Multilayer Metal Oxide / Titanium Anodes for Chlorate/Perchlorate

anomalously soluble stannic oxalate

bismuth compounds solubility

Some of the following references differ from one source and another . But a few interesting things have been found concerning bismuth salts which reveal anomalous solubility .
Mannitol forms an addition compound with Bismuth Nitrate ,
sorbitol and dulcitol are mentioned also , as well as ordinary glycerin , and the usual hydrolysis of Bi(NO3)3 - 5H2O upon dilution is inhibited greatly for these mixtures . All of these materials are polyhydric alcohols and the anomalous solubility may possibly be due to formation of a bismuth alcoholate or "alcoholoxide" substituted hydroxide sol .

Also a citrate salt of bismuth may be gotten from boiling the subnitrate in suspension in citric acid , and the precipitated bismuth citrate rinsed and filtered . This material acts as a monoacid towards ammonia and when neutralized is freely soluble in H2O so long as the solution is neutral to very slightly basic with ammonia . A bismuth acetate crystallizes from the double decomposition of lead acetate and Bi(NO3)3 solutions . A bismuth oxalate can be precipitated from a nitric acid solution of Bi(NO3)3 on boiling with oxalic acid ,
and I could find no information specific to the formation of
a possible peroxalic anhydride derivative with H2O2 as is reported for the stannic anhydride sol , but this seems a good possibility . At the bottom left corner of the attached image the Lowe reference is interesting concerning the
hydrolysis inhibiting effect of acetic acid or 1/300 part of
ammonium nitrate . NH4NO3 was also mentioned in
connection with the citrate in an obscure early pharmaceutical text , as having been used to form more concentrated solutions of Bismuth Ammonium Citrate , but
that older formulation was obsoleted and I could find nothing
further concerning the use of ammonium nitrate for stabilizing bismuth in solutions .



[Edited on 4-3-2008 by Rosco Bodine]

Total Failure

My latest perchlorate anode was my most sophisticated attempt to date, and utilised UMLT* and featured NTT**.

I applied 2 coats of Co3O4, baked at 410 oC to an etched Ti rod.
This was in turn coated with 4 layers baked at 380 oC. These 4 layers each comprised 1 dip 'n dry Co3O4, 5 dip 'n dry MnO2 and 1 dip 'n dry Bi2O3 layers!
After this I considered that the Co and Bi levels might be a "bit" high, so I overcoated all this with another 4 baked layers as above but with about 10 dip 'n dry MnO2 layers!
On top of all this I added another 8 layers each baked at 380 oC. of MnO2 which was doped with Co and Bi.

Total layers was about 88......

The anode lasted about 48 hours in a perchlorate cell. The cell was a dark permanganate colour at the end (it put "Purple Haze" to shame) there was also black MnO2 on the bottom of the cell.

The cell started at 4.4 volts, 2 amps (60mA/cm^2) the voltage dropped to 4.2 volts as the cell warmed up and then steadily rose to 6 volts as the anode passivated and was switched off.
The idea for this anode was based on the concept that if you put on enough layers of variable composition, somewhere in there will be a layer that is "just right". Rosco alluded to this some time ago.

Interestingly, when I did the the first bake with the Bi(NO3)3 dip (I actually did two dip 'n dries, not the one in the "ideal" sequence above) shiny, metallic Bismuth was produced on the outside of the anode (that's why it was reduced to one dip 'n dry). Hints of metallic Bi also appeared in some of the later sequences.

Even with this extensive pyrolytic coating, it was still possible to see deep scratches in the underlying Ti rod, this suggests the coating is still only, what, 50 - 100 um thick! It is difficult to see how this type of anode can compete with a plated on layer of PbO2 which can be millimetres thick, and also more catalytically active for perchlorate. A plated coating would also appear to be a lot easier to apply than 88 pyrolytic coats which took me about 1.5 days to do.

*UMLT - Ultra Multi Layer Techniques
**NTT - No Tin Technology
UMLT and NTT are registered trademarks of the Anode Division - Xenoid Chlorate - Perchlorate Corporation.

Yes, to some extent the "dried" coats were redissolving, this was evidenced by the Mn solution getting darker from Co solution contamination, the Bi solution also took on a slight pink hue as well. It was not possible to obtain a completely "dry" coat in a reasonable time frame, usually they were slightly "gummy". Even if all the coats were perfect and intact the "build up" is still only going to be a few hundred microns at the most (ie. tenths of a mm.) whereas plating can quickley build up coats of a few mm.

Unfortunately my procedures were not very quantitative but at least I expected something that would last longer in a perchlorate cell than just the "straight" MnO2 coating, this was not the case however!

Good luck with the Sn, I had a third attempt at tin nitrate, but just got the same cloudy solution and ppt. as previously. That's why I used NTT ....

Bismuth nitrate solution was no problem, I used about a thumbnail pile of crystals, in a test tube, a few drops of nitric acid and diluted with water up to halfway, this was enough solution to "dip my rod in"....

*Mixed* metal oxide = "doped" (including tin) oxide

Doing the math ......

NTT (no tin technology) = SOL (shit outta luck)

Really , there's probably no getting around the SnO2 .

