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Chaps

I've just come across a claim that a solution of diluted treacle will fully remove rust.  The claim is that it "... contains chelating agents. In practice the chelating agent binds with the rust and makes it water soluble. The rust dissolves into the treacle solution and clean metal is left behind".

I asked google and it came up with this link.

But is it an old wives' tale or does it work?  I'm willing to invest in a tub of Lyle's Blackest if nobody has given it a try yet.

Paul

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I’ve used a bucket of horse feed molasses to remove rust, so I can see treacle working.

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It will work but is geologically slow - think plate tectonics.

 

Bilt Hamber DeOxC is quite cheap and works very well in less than 24Hrs.

 

Roger

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Its an old folk remedy that does work, but as Roger says, it's very slow. And can attract flies, I understand.

The chelates actually steal the iron out of the rust, and sequester it in solution. Same way Evaporust and some other rust products work.

Ed

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Thank you chaps.

However, I was standing in the wrong queue when patience was being handed out, so I will stick to more aggressive methods.

Paul

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Plain old electrolysis with washing soda takes a bit of beating.  Citric acid works pretty well too - pickle with dilute phosphoric acid after to passivate and reduce flash rusting.

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An hour or two in a phosphoric acid solution.  (My bucket wasn't big enough to do the whole manifold in one go).

No batteries, no wires, no battery chargers.  And the inside gets cleaned, too.

Ed

SDC10848a.JPG

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Posted (edited)

It does look nice!   But the reason to use phosphoric acid to treat rust is that iron phophate is almost insoluble in water, so it stays on the metal.     If it's a thin layer, it's a good substrate for paint, or other coating.    However, only the surface of the rust will be converted, and a layer of phosphate over oxide is fragile and will break off, with any coating over it.       To remove rust, other 'weak' organic acids are better, such as citric or acetic, even ordinary vinegar, if left in it long enough, because the product of the reaction with the acid is soluble.

Looks like, Ed, that you removed all rust mechanically before soaking in phosphoric.  Good Plan!  Even if you use another acid before phosphoric, as the bare iron surface will 'flash rust' in minutes after washing off the first acid, that rust can then be stabilised with phosphoric.

JOhn

PS.  Oh, just seen that I'm echoing what Nick said!   

Edited by JohnD

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John.

That's the work of the citric acid not phosphoric acid. The citric acid takes all the rust off without any mechanical removal required.

Only then do you dunk the thing in phosphoric acid to create the iron phosphate layer to stop the fresh iron surface gingering up.

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Posted (edited)

Well, EE, Ed wrote, "An hour or two in a phosphoric acid solution.  (My bucket wasn't big enough to do the whole manifold in one go). No batteries, no wires, no battery chargers.  And the inside gets cleaned, too."

No mention of citric pretreatment, which was why I added my comment.  Do you know differently?

Ed, what did you do?

Edited by JohnD

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John--

No, I just dropped the manifold in the solution without any pre-treatment.  The dark areas in the pic is where the untreated surface is wet from rinsing.

Iron phosphate is pretty insoluble, but I find that when formed from the oxide, it just falls away as a precipitate. The more tenacious phosphate coating seems to only form on the metallic surface. 

Right out of the bath, there is a dark "smut" on the surface, but it is easily cleaned away with a brush and a rinse.

Ed

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Whatever floats the boat, Ed!   Or, possibly in this case, anchors it!

Certainly, you don't get the thick coat of rust on a cast iron manifold that will develop on a piece of mild steel.

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I wouldn't use an acid bath in my garage, i like my tools without the surface rust treatment you get overnight.

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4 minutes ago, RedRooster said:

I wouldn't use an acid bath in my garage, i like my tools without the surface rust treatment you get overnight.

Among common acids, that only really applies to hydrochloric (aka muriatic) acid, because the acid is actually a gas dissolved in water.  Other common acids don't have that rusting-at-a-distance effect.

