Speculation on rusting after Electrolysis

Re: Speculation on rusting after Electrolysis

Dan Donaldson

>Interesting question. Now you have me wondering too. I also wonder if it could have something to do with the fact that the surface is so clean. I wonder if it would do the same thing if you were to clean it with steel wool or sandpaper in a very strong degreaser. (except that you cannot get it anymore, freon comes to mind). If you cleaned it under the surface of the liquid, would it rust as fast when you took it out and dried it. Hmmmm..............

Re: Speculation on rusting after Electrolysis

Tom MacGregor

>I'll let the chemists work out the how & why stuff. After I zap my pieces I spray on a rust inhibitor made by CRC called SP-350. After letting it set for a few minutes I buff it up with a clean rag. I've had no problem with residue on the wood after wipeing it down well, and I have very little problem with rust.

Re: Speculation on rusting after Electrolysis

Dave (Arlington, VA)

>Hi Dan -

In your post, you wondered "I also wonder if it could have something to do with the fact that the surface is so clean. I wonder if it would do the same thing if you were to clean it with steel wool or sandpaper in a very strong degreaser."

I haven't done exactly that but I have tried to flatten the soles of two planes (a #220 block plane and a #3). I used successive grits of sandpaper and followed Paul Bernard's suggestion as was later immortalized in a WC article. I flattened the bottoms up to 600 grit - pretty shinny.

Months later I go down to my shop and three of my planes have rust on them - one fairly minor, and the other two pretty severe (in my judgement). The rust was over a fair amount of the bottom of both planes. Can you guess which two planes it was? Right. The #220 and the #3. During this time the #220 was stored in its original cardboard box resting on a wooden shelf inside a wooden closet. The #3 was resting on its sole on a wooden shelf inside the same wooden closet.

I posted a question at the time, but no one seemed to think it was much more than a coincidence. There didn't seem to be much thought that it could have been as a result of the flattening (cleaning?) of the soles.

But now you have me wondering, too.

Regards -

Dave

the answer

Bill Tindall, E. TN

>The oxygen hypothesis is not promising. Oxygen is made at the other electorde(presuming everything is hooked up properly). With vigorous hydrogen evolution occuring at the cathode one can be sure there is nothing on the iron that is an oxidizing agent.

The answer is surface area. The red iron rust is reduced back to the black oxide(a mix of ferrous and ferric iron) and perhaps some iron metal as well if the conditions are right. Some of these products are very finely divided and hence, they have a large surface area which is exposed to the air and water after treatment. The large surface area promotes rapid reoxidation. Quick drying followed by oiling prevents rerusting, at least in my hands.

Re: Speculation on rusting after Electrolysis

Thom Trail, Powder Springs, GA

>Well, I can't comment on a reducing solution but, a lot of what I've read and experienced goes to prove your point. As I understand it, once zapped, there are lots and lots of iron atoms that really really want to combine with an oxygen atom (rust). Those on the surface have the most access to oxygen, whether it be in water, air or as water vapor.

My best solution is to wash, dry and wax immediatly after zapping. An old hair dryer works great for drying and the heated iron helps the application of the wax.

Thom

Re: Speculation on rusting after Electrolysis

Jack from Maine

>All I know about the why is what I've read here. However I have found that the layer of rust that is quickly formed is easily removed if you don't get it dry quick enough. I still find it amazing how much is still unknown about such simple phenomena as rusting.---Jack

Re: Speculation on rusting after Electrolysis

Jim in Burlington Ontario

>It's a interesting topic we solvent wash various equipment with Nitric Acid and Caustic Soda and usually farm out the boiler cleaning. I know that Nitric acid has a extra oxygen atom to quickly form a protective coat of oxide on the stainless steel. Personally I take it right to the varsol/chemsol sink and wash it down.

Re: Speculation on rusting after Electrolysis

Dale Stansbery

>I rinse well with hot water from the tap immediately out of the electrolysis bath to get the piece hot and help it dry, then oil or wax and have had little trouble with rust. I have had freshly flattened plane soles gain a light layer of rust in my humid shop when I forget to wax them well when not in use. I think clean steel rusts quickly because it is clean and there's nothing to act as a barrier between the metal and oxygen. I had a job years ago where I had equipment sandblasted and the guy who ran the sandblast business indicated that he had to prime and paint immediately to prevent rust.

Re: Speculation on rusting after Electrolysis

Skip in Falls Church

>It's a fairly well known phenomenon that when a clean metal surface is immersed in water it will corrode starting at a relatively rapid rate which declines over time as the metal "passivates". As a film builds up on the surface the oxidation of the metal slows down as an oxidative film builds up.

In general, anything that creates a barrier between oxygen, water and a metal surface will prevent oxidation of the surface. Again, generally, things like oil, wax and paint physically block oxygen from the surface preventing oxidation.

Re: the answer

Skip in Falls Church

>While oxygen is generated at the opposite electrode, the oxygen generated is bubbling up in the form of relatively fine bubbles through the water over the period that the electrolysis is going on. If nothing else, I'd expect the water to be supersaturated with oxygen. I encountered a similar situation just last week in an entirely different situation. Obviously a supersaturated solution of anything is relatively unstable.

If water, supersaturated with oxygen is adsorbed into the pores of the finely divided and, presumably, somewhat porous surface, it would seem that the impact would be pretty severe - especially when that object came into contact with air and started drying.

I suspect that at least part of the answer is "killing" the oxygen at the metal surface. I wonder if the rust inhibitor (SP-350 by CRC) that Tom mentioned in his post contains some sort of antioxidant.

Skip - who worked all night and is going to bed now. :)

not oxygen blocked

Bill Tindall, E. TN

>A thin layer of oil is not a barrier for oxygen, nor is the initial layer of rust that forms. Iron will not rust in the absence of water. The water can be water from high humidity or liquid water. I suspect the way oil and other rust preventitive barriers work is by excluding water from the iron surface, or at least those parts of the surface that are involved in rusting.

Re: the answer

Bill Tindall, E. TN

>The solution will not be supersaturated with oxygen because the hydrogen bubbles will be quite effective in stripping oxygen from the solution.

Agreed, there will be some concentration of oxygen in the solution as well as plenty of bubbles of oxygen, but even if the anode was isolated from the rusty piece, it would still rust after electrolysis if not protected because it is wet and has a high, porous, surface area.

The surface of the iron will be highly reducing as long as the current is on. Any oxygen that finds itself over there will either be physically blasted off by hydrogen evolution or the oxygen will be promptly reduced to water.

Re: Speculation on rusting after Electrolysis

Bill Tindall, E. TN

>Nitric works on stainless steel because it makes a layer of chromium oxide on the surface which is a barrier to further corrosion. (Stainless steels have high concentrations of chromium for corrosion protection).

Don't try nitric on just plain iron or it will dissolve.