Re: Homebrew Anodizing

I don't know squat - but would like to.

I did the draino - battery acid route some time ago and got good results.

Post some links?

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I dunno, but I just got 1,760,000 hits on "how to anodize" on google.

Good Luck! Rich

I just tried "how to anodize" (the phrase) and got 334 hits - but there's a ton of first hand knowledge there.

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Yes, tons of first hand knowledge, but John uses so4 because Jerry used it a couple of months ago because Paul used it a year ago ...

I'd settle for a hearty "it DOESN'T work well" as well as an affirmative answer, but it seems that nobody can give an answer as to why hcl won't work in the stead of h2so4.

Jim

I'm half a chemist, apart from missing those teminally dull lectures and tutorials that had anything to do with the subject......

Anyway, that means you can trust me. Anodizing has got to have something with sticking a layer on it and, since we all know aluminium oxidises, you need some of that oxygen stuff in there to do the job.

Since HCl is H and Cl it looks like it's going to be s*it.

Since H2SO4 smells like it might be bum but has an O4 it's got to be good to go.

All you have to do is sprinkle in the right beetles.

DNA

Yeah, the only problem is HCl will eat aluminum before you manage to apply current...

BTW, H2SO4 is very good for removing broken taps from aluminum.

Well, since there's such a dearth of info about I'd move to the next stage: either it doesn't work, so nobody bothers, or nobody's done the experiment yet, which is an opportunity for you. :-)

Good Luck! Rich

Well, not a chemist but the water in the electrolyte has to be breaking into hydrogen and oxygen while current is applied - no matter what the electrolyte is.

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There you go then. You obviously are a chemist because you deny it so we have to assume you were paying attention and therefore don't know nothing.

QED

The answer is likely about the same as the reason that a mixture of HCl and HNO3 will dissolve gold, but HNO3 alone and HCl alone will not, to any appreciable extent. (I'll pass up the opportunity for a good pun here...)

There are plenty of reference books out there that discuss anodization, both practice and theory. The more interesting topic, to me, is how to dye the anodization layer before it's sealed; but doing a really GOOD job of that seems to involve proprietary dyes. At least, that was my experience with 2024-T3 and black.

T.

Try it, you won't get very far, unless you desire to disassemble your work piece at the atomic level. Both H2SO4 and HCl dissolve Al, but sulfate is much much slower (days as compared to seconds). Purpose of the acid is to minimize solution conductivity, since H2SO4 being a strong acid which means it puts lots of H+ ions in solution, which are the easiest ion in existence to move under an electric field.

So yes, you're right, the sulfate ion is doing squat.

Adam

RST Eng>> I recently posted here about a new method of homebrew anodizing using Drano

Add a little pseudoephedrine and what have you got?

I've also done some anodizing, homestyle, but find this intriguing:

It's a process for producing hard, non-porous ceramic coatings on Al and Ti in a manner similar to anodizing, except that a) high voltages, a.c., are used to produce tiny sparks which produce and fuse the material to the workpiece, and b) the electrolyte is dilute. High voltages allow the production of thick layers by breaking across the thinner, dielectric barrier of the pre-existing layer as it builds.

The above guys are not the only ones with info on the web--multiple outfits seem to have viable processes, though some call it "micro-arcing" instead.

Cheers, James Arthur

Presumably you mean _maximize_ conductivity (or minimize resistance)?

I know that the particular anion of the acid does make a difference in other ways, too. The physical characteristics of the aluminum oxide layer are affected by it (as well as by current density and time, of course). I know that commercially, it at least used to be true that chromic acid was most commonly used for "soft" anodization. Though I used to be a regular customer at an anodization shop, I haven't had any of it done for many years, and haven't paid attention to any changes in the practice, so it may be that now they use something else. Also, I'd be surprised if they didn't add some other things to make a proprietary solution that produces results that are in some ways "better," such as better at taking up their particular dyes, or producing a tighter layer when sealed.

Cheers, Tom

I could also use phosphoric acid as the primer for my students that want to paint instead of anodize their projects, but I can't get phosphoric at FlyByNight Auto Parts. I can get zinc chromate primer and sulphuric (battery) acid there. I can also get hydrochloric (muriatic) acid at HammerThumb Home Store and I use that for PCB etching for their projects. I was hoping to use the muriatic and not have to fill out two hazmat sheets a semester.

Jim

I know that commercially, it at least used to be true that

In James Arthur's post he links to

One of the electrolytes mentioned is oxalic acid - sold commercially, cheaply, for cleaning wood in maritime environments - no haz mat that I'm aware of - bought a jug of it a few years ago and still have plenty. It is a dry powder.

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Yes.

ok, you have corrected me here too. The anion must play a role, even if it doesn't carry much of the solution current. Like most industrial electrochemistry the theory lags behind the practices in the field, and so it becomes an art and not a science, hence the feasibility of secret proprietary blends that customers pay good money for.

Adam

Ospho at Home Depot, or Lowes.

What i do know about it is that there seems to be a oxidization reaction as well as an acid-metal reaction. Some acids are also considered oxidizing (like H2SO4 and HNO3) and some are not (like HCl). I do not expect them to be interchangeable unless something is done to take care of the oxidizing part.