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Author Topic: What should I use to remove rust faster? Weak acid or Strong acid?  (Read 7006 times)

Offline honestdodger

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Hey!! I'll be very grateful is someone answer my simple question :)
I need to remove the rust of some of my frames...  I need to do it FAST, and I want your advice - which should I use, weak acid (like citric, acetic) or strong acid (HCL). Please don't consider other factors, such as the thinning of the metal, because the frame is naturally very thick.  [O8)]Please just tell me which is faster, and WHY a stronger/weaker acid would remove rust faster... I've been curious about this for months! Does it have anything to do with complete ionization, and more hydrogen ions?
Thanks very much! ;)


 

Offline SeanB

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Rust removal is more of mechanical removal, with the weak acid providing only a final chemical cleaning. You need to first remove all loose and flaking material, and use a detergent to remove any oil film before the acid will work. It is dependent on the acid circulating next to the metal, as otherwise a film of reactant products builds up.
 

Offline lightarrow

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It doesn't depend only on the strongness of the acid. It also depend on its complexant ability. Acetic and citric are more complexant but weaker. If you want to remove it really fast you have to use concentrated HF. But you absolutely have to do it in a totally closed hood or your bones will disintegrate...
« Last Edit: 11/05/2011 22:33:28 by lightarrow »
 

Offline Bored chemist

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HF is seriously nasty stuff, I'd not even consider using it.

The quickest way to remove rust is with a wire brush mounted on an angle grinder, but you need to protect yourself from the dust.
One of the commercial rust removers would probably have done the job by now if you had painted it on when you posted the question
 

Offline CZARCAR

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phosphoric acid? similar to DURO RUST TREATMENT? remove flakes + mild sanding & its painted on which then combines with the rust resulting in a black plastic surface= primer which needs real paint on top .....ascorbic aicd [vitamin c] is supposed to work but i never tried it
 

Offline lightarrow

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phosphoric is not useful if the rust is thick because it forms an insoluble, resistant layer of iron phosphate (the "plastic" you were saying) which doesn't allow a deep penetration of the acid.
Ascorbic is Veeery slow. If however you have a lot of time, you could use citric acid (from lemon juice, for example) which is cheaper.
« Last Edit: 12/05/2011 20:14:58 by lightarrow »
 

Offline CliffordK

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For home rust removal, I've known people that effectively used electrolysis.  I haven't done it myself, but there should be instructions on the internet using an ordinary (older style) battery charger, or perhaps a solar panel to generate the voltage difference.

Personally I prefer using a wire brush in an angle grinder (some kind of eye protection is required).

Keep in mind that in many cases Iron Oxide will provide a protective layer to your object, and there are some "rust stabilizer" products available if desired.
 

Offline CZARCAR

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unlike Al which oxidizes into a hard shell, steel oxidizes as a crumbly rust which falls off & O2 can penetrate farther into the steel. The hard plastic primer prvides a solid [not crumbly] finish to whch the next coat of paint can adhere to & minimize the penetration of O2 into the steel?
 

Offline CliffordK

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Rust can flake off...  but for example, cast iron is dependent on the oxidation process being slow, and the oxidation layer giving some surface protection. 

Vehicles last quite well in Oregon with or without undercoating despite getting plenty of winter-time rain because we don't salt our roads.

Rusty farm equipment can last for years, even with relatively thin sheetmetal, although perhaps that is dependent on whether there is trapped water.
 

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