B(a)P
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Platinum coated titanium substrate anode wear
I have a platinum coated titanium substrate anode that has seen a decent amount of use, likely around 10,000 h. It is a mesh construction and 50 x 100
mm in size, spot welded onto a titanium sheet metal tab.
It has been run with a 5.5 V supply at around 5 to 10 A for all of its life. Mostly it has been used for the production of a range of chlorates and
perchlorates as well as some other electrolysis experiments. With chlorate typically using HCl addition for pH balance and often with a small amount
of dichromate added.
The anode no longer performs as it used to. With fresh electrolyte the cell will run fine, but as the cell runs the current quickly drops off. I have
tried different power supplies and get the same result and it is not until the voltage is taken up to something like 10 V before significant current
flow is again observed. If I switch out to a new set of electrodes the cell works fine at 5.5 V.
So my questions are:
- Is my anode worn out?
- Is there anything that can be done to repair it?
- If it is worn, I presume it still has some platinum left on it, is it worth trying to reapply a platinum coating?
Thanks in advance for any assistance.
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Rainwater
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Yes
Yes see question 3
Yes.
It depends on how big of an anode you're talking about.
Something 12x12 you can do yourself,
please be careful with platinum salts,
they are very toxic.
If it's bigger you might want to outsource it.
Anyway, all you need is some platinum wire and hcl.
Connect your warn anode to the negative and
the platinum source to the positive.
I add a little polyethylene glycol (stool softer) to my copper bath.
It increases the throwing power of the solution
Helping the copper evenly coat the substrate
of the solution. I do not know if it will work with platinum
but I do know there are things that do work with platinum
[Edited on 1-2-2023 by Rainwater]
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yobbo II
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IMO and reading in this forum, successful platinum coatings cannot be done unless you have quite a large amount of platinum compound in relation to
the amount of Pt you wish to coat onto substrate.
What you will not be doing is this:
You need to coat on 10 grams of platinum (say)
You may need to purchase 100+ grams of platinum compound containing 100 grams of Pt to do the job.
I don't know what the ratio is but you will not be purchasing 20 grams of Pt (in a compount) and gettng 10 grams of it to plate successfully.
That my opinion.
Yob
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Rainwater
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Ya but the amount of platinum on a typical anode is somewhere between 4~ 10mg per M². You will have to maintain the concentration of the solution,
which is what I believe you're getting at.
10 grams of pt is enough to make a lot of anodes. Like a lot.
Depending on how thick of a coating you want i guess
[Edited on 2-2-2023 by Rainwater]
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mysteriusbhoice
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Quote: Originally posted by B(a)P  | I have a platinum coated titanium substrate anode that has seen a decent amount of use, likely around 10,000 h. It is a mesh construction and 50 x 100
mm in size, spot welded onto a titanium sheet metal tab.
It has been run with a 5.5 V supply at around 5 to 10 A for all of its life. Mostly it has been used for the production of a range of chlorates and
perchlorates as well as some other electrolysis experiments. With chlorate typically using HCl addition for pH balance and often with a small amount
of dichromate added.
The anode no longer performs as it used to. With fresh electrolyte the cell will run fine, but as the cell runs the current quickly drops off. I have
tried different power supplies and get the same result and it is not until the voltage is taken up to something like 10 V before significant current
flow is again observed. If I switch out to a new set of electrodes the cell works fine at 5.5 V.
So my questions are:
- Is my anode worn out?
- Is there anything that can be done to repair it?
- If it is worn, I presume it still has some platinum left on it, is it worth trying to reapply a platinum coating?
Thanks in advance for any assistance. |
The anode is dead basically but it seems i was a good quality because many Pt electrodes spall off a lot earlier due to bad coating processes.
10k hours is a good rating for Pt becaust most only last 2k hours or barely 100 hours if the electrode was very poorly prepared.
Ir-Ta and Ir-Ru MMO is rated at 20k to 30k hours but can last like 50k hours at lower current densities.
To answer your questions I will say this.
1. anode i worn out yes
2. you can repair it by making a totally different coating or recoating it with fresh hexachloroplatinic acid + glycerol bake.
3. these coatings start with 1 micron of Pt baked on the surface of the Ti and upon wear its much less than that like 0.1 or 0.2 microns in some spots
so no its not worth.
4. reapplication of the coating can be done but the anode needs to first be rid of all the Pt on it and re etched in oxalic acid or HCl + NaF/CaF2
before reappling the coating.
The coating process involves making a tincture of chloroplatinic acid and some glycol/glycerol glycol is better and baking it until it hits 600C.
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mysteriusbhoice
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electroplated Pt can also work but these have less stability in high current density applications due to them being literal tiny crystals growing out
of the substrate and not a really nice even baked on layer of Pt.
The electroplated Pt electrode is less stable and these crystals can spall or crack.
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B(a)P
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Thank you all very much for the input. I have been interested in making my own lead dioxide anode for sometime. I might use this anode for that
purpose as I already have another platinum coated titanium substrate anode.
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yobbo II
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Do you know the thickness of the Pt coating on the new (or the old when new) anode?
You appear, IMO, to have got good milage out of the worn anode.
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B(a)P
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I have looked back through my emails and I can't find the specifications for the original anode. I purchased it from a seller on Ebay that I had
recommended to me from SM. My "new" anode was made for me by Antiswat and again, I do not know the thickness, but I do know it has a five layer
coating.
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