CV anodizing and electrolyte Titration

[lcaswell]

Re: CV anodizing and electrolyte Titration

Acidrain:

What size bath are you running?

I'm sure you don't need a history lesson, but for those new to this forum, and to hobby anodizing, I would strongly urge you not to attempt CV anodizing on a small scale. The reasons are as follows:

When we first started offering hobby anodizing kits, over 10 years ago, we also used the CV method, because that's all there was, and the results were sometimes good, sometimes bad, offering very little consistency for the customer.

One part would anodize and dye fine, the next part, with the same dimensions, same parameters etc, would turn out completely differently. Trying to get the same color dyed part over a batch of identical parts was next to impossible.

With the help, and infinite wisdom of Fibergeek, we were able to trace the problems mostly to increased/fluctuating bath temperature due to fluctuating current, and the seemingly infinite combinations of current that parts were subjected to during the process. When hobbyist anodizers were anodizing in 5 gallon buckets, rather than large commercial tanks, the bath was unable to dissipate heat fast enough, and the fluctuations in temperature were causing parts to come out with widely differing pore sizes, and subsequently different shades of color. LCD solved this problem.

Is CC/LCD anodizing better than CV? On a small scale, I would say, absolutely yes! For me, the difference in the number of anodizing tech support calls we field speaks volumes. From 10+ a day, to 2-3 a week, and those calls are frequently from customers who have purchased dye from us and are still using CV anodizing in small buckets.

I'm sure that Randy from Absolute Finishes would scoff at the notion of LCD anodizing, as his method is working fine for him, and that's all he's ever known. Fibergeek was laughed at constantly by "professional" anodizers when he would contact them to talk about LCD anodizing. Metal finishers seems to be a real stubborn bunch!

A good question to research would be, at what point (bath size) does CV anodizing become the preferred method over LCD?

I'm interested to see how your experiments turn out, Acidrain.

[acidrain]

Re: CV anodizing and electrolyte Titration

My next experiments will be to take known materials and anodize in CC mode, noting what the voltages are for each.
It doesn't sound right, but Randy says in CV mode, the batch can be mixed alloys. The 7000 series parts will always ano faster, but they do in CC mode too, so it doesn't matter.
Obviously the Profesionals are anodizing at much higher CD's than us LCD guys, but he is running 15v for 1hr or so. My normal voltage for 6000 series is ~13v (at 6A/sq ft.), and I typically run for 1-1/2hr to 2hrs (depending on the thickness desired).
My fear is that if I was anodizing mostly 7000 series parts (unkown at the time) at that high of a CD, something bad would happen.
I guess only experimentation will tell.
I'm sure Fibergeek is rolling over in his grave right now.
The one thing that is absolutely critical in anodizing with this method is that the conditions have to be exact.
Ano bath temp.
Ano bath acid ratio.
Ano bath aluminum content.
Electrical connections.
Any other variables?

[yoyoboy]

Re: CV anodizing and electrolyte Titration

NICE! so how do calculate the time and voltage?

[acidrain]

Re: CV anodizing and electrolyte Titration

Update:
I titrated my tank today, and had some interesting results...
The following method and parameters are for profesional tanks, so I expected the acid concetration of my tank to be less than normal. It was not.
I have never added aluminum sulfate to my tank, so I expected it to be low. It was.
My acid ratio was 122 gr./L... 180 to 200 is prefered.
My alum. ratio was 1.8 gr./L... 10 to 15 is prefered.
Maybe the low aluminum caused a relative high acid reading. I'll try taking a gallon or so of my acid solution, and add the aluminum sulfate, re-titrating this small batch as an experiment.

Here is the method:

Here is what you will need to titrate your anodize tank and keep it within operating parameters.

