Sciencemadness Discussion Board - Boiling Sodium Hypochlorite in stainless steel pot - strange reaction

Boiling Sodium Hypochlorite in stainless steel pot - strange reaction

RogueRose - 10-6-2016 at 04:34

Starting material is 12% NaOCl. MSDS says it is pure and lists nothing else other than water. The pot that was used is good quality stainless steel. As soon as the solution started to get near BP I noticed a few spots of black around the edge of the liquid - but on the stainless - it looked almost like mold. I thought it may have been something left over from using the pot before but it was cleaned with steel wool and comet with excessive scrubbing.

Once vigourous bubbling (tiny bubbles almost a foam, like a carbonated drink fizzing) statred the black spots increased until it ringed the pot.

The color was also changing to a brownsih so I ended the process.

Here are the pics of what things looked like:

So, I didn't know that SS would be corroded by bleach (I guess hot bleach is what does it). The black is not coming off even with super tough abrasive and barkeepers friend.

The black in the solution seems to have started to settle towards the top, is that most likely nickel? Is there any way to rescue this pot?

ficolas - 10-6-2016 at 05:01

NaOCl oxidizes stainless steel, and you add to that the high temperatures.
http://www.bssa.org.uk/topics.php?article=35

PHILOU Zrealone - 10-6-2016 at 06:08

Not couting with the fact "cleaning with steel wool and comet with excessive scrubbing" will have produced crevices favourizing pitting or crevice corrosion.

In bleach you usually have NaCl, NaOCl, NaOH and water.
Hypochlorite being an oxydant media with chloride, is usually very bad for metals (HNO3/HCl dissolves nearly all metals; HCl/H2O2 is also pretty good).

Upon heating/boiling you have formation of NaOClO and NaOClO2.

Picking corrosion has no cure!

[Edited on 10-6-2016 by PHILOU Zrealone]

hissingnoise - 10-6-2016 at 06:17

Some SS cookware may have aluminium (which may be exposed during finishing) in the base to effect uniform heating and, if exposed, it will dissolve at high pH in bleach!

Cryolite - 10-6-2016 at 11:53

Don't neglect the extreme oxidizing power of the hypochlorite ion! An acidic solution of bleach is capable of dissolving gold, let alone steel. Even a dilute basic solution of sodium hypochlorite is capable of dissolving most metal containers, especially with heat. Boiling bleach (presumably for making chlorates) must be a solely glass-only affair.

[Edited on 10-6-2016 by Cryolite]

SS reaction to bleach

Dwarvensilver - 18-6-2016 at 09:48

It is the same reason that cheap stainless utensils get pitted in the dishwasher from the chloride in the detergent. Chlorides and stainless steel, even 316 stainless is like putting zinc in acid. Well maybe not that fast but you get the idea.
We have had stainless agitator paddles that corroded off the shaft. If it has chlorides in it we use titanium.

[Edited on 18-6-2016 by Dwarvensilver]

mysteriusbhoice - 23-6-2016 at 06:56

DO NOT USE STAINLESS IT FAILS HARD!!
if you are gonna use a metal pot then use aluminum to boil hypochlorite because it passivates!!
i had sucesses with disposable aluminum catering/party trays boiling calcium hypochlorite in the past

it will eventually corrode over time so keep the oxide layer for next batch as it prevents further oxidation!!
i now produce chlorate electrolyticly!!

u can also use one of the new ceramic coated or old teflon coated cooking pots!!
i use those to boil the solution at the end of my runs with good results!!

[Edited on 23-6-2016 by mysteriusbhoice]

PHILOU Zrealone - 23-6-2016 at 16:10

Quote: Originally posted by mysteriusbhoice

DO NOT USE STAINLESS IT FAILS HARD!!
if you are gonna use a metal pot then use aluminum to boil hypochlorite because it passivates!!
i had sucesses with disposable aluminum catering/party trays boiling calcium hypochlorite in the past

it will eventually corrode over time so keep the oxide layer for next batch as it prevents further oxidation!!
i now produce chlorate electrolyticly!!

u can also use one of the new ceramic coated or old teflon coated cooking pots!!
i use those to boil the solution at the end of my runs with good results!!

[Edited on 23-6-2016 by mysteriusbhoice]

Ca hypochlorite is not Na hypochlorite!

NaOH is present in good quantity into the second and this is very bad for Aluminium...it will be chewed very fast especially if heated for concentration.
Al + 3 H2O -NaOH-> Al(OH)3 + H2(g)

Maybe first neutralize the NaOH... by adding a weak acid (acetic acid) or by adding a precipitating cation (Fe(III) acetate) then you will have Na acetate and eventually Fe(OH)3 in the media

mysteriusbhoice - 26-6-2016 at 20:01

damn forgot about that 1 thing oh well the new ceramic coated cook pots work tho!!