My first Electrolysis

[armedandsafe]

We often use vinegar to remove gun bluing, which is a form of rust. I've never used an electrolosys process for that, however.

Pops

[Hopefuldave]

Re the polarity:

A bit of basic electrochemistry, very over-simplified...

Metal ions are generally positively charged, so get attracted to the negative electrode - in stripping the negative is the rebar or whatever, so the chromium ions (in your example) first bind with the chlorine (negative) ions in the muriatic acid freeing up the acid's hydrogen which bubbles off the workpiece, then get attracted to the negative electrode where the chlorine's liberated to take another round trip.

When electrolytically derusting, the workpiece is the negative and the rebar/whatever positive - the rust is composed of iron (positive ions) and oxygen (negative), so the oxygen's attracted to the positive electrode (and oxidises it, making it go rusty), the iron's on the negative terminal and held there by the negative charge. The washing soda in the solution doesn't really take part in the reaction, it's there mostly to make the water conductive so the current can flow through!

Please be aware that if the chrome-stripping solution turns yellow it's a sign that hexavalent chromium is present in the solution - this is **VERY** nasty stuff, carcinogenic, a nerve and liver toxin even in small/trace amounts... I could go on
IF so, before disposal add some sulphuric (battery) acid until the yellow colour disappears and you'll have made it a lot safer - either way, the resulting solution is technically a hazardous chemical and needs proper disposal, usually at a licenced facility (ouch, spendy!)

Please *don't* use stainless as the positive in a derusting setup either - same problem, although it looks like the electrode isn't being eaten away and stays relatively un-encrusted, the chromium is entering solution as the hexavalent form (which is why the solution would turn yellow...)

I've had good results using graphite as an electrode for anodising aluminium, perhaps it would work well for de-rusting?

Dave H. (the other one)

[armedandsafe]

Thanks, Dave. It has been so long since I have worked at any electolysis or plating, I could't remember enough about ions' wanderings to be comfortable posting the internal happenings.

Pops

[Gary Paine]

Sounds to me like your electrolysis cleanup is taking way too long. I suggest the process would be much faster with an appropriately larger piece of sacrificial metal for the anode than the rebar rods. I typically use worn out saw blades or scrap sheet metal. Think current density limits and you will understand the value of larger surface area. I use a cup per gallon of washing soda too. My tank usually runs at 14 volts and self limits at around 2 to 4 amps of current from my power supply. An hour or two would be plenty in such a setup, although I often pull it out early and wipe or scrape off any severe rust build up under running water and then put it in to finish.

[Gadget]

Do a Youtube search on molasses rust removal. Seems to work well.
Dan

[rmuell01]

Sounds to me like your electrolysis cleanup is taking way too long. I suggest the process would be much faster with an appropriately larger piece of sacrificial metal for the anode than the rebar rods. I typically use worn out saw blades or scrap sheet metal. Think current density limits and you will understand the value of larger surface area. I use a cup per gallon of washing soda too. My tank usually runs at 14 volts and self limits at around 2 to 4 amps of current from my power supply. An hour or two would be plenty in such a setup, although I often pull it out early and wipe or scrape off any severe rust build up under running water and then put it in to finish.

Nice Gary,
I will try larger sacrificials as I need to clean up a very old Wilton vise. my charger was running at about 5 volts (out of 12). maybe my connection using the wire wasn't conductive enough?

how do you connect multiple sacrificial pieces?

1 cup per gallon? I'll try increasing my mixture.

[rmuell01]

Do a Youtube search on molasses rust removal. Seems to work well.
Dan

Gadget,

I have researched molasses as the medium, but I don't want a permanent solution of foul smelling, scum infested liquid in my garage. (not that there's anything wrong with that ).

[Gary Paine]

Nice Gary,
I will try larger sacrificials as I need to clean up a very old Wilton vise. my charger was running at about 5 volts (out of 12). maybe my connection using the wire wasn't conductive enough?

how do you connect multiple sacrificial pieces?

1 cup per gallon? I'll try increasing my mixture.

Multiple sacrificial pieces would simply be hooked up in parallel as you did with the rebar. I have used alligator clips or just wire wrapped through holes punched in the sheet metal to get a connection. Without testing it, I am suspicious about the wire wrap on your rebar, wondering if it is really a decent electrical connection. That black coating may be surprisingly high resistance. When using coated or rusty sacrificial metal, I always take a file and get down to bare metal at the connection point (always above the water).
I am surprised to hear you were only getting 5 volts out of your charger. Is it one of the newer type that needs a load to regulate? Most chargers and power supplies will have a maximum power output that will limit either the current or the voltage until the product of the two reaches the maximum. If mine were dragged down to only 5 volts, my current would be several amps. From your posting, I suspect you were no where near that. Do you have a meter with which you can measure current flow?

[gnm109]

Re the polarity:

A bit of basic electrochemistry, very over-simplified...

Metal ions are generally positively charged, so get attracted to the negative electrode - in stripping the negative is the rebar or whatever, so the chromium ions (in your example) first bind with the chlorine (negative) ions in the muriatic acid freeing up the acid's hydrogen which bubbles off the workpiece, then get attracted to the negative electrode where the chlorine's liberated to take another round trip.

When electrolytically derusting, the workpiece is the negative and the rebar/whatever positive - the rust is composed of iron (positive ions) and oxygen (negative), so the oxygen's attracted to the positive electrode (and oxidises it, making it go rusty), the iron's on the negative terminal and held there by the negative charge. The washing soda in the solution doesn't really take part in the reaction, it's there mostly to make the water conductive so the current can flow through!

Please be aware that if the chrome-stripping solution turns yellow it's a sign that hexavalent chromium is present in the solution - this is **VERY** nasty stuff, carcinogenic, a nerve and liver toxin even in small/trace amounts... I could go on
IF so, before disposal add some sulphuric (battery) acid until the yellow colour disappears and you'll have made it a lot safer - either way, the resulting solution is technically a hazardous chemical and needs proper disposal, usually at a licenced facility (ouch, spendy!)

Please *don't* use stainless as the positive in a derusting setup either - same problem, although it looks like the electrode isn't being eaten away and stays relatively un-encrusted, the chromium is entering solution as the hexavalent form (which is why the solution would turn yellow...)

I've had good results using graphite as an electrode for anodising aluminium, perhaps it would work well for de-rusting?

Dave H. (the other one)

That's an excellent explanation. I'm saving it. Thanks.

As to the solution, it didn't change color except the chrome was left floating on top of the mix. I wiped it out and ultimately put a cup of baking soda in the mix which neutralized it.

We have free waste stations near me and I can take the mix there to eliminate it.

[flylo]

Check out this site http://www.oldengine.org/members/orrin/rustdemo.htm
I bought some 11.5" carbon disc to keep the solution cleaner & am going to use a 55 gal plastic barrel lengthwise for the vat.