Pickling with Sulphuric

[Deltic007Participant @deltic007]

Hi

Any idea what percentage Sulphuric acid to water for a decent pickle?

Cheers

[Deltic007Participant @deltic007]

[Rik ShawParticipant @rikshaw]

Years ago my chemist supplied me with a dilute sulphuric acid mix for pickling which was very aggressive and did a super job. I am sorry I cannot advise on percentages but if you DIY bear in mind that you have to be careful.to avoid an explosive mix and I forget which way is safe. There are only two ways to dilute – either add the acid to the water or add the water to the acid. One is safe and the other is lethal.

Rik

[Peter KroghParticipant @peterkrogh76576]

Acid to water, never the other way round.

Pete

 

Edited for typo as requested by Pete

Edited By John Stevenson on 28/12/2015 01:09:55

[Michael Cox 1Participant @michaelcox1]

A 10% solution of sulphuric acid should make a good pickle for brass, copper and steel.

Always add the acid to water with gentle stirring.

I would suggest rubber gloves and face goggles should be worn.

Mike

[Bob RodgersonParticipant @bobrodgerson97362]

Acid to water stirring continuously. Don't use a Bamboo Cane for stirring. They burst with the heat generated. (Don't ask me how I know).

[GeorgineerParticipant @georgineer]

To answer the original question, Engineering Workshop Practice by A.W.Judge, published in the late 1930s, says:

"The usual acid bath consists of 1 part sulphuric acid to 5 to 10 parts of water. If more concentrated solutions of the acid are employed, the pickling process can be done more quickly. When making up the sulphuric-acid solution, always add the acid to the (greater) quantity of water; never pour water into the acid, as a considerable amount of heat is then developed with partially explosive results."

Or, as 'Jake' Hateley taught us in third form chemistry in 1963:

"For safety's sake do as you oughter; Add the acid to the water"

George

[Peter KroghParticipant @peterkrogh76576]

Damn dislexic fingers again. I screwed up as I meant to say it the other way round and after posted couldn't find a way to

edit the post!!!!!

Can snyone edit that so it'sz right?? Please?

Pete_the_typing_idiot

[Peter KroghParticipant @peterkrogh76576]

I really apologise for the bad information folks.

I mess up a lot when typing and try to catch errors before saving/posting but sometimes things 'slip' through.

This is the one board where I can't edit my post when I blow it!

The dyslexia is minor compared to the hand tremor.

Pete

[Deltic007Participant @deltic007]

Thanks for the advice and entertainment

[herbert punterParticipant @herbertpunter99795]

Alas, poor Bill is dead, of him we'll hear no more

For what he thought was H2O was H2SO4!

[AjohnwParticipant @ajohnw51620]

JS really should edit in add slowly while stirring. The problem is that heat will be generated and the rate that builds at needs to be controlled. The actual heat shouldn't worry people too much but mix the other way round and the water will boil instantly splashing the stuff all over the place.

John

–

[mickParticipant @mick65121]

If your using pickle to clean up brazing or silver soldering then lime scale descaler from Tesco takes some beating

[Geoff ShackletonParticipant @geoffshackleton95034]

Hello,

If you are copper boiler making then I would recommend you buy 1N normal solution 98% concentrated sulphuric acid and dilute it to 25 to 1. Leave it any stronger and you will passivate the copper rather than clean it which can lead to problems if you are silver soldering. At 25 to 1 or even 30 to 1 the copper cleans very quickly and requires less scouring to remove the stubborn dirty bits. The last time I bought concentrated 98% acid I bought 2.5 litres from e-Bay and diluted it to fill two 30 litre plastic Jerry cans which are obtainable quite cheaply from Motorswares shops.

Geoff

[AjohnwParticipant @ajohnw51620]

As I found recently it's best to store the stronger stuff diluted. I obtained mine from Cousins and it's clearly too strong to leave in the plastic containers it's supplied in for long periods. It's now in a glass demijohn as I do need it at that strength.

The same thing applies to nitric and hydrochloric even though the hydrochloric is pre diluted some what. About 80% if I remember correctly.

John

–

[Tim StevensParticipant @timstevens64731]

The rule about only adding acid to water applies if you are starting with concentrated acid. This stuff is pretty nasty, much heavier than water and more viscous. I see no reason why any engineer should buy concentrated acid, when the dilute stuff is so readily available, and so much easier/safer etc to handle.

It should be possible to buy battery acid – which is dilute sulphuric – from your local tyre & battery depot. Just remember that battery maintenance involves adding – dare I say it – water to acid … !

