I want to do some anodising, and I am trying to locate a source of sulphuric acid. Battery acid would probably be the easiest way to get hold of it, but all the car part places around me say that they aren't allowed to stock it any more because it is a restricted substance. Curiously, despite being restricted, I can still buy it mail order and have it sent to me through the post
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I can I want to avoid the postage charge for mail order (the cost of the acid is less than the P+P) so does anyone know of any other place that would stock sulphuric acid?
A plating works, I should think. My next door neighbour is involved with one, and they have it. They also do anodising, and have all sorts of people coming in off the street to have little jobs done, and often, they are able to chuck it in with a commercial job, so payment is a few quid for the tea money jar. If you have such a works anywhere nearby, might be worth you giving them a bell, just to ask ... ??
You could try any big builders merchants and look at drain cleaners. Some are sulphuric acid others sodium hydroxide.
Anodising is fiddly. Unless you really want to d-i-y or you have a lot to do or an odd colour it may be worth just asking a local anodiser. I had all the parts for a microscope black anodised by a local works for £10 - less than it would have cost me to set up and do it myself.
Liquid drain cleaner. The acidic ones for unblocking drains are conc. (96%) sulphuric. Just check that it's not either alkaline / basic sodium hydroxide, and that it's not a limescale shifter based on sulphamic or formic acids. Mine (for electroplating) costs me about =A36 / litre and is available from the local hardware shop. It's not hard to find.
Aluminium is a faff to anodise and you might prefer to start with titanium, which is _far_ easier. Use Pepsi as an electrolyte and a variac (with rectification), or else a variable bench PSU that goes to fairly high output voltages.
Thanks for your replies. I'll try the drain cleaner approach.
The closest anodising firm to me is about 15 miles away, and the one time I did go to them they made a mess of one of my parts, and lost another, so I'm not going back there. And yes, titanium may be easier to anodise, but not to machine in the first place!
Liquid drain cleaner. The acidic ones for unblocking drains are conc. (96%) sulphuric. Just check that it's not either alkaline / basic sodium hydroxide, and that it's not a limescale shifter based on sulphamic or formic acids. Mine (for electroplating) costs me about £6 / litre and is available from the local hardware shop. It's not hard to find.
Aluminium is a faff to anodise and you might prefer to start with titanium, which is _far_ easier. Use Pepsi as an electrolyte and a variac (with rectification), or else a variable bench PSU that goes to fairly high output voltages.
A bit vague on the details as it was some years ago that I used to maintain the baths on an anodising plant, but you may find that it is the current that defeats you. You have to have the requisite amount of amps per square metre of surface to be anodised. At home, I could only manage pieces up to a few inches with the battery chargers I had to hand. In our baths we had aluminium girder bus bars that typically took 1500 amp at 12-15 volt. Quite spectacular when one day I happened to drop an aluminium step ladder across them!
Also, you might note that the new coating has to be sealed - typically by boiling in water to make the oxide swell and become less porous. It is this swelling that seals in the various colours you see in saucepan lids for example - the dye being added to the sealing water bath. (We also sealed our printing plates with a chemical solution, but it was nasty stuff, so boiling water is your best bet. That said, I did some of my motorcycle parts boiling in candle wax, and they came out quite nice too.) The water has to be very clean (distilled or deionised) or the coating gets stained/smeared.
Another thing you should note, is that the colour you get depends on the alloy. Most 'aluminium' is actually an alloy with magnesium 'Magalloy' (has a pinkish/bluish tinge), but there is an enormous range of alloys for different applications. These in turn have different sized crystals depending on how they were made and heat treated or cast. The anodising current picks out all the imperfections and crystal boundaries, and the different alloying metals make oxides of varying colours. Result is, you never know quite what you are going to get. Sometimes you get a lovely pattern of big crystals: sometimes you get black (my bike bits came out a nice stony green/black).
Also, the existing oxide on the metal is best removed first - which we did by dipping in well agitated caustic soda solution.
Thus there are lots of ways for this to go 'wrong', but all of them produce interesting results. Just perhaps not what you are after!
I think that's what the farmers up here use it to spray the potato haulms, to kill them off. D'you know any farmers? Farm supply companies might be an alternative.
Trouble is, it's not sulphuric acid but a solution of that and lead sulphate. Don't know how the lead would affect the anodising process, but it would make disposal of the used experimental solutions a problematical issue that you don't want to get into.
S
(PS appols for the confusing joining of Andy Dingley's comment and my added remark in the other thread branch. Don't know how I managed that!)
The suppliers I used to use all the time seem to have largely vanished since I was a lab tech, but here is one:
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at their remarks on how this acid can be used, I would say it is definitely a case of buyer beware. If you were to make for example a chromic acid solution - this used to be a common anodising and plating method - you would have the water board round like a shot if even the tiniest amount got into the drains, and risking some pretty nasty (REALLY) nasty burns in the process.
Our anodising baths were run at around 15% v/v sulphuric.
Battery acid is only about 33% sulphuric and 67% water. You're better off buying the 97% proof stuff with a specific gravity of 1.84. You can dilute that if required.
No end of online suppliers in Google but any local chemical supply or laboratory equipment supply company should be able to sell you it. Try yell.com.
Chromic acid used to be the way to do it, sadly the bloody environmentalists whinge about the toxicity.
You need approximately 15% sulphuric acid (i.e. dilute "battery acid"
50:50 with deionised water). Battery acid i bulk is quite cheap, about £1 per litre. Your problem is that it's a strong acid and expensive to transport which bumps up the price for small quantities.
Don't even begin to think of using old battery acid. The concentration varies and it is contaminated with lead and other gunk which will mess up your attempts to anodise. You should be able to get new battery acid at any half-way decent car parts store.
If you haven't already seen it, this site is good.
Bit of a word of caution to the OP about diluting conc sulphuric acid: the act of hydration causes heat to be liberated - plenty of it. The WRONG way to do this is to add water to acid, which can result in almost instantaneous boiling and ejection of water and acid.
The accepted way - in my day - was to slowly add the acid to the water, with plenty of stirring with e.g. a glass rod. Even so, the solution will get warm. The OP will need to read up more on this.
Modern precautions would probably include a moon suit, licensed premises, Building Control notification, Planning Permission, certificated training, a Part P inspection, Environmental Health clearance, a trained medical team on standby, a raid by anti-terrorist police, and Social Services taking away your kids. Only joking.
"Environmentalists whinge about the toxicity [of chromium compounds]"
If you call this "whinging", then you ain't much of a chemist. There's plenty of whinging out there, but caution around chromium isn't unreasonable, no matter what the valency.
(I've had self-inflicted acute chromium poisoning myself, from plasma- cutting stainless. I don't recommend it).
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