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Fulmen
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@Admagistr: My advice; start with a 1000-1200°C furnace. The challenge grows exponentially with temperature, working at 2000°C with no prior
experience isn't realistic.
We're not banging rocks together here. We know how to put a man back together.
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macckone
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+1 Fulmen
a kitchen oven is 250C.
a propane forge is about 1000C and an electric furnace capable of 1000C is not as easy as it seems.
Getting to even 1300C requires some engineering challenges (upgrading to fuel oil).
Even though the flame temperature of propane is higher than 1300C getting a working forge or furnace that heats that hot is not as intuitive as it may
seem.
Most kilns do not go to cone 10 which is 1305C.
Kanthal A1 is usable up to 1400C with the right wire guage.
But you have to have thick walls (6" of insulation) and the right wattage.
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JohnnyBuckminster
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Quote: Originally posted by macckone  | There are only three normal types of heating that will get you to the temperature necessary to melt aluminum oxide.
1) carbon arc furnace (3000C)
2) hydrogen oxygen furnace (3080C)
3) microwave furnace (2200C for commercially available set ups)
All three use graphite crucibles to contain the melt.
Resistance elements top out at about 1850C with MoSi2
From a practical perspective the second two are better as no carbon particles get in the melt.
The microwave is just barely enough to reach the right temperature.
A hydrogen/oxygen type set up is used to make gem quality and/or clear alumina windows. |
I have been looking for references about option 2, using a graphite crucible in a hydrogen-oxygen furnace, but there doesn't seem to be that common.
Does anybody have any info on this, i.e. how do you use a graphite crucible in a hydrogen-oxygen furnace?
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wg48temp9
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| Quote: Originally posted by JohnnyBuckminster |
I have been looking for references about option 2, using a graphite crucible in a hydrogen-oxygen furnace, but there doesn't seem to be that common.
Does anybody have any info on this, i.e. how do you use a graphite crucible in a hydrogen-oxygen furnace?
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Red hot carbon reacts with water vapor to produce CO and H2. Graphite probably does the same. So a red hot graphite crucible, particularly one at
3,000C, may not last very long when heated with a hydrogen oxygen flame.
I am wg48 but not on my usual pc hence the temp handle.
Thank goodness for Fleming and the fungi.
Old codger' lives matters, wear a mask and help save them.
Be aware of demagoguery, keep your frontal lobes fully engaged.
I don't know who invented mRNA vaccines but they should get a fancy medal and I hope they made a shed load of money from it.
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Admagistr
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| Quote: Originally posted by Fulmen | | @Admagistr: My advice; start with a 1000-1200°C furnace. The challenge grows exponentially with temperature, working at 2000°C with no prior
experience isn't realistic. |
I worked with a laboratory crucible furnace with a temperature up to 1000 C. Some time ago, I purchased a very precisely controlled modern laboratory
furnace, with PID regulation, from a European manufacturer, up to a temperature of 1250 C. So some little experience I have...
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Admagistr
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| Quote: Originally posted by JohnnyBuckminster | | Quote: Originally posted by macckone | There are only three normal types of heating that will get you to the temperature necessary to melt aluminum oxide.
1) carbon arc furnace (3000C)
2) hydrogen oxygen furnace (3080C)
3) microwave furnace (2200C for commercially available set ups)
All three use graphite crucibles to contain the melt.
Resistance elements top out at about 1850C with MoSi2
From a practical perspective the second two are better as no carbon particles get in the melt.
The microwave is just barely enough to reach the right temperature.
A hydrogen/oxygen type set up is used to make gem quality and/or clear alumina windows. |
I have been looking for references about option 2, using a graphite crucible in a hydrogen-oxygen furnace, but there doesn't seem to be that common.
Does anybody have any info on this, i.e. how do you use a graphite crucible in a hydrogen-oxygen furnace?
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Also, I haven't heard anything about oxy-hydrogen furnaces with graphite crucible in which Al2O3 melts...Carbon reacts with water vapor at high
temperatures and creates dangerous gaseous products...In our country, it's called "Water Gas."
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macckone
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You have to use a reverb type set up.
The aluminum oxide is heated from the top, not the bottom.
Hydrogen oxygen flame will ignite graphite.
The graphite crucible is often heated from the bottom with traditional electrical heating to 1400C.
