The first experiment with rust removal went very well. But, I was left with some questions:
I ran electrolysis for 3½ hours with a temperature probe in the water as well as another temperature probe in the air to the side. I used the multiple thermal measurement tool from an earlier project to record the temperature every second of the test.
The result was that the temperature of the water was consistently within one degree Fahrenheit of the air. In other words, there was no measurable temperature increase due to electrolysis.
It could be that my electrolysis sessions involve too low of power usage (6 V @ 0.7 A = 4.2 W) to counteract the heat lost to the air to a measurable extent. Or, it could be that the majority of the electricity is converted chemically, rather than wasted as heat such as in electrical circuits.
As revealed earlier in the article, an inspection of various cast steel drawer pulls treated with electrolysis reveals that the formerly lightly rusted metal shows no pitting, in contrast to the formerly heavily rusted metal that shows significant pitting. So, the most obvious conclusion is that the pitting already existed due to rusting.
Unlike other people on the web, I ran my sessions on 6 volts instead of 12 volts or 18 volts. Perhaps a different voltage would be more effective at converting iron back into its original form?
During one experiment, I briefly turned the voltage up to 12 V, which increased current to 1.2 amps. The amount of bubbling rose significantly. My concern is that overly aggressive agitation may remove desired material, similar to excessive ultrasonic cleaning.
In the first electrolysis session, I used a single anode and occasionally rotated the part. In the second set of electrolysis sessions, I used two anodes (on opposite corner of the container) and did not rotate the part.
In both cases, it was obvious that the areas where the anode and cathode were nearest each other produced the greatest quantity of bubbles. However, my experience in electronics suggests that the more resistant paths will still receive current, just less. (Consider current through parallel resistors.) Indeed, all areas of the piece to be cleaned showed bubbling and cleaning action, even if they were not nearest or “line of sight” with the anode.
Nevertheless, I am convinced that complete de-rusting of the object will occur more quickly, evenly, and efficiently by surrounding the cathode by the anode or by regularly rotating the part. Otherwise, the cleanest portions of the object will waste electricity splitting water until the still-rusted portion receiving the least amount of current is finished. Also, because the cleanest portions will likely conduct electricity better than the rusted areas, and since the anode will become less conductive as it is corroded or coated, the process will become increasingly inefficient.
The steel or iron used as the anode is sacrificed in electrolysis, as the anode rusts (oxidizes) and the cathode de-rusts (reduces). Many people try stainless steel, brass, and aluminum as their anodes, due to the familiar corrosion-resistant properties of those materials. Unfortunately, stainless steel releases toxic materials as it decays, brass deposits copper onto the cathode (which accelerates rusting of steel), and aluminum quickly deteriorates.
However, there is a conductive material that can be successfully utilized as an almost non-sacrificial anode in electrolysis: graphite. Graphite is an electrically conductive form of solid carbon. You probably recognize graphite as the material in the center of a pencil.
Fine-grained graphite rods and plates can be obtained from McMaster-Carr or other distributors. Scrap and worn pieces can be purchased from eBay. I bought a box that had been used for electrical discharge machining (EDM).
Graphite carbon electrodes used in EDM.
EDM (also called spark machining or wire erosion) uses high currents that jump from the electrode to the workpiece to slowly carve away a complex pattern in a hard material. As such, a manufacturer can cut a pattern on a relatively easily-machined material, such as graphite, and reproduce the result on the difficult-to-machine material, such as titanium.
Shaped tips of graphite electrodes used in electrical discharge machining.
Depending on the application, the electrode will wear down beyond tolerances on a single use, or after multiple uses. After that, I guess you recycle it or sell it on eBay.
For this experiment, multiple lightly-rusted pieces were cleaned in a 0.5% sodium carbonate electrolyte with two graphite carbon anodes.
Multiple graphite anodes for rust removal using electrolysis.
Similar to the steel anode experiment, bubbles quickly formed on both the anode and the cathode. As you can see, the portion of the cathode nearest to the anode produces more activity that the portion located farther away.
Bubbles form on both the anode and the cathode.
However, unlike with the steel anode, the liquid did not horribly discolor with red foam. Instead, the water turned a subtle brown with plain white foam.
Graphite carbon anode produces cleaner looking white frothy foam.
To reduce the possibility that the lack of nastiness of the foam was due to the type of metal being cleaned, I tried cleaning a complete drawer pull, similar to the original test. The result was that the foam was still white and fairly clear. Admittedly, the second drawer pull had significantly less corrosion than the first drawer pull.
Examining the graphite anode revealed a considerably different condition compared to the steel anode. The steel anode was fairly corroded and discolored, suggesting that a portion of the red foam came from it. The graphite anode did drop some black particulate around its base, but was not discolored or coated with gunk.
The black particulate was likely disintegrated carbon, but it isn’t yet clear if this occurred due to electrolysis or loss of binding due to being submerged in water with washing soda. Either way, the graphite anode is still sacrificial, although likely not as quickly as the steel.
To me, the graphite anode is a better choice since it:
One last thing. During the restoration process, I noticed the wide variety of nuts holding the drawer pulls in place. As you may have personally experienced, drawer pulls become loose with use over the years. At some point, one or both of the sides of the drawer pull pop out and the nuts get lost. Rather than worrying about the sanctity of matching parts, people seem to replace the nuts with whatever fits.
Old cast and handmade nuts.
My favorites are the square nuts where the nut and the washer are cast together (a flange nut). But, I also ran across a handmade brass nut, made from a piece of hex rod by a man with poor centering skills.
Antique furniture hardware nuts and handle post bolts have unusual threading. Of 12 drawer pull posts, the approximate measured thread diameter and thread pitch per inch (TPI) are:
I would sure appreciate hearing from anyone who restores old furniture or can tell me how to make replacement nuts. I’m looking for an odd tap, for sure.
I made good use of ShapeLock prototype plastic to create a handmade nut. First, I made sure the bolt was clean and free of debris. Then, I took some molten plastic and wrapped it around the threads like a string to insure a snug fit. After that layer cooled, I added a big chunk of plastic on top of the threaded plastic to make a square shape for turning.
Custom drawer pull nut made from moldable plastic.
I let the plastic cool completely before removing it from the bolt and installing them both into the drawer. The plastic nut holds surprisingly well. It might be satisfactory to use permanently. (A few months later, my brother came up with a pile of metal nuts, of which one was a perfect fit.)
If performed carefully and safely, electrolysis is an efficient and effective method for removing rust from steel and iron. Most of the materials can be found at the grocery store, hardware store, or on-hand in your basement, kitchen, garage, and laundry room.
From a restorative perspective, it is amazing how many rusted pieces can probably be saved -- or even cleaned enough for a working replica to be fabricated. Care and wisdom must be applied for valuable, archeological, historical, mechanical, or structural pieces.
All in all, I am satisfied enough with the results to add electrolysis to my mental tool bag of tricks.