Pickle

I have been using diluted 38%Hydrochloric acid for pickling copper. We use it to alter the Ph in swimming pools. Seems to work well.

I needed to remove some heavy calcium deposits on plastic tube, so used the pickle.

Now, when I use the pickle, it cleans the copper, but leaves it a dark straw / brown colour. As a scourer, I use the wife's stainless steel scourer, and have switched to a green scouring pad.

Has the dissolved calcium in the pickle caused this new problem ? Any chemists among us ?

Haven't come across this but I wouldn't use hydrochloric acid as it dissolves copper. I use dilute (5%) sulphuric acid which wll dissolve the flux and the oxides but not the metal. Citric acid is often recommended as it's safer but takes a bit longer.

Be sure to take the appropriate safety precautions.

Russell.

Before I retired my work involved a lot of siler soldering, we used sodium bi sulphate

(sodium hydrogen sulphate) as a pickle. It would start to dissolve the tops of screw threads

if left in the pickle tank for a few days, but as most jobs took only 20-30 mins to pickle

this wasnt a problem. the mix ratio we used 28g to 100g of water, but found that

this ratio wasnt critical. as you say the chemical is used for lowering the ph in swimming pools

the ph plus dosnt work so well. Im sorry but i cant explain why the pickle reacts with the plastic pipe.

hope this helps,         Colin.

Edited By Colin Stewart on 13/03/2012 09:01:54

That's because it's just washing soda sold at a rather inflated price. It won't remove oxides. I just use caustic soda to increase the ph of my pool.

Russell.

As a much retired chemist the following points may help.

1. The pickle used for "calcium deposits" may just have been neutralised so as to be ineffective. Try a fresh diluted solution.

2. The pickle is usually doing two things removing scale - essentially copper oxides - and removing/dissolving flux residues. The oxide should dissolve in any dilute acid, thus hydrochoric,sulphuric or citric will be ok. Sodium Bisulphate (aka Hydogen sulphate) is half neutralised sulphuric acid a should also work OK it is like citric acid a solid which may be more convenient.

3. Nitric acid will also dissolve the scale but even dilute nitric acid will slowly dissolve copper (sulphuric should not).

4. As an aside all acids will remove the zinc from brass leaving it copper coloured

5. Hydrochoric acid is a gas HCl dissolved in water it will tend to escape and attack bare steel and iron intiating serious and rapid rusting. Keep it out of enclosed workshops!

6. What do the elfins allow you to buy in 2012? Even citric acid, from health food shops, has moved under the counter but ask. Hydrochoric acid is sold as patio cleaner. Strongish Sulphuric acid is I guess still available as battery acid and will need carefully diluting acid to water. (pure concentrated 98% ,an oily dense liquid, is probably difficult to obtain and would need very careful diluting as adding the concentrated acid to water generates enough heat to boil the mixture if done too rapidly, AVOID)

Citric acid has gone "under the counter" because it can be used to "cut" other more illegal substances.

Thanks guys - I have plenty of lime stone to neutralise the hydrochloric and start again with sulphuric acid.

You can still get most strong acids from jewellery trade suppliers. You may have to tell them what you want it for, but "pickling" or "metal etching" should be quite acceptable.

Cold sulphuric acid won't attack copper, but it will if hot. I would advise you not to have hydrochloric acid or nitric acid in your workshop - the fumes from either will rapidly corrode steel (and many other things) and even in a sealed bottle some seems to escape. Sulphuric acid is no problem, at least in the fumes aspect. However, if diluting it, NEVER add water to sulphuric acid*; always add the acid to water, very slowly and stirring constantly; it will get very hot. My advice would be, if you are not experienced in handling it, use something else. Sodium bisulphate or citric acid will both do the job, more slowly but with much less risk.

*The reason for this oft-quoted warning is that the acid is much denser than water, and adding water to the acid leaves the water sitting on top. This generates intense heat at the junction, which is highly likely to crack the glass and spatter hot acid all over you. Even in a non-glass container, much spitting of hot acid into you face is likely. You have been warned!

David

Edited By David Littlewood on 13/03/2012 17:24:33

You should be able to get hold of sulphuric acid at a builer's merchant, sold as drain cleaner. Some drain cleaners are however caustic soda so read the label. Dilute it to about 5% (up to 10% in cold weather) but remember to always add the acid to the water NEVER the other way round.

