Salt and vinegar for rust removal

[Sandy]

On Sun, 16 May 2004 18:56:02 -0500, Unknown posted:

Why do you need salt in the acetic acid to increase the rust removal?

[Sandy]

On Thu, 13 May 2004 22:15:37 -0500, Unknown posted:

Iron acetate is surely soluble enough?

Um, surely without the hydrogen ions, you are not going to get any dissolution of anything in the first place. All you need is an anion along with the H+ that does not form an insoluble precipitate with the resulting iron ions.

Yep, that's what "weak" means wrt acids and bases.

Where you have infact neutralised all the acetic acid present.

No, it will remain a solution of iron ions, acetate ions, sodium ions and chloride ions. The iron ions will slowly precipitate to iron hydroxide complexes as the final H+ ions are used up. No?

Yes, if what you had was ferric chloride. You don't. You have a neutral solution of the ions I just mentioned, surely.

[Sandy]

On Fri, 14 May 2004 06:02:58 -0500, Unknown posted:

Much like stable acetate complexes?

Just like in acetic acid solutions?

Where does this ever happen? Surely the rust dissolves in a solution of H+ with a non-precipitating anion?

Yep, the acidic solutioss speed up the atmospheric corrosion process.

Yep. Basic measures to stop atmospheric corrosion.

Which is why I personally would prefer mechanical derusting procedures in ethe medium of non-polar solvents that tend to prevent further corrosion.

Yep! Sad!

Isn't the correct chemistry always the most interesting? :)

[J. Clarke]

You keep asking this question over and over. First, if you have ions they are not "neutral". By definition an ion is electrically charged, hence it is reactive. The solution is neutral because for each cation there is a matching anion with the opposite charge, but the ions themselves are not neutral at all. Second, chlorine is one of the most reactive of all elements, hence any reaction involving chlorine will proceed at a higher rate than one involving acetate. The end result is that by putting some chlorine ions in the solution you end up with a faster reaction.

[Sandy]

On Sun, 16 May 2004 23:21:33 -0400, "J. Clarke" posted:

Perhaps because I've not seen a satisfactory answer yet, and the person who wrote that article quoted, has asked to state the query again?

Huh? Sodium chloride solution is neutral.

Got nothing to do with chemical neutrality, sorry.

I never said ions were neutral -- I was talking about the solution. The solution MUST be electrically neutral, but chemical neutrality has to do with balance between H+ and OH- in the solution.

There is NO elemental chorine involved, sorry.

See above. The chloride ion is arguably more stable than the acetate ion.

Sorry, your premises are wrong so your conclusion is not sound.

[Dan White]

I had a feeling you were the same person as the original post I pasted. Sandy had the original question and I was trying to help. The only thing I still don't understand is exactly what the "complex" is that drives the Fe203 to dissociate and reform this complex with Cl-. Is it some kind of hydrated Fe complexed with Cl-?

thanks, dwhite

[Sandy]

On Mon, 17 May 2004 04:44:41 GMT, "Dan White" posted:

Thanks Dan, that's my question exactly. I can't see the difference between a ferric chloride complex and a ferric acetate complex. The thing that drives the reaction in my understanding is 6H+ + Fe2O3 --> 2Fe+++ + 3H2O That formation of water is what moves the reaction to the right. For me, salt is just going to cause problems down the line when it sets up corrosion cells in the fine interstices of the previous rust pitting. Unless someone can show that it is invaluable in the derusting process with weak acids, I would advise to stay well away from it. As I said, I far prefer mechanical derusting with a non-polar solvent (kerosene or CRC) for anything valuable. YMMV

[Dan White]

Just 2 comments:

1. It may just be that my chemistry was so long ago, but I'm not sure of the usage of the term "complex" in this context. Are we calling an FeCl3 molecule a complex (I didn't think so)? My recollection is that a complex had more to do with Van der Walls forces attracting surrounding molecules such as the solvent to the ion or molecule in question, as if it were chelated or sequestered. What is the complex that results from the rust-chloride reaction?

1. You have to admit that the NaCl is greatly accelerating the reaction rate. Just do like I mentioned and sprinkle salt on a copper pan wetted with vinegar. You will see the fastest reaction where the salt is. It seems you are looking at this from the standpoint that salt does nothing, and are challenging someone to prove otherwise. I think we are both interested in the same thing, but maybe are looking at it from different standpoints.

regards, dwhite

[Sandy]

On Mon, 17 May 2004 05:29:09 GMT, "Dan White" posted:

I guess it might be some sort of hydrated "complex". Like most ionic species in aqueous solution. Our understanding of "complexes" seems to coincide, although that's possibly and artifact of the age of our chemistry learning (me ~ 45 years :)

That's the nub, I suspect, and why it is purportedly different from a similar acetate "complex".

