<VV> Corvair chemistry

[tony.underwood at cox.net]

---- Bryan Blackwell <bryan at skiblack.com> wrote: 
> Greetings,
> 
> So, over the weekend #1 son did a little chemistry experiment - de- 
> rusting using electrolysis.  Basically you make up a mild solution of  
> baking soda in water, put a sacrificial piece of iron in the water,  
> connect your battery charger minus to the piece being de-rusted and  
> the plus to the sacrificial anode.  Turn on the charger for a while  
> and the rust comes off.
> 
> The technique worked well and there are lots of things we could use  
> this for on a Corvair (shrouds would be a perfect candidate).  I  
> recall that the one caveat was you shouldn't do this to load bearing  
> parts (say, connecting rods), I think because of the hydrogen  
> produced as a result of the electrolysis.
> 
> Do I have this right?  Or am I mixing something up?  Any other things  
> to consider?  Thanks.
> 



Use sodium carbonate instead of sodium bicarb (baking soda).   It used to be sold in stores as "washing soda" or "laundry aid", and was pretty popular at one time, not so much now.   You find it a bit easier to turn up in hardware stores anymore, or in some of those mom&pop corner stores in the laundry isle... look for a tub or box of white granular stuff, read the label etc.   Sodium bicarb will work, but not as well.      

Also, far as I know there's no issues with hydrogen embrittlement issue to bother with when you use sodium carbonate as a medium, since even if there's any hydrogen embedded into the work it leaves relatively quickly... and wouldn't be that much of an issue in the first place even if it didn't fix itself in the end.       

Sodium carbonate solution derusting works out pretty well, albeit somewhat slowly.   Its saving grace is that it doesn't erode metal from the work the way acids and media blasting does.   

I've used this trick many times and it does work... last time was to derust a pair of older but rather nice scissors that somehow got put up wet and they had a coating of brown rust all over... cleaned them right up, all bare metal showing after an hour or so of bubbling away in a metal coffee can, scissors suspended from a piece of string tied to a makeshift gizmo made from a coat hanger.    I've heard of people derusting engine blocks this way using a battery charger and a big plastic laundry sink and a sheet of scrap metal as an anode.      

 I recommend a little dish washing detergent (NOT MUCH) in the mix to help break surface tension and help get to the rust through any oils or grease that might  be still present.     Expect to make a mess...  :)   


tony..