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gdflp
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I would expect pottery grade to be good enough for cleaning, and Seattle Pottery Supply and US pigment both sell it for $12/pound. Elemental sells
lab grade potassium dichromate for $13.93/pound. With shipping for that one item it might be $10, but if you combine it with other things, it doesn't
need hazmat shipping so it's not that bad.
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Texium
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Alright, well, I'm glad that it shouldn't affect it. I do still happen to have most of that dichromate that Zyklon-A was referring to, so I'll
probably try cleaning it at some point just for the sake of having it look nice. 
It seems like nitric acid would get rid of it too, since conc. sulfuric is supposed to, but I don't have any.
[Edited on 7-29-2014 by zts16]
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Texium
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Today I went ahead and cleaned the Büchner funnel by pulling chromic acid through. It worked wonders, leaving it looking as good as new. Afterwards I
pulled plenty of distilled water through to make sure and flush out all of the hexavalent chromium, and disposed of the stuff in my hazardous waste
bucket. Definitely would prefer to not work with that stuff, but it really works. Thanks for the suggestion.
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HeYBrO
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Quote: Originally posted by zts16  | | Today I went ahead and cleaned the Büchner funnel by pulling chromic acid through. It worked wonders, leaving it looking as good as new. Afterwards I
pulled plenty of distilled water through to make sure and flush out all of the hexavalent chromium, and disposed of the stuff in my hazardous waste
bucket. Definitely would prefer to not work with that stuff, but it really works. Thanks for the suggestion. |
Did you reduce the chromium before you put it in your bucket?
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Texium
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Yeah, I did. I just let some aluminum foil soak in it until the solution all turned green.
I really hate working with hexavalent chromium, but sometimes it's the only thing that can get the job done.
[Edited on 10-25-2014 by zts16]
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blargish
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I can second that. I had a mortar that had some carbon/organic stains on it that did not want to come off. However, I dropped in a couple flakes of
CrO3 with some sulfuric acid, swirled around with the pestle, flushed with water, and the thing looked as good as new; pretty crazy.
However, like zts said, hexavalent chromium isn't the best thing to be dealing with.
I also remember seeing a youtube video where a guy cleaned a beaker covered in organic gunk by adding to it a combination of an Fe2+
solution and 30% hydrogen peroxide (Fenton's Reagent I think), letting the resulting radicals from the reaction oxidize the organics. I have not done
this myself, but in the video it seems to do a very good job. If I find the vid, I'll post it
BLaRgISH
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Texium
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Luckily for most organics, concentrated NaOH solution seems to work well enough. Burnt cinnamon caked onto the bottom of a flask was no match for it.
The flask was sparkling clean after 15 minutes of soaking.
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DrMario
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For the absolutely most stubborn organic contamination on glassware (or siliconcarbide-ware), we use piranha (H2SO4 + H2O2) at 120C.
Obviously, that stuff will make a nice dent in your hand, pretty much like the famous (and unintentionally hilarious) graphic warns.
[Edited on 26-10-2014 by DrMario]
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blargish
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Here is the video (not mine) of the use of Fenton's reagent to clean organic contamination on glassware.
https://www.youtube.com/watch?v=rJik_EnmgM0
BLaRgISH
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DrMario
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While my sense of wonderment was quite satisfied by that video, I must notice that the procedure is quite wasteful. The price of the beautiful H2O2
used in that demonstration was comparable to the value of the beaker.
The good thing about heated piranha is that you can use it to clean a lot of glass/ceramic/siliconcarbide-ware. The process is slower, but you only
have to dip the glassware in piranha and leave it there.
The bad thing about piranha is that it tries to kill you. Painfully.
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gdflp
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I tried a different method of cleaning glassware today and it worked great. Afterwards I searched and found a mention in an old thread, but I thought
that it would be useful info in this thread as well.
The flask, or whatever glassware needs to be cleaned, is filled with hot water, then some (I used ~20g for a 1L flask) automatic dishwasher detergent
is added and the flask is kept warm on a hot plate. It doesn't need to be terribly hot, ~45°C is fine. Noticeable gas evolution begins almost
immediately and, if the flask isn't clean after about an hour soaking, it is emptied and refilled with fresh solution. I'm guessing that this gas is
mainly CO2, but I haven't tested it. The detergent has it's ingredients listed as sodium carbonate, sodium silicate, and enzymes, and is
dirt cheap, about 1USD/lb. It's remarkably effective, and is much safer than using alcoholic sodium hydroxide, chromic acid, Piranha solution, etc.
The flask I was cleaning had polymerised tar from a failed Hofmann rearrangement, but I tried it on several other flasks with carbon stains and it
removed all of them. I doubt however that it will be as effective on transition metal stains, but it's worth a shot. I have a beaker, stained with
what I believe is some sort of chromium oxide, soaking in it currently, I will update later on the results.
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ave369
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In my country, the "chromium mixture" (hexavalent chromium in sulfuric acid) is typically used for removing organic residue from glassware. And for
stuff that does not react with it, the "nitrochromium mixture" is used, which is hexavalent chromium in concentrated nitric acid. The nitrochromium
mixture should be handled with care and only used for inert stains: if it comes in contact with reactive organics, unpredictable consequences may
ensue.
