Author Topic: Anodizing aluminium without battery acid (Read 53663 times)

jcs0001 · « **on:** October 28, 2011, 08:45:05 AM »

I came across this link on another forum and thoughsodium hydrogen sulfate and is used to lower the ph in home swimming poolst it may be of use. Haven't tried it yet but likely will. In our area battery acid isn't the easiest substance to get so this may be more convenient.

http://www.observationsblog.com/4/post/2011/10/anodizing-and-dying-aluminum-without-battery-acid.html

This method uses sodium hydrogen sulfate which is used to lower the ph in home swimming pools. I haven't sourced it yet but with all the pools in our area I expect it will be easy to come by.

John.

Lew_Merrick_PE · « **Reply #1 on:** October 28, 2011, 11:09:02 AM »

John -- In my area of the world (USA, Pacific Northwest), 5 gal of sulfuric acid runs about $40 at any primary auto supply house (NAPA or other mechanic's part supply house -- not the DIY mechanic's supply houses). If they do not know you, they are likely to require you to sign a waiver stating that you know how to handle and dispose of acid. I use it all the time for passivating stainless steel.

andyf · « **Reply #2 on:** October 28, 2011, 12:07:14 PM »

Hi John,

Hitherto, I have used sulphuric acid for what little anodising I have done. That method looks worth a try and must be safer, though I'm not sure if that particular chemical will be as readily available in the UK. Home swimming pools are rarer here - the weather is a bit against us. Battery acid is hard to find in these days of sealed batteries, but the acid from the dead ones I got for £0.00 from the local tyre/battery shop seems to work perfectly well.

Andy

Rob.Wilson · « **Reply #3 on:** October 28, 2011, 03:03:32 PM »

Hi John ,,,,,,, thanks for posting the link ,,,,,, very interesting

Rob

raynerd · « **Reply #4 on:** October 28, 2011, 07:24:56 PM »

Nice write up, I`ll be giving that a go next week and will let you know how it goes!

jcs0001 · « **Reply #5 on:** October 30, 2011, 01:08:56 PM »

Gentlemen:

Thanks for the replies. I must admit I didn't look too hard locally for sulphuric acid - one of our auto stores did say they could get it in small quantities but the price was high. Our local recycle yard (metal) gets lots of old lead acid batteries in but won't resell or allow any fiddling with them (likely liability concerns).

I look forward to next week's test results.

John.

andyf · « **Reply #6 on:** October 30, 2011, 01:31:16 PM »

Little Timmy took a drink,
But he will drink no more,
For what he thought was H₂O,
Was H₂SO₄.

Different nations have different attitudes to Health'n'Safety. I visit a town in France several times a year, where the local self-service hardware store has 2 litre glass bottles of all sorts of evil chemicals, including sulphuric acid, lined up on its shelves for kids to knock over and break.
Here in the UK, that would cause no end of trouble from those who take it on themselves to tell us what is good and bad for us.

Do let us know how you get on with the safer stuff.

Andy

Doc · « **Reply #7 on:** November 29, 2011, 08:25:45 PM »

After reading this I thought I would give it a try with some of the acid we use in the hot tub "sodium bisulfate"
I didn't clean the part real well and just used a quart jar and mixed some up and hooked up a small part I had laying there.
I put it in hooked up had the power source at 7 amps but didn't register much on the amp gauge. I left it in there for about 45 minutes. Then took it out warm water rinse and put it into some dye mix I left it in the dye about 4 minutes. Anyway this is what I got.
Next time I'll try if on some stuff I want to actually anodize instead of just a test piece plus do a proper degrease and clean.

andyf · « **Reply #8 on:** November 30, 2011, 03:52:11 AM »

That looks pretty good for a quickie test piece, George. I'm not sure if you boiled/steamed it afterwards to close the pores and seal in the dye, but apparently that's what you're supposed to do. The results from my attempts at dyeing can best be described as patchy compared to yours.

A weak solution of sodium hydroxide (aka caustic soda or lye) acts as a pretty good final cleaner before anodising. It shifts fingermarks. The aluminium fizzes a bit and comes out with a satin surface, but you would have to leave it fizzing for a very long time to materially affect the dimensions of the part.

Andy

Doc · « **Reply #9 on:** November 30, 2011, 10:23:57 AM »

Boiling water bath to seal, it took dye pretty good except where I had finger prints actually a little on the dark side need to back off on time in the dye solution. But this was just to see if the sodium bisulfate would work as a substitute and my answer right now would be yes.

fatal-exception · « **Reply #10 on:** December 02, 2011, 04:54:17 PM »

So the question is how durable is the finish? Is it brittle like proper anodizing? Is it non conductive? After your hot water sealing, could you still wipe off the dye?

