Phoshor Bronze and phosphoric acid?

Is phosphor bronze adversely affected by phosphoric acid?
Got some large screws stuck in bronze nuts and need to remove the rust 'below' the nut so I don't do too much damage to the nut as I unscrew it (which will take heat). Access is a tad difficult but I can get a plastic tub of phosphoric acid so the screw is immersed in it but will it dissolve the bronze nut?
AWEM

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Andrew,
I don't know the answer for certain, but genuine bronzes (Cu/Sn alloys) should not be affected by non-oxidising mineral acids, or at least not at an appreciable rate. However, if it contains Zn, this may well be dissolved and you may suffer "de-zincification", as happens to steam boilers if you use brass fittings in them. Your problem is that you have no easy way of knowing the precise composition. Can you scrape a bit off and test it?
If all you want to do is removed rust, it may not need a strong (or strong-ish - phosphoric acid is only what I would call medium strong) acid; a weak organic acid such as citric might well work. With a chelating agent such as EDTA it might work even better. With your experience in water you probably know about this.
David

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According to this
http://www.engineeringtoolbox.com/metal-corrosion-resistance-d_491.html
It's not advised but citric acid looks ok and seems to do the job.
http://www.wkfinetools.com/tRestore/techniques/rust_CitricAcid/rust_CitricAcid1.asp

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Andrew
I don't know if you have good enough access, but electrolytic rust removal might be a good solution. Certainly won't hurt the phosphor bronze.
Mike

mikecb1 wrote:
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What he said - or use citric acid.
Phosphoric acid might leave a layer of insoluble ferric phosphate which might make the threads a little bigger, and thus harder to remove, and phosphoric acid probably wouldn't be too kind to bronze/brass, though this depends on type.
Note, citric acid will dissolve bronze/brass - eventually - if there is air about, but most likely less fast than phosphoric acid will (depends on the exact bras/bronze)
I'm assuming the bronze nuts are more valuable than the steel screws.
-- Peter Fairbrother

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the rust
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unscrew
get a
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but will
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http://www.engineeringtoolbox.com/metal-corrosion-resistance-d_491.html
job.
http://www.wkfinetools.com/tRestore/techniques/rust_CitricAcid/rust_C ...
phosphor
which
and
though
is
(depends
screws.
..sadly not! The screws are about 6 foot long by 1.5" acme and the 'nuts' are carved out of a block of bronze about 2.5" square by 6" long so replacing either is to be avoided if possible!
AWEM

Sucess following advice from the group!
I left one of the four 'screws' with bronze nut upright in a pail of citric acid overnight. Before I could unscrew half a turn using a wacking great spanner when heated with an oxy-acetylene torch. This morning it would unscrew 3/4 turn cold so I left it soaking. Just now 8 hours later I've fully unscrewed it with minimal force. Only 3 more screws to go and perhaps I can get this press dismantled for sand blasting and re-painting! It's been a 'back burner' project for too long.
Citric acid definately works!
AWEM
news:...
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rust
unscrew
will

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Andrew,
Glad to hear it - and thanks for letting us know.
David