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Rust: Chemistry, Prevention, Removal, and Conversion

mhutchinson

Plastic
Joined
Jul 21, 2017
When firearms are browned or rust blued "carding" is part of the process. This removes the loose rust while leaving the patina, which is the desired goal. All a carding wheel amounts to is a fine gauge wire wheel that is not too aggressive if used with light pressure. I keep something along those lines mounted on a bench grinder and most of my "previously owned" tool acquisitions get to face the wheel along with a good oiling afterward. Some I brush more aggressively and then cold blue while others still have a brown patina that just gets oiled.

Small stuff can be gently brushed by hand using a suitably gentle wire brush.

On the note of abrasives...it seems to me that, in situations where you want to retain the patina or bluing on a piece, the best solution is a very fine wire brush or wheel. The best I've seen are the ones used by gunsmiths for rust bluing such as this:

GROBET FILE CO. OF AMERICA INC .25" STAINLESS STEEL BRUSHING WHEELS | Brownells

Another option is the synthetic abrasives like the 3M radial bristle brushes:

Scotch-Brite™ Radial Bristle Brush

I've used these for polishing before but never attempted rust removal with one. Anyone have any experience comparing the two? In my previous, simpleton thought process I figured the only variable with abrasives was coarseness-how big of a scratch it makes-but maybe it's more complicated than that...like everything else in the world...
 

CalG

Diamond
Joined
Dec 30, 2008
Location
Vt USA
I've had good lock reducing rust with an oxy acetylene flame.

I suppose it could cause concern for those items sensitive to heat distortion, such as thin sheet goods.

But massive objects are only heated at the surface. And such accounts for a significant percentage of my needs.

If the part is to be "beauty painted", Phosphoric acid is favored.
 

6PTsocket

Aluminum
Joined
Jun 29, 2014
Location
Jackson,NJ
Good morning folks,
Long-time lurker here, finally ran out of old threads to sift through. Over the months I've spent reading about these things I consistently find good information on this particular forum, so here I am, a young, curious, and enthusiastic-but also inexperienced and probably naive-cowpoke walking through the double-doors of the saloon taking a seat next to the big boys! I'm also sarcastic and not entirely serious about half the time...

Anyway, I'm an amateur woodworker and I enjoy restoring antique tools. I worked in an auto body and mechanical shop throughout high school so I got a rough, general knowledge of some metalworking techniques but nothing substantial. I also took 4 semesters of chemistry in college recently so I understand the basics but, again, nothing substantial.

Over the years I've restored dozens of tools and spent a ridiculous amount of time sanding, grinding, polishing, sandblasting, etc. Part of my quest in tool restoration is to figure out the most effective techniques for various things. The current Holy Grail of endeavors is dealing with that timeless issue that's plagued industry since its birth: rust.

Over the years of exploring methods for rust removal I've tried a number of acids and chemicals, every type of mechanical removal techniques I could find, and a few experiments in converting red rust to the more stable iron oxide. Overall I feel fairly effective in my ability to simply remove rust.

But here's where things get complicated! A lot of old tools have a convenient (sarcasm) combination of rust and patina. The patina is desirable so removing the red rust without losing it is the goal. The old standby is steel wool or some other mild abrasive, and this works well enough with mild rust, but it is tedious and becomes ineffective pretty quickly when dealing with anything other than the mildest surface rust. My current thoughts on how to deal with this:
1) weaken the red rust-though not the patina-enough to make mechanical removal easier
2) convert the red rust (Fe[SUB]2[/SUB]O[SUB]3[/SUB]) to a more stable form like Fe[SUB]3[/SUB]O[SUB]4[/SUB].
3) there are some rust removing chemicals (namely Evaporust) that claim to use "chelating" agents


So far, idea #1 is not working. I've tried mild acids like oxalic and acetic acid-both in fairly dilute solutions-but these are still strong enough to damage the patina. Two variables to play with here:

A) strength of the chemical--perhaps there is something that is just strong enough to damage/weaken red rust but not quite strong enough to eat through patina

B) exposure time--I noticed when using vinegar to remove rust that there is varying results as an item is left in the solution for more or less time. If I timed the ordeal well I could often get rid of all the red rust without the vinegar eating into black rust very much but if I left an object in long enough the vinegar would begin to eat through the black rust that is often underneath the red rust, and I'd end up with a heavily-pitted piece of steel.


