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jpsmith123
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Well my first attempt is looking like a failure...
When electrolyzing saturated NaCl solution, the anode seems to have a "threshold voltage" of about 10 volts, and even if I put 18 volts across it, all
I get is 100 mA of current, which is only about 20 mA per cm^2, and the current is slowly coming down.
So now the question is, where did it go wrong?
Wait a minute...now the strangest thing is happening...the current is slowly increasing! It's increasing rapidly!
It got away from me. I should've set a reasonable current limit on the P.S. The current went to a few amps for a little while...and the coating came
off.
Edit:
This made me remember a paper I read a while ago. The authors describe an "activation process" that the cobalt oxide layer had to have. Maybe that's
what I needed to do and didn't. Perhaps I rushed it and burnt the coating off.
I'm attaching the paper.
[Edited on by jpsmith123]
Attachment: Plasma CoO Anode.pdf (1.8MB)
This file has been downloaded 1101 times
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jpsmith123
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Which type of graphite rods should I use?
I'm ready to try coating a graphite rod.
I have two types of "graphite" rods: (1) one that appears a dull gray color and seems to coat everything it touches with graphite; and, (2) one that
appears shiny and does not come off on everything that touches it.
It seems like the latter is the one to try, but maybe someone more knowledgeable can offer an opinion?
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Xenoid
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Whats the size of the wire you're using? The calculation you make above suggests an area of 5 cm^2 (which seems optimistic) so I guess you would want
to limit the current to 0.5 or 1 Amp max. May be the coating came off because of overloading.
Re. the graphite, I'd go with the harder, shiny, smoother kind.
Regards, Xenoid
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jpsmith123
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The wire is about 0.09" diameter with the coated part about 2.75" long.
I think I need to do that experiment again. I think my plating current density was too high, and I think I need to experiment with the pre-plate
anodizing step; I need to vary the parameters.
Anyway, the cobalt oxide over TiO2 over Ti would be great, but for right now I'll settle for a quick and dirty coating on graphite...as long as it
stays there awhile.
I'll be taking the graphite rod out soon and I'll post a picture.
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Rosco Bodine
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@jpsmith123
As a general rule , probably anodizing is exactly the opposite of what you want to do in preparing the Ti substrate . The possible exceptions are
scenarios where the anodization is a minimal thickness very conductive layer in comparison with the normal oxide which would form if the bare Ti was
left to form its own natural oxide
in an uncontrolled way . The exception here is that it is better to substitute a much more conductive oxide at the interface , to temporarily seal
off the surface and prevent the growth of a thicker and less conductive oxide . That is what the Ruben patent was doing for making a rectifying
junction , but of course the exact same method is not desirable for making an anode , because the development of the rectifying junction is exactly
opposite of what is desired . The only usefulness of the method would be a modification where the anodization was very brief , perhaps allowing only
10% of the time and voltage rise
observed for the growth of the rectifying junction , and
then doping and baking that very minimal layer of suboxide , which should be more absorbent of the baked
on SnO2 or DTO , than would be the natural oxide . This would probably be useful also for the Ruthenium baked dopant schemes .
For a process where there is not going to be any baking on of a doped vitreous coating , any sort of anodizing pretreatment is likely opposite to what
you want to do , which is to produce an ohmic junction , not a rectifying junction . The strategy there with a controlled and brief anodization was a
compromise , by first "going in the wrong direction" to create a not fully developed anodization layer of a "softer" oxide than would normally develop
on baking , so that any dopant applied and baked would penetrate it more readily than the oxide layer which would otherwise develop .
But for processes which are not involving baking , that partial anodizing approach would probably have no value and could be counterproductive .
It actually seemed strange to me that you were anodizing as a surface preparation prior to electrodeposition , as opposed to doing some sort of
"cathodization - hydriding"
which would make more sense for a "cold process" anode
since the idea there is not any vitreous baked and doped boundary layer at all , but essentially a bare Ti metal interface with the electrodeposited
coating , or perhaps
some sort of "chromated" sort of chemical reaction product as the boundary layer at the interface between the Ti metal and the electrodeposited
coating .
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jpsmith123
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Rosco actually the hydriding thing is something I was going to get around to trying (see the attached patent), so it looks like a good call on your
behalf.
The failure of my first attempt means I will get to it shortly...as soon as the graphite electrode is finished.
If it works that would be great, because it would be the natural result of cathodic electrocleaning. I'll sand it, wash in detergent, rinse,
electroclean and hydride in NaOH or Na2CO3, and then electrodeposit.