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gdflp
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So, it appears that the detergent was ineffective on the metal oxide stains, I'm not terribly surprised though. I did try it on some other organic
tars and it worked great on all of them.
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Fantasma4500
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it is possible if you have iron stains in a beaker, running iron-iron electrolysis using a halide-salt the XxO/Xx would very carefully scrape off the
iron stains, and possibly also this could be used for other stains that would react with halides / halide-ites (hypochlorite etc)
its also possible you could turn the glass beaker into a passive electrode with enough current, and maybe into a functional electrode with unrealistic
amounts of electricity
actually about hexavalent chromium and ozone would be possible to form through welding in stainless steel, maybe dragging the air from stainless steel
welding into a beaker could be used in a practical fashion??
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chemrox
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How much FeSO4/ml water is used to make Fenton's reagent Fe solution? I have seen a few different processes calling for Fe II solutions without
adequate documentation as if there were ONE FeSO4 solution.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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solitanze
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At our college we use chromic acid for cleaning basically everything. For really sensitive work boiling nitric acid is used after the chromic acid
treatment.
But in my homelab I'd rather save my nitric acid and dichromates for more interesting purposes. I've had good results with 30% HCl + calcium
hypochlorite for removing organic tars/residues from my glassware. Be wary of the chlorine gas that escapes though.
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Chemetix
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My go to solution for cleaning glassware is a welding 'pickle' that has about 30%nitric 10%HF. Only gentle warming is needed to remove the most
stubborn gunk; organic- inorganic, whatever. Take it from me, I'm a professional scientific glass blower.
After some 'pickle' treatment a cycle through the annealing oven at 585C gets just about everything off. I cant guarantee the glass will be perfectly
translucent anymore, more often than not it's fine. But if you have contaminated the glass that badly with minerals that change the chemistry of the
glass, then there's bound to be some damage done.
[Edited on 26-9-2016 by Chemetix]
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Fantasma4500
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lately i found out that if you have something sticky, an oil or maybe even worse PIB and you dont wanna waste solvents on it, you can simply rub some
dry powder onto it, in my world calcium carbonate is what is at hand, works well and also gets all of the grease off glass as well, the concept is
simple..
a sticky material will remain sticky until its stickyness is absorbed by something dry, such as paper or another dry material, if the powder added is
more susceptible to absorbing the "stickyness" than for instance the glassware you can rub it off easily
i avoid using flour because its a mess to wash off
on a pedantic sidenote directed Chemetix; be very careful with fluoride and fluorine compounds, they are bioaccumulative, approx 50% consumed stays in
body to then cause chronic poisoning
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pneumatician
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hi, I distilled various times tap water and the flask get cloudy.
HCL only remove the limes but the glass remain cloudy, fluorides?
acid niter & sulfuric alone don't work.
no now I don't have cromate, HF... maybe piranha at room temp with h202 at 3%?
[Edited on 18-3-2017 by pneumatician]
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JJay
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Removing Carbon Powder from Glass
I recently ran a reaction that resulted in a small but extremely dark and persistent mass of very finely divided carbon. When cleaning, I made the
mistake of washing it into some other glassware. It sticks to glassware, and it doesn't wash off with water. The only two methods I have found for
removing it are scrubbing and piranha solution, and it is fairly resistant to piranha solution. I can't possibly scrub every surface that it's
touched, and I don't want to have to handle the large quantities of piranha solution that would be required for removing it.
Does anyone know an easy way to remove finely divided carbon from glass?
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unionised
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The carbon may be sticking to grease on that glass, rather than the glass itself.
Washing with a strong base may well work.
Sodium hydroxide in wet alcohol sometimes does a great job.
(Mix about 5 g NaOH, 5g H2O let it cool for a minute or two and then add 90 ml ethanol)
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Chemetix
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There's not much better way to clean organics off than taking it to 400C, ok that's not easy for most ovens. But maybe a heating torch like this:
is one of the tools that is good to have on hand to burn off organics.
I use one to flame anneal borosilicate glassware and it will soften the glass at near full power ( depending on size and thickness of the glass) so
going easy would be recommended.
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JJay
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I guess I might try burning it off with my blowtorch. I have a feeling that will be slow going, though.
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Texium
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Chromic acid would probably work, but that of course is a matter of last resort. I would recommend trying what unionised suggested before you do
anything else.
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Texium
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Threads Merged
6-8-2017 at 07:23 |
SWIM
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OTC glass and tile cleaners can be useful for various glassware deposits.
Lime scale removers (I use Lime-Away) work well for hard water deposits and toilet bowl rust stain removers (Rust Out is a good one) work for iron
oxide and some other metallic crud.
I've also had good results with commercial oven cleaners (I use Viking brand) on carbon deposits and blackish polymerized gunks.
These products are not only convenient to get, but they're engineered to be safe for plumbing and relatively safe for the environment so you can just
flush them down the drain. No depleting your chemicals stockpiles or adding to your waste disposal/recycling woes. This also applies to the earlier
post about dishwasher detergent, an Idea I'm looking forward to trying.
I used to get GREAT results with OTC barbeque grill cleaners, but those have been reformulated(at least in the US) and although they sort of work,
they don't have the same kick they used to. (Small wonder, The one I used to use had dichromates in it  )
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