Metal Pickling

It depends upon the metal.

Phosphoric acid needs to be on the list too!

Oh, go on. Do tell.

Vinegar is good for onions!

What do you want to pickle?????? Avoid HF if at all possible - particularly nasty stuff.

The Germans and Japanese usually use salt to pickle their vegetables.

Good point.

I sure wouldn't consider HF in any concentration. I just hate anything that melts your bones. 4 oz in your lap, instantly into a shower and you are dead the next day because you didn't take off your pants.

True story in a well respected lab.

I had a splash of a single drop on my thumb that I did not notice for an hour. It was no fun cutting the burn-site out with my pocket knife. It oxidizes without causing any pain, so I did not notice it when it happened. I had just taken off my protective equipment and I touched some lab glass that was contaminated.

I don't know of any metal that needs to be pickled with HF, I have seen it used to edge glass, and the process was open and as unsafe as I could imagine. Crazy deal in a Middle East country.

I'm going with phosphoric or HCL.

Cheers,

Bloefeld

Back in the late 70's, there was an automotive product company in the USA selling a wheel cleaner with a minute amount of HF in it. Ever have the skin under your fingernails turn pale grey and burn uncontrollably for 2 weeks? (now I know that putting some Milk of Magnesia on it would have stopped the burning)

check this thread

http://cr4.globalspec.com/thread/35534/Nitric-Acid-or-Citric-Acid-for-Passivation-of-Stainless-Steel

this aspect is covered quite a few times on the forum

Of course, it depends on what are you trying to pickle. If you're talking about steel - sulfuric or hydrochloric. The reaction with the surface oxides is relatively easy to control and in normal conditions they attack the substrate minimally (relative term again). It also depends on the type of the scale (oxide) and the cooling conditions that led to the formation of the scale.

A lot to say about it. The question is - as usual - very general. A little research (such as Google) on your side prior to posting would help getting better answering, as the question becomes more pertinent.

Presuming ferrous materials, Sulfuric acid is cheaper to use; Hydrochloric can be used and can be recycled intop other products more easily than sulfuric in my experience. however, Shotblasting is preferred commercially over pickling because of effluent disposal issues. It almost always is decided based on costs of process under your regulatory situation. If you are smart enough to be able to make a commercially saleable product from the effluent, thatwill be the way to go.

But almost all bar steels in the US and Canada are mechanically descaled, rather than acid pickled.

Vinegar (acetic acid) is used for cucumber and peppers. Buffered with NaCl.

Ascorbic acid and or citric acid is used for fruits.

Sb has provided you good information regarding stainless passivation.

More details about your intent would allow us to give better answers.

milo