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Author: Subject: What about "glassy" carbon as an anode material in a chlorate or perchlorate cell?
jpsmith123
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[*] posted on 2-9-2016 at 05:07


The authors used only 75 mg of boric acid per liter. I see that as a starting point. Maybe they didn't go any higher because along with methyl borate, adding more boric acid would've also made more water.

So what about upping the boric acid to 0.5 grams per liter, but then drying the methanol with zeolite or something?
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wg48
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[*] posted on 3-9-2016 at 11:41


Apparently it works from ethanol, methanol and glycol water solutions and also acetic acid and water (not from the this reference)

From: ELECTRODEPOSITION OF DIAMOND-LIKE CARBON FILMS, Minhua Chen, B.S.


"In 1992, Namba [11] first employed electrochemical methods to deposit DLC films. In
his study, diamond phase carbon films had been grown on silicon substrates at
temperatures of less than 70 ºC by using ethanol solution. The potential applied to silicon
substrates was changed from 0 to -1.2 KV and the current density from 0 to 5 mA/cm2
. By
changing the electrolyte into a water-ethylene glycol solution, Suzuki et al. [12] soon
successfully deposited carbon films on the silicon substrate. After that, this electrolysis
method had been successfully employed to deposit DLC films from a variety of organic
solution including methanol, acetonitrile, N, N-dimethylformamide, nitromethane,
nitroethane, ethanol and acrylonitrile [14-26]. Both DC power and pulse-modulated power
7
were used as energy sources in these attempts. In 1996, Suzuki et al. [13] reported a new
approach to deposit carbon films from organic solutions by electrolytic heating of a water ethanol
solution. This method consisted of discharge-heating a tungsten cathode in a water ethanol
electrolyte under a high DC voltage. At high voltages, glassy carbon and disordered
graphitic carbon were deposited on the tungsten wire. Very similarly, Wang et al. [27] has
employed a thin tungsten wire as anode under high potential and successfully deposited
DLC films on silicon substrates. All of the above electrochemical methods have
demonstrated some obvious advantages over traditional PVD and CVD in terms of low
processing temperature, simple setup and low cost. However, all of them involved the use
of high potential, which greatly increases the difficulty to control the deposition process
and study the mechanism. In 1996, V. P. Novikov et al. [28] proposed a new
electrochemical method to deposit DLC films. They used a solution of acetylene in liquid
ammonia as electrolyte and carried out the electrolysis at a low voltage of 2.5 to 5 V as
well as low temperature -55 oC"
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yobbo II
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[*] posted on 3-9-2016 at 15:31


Paper here (if anyone can get it) where the voltages are more manageable.

http://ieeexplore.ieee.org/document/7131998/
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[*] posted on 4-9-2016 at 06:24


Quote: Originally posted by yobbo II  
Paper here (if anyone can get it) where the voltages are more manageable.

http://ieeexplore.ieee.org/document/7131998/


The abstract from the above paper:

"This paper presents electrodeposition of diamond-like carbon (DLC) thin film deposits on indium tin oxide (ITO) glass substrate under voltage 2.1V~120V with mixing varying acetic acids' portions with deionized water, forming 0.2~0.8% electrolytic solutions. The result shows that at deposition temperature 30°~65°, voltage 50V and 0.8% electrolytic solution concentration of DLC thin films, the reflection index reduced to 60%, and theoretical matching refractive index became 1.32. This finding is applicable on various optoelectronic device like protective or window layer of solar cell."

The abstract does provide the main details. Compared to dry methanol and kvoltages its a much more convenient method as it uses safe voltages and dilute acetic acid water solution.

I would think the current would be in the amps range per cm^2 for a dilute solution of an acid at 50V. Perhaps they used a pulsed supply to reduce the power dissipation in the solution. More details of their set would be very nice.




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jpsmith123
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[*] posted on 4-9-2016 at 06:40


It seems that DLC films have been made (using various processes; CVD, PVD, eletrolysis, sputtering, etc.) from almost anything containing carbon.

