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Author: Subject: Forget everything else, diamond is the answer!
jpsmith123
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[*] posted on 13-12-2007 at 08:08
Forget everything else, diamond is the answer!


According to the attached review paper, doped diamond electrodes may replace MMO, platinum and PbO2.

The paper doesn't explicitly mention suitability for perchlorate production, but it's clearly implied I would say.

Also, U.S. patent app. #20070170070 claims the use of a doped diamond coated anode to make perchloric acid.

Being that graphite can apparently be used as a substrate for diamond deposition, and being that "diamond-like" films can be electrolytically deposited from methanol...this gets me thinking...I wonder if trimethyl borate could be added to the methanol to dope the product with boron?

Attachment: Doped Diamond Electrodes.pdf (804kB)
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Xenoid
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[*] posted on 13-12-2007 at 08:18


Hmmm..... Now all we have to do is erect aerials on our roofs, and wait for a thunderstorm....;)

http://www.sciencemadness.org/talk/viewthread.php?tid=8629&a...

May be we should all try Bob's method after all .... :o

http://members.tm.net/lapointe/Allotropes.html

[Edited on 13-12-2007 by Xenoid]
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JohnWW
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[*] posted on 13-12-2007 at 12:59


The only problem is that diamond is a very good insulator, in fact one of the best. "Doping" it with small amounts of N or B, incorporated into artificial diamonds, which is a very expensive thing to do, has been done to make semiconductors (n and p type respectively), which operate at voltages about 5 times that for Si or Ge based semiconductors, although because of their cost they are still largely experimental.
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[*] posted on 14-12-2007 at 10:14


Actually, not doping synthetic diamond with nitrogen is the difficult bit. Diamonds produced by Gemesis are yellow in colour due to nitrogen impurities. Avoiding this contamination is a major technical challenge.



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12AX7
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[*] posted on 14-12-2007 at 14:31


Odd, I heard that they produce N-doped diamonds because they are more expensive.

Edit: The wiki article implies that a vacuum chamber may be all that is needed. Exclude N2, maybe introduce BH3, etc. as desired. (For that matter, B dissolves in Fe. Even easier.)

Tim

[Edited on 12-14-2007 by 12AX7]




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[*] posted on 15-12-2007 at 11:23


The impure nitrogen-doped diamonds sell for more, because that is how the gem market is stacked, with coloured gems attracting higher prices. However, technically speaking, the nitrogen doping is a flaw in the process.



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dann2
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[*] posted on 15-12-2007 at 12:32


Hello,

I am no diamond expert but I will come in with my 2c's worth. (pun intended).
I think the N doped one sell for more if they are naturally occuring only. If made in the lab (N doped or otherwise) they sell for less.
Lab make diamonds can be told apart from naturally occuring ones by a lab test. Don't think you can tell them apart (the good one's anyways) from visual inspection.

One last gem of info:
Diamond has one of the highest thermal conductivity off all substances. It conducts heat by some weird and wonderful 'lattice vibrations'.

Dann2
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Xenoid
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[*] posted on 15-12-2007 at 14:34


Synthetic diamonds made by the latest techniques are readily distinguished from natural stones by optical microscopic examination, they are FLAWLESS. Natural stones have all sorts of lattice defects and occluded minerals.

I am still waiting for the diamond coated frying pans, which were touted about, several years ago... :o
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[*] posted on 15-12-2007 at 20:40


It also has an anomalous heat capacity, something Einstein and Debye theorized on early in the 20th century. The best explanation is a lattice of relatively stiff oscillators, linked to each other such that one can analyze the exchange of energy as wave particles -- phonons -- bouncing around inside, having energies from about zero up to a cutoff, such that the wavelength of these oscillations must be less than the corresponding distance between atoms.

Diamond is composed of a rather stiff lattice; as a result, these oscillators have steep energy levels and don't store much energy (as heat) at low temperatures. As a result, diamond has significantly less heat capacity than most other materials at room temperature.

Statistical mechanics is interesting, if mathematically intensive. I now know the formulas and derivations explaining this, though it's certainly above and beyond the topic of this thread (and probably of even less interest to most here!).