I can't disagree with you here, (never having tried it), but have difficulty in explaining it to myself. I just hate salt!! It has screwed up masses of our ag land and costs society squillions in damage to just about everything. If it can be avoided, I will avoid it. I once had a car at the beach where the radiator fell apart on the outside (all the fins disappeared) while the inside was perfect.

Well no, but then copper is a different kettle of fish, being on the other side of hydrogen in the electrochemical reactivity series. Next time my wife asks me to get rid of some rust stains, and I have no CLR (another weak organic acid sold for the purpose of removing lime deposits and rust stains) I will try acetic acid with NaCl and without. Stop watch and clip board at the ready! :)

Or fairly similar standpoints. I see the downside of introducing salt to rusted metal, having lived near the beach for a long time.

[J. Clarke]

"The solution" is not what reacts with the rust. What reacts with the rust is individual ions within that solution.

So what is a chlorine ion floating around with its electrical charge exposed if not "elemental chlorine"? What comes in contact with the rust is not sodium and chlorine bound, it's individual sodium ions and individual chlorine ions.

I thought we were talking chemistry here, not physics. A monatomic ion is not "stable" or "unstable" chemically--that's a property of a compound.

No, your understanding of what constitutes an ion is so wrong that you can't follow the argument.

[Sandy]

On Mon, 17 May 2004 06:40:06 -0400, "J. Clarke" posted:

So? What ions are you claiming react with the rust (other than H+)? Can you give balanced equations for this?

A chlorine ion! Elemental chlorine with an extra electron! And electrons are what give chemical moieties their chemical properties.

Which apparently have no effect? The dissolution/neutralisation of Fe2O3 is by H+ ions, surely.

I am talking chemistry. What are you referring to?

A chloride ion is more stable (less likely to change its chemical state) than an acetate ion. A fluoride ion is even MORE stable! Elemental chlorine and fluorine are most UNSTABLE. Stability is, afterall, the ability to resist (chemical) change.

Ummm, OK. Could you explain then what constitutes and ion? There is no argument. What we need explaining is why the presence of sodium chloride in the vinegar is advantageous.

[Charlie Self]

Nah. What we need to know is whether or not it WORKS. I, like most woodwrkers, am not a chemist. Like most woodworkers, I have some tools that I either buy with rust on them, or that are particularly susceptible to rust under certain conditions.

Somewhere about 5 posts ago, an OT should have been added to this thread.

Charlie Self "Bore, n.: A person who talks when you wish him to listen." Ambrose Bierce, The Devil's Dictionary

[Unknown]

If the rust is present as Fe203 then the iron is trivalent and will go into the salt-acetic acid solution predominately as the FeCl6(-3) complex. Note that there is no change in oxidation state of the iron.

That iron complex is a central trivalent iron ion (with a +3 charge) which usually has a coordination number of six. That means there will be six positions around that iron ion that are occupied by some species. Since the concentration of chloride is so high relative to the other anions the predominate species will be FeCl6(-3). The net charge of the complex is -3 because each chloride carries a -1 charge and the iron has a +3 charge. There certainly will be some anions where an acetate ion and/or a hydroxyl ion will replace one or more of the chlorides. For this discussion the exact composition of that iron complex is not only unknown but is of no particular interest. Just remember that if too many of the chlorides in that complex are replaced by hydroxyls or acetates then the iron will precipitate as a hydrous oxide or basic acetate and that is why one uses such a high concentration of chloride.

It is the stability of that iron chloride complex and the whopping excess of chloride ions that drives this reaction. The high solubility of iron chlorides prevents the reaction from coming to a screeching halt due to precipitated of hydrous iron oxides and basic acetates. There is no oxidation or reduction reaction at this point.

That iron complex will oxidize iron metal. The simplified net reaction is

2Fe+3 + Fe(0) --> 3Fe+2

This reaction is one that you don't want to happen because that Fe(0) is the iron metal you presumably are trying to recover rust free. This also should suggest to you why you should keep oxygen (air) out of the solution.

Fe+2 is oxidized to Fe+3 by oxygen and the reaction takes place readily because of the stability of the iron(III)-chloride complex. If you allow air into the process you will be producing more Fe+3 which in turn reacts with the iron metal (see the above reaction). If you bubbled air through the solution this process will continue until you run out of iron metal or the process gets bogged down by precipitation. It is this reaction which will give you an etch line at the liquid surface. Why?...because that is where the oxygen is.

This process works well with Fe203, less well with Fe304.