Since graphite is a pretty good insulator, the aluminum oxide in the crucible stays fluid with the flame heat input and the flame doesn't impinge on
the graphite.
The aluminum oxide is preheated in a chute as it is dropped into the crucible.
This how they do it for large panes of aluminum oxide.
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Fulmen
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@Admagistr: That's good to know, it's hard to give advice without knowing your experience.
We're not banging rocks together here. We know how to put a man back together.
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Admagistr
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| Quote: Originally posted by macckone | You have to use a reverb type set up.
The aluminum oxide is heated from the top, not the bottom.
Hydrogen oxygen flame will ignite graphite.
The graphite crucible is often heated from the bottom with traditional electrical heating to 1400C.
Since graphite is a pretty good insulator, the aluminum oxide in the crucible stays fluid with the flame heat input and the flame doesn't impinge on
the graphite.
The aluminum oxide is preheated in a chute as it is dropped into the crucible.
This how they do it for large panes of aluminum oxide. |
That might work well, thanks for the tip! I've thought about it, too, and I haven't seen a major problem. There's a company in our country that makes
sapphire tubes and crucibles by modified Stepanov method. I spoke to their production experts and they told me they use large vessels of molybdenum
and tungsten, working in a vacuum, or in an argon atmosphere. Those sapphires can then be surface contaminated with molybdenum. I suggested that they
reheat them in the air at a high temperature to oxidize traces of Mo to MoO3, which they did, and when the product came to me it looked completely
clean. I had to pay extra for that. Otherwise, their finished sapphire products have a chemical purity of 99.999%!
I'm also thinking and dreaming about the possibility of melting Al2O3 with an infrared CO2 laser. I don't know if any offered by Chinese retailers
would be appropriate, I'd be more inclined to make my own CO2 laser, there's a few detailed instructions on how to do it on the internet, but it's not
quite simple... The idea is very attractive for me, the laser heating would maintain perfect chemical purity...I even found a video on YouTube where
Al2O3 melts in the focus of a giant solar furnace!
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Twospoons
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A laser is a rather inefficient way to put heat into bulk material. CO2 lasers are about 10% wall-plug to light output.
Helicopter: "helico" -> spiral, "pter" -> with wings
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JohnnyBuckminster
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| Quote: Originally posted by Admagistr | | Quote: Originally posted by macckone | You have to use a reverb type set up.
The aluminum oxide is heated from the top, not the bottom.
Hydrogen oxygen flame will ignite graphite.
The graphite crucible is often heated from the bottom with traditional electrical heating to 1400C.
Since graphite is a pretty good insulator, the aluminum oxide in the crucible stays fluid with the flame heat input and the flame doesn't impinge on
the graphite.
The aluminum oxide is preheated in a chute as it is dropped into the crucible.
This how they do it for large panes of aluminum oxide. |
That might work well, thanks for the tip! I've thought about it, too, and I haven't seen a major problem. There's a company in our country that makes
sapphire tubes and crucibles by modified Stepanov method. I spoke to their production experts and they told me they use large vessels of molybdenum
and tungsten, working in a vacuum, or in an argon atmosphere. Those sapphires can then be surface contaminated with molybdenum. I suggested that they
reheat them in the air at a high temperature to oxidize traces of Mo to MoO3, which they did, and when the product came to me it looked completely
clean. I had to pay extra for that. Otherwise, their finished sapphire products have a chemical purity of 99.999%!
I'm also thinking and dreaming about the possibility of melting Al2O3 with an infrared CO2 laser. I don't know if any offered by Chinese retailers
would be appropriate, I'd be more inclined to make my own CO2 laser, there's a few detailed instructions on how to do it on the internet, but it's not
quite simple... The idea is very attractive for me, the laser heating would maintain perfect chemical purity...I even found a video on YouTube where
Al2O3 melts in the focus of a giant solar furnace!
|
There are some reports about holding Al3+ in graphite crucibles, it is problematic because of the formation of alumina carbides, see for example Hoseinpur & Safarian,
"Results showed that Al in Si–Al melt infiltrates into graphite leading to the formation of aluminum carbides, which accompanies with volume
expansion and therefore the crucible destruction."
That might be why it is necessary to use molybdenum / tungsten crucibles.
