Electrolytic rust removal question

Don't know where you read that but my electrode is a piece of rebar from Home Depot. Works great.

Steve.

Just find the cheapest source of graphite that you can. I found some on eBay.

Whatever you use, remember this: a bit flat piece has much more surface area than a rod. More surface area = more current. I got lucky and found some big graphite blocks that I bandsaw into 1/2" thick plates. (Move your saw outdoors for this. It's a messy job. Don't set the saw on your driveway, either.)

There's a problem with searching for "graphite" on eBay. You'll get thousands of listings of tennis racquets to golf clubs to fishing poles. Instead, search for graphite plate*, graphite stock, graphite bar*, etc. The * is a wild card that will give you hits on both plate and plates.

The binder in some types of graphite doesn't hold up well in the electrolysis vat. I've had some graphite plates dissolve in a day or so. On the other hand, I've had some graphite last for a year, or more, under continuous use.

If you have a foundry or mill that uses an electric arc furnace or an aluminum smelter, nearby, see if you can beg some stub end of their carbon rods.

Here's a tip: If you have a 3,000 psi pressure washer, use it for removing the gunk that forms during electrolysis. It works great and saves lots of elbow grease.

Good luck.

Orrin

First, I'm curious about what the toxic waste issue would be with stainless. Do you have a link or a reference?

For swabbing, I use a 1.25" x .75" x 9" slab of Poco 3 (EDM graphite) that I cut off an old EDM electrode with a hand saw. It cuts about like maple. EDM graphite has no binders and Poco 3 is very dense and strong. It probably will outlast me and the next two generations of my family. I just clamp the battery clamp from my 4A battery charger to the end of it and wear rubber gloves.

For use in a tank, my electrode is a plain sheet of mild steel (the cover off an old microwave oven) that I sanded clean on one side with a disk sander. Just wipe it dry when you're done. I see no need for stainless. However, I do wonder about what could be toxic in using stainless for this job.

Ed Huntress

Could be chromium. Also, you are talking about the *anode*. This is the sacraficial electrode in plating so you will be eroding a metalic anode into your solution thus conaminating it. You won't get the eroded material plating out nicely - concentrations are all wrong for plating. Graphite won't do that so is to be preffered for electrocleaning.

Ted

From my reading about the process (and I know little about electrochemistry myself), it appears there is no erosion of metal involved at all, on either side. That's why I question the idea that stainless causes a problem.

Ed Huntress

I have used stainless because I have some sheet which is about the right size. I have neither seen or measured any loss from the stainless anode although it is very obvious (from current variations) that one must run with reverse polarity regularly to de-polarize the anode. I imagine that carbon would not suffer from this problem???

Mark Rand RTFM

Do a google search on electrolysis, and you'll find quite a bit of info. Here's one particular article written by a friend of mine - Richard Angelico of New Orleans, La. He is a fellow relic-hunter who finds quite a bit of good 'ole Civil War ordinance - specifically - he finds a good many bombs and cannonballs.

He uses 316 stainless for his anode... and his results are fantastic.

Link to his article:

Mark Rand wrote in news: snipped-for-privacy@4ax.com:

Some may be interested to know that they use this method to reduce rust and to remove salt from metal objects recovered from ancient ship wrecks. The time they leave it in the tank is often up to two YEARS. Yike.

Ed Huntress

electrochemistry

I don't know, Mark. The people who seem to know what they're talking about on this subject describe it as a very weak action, which won't even affect black rust (Fe3O4). It only works on red rust. The weak alkaline solution doesn't produce any significant quantity of ionized metal ions. It doesn't do much of anything, in fact, except strip red rust somehow.

The black grunge that remains on the part is mostly black rust. It comes off easily with a light brushing from a stainless brush. In a couple of cases I've used hydrochloric acid to remove the black rust, and then put the part back in the electrolytic process in the hope that it will remove any chloride ions picked up from the acid.