Even if you are just doing test pieces, you should really pretend like you are doing a part that you spent a ton of time machining. You won't learn a whole lot about how good your method is if the part is not prepared properly.

Caustic soda (lye crystals) will strip old anodizing off with ease. Depending on how strong you mix it, it can completely dissolve an aluminum part quickly. The vapor given off is flammable. I wouldn't recommend it for cleaning your part before anodizing. That being said, you can do it the hard way using soap and water and rinsing and all that jazz, or you can spend 5 bucks on a can of brake cleaner and have your part extremely clean and ready for the acid bath in a few seconds. (brake cleaner is an amazing degreaser!

)

I was lucky a few years ago and got a 5 gallon bag of battery acid that was not diluted for about 10 bucks. (I don't think the guy knew what it was worth.) They were getting out of the battery refilling business. I mixed up about 2 gallons with water and have been using the same bath since then. i guess what I'm saying is that the battery acid bath lasts a long time. It's worth it to get the 'right stuff' in my opinion, as it's a tired and true method with professional results.

Here's the swatches of my premixed dyes:

and the largest plates I've done:

AdeV · « **Reply #11 on:** December 02, 2011, 04:57:23 PM »

Quote from: fatal-exception on December 02, 2011, 04:54:17 PM

... or you can spend 5 bucks on a can of brake cleaner and have your part extremely clean and ready for the acid bath in a few seconds. (brake cleaner is an amazing degreaser! )

A quick question - is brake cleaner safe on Ali parts? I need to clean up my BMW sump & I'm thinking there must be something better than Petrol (gasoline) to do it with...

fatal-exception · « **Reply #12 on:** December 02, 2011, 05:01:39 PM »

Quote

A quick question - is brake cleaner safe on Ali parts? I need to clean up my BMW sump & I'm thinking there must be something better than Petrol (gasoline) to do it with...

Absolutely!

The parts above were cleaned with it prior to anodizing.

BTW, your sump project is awesome. I spent a whole afternoon at work one day reading about it.

andyf · « **Reply #13 on:** December 02, 2011, 05:09:19 PM »

Ade, how about colour anodising your sump, to impress the spectators when you roll the car?

Andy

Bluechip · « **Reply #14 on:** December 02, 2011, 05:45:39 PM »

Quote from: andyf on December 02, 2011, 05:09:19 PM

Ade, how about colour anodising your sump, to impress the spectators when you roll the car?

Andy

Ade, that's a splendid idea from Andy.

I think you should give it some serious consideration.
And while you're at it, anodise the roof.
Thereby impressing any spectators under the car ...

BC

AdeV · « **Reply #15 on:** December 02, 2011, 07:09:17 PM »

Quote from: andyf on December 02, 2011, 05:09:19 PM

Ade, how about colour anodising your sump, to impress the spectators when you roll the car?

Quote from: Bluechip on December 02, 2011, 05:45:39 PM

Ade, that's a splendid idea from Andy.
I think you should give it some serious consideration.
And while you're at it, anodise the roof.
Thereby impressing any spectators under the car ...

Unfortunately, the roof is steel, will have to go with a fancy paint effect! Mind you, any spectators under a rolled car will have other things on their mind, e.g. the craftsmanship that went into removing the sunroof (it's got a sheet of tin riveted over the hole) and the remarkable snowplough on the front which, there's a good chance, has just removed their legs

I do like the idea of anodizing it. I've got a couple of knackered car batteries, would it be sensible to use that as the acid, or should I shell out on the proper stuff?

More importantly, what colour??? I can think of red (common), blue (nicer IMHO, but still common), gold (a bit blingy perhaps), green (eco-special V8

)....?

Although it's cut out of ali, there is one steel insert (the threaded bar that holds one of the plugs in), I don't want that to vanish in whatever solution(s) I use.

If I'm going to anodize, I'd like to do it before I skim the top (that bit won't be seen anyway, and I just prefer the idea of it being bare ali).

andyf · « **Reply #16 on:** December 02, 2011, 07:32:00 PM »

Acid from old batteries diluted with the same volume of tap water works OK for me, Ade. You may need more than a couple of batteries to get enough for immersion, though. And I doubt it would do the steel plug much good, though you could probably paint that with some sort of resist.

