Cobalt Oxide Anodes

Chloric, I don't think you'll get it hot enough. It has made a big difference to the MnO2 in going up to 380 oC. Some of these nitrates decompose as low as 120 oC. Have a look at Table 1. in Patent 4,265,728 the MnO2 lifetime doubles, going from 300 oC. to 400 oC.

Probably 410 oC is the optimum temperature for MnO2 and Co3O4 for that matter, as well.

The hot air from my gun (2300 watts) is only about 300 oC in normal operation. I'd wait for your thermocouple and check the calibration with some molten lead, too! You need to do each coat for 10 mins., you don't want to be standing around waving a heat gun....

Shazaam Sargeant Carter , my arms shore are tired from
waving this here heat gun thingie back and forth ....and the handle sure is getting hot , and I'm sweating , and the noise gives me a headache ....would you mind bringing me another glass of lemonade ?

Xenoids right , you are going to need some sort of fixture
to do this right . Even heating is probably required to keep the coatings from cracking .

[Edited on 7-1-2008 by Rosco Bodine]

Quote:

Originally posted by Xenoid [The hot air from my gun (2300 watts) is only about 300 oC in normal operation. I'd wait for your thermocouple and check the calibration with some molten lead, too! You need to do each coat for 10 mins., you don't want to be standing around waving a heat gun....

@Xenoid- my gun is only 1200 watts and it easily gets 300 C in the LOW setting. It is rated for 530 Celsius at full blast. Of coarse that is 1 inch from the nozzel. How big is your gun anyways?

@Rosco-Advice noted I will have to jerry-rig something. I did not even think that these coatings could be fragile. And I will calibrate my setup with my inexpensive stainless steel rod. That thing is almost indestructable! I used it as a stir
stick for heating molybdenum disulfide to roast to the trioxide!

[Edited on 1/7/2008 by chloric1]

@ chloric1 - I just checked my hot air gun it's actually 2000W, it has a mighty air flow, so some of the power is being used there. I made some measurements about 2 cm from the nozzle with dual thermocouples.

Low setting = 50 oC.

Middle setting = 200 oC.

Full setting = 360 oC.

Obviously mine is crap! Are you sure your temperatures aren't in Fahrenheit, you are in the US after all....

Edit: I just found the "instruction pamphlet" and it states temperature range 50 oC. to 600 oC. ... hmmm not sure how they measured the 600 oC. maybe with the concentrator nozzel on to slow air down. Any how it gets nowhere near that in normal operation, firing up the tube. That's why I had to put a baffle on the end and block up some inlets!

@ Rosco - very funny ...

[Edited on 7-1-2008 by Xenoid]

Disaster Strikes Again... !

This really pisses me off...

The power was off for 2 hours this morning for line maintenance, I was aware of it, so I thought I would switch my chlorate cells off just to be safe.

After 6 days of running "Purple Haze", I had removed a batch of KClO3 and recharged it with KCl, there was already another 1 -2 cm built up on the bottom a day or two later!

I switched "Purple Haze" off and disconnected the leads from the supply and made sure they were "open circuit" with respect to the cell. The cell was crystal clear (pink), and the anode looked shiny black, but was emitting a stream of very fine bubbles.

When I returned a couple of hours later, after doing some shopping, the cell was BLACK. The SS cathode was a mess, it was corroded and "moth eaten" with little pits all over it. It had a coating of black and orange-brown gunk. "Hubert" the anode, still looks black, but I can't believe he hasn't lost much of his "coat" given the amount of black crap floating around. I filtered the solution, which seems to have a lot of brown colloidal Fe hydroxide (from the cathode) in it.

I have cleaned everything up (mainly the cathode) and recharged the cell with fresh saturated KCl solution. It seems to be running OK and the electrical parameters are as before, 3.5 volt - 2.0 amps. It hasn't had time to develop the characteristic pink colour yet.

