Citric acid as pickle

[Neil WyattModerator @neilwyatt]

Posted by Speedy Builder5 on 12/04/2017 19:37:49:

I wish I hadn't used citric acid – I am (lead /tin based) soft soldering brass side tanks for SPEEDY, using FLUXITE as my flux. All going well. Went to clean it all up before closing the tank with its last side, so put it in CITRIC acid overnight. Next morning, the brass was a bit cleaner, still residues of fluxite, but all the soft solder has turned BLACK and is no good for sweating in the last side.
Suggestions please.
BobH

If it;'s lead citrate, it should dissolve in alcohol, so try meths and DON'T DRINK IT

[Speedy Builder5Participant @speedybuilder5]

Thanks Neil, I will have a go this AM – If it doesn't work, I will use some 'active' flux which I don't like but works well for plumbing bits.
BobH

[IanTParticipant @iant]

I used to buy little boxes of Citric from the local Chemists, which was expensive but then I discovered I could get a kilogram from eBay for about a fiver (including shipping).

Still got a fair bit left as it goes a long way with care. I use old coke bottles to store any surplus 'made-up' stuff from larger jobs… but this is mainly used to de-rust steel parts (I have a large collection of rusty stuff that machines up nicely but sometimes benefits from a soaking in Citric beforehand). Leave bits in overnight and give them a scrub with wire wool – dump it back if more treatment needed. Wear rubber gloves as it will turn your hands black real quick…

I make fresh mix for pickling any soldered/brazed fabrications (and I don't leave it in too long)

Look in the 'Food' section – it's used in Indian cooking I believe….

Regards,

IanT

[Speedy Builder5Participant @speedybuilder5]

Ian, it wasn't a problem of finding Citric acid, it was the problem it caused with lead solder. Unfortunately Neil's suggestion of meths for cleaning up the solder joint after the citric damage didn't work either. In the end I had to resort to mechanical cleaning before using an active flux. The solder I used was a flux cored (Multicore) solder 60% Tin 40% lead (I happened to have a lot of that to hand). For the second fix, I used some 50/50 unfluxed solder and finally in one awkward corner used form lead free to 'Caulk' up as it has a better gap filling property.
BobH

[SillyOldDufferModerator @sillyoldduffer]

There's a paper here **LINK** that might cast some light on the problem, but the unwanted reactions reported require heat. Did Bob use hot pickle or put a hot boiler into the pickle?

If there was an unwanted reaction, the products are insoluble in alcohol, but are dissolved by boiling water.

Apart from the heat problem, I couldn't find anything negative about Citric Acid pickle. As it seems to be widely used in the electronics industry to remove flux, Bob may have run into something unusual.

Dave

[Speedy Builder5Participant @speedybuilder5]

I am making side water tanks for a loco, no pressure involved, so choice of solders / flux I thought was easier. I used cold Citric acid and a cold brass/ lead soldered jointed tanks.
BobH

[IanTParticipant @iant]

My non-ferrous fabrications are generally silver soldered and the steel ones SIF bronzed where possible (silvered where I can't get enough heat into it) – and I've not had problems using Citric afterwards. Haven't checked but I'd guess the proprietary fluxes I use are borax based – the SIF one certainly is..

I do use soft solders but normally just scrub this work afterwards under hot soapy water as their fluxes (I use both resin & acid) are much 'softer' and relatively easy to remove, as compared to the brazing fluxes which are clearly less so.

Regards,

IanT

[Tim StevensParticipant @timstevens64731]

The problem with submarines was (is) not sulphuric acid and sea water, it was batteries and sea water. The fact that the batteries contained sulphuric acid caused confusion in diagnosis.

Sulphuric Acid and common salt gives a mixture of sodium sulphate and hydrochloric acid – the molecules simply swap partners.

When I was an apprentice (mid 1960s) it was common practice to pull stuff out of sulphuric acid pickle with bare hands. If you did not wash them fairly quickly it would start to itch, and the skin would develop a rough surface for a day or two.

