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Corrosion resistance of titanium nitride coatings against HCl

We are involved with an industrial process which generates hydrogen chloride, which when moisture is added becomes a hydrochloric acid solution. Some surfaces in the process machinery are chromium plated and they are attacked by the hydrochloric acid. Would a titanium nitride overlay on the chromium protect it from the hydrochloric acid solution? I do not know the concentration of HCl in the acid solution.

Irving W. Glater, P.E.
- W. Hartford, Connecticut, USA
2005

Though you don't know the acid concentration and didn't say anything about the base material of the machinery parts I would say TiN is not very suitable for that application. TiN PVD layers indeed resist HCl to some point but they are very thin and hard, so they may soon be perforated or cracked leading to pitting corrosion. In my opinion one of the best choices for mechanical machinery parts would be high phos electroless nickel.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

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I don't think the TiN coating will help a lot, even if it is not attacked by the acid. The problem that you'll likely encounter is that there are bound to be pores in the TiN that project down to the chrome base, so the acid will still attack the chrome. In fact, you may wind with a nice galvanic cell, accelerating the acid attack.

If you do try it, make sure you stay clear of TiN deposited by cathodic arc. Arc coatings are great for wear resistance because they have very good adhesion, but are very porous.

Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California
2005