I don't know. But I have a lot of de-rusted parts to show that it does a good job.

Ed Huntress

That's *nothing* Ed. I personally have some rusty artifacts in my shop that have remained in situ for up to *five* whole years. They seem to be aging quite nicely indeed.

:^)

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Snip

I don't have a reference, but I have about eight years of almost continuous experience using electrolysis.

I was told that stainless steel wouldn't degrade when used as a waste electrode when doing electrolytic derusting. So, I used a thin sheet of SS scrap.

It took a while, but the sheet stainless eventually looked like a lace curtain. Worse, my solution turned yellow: hexavalent chromium.

I once worked at a facility where they pumped their discarded chromate-treated cooling tower water into the ground. That was then. Now, hundreds of millions of yours and my tax dollars are being spent trying to get it pumped back out of the aquifer.

Orrin

That's interesting. Did you use one of the standard, weak alkaline solutions?

Ed Huntress

Ed

If you throw the kind of voltages that are used in this process at an anode something is going to give. You can't pass a current from an electrode into a solution without a chemical reaction. At the anode it is either an oxidation of something in solution or an oxidation of the anode. You must have one or the other to pass a current. If the current is so high that there is nothing available from the solution to oxidize then the anode is going to go.

Ok, I'm just listening, but it strikes me funny, because I've seen no evidence that my graphite- or mild-steel electrodes have eroded. I do have a good triple-beam balance. Maybe I'll start weighing that sheet of mild steel, before and after. I certainly do enough of it that I should be able to measure it.

Ed Huntress

I completely agree that you have to have oxidation at the anode, I just find it hard to belive that you will produce Cr(VI) and not Cr(III). So far as I remember my electrochemistry courses, electrolytic dissolution pretty much always produces the lowest stable oxidation state. I've done a lot of electropolishing of stainless steel, and those solutions always turn green, consistent with Cr(III). Have you chemically verified the presence of hexavalent chromium or did you just trust the color, which could be due to dissolved rust or other metal ions at low concentration (no, I didn't on my solutions)?

-- Regards, Carl Ijames snipped-for-privacy@verizon.net

Snip

I use washing soda with a little lye thrown in to cut any grease or paint that might be on the item.

Orrin

No, I haven't run any chemical analysis. I'm not in a position where I have to prove anything to myself. In eight years I've used a variety of electrodes and have seen just about every color in the solution caused by the rust being removed.

The only time I got a yellow solution is when I used stainless steel that disinegrated as described. I've been around lots of stationary Diesels that used chromate-treated coolant. The appearance was exactly the same. That's good enough for me.

I have never seen a green-tinted electrolyte in my setup.

If I tell people to use stainless electrodes and they go ahead and do. And, if they discard their electrolyte on their property, what position does that put me into?

In this litigious society, I'm going to express every caution that I can think of.

Orrin

I agree that Cr+6 is not going to be produced. I never said that Cr+6 was produced. I doubt if it happens and if it was produced it would be reduced to Cr+3 at the cathode. There is no way one will accumulate chromates in this procedure.

For those who don't believe that the anode can be dissolved note that this fellow has been doing electropolishing. For the uninitiated the piece to be electropolished is the anode. They ramp the voltage up so one gets anodic dissolution in addition to the normal gas evolution. The theory is that the peaks dissolve faster than the valleys so one ends up with a flat surface. In fact the theory is correct and with the proper voltage and proper solutions you can make some pretty nice stainless steel mirrors. In order to make those mirrors one dissolves stainless steel from the surface. I rest my case.

One of those solutions was a mixture of acetic anhydride and perchloric acid. That one is not for the faint of heart. Due to some faulty decisions an entire city block was removed in Los Angles. That gave some more bad publicity to the perchloric acid business. My research director owned the largest plant for producing perchloric acid in the USA at the time. He was not pleased.

Amen, sadly.

-- Regards, Carl Ijames snipped-for-privacy@verizon.net