As for your Mn(NO3)2 becoming cross contaminated with
Co(NO3)2 ......well that's a good thing , and it would probably help the MnO2 to deliberately mix in about 5%
of the Co precursor . The MnO2 without the Co3O4 is an oxygen selective anode coating , and it is only the diffusion which you have been getting from the Co3O4 in underlying layers which has allowed the MnO2 to make chlorate and perchlorate , if the literature which I have seen is correct on this point , as MnO2 alone makes only oxygen and at too low a voltage for chlorate or perchlorate . Tin shifts the selectivity in the right direction also , and both tin and cobalt
toughen the MnO2 mechanically . SnO2 and MnO2 and Co3O4 are all solvent oxides towards each other so they diffuse freely on baking . But there are desirable proportions
which will make for a mixture which sinters to a tough film better than some different proportions .

That old 1857 Chemical Gazette article by Ordway which describes the formation of stable mixtures of tin nitrate and tin chlorides is enlightening . The existence of a mixed valency tin oxide , a "sesquioxide" , and a series of salts
derived from it is something which I have have suspected could be useful in anode precursor mixtures . There seems
to be a niche condition for stable solutions where the higher and lower valency species tend to buffer each other and the result is anomalous solubility and stability for the sol or solution . This should facilitate mixing with precursors for
the dopant materials . Anyway the Ordway article is significant , and I am attaching a cleaned up file which can
be read and printed better than the first attached file I put
in the antimony and tin nitrate thread .

There have been identified several thermally decomposable
precursors for stannic oxide which are highly loaded solutions or sols that are stable across a range of pH values which should make possible mixtures with various dopant precursors . What mixture is best I'm not sure , but I am
pretty certain a *mixture* of the precursors is definitely going to be required to achieve the best MMO end result , as
diffusion alone will be too variable and produce not nearly so intimate a mixture as can be gotten from mixing the precursors before baking .

As an example of compatable pH , what I was thinking for
the Bi doping is using "ammonium stannate" ( ammonia peptized alpha stannic oxyhydroxide sol ) which is alkaline
with the Bismuth Ammonium Citrate which is highly soluble
in alkaline medium ....hoping the two don't immediately react preferentially to precipitate Bismuth Stannate

For a highly acidic compatable pH , what I was thinking for
Bi doping is the Bismuth Oxalate or perhaps the Bi Nitrate ,
along with the peroxalic "stannic anhydride" of the patent
US4924017 and related US4873352 . Glacial acetic acid is
also a solvent for Bi(NO3)3 compatable with a low pH mixture .

For a more neutral pH system like some of the Tin Nitrate
mixed valency compositions described by Ordway in 1857 ,
possibly using the anomalously soluble Bi(NO3)3 addition compound with a polyol like glycerin or mannitol would be
workable . Bi(NO3)3 is also reported soluble in acetone ,
but the reports are conflicting concerning the pH useful ,
so this might be workable either in the middle pH or low pH
mixtures , depending on how that reported acetone solubility sorts out .

And beyond these possible schemes there are always the
alcoholate derivatives , of which those polyol addition compounds are a type . The chemistries involved for
Tin , Bismuth and Antimony are similar , so there should
be possible some reasonably stable mixtures of precursors
useful for dip coating .

Anyway , there are possible mixtures across the entire pH range for dopants useful with SnO2 , so the issue becomes
which combination will produce the best quality , most adherent film on baking . There's really not a lot of help
in the literature in the way of predicting what is best .

One more thing , regarding the sesquioxide of tin in solution as the chloride . This still has a reducing properties , but
it is less reducing than SnCl2 . So this mixture might possibly have usefulness as an oxidative soak deposition precursor ,
as it is already "halfway there" ....it might not attack a spinel
in the same way as does SnCl2 . But really I think a more likely to succeed mixture would be cobalt nitrate or chloride
mixed directly with one of stannic oxide precursors would be better , or a single or double coating of spinel alone , followed by the stannic oxide or cobalt doped stannic oxide
precursor mixture . Getting some Bi doping in that interface
mixture too would be ideal . The goal would be to get the
SnO2 lattice of the interface layer as close to saturation as possible with Bi doping , without phase separation . That
would create the oxygen migration barrier needed for protection of the substrate . The Co3O4 doping would
provide conductivity and toughening also . If Sb doping is added as a grain modifier , it should be held to 1/2 % .
Guessing on the proportions of Co and Bi , I would try 4% Co
and 6% Bi ...the rest Sn .

Edit: Reminder that the terminology of the year 1857 differed in its meaning for "equivalents" than is the usage of the term today , due to chemists misidentification of molecular versus atomic weights for gases like chlorine and hydrogen ,
in which case stannous chloride would be mistakenly identified as SnCl instead of SnCl2 , and stannic chloride would be misidentified as SnCl2 instead of SnCl4 , and water
would be mistakenly identified as HO instead of HOH , ect.
Also I suspect the term "equivalents" may sometimes simply be equal parts by weight without any strict reference to molecular weights be they correct or incorrect , so some
interpretation and verification must be applied to these older texts in order to revise and correct the equations for the described reactions so they are accurate using the modern formulas . Experiments should clarify the meaning for proportions that may be unclear from these old texts .

[Edited on 9-3-2008 by Rosco Bodine]

Attachment: Tin Nitrate stable solutions Ordway (Chemical Gazette 1857) legible printable.pdf (489kB)
This file has been downloaded 804 times

Using dichromate

@ Rosco - I think Ioxoi is meaning adding potassium dichromate to the cell solution!

No, I haven't tried it!

Actually I never got around to posting a footnote to "Hubert" and "Purple Haze" the final yield of KClO3 was 945g, (recrystallised, dried and clean). I used 2299 amp hours and the efficiency was 53.9% - not too bad.

What would be desirable is if the dichromate extended the lifetime of the anode!

