Really high temperature glass

[Shandor]

I have searched the forums and have not found an answer to this, usually beucase the temperatures are too low.

I am working on a device that requires that I hold a vacuum at 1000-1300 degrees. Throughout the products life, the vacuum will go down to room temperature only to return to the high temperature from time to time (once a day or once a week, i am not sure)

I know of only two choices. Fused quartz and sapphire. Sapphire may be too expensive and fused quarts has an issue where it devitrifies and becomes opaque at these high temperatures.

I am currently under the impression that if I can keep the temp below 1100 degrees, then the devitrification will not happen, is this correct?

If I am unable to do that, is there another glass that would stay clear at these temperatures?

I realize there are a number of engineering challenges associated with holding that vacuum, especially at these changing temperatures, but for now I am only interested in the clarity of the glass.

thoughts?

 

[IRstuff]

1100ºC is at the edge of where the quartz will devitrify, i.e., it will take some time before that happens. There's a long amusing story about a former company's IC fab and the desire to drop the temperature of an oxidation step down to 1050ºC to minimize devitrification.

You need to explain your problem more clearly. What does "hold a vacuum at 1000-1300 degrees" mean, exactly? Are you heating the quartz to 1100ºC? or just the contents?

TTFN

FAQ731-376

 

[IRstuff]

For that matter, why do you need to have quartz? It's used in semiconductor furnaces, but thare are other materials that could be used:

http://www.sentrotech.com/ceramictube.php

http://www.thermcraftinc.com/box-fu...advanced&OVADID=1374566521&OVKWID=11419212021

TTFN

FAQ731-376

 

[unclesyd]

Is this a tube or a window?

Besides the temperature what is the enviroment?

 

[kenvlach]

Fused silica has to be kept scrupulously clean, as contaminants (finger prints, Fe⁺², ceramics) all catalyze the crystallization. The reaction begins at the contaminated surface. If the surface turns cloudy, use HF to etch it away to clear material.

 

[Shandor]

Thanks for all this info.

The quartz will be a tube. It must remain clear to let through light. THe inside of the quartz will be a vacuum. the outside of the quartz will be air. The thing making everything hot is at the center of the quartz tube (i cant go into more deatil on that, just know that between the hot thing and the quartz is a vacuum)

I am not married to quartz, but sapphire will probably be too expensive (but I am not throwing it out, yet). If there are other crystal clear (i.e. passes visible light) glasses that can withstand this temperature, i'm all for it, especially if they do not devitrify.

SO, am i correct that if I make sure that the glass does not go over 1050 deg C then I can expect it not to cloud up? Is it the surface that clouds (fixable), or is it impurities within the glass that cause the clouding (probably not fixable)?

as for "holding the vacuum at 1000-1300 deg c", i mean that the hot thing in the center will be between 1100-1500 deg C (not sure yet) and the 'quartz' tube will be at a diameter around it that keeps it at 1000-1300 deg (i am just not sure yet). The space in between will obviously be somewhere between the two and held in vacuum.

ok I dont know how to describe this any clearer. I hope it is enough info.

 

[IRstuff]

But, basically, it's like a diffusion furnace, except for the vacuum. So, I'd get in touch with the usual suspects that make diffusion furnace tubes for the IC industry:

http://www.quartz.com/gedata.html

describes some typical


TTFN

FAQ731-376

 

[Shandor]

Thank you.. that one link alone was very helpful.

 

[powerhound]

There is a difference in the properties of flame fused quartz and electrically fused quartz. Stabilized electrically fused quartz will be good up to around 1250 C but is only available in tubing form. Do a search on HSQ material. Start with HSQ 330 which is electrically fused, high purity. See what you come up with and let me know if I can be of any help. This happens to be my profession.

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[sreid]

I happened to come across Corning Vycor-Might have a price advantage over fused quartz.

http://www.corning.com/lifesciences/products__services/glass__portal/vycor.asp