Ed

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4 hours ago, JohnD said:

Well, EE, Ed wrote, "An hour or two in a phosphoric acid solution.  (My bucket wasn't big enough to do the whole manifold in one go). No batteries, no wires, no battery chargers.  And the inside gets cleaned, too."

No mention of citric pretreatment, which was why I added my comment.  Do you know differently?

Ed, what did you do?

Cross purposes there John i think. The very rusty crossmember bits in my photo just went straight into the bucket of citric acid, rusty scabs, paint and all. Drag it out and wash off any remaining goop with warm water and a stiff brush to clean out the nooks and crannies and you get that shiny surface. Can ginger up quite quickly hence the phosphoric acid treatment afterwards.

Ed. I found the phosphoric acid quite slow on its own hence the citric acid first. What concentration did you use?

Like you I haven't had issues with other stuff going rusty in the garage although I run a dehumidifier which keeps it all pretty dry anyway.

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Out of interest, where are you all buying your citric acid and phosphoric acid from?

And what concentrations etc are ideal?

Cheers,

Phil

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Hi Phil

Citric acid is supplied as a solid powder as bath salts!! I get it on Ebay.

Concentration wise I just make it up as a saturated solution in cold water. It's cheap. At that concentration you don't want it in your eyes or in contact with skin for a long time but it is otherwise pretty safe. 

Phosphoric acid is supplied as a liquid in various concentrations. Available from builders merchants as a concrete cleaner and paint suppliers as an etch. And on Ebay although I haven't bought from there myself. Concentrations up to 85% on there which is getting seriously hazardous to skin and eyes.

I have never used the stronger solutions for rust removal so can't really advise on that.

 

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And from Farmers' Markets, as "Milkstone Remover" for cleaning milking machines.   Of course its also found in Coke, where it provides the 'bite' in the taste.   But even  in that low concn will convert light rust if left overnight!

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I believe the phosphoric I buy is around 40%, and I dilute it maybe 1 or 2 to 1, mainly to make a larger batch.  Diluting it does make it a little slower.  I keep a 5 gallon bucket of it in my shop full time.  When the level gets low due to evaporation or dragout, i just add more acid and water.  Same bucket for at least 6-7 years.

Ed

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Just inspected my first experiment with electrolysis.   My goodness me!

I wanted a short length of tube for a fabrication, but all I had was very rusty from lying about too long, so, give it go.    It's so small that I set it up in a 1 litre jug, with a slightly bigger length of tube as the anode.  There was only an eight of an inch clearance - and the battery charger guage went up to 3!  Amps?  Wow!  It fizzes like mintoes in 7up, and the muck on the surface!   Half an hour later the water is so hot I have to pick up the jug by the handle.   Hmmmmmm!  This might not go well overnight!

Second go was in a bucket, with three pieces of scrap as anodes, just a gentle fizz and the charger stays at 1 ?amp or so.   OK, overnight should be safe.    And it was, the water didn't heat up, but the muck on the anodes!   Like horrible fungal growths, green and brown and black!   And just as soft and squishy!  YUCK!

My cathode piece, the part I want to use,  has no brown rust on it, but lots of black discolouration, like a pox.   I'll use it as is, it'll get a painted later, but for future reference:   Is it worth leaving it in there for longer?   Would the black bits be removed?

John

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Yes John, don't use anything valuable as the sacrificial anode!! Apparently iron creates less filth than steel. You can control the current by varying the clearance between anode & cathode, and strength of solution. 

Don't know if longer will help, I think it depends! When I did it, the stuff didn't come out spotless and shiny but only required a quick once-over with wire brush to clean up.

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I TRied the electrolysis with a wand.

+12V battery to the wand, -ve t the work piece (I think)   I used Halfords Gel rust remover as the electrolite.

It appeared to work but too slow for me.    Bilt Hamber DeOxC in a plastic bucket and do other things while it wrks.

 

Roger

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