Newbie Help (No Results :( ).

[PhilM]

Hiya folks, hopefully you can shed some light on my problems.

I have the following setup;

2ltrs Battery Acid to 5ltrs Deionised water.
Aluminium Wire (v thin, 1mm diamter)
2018 aluminium test peices (1inx4in)
0-16v Rectifier (40A continuous max)
8x8 in aluminium cathode


Okay. Here what i do from the start.

The peices of aluminium to be anodised are firstly cleaned with detergent and then rinsed, and dipped for 5mins in Caustic Soloution (Sodium Hydroxide).

In the Caustic soloution, it bubbles after a minute or so and fizzes away nicely. When i remove the ally from this, it gos from being bright finish, to an almost white looking one.

My aim for this caustic dip is to have it clean up any oxide layer that may be on the aluminium beforehand.

I then place the aluminium test peice in the anodis bath.......volatge is set to 15V and the current on the meter is 0.4A. (Bath is approx 10DegC)

I tap in the surface area and amp reading into the calultors and it says 120mins.

After a bit the cathode has lots of bubbles all over it (small ones), Ammeter is still reading 0.4A. The cathode also appears to have gone a bleached whiteish colour where its been in the acid.

After 2hrs, its still bubbling away slowly on the cathode, the ammeter still reads 0.4A, and i remve the test peice of ally....its a whiteish kind of colour, i rinse it in water quickly (dip), and then submerge in the dye bath (about 20-30degC) for 15mins.

I remove the peice from the dye and it looks just the same as it did before it went into the anodise bath/the ye bath...nothings changed, not even the wire has taken dye .

Im in dispare! Can anyone give me any pointers or see any errors?

Many thanks!

[acidrain]

Well, your current density is way low. It seems you have placed the decimal point in the wrong place.
Check you calculations and try again!

[PhilM]

The thing is with that mate, my rectifier is only CV. So i set to max voltage 15.8V and the part is connected and only 0.4A reads.

However if the copper croc clip touches the acid then i get 25A or so passing through.....its when I have the ally part connected to the power supply that i get next to no current passing .

I am concerned about the oxide layer, if this is still present (after the caustic dip) then that may explain why my current is too low, as its essentially an insulator rather than a conductor!.

Anyone able to shed any light on this?

[scocklin]

I’ll try to go over what you have done and compare it to what the Caswell manual says.

First off you said you washed it in detergent, did you use a professional cleaner such as the SP degreaser? I usually do a pre wash using simple green cleaner and than I dip the part in hot SP degreaser for about 5 minutes. I check it by giving it the water break test. You must insure that the part is absolutely clean, grease and dirt free. Your anodized coating will not grow over grease or dirt.

Sodium Hydroxide is used for stripping the anodized coating off of aluminum. If you want to de-oxidize the aluminum you should use a professional de-oxidizer & de-smut solution. It is a Ferric and Sulfuric acid solution that needs to be diluted with distilled water. Caswell sells the solution with instructions on how to use it.

Are the Aluminum anodes free of any coatings? Do an ohm check across the surface of the anodes to insure that it is only metal on the outside.

The test piece is a piece of aluminum alloy 1 inch x 4 inches in size. That is 4 square inches per side or a total of 8 square inches not counting the thickness which I assume is minimal, 1/8 inch or so?

I’m not sure if you’re using 4.5 Amps per Square Foot or 6 Amps per Square Foot, but we will figure out your current density using 6 ASF.

144 square inches in a square foot = 6 ASF / 144 = 0.0416 amps per square inch.

0.0416 X 8 square inches = .3 amps (decimal point 3 amps) about a third of an amp current density.

Can you set your constant current power supply down to .3 amps? If so you should anodize you aluminum piece any ware from 90 minutes to 120 minutes depending on the coating thickness you’re going for. (720 Rule)

I’m looking at your voltage; 15V looks high. Are you sure your CD (current density) is set to .4 amps?

If you’re seeing a lot of bubbles you’re making hydrogen and probably have your current density set too high. Also you should be using agitation to knock the bubbles off of the aluminum piece. The hydrogen bubbles sticking to the surface of the aluminum will interfere with the anodized coating you are trying to grow if they are allowed to remain on the metal.

A good constant current power supply might solve your problems.

I almost forgot, the battery acid to distilled water ratio for LCD anodizing is 3 parts distilled water to 1 part battery acid. Is that what you have?

How have you connected your aluminum part to the power supply? Connections are most troublesome, read the sticky on “The Importance of Good Connections”

[acidrain]

Oops, my bad. I didn't read your first post thoroughly, and thought you were using a 8x8 inch anode.

Seems Scoclin has given you great advise.

One thing that cought my eye in your post was the description of bubbling cathode. Is it possible that you have the polarity reversed (should be positive to anode).

How about the dye you are using. It seams the current setting is a bit high, but withing working perameters, and all things considered, should be building a coating. Is it posible the dye you are using is not appropriate?

[PhilM]

Thanks guys!

I worked oiut the problem and it eas the elctrolyte (9%).

I have now changed this to 25% soloution and it works fine, I get decent current now.

I do get small bubbles (lots of tiny ones) on the cathode plate, polarity is correct however!

I have now since anodised sucessfully a few peices of ally and its working a treat.

Many thanks!

Phil

[Fibergeek]

Acidrain and Scocklin, good job!