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Thread: Citric Acid

  1. #1
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    Default Citric Acid

    Has anyone used Citric Acid for cleaning the scale of Mild Steel, if so what concentration did you use and what were the results like.
    Shane

    Got the square peg in the round hole, now can't get it out !!

  2. #2
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    Yes, 5% , 5g / Litre water) for 30mins up to several hours. The rust turns black but parent metal is etched very slowly. Parent metal turns grey but can be cleaned up with scotchbrite. If parts are badly rusted there will inevitably be pits in the surface. Rust is essentially dissolved faster than the parent metal. Similar results with Phosphoric acid. Molasses can also be used on very delicate parts but takes a week or so to remove rust.

  3. #3
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    I have used Citric Acid on black bar many times over the last few years and can confirm the observations by Swarfmaker1.

    I can only add that the black scale releases its tight adherence but remains 'stuck on' and must be removed by physical wiping.

    You can wipe a couple of times during the process as the saturated solution is safe on the hands for the short period of immersion, but wash off as soon as possible.

    Only clean when you have a protective process organized as rust forms extremely quickly.

    John

  4. #4
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    Thanks for the replies, I was using Hydrochloric Acid and the fumes were starting to become bothersome.
    Shane

    Got the square peg in the round hole, now can't get it out !!

  5. #5
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    Quote Originally Posted by Swarfmaker1 View Post
    Yes, 5% , 5g / Litre water)
    Wouldn't a 5% solution be 50g/L ?
    Chris

  6. #6
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    Yes you are correct It should be 0.5%. although 5% will naturally be more aggressive.

  7. #7
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    Whatever rate yer use make sure you add the powder to the water. Also, if the mix is to high a percent citric the citric will partially settle out on the bottom of the tank. Citric acid is also an ingredient of Coca Cola and other foods so no worrys putting yer hand in the mix when fresh.

    Edit: Forgot to mention mix rates. Via Google many of the car forums have it covered. One chap did extensive testing and found temperature can affect the mix/rate requirements. I'm still new to citric so havn't yet settled on a mixture strength. My old mix were Molasses which is one to nine.
    ====================================
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  8. #8
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    IME hydrochloric fumes cause rust everywhere. In a confined space (cupboard) fumes from a closed container of HCl will in the long term rust steel items in that cupboard.

    Quote Originally Posted by Auskart View Post
    Thanks for the replies, I was using Hydrochloric Acid and the fumes were starting to become bothersome.

  9. #9
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    Quote Originally Posted by YBAF View Post
    .......... Citric acid is also an ingredient of Coca Cola and other foods so no worries putting yer hand in the mix when fresh.
    CAUTION - the above statement is only true for the very dilute acetic acid solutions used in food stuffs, and then only when the powered acetic acid is mixed as per the manufacturer's recommendations.

    I believe that the "powered citric acid" being referred to in this thread is one of the products sold by the supermarkets for use in jam making and other cookery - McKenzie's Citric Acid being one example. Using the cooking ingredient Powered Citric Acid is a safe way to go for descaling your mild steel (or for descaling the kitchen kettle). The McKenzie's Citric Acid web site entry above recommends for de-scaling a kitchen kettle, that 25 grams of Citric Acid Powder disolved in 1 Litre of water, be placed in the kettle, and the kettle bought to the boil.

    I've used to 25 grams of powdered acetic acid per litre of water solution to remove the scale from silver steel after heat treatment, by boiling the silver steel part for a few minutes in the dilute acid solution. The heat makes the process work much quicker, and the agitation caused by boiling seems to help loosen the scale, so much less scrubbing is needed to remove the scale afterwards.

    I use an old stainless steel saucepan, as I read somewhere on the Internet that using an aluminium saucepan results in the acetic acid attacking the aluminium. I don't know if the "aluminium saucepan" story if an Internet Myth, or fact - but I got a suitable stainless steel saucepan from the local Op Shop for $2.00.

    Mixed up according to the instructions on the McKenzie's Citric Acid pack, the resulting solution is supposedly safe - BUT I still use gloves. But, do not stick your hands in the citric acid solution if you've mixed it up stronger than the strength recommended on the pack. I got a drop of this 25 grams per litre of water acetic acid splashed into my eye, and it stung like crazy, and once washed out with plenty of running water, the eye was red and sore for days. So next time I need to descale an item, I'll also be using eye protection.

    And - don't use any of the concentrated liquid citric acid products that are available in specialist chemical suppliers and photographic darkroom suppliers for descaling metal - unless you really know what you're doing when it comes to calculating acid dilution concentrations. These concentrated acetic acid solutions are far far stronger than the powdered cooking ingredient variety sold in Woolies as a jam making ingredient - and, unless you know exactly what you're doing, you can end up with a diluted acetic acid solution that is plenty strong enough to burn skin, and to cause internal acid burns if you breathe the fumes in.

    I used to use Kodak Acetic Acid Stop Bath as one of the chemicals used when developing film is the long distant past. The fumes from the concentrated acetic acid can cause serious damage to the airways and lungs if they're breathed in. I saw it happen to a friend at a Photography Club back in the late 1970s, when he accidentally dropped a glass bottle of concentrated Kodak Acetic Acid Stop Bath .... which broke. He got out of the room in a few seconds, but he spent weeks in hospital with respiratory tract acid burns, and has has respiratory problems ever since.

    Play Safe !

    RoyG
    Manufacturer of the Finest Quality Off-Cuts.

  10. #10
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    I don't know the difference between Citric and Acetic acids.

    I can say that the following experiences with pure white Citric Acid crystals have no ill effect:
    - a couple of crystals on the tongue is a taste sensation,
    - plunging a hand into a cold saturated solution (but I have always washed off immediately).

    Check the MSDS data to re-assure yourself before use.

    John

  11. #11
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    Default

    Acetic is vinegar. Citric is lemon, orange, grapefruit etc acid.

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