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grannyknot

Citric acid and rust

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Back in the summer there was a thread about a German product, a paste made of Citric acid and sawdust.  I can't find it at the moment but I have been playing around with Citric acid for a couple months now and it has become my go to rust remover.

I have found all the other acid rust removers have some drawbacks to them but Citric has the fewest so far.  It is very inexpensive especially the industrial grade,  I didn't want to purchase 50lbs until I knew it was worth it so bought 10lbs of food grade.  2 cups of dried powder in about a gallon of water makes a strong  solution. Your results may vary depending on the hardness of your water but it should be easy to repeat these results.

The test piece is from the KA24DE engine I'm using in the 510,  2 cups of Citric acid in a gallon of water, all I did was scrape the worst of the flaky rust off.  The shop is cold, just above freezing, when the water is room temp in the summer rust removal happens a lot faster.  If you splash some on your skin you just rinse it off, there is no drama, no burns.

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These next 2 pics are after 20hrs soaking, took it out of the bucket and scrubbed it with an old wire brush and rinsed. The last 2 pics are after an additional 24hrs.

Now that might seem like a long time but I have lots of that so I'm good.  Muriatic acid is 10x faster for sure but I have never found a way to completely neutralize it, the rust always comes back under the paint,  so far that has hasn't happened with the Citric acid pieces.

 

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7 hours ago, grannyknot said:

scrubbed it with an old wire brush

Top tip...  Saw the first 1-2 inch off the brush.. you have a good brush again!  That piece of wood gets in the way with brushing.. now no longer! :pow:

Use a steel saw..

Edited by dutchzcarguy
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This is great!

Just to offer an alternative: I was frankly amazed how good this experiment went.

I bought 6 bottles of the cheapest / nastiest bottled lemon juice off the supermarket shelf.

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Poured into an old ice creme tub and added lots of salt - no scientific measurement, just what felt right. If I had to quantity I would say 2 table spoons.

Degreased parts with thinners, then left them in the lemon juice and salt tub for 12 hours overnight.

See for yourself:

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44 minutes ago, AK260 said:

Poured into an old ice creme tub and added lots of salt - no scientific measurement, just what felt right. If I had to quantity I would say 2 table spoons.

Why did you add salt?

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Why did you add salt?


I read somewhere that it speeds up the reaction. Interesting thing was that the garage / the solution smelled like sulphuric acid after the 12 hour soak. But I’m no chemist.

I reused the solution many times over and it worked well ...

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Before this, I wasted way too much time with a wire wheel and drill achieving lesser results!

OK I’m gonna shut up now, I feel like I’m thread jacking!

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10 hours ago, grannyknot said:

I have been playing around with Citric acid for a couple months now and it has become my go to rust remover.

Brothers from a different mother, I tell ya.   I've gone through thirty pounds of the stuff in the past two months.

It's really hard to get a good picture of the results, but I tried. Here's a handful of misc hardware. Before:
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I put the stuff in a wide mouth plastic container for a couple hours. When I first put the stuff in, it bubbles and becomes a little milky looking from all the tiny bubbles. I think that's the remaining yellow chromate and zinc plating being eaten off:
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And then after a couple hours. They aren't sparkling perfect, but are a whole lot better than when I started:
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Here's about the only good shot I have of before and after:
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I've got parts out for professional plating right now. Should be done soon.....

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44 minutes ago, Namerow said:

Why did you add salt?

That's a trick used with acetic acid to speed up the reaction. Apparently acetic acid works better than citric (but it stinks) and the addition of salt makes it work even faster. So fast, in fact, that they warn you not to put anything aluminum in the solution because it will be damaged. I don't know for positive sure if it has the same effect with citric, but like Granny, I did the same and added a little bit to my mix. I figured it wouldn't hurt, and may help.

From what I understand, the citric does not convert the rust to anything, but it is "chelated" instead. And my (quite limited) understanding of the whole thing goes like this...