1. 0-50ml burette (recommend self zeroing burette)
2. 400ml beaker
3. magnetic stir station
4. stir bar
5. bottle of lab grade 1.0 N NaOH reagent (sodium hydroxide)
6. hand help ph meter
7. 0-10ml Pipette (I have one that I can give you.)
8. PH Buffer Solutions to calibrate PH probe. Get a 3.01, 7.01 and 10.01

TITRATION INSTRUCTIONS

1. FILL BURETTE WITH NaOH
2. PIPETTE 5 ML OF ANODIZE BATH INTO 400ML BEAKER
3. ADD 200ML OF DI WATER TO BEAKER
4. PLACE STIR BAR IN BEAKER AND SET ON MAGNETIC STIR STATION
5. PLACE TIP OF PH PROBE INTO BEAKER CAREFULLY AVOIDING CONTACT WITH STIR BAR
6. SLOWLY ADD NaOH TO BEAKER FROM BURETTE. ADD UNTIL PH METER READS 3.6 THEN RECORD READING FROM BURETTE. THIS IS READING A
7. CONTINUE TO ADD NaOH UNTIL A PH OF 8.5 IS REACHED. RECORD NEXT READING FROM BURETTE. DO NOT TOP OFF BURETTE BETWEEN READINGS. THIS IS READING B

CALCULATION

G/L H2SO4 (SULFURIC ACID) = A x 9.8
G/L ALUMINUM: = (B-A) x 1.8

You want your target of g/l of H2SO4 to be between 180-200 g/l
You want your target aluminum to be between 10-15 %

If you’re over 15% remove half of your bath and top off with DI water then re-titrate. If your aluminum content is below 10% calculate how many pounds of aluminum sulfate to add to the bath to bring it back up to 10%.

[acidrain]

Re: CV anodizing and electrolyte Titration

Well, I have all the stuff now, so I'm going to give it a shot.
I'll let you all know how this turns out...

[UFpball7]

Re: CV anodizing and electrolyte Titration

well you helped me earlier so ill try to return the favor. as a chemical engineer i am pretty familiar with titrations. basically there are 2 ways to do them. one is with the ph meter discussed above or you can use a color indicator. the object is to get as close to the equivalence point as you can(add titrant very slowly near end point). the concentration of your titrant must be know. since you are titrating sulfuric acid(H2SO3) you must be carefull when calculating the concentration since it will dissociate into 2 hygrogen ions. if you are using NaOH to titrate it will create 1 OH ion.this reaction is 2:1 stoichiometry. if the aluminum you wish to tritrate is in the same solution this will make things more complicated since the NaOH will react with the aluminum to produce aluminum hydroxyed. this will precipated out of the solution as the solution becomes less acidic. it is hard to cover all the details on a forum. after all it took me an entire semester for it. if you have any questions hopefully i can help.

[sswee]

Re: CV anodizing and electrolyte Titration

Been a while since I read up on it so it's all a little fuzzy. I ran across titration when I was curious about checking acid concentration of an unknown mixture ratio. In a nutshell, you take a specified amount of electrolyte and add increments of a base buffer solution while checking the changes in Ph level. When you neutralize the Ph, you see how much of the buffer it took to get a neutral Ph and calculate the acid concentration. I saw mention of using titration for the aluminum concentration but was cross-eyed by that time and didn't get into it.

Appreciate the info on the CV. It adds a couple more pieces to the puzzle. It fits with the info I had gotten on the subject. Guess I should have paid more attention in chemistry class.
SS

[acidrain]

I've been having in-depth conversations with Randy from Absolute Finishes here in Washington regarding how he has been doing paintball guns at his facility. Let me preface by stating Randy is well respected, designed his own shop, and his services include: Certified Mil Spec Type II, III anodizing, ISO-8080 Titanium anodizing.
Graphic Anodizing Services: Tattoos, Splash, Fade, Acid wash, AnoTat's
Polishing Services: Hand Polish, Electro-polish, AnoBright
Other Services: Teflon Barrel Coatings, TCP-HF Conversion coatings.

He suggested I try CV anodizing. Just set the volts to 15, and let it rip for 1hr to 1 hr, 10min.. I asked about acid concentration, etc., and he says "Oh yeah, you have to Titrate your tank". Hmmm... titrate my tank
OK, so he gives me the entire procedure, and I go buy about $150 worth of equipment and chemicals to test and determine the sulfuric acid and dissolved aluminum concentrations.

I haven't actually performed the test yet (still just trying to figure out how to calibrate my PH meter (it was way off).

Anybody else done this, or even heard of it? It's how he does all his small, irregular parts, and they consistently come out flawless.