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Anodizing Refractory Metals


#1

Hello.

I am trying to anodize some tantalum and titanium items and I have
not been able to find a good protocol.

  1. What is the ‘friendliest’ method of preparing the surface of
    pieces prior to anodizing?

  2. How do different electrolytes affect the finished product? I have
    tried 5% phoshoric acid. It seems ok, fairly clean, though I don’t
    like the idea of aerosolized acid. Is there an optimal formulation
    for the bath?

  3. I am using an EC Apparatus variable voltage power supply. Does
    adjusting the amperage settings on this unit have any affect on the
    quality?

  4. For higher voltages, is it better to incrementally increase the
    voltage? For example for a piece to be anodized at 200v will I get
    better results by fully anodizing the piece at 25-50v increments?

  5. There seems to be a lot of sparking and gas liberation at higher
    voltages. The piece almost looks like it is frying. Can this be
    minimized?

  6. The point of contact with the leads does not seem to take even
    when I immerse that part in bath. How can I ensure that the whole
    piece is anodized?

  7. How critical is it that cathode and anode be of the same size?

  8. Will the process be more gentle, particularly at higher voltages
    if I increase the disance between cathode and anode? A lot of heat
    gets generated.

Many thanks
Ken


#2

First, the best thing you can do is get in touch with the Reactive
Metals folks, Bill literally wrote the book on small batch jewelry
anodizing and has come up with an etch/pre-bath for titanium and
niobium.

Reactive Metals Studio, Inc
928-634-3434, 800-876-3434, 928-634-6734fx

That being said, I find I do not need a prebath with CP1 titanium,
niobium or tantalum (I don’t see many jewelers using tantalum - too
expensive compared to other reactive metals, but oh so soft and fun
to work). I know that Bill recommends a procedure in his literature,
I have never used it.

Regarding voltages, I rarely have a need to exceed 70 volts or so,
and when have tried on small objects, I run into problems with spot
"burning". I generally set the maximum voltage and then control the
play of color with time, nearness to the electrode, submersion depth
and so forth. The bubbling and sparking may well be that you are
going to the maximum voltage too fast. One trick I sometimes use is
to put a resistor in line with the electrode. It does not stop the
max voltage, just delays it, allows for a slower development of the
oxide film.

I have found little difference in electrolytes, I generally use
trisodium phosphate (TSP).

I have had a problem with the contact point also. I can generally
get proper color by moving the contact point and re anodizing, but I
use lower voltages and when I have had a problem, I try to contact
in a less noticeable place or with the edge of the article.

I never worry about like size of cathode and anode - I use a
stainless steel beaker to hold the bath.

Good luck, and do call Bill at Reactive.
Marlin in Denver


#3

Ok, Ken let me see what I can do heRe: Disclaimer: These answer can
not cover all the possibilities.

  1. What is the ‘friendliest’ method of preparing the surface of
    pieces prior to anodizing?

Tanatalum = Anything will work. Beat on it with a rock. Needs =
nothing.

Titanium = may need chemical prep. Much depends on the “Grade” and
other processing. Our MultiEtch product is “friendlier” then most.

  1. How do different electrolytes affect the finished product? I have
    tried 5% phosphoric acid. It seems ok, fairly clean, though I don’t
    like the idea of aerosolized acid. Is there an optimal formulation
    for the bath?

Soapy water. Just about anything will work. Coca-Cola, or Pepsi or
salt water, or sulfuric acid. whatever makes you happy. We prefer
TSP. If you start with distilled, de-ionized water, nothing happens.
Add a contaminate, and why not use something that helps clean the
meta, and current starts to flow. You can control the speed of
anodizing with the density of the bath.

  1. I am using an EC Apparatus variable voltage power supply. Does
    adjusting the amperage settings on this unit have any affect on the
    quality?

Sorry, do not what an “EC Apparatus” is. You need a DC voltage power
supply producing 0-120+ volts and some 1-3 amps. Helps if amperage
and voltage are both infinitely variable. Voltage controls color
(thickness of oxide), Amperage controls the speed and heat produced.

  1. For higher voltages, is it better to incrementally increase the
    voltage? For example for a piece to be anodized at 200v will I get
    better results by fully anodizing the piece at 25-50v increments? At
    that high a voltage you are pushing the envelope! You best go up in
    steps. Most jewelry anodizing is produced between 0-120 volts. I have
    anodized in the labs at KU to 350 volts. So it can be done.

  2. There seems to be a lot of sparking and gas liberation at higher
    voltages. The piece almost looks like it is frying. Can this be
    minimized?

Control the amperage! Cool the bath. The oxide is “pin holeing”. One
little spot breaks down and the current begins to flow unrestricted
through the hole: heat increase, other areas start to break down and
sparks start to run across the surfaces. It is really kind of fun to
watch! To stop it you may have to circulate the bath through
refrigeration.

  1. The point of contact with the leads does not seem to take even
    when I immerse that part in bath. How can I ensure that the whole
    piece is anodized?

Use only Ti, Nb or Ta for you connection in the bath. Design a
mechanism that holds the piece with spring tension. Make the
connection tight and solid and maybe increase the area of contact or
increase the number of contacts. Everything you are pushing through
this circuit is funneled through the connection.

  1. How critical is it that cathode and anode be of the same size? The
    cathode should always be equal or bigger. We use stainless steel
    "steam table" pans and connect directly to the pan. This process has
    a “very short throw.” If you were to try to do a tube, a cathode
    would have to be fed through the center.

  2. Will the process be more gentle, particularly at higher voltages
    if I increase the distance between cathode and anode? A lot of heat
    gets generated. See all the above.

Bill, Deborah, Michele & Sarah
Reactive Metals Studio, Inc
928-634-3434, 800-876-3434, 928-634-6734fx