Re: Another Ziatype question

From: Martin Angerman <paleophoto@adelphia.net>
Subject: Re: Another Ziatype question
Date: Mon, 11 Oct 2004 20:28:04 -0700

> We have a lot of stainless steel piping at work. Part of the major
> maintenance is called "passivation." Essentially it removes any surface
> iron oxide, giving a chrome and nickel rich surface. The preferred
> chemicals are citric acid with EDTA, followed by citric acid alone, then
> phosphoric.

I bet this treatment is doen to increase the corrosion resistance
rather than to remove iron as discussed here. Of course EDTA and
citric acid mixture helps to reduce iron but phosphoric acid would
convert iron to iron phosphate, which is very insoluble.

> As far as to which type of EDTA to use, as a general chemistry
> reagent, the main difference is in the solubility. Once again,
> usually in much greater concentrations than for printing.

They also differ in acidity. I think solubility is not much of an
issue here, because EDTA is often used way below solubility limit.

--
Ryuji Suzuki
"You have to realize that junk is not the problem in and of itself.
Junk is the symptom, not the problem."
(Bob Dylan 1971; source: No Direction Home by Robert Shelton)