And sulphuric acid does not dry out. As water evaporates from it it becomes deliquescent – which is a posh way of saying that strong acid absorbs water from the atmosphere. It is its greed for water that makes concentrated acid so dangerous.

Cheers, Tim

[SillyOldDufferModerator @sillyoldduffer]

Posted by Tim Stevens on 14/04/2017 12:44:21:

The problem with submarines was (is) not sulphuric acid and sea water, it was batteries and sea water. The fact that the batteries contained sulphuric acid caused confusion in diagnosis.

…

Cheers, Tim

Stories of Chlorine in submarines have had me baffled for decades – the chemistry doesn't support it. Now you've said the source is the battery, all becomes clear. Of course electrolysis of brine produces Chlorine. Doh…

Dave

[Tim StevensParticipant @timstevens64731]

Glad to be of service, Dave

Tim

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Tim Stevens on 14/04/2017 12:44:21:

And sulphuric acid does not dry out. As water evaporates from it it becomes deliquescent – which is a posh way of saying that strong acid absorbs water from the atmosphere. It is its greed for water that makes concentrated acid so dangerous.

I seem to remember reading that Dr John Bradbury Winter kept his scale model of Como in a display case with a tray of concentrated sulphuric acid that would absorb any water and prevent rust on the bright work. I think I'll stick with silica gel.

Rod

[Andy AshParticipant @andyash24902]

Posted by Speedy Builder5 on 13/04/2017 11:36:49:

Ian, it wasn't a problem of finding Citric acid, it was the problem it caused with lead solder. Unfortunately Neil's suggestion of meths for cleaning up the solder joint after the citric damage didn't work either. In the end I had to resort to mechanical cleaning before using an active flux. The solder I used was a flux cored (Multicore) solder 60% Tin 40% lead (I happened to have a lot of that to hand). For the second fix, I used some 50/50 unfluxed solder and finally in one awkward corner used form lead free to 'Caulk' up as it has a better gap filling property.
BobH

I'm an advocate of Citric, particularly hot Citric, which is every bit as effective as other more powerful acids.

Some of those more powerful acids don't benefit (as much) from heat, not that you would want to use them that way anyhow.

I've only ever used acid pickle on hard soldered joints. Mainly because the borax flux is so tough to remove.

For soft soldered joints, especially with acid flux, you can just use warm water to clean up. For that I usually use Fry's Powerflow flux and it just works very well indeed.

If you use Rosin cored solder, then you do get a residue. Meths is a disaster for that. It won't shift anything and you get a white deposit which looks really gross. The best stuff I've ever come across for rosin cored solder flux removal is from Electrolube. It's in an aerosol, called LFFR (Lead Free Flux Remover). It even smells fairly nice. Don't breathe it though, it's Cyclohexane. I've no idea what that is, but rest assured that one day someone will recognise it as being bad to small furry nylon bears.

Farnell Pt. No. 1098276

It will lift the sticky deposits. All you have to do is make sure that the solvent has been wiped away before it evaporates. Wherever the solvent evaporates, the Rosin residue will be left. The aerosol has a brush nozzle. You give it a squirt, mush it in with the built in brush, and then dry the solvent with a paper towel. Job done.

Edited By Andy Ash on 14/04/2017 23:00:04

[Speedy Builder5Participant @speedybuilder5]

Thanks Andy – A pretty comprehensive post on what I should have done, my problem is that the tanks are about 15" x 4" x 6" soit will take more than a plastic bucket to get them in – especially when hot. Again, the Farnell product couldn't be used inside as there wasn't the access. Anyway, job done now. On the second tank, I will review my construction methods.
BobH

[Anthony KnightsParticipant @anthonyknights16741]

CYCLOHEXANE

Used in the synthesis of Nylon and was responsible for the huge explosion at Flixborough.

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