, i didnt believe any metal other than iridium perhaps would survive hcl at those temperatures and pressures. coiuldnt you simply place your sealed ampule inside a regular autoclave with i dont know some water, then charcoal the lot?


I'll take another look at the resistance of tantalum to HCl. For iridium, it is reported to dissolve in concentrated HCl under high pressure, in the presence of NaClO4. Thanks for the idea of putting the sealed glass ampoule in the autoclave along with some water! If tantalum could withstand hot HCl under these pressures, that would be great, because getting tantalum autoclave would be much more real than the iridium...Can anyone give us some advice?



Any rxn that produces hcl gas in a closed vessel will explode quickly, add heat and pressure and it is guaranteed to go to shit
The ampule in the autoclave with water in it would either be limited to temp of
125'c or so or however hot you can get water in a pressure cooker leading to no
result at all or let's say you do superheat the steam inside your internal psi will shatter the ampule leading to a corroded reactor and no rubies. Whether any internal psi from evolving hcl shatters the ampule first or external psi from steam pushing on a thin glass tube breaks the ampule is anyone's guess. Your wasting time and effort by bringing glass or an autoclave into the equation. A $5 crucible from eBay will get you a result without learning a costly hazardous lesson on how to not do it. also why not just do the usual al2o3 route? Why try to reinvent the wheel by going through the chloride?

Bezaleel - 20-11-2021 at 09:17

@draculic acid69 I was wondering too why Admagistr would pursue the HCl route, but I guess he's just looking into it out of curiosity - can it be done at a lower temperature with a different setup?

I wonder what would happen if you would put a PTFE vial into an autoclave which external size would be almost the interior of the autoclave. PTFE has some flexibility and is not likely to explode if it has support from the autoclave walls. PTFE's MP is 327 °C, and the required temperature is > 350 °C. How liquid is PTFE at 327 - 350 °C?

Admagistr - 20-11-2021 at 14:29

Quote: Originally posted by Bezaleel  
@draculic acid69 I was wondering too why Admagistr would pursue the HCl route, but I guess he's just looking into it out of curiosity - can it be done at a lower temperature with a different setup?

I wonder what would happen if you would put a PTFE vial into an autoclave which external size would be almost the interior of the autoclave. PTFE has some flexibility and is not likely to explode if it has support from the autoclave walls. PTFE's MP is 327 °C, and the required temperature is > 350 °C. How liquid is PTFE at 327 - 350 °C?


Yes guys, I want to do it out of my curiosity. It can also be used Al2(SO4)3.18H2O, mixed with urea, or it can be used instead of AlCl3.6H2O, Cr3+ iont spiced Al(NO3)3.9H2O. The aluminium chloride method is most closely related to the natural processes that occur in the formation of pegmatites and in the pegmatites of the resulting gemstones. The problem is, at lower temperatures, the chromium diaspore-AlOOH is produced, not the rubies! Possibly resulting in a mixture of Cr-diaspore and rubies. Draculic acid69-What crucible of Ebay do you mean?? I've read that rubies from AlCl3.6H2O were created in experiments many times, but the information is very brief and doesn't mention the materials the autoclave was composed of. They just point out that a temperature of 350 C is needed! It's an interesting idea with the Teflon, thanks for the discussion!

[Edited on 20-11-2021 by Admagistr]

draculic acid69 - 22-11-2021 at 05:02

Quote: Originally posted by Bezaleel  
@draculic acid69 I was wondering too why Admagistr would pursue the HCl route, but I guess he's just looking into it out of curiosity - can it be done at a lower temperature with a different setup?

I wonder what would happen if you would put a PTFE vial into an autoclave which external size would be almost the interior of the autoclave. PTFE has some flexibility and is not likely to explode if it has support from the autoclave walls. PTFE's MP is 327 °C, and the required temperature is > 350 °C. How liquid is PTFE at 327 - 350 °C?


