What's your favorite non-nitric acid passivating method?

Just got done noodling methods of getting rid of iron on the surface of a stainless steel sculpture. It had been erroneously polished with a
steel wire wheel and now it rusts when you throw some water at it. The guy has tried citric acid and a couple of other things.
What works for you, assuming that nitric acid is hard to get unless you are licensed or something.
Pete Stanaitis ---------------------------------
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You're in for a serious repolishing...
Find a way to immerse it in strong citric, not just spray it on.
Karl

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Reverse electroplating? Hopefully it won't affect the stainless too much, but it might also give the SS a nice finish as well. Wire wheel a scrap pc of SS, do the electrolysis on it, see what happens.
If the sculpture is too big too immerse, you might could get away with doing this on a spray basis as well, by making a kind of basin for the sculpture to catch the runoff, and serve as the anode/cathode etc. If sprayed continuously enough, area by area, there should be enough fluid conduction to eventually electrolyze the whole surface.
--
EA


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> Pete Stanaitis
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Since when does it require a license to buy nitric acid?
Google nitric acid and many distributors pop up. Nothing I have seen suggests that it is unobtanium.
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
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With the Hazmat ship charge added, it is however, expensium.
I buffed the piss out of a SS304 chum ladle for my charter boat chaptain, and then soaked it in citric from mcmaster carr. No rust at all after a year of use. If this workes for something soaked in salt water and ground fish guts, a statue should be a piece of cake.
karl
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I was googling, that stuff seems to be pricy. Maybe I was finding chemistry grade stuff.
Sulfuric acid and KNO3 are fairly cheap. Seems like nitric acid would be cheap to make.
I looked at this link:
http://www.ehow.com/how_4480572_make-nitric-acid.html
The site authors seemed to believe nitric acid is pretty nasty as far as containing it.
Okay chemists on the list, time to tell us what we don't know and thanks in advance.
Wes
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I think I figured out one tidbit. You can use nitric acid to make nitrocellulose.
http://en.wikipedia.org/wiki/Nitrocellulose
My organic memory storage system (brain) was a bit slow tonight.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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Nitrates in general have a lot of interest from various government groups, some because of the Hazmat bit, some because they are explosive precursors or explosives themselves. Nitric acid isn't THAT cheap to make, you either have to have nitrates and sulphuric acid or some fairly expensive high pressure/high temperature catalytic equipment to make it from ammonia and air. If you have that, you can make ammonium nitrate and we know how sensitive that is legally right now. At one time there was a process that used an electrical discharge to make it directly from air, was really energy intensive and didn't last once the catalytic setup was developed.
I don't know of any particular federal requirement to register yourself or the nitric acid, I imagine OSHA/EPA have some regulations as to how and when it can be bought and used, though. And it is fairly nasty stuff, if it doesn't eat your flesh, it'll turn it yellow, reacts with just about anything, the liquid outgasses worse than HCL and the nitrogen oxides it leaves aren't anything you want around to breathe. It's nothing you want to leave around finished metal surfaces, what just the vapors do to polished steel is a crime. It's a great etchant, though, and there are things it's hard to replace with. I can still remember removing an electroplated copper film off a platinum mesh electrode with a beaker full, just a chuff, a puff of brown smoke and the platinum was clean... I did it in a fume hood, otherwise I'd still be coughing.
Stan
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Citric acid is my favorite. 5-10% by volume in water, 150-170 deg F, agitate for at least 10 minutes (I believe in overkill and time is cheap so I usually do several hours). How big is this sculpture, and was he able to submerge it or did he just try wiping with room temperature liquid? Don't know if it follows the same rule of thumb as simple reactions but a factor of 2 every 10C or 20F implies about a 30-fold speedup at 170F vs 70F. If it is too big to submerge, either sit it in a pan or build a dam around the base and fill with citric acid solution. Put in a $10 pond pump from Harbor Freight to pump the liquid up to the top and let it run down the sides. Put in an aquarium heater set on max or find some other way to get the temp up as much as possible, add water as necessary to make up for evaporation, and let it go a few days, moving the hose as needed. Scrub with a plastic brush as much as you can to help it along.
----- Regards, Carl Ijames

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Thanks for all the input, guys. I have passed it on. And no, the guy has not been able to submerge it, yet, anyway. Nor has he yet heated the passivating solution. His next step will be to make a test panel and (mis)treat it the same way he did on the sculpture, so he doesn't make things worse while figuring out a solution (no pun intended).
He is working with 304.
Pete Stanaitis -----------------
spaco wrote:

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wrote:

Electrolytic cleaning is very effective for removing weld discoloration on SS and would probably do what you need. Sufuric acid applied with a wand wrapped in fiberglass cloth and attached to a current limited power supply works well and is easy to set up. I have an old pamphlet from Armco that recommends phosphoric acid as the electrolyte, and no doubt there are other alternatives.
Here's a commercial setup that apparently uses a pump to deliver the electrolyte to the wand. http://www.revolutionmaterials.com.au/103.php
--
Ned Simmons

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