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Admagistr
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| Quote: Originally posted by JohnnyBuckminster | | Quote: Originally posted by Admagistr | | Quote: Originally posted by macckone | You have to use a reverb type set up.
The aluminum oxide is heated from the top, not the bottom.
Hydrogen oxygen flame will ignite graphite.
The graphite crucible is often heated from the bottom with traditional electrical heating to 1400C.
Since graphite is a pretty good insulator, the aluminum oxide in the crucible stays fluid with the flame heat input and the flame doesn't impinge on
the graphite.
The aluminum oxide is preheated in a chute as it is dropped into the crucible.
This how they do it for large panes of aluminum oxide. |
That might work well, thanks for the tip! I've thought about it, too, and I haven't seen a major problem. There's a company in our country that makes
sapphire tubes and crucibles by modified Stepanov method. I spoke to their production experts and they told me they use large vessels of molybdenum
and tungsten, working in a vacuum, or in an argon atmosphere. Those sapphires can then be surface contaminated with molybdenum. I suggested that they
reheat them in the air at a high temperature to oxidize traces of Mo to MoO3, which they did, and when the product came to me it looked completely
clean. I had to pay extra for that. Otherwise, their finished sapphire products have a chemical purity of 99.999%!
I'm also thinking and dreaming about the possibility of melting Al2O3 with an infrared CO2 laser. I don't know if any offered by Chinese retailers
would be appropriate, I'd be more inclined to make my own CO2 laser, there's a few detailed instructions on how to do it on the internet, but it's not
quite simple... The idea is very attractive for me, the laser heating would maintain perfect chemical purity...I even found a video on YouTube where
Al2O3 melts in the focus of a giant solar furnace!
|
There are some reports about holding Al3+ in graphite crucibles, it is problematic because of the formation of alumina carbides, see for example Hoseinpur & Safarian,
"Results showed that Al in Si–Al melt infiltrates into graphite leading to the formation of aluminum carbides, which accompanies with volume
expansion and therefore the crucible destruction."
That might be why it is necessary to use molybdenum / tungsten crucibles.
|
On the other hand, Henry Moissan, winner of the Nobel Prize in Chemistry, successfully used his electric arc furnace and graphite crucible to
synthesize rubies! I wrote a new topic here recently in a forum. So you can see that even graphite can be used, albeit in a limited way...
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JohnnyBuckminster
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| Quote: Originally posted by Admagistr | | Quote: Originally posted by JohnnyBuckminster | | Quote: Originally posted by Admagistr | | Quote: Originally posted by macckone | You have to use a reverb type set up.
The aluminum oxide is heated from the top, not the bottom.
Hydrogen oxygen flame will ignite graphite.
The graphite crucible is often heated from the bottom with traditional electrical heating to 1400C.
Since graphite is a pretty good insulator, the aluminum oxide in the crucible stays fluid with the flame heat input and the flame doesn't impinge on
the graphite.
The aluminum oxide is preheated in a chute as it is dropped into the crucible.
This how they do it for large panes of aluminum oxide. |
That might work well, thanks for the tip! I've thought about it, too, and I haven't seen a major problem. There's a company in our country that makes
sapphire tubes and crucibles by modified Stepanov method. I spoke to their production experts and they told me they use large vessels of molybdenum
and tungsten, working in a vacuum, or in an argon atmosphere. Those sapphires can then be surface contaminated with molybdenum. I suggested that they
reheat them in the air at a high temperature to oxidize traces of Mo to MoO3, which they did, and when the product came to me it looked completely
clean. I had to pay extra for that. Otherwise, their finished sapphire products have a chemical purity of 99.999%!
I'm also thinking and dreaming about the possibility of melting Al2O3 with an infrared CO2 laser. I don't know if any offered by Chinese retailers
would be appropriate, I'd be more inclined to make my own CO2 laser, there's a few detailed instructions on how to do it on the internet, but it's not
quite simple... The idea is very attractive for me, the laser heating would maintain perfect chemical purity...I even found a video on YouTube where
Al2O3 melts in the focus of a giant solar furnace!
|
There are some reports about holding Al3+ in graphite crucibles, it is problematic because of the formation of alumina carbides, see for example Hoseinpur & Safarian,
"Results showed that Al in Si–Al melt infiltrates into graphite leading to the formation of aluminum carbides, which accompanies with volume
expansion and therefore the crucible destruction."