Russell.

Edited By russell eberhardt on 13/03/2012 20:52:54

The phosphonic acid commercial kitchen descaler I've been using works wonders. Almost instant rsults used neat but I ended up diluting the getting tired solution about 10:1 for some larger parts which made it a lot less agressive but it's still doing a good job on steel, copper and brass over about 1/4-1/2 hour.

Neil

Citric acid is freely available and has not 'gone under the counter', I regularly buy from my local pharmacist or homebrew store in the UK. Try eBay you can buy as much as you like and it makes a great pickle for copper.

If anyone wanted it for 'illegal substances' they could just squeeze a few lemons

T

Edited By Terryd on 14/03/2012 21:52:56

Neil,

I think you meant "phosphoric acid" - H3PO4 - just in case anyone tries a search.

David

Terryd.....I think that what KWIL meant was that citric acid has been used by drug dealers to bulk out controlled drugs thereby making their already lucrative trade even more profitable. But thereagain drugs have been bulked out with everything from glucose powder to brick dust and there is no sign of these going under the counter. I must say that I find this self imposed, jobsworth type, petty regulation somewhat tiresome. I was once told by a Boots pharmacist that he could not sell me copper sulphate in case I was a terrorist (perhaps Pensioners' Liberation Army) and wanted to make a bomb with it !!!!!! At the same branch I had to do a covert deal "under the counter" to buy some hypodermic syringes after some interrogation as to whether I was a junkie. I bought some copper sulphate at a garden centre (can't say where in case the urban terrorists are tuned in) and got some extra syringes at a car boot sale (can't say where in case the junkies get in on it). Of course there is nothing illegal about buying these things which should be freely available. In fact if I were a junkie, needles and syringes are freely available at drop-in points.

Amonium sulphate is the the one I think of in relation to bomb making, you get that at the garden shop, the price there is highly inflated, about $NZ 1 per Kg. You can get the citric acid there too, or at an agricultural supply store ( how many tonne did you need), I get mine from the home brew shop. Ian S C

Hi Mark,

Citric acid is not used to 'bulk out' drugs but to help dissolve heroin for injection as that drug is not soluble in water. Lemon juice or even vinegar can be used to acidify the drug for dissolving. Citric acid is preferred due to the possible impurities in juice etc but a desperate addict will resort to anything. The possibility of use of impure acids is the reason that citric acid is not banned as otherwise addicts will use such substances with possibly lethal effect.

It may be that citric acid is pre-added to heroin for those who inject, but it is not for 'bulking out'

Best regards

Terry

Ammonium sulphate is not an explosive, but ammonium nitrate is. It was used in vast quantities in the two world wars, either alone or mixed with aluminium powder ("Amatol" IIRC) and is used today in the oil and mining industries mixed with fuel oil (ANFO).

David

PS could someone please tell the web "designer" to stop this thing automatically changing " followed by ) into a bloody smiley.

Edited By David Littlewood on 15/03/2012 11:45:54

I buy both caustic soda and hydrochloric acid from my local hardware shop in Fenny Stratford. Both chemicals are supplied by Challs International of Ipswich www.challs.com

The hydrochoric acic is sold in 500ml plasitc bottles as " MAX super strength acid cleaner - spirit of salts" I have used this satisfactorily for pickling steel and brass items.

The caustic soda is in the form of pure granules and is sold in a 500g plastic bottle as "MAX strength caustic soda"

Caustic soda (sodium hdroxide) is utterly useless for pickling purposes. It is also highly dangerous to eyes - it will cause permanent damage to eyesight a lot faster than will strong acid. Adding to water generates a lot of heat, which can cause the solution to boil and spit. Avoid, unless you know what you are doing.

David

Hi try one shot from ebay it works well item no 190590736450 it is only £4.50 plus £6.00 PP but take care with it.

TY Kevin

Edited By Kevin Bennett on 15/03/2012 12:46:32

Sorry David, my mistake, you'r quite right about the ammonium nitrate, although going by a list on google the sulphate well could be as are a lot of unlikely chemicals. Ian S C    sulphate of ammonia, one of the components of a good stink bomb

Edited By Ian S C on 15/03/2012 13:37:32