Citric acid and rust

[grannyknot]

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.

[Namerow]

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.

[Captain Obvious]

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. 

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

[Captain Obvious]

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.

[grannyknot]

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.

[Captain Obvious]

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.

[AK260]

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.

[grannyknot]

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.

[Captain Obvious]

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?

[Captain Obvious]

5 hours ago, AK260 said:

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

 

 

   Haha!!! One would assume!

[AK260]

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 ...



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?

[dutchzcarguy]

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 November 27, 2020 by dutchzcarguy