IMO, the question is: which method is relatively simple to do at home which will give a reasonably "high quality" (e.g., adherent, relatively pinhole-free, boron-doped film) with a reasonable conductivity?

After reading everything I can find on the subject, it seems that in the case of processes using liquid and vapor phase precursors, methanol generally gives the best results.

Anyway, as I see it, for the purpose of making a perchlorate-capable anode for hobby purposes, we don't necessarily need a super high quality film, because if the process is simple enough, it shouldn't be too much trouble to re-coat the anode after a few runs.

One thing I'd like to know is: How much if at all does perchlorate production at a BDD surface depend on current density? (From what I've read, electrodeposited BDD films have lower conductivity than CVD-produced films, so they are not as good for high current applications, but if there is no lower limit on current density then this may not be a show-stopper but merely an inconvenience).

Edit: Here's a paper I just found: "Electrodeposition of DLC films on carbon steel from acetic acid solutions"
http://www.tandfonline.com/doi/pdf/10.1179/0020296714Z.00000...




[Edited on 4-9-2016 by jpsmith123]
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wg48
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[*] posted on 4-9-2016 at 07:53


Quote: Originally posted by jpsmith123  
It seems that DLC films have been made (using various processes; CVD, PVD, eletrolysis, sputtering, etc.) from almost anything containing carbon.

IMO, the question is: which method is relatively simple to do at home which will give a reasonably "high quality" (e.g., adherent, relatively pinhole-free, boron-doped film) with a reasonable conductivity?

After reading everything I can find on the subject, it seems that in the case of processes using liquid and vapor phase precursors, methanol generally gives the best results.

Anyway, as I see it, for the purpose of making a perchlorate-capable anode for hobby purposes, we don't necessarily need a super high quality film, because if the process is simple enough, it shouldn't be too much trouble to re-coat the anode after a few runs.

One thing I'd like to know is: How much if at all does perchlorate production at a BDD surface depend on current density? (From what I've read, electrodeposited BDD films have lower conductivity than CVD-produced films, so they are not as good for high current applications, but if there is no lower limit on current density then this may not be a show-stopper but merely an inconvenience).

Edit: Here's a paper I just found: "Electrodeposition of DLC films on carbon steel from acetic acid solutions"
http://www.tandfonline.com/doi/pdf/10.1179/0020296714Z.00000...

[Edited on 4-9-2016 by jpsmith123]


Great find thanks.

The paper suggests a mechanism:

"According to Roy et al.,
14 acetic acid in water
ionises and is transported in the electrolyte under high
electric field, according to reaction (1):
CH3COOH = CH3 + CO + OH- (edited to display correctly)
The positively charged methyl groups are attracted to
the cathode to form diamond-like carbon films through
reaction (2).14
2 CHz
3 z2e{?2Cz3H2 (2)
The negatively charged hydroxyl groups, in contrast,
migrate towards the anode, where they undergo reaction
(3).18
2OH{?O2zH2Oz4e{"

That does not make sense to me. Acetic acid ionising to produce Ch3+, CO and OH- ??? that would be an alkali.

I would believe that an acetic acid ion is neutralized and decomposes into CO2 and a methyl radical.

Presumably the coating can be doped with boron via boric acid or nitrogen via urea to increase its conduction.



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jpsmith123
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[*] posted on 5-9-2016 at 18:14


Nowadays, BDD nanopowder is available from places like www.us-nano.com (5 grams for $65). So another possible way to a BDD coated anode might be electrophoretic deposition of BDD powder onto a substrate.

BTW IIRC in one of Beer's MMO patents, he created a MMO coating on an anode by contacting the surface of the substrate with the powdered oxide material and then applying mechanical pressure. (The anode substrate may have been a graphite rod that was just rolled over the powdered MMO on a flat surface or something like that).


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