Sorry for not posting for a while, but after my last disasterous attempt at an anode I thought I would have a break for a while! I'll wait for someone to make a breakthrough....

Image shows dried KClO3 from "Purple Haze" in roasting dish.

MnO2 (or Co Oxide) in Diaphram cell

Well OK,

Here is my break through

Rosco, a long time ago posted a patent for making Perchlorate using Graphite in a cell that had a diaphram. It is an old patent but probably perfectly workable.
Would it work with MnO2 anode (instead of Graphite)?? That would allow MnO2 to make Perchlorate and not erode???

What do ya's think.

Patent attached:

Dann2

Attachment: us1279593.pdf (173kB)
This file has been downloaded 690 times

@Xenoid
Yeah it could be good for dichromate in the electrolyte too .
It may work via similar mechanism wherever it is in the system , but in the electrolyte it could have effect at the cathode also .

@dann2
Hmmm , I'm not sure , but it seems simpler to work out a coating scheme that doesn't need a divided cell . I think the MnO2 will toughen up with added SnO2 , Co3O4 , Bi2O3 .

Time for my diva fix

http://www.youtube.com/watch?v=zo5n0HwaRmQ&feature=relat...

http://www.youtube.com/watch?v=rh-q8RNLr3Q&feature=relat...

http://www.youtube.com/watch?v=nDVgb4pJMdI&NR=1

Xenoid is not posting on this thread and jpsmith resurfaces from the abyss of ambiquity?? What happened here?


@jpsmith-They stated porous cup many times in that patent which basically means unglazed pottery. If kilnless like myself, find one of those outfits that lets you fire your wares and simply make your own "cups". I have wanted to do that but not sure what the best clay is yet.
@rosco-Well, I do not think the divided cell idea is too difficult. The main disadvantage is using higher voltage to drive the current needed. I was a little suspect of the patent becuase they mention perbromates as if they can be whipped up by the kilo. AFAIK perbromates where not successfully isolated until at least 50 years after this patent was published and that was done via fluorine oxidation. So, I wonder if this design is not some electrochemist's wetdream scribbled on a coffeehouse napkin.

Hello,

There is some info here on Perchlorate formation which you may have seen before.

http://www.geocities.com/lllwolly/further/perkform.zip

I have not really read up on it myself, but will now!. (I know sfa about it).
In the patent (@100) they may be just referring to the fact that if you have cups (as opposed to not having any) then the cathodes WILL be surrounded with the 'hydroxid liquid', and not the usual bulk Perchlorate cell electrolyte (whatever that usually is).

I had not intended to try this myself but I am beginning to wonder. It's may be a good way for the home producer to go.

Would flower pots, red unglazed ones with no hole in the bottom, do. Xenoid used them for something somewhere.
Like most of these's things, the only way is to 'suck it and see' (as put very elegantly my someone else in here).

I have me doubts about their being some combination(s) of coatings that when put together will suddenly create a Perchlorate cell resistant, Perchlorate producing anode.
May be wrong though. Xenoid is has done a hugh amount of work.

Dann2

[Edited on 17-3-2008 by dann2]

Hello,

@Chloric1. T'was yourself that was using the flower pot, now that I think of it, though I think Xenoid was doing something that caused a hole to appear in the bottom of the flower pot due to the magnetic stirrer bar.

Anyhow, the cell would be in interesting project. It may make Perchlorate easily achievable using Graphite alone, or MnO2 for total 'mess free' Perchlorate.
You could always start with just one flower pot with the anode in it, as opposed to a number of pots with cathodes in each of them, and see how it goes (suck and see, SAS ).

Graphite as far as I can tell (from my own experience) will not make Perchlorate in significant quantities. Apart from the erosion, there is damm all Perchlorate available from the cell ( Perchlorate cell using Graphite), when it is run for a ridiculous amount of Amper Hours. The Graphite just does not seem to have the required catalytic effect in the normal Perchlorate cell. But that may all change in this type of cell where conditions are different (apart from having less erosion). The time I ran my Perchlorate cell, using Graphite, the pH was inclined to go acidic though.
Some info. here for what it's worth (you seen this before).
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

Two refs. for Perchlorate making with Graphite are here:
Sihvonen, G., Suomen Kemistilehti, 10B, 27 (1937)

Ullman, Frits, "Enzyklopadie der technischen Chemie", Vol. 3, p 299-307, Berlin, Urban & Schwarzenberg, 1929

...........if anyone is rambling around the more dustier shelves of their favourite library.......

@JP Smith. About the MMO (at least the anode I have, which is an anti corrosion anode. I think it consists of Ir Oxides on the outside), I attempted to make Perchlorate with it some time ago. No Perchlorate formed at all. (120mA per square cm, 0.5 liter cell with 250g Na Chlorate in it. Ran cell for 25 days
But conditions are different in the cell with the diaphram, so who knows. Also with different MMO's things will be different too.

Dann2

Okay I'll go out on a limb .

What I have been thinking about is a mixed nitrates derived mixed oxides of that similar configuration having a percentage basis expressed as the sintered oxides of SnO2 82% , MnO2 8% , Co3O4 5% , Bi2O3 5% , ....used as an interface coating as well as a build coating . If it doesn't work well as an initial interface coating , then what I would try next is to use *one coat* of straight Co3O4 as the interface coat baked , followed by *one coat* of plain tin oxide baked , and then proceed with build coatings of the above proportions . It may work better with the MnO2 omitted if porosity problems occur , in which case the SnO2 percentage would simply raise to 90% . It's sort of coin toss on whether that porosity will occur , my best guess is it won't be a problem .

