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cleaning glass frit

Arthur Dent - 20-3-2011 at 06:27

Mystery Stain...

quick question about cleaning the glass frit of a nice buschner funnel I acquired yesterday. It's an used Pyrex 60 ml and when I got it, I noticed it had a rather deep purple stain on the upper surface, less on the lower surface. The guy at the shop gave me a substancial rebate because of the stain. Yay!

Stain unknown... so I first washed the funnel with hot water, then dunked it for a couple of hours in a bath of 20% HCl. All the other glassware in the bath had become spotless but the stain in the funnel seemed unaffected.

I put the funnel upside down in a beaker and dropped 32% HCl in the spout. Nothing. So I washed it thoroughly again with hot water and decided to try 98% Sulphuric acid, again with the funnel upside down in a beaker.

There is some improvement, and the lower surface looks less stained. The H2SO4 has acquired a vaguely yellowish tinge, but the stain is still there on the upper surface.

It's a really nice funnel and i'd like to bring it back to brand new if possible, but I read that piranha is not recommended because of the risk of explosion, and NaOH could damage and weaken the frit.

Chomic acid is unavailable to me, but I do have HNO3 if this could be useable. Or should I leave the sulphuric acid eating away at the stain for a long time?

Not knowing what was the chemical that stained the frit is a problem, but the purple might hint at a iodine compound?

Robert

hissingnoise - 20-3-2011 at 06:41

Quote:

Not knowing what was the chemical that stained the frit is a problem, but the purple might hint at a iodine compound?

Or free iodine - try washing with ethanol . . .

[Edited on 20-3-2011 by hissingnoise]

Arthur Dent - 20-3-2011 at 14:32

After the relative success of the H2SO4, the stain was notieably lighter in places, so I rinsed the funnel thoroughly and tried hydrogen peroxide and to my surprise, the stain is almost gone!

So i'm leaving the frit happily bubbling away while the stain right now is 10% in intensity of that it was at the beginning. Hopefully in a few hours, it'll be all gone. Still don't know what that mystery compound was, but it seems H2O2 does the trick!

That was the bottom before the peroxide, right now, the bottom is porcelain white and the top still exhibits a bit of grayish purple on the outer edge of the frit

BTW this is not the medical 3% peroxide but the 10% hair bleaching grade.

Robert

[Edited on 20-3-2011 by Arthur Dent]

SHADYCHASE54 - 20-3-2011 at 16:46

I have run into a similar problem the glass frit on the end of my gas washing bottle is stained purple from a solution of potassium permangnate. Does anyone have any ideas on how I might rid myself of this ugly discoloration?

Lambda-Eyde - 20-3-2011 at 16:52

Hydrogen peroxide + sulfuric acid (both dilute). The peroxide will reduce MnO2 and residual KMnO4 in an acidic environment.

Arthur Dent - 20-3-2011 at 17:54

Wow! I'm impressed! The hydrogen peroxide dit it. The funnel's frit is absolutely spotless! It looks like brand new! Took about 5 hours with 20 ml of 10% H2O2.

I did a final wash in hot water and then poured some acetone in it to displace the remaining traces of water. Yay!

Robert

ScienceHideout - 23-3-2011 at 12:15

If it is iodine, sodium thiosulphate works to get it out.

jamit - 6-4-2011 at 11:36

Can anyone tell me what the frit is made of? What can't you pour down these filter funnels?

atomicfire - 6-4-2011 at 11:48

From Adams & Chittenden Scientific:

"Fritted discs are made by heating glass particles or fibers at a high enough temperature that they fuse together sufficiently that they become a relatively strong object. In our case, the glass is borosilicate glass, and is the same as the standard material for laboratory apparatus, i.e. Pyrex 7740, Kimax KG-33, or Schott Duran."

http://www.adamschittenden.com/Frit_info.html

I did always wonder how they detemined pore size, and apparently they use air.

jamit - 6-4-2011 at 19:11

Thanks Atomicfire. I guess that means you can just about filter anything even concentrated acids (except hydrofloric acid and naoh).

I heard that one should avoid filtering any carbon since that would be next to impossible to remove.

Fleaker - 6-4-2011 at 19:36

Carbon isn't impossible to remove. Quick whirl in a box oven overnight usually does it. My glassblower says that the fritted pieces will usually crack right after the frit's been put in there, but it's unlikely afterward. That's how we cleaned our stuff that wasn't metal contaminated--after we got it as clean as we could, it was baked overnight with the schlenkware to 580*C.

Aqua regia works really well. I use that to remove Pt, Pd, Au from my frit-ware.

jamit - 7-4-2011 at 02:09

Thanks Fleaker for that info.

I bought some glass frit from ebay and it looks clean... should I bake it in the oven overnight just to make sure it is clean? Any suggestions?

deathmetals - 7-4-2011 at 03:45

Quote: Originally posted by SHADYCHASE54

I have run into a similar problem the glass frit on the end of my gas washing bottle is stained purple from a solution of potassium permangnate. Does anyone have any ideas on how I might rid myself of this ugly discoloration?

oxalic acid and mild heating to 80c is quantitive.(with a bit sulfuric acid
it only takes 30 minutes.
another use is a rust remover worked perfectly with my bike chain.
make sure you wash well with water after using it on metal objects.

edit: make sure to avoid contact with it, as it will cause kidneystones witch are calciumoxalate

standerdization of permangenate solution

ny times article about kidney stones

[Edited on 7-4-2011 by deathmetals]

jamit - 7-4-2011 at 18:14

Are these glass frit a substitute for filter paper or are there specific purpose for using glass frit for filtering?

