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Managing Rust

Vinegar is a great [and cheap] way to remove rust, but.. after treatment the rust may accelerate and turn black and/or even gunky.

Here is a forum answer i like to the following question;

Q. What to do after the vinager rust remover?

Basic answer: Since coatings slow the process of corrosion, clean and coat the item. The same oil you use on a sharpening stone works great on knives, but you'll have to renew it regularly since it doesn't stay in place like paint.

Better answer: Since you've removed all the rust (oxidation), including the thin surface film of oxide normally present, it's quite reasonable for the fresh metal exposed to the air to immediately become rust-prone until it's replaced with a new coating to resist further oxidation. Ideally if you allow a very thin film of smooth hard oxide to form, it should help protect the metal from deeper rust, but the pitting on an old rusty item can make it difficult for a smooth, unbroken layer to form.

Also note that acids not only dissolve rust, they also chemically accelerate rust formation, so any acid remaining on the metal will continue to slowly eat away at the item unless removed or neutralized. Baking soda can neutralize vinegar, and if you're not going to coat the metal, then rubbing alcohol or WD-40 can displace any residual water, but this won't work nearly as well as applying some sort of protective coating.

Best answer: If the item is delicate or valuable, such that you don't want to remove any of the original metal with the acid, then electrolysis might be a better method than vinegar. That's because the acid removes the rust (and a little metal), while electrolysis only removes the oxygen from the oxidized metal, transforming the surface rust back into metallic iron. Once the rust is gone the reaction stops, but you must immediately clean and coat the item or it will quickly rust again. (Also remember that electrolysis produces explosive hydrogen gas, so this method can kill if simple safety precautions are not followed!)

Explanation: Any acid will work to remove rust: vinegar (acetic acid), lemon juice (citric acid), cola (phosphoric acid), HCl (muriatic acid). Vinegar is cheap and easiest to work with, because lemon is too weak, cola contains unwanted sugar, and hydrochloric acid is potentially dangerous and works so fast that it can remove too much metal. Vinegar works in any form, so ketchup or mayonnaise will also slowly remove rust!

The basic reaction is acetic acid + rust => water + iron acetate (which is a water soluble salt), although life is rarely so simple outside of laboratory conditions. There are 16 different iron oxides, but only a few of them are commonly called rust, which is hydrated iron(III) oxide, formed by oxidation in the presence of moisture. The smooth hard oxide often used as a protective film (such as in bluing) is known as a passivation layer (makes the iron passive), and is basically a black iron oxide coating (instead of red iron oxide rust) usually formed by phosphate conversion coating (similar to Parkerizing). Although the goal is rust proofing, phosphate coatings are too porous to accomplish that alone, however those pores do a great job of grabbing onto oil, paint, or other coatings. However on old rusty items, both of those coating layers are usually removed by the acid, leaving the metal without protection.

There are tons of guides to removing rust available online, the best ones often focus on vehicle parts. I like this one for the clear explanations of each option: http://www.mopedarmy.com/wiki/Removi...rom_a_gas_tank. And here's a general overview of rust prevention options: http://en.wikipedia.org/wiki/Rust#Prevention. If in doubt, sharpening stone oil works great. Good luck!

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Page last modified on September 18, 2017, at 08:34 AM