how to improve flux wetting?

Discussion in 'Techniques' started by michl080, 11 June 2020.

  1. michl080

    michl080 Western Thunderer

    Hi,
    I am using 20% phosphoric acid as flux and love it after testing many other agents.
    However, I am not happy with the wetting capability. I tends to form local drops on brass, even if the brass has been degreased with acetone before. Technically, it has a high contact angle on brass.
    Is any of my fellow thunderers using a wetting agent with phosphoric acid to improve wetting?

    I have been testing ox bile, but the result looks ghastly. :eek:

    As some may know, I am not UK based, so brand names won't help much.

    thanks for your input.

    Michael
     
  2. A few drops of isopropanol (ipa - but not the beer!) usually does it. Failing that try a few drops of screenwash or even washing-up liquid. You're basically trying to reduce the surface tension of the droplets.
     
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  3. simond

    simond Western Thunderer

    worth looking at citric acid too, if you have not already tried it. I use it in saturated solution with water, and ipa added, approx 30% by volume. Im told that this might be too much ipa, but it does wet the brass.

    atb
    Simon
     
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  4. michl080

    michl080 Western Thunderer

    Thanks!

    I will try and report back.

    Michael
     
  5. neaston

    neaston Active Member

    I think you can reduce the concentration by half. I've been using it at 10% for about fifty years with no problems at all.
    Never had a problem with wetting I just apply it along a short length of the joint with a bit of wire.
    Nick
     
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  6. SimonT

    SimonT Western Thunderer

    Nick,
    that is useful information as I have followed SimonD's path. I was amazed to find that citric acid flux worked to solder steel rail, so no more of the nasty Carr's Green. The only problem is that it leaves a sticky residue that needs to be washed off to do any cleaning up. Warm water a washes it off but a thinner solution might reduce the need for the trip to the sink.
    Simon
     
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  7. simond

    simond Western Thunderer

    Nick,

    thanks

    Which concentration? Citric or alcohol?

    Sounds like a martini! Shaken or stirred, sir?

    Atb
    Simon
     
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  8. Deano747

    Deano747 Western Thunderer

    I have recently purchased some 45% phosphoric acid and by mixing 10ml acid to 25ml distilled water gives me 15% (14.7% to be precise) and I added 5% viakal as a wetting agent which may help prevent corrosion. Early days yet but seems to work ok so far. Will report back in due course.

    Regards, Deano.