That might be why it is necessary to use molybdenum / tungsten crucibles.
|
On the other hand, Henry Moissan, winner of the Nobel Prize in Chemistry, successfully used his electric arc furnace and graphite crucible to
synthesize rubies! I wrote a new topic here recently in a forum. So you can see that even graphite can be used, albeit in a limited way...
|
Moissan, didn't he just throw everything into water, so the crucible was "consumed" in the experiment?
Forth and back, I have been thinking about a small scale furnace, ~50 ml volume, for high-temperature experiments, > 2 000 C. I ruled out the
electric arc furnace because it seems difficult to control. A hydrogen-oxygen furnace is appealing, highly controllable, can reach temperatures up to
3 000 C, and you don't need to worry about blowing the fuses. But, unwanted chemistry can be induced, because of the atmosphere.
A Nernst lamp is a very interesting option as a heat source, it should be highly controllable, and can operate in an ordinary atmosphere.
The company in your country, that makes sapphire tubes in molybdenum and tungsten crucibles, how do they heat the crucible?
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metalresearcher
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Maybe this Chinese supplier of induction furnace might give you an idea ?
https://www.cdocast.com/category/precious-metal-melting-furn...
Or (cheaper and easier) the Youtube channel of Nighthawkinglight, he has some nice ideas of obtaining high temperatures.
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Admagistr
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Moissan doesn't say if the crucible went down or not, it just says what voltage and current he used and how long the meltdown lasted, it was only 10
to 15 minutes! Our manufacturer uses induction heating, it's standard procedure for the Czochralski method and its like. The manufacturer is CRYTUR
and is based in Turnov, Czech Republic. It has a great tradition and experience, now it is focused on the American market. I thought of powering up
that Moissan furnace with four 12V batteries, designed for automobiles, and using an induction, a silencer, some coil to guard the batteries for
overload and to keep them from exceeding the prescribed current. An electrician told me that he had once built a similar battery power suply and it
worked as a welder for him. In Prague, at Charles University, they use an optical furnace to synthesize rubies and sapphires and other gems, when the
necessary temperature is generated in a pipe of quartz glass, in the focus of ellipsoidal mirrors! They use for it powerful halogen lamps. I spoke to
their expert and he invited me to tour their labs. I haven't been there yet, because of Covid. Thanks so much for the link and the tips, Greetings
German colleagues and friends!
[Edited on 8-12-2021 by Admagistr]
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JohnnyBuckminster
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| Quote: Originally posted by Admagistr | | Quote: Originally posted by macckone | You have to use a reverb type set up.
The aluminum oxide is heated from the top, not the bottom.
Hydrogen oxygen flame will ignite graphite.
The graphite crucible is often heated from the bottom with traditional electrical heating to 1400C.
Since graphite is a pretty good insulator, the aluminum oxide in the crucible stays fluid with the flame heat input and the flame doesn't impinge on
the graphite.
The aluminum oxide is preheated in a chute as it is dropped into the crucible.
This how they do it for large panes of aluminum oxide. |
That might work well, thanks for the tip! I've thought about it, too, and I haven't seen a major problem. There's a company in our country that makes
sapphire tubes and crucibles by modified Stepanov method. I spoke to their production experts and they told me they use large vessels of molybdenum
and tungsten, working in a vacuum, or in an argon atmosphere. Those sapphires can then be surface contaminated with molybdenum. I suggested
that they reheat them in the air at a high temperature to oxidize traces of Mo to MoO3, which they did, and when the product came to me it looked
completely clean. I had to pay extra for that. Otherwise, their finished sapphire products have a chemical purity of 99.999%!
I'm also thinking and dreaming about the possibility of melting Al2O3 with an infrared CO2 laser. I don't know if any offered by Chinese retailers
would be appropriate, I'd be more inclined to make my own CO2 laser, there's a few detailed instructions on how to do it on the internet, but it's not
quite simple... The idea is very attractive for me, the laser heating would maintain perfect chemical purity...I even found a video on YouTube where
Al2O3 melts in the focus of a giant solar furnace!
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Did you get any information about why they work in vacuum or in an argon atmosphere, is it to protect the crucible or the melt?
