Tannic acid is a specific form of tannin, a type of polyphenol. Its weak acidity (pKa around 6) is due to the numerous phenol groups in the structure.So I could not even tell if they had done ANYTHING!! But the receipt said they did and the price was hefty (twice as much as the weld repair!!). So I went back to my phosphoric acid treatment - you can see why it's so much better than the tannic acid treatment!!
So pH is logarithmic meaning each point is actually 1 time less in power (inverse exponential growth as doubling in strength). So tannic acid is 6 times LESS powerful than phosphoric acid. The sales manager said it was about the same stuff as phosphoric acid. haha. NOT NEARLY the same! No wonder they would not even talk to me in person - just said, "ready" and "Ok."Orthophosphoric pH is 1.5
So I was buying SEM Rust Mort which is very pricey at at quart. So I just ordered a gallon for the same price - meaning 4 times less.
Evaporust is mostly Citric Acid not Phosphoric Acid.Citric Acid is 2.2 pH
Put rusted iron into a citric acid solution - it bubbles until the acid is depleted, and if you leave it in too long, you'll eat into the good iron until the acid is consumed....Place rusted iron in Evaporust - no bubbles, you can leave iron in the solution for weeks and nothing will happen to the base material, and when the rust is removed, the remaining active ingredient is unaffected. Ph - effectively neutral - varies from very slightly acidic to very slightly basic as the active ingredients are consumed.
When I've left items in citric or phosphoric for extended periods (memory lapse) both of them ate at the steel, but the Evaporust doesn't.https://www.practicalmachinist.com/vb/general/phosphoric-acid-rust-removal-210082/index2.html?s=a281a58f4001ea5e0f7ce51e58858b40
Evaporust is a combination of a chelator and iron sequestration chemical. The chelator is based on EDTA (ethylene diamine tetraacetic acid), the sequestration agent is a sulfo-pyridinium compound.
Maybe that is the acetic acid [vinegar] link. Anyway, the safety/biodegradibility issues led me to a similar but more degradable chelating agent, EDDS. Maybe that's one magic ingredient in evaporust.
The advantage to chelation vs. acid is that you cannot etch iron this way, and it allows for very little "flash rust" problem. It is also much faster. There is really nothing dangerous here, it is just that pure sodium hydroxide is extremely basic, and will burn you just as fast as a strong acid.
I don't know anything about alternative medicine, but I have heard medical experts describe human aging as a sort of "rusting" or oxidation that occurs to the body. That's why antioxidants are all the rage. I suppose it's inevitable somebody takes it a step farther and sells a chelation agent as a powerful antioxidant...EvapORust for your body...
Oh look! "Chelation Therapy"!!!
Mebbe I'll be washing down my gopher with EOR!! (Not!)
So two time LESS powerful than phosphoric acid. Someone is contesting that Evaporust is citric acid - since it's proprietary - but it could be tannic acid. Phenolic Resin is also tannic acid - so the Eastwood spray is probably tannic acid.
So this is four times less costly then then automotive product.1 Gallon 85% Food Grade Phosphoric Acid Rust Remover Clean Etch Metal
Converts iron oxide to iron phosphate and works well!
I bought it to use on my rusted 1988 Olds. It worked perfect. Now to get it painted.So the other auto rust Prep converts sold - in several brands - are only about 40% concentration - not like SEM Rust Mort at 85% concentration - same as this food grade phosphoric acid.
The concrete cleaner phosphoric acid is more like 40% concentration also - and has other chemicals added.
I stay away from so-called muriatic acid. It's nothing more nor less than hydrochloric acid and, although it's widely used in industry to pickle metal, if you leave it unattended too long, it will eat your metal. Unlke phosphoric acid, which is not too terribly bad if you happen to get incidental contact on your skin, muriatic acid will cause real problems much more quickly.
Hydrochloric acid is a much stronger acid than phosphoric acid. This means that in solution, virtually all the hydrochloric acid molecules will have donated a hydrogen ion to a water [oxygen] molecule, while in a phosphoric acid solution, only a fraction of the phosphoric acid molecules have given up their hydrogen ions.
Phosphoric acid has the molecular formula H3PO4. If it loses all three protons -- as would happen in an alkaline solution -- the remaining ion is the phosphate ion, PO4 with a -3 charge.So people say you don't need it at 85% full concentration but they are SOAKING metal whereas Australia sells a gel - since the spray otherwise runs off and only works on surface rust. The gel is to stay on longer. So spraying a stronger concentration will counteract not staying on as long.
Loss Of Electrons = oxidation, Gain Of Electrons = reduction. Rusting, oxidation, is thus a loss of electrons from the iron.
"When applied to rusted surfaces, Ospho [40% phosphoric acid] causes iron oxide (rust) to chemically change to iron phosphate - an inert, hard substance that turns the metal black. Where rust is exceedingly heavy, two coats of Ospho may be necessary to thoroughly penetrate and blacken the surface to be painted. A dry, powdery grayish-white surface usually develops. Brush off any loose powder before painting."Phosphate Etching as Parkerizing vid
the paint will then Impregnate the metal....
Parkerizing Steel vid turns it black as corrosion resistance
The most important difference between muriatic acid (Hydrochloric acid) and phosphoric acid is that the muriatic will continue to attack the voids and holes in the iron even after someone believes they've completely neutralized it due to the properties of the acid versus phosphoric acid will not readily react with bare iron under normal conditions.https://www.garagejournal.com/forum/showthread.php?s=44c63396d51f850357683144c83c6e11&t=69793&page=2
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