What does “passivated” mean? Sounds like me in my armchair with a
drink and a good movie playing, after a very hard day.
Dan Woodard, IJS
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Thanks, Judy. I expect at least some of the “dirt” came from the
inside of the shaker’s bowl. The batch consisted of relatively clean
sprues as I use surface copper depletion on my castings. However,
there were some sharp points that could have damaged the bowl itself.
What are you teaching this summer? I still feel like a first grader
itching to move on to second grade. Thanks again,
Joyce Albers
What does "passivated" mean? Sounds like me in my armchair with a drink and a good movie playing, after a very hard day.
Actually, that’s pretty much what it means. Passivated means, “made
passive” i.e., not active or not reactive. A metal that has been
passivated, no longer reacts like the normal metal. Many metals
become passivated by forming an EXTREMELY thin film of oxide on their
surface. A good example of a passivated metal is stainless steel. If
you put regular steel wire and stainless steel wire in Sodium
Bisulfate pickle, the regular steel will dissolve (been there, done
that) but the stainless wire will just sit there (like you in your
armchair). For those of you who use Hydrochloric acid as a pickle, be
advised that both wires will eventually dissolve. WHY? You ask.
Because the Chloride ion, (Cl) in HCl, de-passivates the stainless
steel by removing its protective oxide layer. Then the Hydrochloric
acid can do its dastardly deed and dissolve the wire. However, there
are MANY, MANY types of stainless steel. Some resist de-passivation
better than others and some may resist dissolving in HCl, but I can’t
tell you which ones they are (don’t know).
Regards…Bob Williams
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What does "passivated" mean? Sounds like me in my armchair with a drink and a good movie playing, after a very hard day.
G’day; for an item to be passivated means that it is made resistant
to attack by various corrosive reagents including air. F’rinstance;
the moment the surface of aluminium is exposed to the air it is
grabbed by oxygen - and the consequent formation of a very thin film
of aluminium oxide very effectively ‘pacifies’ the surface so that
further activity or corrosion cannot occur. Another example is that
of iron or steel dipped in concentrated nitric acid. Instantly a film
of ferric nitrate is formed and that is converted to iron oxides,
which ‘pacify’ the metal against further attack.
One of the lecturers in Chemistry at a University where I worked set
such a question in his exam paper. “Should an aluminium roof
dissolve in the rain? Supply complete proofs in your answer.” The
answer is that theoretically the roof SHOULD dissolve! The reason why
it does not is the formation of aluminium oxide which protects the
metal. Sounds simple, doesn’t it? - but the lecturer wanted a far
more detailed and complex answer than that from his senior students!
It took up to about a page to give a full answer. Cheers, PS: I
haven’t had ‘hard days’ for 15 years - and envy gets you nowhere. –
John Burgess; @John_Burgess2 of Mapua Nelson NZ
It’s not often I come upon a word I’ve never heard of. I read the
definition to my husband, and he showed me a cat scratch on his hand
that had begun to form a scab and said, "it’s been passivated."
Thanks, John!
Janet Kofoed
Dan: Passivation is an acid cleaning process used for stainless steel.
It’s essentially a pickling process. The most common method is
immersing the metal in nitric acid. Some passivation processes use
electricity and acid to electro-strip the metal. I have seen an
industrial passivation line at Snap-On tools and it looks quite
similar to a plating line. Tim