This is a major set back, the anode was performing extremely well, I was starting to think it would be good for several runs. However if this is what happens to an anode/cell combination when the power is removed for just 2 hours, I am thinking MnO2 anodes are not viable. I remembered Rosco saying something about oxide coatings reacting with the electrolyte, and I almost pulled the anode out of the cell, but when I saw how few bubbles were coming off, I didn't bother...

Can anyone think what reactions were going on here! It's a puzzle because the cell was open circuit. Cell pH during normal operation was 8.1, the pH of the electrolyte after the disaster was 7.1

Don't be so mad Xenoid. It is the stainless steel's fault. When I ran with graphite last September, the stainless steel corroded and when the power went off, the cathode was bit in half by some disgruntled hypochlorite moleculs When I get my thermocouple and a decent 1 1/2 inch diameter aluminum tube I will give it ago. In my chlorate/perchlorate cells I will be using titanium sheet as the cathode. Hopefully I won't need to hydride this for cathode use.

By the way my gun is VERY cheap and has two setting Low is 750°F and High 1000°F(398°C/538°) the box list both units becuase we in the US are Bithermal, some of us understand there are two main temperature measuring units. Eighty percent of the energy is heat, it does not blow very hard.

Push on HUBERT! I know you can do it!

I think your anode is just fine. The first chlorate cell I ever ran used a platinum wire anode and a coiled copper cathode. I remember letting it run for a few hours, and then for whatever reason, I had to leave and turned it off. When I returned several hours later I found the entire copper spiral had formed blue green stalacites all over, there was just a collumn of insoluble material where the anode was.

I chalked it up to chlorine/HOCl(reduction potential 0.84V) in solution oxidizing the copper, and the base formed in the reduction of hypochlorite precipitating the copper.

EDIT: Chloric, titanium holds up just fine in a chlorate cell that is off



[Edited on 9-1-2008 by The_Davster]

Quote:

I remembered Rosco saying something about oxide coatings reacting with the electrolyte, and I almost pulled the anode out of the cell, but when I saw how few bubbles were coming off, I didn't bother...

Doh (sp?)..... Duh ......that's it

Actually, rinsing and drying would have been very EASY as the whole electrode assembly is attached to the lid ...

I checked the instantaneous voltage generated by "Purple Haze" at the moment the power is removed, it is around 1.85 volts, but drops rapidly to about 1.5 volts and more slowly after that, I didn't let it get any further. When I turn down the current on my supply it reaches about 10 - 20 mA at about 1.5 volts, so I guess just connecting an alkaline "D" cell across would maintain a trickle current or at least a stable state. Having it switched in with a simple relay, when power is cut would be easy to organise.

What annoys me most, is now I will never know the true lifetime of "Hubert". I was planning on putting him in a perchlorate cell, or testing at higher current densities.

Oh well, I guess I'll have to fork out another 10 cents worth of chemicals and an afternoon to fix him up, but I'll run him to total destruction first!

@Xenoid : sorry for asking to be a bit spoonfed, but I would really like a brief but detailed description of the process, I mean what conc. the solution is , purity etc. .... sorry for the spam

.... precisely! I got a bit carried away with my latest effort, I started after lunch and didn't finish until about 9.00pm ....
But even with my simple set-up I could just as easily have made 3 at the same time. With a better baking apparatus (did I mention toaster ovens) it would be just as easy to make 10 at a time ....

Have fun cleaning up your KClO3 from all that gouging rod rubbish ...

Early in this thread it was an idea to maybe wet sand the Ti rod substrate with glycerin as a way of abrading the passivating layer of TiO2 , and possibly getting a film of
Ti "glyceryloxide" as an interface layer which might be easily dopable .

And with it later turning out that Bismuth doping is reportedly a useful thing in any of the coatings layers , including the initial interface with the Ti substrate .......
and that glycerin turns out also to be an excellent
solvent for Bi(NO3)3 , it seems like it could be possible
to form that Bi doped Ti suboxide interface via a mixed
alcoholate ( Ti-Bi glycerylate ) by wetsanding the Ti rod
substrate with glycerin in which is dissolved Bi(NO3)3 ,
and then baking .