There are more complicated alternating schemes that I have been thinking might be good but the above is about the simplest in the way of a mixed nitrates or mixed nitrates and chlorides precursor salts mixture which likely would be a sealing as well as being a working coating . This is just an educated guess however , based upon a collection of
references , and unproven hypotheses of my own , derived
from what I think it all means so there are no guarantees .
What I think is the SnO2 and Co3O4 and MnO2 will function as a tertiary solvent oxide system , something like fluxes for the Bi2O3 . This mixture is something expected to be more like a glass , a ceramic glaze than the more usual dopant filled tin oxide lattice polycrystalline layer ...
although it works the same way ....what I am theorizing
is that the polycrystalline structure from this mix will be something like a complex spinel structure itself , having
bi-electrode regions of amorphous glass mingled with definitely structured crystalline regions of varying composition. The whole surface should end up tiled with slightly differing composition adjacent tiles of nanometer dimension , some having crystallinity and some a having glass like character plates with fused boundaries like grout
between the tiles *if* my guess is correct .

This scheme possibly may be enhanced as alternating coats with the mixed valency stannic/stannous nitrates/chlorides
"dyers tin mordant" sort of composition described in that
Ordway paper . There is probably enough dopant in the alternating layers that diffusion would take care of any
doping for conductivity .

Yeah , I think the *stannic* nitrate , perhaps in some mixture
with stannic chloride , or some other entirely stannic composition may be required in order to prevent the dopant
salts from being reduced to their metals , as might occur
with stannous salts or mixed valency tin precursors . However there definitely are Pytlewski model mixed valency stannic oxide polymers , hydrosols , where the dopant is actually substituted in the complex monomer unit and does not precipitate , and is not reduced to the metal . So how the precursor is prepared to include the dopant is important where an intermediate is formed in the mixture . The sequence and technique in preparing the precursor mixtures
could become more complicated than simply dumping everything together and mixing , where mixed valency materials are involved .

There is a surplus of oxygen provided from the nitrate precursors which could be useful in the conversion of other precursors to the desired oxide , but compatability in a mixture that is entirely nitrates for example would be likely , absent the manifestation of some insoluble multiple salt which could complicate things . There's one way to find out for sure , try it and see what mixes okay

[Edited on 20-3-2008 by Rosco Bodine]

The figures have been posted before but it's been awhile
and I forgot , will have to go back and check ...but there is
an optimum concentration for the precursors coating solution with regards to film formation and IIRC it is about 8% solids loading , expressed as final SnO2 basis . That works out to be a pretty concentrated mixture of precursor salts , and
some viscosity is desirable also , so if it is a bit syrupy ,
even better .

One of the described compositions in those
old writings about tin mordants IIRC regarded one of the tin nitrate mixtures which was syrupy , which is good ,
and which would gell suddenly when heated , which is
grrrrreat . Because if that behavior held true when the dopants are mixed with it , the gelling would tend to set
the coating with all the dopants distributed and trapped
in a dispersed state in that gell , where there would be no
tendency to separate and the film would not sag but would
keep an even thickness . An idea I had is to chuck the anode rod in a slow speed stir motor like a zero max ,
( I have one ) and dip it , then rotate it horizontally at slow speed like a barbecue rotissierie while manually sweeping
it with gentle heating from the heat gun , to gell and dry
the coating pretty good , before the sintering bake . That
should set the coating at a very even thickness which shouldn't creep during sintering .

[Edited on 20-3-2008 by Rosco Bodine]

The color is something I really couldn't guess , or even if it might be clear actually , but I was thinking it could be blue
to brown . That it is shiny tracks with guess about the
tertiary solvent property of the SnO2/MnO2/Co3O4 fluxing the Bi2O3 into a glass . Because the dopant percentages
for MnO2/Co3O4/Bi2O3 at 20% would already be double
what would be expected to rupture the usual SnO2 lattice
and result in an opaque coating , even a black coating ,
unless everything was basically dissolved in solid solution ,
in particles so small that it is less than the wavelength of light , where usually what would be black is now lightly colored or clear This is great news and it means the
level of dopant saturation is intermediate and could be increased if wanted . The bismuth would be the dopant percentage to attempt increasing . The color would be expected to deepen and darken with increased doping and
it might shift color also , probably to a brown or coffee color .

The way you describe the shiny oily look of the coating it almost sounds like a lacquered gold anodizing sort of appearance . That sounds like it probably has good adhesion and clarity , like it's definitely a dense coating .


[Edited on 21-3-2008 by Rosco Bodine]

Yeah the whole idea of using the less stable stannic nitrate SnO2 precursor is to get the hydrated SnO2 matrix formation to *precede* the dopant decomposition so all the dopant is entrapped in a dispersed state . Then the dehydration and dopant pyrolysis proceeds and the SnO2 lattice collapses locking everything in place on sintering .

Having the reaction order reversed would royally screw up that whole plan

The only way to use the SnCl4 in a dip coating is probably to convert it to an alcoholate which has less stability than the SnCl4 itself . IIRC the only way that straight SnCl4 alone was ever useful was as a spray pyrolysis precursor .

I have the pdf Merck tables for densities / molarities on common acids and bases including NH4OH , I can post if needed . The tetrahydrate of Mn nitrate should be mole weight of 251.01 .

I think the easiest way of calculating the precursor solution
would be to use "precursor equivalents" which provide
the correct percentage ratios of oxides after pyrolysis ,
and then account for the dilution to whatever matches the
~8% SnO2 . I have a good idea how to dilute to the required
concentration , based on weight , using an adjusted reciprocal of 8% as a mulitplier to determine the end weight for the mixed composition . I'm working it out and I'll post the details along with the weights .

