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JJay
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[*] posted on 11-2-2016 at 16:29
High Temperature Stoppers


I've been trying to figure out what to use as high temperature stoppers for quartz tubes. Using ground quartz (with borosilicate gradient adapters) would be nice but is a little outrageously expensive.

I was thinking about soaking corks in sodium silicate and perhaps covering them with ceramic paper. I've heard of sodium silicate soaked cork being used as engine gaskets, so I think that this might actually work. Or I might try just wadding/wrapping ceramic paper and using it as a stopper. I'm not sure how well either of these solutions will work, and I'm not sure what temperatures they will tolerate; the ceramic paper plug will likely tolerate high temperatures, but of course I would prefer to avoid filling the room with 1000 C hydrogen chloride gas or allowing hydrogen to escape the apparatus at red heat (or hypothetically leaking white phosphorus vapor, not that I have plans to make phosphorus), so I'm not too sure about that idea.

Does anyone have any ideas/experience in this area?
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Pyro
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[*] posted on 11-2-2016 at 16:58


1000*C I hope that's a typo! If not, are you aware that borosilicate melts at that temperature and steel is nearly bright yellow.

If you are using steel, why not use steel (screw on) caps?




all above information is intellectual property of Pyro. :D
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JJay
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[*] posted on 11-2-2016 at 17:13


That is definitely not a typo. Please read the entire post before responding; I clearly specified quartz.
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[*] posted on 11-2-2016 at 17:24


What is the diameter of the quartz tube? Is it open from both ends, and you plan to heat in the middle of the tube?



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JJay
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[*] posted on 11-2-2016 at 17:34


Right now I'm looking at several quartz tubes that are open on both ends; they are 25-50 mm OD. My plan is to wrap the tube with ceramic paper and Kanthal wire and run a removeable tube through it.
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BromicAcid
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[*] posted on 11-2-2016 at 17:59


You could mold something out of fireplace cement and then use a blowtorch to 'cure' it for use. That might be quick enough to try, fireplace cement is mostly silicates, just make sure you wear gloves, it bonds to your skin on drying and you end up peeling off pieces of skin. You might even want to incorporate some rockwool or other high temp insulation in with the fireplace cement to give it more form before you set it up with fire. The only worry would be how much will it expand on heating? Quarts has a ridiculously low expansion coefficent so the fireplace cement, if it is a tight fit, might expand and crack the tube, than again it will likely shrink once you fire it so you might end up breaking even in the end (not that I have done the calculation, it would just be funny).

However, usually the stopper does not get the bulk of heat, if your stopper is going to be sticking out of your furnace or not in your direct heat then you might be able to get away with sodium silicate soaked cork. I have never tried it myself but do remember reading about it plenty in older texts.

If you really want to get fancy you may be able to use a soft mineral and carve your own stoppers, one of the texts on making fluorine gas used stoppers carved from cryolite (which only has a hardness of 2.5-3 on the Mohs scale) or fluorite (hardness of 4) but I cannot remember which. I would think with metal there would just be too much expansion to give that a try. Maybe just use wood, make a stopper larger than you need out of wood, put it in a metal box and bake it to turn it into charcoal, it will shrink, it will be brittle, but I'm just spit-balling ideas here. Actually, graphite would be pretty good too but might require a bit more investment. Actually, looking into it, it might not be too bad to buy a graphite rod with a slightly larger OD than the quartz tube then just tapering it down by hand using a file/steel wool.

Let us know how it works out.




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blogfast25
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[*] posted on 11-2-2016 at 19:31


@JJay:

I think the solution depends a lot on what exactly you want to achieve with the quartz tube. Maybe elaborate a little on that? Often the inlet and outlet of a reactor can be maintained at much lower temperature than the tube's reaction zone.

[Edited on 12-2-2016 by blogfast25]




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[*] posted on 11-2-2016 at 20:27


Wood or cork, cork is wood, might puff up on heating + carbonization. Whether the force generated before the vapor is expelled through cracks and pores is enough to crack your tube is an open question.

[Edited on 12-2-2016 by halogen]




F. de Lalande and M. Prud'homme showed that a mixture of boric oxide and sodium chloride is decomposed in a stream of dry air or oxygen at a red heat with the evolution of chlorine.
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JJay
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[*] posted on 11-2-2016 at 23:31


Quote: Originally posted by blogfast25  
@JJay:

I think the solution depends a lot on what exactly you want to achieve with the quartz tube. Maybe elaborate a little on that? Often the inlet and outlet of a reactor can be maintained at much lower temperature than the tube's reaction zone.

[Edited on 12-2-2016 by blogfast25]


I am planning on making aluminum chloride and lithium hydride. I have also considered several pyrolysis reactions, as well as carbon reductions, gas phase reactions of carboxylic acids, calcinations, etc.
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[*] posted on 12-2-2016 at 08:00


Quote: Originally posted by JJay  


I am planning on making aluminum chloride and lithium hydride. I have also considered several pyrolysis reactions, as well as carbon reductions, gas phase reactions of carboxylic acids, calcinations, etc.


