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Can HCl vapour be used for pickling?

I'm investigating the uses of HCl vapour, and I was wondering if you think it would be possible to preform a process similar to pickling, i.e., do you think that HCl vapour, would be able to remove the scale, that builds when steel is manufactured. Also what is the ratio of waste, to product? Not sure that is worded quite right but I hope you understand. Because I'll be working with a relatively small chamber 115 mm inner diameter, I am worried that the waste, may clog the holes which let the vapour in? I've done some research around steel pickling, and it is the amount of waste mentioned that worries me.

Emmy Sharples
Research student, St Andrews uni - St Andrews, Fife, Scotland
June 25, 2010

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June 25, 2010

Hi, Emmy. This is an interesting project. HCl vapor is certainly corrosive enough, but when HCl is used as a pickling acid, it often includes inhibitors that do not slow the removal of rust, but do inhibit the dissolution of the raw metal into the acid. So, in addition to the physical problems of washing away the dissolved rust, this will perhaps present a second problem. Good luck with it.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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July 1, 2010

Hi Emmy

An interesting idea and I hate to discourage research but I see a few problems.

Hydrochloric acid not only converts oxides to soluble chlorides, but also removes the chlorides in solution leaving an easily rinsed surface for further processing. HCl may produce chlorides but how do they get removed?

Safety is, I suggest, a more immediate concern to most operators than waste (could you elaborate on what you mean by waste?) and the prospect of using HCl gas in an industrial situation is daunting.

There are many possibilities with respect to scale.
Avoid it - lower temperature or less oxidising conditions, Quench in reducing conditions.

Physical removal - grit blasting or machine the surface

Pickle in sulfuric acid - The only disadvantage against HCl is that it needs modest heating.

As a final thought - One man's waste is another man's raw material.

Geoff Smith
Hampshire, England