IIRC the 8% SnO2 loading was about maximum before the smooth SnO2 coatings transitioned to cracked mud sort of coatings on sintering . It's exactly like the scenario with coatings of lacquer , there's an optimum solvent to "resin"
ratio which forms the best continuous film residue as the solvent leaves .

This whole thing will need to be done on weights to get it
accurate , the first time , not knowing the solution densities
for such a mixture .

I think the easiest way to do this is simply to look at the
percentages as being grams in a total of 100 grams of
total oxides after pyrolysis . So 82% SnO2 becomes 82 grams of SnO2 , 8% MnO2 becomes 8 grams MnO2 , ect .
Then just calculate the molar equivalents of precursors required for the x number of grams needed for that oxide .

The dilution weight will then have to be derived from the outcome of those calculations .

From what I can see already .....
we do arithmetic differently
Here's a quick look based on the first calculations I have done on parts totaling 100 of the mixed oxides as related
to precursors for producing 82% SnO2 , 8% MnO2 , 5% Co3O4 , 5% Bi2O3 .......precursor quantities as follows
should produce 100 grams total of the above mixed oxides
represented in their designated percentages .

82 g SnO2 from 190.77 g SnCl4 - 5 H2O (nitrate precursor)

190.77 g SnCl4 - 5 H2O ------> 199.6 g Sn(NO3)4

8 g MnO2 from 23.1 g Mn(NO3)2 - 4 H2O

5 g Co3O4 from 18.13 g Co(NO3)2 - 6 H2O

5 g Bi2O3 from 5 g Bi2O3 (nitrate precursor)

with 4.06 g HNO3 -----> 10.41 g of Bi(NO3)3 - 5 H2O

A solution weighing 1025 grams containing the above
precursors would have an 8% SnO2 loading .
That dilution involves ~784 ml H2O , less whatever
small additional weight of acid , glycerin , ect. is used .

A reasonable sized experimental batch would probably
be one tenth to two tenths the above quantities .

My inclination would be to not dilute it that much and
try it at the syrupy stage first to see how it goes .
It may be that the "glassiness" expected of this mixture
is not as susceptible to the cracked mud kind of problem
as appears at 8% loading on ordinary SnO2 sols and
it may stand a much higher loading which would be good
because it will build thickness faster if it does work out
that way .

It might also be worthwhile to use a mixture of chlorides
and nitrates to possibly utilize the oxygen surplus of the nitrates in aiding the conversion of the chlorides to the oxides , as something towards an "oxygen balanced"
mixture . I would still keep it on the oxygen rich side
however by perhaps 150% of theory for O2 balance if that modification is tried , and still the higher temps are going to be needed to assure completion . This is another totally unreferenced idea , so I can't point to any justification .
It could aid the stability of the precursor solutions , and spread the pyrolysis and diffusion process across a range of temperature , improving the coating by gradualizing the sintering . Or it may not help at all .


[Edited on 22-3-2008 by Rosco Bodine]

9.75% Bi2O3 doped SnO2 optical quality film US6777477

The question was asked earlier about possibly using the alpha stannic oxyhydroxide directly as a coating precursor .
It can't be used directly , but after peptization which is very easy , it definitely can be used . This is the exception I should have mentioned before .

The patent US6777477 has been brought up several times before as being of possible ( probable) interest , and this seems like a good point to bring it up once again . This patent was mentioned most recently on page 7 of this same thread
http://www.sciencemadness.org/talk/viewthread.php?goto=lastp...
where I was observing that all of these coatings schemes
involve a sol transition , and indeed there are a few schemes
where the peptized , relatively pure hydrosol gotten from
the alpha stannic oxydroxide and its dopants can be used
as a baked coating precursor . This is the exception for
the matter where the directly precipitated alpha oxyhydroxide cannot be used as a coating , as its particle size is too large and it does not sinter to an adherent film
but dusts instead . Ammonia or organic amines change the
surface property and reduce the size of the colloidal particles , acting something like a detergent or emulsifier ,
so that the precipitated larger particles resuspend , and
"redissolve" , something like a controlled reversal of the
neutralization which precipitated the oxyhydroxide , to
form a hydrosol , which is something like an induced supersaturated solution , a colloidal dispersion of the hydrated oxides . Upon evaporation of the water , along with
loss of the volatile amine which is acting as the dispersant , this system will dehydrate and sinter to an adherent film .

See Example #2 for the 9.75% Bi2O3 doped SnO2
http://www.sciencemadness.org/talk/viewthread.php?action=att...
Attachment: US6777477 Sb2O3 doped SnO2 via ammonia soluble derivative.pdf (67.31 KiB)

This patent method avoids the nitrates of tin and avoids alcoholates , yet reports a way of making use of chloride precursors to produce optical quality films via dip coating , which are highly doped with either antimony or bismuth ....
a result which fits our purpose nicely .

When the oxidative soak deposition proved unworkable
using SnCl2 because of it reducing the cobalt spinel interface
coating , this patent method was suggested as an alternative for applying a "sealing layer" over the spinel ,
and it still seems like this should work fine .

This 9.75% Bi2O3 doped SnO2 could serve as a working anode coating , it may even work as an interface coating
but my guess is it would do best to use the Co3O4 spinel
as the interface and then seal it and overlayer it with this
patent composition . The Bi doping is in the range of those
Bi doped SnO2 described in US4272354 as useful , at about
the lowest Bi2O3 in the 9:1 to 4:1 SnO2 to Bi2O3 preferred ratios . The Bi doping percentage could likely be increased
above the 9.75% which provides the optical quality film of
the US677477 patent , to achieve the higher percentage doping described in the US4272354 perchlorate anode patent .

