Help!!! - Rust Removal Gone Wrong

[amflud]

Plain toothpaste, not the gel. The paste has abrasives in it and it works surprisingly well.

 

[Bill Hoffman]

Used to use toothpaste to polish out furniture finishes when I did
repair work. Works great and doesn't scratch.

I think Naval Jelly leaves you with a coating of iron phosphate which
prepares for paint. I'm sure somebody will correct me if I miswrote.

Bill

 

[Honed_Edge]

Let's clarify what that black is, then we can figure out removal.

Google: Naval Jelly http://www.henkelcamsds.com/pdf/553472_235119_Loctite_Naval_Jelly_Rust_Dissolver.pdf
The most important thing to note is phosphoric acid, maybe the sulfuric acid plays a small role.



Bivalent metals like iron (metals with two valence electrons) can give up those electrons and become positive metal cations with a charge of 2+. The acid dissociates into H+ ions and PO4- ions. The iron gives up electrons to the H+ ions making hydrogen gas. Now the Fe2+ ions react with the phosphate PO4- ions making iron phosphate. Fe3(PO4)2


Reactants.....3Fe................+....................6(H+)............................+.................2(PO4)3-
..............Iron from knife.................Hydrogen ions from acid..........................phosphate ions from acid


Next...........3(Fe)2+..............+.....................3(H2)........................+..................2(PO4)3-
..............Iron ions...................................Hydrogen gas.............................phosphate ions from acid

Now the oxidized iron ions (Fe2+) combine with the phosphate ions(PO4)3- making iron phosphate Fe3(PO4)2. This is the dark spots you are seeing.




Well, that's the chemistry of it.... now what to do about it..? Others have good suggestions, try them out. IF SOMETHING IS WRONG HERE PLEASE POINT IT OUT!