Model A & B

Graphite Carbon Anode Electrolytic Rust Removal Method

Overview

Graphite carbon anode electrolysis is an excellent non-abrasive and non-toxic method for electrolytic rust removal from iron and steel.

This is a basic electrolytic rust removal process using a DC power supply, a sacrificial electrode (anode), and a solution of water and sodium carbonate (Na2CO3) as the electrolyte. The part to be de-rusted is used as the cathode in the electrolysis circuit.

Note: Sodium carbonate is 'washing soda', not baking soda.

Use Washing Soda! Soda Ash! Sodium Carbonate! Got it?

Arm & Hammer brand washing soda is the most readily available consumer source of sodium carbonate. Use one to two tablespoons per gallon, or one-half cup per five gallons of hot tap water and mix thoroughly.

The electrolysis of water occurs during this de-rusting process and oxygen gas (O2) is released at the anode. Hydrogen gas (H2) is released at the cathode, so it is advisable that this be done outdoors or in a well ventilated area. Your basement next to your gas-fired hot water heater is probably not the best choice for a workshop location!

Additionally, the formation of migrating bubbles of hydrogen gas on the surface of the part also cleans as it de-rusts, lifting and dislodging paint, dirt, and organic solids from the surface. This is similar to the cavitation surface cleaning action that ultrasonic cleaners are based on.

Carbon Anode Recommendation

Graphite is a particular structure of carbon, and is what's used for electrolytic de-rusting. One major advantage of using carbon (graphite) material for the sacrificial anode is that no dissociated iron is deposited on the part being de-rusted. Instead, the part gets a loose 'plating' of carbon, which is pretty easily washed and brushed off, and does not promote subsequent re-rusting.

Additionally, the carbon anode does not decompose into any hazardous compounds in solution, unlike other metals such as stainless steel when used as an anode.

Conversely, when using a mild steel anode like steel re-bar, the red Fe2O3 (ferric oxide) surface rust is converted to a layer of black Fe3O4 (magnetite) on the cathode. The magnetite forms a porous iron 'plating' on the part being de-rusted, which then promotes re-rusting after rinsing, and must typically be removed with a wire brush or glass bead blasting.

I do not recommend using a stainless steel anode due to the decomposition and toxicity of the chrome ions released in the solution when a stainless steel anode is dissociated.

I also do not recommend using a carbon steel or iron anode due to the unnecessary messiness of the solution and the easy re-rusting of the part when an iron or steel anode is dissociated.

I only recommend using a non-metallic (graphite carbon) anode.

Carbon Electrodes

Pictured above are carbon (graphite) electrodes I use for the anode. A fresh one is on top and a used one on the bottom. Some erosion of the used carbon is visible. These carbons are 5/8 inch diameter by 8 inches long.

Some people have recommended the following link at McMaster-Carr as a good source for affordable carbon rods. Order the plain ones, not the copper coated ones.

Much more affordable carbon anodes can be found on eBay. Though the quality of those graphites might not be as high, they work fine as a sacrificial anode.

I drilled a 4 mm hole in the end of the carbon rod and inserted a terminal end from a lab power supply jumper cable to use as the electrical connection to the carbon.

Another technique to connect electrically to the anode is to use a big steel "binder clip" from the stationary/office supply store to clip on the carbon rod, and then use conventional alligator clips from the power supply to attach to the binder clip.

Do not let any copper wires or jumpers or any clips or connectors be in the solution. Keep all your power supply connections outside the solution. Use a steel wire, not copper, on the part to bring the connection point outside the solution if necessary.

Power Supply

Pictured above is a very nice little 100 watt, regulated 12 volt DC output power supply. It is sold for use with computer/electrical equipment. You can use simple non-electronic manual 6/12 volt DC automotive battery chargers as well.

All that is required for the electrolysis process to work well is that the part surfaces are charged with sufficient DC power (current density) and are in the electrolyte solution. The positive red lead from the power supply is attached to the sacrificial carbon anode. The negative black lead from the power supply is attached to the part being de-rusted (cathode). The current flowing through the electrolyte solution completes the circuit between them.

Some higher end DC power supplies are switchable between Constant Current (CC), or Constant Voltage (CV). In either case, the voltage or current will be modulated by the actual electrical conductivity of the electrolyte solution. The amount of washing soda in the electrolyte solution (and its resistance) is what determines how much current can be pushed at the applied voltage.

Automotive battery chargers and regulated power supplies used alone are typically protected internally against external shorts (having an internal self resetting circuit breaker), and can supply all the DC current needed for electrolysis. More importantly, they will cut off if the leads are shorted, protecting both the workpiece and the power supply, as well as your eyeballs!

