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  1. #16
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    Hi Bob,

    Your findings are pretty much as I expected. Particularly using Oxalic acid !
    A lot of military equipment using steel in their construction, treated it with oxalic acid for rust prevention. In particular equipment that was being shipped out to North Africa. Places where rapid temperature extremes could cause condensation. They also used gell bags all over the place as well. I used to collect those at one time and dry them out, at least until the mice got to them.
    Best Regards:
    Baron J.

  2. #17
    BobL is offline Member: Blue and white apron brigade
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    Thanks BJ. I have had Oxalic in my shed for years for use a timber cleaner but didn't know about it being used as a rust remover.
    Anyway here are the pieces after 6 days.
    The only obvious difference to yesterday is the piece exposed to the citric acid (Ci) is now clearly developing more rust.
    6days.jpg

  3. #18
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    I have a ready source of Oxalic acid in my garden in the form of Sour Sobs (oxalis) maybe I can combine weeding and de-rusting?

  4. #19
    BobL is offline Member: Blue and white apron brigade
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    Now for some rust removal experiments using the same acids tested above (4% HCL, 4% Vinegar, 4% Oxalic and 4% citric).

    I put some (different) pieces of MS outside under the garden retic (runs for 15 mins twice a week) and they have been there for ~4weeks
    Prior to exposure and rusting all pieces were bought back to bare metal using an 80 grit belt.

    Allrusted.jpg

    Then I dunked them in the same 4 acids and removed a pulled them out and photographed them after certain amounts of time.
    The metals/acids are the same order for all photos. HCl, Acetic, Oxalic and Citric

    The times are those shown on the stop watch in each photo.

    5mins.jpg
    5 Mins; L to R; HCl, Acetic, Oxalic and Citric - most of the rust gone on the Oxalic, HCL and Acetic about the same.


    10mins.jpg
    10 Mins; L to R; HCl, Acetic, Oxalic and Citric. not that different than after 5 mins. HCl starting to clear.

    15mins.jpg
    15 Mins; L to R; HCl, Acetic, Oxalic and Citric. Citric almost clear


    20mins.jpg
    20 Mins; L to R; HCl, Acetic, Oxalic and Citric - not much different to 15 minutes

    35mins.jpg
    35 Mins; L to R; HCl, Acetic, Oxalic and Citric - HCl definitely clearing faster than Acetic

    60mins.jpg
    60 Mins; L to R; HCl, Acetic, and Citric (Oxalic not shown) overall not that different to 35 minutes.


    120mins.jpg
    120 Mins; L to R; HCl, Acetic, Oxalic and Citric - HCl, Oxalic and Citric all clear and most of the rust now gone on the Acetic.
    HCl and Acetic have been rubbed with a gloved hand to get this result.

    Comments
    The Oxalic appears to easily be the quickest at dissolving away the rust by itself. I was surprised because I thought the HCL would be faster.
    The next quickest is the Citric followed by the HCL with Acetic being well behind the others.
    The Acetic appeared really slow but after an hour I found I was able to rub away some of rust with a gloved hand - it's as though the acid was dissolving away the bonds between the rust and the metal but leaving the rust on the surface. This is not a problem if the rust is all on the outside of an object but could be a problem if it was in a hard to reach spot.
    The same applied but to a lesser extent to the HCl.

    Of course you can always increase the concentration of the other acids to speed things up but then you may risk dissolving more metal in a "go away and forget about it" situation.
    There seems to be two stages of rust removal - the thin surface stuff and then the rust that is in small pits.
    The Oxalic quickly dissolved the surface and pit rust, the Citric was quick on the surface rust but took some time to dissolved out the rust in the pits.
    HCl took its time but eventually showed up quicker than the Acetic.

    I have been doing some follow up testing of Oxalic on real objects that have a much scalier and crustier rust deposit and it's taking considerably longer than the times shown in the tests above. I think I will re-sand the metal strips and leave them outside for much longer so that they develop a thicker layer of rust.

  5. #20
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    Feb 2009
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    Hi Bob,

    Your Oxalic Acid results are interesting. I didn't think that it would work so quickly, but I suppose everyone's grandmother was in the habit of boiling a few rhubarb leaves to clean saucepans and kettles, so it shouldn't have been such a surprise.

    I noticed that a scrap steel heap stored under a Peppermint Gum turned black and stopped rusting. That was before I worked out that quite a few commercial rust converters contain Tannic Acid. I have soaked rusty parts in the water left over from washing out brushes used to apply some rust converters and found that the rust was eventually removed from the part rather than just "coated". It didn't seem to remove anything that wasn't rust, but that was just a casual observation.

    Is it Acetic Acid that is produced in those molasses baths that the hot-rodders use to de-rust car doors etc? I'm thinking of setting up something like that to clean some of my bigger, rustier projects that wont fit in my electrolysis tub. Supposedly, the process will not eat away your parts, just the rust. Have you tried using molasses to remove rust?

    If you want to produce a good layer of rust, try wiping the test pieces with Baker's Soldering Fluid and then store them somewhere a bit damp. Just storing metal tools near the Bakers Fluid bottle tends to get them pretty rusty around here. Also, you could try the knife steel trick and coat the test pieces with iodine as that will produce some nice pits in the steel.

    Interesting experiment anyway. I look forward to seeing what else you can discover.

    Simon

  6. #21
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by XJ9OX View Post
    Hi Bob,
    Your Oxalic Acid results are interesting. I didn't think that it would work so quickly, but I suppose everyone's grandmother was in the habit of boiling a few rhubarb leaves to clean saucepans and kettles, so it shouldn't have been such a surprise.
    Have since found out it is also widely used in industry.

