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Alodine question

Stockmanreef

Well Known Member
Do I have to use the Alumiprep-33 on a part prior to Alodining the part? Or can I just scottbrite, soap, water, acetone rinse?

Alodine is bad enough, but the Alumiprep actually sort of scares me. There is HF in the stuff. And low concentrations, which is worse than higher concentrations. HF absorbs through the skin and eats your bones. Low concentrations can't be felt on the skin.

Thanks
ken
 
There is HF in the stuff.
Nah, it's Phosphoric acid. You really want to use it to get a chemically clean surface. Just be sure to flush off The Alumi-Prep with copious amounts of water. On the Space Shuttle, we tested for residual acid with litmus paper before applying the Alodyne.
 
I think there is also a detergent in Alumiprep 33. This is the stuff Henkel recommends for preparation of Alodine, and I don't think the chemicals in either one are worse than the other. Use the recommended protective equipment: goggles, proper rubber gloves and boots, respirator and protective clothing (I used a vinyl rain jacket and pants). Use good drinking water as a rinse.

Why compromise the preparation?
 
Alodine can't do its job without the alumiprep (hint: 'prep') first. My understanding is that alodine is a 'conversion coating', which is effectively another term for a special kind of 'corrosion' that then protects the aluminum from further corrosion. It 'converts' a microscopic surface layer of un-oxidized aluminum to something that protects from further corrosion. It won't work on the corrosion that already exists on any aluminum that's been exposed to the atmosphere for more than a few hours, hence the need for alumiprep. The alumiprep etches away the existing corrosion, allowing the alodine to do its work. BTW, the alumiprep can't do *its* work if there's dirt/oil on the surface.

Again, just my understanding; I could be wrong.

Charlie

edit: Phosphoric acid is phosphoric acid, but that doesn't address concentration. If you can match the recommended concentration of diluted alumiprep, then you're good to go. But be aware that even undiluted alumiprep will eat right through concrete. Ask me how I know.
 
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Please just dispose of the used Alodine at a household hazardous waste site. Don't dump it down the drain or pour it on the ground. It contains hexavalent chromium, which is right up there with dioxin and plutonium in terms of toxicity and it permiates right into ground water or right into rivers and bays with discharge from water treatment plants.
 
Surface prep

Actually, my $.02, you can use other methods. I tried several. My standard for paint work is a good scrub with scotch rite and Bon Ami cleanser. I compared this method to Alumiprep and saw no noticeable difference in the conversion with the Alodine. That said, I actually used the Alumiprep as I was working through the Winter inside and the scrub method was impossible on the assembled fuse and wings in the garage.
As others have said, treat all chemicals as if they are all dangerous. Gloves, respirator, etc.
Dispose of chemicals and wash water properly. I scavenged all byproducts using a hole made sluice into a large storage bin. It went into a storage building till most of the water had evaporated then the rest poured into a stable container and taken to a haz mat disposal facility. Look at my blog for a tip on the sluice.
 
Actually, my $.02, you can use other methods. I tried several. My standard for paint work is a good scrub with scotch rite and Bon Ami cleanser. I compared this method to Alumiprep and saw no noticeable difference in the conversion with the Alodine. That said, I actually used the Alumiprep as I was working through the Winter inside and the scrub method was impossible on the assembled fuse and wings in the garage.
As others have said, treat all chemicals as if they are all dangerous. Gloves, respirator, etc.
Dispose of chemicals and wash water properly. I scavenged all byproducts using a hole made sluice into a large storage bin. It went into a storage building till most of the water had evaporated then the rest poured into a stable container and taken to a haz mat disposal facility. Look at my blog for a tip on the sluice.

Bravo! I hope everyone follows your lead.
Good idea to let the water evaporate and create a concentrated, smaller volume. No point paying the hazmat folks to dispose of water.
 
so can I just use phosphoric acid?

