RogueRose
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Boiling Sodium Hypochlorite in stainless steel pot - strange reaction
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?
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ficolas
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NaOCl oxidizes stainless steel, and you add to that the high temperatures.
http://www.bssa.org.uk/topics.php?article=35
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PHILOU Zrealone
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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]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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hissingnoise
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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!
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Cryolite
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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]
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Dwarvensilver
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SS reaction to bleach
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]
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mysteriusbhoice
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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]
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PHILOU Zrealone
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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
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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mysteriusbhoice
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damn forgot about that 1 thing oh well the new ceramic coated cook pots work tho!!
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