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Thread: Strength of phosphoric acid?
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23rd Nov 2011, 01:37 PM #1Mechanical Butcher
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Strength of phosphoric acid?
I want to buy some phosphoric acid for rust removal.
The local hardware has small bottles of 85% concentration.
A chemical supplier has 81%, which they say will be OK for my needs.
Is the 4% difference anything to worry about?
JordanLast edited by nadroj; 23rd Nov 2011 at 01:37 PM. Reason: spelling
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23rd Nov 2011, 01:52 PM #2Most Valued Member
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Hi Jordan,
Well the rust remover I have in the shed is 35%. So assuming more is better, you're a long way in front of that.
Stuart
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23rd Nov 2011, 03:31 PM #3New Member
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no noticable difference
4% will not be noticed for what you want to do
Gfreg
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23rd Nov 2011, 03:53 PM #4.
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Maybe an alternative.
Hello Jordan,
When I acquired my little No. O mill it was in a fairly appalling condition as a result of exposure to water based coolant and general mistreatment. The non painted surfaces were all discoloured with rust, some of it quite heavy. My brother in law, a farmer, had encountered Corro Dip at some country show and swore by it. As a result of immersion of those parts in Corro Dip, I do too.
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BT
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23rd Nov 2011, 04:12 PM #5Mechanical Butcher
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Thanks for the advice folks.
Bob - the CorroDip looks like a quality product, and likely has phosphoric acid in it at a guess. I have some steel that I want to clean up before painting, and will give the 81% stuff a go.
Jordan
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23rd Nov 2011, 04:40 PM #6.
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Whatever you use Jordan, don't spill the stuff on concrete and leave it. I have a depression the size of a cereal dowl in the shed floor where some Corro Dip bled out over a few days from a useless plastic milk bottle..
BT
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23rd Nov 2011, 07:07 PM #7Most Valued Member
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24th Nov 2011, 01:25 PM #8Most Valued Member
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Jordan,
I'm not a chemist, but with acid I would not assume stronger is better. If you are going to use it for rust conversion I would dilute it to 30-35% if that's what concentration the commercial rust converting products use.
Lower concentrations will be safer for you and anything you happen to spill the stuff on.
BTW what purpose is the 85% phosphoric product sold for?
Good luck with the project.
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24th Nov 2011, 02:47 PM #9
I've found the 30-35% "Rust Dissolver" to be fine for most purposes, especially when applied with fine steel wool.
Just keep it away from any aluminium parts; it will remove anodising colour as well !
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24th Nov 2011, 03:00 PM #10Most Valued Member
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What would you thin it down with?
Water just sounds wrong.
Stuart
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24th Nov 2011, 03:02 PM #11Member: Blue and white apron brigade
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Water is the go for dilution, plus a couple of drops of wetting agent per litre - dishwashing liquid is fine.
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24th Nov 2011, 03:08 PM #12
The wetting agent is a good idea, as the stuff doesn't wet a surface very evenly without.
I use this stuff on machinery surfaces all the time - stinks a bit, but very effective indeed.
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24th Nov 2011, 03:11 PM #13Member: Blue and white apron brigade
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If it too concentrated it will not dry properly and sits on the surface absorbing water and forms a horrible gooey messy. To speed up the drying I bake the derusted objects in a BBQ oven on low for an hour and it goes a sort of grey-white colour which can be readily painted over.
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24th Nov 2011, 08:07 PM #14Mechanical Butcher
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Last edited by nadroj; 24th Nov 2011 at 08:10 PM. Reason: addit
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24th Nov 2011, 08:20 PM #15Member: Blue and white apron brigade
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