Sciencemadness Discussion Board

On the practical use of piranha solution

Panache - 20-4-2021 at 20:23

So how do you piranha a larger vessel? All the seemingly obvious answers to that question are rather unacceptable, either on the basis of cost (both monetarily and environmentally), or safety.
Has anyone ever made up 5l of piranha, does the temperature ramp past boiling? That would be horrible, I’ve had it spew over due to metal ions catalysing it’s breakdown too quickly but it wasn’t boiling and it wasn’t 5l, still ate a hole in my nicely finished timber bench.
I know analytical heads often use piranha on glassware, so there must be a way better than swirling.
Does remind me of that old chemistry adage ‘only the inside of the flask needs to be clean...’

Sulaiman - 21-4-2021 at 09:02

For a 5l rbf, a H2O2 + HCl solution will clean most stains,
no need for 5l of solution - just stopper all but one hole and swirl occasionally,
quicker/more active if heated but often not required.

Cheaper is a moderately concentrated KOH solution.
I've not tried an alcohol base bath but they seem to be highly recommended.

I think that the best is to know what you are trying to dissolve and use a suitable solvent.

Texium - 21-4-2021 at 09:11

Quote: Originally posted by Sulaiman  

I've not tried an alcohol base bath but they seem to be highly recommended.
Yeah, they're great! Glass comes out shiny and brand-new looking every time, and the problems with etching are over-exaggerated. As long as you don't soak it for a week or more you won't have issues, and even the enameled labels on the glass (as long as it's a reputable brand that uses a durable enamel) will not come off under those conditions, in my experience.

If you use your glassware regularly, and you can afford to, buy a drum of anhydrous isopropanol and a couple kg of KOH. Get a 5 gallon bucket with a lid from the hardware store, and dissolve about 500 grams of KOH per 4 liters of isopropanol. Keep the lid on at all times to prevent evaporation and fumes. Avoid putting wet glassware in, to prevent dilution of the bath with water, and it will last you a really long time before you need to change it out.

Panache - 21-4-2021 at 09:37

Quote: Originally posted by Texium (zts16)  
Quote: Originally posted by Sulaiman  

I've not tried an alcohol base bath but they seem to be highly recommended.
Yeah, they're great! Glass comes out shiny and brand-new looking every time, and the problems with etching are over-exaggerated. As long as you don't soak it for a week or more you won't have issues, and even the enameled labels on the glass (as long as it's a reputable brand that uses a durable enamel) will not come off under those conditions, in my experience.

If you use your glassware regularly, and you can afford to, buy a drum of anhydrous isopropanol and a couple kg of KOH. Get a 5 gallon bucket with a lid from the hardware store, and dissolve about 500 grams of KOH per 4 liters of isopropanol. Keep the lid on at all times to prevent evaporation and fumes. Avoid putting wet glassware in, to prevent dilution of the bath with water, and it will last you a really long time before you need to change it out.

This is an excellent idea and I actually have a spare 20l of ipa, is it essential that’s its Koh or is naoh to all intents and purpose identical.

Texium - 21-4-2021 at 09:55

I believe that KOH is preferred because it is more soluble in isopropanol than NaOH. NaOH may still work well enough, but I haven’t tried it before.

clearly_not_atara - 21-4-2021 at 10:41

^on the contrary, I think KOH is preferred because it is less corrosive to glassware.

http://www.sciencemadness.org/talk/viewthread.php?tid=15633#...
http://doi.org/10.1007/BF00911336
Sodium hydroxide corrodes silicate glasses of all compositions to a greater extent than all the other hydroxides. It is proposed to call this phenomenon the “sodium anomaly.”

Bmoore55 - 21-4-2021 at 10:50

I am currently using a piranha solution to clean some alumina crucibles right now. But when it comes to glassware I have always used a KOH base bath to remove organics. And Texium is right, the etching problem is usually very exaggerated.

Texium - 21-4-2021 at 12:32

Quote: Originally posted by clearly_not_atara  
^on the contrary, I think KOH is preferred because it is less corrosive to glassware.
Interesting! I had no idea

draculic acid69 - 26-4-2021 at 02:46

I also thought Koh would be just as damaging as naoh.
Nurdrage dried lioh in a flask and no noticeable damage
was observed.guess it is just sodium