Tim




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[*] posted on 16-12-2007 at 07:26


We only need a plasma at 2200 to 2800. Comeon it is not that hard to do in the garage.:P


Seriousy though, microwave energy was mentioned and someone that reads here who has telecommunication expertice might be able to make a microwave gun that can be tuned to energize some organic vapors. Microwaves are definately able to heat certain things up to insane temperatures in a hurry.


Silicon as a substrate? Wow! That's just crazy cool! Of coarse not practical for large electrodes but it would nice for a pocket model. I would like to known in my neighborhood as"The guy who makes doped diamond silicon substrate anodes" I wonder how well they could sell on ebay.:cool:




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[*] posted on 16-12-2007 at 14:29


Of the diamond CVD papers I've seen, the most common (and accessible for us) method is simply a hot tungsten filament in a low pressure atmosphere of H2, CH4, CO2. Even the pressure requirements are not difficult ( 1or 2 torr IIRC). Typical substrates were tungsten sheet rubbed with diamond dust (for nucleation). Deposition rates are slow - μm per hour - so it would likely take a week or two to build a working coat.



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[*] posted on 16-12-2007 at 15:26


I've seen a patent claiming that you can use water/alcohol vapor instead of H2 & CH4.

But anyone with a high voltage DC power supply can try the electrolysis of methanol as per the attached paper.

Attachment: Electrolysis of Methanol.pdf (132kB)
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[*] posted on 17-12-2007 at 04:45


Quote:
Originally posted by jpsmith123
I've seen a patent claiming that you can use water/alcohol vapor instead of H2 & CH4.

But anyone with a high voltage DC power supply can try the electrolysis of methanol as per the attached paper.

I wonder if there's any benefit to going for a higher voltage (I can do about 150 kV at the suggested 20 mA current density), at least in terms of being able to deposit a thicker film. The only thing I'm missing to try that experiment is the HF for cleaning the substrate (and I have no clue how to obtain any). And how would one go about doping such a film?

[Edit:] By the way, I'm still waiting for you to answer my message from a long time ago :|

[Edited on 17-12-2007 by Nixie]




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jpsmith123
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[*] posted on 17-12-2007 at 05:54


I'd bet that you could use a graphite substrate with the surface prepared by anodic etching in NaOH, Na2CO3, Na3PO4, etc. Maybe electrocleaned and hydrided titanium would work, too.

IMO, one interesting experimental aspect would be to see if the coatings could be made conductive by adding small amounts of, say, methyl borate or some other boron containing compound to the methanol.

(BTW sorry about the lapse. I was forced to move a few times, unexpectedly, and I had little or no internet access and no access to my files, etc., for a few months. Are you still involveed with that project?)
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[*] posted on 17-12-2007 at 14:46


I am; not in a hurry as work is busy at the moment, but I hope to get back to it early '08. It'd help if I knew what else I'd need to purchase so I watch out on eBay and surplus places.



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[*] posted on 8-1-2008 at 07:10


I'm still thinking about this, especially since none of other efforts have yet produced a reliable perchlorate anode.

Ok here's the idea:

It seems that many places are selling diamond powder on line...I've seen it for a few dollars per gram. I would guess that at least some of these powders are "contaminated" with something else e.g. nitrogen, and are therefore conductive.

In several of his patents Beer talks about "rolling" the noble metal oxide into the titanium, or electrophoretic deposition, or just painting on an oxide slurry, followed by baking at high temperature.

According to several patents, titanium hydride can be used to create a bond to diamond; just mix the hydride with diamond and heat to decompose the hydride (preferably in an inert or a reducing atmosphere).

So why not take a piece of Ti, hydride it, coat it with diamond powder, and bake to create the bond?

[Edited on by jpsmith123]
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[*] posted on 8-1-2008 at 07:19


If electrolyzing methanol at kilovolts is annoying, what about DMSO at 150V?