Since the concern about using chloride has been mentioned I will address that issue as well. The chloride will be pretty well rinsed off of the surface. The freshly cleaned iron surface is quite reactive and needs some type of protection. If you keep iron dry it won't rust. WD-40 is not a good option as it will pick up water.

Chloride can remain in microscopic cracks where it can accelerate stress corrosion. If you are cleaning up an I-beam for a bridge this process might not be a good choice. If you are cleaning a wrench e.g. that is not an antique I wouldn't worry about stress corrosion. If I am cleaning some tool that the kids left out in the rain I probably will dunk it in a 5% solution of muriatic acid, rinse it and apply a light wax.

If you have a valuable antique get some advice from someone else as cleaning may not be appropriate.

Why not use vinegar without the chloride? Vinegar is ~5% acetic acid. Now for a little of the requested math. The dissociation constant of HAc (acetic acid) is ~10^-5. (Ten to the minus five) In simplified terms the H+ concentration in solution times the Ac-1 equals ten to the minus five. Since the H+ = Ac-1 the acetate and the hydrogen ion concentration in 5% acetic acid will equal the square root of 10^-5 or somewhere around .02 molar. If someone wants to be picky it actually calculates to be a tad more concentrated. That concentration of hydrogen ions won't keep trivalent iron in solution.

This thread has stirred up some interest. I will stick with it at least for a while. Let's see if this answers some of the questions or if I have everyone more confused.

[Sandy]

On 17 May 2004 12:06:40 GMT, [e-mail] (Charlie Self) posted:

Speak for yourself. If that satisfies you, then I'm happy for you :) Until you understand it, you won't know whether it works or not.

Are woodworkers prevented from being chemists? I'm not a chemist, but I have wide interests in many areas. I know several chemists who are woodworkers. Will you tell them, or should I?

If they were mine, and I valued them, I would not use salt and vinegar on them. This comes from my understanding of chemistry.

Why? Is it not pertinent to restoring woodworking tools? I suggest you are being selfish :)

[Sandy]

On Mon, 17 May 2004 07:10:31 -0500, Unknown posted:

So with excess acetic acid present, "hydrous oxides or basic acetates" will be precipitated? Surely they will be redissolved by the excess acetic acid as soluble acetates?

What is formed from the stable soluble ferric acetate that is taken out of the process? If all this chloride is "taken out of the scene" what happens to all those lonely sodium ions?

Surely excess acetic acid does the same thing?

Only when exposed to atmospheric oxygen, No?

Yep.

Magnetite is quite resistant to any attack. It usually just falls to the bottom as a black sludge IME.

WD-40 surely repels water. I suggest that heavily pitted iron which has had salt solution soaking into the pits will be quite difficult to rinse clean.

That's what I said. I thought you were contradicting this above.

Further corrosion? I would certainly not want that. Wrenches in my hands suffer extreme stress. I've broken several :)

Hooley Dooley, how long will that last? What's wrong with a quick squirt of CRC or WD 40 and a wipe with a rag?

And certainly don't use hydrochloric acid (shudder) or salt and vinegar. Save the latter for your fish and chips :)

So you're saying that acetic acid won't dissolve Fe2O3? It does for me. The label of my vinegar does not list sodium chloride.

I'm still struggling with your claim that ferric acetate in excess acetic acid is unstable. If you say that the sodium chloride keeps it in solution and stops it precipitaing out as ~ ferric hydroxide, then that is not my experience. I end up with a dirty yellow solution when I soak rust in vinegar. I have never used salt in the vinegar, but next time I have need to clean some rust, I will try with and without, to see if the claimed speed increase occurs, or you claim of precipitation of ferric hydroxide occurs and does not occur.

Museums soak very rusty items in sodium hydroxide solutions. I believe this just stops further corrosion until the rust can be removed by other means.

[Charlie Self]

Sandy responds:

Nonsense. What you're saying is that if you don't understand the mechanisms of flight, you don't know that there are aircraft overhead.

Nothing to tell them. I know chemists, electrical engineers, computer programmers and a host of other tech types. So what? Where did I say that chemists shouldn't be woodworkers, incidentally?

Well, I probably won't either, but that's because I have used electrolysis for years.

How is a thread on ionization and covalents and whatever else pertinent to restoring woodworking tools?

It won't matter to me, as I've just trashed this thread, but the fact is, none of you seems capable of snipping, and there is absolutely no way for an average woodworker to tell which of you guys is full of beans, so there's not much value here to the woodworker. It remains a choice that may or may not work. And that may or may not damage tools because of the presence of salt. Depends on which of you a person chooses to believe, because there has been no coherent and definitive explanation by anyone.

If that makes me selfish, so be it. If you think that's a new cutesy on my name, then you're about 400 years behind the times there.

