[AJD] washing soda

[Steve Treimer]

David,
  You were right on track too, just thought some might be interested in the why not just the what.  Always helps me remember that way.  I thought some more last night about it.  Wish I had the time to pursue the research, but Duane can understand that too, right!  
  The cathode should be connected to the part needing to be derusted.  The cathode is where the hydrogen is made when water is split into hydrogen and oxygen.  Hydrogen actually serves two purposes here.  The primary and most important purpose is to dislodge the rust and scale.  But also there's another neat property of hydrogen that helps us too.  Something that is bathed in hydrogen gas is in a "reducing" atmosphere.  Rust is iron oxide, the oxygen that got to the iron part "oxidized" it.  That opposite of oxidation is reduction, so by bathing the part in bubbles of hydrogen, the hydrogen passivates the part, at least temporarily.  It's too bad that we don't recovert that iron oxide back to iron, but this would be a truly monumental feat.  But once the scale is off, the bare metal comes out glistening clean because the hydrogen bubbles are preserving the bare iron.  The high pH of the bath prevents oxygen from forming at the anode which in turn allows hydrogen to be produce
 d at the
 cathode instead.  This is where the term "efficiency" kind of applies.  Actually, you're just changing the ingredients of this reaction to get the product that you want - that is hydrogen bubbles at the cathode and no bubbles at the anode.  If you were in an acidic bath, oxygen would come of your anode quite readily when voltage was applied and long before any hydrogen was ever produced at the cathode and all you'd do is ruin/dissolve/oxidize the anode and the acid would be able to oxidize your iron part even though it was connected to the cathode.  
  Sorry everyone is that is just TMI, just kind of fun revisiting the stuff I let grow dusty in the closet I sometimes call a brain.
  Have great holidays!
  steve

David Bruce <davidbruce at yadtel.net> wrote:
  Steve,
You did a much better job than I explaining things. Back in the old 
days lye was always Potassium Hydroxide but now it seems the term is 
used for KOH and NaOH both. (potassium hydroxide and sodium hydroxide).
My thoughts is soda ash (washing soda) would provide a high enough pH 
but maybe sodium bicarbonate (baking soda) wouldn't when looking at 
electrolysis.

David
NW NC

Steve Treimer wrote:

>For electrolysis, the primary thing you need is an electrolyte to allow the charge to pass through the solution to work on the metal. This could be as simple as table salt depending on what your goal was.
> For derusting electrolysis, baking soda would work just fine as an electrolyte, except the pH of the solution it produces when dissolved is fairly low. Someone was correct when they said the carbonate (not the bicarbonate in baking soda) is more alkaline/basic, i.e., it generates a bath that has a higher pH. Sodium Hydroxide (Lye) would produce an even more alkaline bath (higher pH). The only precaution you must use is that sodium hydroxide is aggressive enough to burn if you don't treat it with respect. It is referred to as a Strong Base in chemistry. 
> 
> Why do you want a high pH solution from a strong base to do this job? Efficiency is the correct answer, but I'll explain. Oxygen is produced at the anode. Hydrogen at the cathode. If you understand how these are produced from the splitting of water, you see that how easily it is made depends on how acidic the bath is (how much H+ ion is in there for those that care). You don't want oxygen to be made easily when doing this procedure. It reduces your electrolysis efficiency. So the higher the pH the better. If I were doing it, I too would use regular old Lye and just use care with it and make sure my kids knew it was off limits.
> 
> Hope it helps.
> Steve
> 
> 
>DAVID BRUCE wrote:
> Not really being familiar with a 'Hot Tank' solution I risk going out on a
>limb but ...
>Probably the hot tank solution is basically lye (potassium hydroxide or
>sodium hydroxide) in solution. If that is true, the hydroxide solutions
>are "stronger" than Washing Soda (sodium carbonate or soda ash) but other
>than taking the appropriate safety precautions I would think it will work
>as well for the electrolytic rust removal. Now using washing soda in a
>'Hot Tank' might not work as well. Just my opinion with a significant
>lack of information - ymmv - and I'm sure there are others here that have
>more practical experience than I do.
>
>David
>NW NC
>
> 
>
>>Possibly a dumb question,
>>
>>So is Soda Washing similar to a 'Hot Tank'
>>solution? Or will it remove rust as well? This
>>sounds like something I need to try...
>>
>>Chris
>>
>> 
>>
>
>
>
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