Rust is not normally soluble in water, but additions of certain additives (like these mild acids) make it so that rust IS slightly soluble in the solution. I think that makes the acid additions to the water "chelating agents". So once you add citric acid to the water, rust becomes slightly soluble and "washes" off the parts. Doesn't happen quickly, but it happens.

So back to my very limited understanding... There are several different combinations of iron and oxygen that can be called "rust", and the addition of salt changes the ionic characteristics of the solution and makes a broader range of them soluble. So in other words, "a wider range of rust types are soluble".

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3 hours ago, Captain Obvious said:

I've got parts out for professional plating right now. Should be done soon.....

Does surface rusting restart once it is out of the solution? Or the chelating removes all of the rust particles and as long as the part is dry between removal and plating, it won't start to rust? 

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 I use Ospho which uses phosphoric acid as the active ingredient. It removes rust quite well and leaves a film of iron phosphate. When I'm ready to paint I wipe the area down with a little baking soda, and water on a sponge. Then a water rinse and a wipe down with lacquer thinner.

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Does surface rusting restart once it is out of the solution? Or the chelating removes all of the rust particles and as long as the part is dry between removal and plating, it won't start to rust? 


So with my solution, I dropped the parts into clean water straight away to flush them. Then I would drop them into a container of Jenolite and ensure all surfaces were covered. This converts the surface into something that turns it purple and supposedly doesn’t rust.

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The parts I didn’t Jenolite started to turn dull all too quickly as those pesky o2 atoms started to attach themselves!!!

After the allotted time and drying throughly, I just painted them; as at the time we were in serious lockdown and I couldn’t get to the plating place.

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8 hours ago, Captain Obvious said:

I've gone through thirty pounds of the stuff in the past two months.

So far it's the best way I have found for a number of reasons, the industrial powder is cheap, like $2 per lb. It doesn't smell, it doesn't burn you when you get some on your skin, I have found it doesn't flash rusts as quickly the way other acids do.  It's also very easy to dispose of.

I'll have to try some salt with it.

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1 hour ago, grannyknot said:

So far it's the best way I have found for a number of reasons, the industrial powder is cheap, like $2 per lb. It doesn't smell, it doesn't burn you when you get some on your skin, I have found it doesn't flash rusts as quickly the way other acids do.  It's also very easy to dispose of.

I'll have to try some salt with it.

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8 hours ago, Muzez said:

Does surface rusting restart once it is out of the solution?

Yes, I did have issues with rusting after it came out of the citric acid solution, and no, the fact that it was chelated didn't do anything to prevent it.

I started this whole process near the end of fall when it was still in the 80's in the afternoons and sunny. At that time, I would dump the hardware jars into a bucket, take them inside and rinse them off in the sink. Then take them back outside and dump them all on the hot black driveway to dry. It seemed that the faster they dried, the better the results (makes sense, right?).

But I ran out of calendar time, and by the end of this process, it was in the sixties and there wasn't much direct sun to dry stuff on the driveway. So I set up a three stage rinse bath:

1) Pick out a part or two from the citric acid bath and shake it around in a  bucket of clean water.
2) Move it from that bucket into another bucket with "cleaner" water and shake it around.
3) Move it from second water bucket into a small container of methyl alcohol (methanol). My thoughts were that a) it evaporated faster than water, and b) water is miscible with the alcohol so it would go into solution and help get H2O off the surface.

Then after all that, lay it out on the semi-warm driveway to dry. That process got me through the end of the parts and the cooler fall days.

Most of the larger parts got a quick wizz on the wire wheel after that just because I heard they looked better after plating if you did that. I didn't do the small hardware stuff because it was hard to hold. And yes, I zinnnnnngggged a couple parts across the yard. Only lost one piece in the end, and thankfully didn't put anything through any windows.  LOL

 Yes, it was a PITA, and yes it's done.

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4 hours ago, AK260 said:

Then I would drop them into a container of Jenolite and ensure all surfaces were covered.

 

All of that stuff is phosphoric acid based. Ospho, Naval Jelly, etc. All creates a barrier of iron phosphate which helps deter the formation of rust in the future. I would have used a phosphoric based compound, but like Granny mentioned, the citric is so much safer. I mean the phosphoric isn't really that bad, but the citric is safer.