Idea #2 is not working yet but I haven't had enough time. My first thought was just to card off as much red rust as possible and then just apply oil over the rest, hoping that the blocking out of oxygen will eventually convert the red rust to black iron oxide. But this might take a while...the other method I've heard about but haven't tried yet is boiling. Still have to read more about that before I'd feel comfortable trying it.

So, that's where I am with my experiments. I'd love to hear suggestions or advice from others who have engaged in this tedious battle over the years. I'm also always looking for good, science-based sources of information on the chemistry beneath all these ideas because without science it's all just old wives' tales. For example, I'm assuming that patina is black iron oxide-Fe[SUB]3[/SUB]O[SUB]4[/SUB]-but I have no way to confirm that. Knowing exactly what it is and what's going on chemically would be helpful.

Any chemists in the house?

Thanks,
Matt
I have not heard of intentntionally converting between ferric and ferrus oxide but the most popular conversion is using phosphoric acid to convert rust to a black coating of iron phosphate, which is less porous than rust so it offers some protection. It is the active ingredient in Naval Jelly and a lot of other products including Coke. It will etch good metal if left in too long. Evaporust just combines with rust and falls off. It will not attack sound iron/steel. It also is a very mild, water based product. Keep it. covered when using to prevent evaporation Other acids, like acetic ( vinegar) and oxalic acid, often used for wood bleach, also work but these weak acids leave no protective conversion coating. A home brew version of Evaporust is molasses diluted 10:1 with water. It works but takes forever. I am not a chemst but I had a little college chemistry and I read a lot. There is also electrolyisis that a lot of people have had succes with. There is a lot of info out there if you are intersted. It is a pretty simple process.

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6PTsocket

Aluminum
Joined
Jun 29, 2014
Location
Jackson,NJ
Franz[emoji767 said:
;3013888]There's an encyclopedia to be written on rust removal and conversion, and there already exists two full volumes of disinformation on the process mislabeled "Electrolysis".
"Electrolysis" is really electroplating, and the only electrolytic action in the tank is ofr minimal water as occurs in any plating tank. We'll need at east a book on the difference between salt water caused rust and nonsalt containing rust.
Going to need a chapter on accumulating electrodes too, and minimally a chapter from guys who are sure carbon (Graphite) electrodes offer no advantage because they read on some site someplace where a guy hooked an elevator contact to his welder at 200 amps and it didn't derust the 4x8 sheet of steel any faster than the lawnmower blade he used in the B tank. Better add a chapter for the guys who insist on using Sodium Hydroxide and another for the high current group too. Most of the high voltage advocates died off forgetting to disconnect the tank before they reached in, so a page will cover them.

All I know is I can run my tank 24/7 at 24 volts 10 amps with graphite electrodes and filtration maintaining a clean clear electrolyte, and watch the rust walk off the object I'm cleaning.
It's a good method as long as the person doing it makes good connections and keeps grease & dirt out of the tank. It's a 2 step process in the case of salt water rust, possibly 3 to remove the salt first to prevent electrolyte contamination.
It will not maintain patina though, although that can be restored by allowing flash rust and polishing.
The process will work down to 31°f, and can be helped to heat itself by increasing current.

Chelation- is another whole volume unto itself. I do NOT encourage the use of overpriced miracle slop in a bucket sold at Horrible Freight or other vendors.
The process is well known and understood, and has probably been around for 100 years. Go to the nearby feed store, buy yourself a bag of cow molasses, and mix it up in a plastic bucket you can and should set outside away from your living area. The bucket will stink, it will grow mold, and it will attract flys and other creatures. The process is slow, and stops working below about 50°f. It is a very forgiving process unless you forget what you left in the tank for a month.
Molasses doesn't care if the rust is salt containing.
Months of scientific screwing around have demonstrated no gain by adding DC current to this process.

Vinegar & Muriatic acids will eat rust. They will also eat iron.
Neither belongs in any derusting process unless it is a high speed industrial process under constant monitoring.

If you have something you really want to screw up, use vinegar. What you pull out might look clean, but most iron that was there is gone and you have a hunk of carbon.