Earlier on page 6 of this thread Xenoid pointed to this
US4272354 patent as a principal interest , and indeed there is something of a nexus between the US4272354 patent
and the US677477 patent Example #2 , for Bi2O3 doping of SnO2 . Sorry for the aggravation if this seems circular ,
once again , but these two patents are very significant
if indeed the Bi2O3 doping should prove out as valuable
for the working coating dopant which indeed is the required
"special ingredient" catalytic for perchlorate .

Simply combining the cobalt spinel interface method which
is already proven , with this Bi2O3 doped SnO2 sealing and working coating , may be the simplest baked coating scheme
which is workable for a perchlorate anode .

My 35 year old CRC says colorless to rose monoclinic
d 1.82 . IIRC there is a hexahydrate which exists in solution at ordinary temperature . But if you have the solid at room temperature it is probably the tetrahydrate .
Using a prepared reagent which is so hygroscopic ,
what I would do is go by solution density entirely for
an already existing nitrate solution , or boiling point
indicating the tetrahydrate . But the way to be sure
of molarity is probably to make the nitrate from the carbonate with nitric acid .

The brown color may be some decomposition , or impurity .
A drop of nitric acid may clear it up , it is probably pH sensitive . Seems like I have seen the commercial 50%
packed with as much as 5% HNO3 .

I have looked into this further and found conflicting references , as well as some acknowledgement in the literature of conflicting references and some attempts at explanation of why . The composition of the hydrates of manganese nitrates will usually be a mixture of different hydrates which can have very close melting points which
confounds identification , and it is also possible for a
manganic as well as a manganous oxidation state to be coexistant , complicating the matter further .

This is why it is difficult to be sure precisely what quantity of
manganese is actually present , absent analysis of a sample ,
or direct preparation from a more easily quantifiable intermediate like the carbonate . Know you got to love that


[Edited on 24-3-2008 by Rosco Bodine]

Attachment: US2017980 Crystallization Process for Manganese Nitrate Hydrate.pdf (44kB)
This file has been downloaded 779 times

You are right , that is a very good sign .

The coating which did sinter is tough enough to endure an etching bath and not just rinse away . It reveals the vitrification to an adherent film of ceramic material did occur . So *if* the conductivity and catalytic activity remain present for that vitrified coating .....bingo! ,
one baked coating perchlorate anode
is what it (very probably) will be .

The dopant levels may bear significant increasing of
their percentages for increased activity of a working coating , but for the interface and near interface sealing coatings it is probably best to keep the dopant levels
conservative , aiming for conductivity and a good sealing effect .

From the higher percentages allowable for Bi2O3 doping
of SnO2 , even to the point where it would seem the
SnO2 is the dopant for the Bi2O3 ....the physical compatability is much better for bismuth and SnO2 than
is the case with antimony . The Bi2O3 is a sinterable
film former all by itself , as is SnO2 but of course there
isn't enough conductivity for the pure films to be useful ,
as they are quite good dielectrics . But with added
conductivity from the cobalt and manganese doping ,
then a ceramic semiconductor material is produced .

I wonder if silver oxide or lead oxide might even be useful as an included dopant in a composition like this . If it is
well entrapped in a glass like coating it may be perfectly
stable and could have catalytic activity .

Dumping the gell into a larger volume of very faintly alkaline cool ammonia water ( pH 7.5 - 8 ) may facilitate breakup of the gell and settling as a manageable , rinseable precipitate .

You have to be careful with the excess of ammonia because it will only to a point help settle the precipitate , but then more will begin to peptize that hydrated oxide to
a hydrosol , with some conversion to ammonium stannate .

From what I have gotten from a couple of patents the
alkalinity should be 7 to 8 pH , higher pH will peptize ,
lower pH will gell .....so it is quite sensitive .

Also it looks like solutions in the range of 5-10% SnCl4
will gell , so it may be that lower concentrations would be
better . I have never done this precipitation so this would
need to be checked , but what I would suggest is using
relatively dilute SnCl4 in water , say a cold 2-3% solution ,
mixed with cold ammonium hydroxide also of 2-3% concentration with good agitation , the quantities being
calculated at the neutralization equivalents . For convenience what I would do is simply match the two prepared equivalent solution volumes by dilution of the lesser to match the greater volume , and then do a
simultaneous rapid pouring of the two cold solutions together into a beaker with a large stirbar already spinning , and check the pH immediately on the still cold solutions , adjusting it as needed with dilute NH4OH or HCl
until about 7.5 to 8 pH is achieved , then gradually warm
the stirred mixture to perhaps 60C - 70C .

*If* my guess is correct .....
( yeah another one of those maybe huge "ifs" )
this sort of manipulation should facilitate a controlled precipitation of a settling and decantation rinseable ,
filterable precipitate , as opposed to having a beaker full of white jello .

I have looked for a published preparation but so far
haven't found one .

Edit: deleted remarks about suggesting possible usefulness
of NH4NO3 in part substituted for some of the NH4NO3 as per Lowenthal , as it appears likely that the hydrated metastannic rather than the hydrated alpha stannic oxide
desired would be the product of the Lowenthal method .