Most autoclave reactors have Teflon inserts

draculic acid69 - 22-11-2021 at 05:31

Quote: Originally posted by Admagistr  
Quote: Originally posted by Bezaleel  
@draculic acid69 I was wondering too why Admagistr would pursue the HCl route, but I guess he's just looking into it out of curiosity - can it be done at a lower temperature with a different setup?

I wonder what would happen if you would put a PTFE vial into an autoclave which external size would be almost the interior of the autoclave. PTFE has some flexibility and is not likely to explode if it has support from the autoclave walls. PTFE's MP is 327 °C, and the required temperature is > 350 °C. How liquid is PTFE at 327 - 350 °C?


Yes guys, I want to do it out of my curiosity. It can also be used Al2(SO4)3.18H2O, mixed with urea, or it can be used instead of AlCl3.6H2O, Cr3+ iont spiced Al(NO3)3.9H2O. The aluminium chloride method is most closely related to the natural processes that occur in the formation of pegmatites and in the pegmatites of the resulting gemstones. The problem is, at lower temperatures, the chromium diaspore-AlOOH is produced, not the rubies! Possibly resulting in a mixture of Cr-diaspore and rubies. Draculic acid69-What crucible of Ebay do you mean?? I've read that rubies from AlCl3.6H2O were created in experiments many times, but the information is very brief and doesn't mention the materials the autoclave was composed of. They just point out that a temperature of 350 C is needed! It's an interesting idea with the Teflon, thanks for the discussion!

[Edited on 20-11-2021 by Admagistr]


https://m.youtube.com/watch?v=MLV1pPvTpIw
He's using a graphite crucible.they Costa few $$ on eBay.

Admagistr - 22-11-2021 at 15:52

Quote: Originally posted by draculic acid69  
Quote: Originally posted by Admagistr  
Quote: Originally posted by Bezaleel  
@draculic acid69 I was wondering too why Admagistr would pursue the HCl route, but I guess he's just looking into it out of curiosity - can it be done at a lower temperature with a different setup?

I wonder what would happen if you would put a PTFE vial into an autoclave which external size would be almost the interior of the autoclave. PTFE has some flexibility and is not likely to explode if it has support from the autoclave walls. PTFE's MP is 327 °C, and the required temperature is > 350 °C. How liquid is PTFE at 327 - 350 °C?


Yes guys, I want to do it out of my curiosity. It can also be used Al2(SO4)3.18H2O, mixed with urea, or it can be used instead of AlCl3.6H2O, Cr3+ iont spiced Al(NO3)3.9H2O. The aluminium chloride method is most closely related to the natural processes that occur in the formation of pegmatites and in the pegmatites of the resulting gemstones. The problem is, at lower temperatures, the chromium diaspore-AlOOH is produced, not the rubies! Possibly resulting in a mixture of Cr-diaspore and rubies. Draculic acid69-What crucible of Ebay do you mean?? I've read that rubies from AlCl3.6H2O were created in experiments many times, but the information is very brief and doesn't mention the materials the autoclave was composed of. They just point out that a temperature of 350 C is needed! It's an interesting idea with the Teflon, thanks for the discussion!

[Edited on 20-11-2021 by Admagistr]


https://m.youtube.com/watch?v=MLV1pPvTpIw
He's using a graphite crucible.they Costa few $$ on eBay.



This is an interesting, inexpensive and simple way to prepare the corundum, but this is the way to prepare the red corundum, not the ruby, in the actual meaning of the word ruby. The ruby should be clear, transparent and nicely coloured. And that's what the hydrothermal synthesis method can provide. The aforementioned and inexpensive way hardly...Moreover, it's a melt that's crystalline in physical terms, but far from a well-defined crystal...

draculic acid69 - 23-11-2021 at 19:54

I think for a clear gem quality ruby it's about using a "buole" and drawing the melt out slowly or something. I doubt it's recreateable in an ampule or whatever easily. If U watch the video it shows a gem quality ruby half made using some process with a buole still attached. Just try iyour method and see what you can get out of it.

[Edited on 24-11-2021 by draculic acid69]