White Yeti
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MnO2 anodes...
Manganese dioxide coated titanium electrodes seem to be great substitutes for platinized titanium electrodes. Unfortunately, they seem to flake and
break down if used for extended periods of time.
The use of a cobalt oxide layer between the manganese oxide and titanium metal could be a reason why the MnO2 loses adhesion. This amorphous oxide
layer adheres very well to the titanium, but anything that is deposited on top of the cobalt oxide adheres very poorly. This is probably due to the
low mechanical strength of cobalt oxide.
Then I had this idea:
What if I plated the titanium substrate with a rather thick layer of (zinc) metal? If slow galvanisation process proceeds for a very long time,
dendrites of zinc metal start to form. From personal experience, I know these dendrites are very fragile if they become too big. But if I let these
dendrites grow without becoming too big, they could potentially provide a rough surface for the MnO2 to adhere to.
Then I need to treat the zinc dendrite layer with a very thin layer of cobalt oxide (MnO2 would attack the zinc and cause it to passivate). The cobalt
oxide would fill up the pits instead of evenly coating the entire zinc surface.
This could be a good thing; the cobalt oxide would provide electrical contact between the zinc pits and the manganese dioxide layer, while the
dendrites hold the manganese oxide layer in place. In that case, should I electroplate the titanium substrate with a strong metal, like molybdenum?
I feel like this thread is not very clear, so I drew a picture to illustrate the idea:
So, do you guys think this anode design will work?
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watson.fawkes
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Please go do some basic reading on the
subject. There's huge amounts of it in the material science literature, much of it driven by the semiconductor industry. It's clear your understanding
of basic facts is deficient. When you say "probably" in the quoted sentence, I read that as "I know nothing about what I'm saying, and this is the
only thing I can imagine". So that I'm not completely unhelpful, go learn all about film adhesion vs. thermal coefficient of expansion. You should
probably learn what an ionic conductor is, too.
And finally, at this scale nothing is held in place by mechanical keying.
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White Yeti
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I understand.
I have researched this topic for weeks, but I can't find any decent articles regarding the subject. Do you have links to articles regarding the
deposition of manganese dioxide onto anode surfaces? It's easy to point out a problem, but finding a solution is a bit more difficult.
This does not take away from the fact that manganese dioxide overcoats degrade rapidly and flake. If the cobalt oxide layer is not the problem, then
what is? When I made these anodes, the manganese dioxide flaked off and the cobalt oxide remained intact. What is the solution to this problem?
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dann2
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So why did you not carry on with the Cobalt Oxide? (which remained intact!?!)
There is no need for the Cobalt Oxide layer at all IMO.
MnO2 Anodes are not a great substitute for Platinized Ti Anodes (unfortunately).
They make Chlorate only. I presume that is what you are doing with these Anodes?
Dann2
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White Yeti
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You presume correctly.
I wanted to make chlorates with an MnO2 anode. But the manganese layer started flaking off, and I only applied about 3-4 layers of cobalt (don't have
much cobalt nitrate left). I wasn't sure if the cobalt electrode would survive several days in a chlorate cell, so I decided to turn off the cell and
start looking for ways to improve the anode design.
I have a list of transition metal oxides that conduct electricity:
NbO
VO
PbO2 (duh)
RuO2
ReO3
RhO2
(excluding cobalt and manganese oxide)
I don't have the time or money to try all of these out, so I'll be trying to narrow this list down to the metal oxides that will work best.
I've heard of another user who used a layer of vanadium pentoxide and nickel oxide to protect a titanium electrode from the conditions in a chlorate
cell. I'm allergic to nickel, so I won't be trying that out, unfortunately.
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