tom haggen - 28-7-2004 at 17:11
Hello all,
I was just wondering if anyone knew off the top of their head what the oxidation like water spots on galvanized sheet metal are. They are a white
color and are spread all over the sheet metal in the emission accelerators I’m build at work for a pharmaceutical company. Anyway, I was wondering
if there was a good solvent or even a solution I could mix to remove this oxidation. I would like to avoid having to buff it out with a cotton wheel
and some jeweler's rouge. I have access to methyl ethyl ketone, and hydrochloric acid. But I can always go buy other chemicals if necessary.
Sincerely,
Tom Hagen
[Edited on 1-8-2004 by chemoleo]
Hang-Man - 29-7-2004 at 06:32
Sounds like Zinc Oxide, a fine white powder. If you could scrape some off and heat it, it should turn yellow. Confirming zinc oxide.
I would clean it with dilute HCl, as it attacks zinc and its oxides. Make sure its quite dilute though, the zinc coating could be quite thin.
chemoleo - 29-7-2004 at 10:34
The only problem being, those spots will return... unless you dissolve away the whole Zn layer. But then, what guarantee do you have that the
underlying metal won't get dissolved?
Besides, normally metal IS galvanised with Zn precisely in order to prevent oxidation of the metal underneath. So you wouldnt want to
dissolve it away!
hpc - 29-7-2004 at 11:09
Tom, I know this might seem very "unscientific", but have you tried good ole WD40 ? I use it to remove water spots from stainless steel. it
might work on your galvanized.
Esplosivo - 29-7-2004 at 12:52
I think using dilute NaOH solution would work better since it would react with the zinc/zinc oxide layer without reacting with the metal layer beneath
(which I am supposing is iron).
As chemoleo said though, removing the zinc will remove the protection of the metal from oxidation.
tom haggen - 29-7-2004 at 18:54
Yes I thought about using some sort of acid to remove the oxides. However, I just want to be cautious because I don't want to remove the whole
galvanized coating. I suppose I could try sodium hydroxide. What if I use a dilute sodium hydroxide solution to remove the oxides and then quickly
rinse with water to prevent decomposition of the whole galvanized layer. Luckily the water spots are not that serious; I don't think they have
penetrated the whole galvanized layer.
[Edited on 30-7-2004 by tom haggen]
unionised - 31-7-2004 at 13:17
IIRC zinc oxide should dissolve in NH3 soln but the free metal shouln't be attacked.
NH3 sol., let's try it... I love empirism....
axehandle - 31-7-2004 at 14:44
Ok, just rubbed my galvanized trash bin with 25% industrial ammonia solution. Result: Zinc layer more shiny, no visible damage to it. Seems it works,
but your mileage may vary...
[Edited on 2004-7-31 by axehandle]
tom haggen - 1-8-2004 at 05:42
Ya I tried sodium hydroxide, and it made the surface finish more dull. It did work a little but did not remove all of the water spots. I don't
really know where to get industrial ammonia.