Chemistry question

[intrepidity]

This is regarding the product "Evaporust", which is an aqueous rust-chelating solution.

No doubt the formula is proprietary, so we'll have to rely on educated guessing.

So here's my question: if I leave an iron-based metal in the solution indefinitely, will it eventually rust, presumably when the chelator is exhausted? And will the metal continue oxidizing the whole time, just not visibly evident? Is it comparable, in terms of corrosive effect, to just leaving the item in water?

From a practical standpoint, what I'm wondering is whether leaving rust-prone items (tools, etc) in Evaporust is a viable storage method, so tools are always rust-free.

Or will the metal eventually just disappear? It'd be interesting if the product were somehow self-renewing, but who'd bring such a thing to market?

Btw, I highly recommend this product I'm cleaning up all the rusty items in my household, and is it satisfying!

On a related note, is there a known way to easily remove water from WD40? This whole issue came up because after de-rusting items, I would place them in a container and spray with WD40, saving the runoff--then dumped a bunch of small items into that pool and left them there, thinking they'd be safe. But they started rusting again after a couple days. I figured it was from the accumulated water.

[Otto_Harper]

1. The one thing you should know about WD-40

is that it was originally developed to spray down rockets to displace and remove water, to insure against the thing having to haul ice aloft as it struggled to get off the pad.

That's where the WD in its name comes from. "Water Displacer - formula #40". It was specifically designed to grab water and drag it off of metallic surfaces, leaving the metallic surface with a thin lubricating coat, which is designed to shed water.

The fact that the product can be used in a zillion ways in homes, shops and industry is a fortuitous happenstance.

So, the fact that used WD-40 contains a lot of entrained water is not only not a surprise, it is anticipated.

[intrepidity]

2. Yep

I use it to remove the excess water from the tools, so I expected it. I just hate wasting the runoff.

[eppur_se_muova]

3. Iron actually reacts very slowly with water -- it is the oxygen in the air which does the work.

Water accelerates the process, by complexing reversibly with the iron atoms. So, a water solution of a chelating agent, exposed to air, would likely help accelerate rusting in the same way. I'm pretty sure the instructions say to wash and wipe it off thoroughly when you're done, and for good reason.

Coating steel tools with oil is the traditional way to prevent rust. Good mineral oil will do the job, though some vegetable oils are traditionally used. Camellia oil, for example, has long been used in Japan, but apparently mineral oil is better. One thing to try is to add a few percent of clove oil, or more economically, witch hazel oil*, to the mineral oil to inhibit bacterial growth which can accelerate rusting, though only woodworkers usually go this far, to protect their very expensive and very sharp tools.

You can even use spray vegetable oil: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16760


* NOT witch hazel extract, which contains water and alcohol ! I have a huge bottle of witch hazel oil which I bought for under $3 at the drugstore years back. It works as well as the much more expensive clove oil (which is favored by dentists, because it comes into contact with sensitive tissues, without any harm).

[intrepidity]

4. Nice, thanks for all that good info!

The instructions *do* say to rinse after; however, I have tried some without rinsing, and seems to be ok, was debating whether I actually needed to rinse.

If the chelation is reversible, what do you imagine the reverse reaction might be? This stuff is expensive, so I'm trying to stretch it as far as possible--like filtering out the rust after use. Any other suggestions?

Thanks for the input!

[eppur_se_muova]

6. Strong chelating agents are chosen precisely because the complexation is strong ...

... therefore, difficult to reverse. I've checked out the prices myself, and while the stuff is expensive, there's probably not a simple (and safe) way to regenerate it that's cheaper than just buying more.

[Javaman]

7. yup, that's what we did in my dads garage. all our tools were coated in oil.

one of my least favorite jobs was taking a rag with a bit of oil on it and wiping down ALL the tools. so many tools...

[NNadir]

5. I'd guess the rust remover product is a solution of citric acid.

Citric acid complexes iron quite well. There are probably some other components as well, perhaps buffering agents.

To some extent oxide coatings passivate metals, and the exposed metal, once cleaned will be as subject to oxidation (rusting) as before, perhaps at a slightly faster rate than when coated with rust.

The passivation effects differ with different metals. The existence of aluminum metal is only possible because of this passivation by alumina, Al2O3, which is a kind of "rust" but is impermeable to oxygen and water at a neutral pH. In iron, the oxide coating is weakly bound to the metal surface, allowing the entry of oxygen (or electrolytes) to interact with the metal

Corrosive salts can demonstrate the same effect on iron as does citric acid, since iron forms stable chloride complexes, but it also acts as an electrolyte, causing a kind of electrochemical cell to form between oxygen in the air and the iron surface. (Oxygen reduction by an electrolyte as a kind of holy grail in battery engineering to make metal/air batteries; the effect is not rapid enough in the chloride catalyzed rusting case to generate an appreciable current however: The kinetics are way too slow. The rate limiting step is the 4 electron transfer required to generate oxide from O2 gas.) At slightly acidic pH's as may arise from the uptake of carbon dioxide, chloride solutions can behave like weak hydrochloric acid, which readily attacks iron.

I hope this helps.