The Shop > Finishing
Anodizing aluminium without battery acid
jcs0001:
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:
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:
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:
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:
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.
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