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macckone
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They use an inert environment to protect the crucible.
The melt is a very stable oxide.
Graphite crucibles used in industry have a very limited life span but are considerably cheaper than molybdenum or tungsten in the same size.
Once the large chunk is made, they cut off the edges that are 'imperfect' then slice it to make windows.
Diamond saw blades etc, the waste dust is used as a polishing abrasive.
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Ubya
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https://www.youtube.com/watch?v=VTzKIs19eZE
i have no idea the temperature that could be reached with this arc furnace, but it is small, uses "common" materials and it is pretty simple to
operate (even though i wouldn't call it 100% safe foor newbies).
the electrodes get burned pretty quickly, and the insulating brick he used in the video got pretty beat up by the heat, so i suppose finding a
refractory/insulating brick that survives 2.000°C is a challange in itself
i know this post was about a small furnace that uses nerst elements, i have 0 experience with nerst lamps (i only know of them because i had an IR
spectroscopy course)
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feel free to correct my grammar, or any mistakes i make
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Admagistr
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| Quote: Originally posted by Ubya | https://www.youtube.com/watch?v=VTzKIs19eZE
i have no idea the temperature that could be reached with this arc furnace, but it is small, uses "common" materials and it is pretty simple to
operate (even though i wouldn't call it 100% safe foor newbies).
the electrodes get burned pretty quickly, and the insulating brick he used in the video got pretty beat up by the heat, so i suppose finding a
refractory/insulating brick that survives 2.000°C is a challange in itself
i know this post was about a small furnace that uses nerst elements, i have 0 experience with nerst lamps (i only know of them because i had an IR
spectroscopy course) |
Great video, thanks! I'll be making a brick of zirconia (ZrO2) reinforced with sodium silicate solution! Zirconia has a melting temperature of 2700C!
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yobbo II
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Once you 'reinforce' the ZrO2 you will decrease its melting temp.
PURE ZrO2 has a melting temp. of 2700C.
Pure bricks are very expensive. I think it's because they are pure or perhaps they are a low volume produced product or both?
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Admagistr
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| Quote: Originally posted by yobbo II |
Once you 'reinforce' the ZrO2 you will decrease its melting temp.
PURE ZrO2 has a melting temp. of 2700C.
Pure bricks are very expensive. I think it's because they are pure or perhaps they are a low volume produced product or both? |
That's a good point, and unfortunately true...Thanks for that. In which case, it would be better to use sodium zirconiate, or a zirconium dioxide
water gel... Some of the "zirconia" bricks are actually ZrSiO4, not ZrO2. Also, ZrO2 is mixed with Al2O3 for those purposes. Why these bricks are so
expensive I don't know, but maybe because the sintering process that they're probably making takes a long time and high temperatures. Plus ZrO2 is
much more expensive than, say, Al2O3...
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yobbo II
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There is a link here showing Zirconia blocks. They range from 99% to 99.999%
https://www.americanelements.com/zirconium-blocks-7440-67-7
Funny thing is they give the same melting temperautres?
Bricks here at about 12 bucks each!
https://www.ebay.co.uk/itm/264205633418?_trkparms=amclksrc%3...
Tubes of ZiO2+Yit Oxide here but they are probably a silly price.
https://www.preciseceramic.com/products/zirconia-ysz-tube/
Yob
[Edited on 11-12-2021 by yobbo II]
[Edited on 11-12-2021 by yobbo II]
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metalresearcher
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You can also use magnesia (mp 2800 C). I tried to find a supplier of MgO bricks, but could not find one.
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Admagistr
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Thanks a lot! That would be a cheaper solution, I believe . Moissan used calcium
oxide in his furnace as thermal insulation, which surprises me, because of its, to water rather reactive and then corrosive nature...Before it turns
into CaCO3.
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macckone
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Magnesia is easily synthesized.
Start with sorel cement, heat until all the HCl is given off.
To make it impermeable you can treat it with milk of magnesia (use the low sodium variety).
Then treat with linseed oil, which will crosslink and carbonize under heat.
At the working temperature you are hoping to achieve, the carbon with graphitize.
This yields a magnesia/graphite composite that is very durable and capable of withstanding all but the highest temperatures (> 2500C) and is more
resistant to oxidizing conditions.
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