[Edited on by jpsmith123]
Or I suppose I could do a cathodic etch in an acid solution, and adjust the voltage to go from etching to hydriding.
[Edited on by jpsmith123]
Attachment: 4222842.pdf (282kB)
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Rosco Bodine
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That file you just posted may be broken , but I got it directly from the patent server .http://www.google.com/patents?id=w8c1AAAAEBAJ&dq=patent:...
I did some searching awhile back concerning the hydriding scheme and posted some about it in another thread .
I don't remember exactly what these patents were and haven't reviewed them but posted the following numbers
as possible interest
US5368719 , US5456819 , US2801213 , US4153742
http://www.sciencemadness.org/talk/viewthread.php?goto=lastp...
I am still intrigued by the cobalt and bismuth since both reportedly have catalytic activity in perchlorate production .
Maybe some sort of spinel or even some cold formable compound or complex involving them could be useful .
I have seen references to their usefulness separately , but nothing for both put together in some way .
[Edited on 26-11-2007 by Rosco Bodine]
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jpsmith123
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Well I have a piece of Ti wire hooked up as cathode right now in a 10% NaOH solution. It's running at about 100 mA/cm^2. I wonder how long I should
leave it in there?
I took the graphite rod out of the solution. It's very hard to see the coating in a picture. The coating seems uniform although it's very thin, and if
I rub hard with a rag it leaves a noticeable black trace on the rag.
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Rosco Bodine
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I wouldn't use NaOH for the hydriding , but HCl or oxalic acid . You want to hold a low cathodic voltage so that etching of the naked metal occurs ,
and then raise the negative voltage so that hydrogen evolution occurs , for the hydrogen in excess of what is being adsorbed .
You see there is a window potential where the Ti is exposed by mild cathodization , not yet strong enough
to produce a protective layer of hydrogen . That initial low voltage cathodization lays bare the Ti to the etching effect of the acid , exposing the
active metal to the hydrogen
which will follow when the negative voltage is increased .
This may occur in a basic electrolyte , but IIRC from the Pourbaix diagrams it does the desired deed more readily in an acidic electrolyte .
Yes I just checked and you definitely want the acidic medium , and the idea is to cycle from the "corrosion" portion of the diagram which is the
etching of the metal , to the
"immune" portion which is the hydriding condition .
[Edited on 26-11-2007 by Rosco Bodine]
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chloric1
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@jpsmith- I was under the impression that the cobalt oxide coating needed to be applied at pretty low current densities simular to lead dioxide over a
long run. Perhaps running the cobalt oxide bath at 3 to 8 mA per cm^2. Try activating your cobalt anode in a 5% NaCl for awhile before doing
saturated brines and what not.
Oh and here is the patent I am referring to
[Edited on 11/26/2007 by chloric1]
Attachment: US3399966 Cobat Oxide anode.pdf (180kB)
This file has been downloaded 798 times
Fellow molecular manipulator
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jpsmith123
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I've been keeping it at 10 mA/cm^2 or less.
Right now as I type this I'm coating another graphite rod; this one at a current density of 5 mA/cm^2. I also took more care in preparing the surface
of the rod this time. I electrocleaned and then anodically etched it in 10% NaOH.
Tomorrow I'm going to have another go at the titanium. I'll try Rosco's idea with the cathodic etch and then hydriding in 10% oxalic acid.
If I have time tomorrow also I'm going to immerse the sal-chlor chlorinator cell I have into the CoSO4 solution, and see how the cobalt oxide goes on
over the MMO.
Edit:
This graphite rod has been plating now for about 3 hours. I think I'll let it go for another 4 or 5 hours.
BTW if this process can be made to work (and I know that's a big if), I found the perfect OTC plating tank for rod type substrates.
This stainless steel canister is not only the right size and shape, but it's inexpensive, and it has an acrylic lid with a gasket, so the plating
solution can be stored inside it.
Then when an anode is needed, just hang the rod from a clamp on a ring stand, for example, with the canister being the cathode sitting on the base or
on a hot plate/stirrer or something with an insulator in between.
[Edited on by jpsmith123]
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Rosco Bodine
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If that US3399966 patent is correct , then the substoichiometric cobalt oxide should give much better performance on a graphite substrate than does
PbO2 ,
because the catalytic effect of the cobalt enables the
cell to operate at a half volt lower potential for the same effect in electrolysis of brine , than is required for the PbO2 on graphite . Just that
slight reduction in operating voltage drops into the range where erosion of any exposed graphite is greatly reduced , in comparison with the PbO2
coated graphite scenario .
So if the cobalt suboxide works out as claimed , then
graphite becomes a practical substrate for a durable anode, and the complexities of a titanium substrate can be avoided entirely .
