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"Anodizing titanium with trisodium phosphate (TSP)"



Current question:

September 14, 2021

Q. I wanted to perform a test to check the consistency of "bulk" anodized titanium parts in our line vs "pan" anodizing. Basically we anodize some very small titanium parts (Grade 23) and we don't have a great racking solution for them so we do them in a a small tabletop pan full of TSP solution. To test the production line I mounted a cheap titanium (grade 2) tea strainer I found online to a grade 23 rod attached to a copper hook so we could use it in our production line. Both used the same TSP solution and were both at the same temperature 68°F. The thing that is confusing me is the line took significantly longer for the parts to anodize. The parts done in the pan were done at right around a minute but the parts done in the line took almost 7 minutes to reach the final color. I would expect the line to have higher amperage as there is a lot more surface area with the basket but what I don't understand is why the time was so much longer given the voltages and solution were the same? Both produced acceptable results on all the parts but I'm stumped on why it took so much longer in the line than the pan?

Parts: Small Grade 23 Screws
Quantity: 30

Pan:
Tank Size: 2 gallons
Target Voltage: 26.5V
Voltage Ramp Rate: 0.5 V/s
Total Time: 1 minute
Max Amps Reached: 1.1A
End Amps: 0.02A
Anode: Niobium Rod "Magic Wand"

Line:
Tank Size: 30 gallons
Target Voltage: 26.5V
Ramp Time 0-Target: 2 minutes
Hold Time: 5 minutes
Total Time: 7 minutes
Max Amps Reached: 6A
End Amps: 1A
Anode: Grade 2 titanium basket, Grade 23 titanium rod, copper hook.

Scott Bruins
- Lakeville Minnesota
^


September 2021

A. Hi Scott. Although I don't know exactly how to account for the time difference in your two scenarios, I remain confident that Faraday's Law holds in this case and all cases.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^




Closely related Q&A's, oldest first:

Q. I'm curious about the safety of anodizing titanium in a weak trisodium phosphate [affil. link to info/product on Amazon] solution, using a home-built 0-180 vdc variable power supply I made for artwork & jewelry purposes.

The power supply is safe and short-protected, and I use it in a safe way, but after skimming through the plating FAQ's I'm concerned about chemistry/fumes issues, of which I'm ignorant.

1. Does the cathode metal matter safety-wise? I can get good results from any--usually I use a strip of copper. Have used fine silver, aluminum, and titanium also.

2. If I quickly insert a part with the voltage up high, I can see a tiny stream of either gas or steam. Which is it, and is it safe?

3. Is it safe to leave a jar of weak trisodium phosphate out in the open?

4. I took a tiny (1 sq cm) piece of brass and used it for the anode instead of titanium. The result was some gleaming bright green stuff in the water, and a very nice orange patina to the brass. The cathode was copper. I would like the orange patina for certain jewelry but will only use it if it's safe. Was I plating copper onto the brass somehow? I had done a lot of titanium anodizing in the same solution using a copper cathode beforehand. I'm using copper clips which end up in the solution a lot, also.

Interesting web site, lots of fun reading...

Sincerely,

Joe DavissonJoe Davisson signature
Joe Davisson
St. Louis, Missouri
^


A. If I were you, I'd still be most concerned about your home-built 180 VDC power supply, as that is way more than adequate to kill you if you didn't design and construct it properly.

1. Trisodium phosphate is a pretty mild chemical; I can't foresee any violent reaction with copper, silver, aluminum, or titanium.

2. What is the gas? Probably hydrogen. Depending on pH and other conditions, water separates into 2 parts hydrogen and 1 part oxygen, or 1 part hydrogen and one part OH-

3. Again, trisodium phosphate is a pretty mild chemical, not much different than cola. But there is probably metal dissolved in the solution, so it's somewhat poisonous. Is it safe to leave an open container out? Well, is it safe to leave an open bottle of aspirin out in the open? Yes if you're the only one around; no if there's a toddler about.

4. Ionized copper is normally blue rather than green, still the color is probably coming from the copper. No, you certainly weren't plating copper onto an anode! You were probably oxidizing the brass, and perhaps surface enriching it by leaching out some of the zinc.

As you probably know, you ask for reassurance that what you are doing is safe, and pose questions where we can't foresee a direct danger. Which leaves us sort of implying: "yeah, that's safe . . . yep, that's safe too . . . uh-huh, no problem with #3 either . . . you're okay with #4, too.

So now you've heard this 4-part mantra of how we see nothing dangerous in what you are doing, and you are probably reassured that you can experiment to your heart's content, although you've acquired no appreciation of the chemistry. So you are right on track to tossing a cup of table salt into your bucket and killing yourself with chlorine gas, or knocking a beaker of solution onto your power supply and lunging for it just as the highly conductive solution runs down into the AC side, or who knows what :-)

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^


1999

A. If you used an isolation transformer in the unit , you are fairly safe. Not everyone can stand the same amount of electricity. 180 V is obviously a lot more dangerous than 6 volts and deserves due caution. Amperage is the other part of electricity killing people. Fuse it or circuit breaker the output side with "quick blow" units and fuse to the minimum amount that you can get by with. TSP is still sold for cleaning before wall papering and was the main ingredient of some detergents until it was found to grow great amounts of algae. I would keep the other metals out of the tank. They are dissolving and you are really into some nasty waste disposal problems. Titanium is non regulated and very very little dissolves when used as a cathode. (or anode) Normally a very well organized and neat line with normal lab practices is safe. Rubber Rubber Gloves [affil. link to info/product on Amazon] and safety glasses. Nothing can save you from stupid mistakes, so follow good practices and enjoy the product.

James Watts
- Navarre, Florida
^


1999

thumbs up sign Yeah, I only anodize titanium using the 'normal' process I learned under supervision years ago. I've seen it repeated over & over again from different sources also, so figured it was safe enough. But I wouldn't recommend that anyone build any power supply unless they have enough experience with them. It's like a hair dryer in the bathtub the whole time when you anodize, and you must treat it as such. Dry, heavy rubber gloves are absolutely mandatory at all times! I also would never have the power supply on while manipulating items. Makes *nice* colors though, I've made chains from one type of titanium and simple rings from another. Beautiful metal with lots of possibilities! Makes it worth the trouble.

Joe DavissonJoe Davisson signature
Joe Davisson
St. Louis, Missouri
^

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