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Author Topic: Can corundum be made with thermite?  (Read 3403 times)

Offline eric2011

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Can corundum be made with thermite?
« on: 03/11/2015 00:13:18 »
Hello

I know that  make sillicon metal from thermite reaction but is it possible to make corundum crystalsor diamonds with thermite? And what mixtures to use?
« Last Edit: 04/11/2015 11:07:06 by chris »


 

Offline SorryDnoodle

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Re: Making corundum with thermite
« Reply #1 on: 03/11/2015 16:37:51 »
No, Corundum is Al2O3 crystals with impurities like titanium imbedded in the crystals, a thermite reaction leaves you with a molten pool of a metal such as Iron and aluminium oxides, it will not form any crystals, to make crystals you need to slowly deposits atoms on a solid surface, you cannot make them quick n' easy.
 

Offline eric2011

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Re: Making corundum with thermite
« Reply #2 on: 03/11/2015 21:37:37 »
No, Corundum is Al2O3 crystals with impurities like titanium imbedded in the crystals, a thermite reaction leaves you with a molten pool of a metal such as Iron and aluminium oxides, it will not form any crystals, to make crystals you need to slowly deposits atoms on a solid surface, you cannot make them quick n' easy.

I found this text when I searched in the net and this book says that without going into details:

Simplified synthetic diamond produced by means of thermite; a mixture of aluminum or magnesium powder and barium peroxide or other metal oxide (1:1). When ignited by magnesium ribbon very high temperature about 2,200C are produced. Soapstone mixed with thermite is also used for production of synthetic diamond. Saponite mixture is placed in a hollow sphere in the center of this sphere will placed another hollow sphere of tantalum, and in the last hollow sphere center is placed the reagent composed of graphite and iron carbide.

Can anyone explain how to set up this setup
 

Offline chiralSPO

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Re: Making corundum with thermite
« Reply #3 on: 03/11/2015 23:26:45 »
It sounds like they are using thermite as the heat source, but it is the graphite that is converted into diamonds.

Thermite will generate aluminum oxide, which, if it crystallizes right will be corundum, but I don't think the thermite reaction gets hot enough or cools down slowly enough to generate any substantial crystals of aluminum oxide. Also, the large amount of iron will be problematic.

One could imagine reacting just aluminum and oxygen  to get the corundum, it would certainly get pretty hot by itself, though you may need to add more heat to get crystals of any reasonable size.

At ambient temperatures aluminum metal is well protected by an oxide coating, but this can be disrupted by mercury (don't try this at home!) The mercury catalyzes the oxidation reaction, and aluminum is converted to the oxide over the course of minutes to hours. I found some demonstrations of this on youtube (for instance this:
).

I don't know what sort of crystal structure would be formed, but you might be able to grow crystals of aluminum oxide (probably hydrated) from aqueous solution. Aluminum oxide is almost completely insoluble in neutral water, but is quite soluble at high pH. Perhaps a solution of aluminum oxide/hydroxide in alkaline solution could be neutralized very slowly, resulting in crystals as the alumina precipitates out...

(this may also be of interest: http://www.ars.usda.gov/SP2UserFiles/Place/20360500/pdf_pubs/P1381.pdf)
 

Offline SorryDnoodle

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Re: Can corundum be made with thermite?
« Reply #4 on: 04/11/2015 14:57:06 »
Making these types of crystals is not easy, and I do not recommend it for the novice.

The most feasible way I found was using the Verneuil process.

https://en.wikipedia.org/wiki/Verneuil_process
 

Offline puppypower

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Re: Can corundum be made with thermite?
« Reply #5 on: 04/11/2015 20:19:01 »
The Verneuil method uses a hydrogen and oxygen flame. In this technique you slowly sprinkle aluminum oxide dust, through the flame where it melts and then deposits on a collection blob. This technique made rubies very cheap so they could be used in all types of tech applications. A cheap laser pointer is now only a few bucks due to cheap rubies. This is 1950's tech that is still used today.

Another common technique is a molten flux technique. This is where you use a bath of molten salt, such as  Na3AlF6 ; lava in a bowl. This molten salt bath will allow the aluminum oxide to dissolve at a reasonable temperature, since the molten salt acts as a solvent. This can be done in a lab furnace using platinum crucibles. Next, you add seed crystals of corundum and cool the saturated flux. If you cool the entire flux slowly or set up a thermal gradient in the flux, the aluminum oxide will precipitate out onto the crystal making the seeds grow. This forms high quality crystals but they will have some flux inclusions that a professional jeweler would see and know it was synthetic. Natural have different incisions.

Years ago I did research growing gem quality crystals. I found that the molten flux technique can be modified, so the flux not only dissolves the aluminum oxide, but the flux can be used to chemically guide the growth habit of the crystals. This allows you to grow crystals with facets already on them. One flux I found could make hexagonal bi-pyramids.

Another alternative to make rubies and sapphires is using hydrothermal techniques, where you use water at high temperature and pressure in sealed containers. If you use super critical water with some small dissolve ions, this hydrothermal brine a very aggressive solvent for most minerals. In this technique, you set up a thermal gradient. This technique requires special moly-steels that can handle the temperature and pressure.

Although diverging slightly from the topic at hand, researching hydrothermal techniques for making crystals led to a theory I had many years ago. Water, especially sea water, due to the dissolve minerals, should be able to eat its way to the earth's mantle, if the water is contained under hydrothermal conditions, with a thermal gradient. 

In hydrothermal techniques, the raw aluminum oxide material is placed on the bottom, where it is hotter. The seed is at the top where it is slightly cooler. The entire thing is contained and pressurized.

The water will eat downward in the direction of higher temperate due to the higher solubility of minerals at higher temperature. The hotter water flows upward via thermal convection, and deposits material at the cooler top, where the mineral is less soluble. This cooler water sinks downward via convection ready to dissolve more.

