Removing rust with voltage plus acid

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I did a pulley today using about a cup of aluminum wheel brightener in 2 gal of water. The current was 3 amps at about 10 volts. I ran it for 3 hours. The pulley was on the positive lead which is reversed from the washing soda setup.The water turned a dark green. Is there a chemist in the house? The pulley was not completely rusted but had some thick rust in one of the groves.Before and after pics: http://img36.photobucket.com/albums/...c=DSC00290.jpg
Reply:Green aqueous (water) solutions are usually atributed to cuprous oxide.  Cuprous oxide is a form of copper oxide.  I will guess you used copper leads.  Also aluminum wheel brightner usually contains some flouride ion and will aid in etching metals.  I will recommend that you do something to passivate the surface.  There are several phosphate based chemicals on the market.  Metalready is one of them, they are used to passivate ferrous metals prior to painting.  They would work well prior to use and or painting.  What they do is deposit a zinc or iron phosphate coating on the surface which imparts some corrosion protection and gives the paint something to adhere to.Last edited by Shade Tree Welder; 06-01-2004 at 12:47 AM.Ron ShopFloorTalk Millermatic 350P, M-25, M-40 gunsDynasty 300DX, Coolmate 3, Crafter CS-310 TorchTrailblazer 302, 12RC, WC-2430A spoolgunSpectrum 2050Thermal Arc Plasma Welder PS-3000/WC-100B
Reply:Mike,What was the purpose of running the pulley on the positive electrode?
Reply:It didn't seem to work the other way. There was only about 1/2" of bare copper in the water. I wish I did better in chemistry. Last edited by Mike W; 06-01-2004 at 03:41 AM.
Reply:Originally posted by Mike W It didn't seem to work the other way. There was only about 1/2" of bare copper in the water. I wish I did better in chemistry.
Reply:Mike,Can you clarify "didn't seem to work?"  Do you mean you got no bubbling or you didn't get rust removal?Seems to me that the primary purpose of the borax or lye is to provide ions to the water -- to make it more electrically conductive.  If I recall, the solution is never "used up."  So that would lead me to believe that the salts added aren't actually part of the reaction.  Of course, a strong base like lye will give the additional benefit of paint removal and may be used up in that way.  Using a strong base instead of an acid also provides an additional benefit of reducing flash rust on the part being cleaned since iron is more resistant to oxidation at higher pH. The purpose of using a strong base instead of a weak one such as sodium bicarbonate (baking soda) is that the strong base completely disassociated into it's ions when dissolved in solution and provides more ions (just guessing here).Maybe my chemistry is off but here's how I see the process working.  Our anode (part) is Fe2O3.  We provide electrons to it and the electrons replace the lost ones in the Fe+++ portion of rust.  This breaks off the three O-- and 2 of those ions combine to form O2 (aka oxygen) and the other O-- combines with the next free O-- to form another molecule of oxygen.On the positive electrode, the water on that side is being broken by the same reaction and the O-- ions are attracted to that cathode while the H+ are either staying combined or recombining into H2 (hydrogen gas).  I tend to think the former as our solution is not changing ph which would happen if we had free H+ ions with our OH- or CO3-- ions.  Regardless, we have the production of hydrogen gas and the oxidation of a metal at the cathode/electrolyte junction.So what's my point?  It really shouldn't matter what we use to ionize the water.  I've seen electrical etching done with table salt -- an ionic compound that produces a ph7 solution.  I tend to think that the only benefit of running electricity in your setup was a simple stirring action produced by the bubbling of the electrolyte.  If anything, the positve charge on the pulley would tend to push the H+ ions (the acid) away from the part.  Then again, why didn't it work with the part as the anode?I can only see one difference in your setup.  You were likely using a weak acid, such as phosphoric that doesn't completely ionize whereas the standard electrolyte uses a strong base that completely ionizes.  Should this disparity in pH extremes make a difference?  I don't know.
Reply:I got bubbling but it didn't seem to be removing the rust. I then remembered a note I had about a solution to remove rust and chrome. This showed 2 parts water and 1 part muriatic acid. Plus the object to be de-plated went to the positive lead.The bottle of wheel brightener mentioned hydrofloric acid.
Reply:Is that pulley aluminum or steel?
Reply:The bottle of wheel brightener mentioned hydrofloric acid.
Reply:Keep thinking out loud david_r.  The pulley was steel. The shop that I bought the wheel brightener from said it would work to take rust off of steel. It is made to spray on aluminum wheels for a min or 2 and then wash off. I have dunked steel parts in a quart of it and 3 gallons of water. It did work but not real fast. I once left a 1/16 welding rod in for a couple of days and it became a 1/32" rod.I was impressed with how much faster it worked with the current. It got the real deep rust on the pulley. Also, you don't get the nasty brown effect in the solution that you get with the washing soda. More experiments are coming up. I am actually developing an interest in chemistry.
Reply:guess I should take the time to look at the pictures.......DOH!