[Edited on 26-11-2007 by Rosco Bodine]
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jpsmith123
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Exactly. That's the main reason why I'm trying to do something with these graphite rods.
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dann2
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Hello,
Busy thread!!
Made up a DTOing solution using Ethanol (instead if ISO P alcohol) + HCl + Sn(IV) + Antimony Cl.
I used the soak, shake and bake.
Hung up Ti after soaking for about half hour and then dried very gentally using a flame. (Heat gun has given up the ghost). The Ti was not going to
dry on its own as weather is too damp.
One coat one bake then another coat and bake.
Coating was a dark yellowish brown.
Decided to try in a NaCl solution, I was not going to bother but luckily I did.
It has worked now for about 3 hours! and still going so I guess it is good enough for using as a LD/Ti interface.
Current density about 27 mA/CM2. Voltage accross cell about 5.5 volts. This is a lower voltage than all other coated Ti strips I have tested.
Dann2
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jpsmith123
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Hello Dann2,
After you've put a coating of something on your substrate, do you generally do any kind of subjective adhesion test? For example, regarding the
coating you've just described, did you rub it with a rag or anything to see how well it adheres?
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Xenoid
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Has that US3399966 patent been posted before?
It makes everything look incredibly simple. Almost any Co salt can be used, concentration not critical, pH not critical (2 - 6), temperature not
critical (room - 80 oC.), time/thickness of coating not critical, substrate (just about anything) etc. etc.
I just had to have a go at this! I'm currently (no pun intended) coating a 14cm length of gouging rod. I'm using acidified pottery grade cobalt
sulphate in a 1 litre bottling jar. The anode is surrounded by a tubular SS cathode. I'm using a current of about 100mA at 2.2 volts. The current
density works out at less than 3mA / cm^2. I can't actually see what's happening to the anode, but there is only miniscule bubble formation on the
cathode at this current. I'm actually using the same jar and electrode assembly I used for an unsuccessful attempt to make an MnO2 coated anode.
Perhaps this will be more productive, we shall see!
Regards, Xenoid
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jpsmith123
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Hello Xenoid,
Yep, Rosco posted that patent here several months ago. There are at least two or three other patents regarding cobalt oxide anode coatings, but rather
than electrodeposition, they involve thermal decomposition of cobalt salts, usually the nitrate, to get the oxide coating.
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Rosco Bodine
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| Quote: | Originally posted by Xenoid
Has that US3399966 patent been posted before? |
Hmmmm , give me a minute and I'll check 
Yeah it looks like somebody posted it about five months ago in this thread back on about page 18
http://www.sciencemadness.org/talk/viewthread.php?goto=lastp...
| Quote: |
It makes everything look incredibly simple. Almost any Co salt can be used, concentration not critical, pH not critical (2 - 6), temperature not
critical (room - 80 oC.), time/thickness of coating not critical, substrate (just about anything) etc. etc.
I just had to have a go at this! I'm currently (no pun intended) coating a 14cm length of gouging rod. I'm using acidified pottery grade cobalt
sulphate in a 1 litre bottling jar. The anode is surrounded by a tubular SS cathode. I'm using a current of about 100mA at 2.2 volts. The current
density works out at less than 3mA / cm^2. I can't actually see what's happening to the anode, but there is only miniscule bubble formation on the
cathode at this current. I'm actually using the same jar and electrode assembly I used for an unsuccessful attempt to make an MnO2 coated anode.
Perhaps this will be more productive, we shall see!
Regards, Xenoid |
Yeah cobalt has a lot of possibilities . The spinels are interesting too as baked coatings , and the cold oxidative soak deposition method works for
cobalt oxide too . This
low deposition rate anodic electrodeposition is not wildly different from the cold oxidative soak deposition , and it just might be possible to
similarly use a low rate electrodeposition of tin oxide onto titanium by the same scheme . I would expect there is probably an optimum pH and
temperature and concentration for the electrolyte , along with an optimum electrodeposition rate which provides the best adhesion .
And the figures from the data charted in the cold oxidative soak method might translate directly to electrodeposition .
A similar chemistry is occurring in either case that is responsible for causing the oxide to "plate out" and the dissolved reagents shouldn't care
whether the oxidation
is being supplied from an electrode , or from an oxidant
added to the system , like H2O2 or a nitrate or a bromate ,
as whatever shifts the equilibrium at a similar rate should cause the same result . And electricity for sure does that job . All it takes is
something having a higher oxidation potential than the potential of the thing being oxidized
to a less soluble higher oxidation state , and then nothing on earth will keep it from plating out  It might even be possible to combine the two methods of oxidative soak and electrodeposition , letting the initial
coating deposit via the electroless oxidative soak method which produces that extremely adherent "strike" plating of oxide that is so tough
it can't be scraped off with a knife , and then turning on the current to slowly increase the build rate by electrodeposition , ramping up the process
for a seamless
transition in the material .
