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Author: Subject: heating a cracked dewar
CouchHatter
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thumbdown.gif posted on 30-7-2018 at 18:04
heating a cracked dewar


I have obtained a 4.5L Dilvac dewar, vacuum flask in stainless steel. The top wall of the glass is cracked so I have no wish to use it for storage.

Ignoring the inefficient heating aspect, would this vessel be suitable for concentrating acids? Would heating something intended to insulate just be ineffective and stupid? It's not like I can use a hemispheric heating mantle.

I'm imagining that small amounts of hot acid vapors might enter and stress the glass, and suddenly extending the crack further down the sides, react with the steel.
Or perhaps the moisture in the air in the glass will condense at the mouth of the crack, before the sulfuric acid, and drip into the hot acid causing an exothermic reaction.
Maybe the heating would be near-comparable to a non-vacuum flask, now that the vacuum is compromised. Or maybe the silvering would still keep out half of the thermal energy and I would waste a lot of electricity. I've half a mind to put it all in my fume hood behind safety glass and let it run its course.

Any thoughts? Any use I can get out of it, even if its just repurposing the steel lever clips on the lid, will be a bonus. It'd make a nice thermos:P

DSC_0587 - Copy.jpg - 850kB DSC_0586 - Copy.jpg - 789kB

[Edited on 31-7-2018 by CouchHatter]
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Ubya
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[*] posted on 30-7-2018 at 22:19


mh i can't see how something made to insulate its inside would work as a good heating flask, plus it's cracked, and you want to stress it i suppose concentrating sulphuric acid?
bad idea





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Sulaiman
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[*] posted on 31-7-2018 at 01:06


As far as I can determine from the photo's, the glass is worse than useless.
There is probably no vacuum so not much use as a Dewar/Thermos flask,
and I guess that extreme cold or heat will cause the crack to propagate.

I would investigate the cost of repairing (unlikely) or replacing the glass.

If the glass cannot be reasonably repaired or replaced then I would smash the glass and clean out the stainless steel bucket.

Although boiling concentrated sulphuric acid will slowly corrode stainless steel,
you could use the stainless steel for concentrating sulphuric acid.

I believe hot dilute nitric acid would eat through the steel pretty quickly,
unless you first passivate the surface with conc. nitric acid.

I doubt that there is a way to boil HCl without rapidly digesting the steel.
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