That said... I did have a couple parts that were really bad (like an ashtray). For those parts, I did resort to the phosphoric stuff spot treatment method. Then once most of the rust was off in the worst spots, I put them in the citric bath with other parts.

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9 hours ago, Captain Obvious said:

but like Granny mentioned, the citric is so much safer. I mean the phosphoric isn't really that bad, but the citric is safer.

My main beef with phosphoric acid is not one of safety but with the active rust that is still under that layer of black iron phosphate, eventually it pushes back up and bubbles the paint.  For me I've found it's just easier to keep working the piece until it's down to bare metal.

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Gotcha. And I also tried to do what you said and keep working it until it's down to bare metal. You'll see the pits where the rust used to be, but the rust is gone.

So some other stuff I noticed with the citric acid bath... Some of the parts seemed to develop a black coating when left in the acid for long times. I assume it's due to the composition of the metal itself because it really followed the same type of part. If I had to guess, I would guess it was a higher carbon content steel parts and that was somehow causing a black oxide coating to form.

For example...  Shepherds hooks got black and so did throttle body mounting socket head cap screws. Most of the stuff didn't seem to care how long it was left in the bath or what temperature it was, but there were a couple things that didn't like extended soak.

And (especially on the cold days towards the end of the process) I usually heated up the citric acid bath a little in the microwave to try to speed the de-rusting process, and it seemed the hotter I made it, the more likely that black coating occurred. My temps ranged from "just barely noticeable" to "I can still carry it without a hot mitt, but it's pretty hot". I didn't stick a thermometer in anything.

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I didn't stick a thermometer in anything.


One assumes you are still referring to the de-rusting topic!? Otherwise, thank goodness!!! :o

But then again, if that’s your bag baby, then bat on and hope for a good wicket old chap.

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8 hours ago, Captain Obvious said:

Some of the parts seemed to develop a black coating when left in the acid for long times. I assume it's due to the composition of the metal itself because it really followed the same type of part.

Interesting, I haven't seen that yet.  Does it rub off or is it fixed to the metal?

Something you mentioned earlier about the rust just falling off, yes most of the rust accumulates at the bottom of the bucket, I think that might be part of the reason why the solution keeps working for so long.  I've had a bucket of solution working for up to 6 wks with it cleaning dozens of parts before it 's used up.

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The black coating did not come easily with a finger. Came off with the wire wheel on the grinder, but even after that, the metal seemed to have a darker color to it.

However, all that said, I just got the parts back from the plater, and it did not seem to affect how the parts looked after plating. Of course, I'm just looking at the yellow chromate coating and not the zinc underneath, but the parts look great. Couple small issues, but overall, I think it was a success.

Everyone loves pics of boxes of newly plated parts, right?
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5 hours ago, AK260 said:

One assumes you are still referring to the de-rusting topic!? Otherwise, thank goodness!!!

 

 

LOL   Haha!!! One would assume!

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Everyone loves pics of boxes of newly plated parts, right?




Absolutely right! Loving how that inspection lamp came out!!!

I geeked out on my box of shiny bits ...

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Obviously my wife was delighted with me laying it all out and labelling on the kitchen counter!

Does anyone else here think we need to get a life?
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5 hours ago, AK260 said:

I geeked out on my box of shiny bits ...

As a "college restorer" of mine always says... "Ut zien net krehjuh.. ast mar blihnkt"   A very local saying.. in dutch: Het zijn net kraaien... als het maar blinkt!   Translation would be: They all are like crows, it has to be shiny!!!   Hahaha...  it's true! 😜 

Edited by dutchzcarguy
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8 hours ago, Captain Obvious said:

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top tip: Now if you have to plate long springs  I put an elongated piece of steel with notches in the ends IN the spring so that it is stretched and the spring becomes perfectly plated.. 👍

Your parts look very nice CO!

 

Edited by dutchzcarguy
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