I'm curious, it seems like a waste using filter paper if you can buy one of these glass frit with various porosity.

[Edited on 8-4-2011 by jamit]

jamit - 8-4-2011 at 09:30

For regular use why wouldn't you just use a glass frit to filter everything?

Or is the glass frit filter used for specific purpose?

Can someone help me to understand the difference and usage for glass frit vs regular filter paper funnel? thanks.

Arthur Dent - 8-4-2011 at 15:08

The regular filter paper funnel works with gravity to make a liquid filter through the pores of filter paper. So you can use this with any compound that is easily filterable, like a salt solution with a coarse precipitate.

The glass frit vessel, like a buschner funnel is used in association with a vacuum apparatus, like a flask with a sidearm to apply a vacuum to help "sucking out" the liquide fom a dense precipitate that would otherwise clog the pores of a regular filter paper.

A glass frit of couse, is fragile since it's made of sintered particles of glass, and must be handled carefully, must never be submitted to compounds that are corrosive to glass, like HF, KOH and NaOH.

A third alternative, is the fritless ceramic buschner funnel that uses vacuum like a glass frit buschner funnel, but has a solid bottom that's punctured with several tiny holes and you just drop a round filter paper on it. Often bigger and more resistant than a glass frit, but less delicate for the really fine stuff.

Hope this helps

Robert

jamit - 16-9-2011 at 14:37

I just purchased a set of glass fritted buchner funnel but several of them are badly colored. it got even more discolored after filtering a hot solution of badly contaminated pottery grade potassium nitrate -- dark amber solution.

I tried to clean it with hydrochloric acid, then tried hydrogen peroxide as suggested by arthur dent, then sodium metabisulfite, then acetone, then isoprophyl alcohol, but nothing. :mad:

I wonder if the fine particles that is stuck in the frit is carbon and if so how can you remove carbon... isn't it next to impossible?

Any help would be appreciated. thanks.

hkparker - 16-9-2011 at 14:49

Quote: Originally posted by Fleaker

Carbon isn't impossible to remove. Quick whirl in a box oven overnight usually does it. My glassblower says that the fritted pieces will usually crack right after the frit's been put in there, but it's unlikely afterward. That's how we cleaned our stuff that wasn't metal contaminated--after we got it as clean as we could, it was baked overnight with the schlenkware to 580*C.

If its carbon that sounds like your best bet. I would also try thiosulfate solution or maybe aqua regia.

ScienceHideout - 16-9-2011 at 19:32

Who bumped this?

hkparker - 16-9-2011 at 23:59

Quote: Originally posted by ScienceHideout

Who bumped this?

...why? Just look at the dates on the posts (top left) and see when it was.

It was jamit.

Arthur Dent posted on 8-4-2011 at 15:08
jamit posted on 16-9-2011 at 14:37

ScienceHideout - 17-9-2011 at 12:05

ArthurDent posted in April. Jamit posted a half a year later... A topic this old should be Detritus?

hkparker - 17-9-2011 at 12:47

No! The topic is useful, detritus is for useless posts. Who cares how old the original thread was, if there is something new to add or a question then that's fine.

Otherwise, jamit would be posting a new thread about something that has already been discussed. I'm glad he used the search engine.

Endimion17 - 17-9-2011 at 14:42

Quote: Originally posted by jamit

I just purchased a set of glass fritted buchner funnel but several of them are badly colored. it got even more discolored after filtering a hot solution of badly contaminated pottery grade potassium nitrate -- dark amber solution.

I tried to clean it with hydrochloric acid, then tried hydrogen peroxide as suggested by arthur dent, then sodium metabisulfite, then acetone, then isoprophyl alcohol, but nothing. :mad:

I wonder if the fine particles that is stuck in the frit is carbon and if so how can you remove carbon... isn't it next to impossible?

Any help would be appreciated. thanks.

It's probably carbon, but might not be. I had the exact same problem, and solved it.
Try with fresh, room temperature chromic acid first. If it fails, use a moderately hot one. Be very careful. Always treat these things like they'll suddenly go bang.

If it fails, fresh acidic piranha. That's the last resort, used only when everything else fails, because this indicates that the residue is pretty inert and will not react abruptly (probably) with this extreme solution.
Use extreme precaution. If you have no experience with piranha solutions, I really don't recommend trying to clean something with it.

Acidic piranha will oxidize carbon and leave your frit daisy fresh.
Also, it will rip your flesh, chew it and spit it out. It's a nightmare.

Be sure not to cause excessive temperature differences in your funnel. I used piranha to clean one fritted vintage piece of glass and it just cracked. Not the fritted part, though.
If you worked with piranha, proceed, and ask for help if you're not sure what to do now.
If you never worked with it, stay away from these attempts. It's for your own good, trust me.

There are few procedures available online, if you google them.
I always found sentences like this one:

In case of contact with the skin, may cause skin burns.

Who, in the name of god, writes this stuff? May? It will cause burns. It eats skin. Eats. :mad:

What's up with using such stupid language in warning protocols and warning labels? "It might cause poisoning if swallowed", on mercury salt bottles.

[Edited on 17-9-2011 by Endimion17]