    I noticed that a scrap steel heap stored under a Peppermint Gum turned black and stopped rusting. That was before I worked out that quite a few commercial rust converters contain Tannic Acid.
    I'm a big fan of Tannic acid as rust converter but given how expensive the commercial versions are I make up my own according to a recipe from a Canadian museum and find it works well but it does have some limitations such as it does not form a physically tough layer and some comes away if you handle a converted object. The converted layer is one of the thinnest around and it overpaints really nicely.

    I have soaked rusty parts in the water left over from washing out brushes used to apply some rust converters and found that the rust was eventually removed from the part rather than just "coated". It didn't seem to remove anything that wasn't rust, but that was just a casual observation.
    Yes I have seen this as well.

    Is it Acetic Acid that is produced in those molasses baths that the hot-rodders use to de-rust car doors etc? I'm thinking of setting up something like that to clean some of my bigger, rustier projects that wont fit in my electrolysis tub. Supposedly, the process will not eat away your parts, just the rust. Have you tried using molasses to remove rust?
    Molasses is a mix of about a dozen different acids in various concentrations. I have not used it but my understanding is that it is slow and it stinks. Given how quick Citric and Oxalic remove rust and how little metal they removed even after a long time I doubt I will ever bother with it.

    If you want to produce a good layer of rust, try wiping the test pieces with Baker's Soldering Fluid and then store them somewhere a bit damp. Just storing metal tools near the Bakers Fluid bottle tends to get them pretty rusty around here. Also, you could try the knife steel trick and coat the test pieces with iodine as that will produce some nice pits in the steel.
    Concentrated Vinegar will also do it but an even quicker way is to use hydrogen peroxide and salt and it literally rusts before your eyes.
    This is about 10s after brushing it onto some steel parts,
    application.jpg
    However I reckon there is a difference between this sort of chemically engineered rust and natural rust and this is reflected in natural rust being more difficult to remove chemically especially if it is at or near a marine environment where salt and other minerals then become part of teh rust.

    Interesting experiment anyway. I look forward to seeing what else you can discover.
    I haven't got anything else planned but am open to putting suggestions on a ToDo list.

  7. #22
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    If I understand the process correctly, molasses and a couple of commercially available 'rust converters' (not acid-based ones) are actually 'chelating agents' and convert iron oxide to iron tri-oxide and some of it back to iron by de-oxiding it. They are said to deal with deep pores better than acids and are said not to remove any base metal. I can't confirm any of this from experience though. Chemically, any iron 'recreated' in chelation remains loose on the surface and gets washed or brushed away after treatment - so it does not 'rebuild' the corroded metal.
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  8. #23
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by jhovel View Post
    If I understand the process correctly, molasses and a couple of commercially available 'rust converters' (not acid-based ones) are actually 'chelating agents' and convert iron oxide to iron tri-oxide and some of it back to iron by de-oxiding it. They are said to deal with deep pores better than acids and are said not to remove any base metal. I can't confirm any of this from experience though. Chemically, any iron 'recreated' in chelation remains loose on the surface and gets washed or brushed away after treatment - so it does not 'rebuild' the corroded metal.
    Until I did this experiment and a bit of reading was also of the same view.
    However, fave since found out that oxalic, citric and vinegar being "organic" acids have chelating properties and Oxalic acid is routinely used in industry as a chelating agent.

    There is nothing particularly special about molasses as it contains a bunch of different organic acids, typically at the <1% concentration for each, which combined with its viscous/sticky nature results in slow rust removal and an even lower metal loss per unit time. Apart from being slow it can also stink. For slower rust removal with lowest metal loss and no stink it would be better to use something like dilute oxalic acid.

    I should point out that repeated exposure to concentrated Oxalic acid can cause kidney stones and even kidney failure, and joint pain. The human body can tolerate a certain amount, as it is present in many vegetables, especially parsley, spinach, chives and cassava which contain about 1% oxalic acid.

  9. #24
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    First job I had when I left school was at a wrought iron maker of outdoor furniture. My job was to gather the newly built pieces and place them in a big fiberglass tank full of hydrochloric acid, the acid was diluted with water, lots of water, clearly remember putting my un gloved hands in there to remove the bits I put in, wash them down with water, place them in an oven to dry before painting. Always seemed to miss an area around the scrolls, thats where the paint would bubble from the acud residue.

    DD

  10. #25
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Dingo Dog View Post
    First job I had when I left school was at a wrought iron maker of outdoor furniture. My job was to gather the newly built pieces and place them in a big fiberglass tank full of hydrochloric acid, the acid was diluted with water, lots of water, clearly remember putting my un gloved hands in there to remove the bits I put in, wash them down with water, place them in an oven to dry before painting. Always seemed to miss an area around the scrolls, thats where the paint would bubble from the acud residue.
    To get the acid residue out of cracks etc I'd be boiling them in water, then ultrasonicating in a water soluble solvent like meths and then putting them in an oven.

  11. #26
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    In the home anodising world they neutralise the sulphuric acid from the anodising bath in a tank of 60g/L bicarb soda solution.
    Last edited by jack620; 18th Dec 2018 at 12:36 PM. Reason: spelling
    Chris

  12. #27
    BobL is offline Member: Blue and white apron brigade
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    Here is a follow up picture some 14 weeks after the experiment where I left the steel pieces in the dilute acids to act a rust removers and was testing to see how much weight they would lose..
    When I pulled them out of the acids I blew them dry wit compressed air and then weighed them and they have been hanging around inside my shed since then - some days have been quite humid.

    Again L to R - HCl , Acetic, Oxalic, CItric.
    The oxalic is still looking really good but the citric and acetic are not too bad either.
    10weeks.jpg

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