Sealing

[coyoteboy]

Just a fundamental really - I was under the impression that pore sealing was a thermal operation, not a chemical one. But then that doesnt follow or we wouldn't seal in a liquid, we'd just stick them in the oven. Anyone care to enlighten me? I'm aware the sealing additives aid the process but how?

[mkriegs]

I've heard of sealing by just boiling parts in water for 30 minutes but I'm not sure how well that works.

[acidrain]

Actually, hanging in live steam is a good option.
If you submerge in boiling water, the dye may leach out a bit.

[coyoteboy]

I currently seal with boiling water no problems, i seem to get a nice colour fast surface with about 10-15 minutes in a boiling tank. However since it seems it has nothing to do with being a) out of the air or b) in water, I would have thought you could just throw the item in an oven instead - heating an oven to 100 C or more takes a lot less energy than heating a pan of water to 100C and holding it there for a long period.

? I might try it for the sake of experimentation.

[chromo]

If you try just baking the parts for sealing it would be great to know if that works as well as boiling or other methodes.
Would remove a tank from the anodize setups (save room and other stuff) and get more use from a powder coat oven if it works as well.
For those doing both types work this would be a good thing.

[LOON]

I think water or at least steam is essential....you need it to get a chemical reaction...no water - no hydrates...

just my 2 cents

[dedalus]

Sealing is a chemical reaction that's best done by immersion.

When a part is anodized, there's a layer of oxide produced on the surface. Since this oxide doesn't conduct electricity, the underlying metal maintains contact with the solution by means of a series of pores in the oxide coating. If you dye your anodized aluminium, that's where the dye goes - in those pores.

Before you put the workpiece in service, those pores have to be sealed, or the coating will fail a lot sooner. A seal solution contains chemicals that precipitate inside them.

Though, I understand that you can also seal anodized parts in very hot, plain water. I'm not sure how that works.

[coyoteboy]

Yeah, im aware that the dye sits in the pores and that sealing closes the pores, and that the chemical methods precipitate into the pores to close them, however the point i was confused about was whether the hot-water (and some say steam too) method precipitates anything (if so, what) and if not is it a thermal process?

[sswee]

It's primarily a thermal process. The sealers aid in the process and have additional benefits.
SS

[luminous]

It takes more than heat. It needs moisture to complete the chemical process that seals the pores.

Here's a short snippet from a very good article on anodizing:

"For clear coatings, sealing in boiling deionized water converts the amorphous form of aluminum oxide to a more stable crystalline hydrate form.
This reaction tends to “plug” and “cap” the oxide pores. Dyed anodized aluminum requires specialized sealing in nickel acetate, to prevent bleeding and to improve light fastness."

The rest of the article (8 page PDF) is here:
http://www.p2pays.org/ref/02/01433.pdf
I found it to be a worthy read...


steve