Charlie Self "Bore, n.: A person who talks when you wish him to listen." Ambrose Bierce, The Devil's Dictionary

[alexy]

Disagree. One can observe a cause and effect repeatedly and draw valid conclusions without understanding the mechanism. Folks knew that dropping a stone on their foot would hurt long before Newton and an understanding of the nervous system (and do we yet fully understand the mechanism of gravity, or just have more sophisticated observations about it?) Charlie's point is valid; all we NEED to know is whether it works. I'm with you in fascination with understanding why it works, but that understanding is a want more than a need.

Reread the sentence you quoted.

Tell them what? That most woodworkers are not chemists? You tell them. I hate the "you idiot" stares I sometimes get when stating the obvious.

Why? What are the bad effects predicted by your understanding of chemistry, and do they prove out in practice?

Yes. I agree that it is not OT.

I suggest that he is stating his interest.

[Sandy]

On 17 May 2004 13:37:10 GMT, [e-mail] (Charlie Self) posted:

No, I'm saying that if you don't understand flight, you can't successfully pilot those aircraft.

Umm, the bit you snipped? Here it is again:

Now what point was that making?

So why are you apparently criticising my reasons for not recommending salt and vinegar? Sheesh, we've got one guy who cleans tools left in the rain by the kids with hydrochloric acid! And he claims to be a chemist!

Because it helps understand the chemistry of corrosion and how to stop it and remove it. If you don't want to understand it, then why do you read it? Do you not understand electrolysis? I do hope you understand it enough to know the dangers involved.

To you, perhaps, but there are some of us benefitting from the discussion. As I said previously, if you are not interested, why do you read it?

And you apparently don't want to find out. That's fine, but why did you join in, if that's the case?

Oh, salt damages them, but I might discover that the benefits outweigh the disadvantages. But then you are not interested apart from complaining that others are.

Not that you understand, apparently. But if you are not interested in learning...

Complaining about a discussion others are having that you are not interested in? Yes.

No, I realised the simiarity after I wrote it. I decided not to pander to your sensibilities by changing it.

[Sandy]

On Mon, 17 May 2004 13:39:46 GMT, alexy posted:

Disagree. If you don't understand the mechanism, or the rationale, you are very likely to c*ck it up when things don't go exactly as expected. Especially with complex procedures. That's why they teach theory in all trade courses.

And does it? Charlie will likely never be quite sure. Someone has to figure out how it works to be able to do it competently. Not much is likely to go wrong with your strange hobby of dropping rocks on your foot, I would have thought. Now chemical procedures...

Again I disagree. So many things can go wrong with things chemical. So many things waiting to bite you on the ass. DAMHIKT.

Yes, and what point is it trying to make? Charlie is not a chemist, so woodworkers don't need to know any chemistry? Well if that's how he feels, why is he whining about our discussion about derusting tools?

See above.

Yep. Salt will enter the fine pits and interstices of the corroded surface and perpetuate future corrosion. Very difficult to clean thoroughly. There was a guy once who ignored chemistry and shot-blasted his aluminium boat with copper shot. It lasted but a few weeks. Chemistry is VERY important!

So Charlie is being selfish in complaining about the discussion we are having?

Why? In a thread that he is complaining about being irrelevant? Sounds like "dog in the manger" to me.

[alexy]

LOL! Do you really think that the inorganic chemistry involved in the derusting process is more complex than the operation of the gravitational force and the organic chemistry and electrical processes involved in the sensing, transmittal, and interpretation of the pain signal?

Understanding theory does help immensely, when deviating from experience, but empirical evidence can be adequate for some instances, such as derusting some particular steel. Where I see theoretical knowledge of the mechanism helping is knowing how it might work on a different alloy, how different solutions might work if the known one is not available, predicting long-term effects if evidence is not available, etc.

I'd like to know.

No, I can quite competently grill a steak without understanding the physical and chemical changes taking place in the steak when it is heated. And a steak is, I would suggest, a far more complex object than a piece of rusted steel, and the processes involved are also more complex.

I'm sure you think they are more complex than the elemental forces of physics or biological systems. We might just have to agree to disagree on that!

Yep. Sometimes I overcook a steak, and wonder if a more thorough knowledge of the chemical changes going on in it might have kept me from getting a medium-well steak when I wanted it medium.

No. That he is not a chemist, and that most woodworkers are not chemists, and are probably more interested in whether it works than how it works. Do you disagree? Do you really think that most woodworkers ARE chemists?

That's good for part 1 of my question. And I believe I saw in another post that you were going to do an experiment to find out part 2? I'll be interested in hearing your results.

Absolutely! And this is an excellent example where theory is important to predicting the result of an untried process.