Alodine or No Alodine

Discussion in 'Maintenance Bay' started by Huckster79, Apr 15, 2019 at 12:07 PM.

  1. Huckster79

    Huckster79 Line Up and Wait

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    So in getting ready to do some touchups from dings, a few filiform corrosion spots, etc. I am getting some conflicting info on the need for Alodine. I had it as part of my plan of remove paint (for the filiform spots) chemically, clean up with alumiprep and rinse, then alodine 1201 with a brush the now cleaned bare spots, rinse and then a self etching primer from Duplicolor and a top coat of of Duplicolor color match via rattle can, dauber and duplicolor pen depending on the spot. Duplicolor makes my plane's white as it was on old GM white...

    The conflicting info I have is, to for sure use alodine vs use alumiprep and within same day use the self etch primer and roll. That school of thought tells me alodine doesn't really do much if you are covering it right away but would be useful if there is time between prepping and priming.

    What say you? I have no problem buying the $40 quart of Alodine, but if its not adding value to the process if I take a section and work it start to finish in one morning then I don't want to spend the time and money doing it. If it is of benefit even if the surface is covered right away I won't think twice about doing it...
     
  2. sarangan

    sarangan Pre-takeoff checklist

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    Alumiprep is basically phosphoric acid with a surfactant, and it etches the aluminum oxide. Alodine creates a corrision-resistant chromium compound with the aluminum base. Perhaps the "same day" is with reference to how long you can wait between alumiprep and alodine, because a clean aluminum will quickly oxidize in air. My recollection is that alodine does not need a top coat, but it does provide a good base for a top coat to be applied (without needing a primer).
     
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  3. Tom-D

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    Correction,, Alodine creates an artificial hydroxide coating
    Aluma-prep is an etch, so is alidine, Alodine is Chromic acid,
    When the surface has already been etched, it does not need a self etching primer.
     
  4. Huckster79

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    So I can use the self etch primer I bought for something else it sounds like no matter what. Sounds like self etch primer would be for a quick and dirty touch up of a chip if ones not going to go through all the steps.

    So my questions remains then: If I Alumiprep it and once rinsed and dried, prime it right away, the same day, does the alodine offer a benefit? Or does it only offer a benefit if I am not going to prime right away, such as etching it one day and priming it a week later?
     
  5. Tom-D

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    Clean with Aluma-prep, until all corrosion products are gone, rinse, allow to dry. then apply alodine 1201 until you get a golden hue rinse and allow to dry, then paint.
     
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  6. Huckster79

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    So in essence the Alodine is my "primer", put the top coat right on the alodine 1201?
     
  7. Tom-D

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    Yes it will form an artificial Hydroxide coating to protect the aluminum.
     
  8. Tom-D

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    After the alodine has been rinsed and dried, prime it, then top coat.
     
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  9. Huckster79

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    Thanks for all your help, I know I've asked a lot of questions on this, but I figure with all the hassle it is to do it right, I want to make sure I do it right... I would prefer this is the last touch up job (Besides incidental chips) I give her until the budget allows for a full paint- which may be some time...
     
  10. Tom-D

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    Remember never use a red iron oxide primer on aluminum.

    IF/WHEN you do that you set up a galvanic cell.
     
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  11. Cap'n Jack

    Cap'n Jack Final Approach

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    Posting beyond your knowledge again? That's NOT how it works. Aluminum hydroxide is a rather weak, non-protective compound.
    You'll get a protective oxide coating with chromic oxide:
    2Al+2Na2CrO4→Al2O3+2Na2O+Cr2O3

    Since alodine is acidic, there's no way you'll form aluminum hydroxide with that stuff.

    For further reading:
    http://www.kaehr.com/chromate-conversion-coatings.cfm
    https://www.sciencedirect.com/topics/engineering/chromate-conversion-coating
    https://materialsdata.nist.gov/bitstream/handle/11115/198/Chromate Conversion Coatings.pdf?sequence=3
     
    Last edited: Apr 15, 2019 at 6:40 PM
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  12. Kenny Phillips

    Kenny Phillips Pattern Altitude

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    Slow-acting thermite.
     
  13. Cap'n Jack

    Cap'n Jack Final Approach

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    After it gets wet.
     
  14. weirdjim

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    So what is the value of using Alodine versus a thorough cleaning and perhaps etching with Alumiprep (or other weak acid) and then a thin layer of zinc chromate from a rattle can?

    As I vaguely recall from Chem 101 some 60 years ago, the raw aluminum surface grows the oxide layer in a matter of fractions of a second. DId I sleep through that lecture?

    And yes, I was interested in the redox equation from taking acidic Alodine and coming out with a basic hydroxide. Ain't gonna happen.

    Jim
     
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  15. Tom-D

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    Without chromic acid, you get no hydroxide coating.
     
  16. Cap'n Jack

    Cap'n Jack Final Approach

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    You don't get a hydroxide coating WITH an acid, chromic or otherwise.
    Aluminum hydroxide forms under BASIC conditions.
     
  17. bluerooster

    bluerooster Pattern Altitude

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    I quit using Alodine years ago. For a small spot I found that it's not worth the effort. And for large areas, it's a pain to use. I also quit using acid etch as well. I now use EAP-12, spray, or wipe it on, let it dry, and prime, or paint.
     