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=n...
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[*] posted on 8-1-2008 at 07:24


Quote:
Originally posted by Xenoid
I am still waiting for the diamond coated frying pans, which were touted about, several years ago... :o


I got to try one of these out some years ago -- a friend of mine ran a materials lab, and one of their collaborators was looking at starting up a company to make them. It was disappointing. It was a lot stickier than Teflon, or even well-seasoned cast-iron, and it certainly appeared to be scratched by stainless-steel utensils, although I suppose I may just have been leaving stainless-steel streaks on it. There is something cool, though, about the idea of serving breakfast out of a diamond skillet...
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[*] posted on 8-1-2008 at 07:48


Assuming you have some sort of furnace which can achieve the required
temperature in an atmosphere which doesn't burn your diamonds, this
sounds like something interesting to try. This is the sort of procedure used
to make diamond files. At any rate, it would be interesting to be able to do
this at home --- I would certainly be curious to know how your attempts turn
out since high temperature stuff interests me.

As for use as an anode, an obvious point is that the substrate holding the
diamond is metal (titanium in this case) and therefore also conducts so,
if your purpose were to create an anode in which the conducting surface
were purely diamond, this would not do. Rather, you would have a mixed
titainium-diamond electrode. Looking at one of my diamond files, I see that
something like half the surface area is metal substrate, To have only the
diamond be in contact with the electrolyte, you would somehow have to
cover the titanium which holds the diamond grains in place with an insulator.
Maybe this could be done by some process like painting the electrode with
an insulator, then rubbing out the high spots so the diamonds show through
or maybe you could cover the Ti with a non-conductive oxide layer by anodizing it.

[Edited on 8-1-2008 by microcosmicus]
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jpsmith123
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[*] posted on 8-1-2008 at 08:11


@-jeffB: Thanks for the reference. I've posted a request for the full paper.

@microcosmicus: Theoretically it's ok to have titanium exposed to the electrolyte, as it forms a self-protecting oxide layer. (That's why titanium and the other so-called "valve" metals are preferred as substrate materials).
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microcosmicus
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[*] posted on 8-1-2008 at 09:53


@jpsmith123
In that case, what about stainless steel --- an oxide coating is what
makes it stainless, after all. Or is titanium oxide more resistant to
the stuff found in chlorate cells than chromium oxide? Diamond in a
SS substrate is quite easy to find in the form of diamond files, laps,
knife sharpeners, etc.

Duh -- using the stuff as an anode would automatically anodize it,
wouldn't it :)

[Edited on 8-1-2008 by microcosmicus]
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[*] posted on 8-1-2008 at 10:23


I'm learning every day, more and more, just how fucking resilient TiO2 is. Even to fluorides. . .

Stainless does not compare, period.

Tim




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[*] posted on 8-1-2008 at 12:47
Here's another interesting paper.


This paper describes some diamond coated anodes. Note the current densities they tested them at.

"However until now, diamond has not been introduced in electrochemical applications because of the limited availability of diamond for large-area electrodes. In the last years large-area chemical vapour deposition (CVD) of polycrystalline diamond films has been developed, yielding deposition areas of up to 0.3 m2 on metallic and ceramic substrates. These boron doped conductive diamond electrodes are semiconductor electrodes with a
microcrystalline structure and comparatively rough surfaces. Diamond-coated electrodes are chemically, mechanically and thermally very resistant (4) and show no significant corrosion even under high electrochemical load (5, 6). Galvanostatic investigations show no detectable changes of the electrodes for example after several hours in a solution of NaF in concentrated nitric acid at 50 °C (6) or in sulphuric acid (7). Over several weeks at 2 to 10 A cm-2 and thousands of Ah cm-2 the electrochemical activity of these diamond electrodes remains also constant in contrast to other conventional carbon electrodes (8)."

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[*] posted on 8-1-2008 at 14:02


What is the maximum temperature diamond can withstand in air for a prolonged period of time? I platinum-plated my tunsten plasma electrodes, but I'm wondering if diamond would last longer or allow a higher temperature.

[Edited on 8-1-2008 by Nixie]




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[*] posted on 8-1-2008 at 14:57


IIRC it starts to oxidize around 700 C or something like that, so you're probably better off with platinum.

What'd you do, electroplate the platinum onto the electrodes?
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