Yes (or sulphuric or hydrochloric for that matter) but you also want to lift any grease so the acid will get to the oxide. Alumiprep contains a mix of solvents and detergents that helps with that. Or you can just use this stuff at half the price of Alumiprep, similar mix. Also good for etching your patio before paint. :p
 
Thanks for the replies. Plutonium is a dead-right-now acute poison. Albeit not as toxic as Polonium. Hexavalent chromium is a dead-in-the-future sort of thing. Phosphoric acid is not a big deal--it is just that there is HF in Alumiprep-33. And if you want to scare yourself, then look up what HF will do to you if you get it on you. You should alway have calcium gluconate cream around when using anything with HF.

My biggest concern is getting rid of the waste and generating it in the first place. I am also getting tired of working with nasty stuff when I don't have to. I might start working with stuff at work that will cause blindness or kill you quickly if inhaled. Oh the joys of being a chemist.

I do like the Prep and Etch stuff. Only phosphoric acid.

What I want to do small parts--gear brackets and I thought that alodining the parts would be better than paint. I assume that most of the paint would scrape off when putting things together.

Maybe I will just find a place to anodize the parts.
 
Be aware that anodizing reduces aluminum's fatigue life by a huge amount. Van's allowed for that with the wing spars, but you're rolling the dice with anything else structural.
 
Good to hear others have successfully evaporated the water from old alodine. I have several containers slowly doing that now.

On the prep - I tried the easiest on several samples. Even the alumiprep will not remove oils, I used isopropyl or denatured if handy, lastly acetone (due to smell) to degrease, then dipped in alum prep for 3 min then alodine for 4-7 min depending on the age and resulting color. Rinsed with distilled water after each dip.

Like Wirejock, I tried the hand mechanical method and it produced just as nice a finish and color/time as the alumiprep. I chose ap just due to the faster speed of processing.
 
Like Wirejock, I tried the hand mechanical method and it produced just as nice a finish and color/time as the alumiprep. I chose ap just due to the faster speed of processing.

Or you could slap one of these onto your buffer/polisher, spray the surface with simple green (has phosphoric acid) and let 'er rip. Much faster than alumiprep or elbow grease.
 
Yes. See the award winning Safari helicopter accident report for a real-world example. The issue is a reduction in fatigue life due to micro crack initiation at the hardened surface...I think.
 
I am reading two seperate discussions going in one tread.

1. Alodine
2. Embrittlement caused by Anodizing.

The OP was only referring only to surface prep for ALODiNE and nothing for ANODIZING.

Let's point out this conflict and not make readers confused. Alodine is a very good corrosion protection without any structural side effects.

New builders or future builders who doesn't know the difference may easily be misinformed.
 
See post #10; the op raised the idea as an alternative to alodine.

Ken,

I'm far from qualified to give you a technical explanation, so I didn't try. But I am aware of the risk, so just wanted to make you aware. IIRC, there was an article published by Van's years ago that gave a layman's description. Apparently an engineer can estimate the number of cycles to fatigue failure in un-anodized aluminum (all aluminum has a fatigue life), and also estimate the reduction in cycles due to anodizing. Again, IIRC, the article said that the estimated cycles to failure of the anodized spar was high enough that there was little chance of reaching that number in a typical RV's lifetime. My point was that we don't know the fatigue life of other structural components if they get anodized.

Hopefully, a qualified structures guy will jump in with a better explanation.
 
I sure missed that last sentence he wrote on post #10. :)

On the other hand alodining those small parts may not protect them for corrosion either if those surfaces are subject to wear. It will actually provide less protection than a well applied good quality scratch proof primer. Alodine is not scratch proof and it is very thin.
 
Ken,

I'm far from qualified to give you a technical explanation, so I didn't try. But I am aware of the risk, so just wanted to make you aware. IIRC, there was an article published by Van's years ago that gave a layman's description. Apparently an engineer can estimate the number of cycles to fatigue failure in un-anodized aluminum (all aluminum has a fatigue life), and also estimate the reduction in cycles due to anodizing. Again, IIRC, the article said that the estimated cycles to failure of the anodized spar was high enough that there was little chance of reaching that number in a typical RV's lifetime. My point was that we don't know the fatigue life of other structural components if they get anodized.

Hopefully, a qualified structures guy will jump in with a better explanation.

Good point!
 
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