  18. Tom-D

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    From AC 43-13
    (1) Chemical pretreatment such as the following chromic acid solution (Conversion coat conforming to Spec. MIL-M-3171, type VI) provides a passive surface layer with an inhibitive characteristic that resists corro sive attack and also provides a bond for subse quent coatings. Properly-applied magnesium pretreatment tend to neutralize corrosion me dia in contact with the surface.
    Call it what you please, but that is what it does.
    I've always been taught it was an "Artificial hydroxide coating"
    all the navy training manuals call it that.

    bottom line, no alodine no coating.
     
  19. Cap'n Jack

    Cap'n Jack Final Approach

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    That passive surface layer that you highlighted from AC43-13 is a mixture of aluminum oxide and chromium oxide. NO hydroxide. You get aluminum hydroxide under basic conditions, not acidic conditions. Aluminum hydroxide doesn't protect aluminum.

    BTW- Alodine 5700 has no chromium, it forms a zirconium complex.
     
  20. Tom-D

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    Spec. MIL-M-3171, type VI)
    MIL-M-3171, type VI) is for Mag.. it is not alodine.​
     
  21. Tom-D

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  22. Tom-D

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  23. Cap'n Jack

    Cap'n Jack Final Approach

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    Your first reference is from a web board, such as this one, so it really isn't credible.

    The second reference contradicts itself. It correctly states that:
    But then, incorrectly, states :
    The reason I say they contradict themselves is due to this information:
    upload_2019-4-16_7-51-15.png

    Note the "Alodine" products with NO chromium at all. Alodine is simply a name trademarked to Henkel. It is best to specify the full product name, with the number or the MIL spec number to make sure the correct product is being used.

    You were taught wrongly, you don't remember correctly, or you are making something up. Your references don't mention "hydroxide" at all. That's because aluminum hydroxide doesn't form in acid.
    I understand your confusion, since you believe ammonium hydroxide is an acid, although it is a base. (https://www.pilotsofamerica.com/community/threads/paint-stripping.101772/)
     
  24. Tom-D

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    I will give you this.
    The Bondrite 1201 that I have now is not the Chromate solution we once called Alodine.
    I've probably made more chromate solution than you've ever seen. we hung bull Durham sacks full of chromate crystal in the bilge of the P-5-M, and I still have a 5 pound can of it.

    EPA has changed a lot of things we did in the past.
    So you can take your new era thinking, and be the expert you think you are.
    Because it makes no difference to me.
     
  25. Cap'n Jack

    Cap'n Jack Final Approach

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    This site seems to claim Bonderite 1201 = Alodine 1201 :https://www.aircraftspruce.com/catalog/cspages/alodine1201.php

    If things have truly changed from the way you did them in the past, you should be giving advice on how things are done now.

    Nothing about new era thinking (whatever you mean by that) changed chemistry behind the chromate conversion, it never made a "hydroxide coating", in the past or now.

    BTW, with a graduate degree in chemistry, I actually am an expert, at least in this field. You do yourself no favors posting beyond your knowledge. Like a news outlet that supplies a mixture of real and fake news, it gets difficult to know whether you actually know what you are taking about, or just making it up.

    To the OP- research the products, and follow the instructions that come with the option that you choose. That is the way to get the most correct, up-to-date information.
     
    Last edited: Apr 16, 2019 at 11:46 AM
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  26. Bell206

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  27. Bell206

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    I thought a chromate solution was used to pickle magnesium alloy?
     
  28. Tom-D

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    There are solutions to do that. it is not the same as used for aluminum.
    The product most used for Mag is Dow-19
     
  29. Tom-D

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  30. Cap'n Jack

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  31. Cap'n Jack

    Cap'n Jack Final Approach

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  32. Rob58

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    Question for the esteemed experts on this thread... if I treat an aluminum surface with an Alodine 1201 (Bonderite) coating, can I do without painting and expect some decent corrosion protection for several years?
     
  33. Tom-D

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    No
     
  34. Cap'n Jack

    Cap'n Jack Final Approach

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    For items exposed outside, no because it does weather away. The chromate conversion can make a fine base for paint.
    See: http://www.kaehr.com/chromate-conversion-coatings.cfm
     
  35. JAWS

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  36. 1RTK1

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    What is so bad about using a self etching primer and then painting? I’ve seen it done many times over the years with good results. What am I missing?
     
  37. Tom-D

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  38. Tom-D

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    Probably nothing. but it will not remove corrosion products, or clean the surface prior to paining
     
  39. 1RTK1

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  40. Huckster79

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    Thank you! I think I will go with these guys as I bet those small amounts will be plenty for touch ups I would think as I’m assuming the stuff goes a long way, especially when doing chips and small flaked spots. I have one larger area I’m going to do if the touch ups elsewhere blend in nice color wise which I believe they will. Someone, not me, left a seatbelt dangling out pilot door so I think best touch up there is to just paint the whole section... or it would be a panel with 400 dabbed spots...

    Any concern with alumiprep or alodine on surrounding paint? As in if I clean a dime sized spot to bare aluminum is it okay to apply the alumiprep and alodine to a nickel sized area then prime and paint a quarter sized area?