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Rosco Bodine
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@dann2
Here is something you might try with some of your mixed chlorides leftover solution . Take a rotary file to some of
your 95/5 wire solder and grind off a half teaspoonful of filings . Boil off any excess HCl , perhaps adding a little makeup water along , until you
get a bit of cloudiness or precipitate . Add the filings and stopper the container
and set it aside for a week or longer , a month , whatever . Decant some of the liquid portion and try
it as a dip coating on an oxalic acid etched and hydrided
titanium strip . Then do your baking .
I must say you do seem to have an enduring confidence in the usefulness of HCl as a component in the DTO precursor mixture .
Is trying anything different even distantly on your radar ?
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jpsmith123
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It's not sticking to graphite very well...
Xenoid I don't know how your experiment is going but I'm finding that the as-deposited cobalt oxide (maybe baking would help?) doesn't stick to the
graphite rods I'm using; basically it can all be rubbed off with a piece of paper towel, without exerting very much pressure, I might add.
I suppose there may be some combination of surface preparation, choice of precursor, plating current density, pH, temperature, etc., that would work
better, but with my limited working space, I'm unfortunately not in a position to investigate it any further right now.
So I'm going to write off the graphite for now and try a few more things with Ti, and possibly with the sal-chlor anode I have.
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Rosco Bodine
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IIRC , there were worked out some PbO2 plating schemes
onto graphite which had excellent adhesion and conductivity . Perhaps doing an initial deposit of PbO2 onto the graphite , and then plating the
cobalt oxide onto that PbO2 primer coat could be useful , if the cobalt oxide would stick better to the PbO2 . The cobalt oxide would probably retain
its usefulness otherwise with regards to operating at reduced voltage .
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Xenoid
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@ jpsmith123
Well I've just had a look at my gouging rod and it's the same story! The cobalt oxide is just visible as a darker, duller coating but it rubs off with
the light touch of a finger to show the "shiny" graphite underneath.
This run lasted for about 14 hours, the first few hours were at about 3mA/cm^2 but I lowered the current even further to about 2mA/cm^2 for the rest.
I'll "play around" with this a bit, I have some Ti, proper graphite and even a bit of Pt. The Co is much nicer to work with compared to that
disgusting Mn, which changes oxidation state at the drop of a hat!
Regards, Xenoid
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Eclectic
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@Rosco
It sounds like Dann has actually gotten this to work finally with my Shake & Bake ® method. 
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dann2
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Hello,
DTO coating has worked for approx. 7 hours before partial failure.
About testing DTO. Since it mentioned in a patent (or patents) that a shiny black coat would form when the DTO coating was rubbed with a wire brush, I
was rubbing DTO coatings with fine steel wool. (OOOO grade) to see of coating would shine or come off. I have not been bothering to do this of late.
Just electrolysize in NaCl and see how it goes.
Call it the Dann2 DTO test
About the other possible methods of getting a DTO coat, I don't have time to try everything.
What is wrong with the presence of free HCl in the DTO precusor? It is mentioned in all the DTO (Anode) patents.
I can try without HCl, (No HCl in DTO precursor on radar )
I switched my solvent from ISO Prop. Alcohol to Ethanol. Perhaps this is what made the difference or was it the 'shake and bake'. I will try again
with Ethanol with my more usual 'painting' method.
Will also try another two tests without HCl.
It is interesting to note that just about ALL the patent have used Buthanol (I have no Buthanol) as the solvent.
Good luck with the Cobalt. It would be good to leave the Lead behind and move over to a process where one is more comfortable getting one's hands
dirty (literally).
To throw something else in I seen in The Perchlorates (see reference section) that there is a Japinese pat. for an LD anode using powdered LD + Vinyl
Chloride.
It is in the preface (or is it the history) of the book.
Can Japenese pats he had?
Dann2
[Edited on 27-11-2007 by dann2]
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Eclectic
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There is absolutely NOTHING wrong with using HCl if you are using tin chlorides. You need some in your solution to prevent premature hydrolysis. The
heat drives it off, and it can keep the Ti surface clean while tin and tin oxides are laid down.
There IS a problem with using so much solution that you have puddles of standing liquid. Many thin coats between bakes, not all at once.
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