Phosphoric acid is both a remover and a converter, depending on the acid concentration. 4 - 8% by volume will convert rust to either a black or white phosphate coating depending on steel composition. Add some Magnesium to the solution and you get a slightly different coating simulating Parkerizing.
The nice thing about Phosphoric is it does NOT attack good steel. The second nice thing is the Iron Phosphate layer is bonded to the steel, and provides an excellent layer for paint & coating adhesion, eliminating the need to prime.
You can even tent and vaporize Phosphoric to treat oddly shaped objects.
The key to success with Phosphoric acid is complete wetting. That generally requires time with rust contacting acid.
There is a product line called POR based on marine phosphoric polymeric coatings that has developed a following. It is only a TEMPORARY coating, as is specified in the literature for use in marine environments. POR spends a lot on advertising, and people spend too much on POR products.

Oxcalic Acid works too, slow soak tank, and not really damaging to good steel. Just remember to rinse well.

Tannic acid is a converter, not as good as Phosphoric, but if you have tea sitting around, with lemon, NOT milk, why not try it.

Media blasting including water, will remove some of the rust you can see. It will also peen shut little rust gardens waiting for water and oxygen to grow and spall coatings off.

Soda blasting is not a process for removing rust. Soda is for removing "soft" deposits like tar and grease.

If money is no object in your consideration, red laser at high power will blow rust off surfaces.
From what I hear on dililute molasses, it is VERY SLOW. Fine if you have a big job and a big tub. The "miracle slop" works pretty well. I have seen discussions about what is in there and where to gt the principal ingredient cheap ,but I have forgotten the details. While it is expensive, if you don't let it evaporate, it can be reused quite a few times ad I am satisfied with the results.

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JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
I have not heard of intentntionally converting between ferric and ferrus oxide but the most popular conversion is using phosphoric acid to convert rust to a black coating of iron phosphate, which is less porous than rust so it offers some protection. It is the active ingredient in Naval Jelly and a lot of other products including Coke. It will etch good metal if left in too long. Evaporust just combines with rust and falls off. It will not attack sound iron/steel. It also is a very mild, water based product. Keep it. covered when using to prevent evaporation Other acids, like acetic ( vinegar) and oxalic acid, often used for wood bleach, also work but these weak acids leave no protective conversion coating. A home brew version of Evaporust is molasses diluted 10:1 with water. It works but takes forever. I am not a chemst but I had a little college chemistry and I read a lot. There is also electrolyisis that a lot of people have had succes with. There is a lot of info out there if you are intersted. It is a pretty simple process.

Sent from my SM-G900V using Tapatalk



In my experience, phosphoric does not just turn the rust to iron phosphate. It actually removes it. A very minor amount of brushing removes whatever coating may exist.

If you leave the item in longer than needed to remove rust, you may get a dark gray phosphate coating on the part.
 

georgesbasement

Aluminum
Joined
Dec 9, 2004
Location
southeast Pennsylvania
There's another aspect to this business of getting rust out of the way:

That is when the rust causes a couple of pieces of steel to get stuck. My best experience is the disassembly of the adjustable-track front axle of a FarmalL A tractor that had lain neglected in a field for many years. The two nested steel tubes had a layer of red rust trapped between them, and no amount of mechanical persuasion would break the standoff until it dawned on me that red rust contains water of hydration: Fe2O3*H2O. That's why it expands so destructively. Therefore, driving off that water should reduce the volume of the trapped red rust.

Therefore, I heated the assembled tubes with a propane torch until I saw volumes of wispy vapor emanating from between the tubes. All the while I was applying force with an hydraulically operated Rube Goldberg affair with a two:one mechanical advantage so that the 5 ton jack could generate about 20,000 pounds axial force. Eventually, even before the remaining paint on the tubes started to blacken, it started to move, and I got 'em apart. The water vapor condensed visibly in my rather dark, humid basement, proving my theoretical analysis of the situation. Don't try this in the bright sun, as you'll miss the wispy vapor. This also works for rusted-in brake lines, which I learned from an auto mechanic, and stuck bolts. When loosening brake lines this way, have a fire extinguisher handy nearby.

Before I re-assembled everything, I painted it all with a primer containing powdered zinc. Haven't had to adjust the track since then, however. Now, about 35 years later, it awaits a new head gasket & exhaust manifold.

George Langford
georgesbasement
 

lo7us

Plastic
Joined
Oct 11, 2014
Evapo-rust worked for me

I just used Evapo-Rust and 20 hours later it took off 60 years of rust on my Hossfield #2 bender and dies
 








 
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