How does patina .. .

Someone smarter than me will chime in but I look at it like this. Your trading a good looking "rust and corrosion" for a bad one.
 
Stainless steel works by being coated with a layer of chromium oxide that prevents further corrosion. If the steel is in an environment where that layer can't form (like in the mud under a swamp) then the stainless isn't and it corrodes. Patina functions similarly by providing a surface layer that prevents further oxidation of the underlying steel. The process is most famous for occurring on copper alloys but it happens on steel as well.
 
Fancier said:
Stainless steel works by being coated with a layer of chromium oxide that prevents further corrosion. If the steel is in an environment where that layer can't form (like in the mud under a swamp) then the stainless isn't and it corrodes. Patina functions similarly by providing a surface layer that prevents further oxidation of the underlying steel. The process is most famous for occurring on copper alloys but it happens on steel as well.
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it is why the Statue of Liberty is green....When it was first erected it was dull copper color. It eventually formed a patina of copper carbonate that protected the copper from further corrosion.
 
Screwdriver and Fancier both have it right. A patina is technically a thin layer of corrosion, but of a form that is neither pitting nor damaging. This thin top layer of corroded (reacted) steel creates a layer of protection against air, water, et cetera. It is this protection from the patina that helps to mitigate further oxidation of the steel underneath.
 
Chemically speaking, patination is the formation of Iron(2,3)Oxide on the surface of an iron-containing metal by exposure to a strong base. This is why things like vinegar cause carbon steels to patinate. The acetic acid (a weak acid) creates Fe2+ and Fe3+ ions and is converted to acetate, a fairly strong base. The acetate cause the iron ions to form iron(2,3)oxide. If your steel is coated with iron(2,3)oxide, then it won't form iron(3)oxide aka rust! If you want a super patina, boil some acetic acid, coat your blade with it, then wash with water to neutralize the reaction. It will turn the steel near black, but it won't rust :)
 
"If you want a super patina, boil some acetic acid, coat your blade with it, then wash with water to neutralize the reaction. It will turn the steel near black, but it won't rust. "

Interesting!
Why boil?
 
landromus said:
"If you want a super patina, boil some acetic acid, coat your blade with it, then wash with water to neutralize the reaction. It will turn the steel near black, but it won't rust. "

Interesting!
Why boil?
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Many chemical reactions occur quicker at hotter temperatures. Don't ask me why, I'm not a chemist, just something I picked up years back in high school :p
 
Invective said:
Many chemical reactions occur quicker at hotter temperatures. Don't ask me why, I'm not a chemist, just something I picked up years back in high school :p
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Heat excites the molecules. Faster moving molecules equals faster reaction.

The patina concept is also used on many iron and steel structures. The steel or iron is made with a fast oxidizing alloy on the outside and a progressively more "stainless" steel toward the inside. The rust that forms on the outside is superficial and protects the structure from further, more serious, rust.
 
Invective said:
Many chemical reactions occur quicker at hotter temperatures. Don't ask me why, I'm not a chemist, just something I picked up years back in high school :p
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To completely dork out on the chemistry, heat equals energy, and some reactions require a certain level of energy before they occur at a reasonable rate. I could blither on about activation energies, entrophy, enthalapy, and Gibb's free energy, but if those terms mean anything to you then I'd be wasting even more of our time. Succinctly, divalent iron (+2) creates less problematic oxides and trivalent iron (+3) creates more problematic oxides. Divalent iron is patina, trivalent iron is rust. If you create a coating of divalent iron oxides then the trivalent iron oxides are less likely to form.
 
Okay I think I understand now

[video=youtube;rJp86_tj9KQ]https://www.youtube.com/watch?v=rJp86_tj9KQ[/video]
 
Simply put, weak acids don't work that well at being acidic. They're pretty stable as is. They need the extra vibrational energy afforded by heat to kick off a proton and turn into a strong base. Hence, boil your acetic acid. There's a thread somewhere in the traditional forum with examples of this being done. The results are pretty striking.
 
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