Sciencemadness Discussion Board

Glass KNO3 chemical treatment

deadrush - 30-12-2025 at 11:20

Has anyone ever chemically treated their lab glassware?

For those who are unaware, glass that is submerged in melted KNO3 (like 334C, 640F) will go through surface ion exchange. The Na+ ions in the glass will be replaced with larger K+ ions. This results in the glass being more scratch resistant, harder, and more chemically & thermally resistant.

Anyone ever attempt it at home? I want to try this but I've never had the best luck with glass working.

[Edited on 30-12-2025 by deadrush]

[Edited on 30-12-2025 by deadrush]

bnull - 30-12-2025 at 13:04

I shared a paper dealing with alkaline cation exchange some time ago in the context of glass embrittlement (https://www.sciencemadness.org/whisper/viewthread.php?tid=15...). It may be worth a look.

random thoughts:

Sulaiman - 30-12-2025 at 22:54

if anything organic enters a bath of molten kno3
I would like to watch the video ! ;)
... same goes for anything flammable or even oxidisable.

{true story : a cicak (aka gecko) once pooped into my coffee mug.. ploop!
it then ran off across the ceiling - laughing !}

the heating and cooling stresses on the glass would, I guess, be significant.
bnull pointed to his post describing a rugged 100ml RBF,
I suspect that the main reason for its survival is that
it was not his one and only treasured 100ml rbf
- they only break when you care about them or need them.

"Has anyone ever chemically treated their lab glassware?"
I think that we all have - but not in a good way,
maybe mistreated is a more appropriate word ;)

the idea of a pot of molten kno3 is still in my head,
you will need excellent ppe
or a disposable lab assistant :)

Happy New Year :)

[Edited on 1-1-2026 by Sulaiman]

jackchem2001 - 2-1-2026 at 04:46

If the phenomenon/deliberate treatment of ion exchange is observed with molten salts, then it would explain why that flask suffered no damage (or at least seemed to). The reaction mixture it was exposed to sinters but does not melt, even at the very high temperature. I still have the flask and it appears undamaged, though I do not use it

fx-991ex - 2-1-2026 at 07:08

i guess someone could preheat the flask in a oven or something similar.

Deathunter88 - 2-1-2026 at 12:07

Quote: Originally posted by Sulaiman  
if anything organic enters a bath of molten kno3
I would like to watch the video ! ;)
... same goes for anything flammable or even oxidisable.

{true story : a cicak (aka gecko) once pooped into my coffee mug.. ploop!
it then ran off across the ceiling - laughing !}

the heating and cooling stresses on the glass would, I guess, be significant.
bnull pointed to his post describing a rugged 100ml RBF,
I suspect that the main reason for its survival is that
it was not his one and only treasured 100ml rbf
- they only break when you care about them or need them.

"Has anyone ever chemically treated their lab glassware?"
I think that we all have - but not in a good way,
maybe mistreated is a more appropriate word ;)

the idea of a pot of molten kno3 is still in my head,
you will need excellent ppe
or a disposable lab assistant :)

Happy New Year :)

[Edited on 1-1-2026 by Sulaiman]


Molten KNO3 is not nearly as scary or oxidizing as you seem to fear it is. Anything organic that falls in will likely just decompose or maybe catch fire, but not explode violently. 334C is pretty hot, but is nowhere near the softening point of borosilicate, so if this is done carefully I don't see a problem.

BromicAcid - 2-1-2026 at 13:03

I used to clean my flasks with molten NaNO3, I did a lot of attempts at making CS2 from carbon and sulfur and it made a mess (to say the least). I'd clean out what I could and then for the residue would just add solid NaNO3 and heat it with a blowtorch (gently). The MP of KNO3 isn't much hotter (a quick search of google for the Mp was complicated since it assumes the word nitrate is unrelated and instead provides all the information for just potassium - thanks AI).

Anyway, I did some work with silyl chlorides awhile back and I still end up using the graduate cylinder that I used that is still hydrophobic despite several cleanings. It's interesting the way the water drops fall out when you empty it. I suppose it's just like Rain-X.

pesco - 31-1-2026 at 04:04

BromicAcid, can you give more details please? Hydrophobic glass can be useful at times.


Thanks deadrush, interesting option in light of larger scale synthesis of CuxSy via melting S with metallic Cu that I am planning.




jackchem2001 - 28-2-2026 at 03:09

All of my joints are hydrophobic from a thin layer of absorbed silicone grease, lol
They don't get wetted by water. They are not sticky to the touch or anything like that

Melting point of KNO3 is roughly 340 degC if memory serves