The major hurdle might be the current required. I've read figures like "between 30 and 300 amps per square metre". I've no idea of the surface area of the outside of your sump, but you may need a pretty hefty PSU for the job.

Andy

PS It might be easiest to contract out the anodising.

AdeV · « **Reply #17 on:** December 02, 2011, 07:40:27 PM »

I have a 350amp battery booster, trouble is i can only run it at that level for 10 seconds in every 60...

AdeV · « **Reply #18 on:** December 02, 2011, 07:52:54 PM »

Quote from: andyf on October 28, 2011, 12:07:14 PM

Hitherto, I have used sulphuric acid for what little anodising I have done. That method looks worth a try and must be safer

Andy, from the write-up, I'm not convinced it will be any safer. He quotes a 20% solution of Sodium Bisulphate, with a Ph of between 1 & 2 - well, that's about the same as Sulphuric! Ph 1 is about as acidic as it gets, and Ph2 is not far behind. Ph 7, of course, is (roughly) human acidity (hmm, some may be more acidic than others) & on down to Ph 14 for the alkalines.

Brought to you by GCSE Chemistry, 1989 style. Since I pretty much failed Chemistry at A-level (follow-on from GCSE), there's a damn good chance the above is completely wrong! But either way, I wouldn't stick my hand in either solution!

Doc · « **Reply #19 on:** December 02, 2011, 08:36:59 PM »

Quote from: fatal-exception on December 02, 2011, 04:54:17 PM

So the question is how durable is the finish? Is it brittle like proper anodizing? Is it non conductive? After your hot water sealing, could you still wipe off the dye?

No you can not wipe off the dye and yes it does have the hard like crust.

Quote

Even if you are just doing test pieces, you should really pretend like you are doing a part that you spent a ton of time machining. You won't learn a whole lot about how good your method is if the part is not prepared properly.

I agree before I do any machined parts it will get tested correctly I only did a quick test just to see if it would work at all and I did get an answer to that question.

jcs0001 · « **Reply #20 on:** December 08, 2011, 05:38:46 PM »

Doc:

Thanks for doing the experiment and posting the results. I haven't used either method but it is great to see that there are at least a couple of choices. Perhaps when the weather warms up I will give it a try.

John.

Aaronpifow · « **Reply #21 on:** September 10, 2017, 04:03:45 PM »

Hi there.

Im about to try my hand at diy anodizing. I was wondering if anyone knew a good source of sulphuric acid. I tried bunnings today, with little luck.

Ill try supercheap auto for car battery top up liquid, but other than that, Im out of ideas.

Has anybody tried this before? Will car battery acid be strongpure enough?

awemawson · « **Reply #22 on:** September 10, 2017, 04:26:03 PM »

Battery 'top up liquid' is distilled water - you need battery acid as used to initially fill a new battery

AdeV · « **Reply #23 on:** September 10, 2017, 08:06:40 PM »

Quote from: Aaronpifow on September 10, 2017, 04:03:45 PM

Hi there.

Im about to try my hand at diy anodizing. I was wondering if anyone knew a good source of sulphuric acid. I tried bunnings today, with little luck.

Ill try supercheap auto for car battery top up liquid, but other than that, Im out of ideas.

Has anybody tried this before? Will car battery acid be strongpure enough?

Sulphuric acid disappeared off UK shelves a while ago (I don't know when), but it still easily available mail order - try eBay, Amazon, or just google for suppliers (there are many). I bought some 98% concentrated sulphuric a while back, mainly to guard against it becoming unobtainuim (apart from in used car batteries, which will be highly contaminated with lead, and other chemicals no doubt). Be aware that concentrated sulphuric is very nasty stuff indeed (although not quite as deadly as fuming nitric acid, or the real nasty hydroflouric acid - which tends to soak straight through the skin & starts attacking the internal bits of the body).

Anyway, warnings aside... fresh battery acid (around 28-32% concentrated) would, I'm sure, be plenty strong enough for anodising aluminium. You may even want to dilute it further... This page may contain some useful info (I only read a bit).

SwarfnStuff · « **Reply #24 on:** September 11, 2017, 03:56:47 AM »

My 2c worth on pH as mentioned above.
If you check the pH of a can of coke (phosphoric acid) or for that matter a lemon (citric acid) you will get a pH in the 2.5 - 2 range from memory.

Point is, pH is not the problem, the type of acid at these levels definitely is. That said, careful handling of strong acid or strong alkali solutions is always wise.

John B

News:

Author Topic: Anodizing aluminium without battery acid (Read 53663 times)

Rob.Wilson