Hot Rods Rust Removal - Tools or Parts

Bear with me while I put my tinfoil hat on.

At low pH, citric acid (C6H8O7) acts like a normal acid. It will eat rust, and make bubbly hydrogen:
C6H8O7 + Fe2O3 → 2 FeO + 6 CO + 2 H2O + 2 H2
This is similar to how that stanky vinegar works.

If you bump the pH up (by adding something like washing soda), then citric acid stops playing like an acid and starts "chelating". Chelating is a fancy word for when stuff (like citric acid) makes LOTS of links to metals. In this case, the citric acid grabs the iron out of the rust and latches on to it, like this:

C6H8O7 + FeO → Fe(HC6H5O7) + H2O
3C6H8O7 + Fe2O3 + Feº → 3Fe(HC6H5O7 + 3H2O
4C6H8O7 + Fe3O4 + Feº → 4Fe(HC6H5O7) + 4H2O

Class, can we go back to burning magnesium ribbon and using the bunsen burner hose to blow frogs up?

Cheers,
Harv

 

Can you do a “for dummies” version?
About the only thing I recall from HS Chemistry is the word/phrase “Avagadros number”.
I think it started with a 6.


Edit: Google says…. Yes it starts with a 6!
Dang, Mr Violini would be proud!!

 

^^^^ HAHAHA !!! ^^^^

....

 

Very interesting and informative. Chemistry was never my bag...Bio and a bit of Physics for me!

 

Washing soda IS ddifferent than baking soda. The ratio of citric acid to soda is this in the BB video:

100g citric acid to 40g washing soda. 1:0.4
Or
100g citric acid to 63g baking soda. 1:1
Edit corrected baking soda amount.

I don’t know the difference, but there is one. They are both supposed to work. I don’t know if either is specifically better. I was out of washing soda so in my personal test it has been the 1:1 ratio for baking soda. Works like a champ.


An old PROTO center punch - not perfect, but I can throw it back in for a day and see if the rest comes off.

 

The solution was mixed 8/22/24.

I will update with more images and I will note when it “feels” like it starts degrading in performance.

 

What he said - totally have no idea but it sounds legit!

 

Thanks for info

 

Just ordered washing soda,,,,,time for experimenting!

 

I figured baking soda in my numbers above from the point of view of about every household has baking soda or at least all that I could remember vs having washing soda.

...BTW The original OP video the formula calls for 40 grams washing soda vs 63 grams baking soda....

...

 

You are correct. I was mistaken on my baking soda number. It is 63g per 100g of citric acid. Oddly enough, I think I buffed when I mixed up my #1 test solution and it still works fine. My next batch will be at 63g or I will have purchased more washing soda. I will let you know how it goes!

hate it when I mess up the numbers…

 

Screenshot from the video.

 

That video advice is good science. There is nothing magic about "baking" or "washing" sodas. They are just a means of raising pH without the citric acid making any nasty byproducts. They each have different strengths, so you use more or less of them. Caustic soda does the same, again with a different strength.

Cheers,
Harv

 

Does this goop wear out or do you have to top up the chemicals after a while? Does the rust settle down the bottom?

 

I am still on my first run of the stuff so I can’t answer yet.

 

I've had good results with vinegar, but as mentioned, the smell.. I have heard thru the grapevine that oxalic acid (wood bleach) works well, has anybody tried that??

 

Washing soda is Sodium Carbonate. Much bubbling as the carbon dioxide from the carbonate is released on reacting with the acid.

Baking soda is Sodium Bicarbonate. Beaucoup bubbling because there's even more carbonate than in Sodium Carbonate.

Lye is Sodium Hydroxide. Mixing it with the Citric acid should make no bubbling since there's no carbonate in its makeup.

 

how about electrolysis ?

some thing better than a 9V battery

 

I have been using citric acid for years, with nothing but city water.

A chemical plant that I designed and built uses it in bulk, but won't touch a damaged 50lb bag. I get those for free.

I put my barrel in the truck and head over whenever the have a few for me.

 

Oh I'm not worried about the connections or the voltage. been doing it for years. I'm just saying if you use a carbon anode instead of steel, you dont have hardly any cleanup and practically never have to replace the water. I used to use castoff carbon motor brushes before i bought the gouging rods from McMastercarr. None of that orange scum to clean up. I was just commenting that the chelation method means not having to wire up all 65 pieces that I want derusted when I do a batch of small parts.

-rick

 

Oxalic acid and Vinegar do eat rust. But they do it so slowly that the acid also attacks and pits the base metal. This whole thread is about the process of chelation- you take an acid that likes to bond with rust (citric acid), then you neutralize the ph a bit with a base like washing soda, baking soda, or soda ash, then you are left with a less strong acid that still really likes to bond to rust so the good metal underneath isn't harmed.

-rick

 

This was a heavily rusted rotor submerised in 16 ozs of vinegar and enough water to cover it, soaked for 24 hrs with a couple light wire brush scrubs along the way.

 

Here are a couple pics from the tech thread I did a few years back. Just Citric Acid & Water. No special tricks, just soak and rinse. Great thing is I can just pour it in the side yard or gravel drive when Im done. It Doesnt even kill the grass. To me it's much easier to tolerate the smell over vinegar or putrid Molasses & much easier to dispose of. I use a batch until it weakens up then mix up a fresh one. It's so cheap you'll likely buy one big bag that will last for years.

 

I use the washing soda (sodium carbonate) in my solution for electrolysis rust removing. Last night we found a bottle at walmart that someone put down after carrying around the store. It caught our eye because it was a pool supply marked PH-UP to be used to adjust ph of swimming pools.

I checked the bottle- 100% sodium cabonate (washing soda). Marked down from clearance aisle to 50cents. I went to clearance aisle and got all the rest of them-9 bottles-50 cents each. Score!

Also, the reason we noticed pool chemicals, is because our side gig is running a church group retreat center (basically a summer camp) and we have a pool to take care of that's 40foot by 80foot- 135,000 gallons. And let me tell you something- now that the time to close the pool is near, I've been thinking long and hard about dropping the whole car in it and wiring up my welder power supply....

It's been done, I know-I'm waiting for an email back from a guy that can share his experience. But maybe If I can use the chelation method to do easy batches of parts then doing the carcass itself without the pool will help keep me employed there a little longer, lol.

-rick

 

Working on an 04 VW - definitely not HAMB worthy, but my kid needs the car… put a corroded shock top in and added some lug and brake bolts. For once I can win at hide and seek!


After an hour or so, the edges getting worked on showed up in the top of the soup!