[Edited on 25-3-2008 by Rosco Bodine]

That's a coincidence you should mention the H2O2 , as I remembered H2O2 being mentioned in a couple of references as producing precipitation similarly as does NH4NO3 , even in acidic but dilute solutions . I have been looking for a couple of hours to try to find that reference which was basically two sentences with no elaboration .
I think I even wrote something about it in one of these threads but I can't remember where . There's so much data I have been accumulating I can't keep track of it anymore

Those proportions that I put down above which were
derived from the parts per hundred , totaling one hundred
are correct . But you would have to adjust the carbonate weights if you use the carbonates instead of the nitrates
of cobalt and manganese . Instead of what I showed above for the cobalt nitrate hexahydrate , you would
use 7.4 grams of cobalt carbonate and 10.6 grams of
manganese carbonate , 5 grams Bi2O3 , and the stannic nitrate derived from conversion of 190.8 grams of stannic chloride pentahydrate . The additional HNO3
for the two carbonates will be 19.5 grams HNO3 pure basis plus 4.1 grams HNO3 for the Bi2O3 , 25 grams HNO3
pure basis would probably be required . And water about 750 ml for these quantitites would put the SnO2 loading at about 8% , but I would try it more concentrated .
An additional 137.2 grams HNO3 pure basis , will be needed for conversion of the stannic oxyhydroxide to stannic nitrate.
For the neutralization of the 190.8 grams of SnCl4 - 5 H2O
would be needed 141.35 ml of 29.4% 26 degree Baume
NH4OH .

You can derive a multiplier for any desired quantity
and multiply with these figures to make a different sized batch .

BTW I found a published English translation of the Lowenthal article today , which is the same article as woelen translated
a few weeks ago . And please note that the SnCl2 shown
in the article is actually in todays corrected formula SnCl4 ,
as the numerical formulas of the time had the number of Chlorines wrong by one half , even though the designation
of stannous compounds and stannic compounds with respect
to oxygen content of oxides is correct . The "protochloride"
designation is the stannous salt , while the "perchloride" designation is the stannic salt .

Edit: Some references say that the precipitate of hydrated
stannic oxide gotten by the Lowenthal method may be rinsed with 10% nitric acid , which indicates that is the metastannic hydrated oxide , rather than the alpha stannic hydrated oxide which is required for dissolution in HNO3 to form the nitrate . So the Lowenthal method is likely useless
if the intention is producing an intermediate for conversion
to stannic nitrate .

[Edited on 25-3-2008 by Rosco Bodine]

Attachment: Lowenthal translation Chemical_Gazette.pdf (234kB)
This file has been downloaded 836 times

From what I have read it seems that the alpha stannic oxyhydroxide is unstable , so it is a delicate matter to
precipitate it in manageable form where its density and level of hydration are just right . The concentration of the precursor solutions should be dilute and the neutralization
and precipitation condition controlled . There's other
materials which show similar difficulty .

I know in that US6777477 patent they describe pH 8
as precipitating , but then pH 10.5 is peptizing and that
isn't a very wide transition . That's where the NH4NO3
and heating could help . But then heating tends to polymerize the alpha to the meta form .

You may have the H2O2 use mixed up with another purpose . I can't find the reference on H2O2 and I'm thinking it may have applied to the stannous salt for another purpose and product , like for raising the SnCl2 to SnCl4 .....so you may not have what you think ,
but a metastannic oxyhydroxide instead . It's the hydration state and level of polymerization which
determines which isomer you have . The only other place I recall H2O2 being used was with the peroxyorganic acid
substituted metastannic acid sols .

Wait a minute ....I found that obscure reference on H2O2
See page 6 of the attached excerpt , (page 270 item #14) .
This may be a variation on the Lowenthal synthesis because
a careful neutralization is used in the Lowenthal method
also whose purpose is in fact to produce an easily filtered
and clean and pure precipitate to facilitate analysis . However
the precipitate is not really the hydroxide but a basic hydroxide or "oxyhydroxide" for the Lowenthal method ,
and I suspect these may be the same products . Very interesting , I meant to look into this before but something else came up and I forgot about it .

*Stannous* salts are used with this H2O2 here though , I
was right about that . I suppose what probably happens
here is something similar to the oxidative soak deposition ,
but here the process is a bulk precipitation so rapid that
the hydration level is maintained . This could be a shortcut
method from the metal or SnCl2 , however to a precipitate
which might be filterable . Somehow I don't think this
would go as well as working from the already oxidized
stannic salt , as per Lowenthal or ordinary neutralization
with NH4OH . Later references have indicated the Lowenthal method likely produces the metastannic hydrated oxide which is unreactive with nitric acid .

However ammonium carbonate , and likely ammonium bicarbonate , should produce the desired alpha stannic oxyhydroxide in the same manner as does ammonium hydroxide , and use of these carbonate of ammonia makes
the neutralization pH less critical , as the precipitated alpha
stannic oxyhydroxide is insoluble in excess of ammonium carbonate , not forming ammonium stannate and peptizing
as would be the case with an excess of ammonium hydroxide .

[Edited on 25-3-2008 by Rosco Bodine]

Attachment: Pages from 265 Analytical_Chemistry.pdf (299kB)
This file has been downloaded 5880 times

I'm not sure about the pH monitoring . What would
be great is some sort of color indicator , nothing to break or corrode

See my edit above , I found that H2O2 reference .

BTW , using only 8 grams of SnCl4 , is that just a test run ,
because you are making not much , like a large test tube amount .