This might also work as tertiary system with Co(NO3)2 .

I just finished rereading this thread , and I think what
was revealed here in experiments continued into the
MMO anode thread , still seems on track , with the single exception having been found that the oxidative cold soak deposition of SnO2 cannot be used with Co3O4 due to the
reducing effect of the SnCl2 attacking the Co3O4 before
depositing SnO2 can seal it off . The possible usefulness of tin nitrate , stannic and metastannic sols , and ammonium stannate and other precursors , including alcoholates derived from stannic chloride remains a valid proposition .



[Edited on 5-3-2008 by Rosco Bodine]

manganese nitrate

Hi dann2 - I guess from your posts about preparing manganese nitrate you are going to have (another) go at MnO2 anodes.

I revisited MnO2 a few months ago, in an attempt to coat some MMO mesh. This was successful, but I had the same old problems with "Purple Haze". I wrote up some notes, but never got around to posting them at the time. They are a bit garbled, but you (and others)may find them interesting and of some use.

I'm not sure why you are posting this MnO2 stuff in the cobalt oxide thread, but I'll post my MnO2/MMO anode material in the Multilayer Metal Oxide / Titanium Anodes for Chlorate/Perchlorate thread as it doesn't appear to have been visited recently.

Quote: Originally posted by papaya

Anyone has access to this? http://onlinelibrary.wiley.com/doi/10.1111/j.1744-7402.2011.... [Edited on 28-1-2014 by papaya]

Quote: Originally posted by plante1999

Quite interesting, keep us updated.

Well, I'm very pleased with preliminary results which that particular Cu0.3Co2.7O4 coated anode shows. As I told I put it into the cell five days ago, and it's still running perfectly and it seems it is not going to die in the near future, as it looks very good and doesn't lose any noticeable quantity from coating (the liquid is really clear, only very slight brown layer is attached to the bottom of the cell, that I think came out of CATHODE when I turned off the cell for a minute).
BUT there's something that you must know in case if you want to try it (I encourage everyone interested to test it himself as to compare the results).
(1) When first prepared and put into cell the anode will lose some amount of loosely bound stuff in the first 24-36hours of working - this is NOT the real degradation rate.
After I washed it and put into a fresh cell, it showed only negligible amount of the same stuff in next 24 hours. That time the anode was running at current density of 40-50mA/cm^2 at max., so I wanted to see what happens if I put the whole 100mA/cm^2 and adjusted the voltage to achieve that. In the next 12 hours I found at the bottom of the cell black dense precipitation that looked like the same as coating on the anode - it seems it crackled and detached from the surface and fell down. However anode looked still OK so I washed it, filtered the solution and put it back to 40-50mA/cm^2 mode. After 36 hours of run cell is PERFECTLY clean, unbelievable, so the second point is
(2) never exceed 50mA/cm^2 current density, seems 30-40 will be optimal for a long run.
I cannot see the reason WHY at higher current density(2x) the wear rate becomes so unproportionally high, it may be even the thermal effect of the hotter cell
so point (2.1) is keep the cell below 40°C (though not sure on this point)
(3, maybe important or not) I baked anode at low temps, on the hot plate, not exceeding 300°C, put 5 coats, not rubbing the surface in between. When applying last coats it seemed like previous layers absorbed the liquid on contact, even they were HARD(in contrast to soot-like).

I think I'll run this particular cell (anode) for some more time without much intervention, only adding water/salt, but I already see it's really tough and maybe will not run for months until it dies some day.
In addition here is the article that made my mind to try it :http://libgen.org/scimag/get.php?doi=10.1016%2Fj.electacta.2010.04.026

I also have some ideas on MnxCo3-xO4 spinel that may become next thing to try (one formulation is not enough )as I found it exists as a single phase up to x=1.3 and is possible to make straight from mixed nitrate solutions, however couldn't find anything on it's durability, see about it here http://libgen.org/scimag/get.php?doi=10.1016%2Fs0013-4686%28...