For AlCl3 (Al plus Cl2 or HCl) you really won't need any stoppering, because you'll only end up blocking any tubing you run though it with condensed AlCl3 (been there, done that). A wide cold trap attached to the cool part of the reactor tube is really all you can do.

Re LiH, obviously you want to be able to vent off any unreacted H2 safely. Assuming your Q-tube is long enough, your stoppers won't be exposed to high temperature, as the excess H2 cools down quickly in the unheated part of the Q-tube.

I've found ordinary (NR/SBR) lab stoppers carefully wrapped in Teflon 'gas tape' to resist quite hot chemicals quite well.

[Edited on 12-2-2016 by blogfast25]




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Heavy Walter
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[*] posted on 12-2-2016 at 11:59


JJay
If you plan to put the stopper in the borosilicate side of your transition quartz/glass, the stopper will have equal or lower temp than the borosilicate side, so no worry.
As someone said, if the borosilicate side can rest away of the oven, temp will be much lower.

I suggest to do a test, without chemicals inside and with thermocouples in order to get a thermal profile.
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[*] posted on 12-2-2016 at 15:09


High temperature stoppers? Not, I fear, for the temperatures you contemplate.

As I recall, long long long tubes are called for. So that, the ends of your tubes are rather cool, in relation to the fiery conditions in your reaction zone.

Sadly, those long tubes ain't cheap.
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JJay
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[*] posted on 12-2-2016 at 19:18


Quote: Originally posted by zed  
High temperature stoppers? Not, I fear, for the temperatures you contemplate.

As I recall, long long long tubes are called for. So that, the ends of your tubes are rather cool, in relation to the fiery conditions in your reaction zone.

Sadly, those long tubes ain't cheap.


Using rather long tubes seems like a good idea, especially when making aluminum chloride. 1m quartz tubes aren't too expensive, although alumina tubes get rather outrageously expensive in that size.

I might give furnace cement a try.
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[*] posted on 12-2-2016 at 19:46


Quote: Originally posted by BromicAcid  

If you really want to get fancy you may be able to use a soft mineral and carve your own stoppers, one of the texts on making fluorine gas used stoppers carved from cryolite (which only has a hardness of 2.5-3 on the Mohs scale) or fluorite (hardness of 4) but I cannot remember which.


How about soapstone (steatite)? It is famous for not cracking when subjected to strong heating. It is used in traditional societies as a cooking pot material. It is also very soft (Moh 1), easily carved with a knife. Its coefficient of thermal expansion is similar to Pyrex.

Welding supply places (or any place with welding supplies) carry soapstone sticks, but they may be to narrow to use as stopper material.

[Edited on 13-2-2016 by careysub]

[Edited on 13-2-2016 by careysub]
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[*] posted on 12-2-2016 at 23:19


I definitely don't want to crack any tubes. I wonder if aerogel would work... it is very expensive, though....
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[*] posted on 13-2-2016 at 09:58


One problem is that you're wanting to work with quartz. It conveys optical energy very efficiently, similar to fiber optic cable. Even if the end of the tube itself feels cool, optical energy travels down the tube to the stoppers, where it gets dissipated as heat. This can happen even with fairly long tubing.

Ever notice that if you bend fiber optic cable too tightly, that light escapes around the area of the bend? There's a certain minimum radius in the material that is needed for light to conduct efficiently. Energy transfer can be manipulated in quartz tubing the same way, by means of compressing several quartz "rings" at either end of the tube. The idea is for most of the energy to escape the tight bends in the rings, before it makes it to the stoppers. A custom glass blower would be needed for this, and it requires a lathe.

Here's a website explaining the same thing in a different way:

http://www.ilpi.com/glassblowing/quartzmaria.html




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[*] posted on 13-2-2016 at 11:06


Illuminating procedure! (No pun intended)
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JJay
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[*] posted on 13-2-2016 at 12:25


Quote: Originally posted by WGTR  
One problem is that you're wanting to work with quartz. It conveys optical energy very efficiently, similar to fiber optic cable. Even if the end of the tube itself feels cool, optical energy travels down the tube to the stoppers, where it gets dissipated as heat. This can happen even with fairly long tubing.

Ever notice that if you bend fiber optic cable too tightly, that light escapes around the area of the bend? There's a certain minimum radius in the material that is needed for light to conduct efficiently. Energy transfer can be manipulated in quartz tubing the same way, by means of compressing several quartz "rings" at either end of the tube. The idea is for most of the energy to escape the tight bends in the rings, before it makes it to the stoppers. A custom glass blower would be needed for this, and it requires a lathe.

Here's a website explaining the same thing in a different way:

http://www.ilpi.com/glassblowing/quartzmaria.html


Good to know. I'm trying to avoid any glassblowing, but it could be an option... I wonder what the disadvantages of using opaque quartz are.
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