A MANUAL automotive battery charger can be used as a power supply, however DO NOT USE A BATTERY with any charger. Use just the charger alone.

Typical manual automotive battery chargers use a simple internal AC transformer and an inexpensive half-bridge rectifier to produce a low quality DC output voltage and current. Though not as clean a DC output as a lab-grade regulated DC power supply, the output from an automotive battery charger can work fine for most electrolytic de-rusting. A lab-grade regulated DC power supply could perform 'better' for de-rusting in some cases.

An AUTOMATIC automotive battery charger will not work without a battery present, and is unacceptable for electrolytic de-rusting power supplies. Automatic chargers require a battery to sense reference voltage and charge state, and electronically vary and taper the charger output depending upon the battery state.

I DO NOT recommend using a battery by itself as the sole power supply, nor in parallel with any battery charger or a power supply. Shorted batteries can explode, whereas shorted power supplies trip their internal circuit breakers.

There is always a risk of the anode and cathode contacting momentarily in the electrolyte and/or tank. Contact would create a direct short across the battery, which can quickly and dramatically release a considerable amount of stored energy!

In the case of a short, a battery can do a lot of damage to the part and possibly itself. It can discharge itself quickly and uncontrollably across a short between the anode and cathode, and the battery can explode.

Do not use a battery in your setup!

I recommend using a regulated DC power supply or an old-school manual DC automotive battery charger for electrolytic de-rusting.

Pictured above is my first victim, a mildly rusted iron carburetor casting.

The pic above shows the basic electrolysis setup for rust removal starting to work, with the positive (red) power supply lead applied to the carbon anode, and the negative (black) power supply lead attached to the cast iron carburetor casting.

It may not be evident in this photo, but the part and the carbon electrode are electrically isolated, so all current must transfer through the electrolyte solution.

Hydrogen gas bubbles are emanating from around the cathode (the carburetor). Oxygen gas bubbles are emanating from around the carbon rod (anode).

Here is the solution after half a day 'cooking'. The water is mostly just black carbon stained, with very little evidence of "rust" or other scum accumulating. The residuals have all settled to the bottom of the bucket.

This is due to the fact that the casting actually had very little red rust (Fe2O3), and had no rust scale buildup before the process. Using carbon rather than steel as the sacrificial anode is also cleaner.

If you use a piece of steel (like a piece of re-bar) for the anode, it makes the solution much messier as the steel anode is decomposed (sacrificed) in the process.

The part looks pretty good after washing in warm water and air drying. I have read that some people recommend to rinse the part in alcohol to help it dry without re-forming new orange surface rust, but I do not do it. Re-rusting is not an issue when using carbon anodes.

Obviously my first test was no challenge! No worry, I have a rusted original RH tail lamp bracket from New Zealand which might be a little tougher.

This is a rare (in the US) original stamped steel RH tail lamp bracket for a 1930-31 Model A Ford. It has original black baked enamel paint and two later layers of white and green enamel on top, and rust on the inside.

Line-of-Sight

Line-of-site between the carbon anode and the part surface to be cleaned is desirable and may speed the process somewhat, but is not required.

Line-of-site is much more critical in plating operations, where there is metal migration and the objective is to lay down uniform layers of the metals. With electrolytic rust removal, there is not a goal or desire to deposit a uniform layer of anything on the part being cleaned.

Carbon is deposited on the part in the de-rusting process, but this is not the objective. The varying amounts of loose carbon deposited on the part over time during this process are easily removed with a nylon brush and washed off.

Also, the 'rust' does not attract or 'attach' to the carbon anode. The process dissociates the bond between the part and the rust (and also to dirt, oils, and paint). All of the residuals are in solution and sink to the bottom of the bucket and do not deposit on the carbon anode. The sacrificial carbon anode is also slowly broken down, eroded, and consumed in this process.

Pictured above is the bracket after two hours. The water is mostly just dirty with some 'rust' and dirt scum floating on top.

The paint is mostly softened and beginning to slough off, and the rust is being converted and dissociated.

The pic above shows the bracket after about 10 hours. The water is mostly just black carbon stained now. The residuals have all settled to the bottom of the bucket.

Most of the paint and rust are gone, with just some small tenacious paint remaining.

After 24 hours the rust and dirt and paint is all gone, and the part is covered with a layer of carbon which has been loosely 'plated' on.

The pic above shows the bracket after cleaning in warm water with a nylon brush to remove the loose carbon.

Here is what it looks like after rinsing with warm water and a light scour with a stainless steel bristle brush.

I have now used this process with excellent results for a few years on dozens and dozens of iron carburetors, as well as all manner of other rusted iron and steel chassis and sheet metal parts. Try it for yourself!

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October 2008