Cheers, Tim

[John LintornParticipant @johnlintorn87585]

Hi guys! Being new to all this and seeing some of the really nice finished boilers, I get frustrated when, after soldering I put my boiler in the pickle solution (and I have tried dry acid from glr, dishwasher descaler, and household kettle descaler) it come out still black and grimy with some flux still attached. Sometimes I feel like using a pick axe because the stuff is still so hard. I am using easy flow flux so what am I doing wrong?

[julian atkinsParticipant @julianatkins58923]

Hi John,

My procedure is to carefully insert the boiler or sub assembly into dilute sulphuric acid when hot but after it has cooled down quite a bit. If the copper does not come out sort of dirty pink there is something wrong with your acid – it may not be strong enough or it may be contaminated.

The boiler is then hosed down with the garden hose.

The boiler then gets transfered to the domestic draining board and scrubbed with hot soapy water. It is surprising what extra muck comes off at this stage.

Flux – firstly you are using the wrong type of flux anyway for boiler work. Due to the longer heat ups J&M Easyflo flux will be exhausted too quickly. Also depending on what grade silver solder you are using you need a more active flux anyway. So instead use J&M Tenacity 4A, or Thessco F flux, or the equivalent grade supplied by CupAlloys.

To remove glass hard deposits of flux J&M recommend soaking in a hot strong solution of Sodium Hydroxide/Caustic Soda. It is very cheap and available from Wilkos etc. Do this after the pickling, rinsing, and scrubbing stages.

You may need to pick about at the flux deposits a bit with a dental probe or scriber.

Cheers,

Julian

Edited By julian atkins on 19/08/2016 10:11:41

[Brian HParticipant @brianh50089]

I use a 5% solution for pickling copper etc. It is slower in action but at least parts do not come out lacy!

I keep mine in a plastic tub intended for do-it-yourself beer brewing. The lid is a really tight snap-on one that does not leak.

The container should be marked with labels to explain exactly what is inside.

DO NOT use used battery acid as it will contain lead that will seriously contaminate anything dipped into it.

[Martin KyteParticipant @martinkyte99762]

The idea of adding concentrated acid to water instead of the other way round is when you get a splash it's dilute acid and not concentrated.

Martin

[Glyn DaviesParticipant @glyndavies49417]

Herbert's post brought back chemistry lesson memories:

Poor old Joe, he's gone below

His face we'll see no more

For what he thought was H2O was H2 SO4.

and

Nitrous oxide, we must know

Is laughing gas, haha hoho

To get some, haha hehe

Heat NH4NO3

 

DH, Roundhay School, 1966

Edited By Otley on 19/08/2016 11:02:11

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by Martin Kyte on 19/08/2016 10:39:55:

The idea of adding concentrated acid to water instead of the other way round is when you get a splash it's dilute acid and not concentrated.

Well partly that. The reaction between concentrated sulphuric acid and water is violently exothermic – that means it gives off heat. If you add a small amount of water to the acid the chemical reaction quickly heats up and boils the water. The rapid evolution of steam causes spitting and spluttering which will eject concentrated acid. Because there is an excess of concentrated acid the reaction will continue until all the water has reacted. Conversely, if you add the acid to water, the reaction is rapidly quenched by the excess water and the whole process is much more benign.

HTH

Rod

Edited By Roderick Jenkins on 19/08/2016 11:21:20

[Martin KyteParticipant @martinkyte99762]

Not convinced Roderick. The heat comes from the hydration of H⁺ ions to form H₃O^{+ .} Not as one may suppose from the dis-association of the acid.

So the heat generated is only dependent on the quantity of the input reagents. It really does not matter if the reaction stops because it runs out of water or of acid. The heat produced is the same. It then becomes a calorimetry question as to temperature rise. As the water has a higher specific heat capacity than the acid the temperature will go up less when the bulk of the liquid is water as when adding acid to water. So the heat is produced by the chemistry which is the same in either case (ultimately you add the same quantities of acid and water together to get the desired concentration) but the temperature profile is down to the physics.

I think we are essentially saying the same thing which is add acid to water and the worst thing that can happen is a splash with dilute acid.

Personally I find the dry salts sold by many of the suppliers work perfectly well and saves all the bother of hard to obtain wet acid whilst avoiding the dilution issues.

best regards Martin

[Ian S CParticipant @iansc]

If you splash dilute acid on your clothes, the H2O evaporates, and the acid becomes concentrated, so neutralize it as soon as the splash happens, washing soda should be on hand when using acid.

Ian S C

[Neil WyattModerator @neilwyatt]

Loads of organic acids that do the same job well enough I can't see why anyone would use sulphuric.

[Author]

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