Cleaning corroded zinc plating

[Kiwi BlokeParticipant @kiwibloke62605]

I wish to remove the surface roughness that corrosion has caused on some small, slender zinc-plated steel items. They are rather delicate and do not lend themselves to attack by abrasive devices or materials. I don't wish to damage what remains of the plating. Is there a practicable chemical method to safely remove the zinc hydroxide/oxide without significant risk to the remaining zinc and steel?

[Kiwi BlokeParticipant @kiwibloke62605]

Chemical cleaning?

[old martParticipant @oldmart]

You are talking about tarnish to the zinc, I presume, corrosion of the steel beneath would be brown rust coloured. Zinc can be passivated like cadmium plating, this link may help.**LINK**

[Kiwi BlokeParticipant @kiwibloke62605]

I'm talking about what is sometimes called 'white rust'. This is zinc hydroxide which forms when zinc is exposed to atmospheric moisture, before the corrosion-protective zinc oxide surface film has become established. It's a similar situation to aluminium and its oxide coat (either 'natural' or from anodizing) being protective. Sometimes 'white rust' occurs on zinc surfaces that should have had an established oxide film. I think this is more likely in aggressive environments, particularly where chlorides are about, such as near the sea.

Treatment with dilute acetic or phosphoric acid is advocated as a treatment, but I'm worried that this will strip off any remaining zinc plating. OK, re-plating is the way to go, but it ain't going to happen…

Any ideas?

[lee websterParticipant @leewebster72680]

A metal polish such as Solvol Autosol might do it.

[HopperParticipant @hopper]

Scotchbrite green kitchen pads are what I use on old motorbike small nuts and bolts, down to small sizes on carbs and ignitions etc. Then a spray and wipe with WD40.

[Ex contributorParticipant @mgnbuk]

This isn't so much a recommendation, but a recollection from many years ago.

I decarbonised the exhaust system of a Suzuki GT750 motorcycle in the time-honored way using a caustic soda solution. The pipes were bunged at one end with potatoes & to get the (very strong – maybe saturated, near boiling) caustic solution into the pipes I used a galvanised watering can. I recall being rather suprised afterwards that the inside of the watering can had come up like new – really bright galvanising, rather than the dull grey that it had started out.

Maybe worth experimenting with ? Be very careful with strong caustic soda solutions – splashes can irreperably damage your eyes in an instant & cause nasty burns elsewhere, so employ substantial protective precautions.

Nigel B.

[HopperParticipant @hopper]

Posted by mgnbuk on 16/08/2022 09:41:10:

Maybe worth experimenting with ? Be very careful with strong caustic soda solutions – splashes can irreperably damage your eyes in an instant & cause nasty burns elsewhere, so employ substantial protective precautions.

Nigel B.

Yes, be very careful going to the toilet after handling caustic soda. Be sure to wash any residue off your hands before handling anything of a sensitive nature! I learned this as an apprentice tasked with filling the caustic soda tanks in the boiler water treatment plant. Ouch!

[Kiwi BlokeParticipant @kiwibloke62605]

Well, if anyone's still interested… Mindful of Hopper's warning (hope you didn't suffer permanent damage), and not having any NaOH on site, I gently rubbed the bits with a bit of gentle (grey) Scotchbrite in some approx. 5% phosphoric acid solution. Job done!

[Paul RhodesParticipant @paulrhodes20292]

Kiwi Bloke ,pleased that you attained satisfaction by rubbing your bits with Scotchbrite and phosphoric acid.

[Nick Clarke 3Participant @nickclarke3]

Posted by Hopper on 16/08/2022 09:47:03:

Yes, be very careful going to the toilet after handling caustic soda. Be sure to wash any residue off your hands before handling anything of a sensitive nature! I learned this as an apprentice tasked with filling the caustic soda tanks in the boiler water treatment plant. Ouch!

I was given the same advice years ago when working in a dodgy back street garage as used oil can be carcinogenic!

[Kiwi BlokeParticipant @kiwibloke62605]

Posted by Paul Rhodes on 17/08/2022 09:48:56:

Kiwi Bloke ,pleased that you attained satisfaction by rubbing your bits with Scotchbrite and phosphoric acid.

Thanks. It all came up lovely. My wife was pleased too.

[Tim StevensParticipant @timstevens64731]

Good – because caustic soda (NaOH) dissolves zinc almost as quickly as it dissolves aluminium.

Cheers, Tim

[Michael Cox 1Participant @michaelcox1]

Ammonia solution (eg household Ammonia) should remove zinc oxide and hydroxide rapidly. It attacks the zinc metal very slowly in the presence of air but the oxide and hydroxide is removed rapidly. Afterwards wash in plenty of clean water.

Mike

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