Electrolytic Derusting, Baking Soda or Washing Soda?
On Mon, 28 Sep 2009 16:44:13 -0700, "Michael Koblic"
wrote: "Terry" wrote in message .. . The rust isn't being *transferred* in electrolytic derusting. In any electrochemical cell, such as the cell constructed for derusting, something at the cathode (to be derusted) is being "reduced" which means "gains electrons". If the cathode is a rusty object, the oxygen of the rust (Fe2O3) is being converted to water or hydroxide ion, depending. (If it's an inert piece of metal or graphite, water is converted to hydrogen gas.) Rust-free iron metal is the product. Clean it up and oil it quickly! The iron surface usually has a fair bit of surface area and will rust again very quickly. Something at the anode is being oxidized (which, chemically speaking, means "loses electrons". If the anode is a piece of iron, the oxygen in the water is converted to hydroxide ions, and the result is iron hydroxide or hydrated iron oxide. No argument with the principles. It is the details that puzzle me. If you hook up iron as anode and stainless steel/copper as cathode in a saturated solution of NaCl you get H2 coming out and a Fe(OH) sediment forming at the cathode. At the anode you get Fe entering the solution as Fe2+ ions, effectively dissolving the anode: http://electrochem.cwru.edu/encycl/a...-machining.htm http://school.mech.uwa.edu.au/~james...-chem/ecm.html It works, 'cos I done it. What I do not understand how is the de-rusting process different in that it dissolves the iron oxides preferrentially. Is the underlying iron spared? I would have thought that the process is not dissimilar from the above and there will be some dissolution of the non-rusted iron but my chemistry does not stretch that far. The cathode is where the electrons are going. Whatever is at the cathode will be reduced----if it *can* be reduced. Iron can be reduced (accept electrons) if it's in an ionic state such as +2 or +3, but once it's in the metallic state (oxidation number of zero) it can't accept electrons anymore. (Metals don't form negative ions easily at all.) So instead, the hydrogen ion near the electrode is reduced to hydrogen gas. Terry |
All times are GMT +1. The time now is 11:00 AM. |
Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004 - 2014 DIYbanter