Pools of super critical mineral water trapped in the crust, that sees a thermal gradient; mantle is hottest, will eat downward toward the heat, like a worm, sealing behind itself, renewing its solvent power.
 

Offline Bored chemist

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Re: Can corundum be made with thermite?
« Reply #6 on: 04/11/2015 22:16:22 »
"A cheap laser pointer is now only a few bucks due to cheap rubies."
No it isn't.
No rubies are involved, though some of the processes are similar the KDP and Nd YAG crystals are not made by the Verneuil process.
 

Offline SorryDnoodle

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Re: Can corundum be made with thermite?
« Reply #7 on: 04/11/2015 22:31:37 »
"A cheap laser pointer is now only a few bucks due to cheap rubies."
No it isn't.
No rubies are involved, though some of the processes are similar the KDP and Nd YAG crystals are not made by the Verneuil process.

Out of curiosity, how are these crystals made?
 

Offline puppypower

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Re: Can corundum be made with thermite?
« Reply #8 on: 05/11/2015 21:01:53 »
My mistake, the cheapest ruby lasers are about $200.00 on eBay. I found a 200 plus carat synthetic ruby rod for a laser for about $4000. That rod would have been made by the Verneuil process. The hydrogen oxygen flame melts aluminum oxide power into a liquid that drips onto a boule where it will solidify. This method makes rubies of low quality in terms of crystal perfection, which is why they are so cheap. They are not gem quality but laser quality.

There was another method that begins with a boule from the Verneuil process. The boule is still of high material purity and just needs to be tweaked at the level of the crystal lattice. This method is called the moving film process.

In this process, you would start with a low quality boule crystal of high material purity. You use a thin molten flux film on the boule and a thermal gradient. The molten flux will melt and then begin to dissolve its way through the boule, toward the heat, depositing high quality ruby crystal behind it. It moves very slow allowing the crystalize to be high quality.

The moving film process may have been what inspired the idea of supercritical water, especially supercritical seawater with plenty of ions, dissolving to the mantle, redepositing the crust material behind itself as it moves forward.
 

Offline eric2011

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Re: Can corundum be made with thermite?
« Reply #9 on: 06/11/2015 03:32:42 »
The Verneuil method uses a hydrogen and oxygen flame. In this technique you slowly sprinkle aluminum oxide dust, through the flame where it melts and then deposits on a collection blob. This technique made rubies very cheap so they could be used in all types of tech applications. A cheap laser pointer is now only a few bucks due to cheap rubies. This is 1950's tech that is still used today.

Another common technique is a molten flux technique. This is where you use a bath of molten salt, such as  Na3AlF6 ; lava in a bowl. This molten salt bath will allow the aluminum oxide to dissolve at a reasonable temperature, since the molten salt acts as a solvent. This can be done in a lab furnace using platinum crucibles. Next, you add seed crystals of corundum and cool the saturated flux. If you cool the entire flux slowly or set up a thermal gradient in the flux, the aluminum oxide will precipitate out onto the crystal making the seeds grow. This forms high quality crystals but they will have some flux inclusions that a professional jeweler would see and know it was synthetic. Natural have different incisions.

Years ago I did research growing gem quality crystals. I found that the molten flux technique can be modified, so the flux not only dissolves the aluminum oxide, but the flux can be used to chemically guide the growth habit of the crystals. This allows you to grow crystals with facets already on them. One flux I found could make hexagonal bi-pyramids.

Another alternative to make rubies and sapphires is using hydrothermal techniques, where you use water at high temperature and pressure in sealed containers. If you use super critical water with some small dissolve ions, this hydrothermal brine a very aggressive solvent for most minerals. In this technique, you set up a thermal gradient. This technique requires special moly-steels that can handle the temperature and pressure.

Although diverging slightly from the topic at hand, researching hydrothermal techniques for making crystals led to a theory I had many years ago. Water, especially sea water, due to the dissolve minerals, should be able to eat its way to the earth's mantle, if the water is contained under hydrothermal conditions, with a thermal gradient. 

In hydrothermal techniques, the raw aluminum oxide material is placed on the bottom, where it is hotter. The seed is at the top where it is slightly cooler. The entire thing is contained and pressurized.

The water will eat downward in the direction of higher temperate due to the higher solubility of minerals at higher temperature. The hotter water flows upward via thermal convection, and deposits material at the cooler top, where the mineral is less soluble. This cooler water sinks downward via convection ready to dissolve more.

Pools of super critical mineral water trapped in the crust, that sees a thermal gradient; mantle is hottest, will eat downward toward the heat, like a worm, sealing behind itself, renewing its solvent power.

How to sprinkle without splatterall over the place?
 

Offline puppypower

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Re: Can corundum be made with thermite?
« Reply #10 on: 11/11/2015 20:40:46 »
Quote
The Verneuil process, also called flame fusion, was the first commercially successful method of manufacturing synthetic gemstones, developed in 1902 by the French chemist Auguste Verneuil. It is primarily used to produce the ruby and sapphire varieties of corundum, as well as the diamond simulants rutile and strontium titanate. The principle of the process involves melting a finely powdered substance using an oxyhydrogen flame, and crystallising the melted droplets into a boule. The process is considered to be the founding step of modern industrial crystal growth technology, and remains in wide use to this day.

Below is the link to the Wiki article.

https://en.wikipedia.org/wiki/Verneuil_process

From the diagram below it that appears that fine and ultra pure Al2O3 powder is blown/tapped in with the oxygen stream. These will then combine with the hydrogen gas stream to put the powder into the flame,  melting the power onto the boule. Below are a few boules made by this method.



 

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Re: Can corundum be made with thermite?
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