After doing some more reading , it appears that the most desirable reagent for neutralization of the stannic chloride
to produce alpha stannic oxyhydroxide with least difficulty ,
is ammonium carbonate . The neutralization pH is not
critical , as the precipitate is not soluble in an excess of
the ammonium carbonate . Now that I have rediscovered
this , I am nearly certain this was declared in one of the patents which has been posted , or perhaps one that I have
already but have not posted .....this bicarbonate and/or
carbonate neutralizer seems extremely familiar and I know I have seen it somewhere before .

[Edited on 26-3-2008 by Rosco Bodine]

You might try the precipitation conditions described in US6777477 .

Alternately try limiting concentration of the SnCl4 to the 2 to 3% level , and doing a rapid simultaneous pour mixing of cool solutions into a like volume of cool H2O containing the bare neutralization equivalent of NH4OH .

I am going to say limit the warming I suggested earlier to more like 40C , barely warm because of the attached reference which reports 60C will convert the alpha to the meta stannic acid . This confirms what I suspected about the
instability of the alpha form , but describes the alpha as being even more prone to polymerization to meta at a lower temperature than I expected . Evidently the precipitation temperature will be determinate on whether the alpha or the meta form is produced .

The attached patent US2460734 describes that the SnCl4 diluted in H2O to less than 4% concentration hydrolyzes completely in one hour at room temperature to a dispersion , a sol of alpha stannic acid , and free hydrochloric acid .
So it is simply a matter of then neutralizing the free HCl and salting out the hydrated SnO2 by destabilizing the already existing sol .

I am going to get some ammonium bicarbonate so the method of US4775412 can be followed for precipitation of the alpha stannic oxyhydroxide .
Technically , this looks the easiest sure way .

A heat gun is going to be really pressed to do the job on the
tin oxide sintering . A well insulated furnace tube and maybe even some sort of thermal breaked holder for the anode substrate is probably needed .

The pure stannic nitrate which is being made here is not going to have good stability by itself . There may be improved stability required by addition of a small amount of
ammonium nitrate , if there isn't sufficent residual ammonia
in the precipitated alpha stannic acid to supply it when the nitric acid is used for conversion to the nitrate . Also
a small amount of acetic or tartaric acid may be needed
to stabilize .

The compositions described in the Ordway article which are
complex mixtures have better stability than pure stannic nitrate , and may prove to be better precursors . Those
complex mixtures have stability better than straight stannic nitrate , but lower stability than the chlorides derived sols or alcoholates . The patents which mentioned the usefulness
of the tin nitrate did not specify anything about the nature
of the tin nitrate composition to be used , so there could be
some tuning of that nitrate precursor required to get it right .

For example the precursor which works best could not surprisingly turn out to be a mixture of stannic nitrate and stannic chloride with acetic acid or tartaric acid in small amount , or the mixture most desirable could be one of
the Ordway mixtures . Or it could fit the composition of
one of the Pytlewski mixed valency sort of polymers which
are also involved in some of the Ordway described mixtures .

Stannic nitrate alone may not prove to be the single answer
as an SnO2 precursor but only a component . Just pointing this uncertainty out concerning the stannic nitrate and the
context in which it is useful , is a long way from being fully described in any existing literature .....so what we are doing
is basically pure experimentation with regards to the finer points which do involve a few unknowns .

Attachment: US2460734 Alpha Stannic Acid process.pdf (123kB)
This file has been downloaded 1239 times

Inorganic polymers and their quasi-inhibited precursors
are a barrel of fun , huh ?

From everything I have read the alpha stannic hydroxide
is definitely unstable and heat sensitive , as is the stannic nitrate . So it may very well be better to go the Ordway route where some mixed chloride and nitrate , as well as mixed valency polymer is present , in order to achieve stability .

There are references to alpha stannic acid which has been precipitated via hydrolysis of a heated very dilute solution
of a stannic salt , being converted to metastannic acid
if the solution is boiled more than just briefly . It may be partly polymerized at lower temperature over longer time .
So dilution , temperature and pH influence the precipitation and obviously there is a reaction conditions window which is favorable , but there is a time window also , as the alpha form will tend to polymerize to the meta form at some unknown rate made worse by passing time and also by heating .

It would probably be best to avoid letting the alpha stannic acid precipitate stand for any extended time as it is unknown what its half-life may be .

The higher temperatures being required for complete conversion of the SnCl4 to SnO2 is a good reason by itself
to use something else as the precursor .

[Edited on 2-4-2008 by Rosco Bodine]

another MMO of possible interest

Plate MMO

diva update

interesting recipe

possibly adaptable to MnCo2O4 spinel

The above patent is possibly applicable also in benefitting
the formation of better baked coatings of mixed nitrate precursors for bimetal spinels like MnCo2O4, or for mixed Co and Ni spinel , or the monometal spinels.

The technique could certainly be easily enough tested to see if indeed a tougher baked coating results. The photosensitivity of the precursor mixture is certainly new information that is noteworthy.

Attached is the journal article I mentioned earlier about the
effect of carbon in reaction with the nitrate precursors. I have hypothesized that mixed valency precursor salts
where some of the nitrate oxygen is available for reaction
with the lower valence metal ion should have a similar effect on promoting the pyrolysis.

Decomposition of mixed Mn and Co nitrates supported on carbon ( attached )

Definitely time for a diva break

http://www.youtube.com/watch?v=VRFS_WxtMoA&feature=relat...

[Edited on 7-10-2008 by Rosco Bodine]

Attachment: Decomposition of mixed Mn and Co nitrates supported on carbon.pdf (236kB)
This file has been downloaded 2418 times

Niobium DTO anti-depassivation coated Ti Anode

Bismuth has already been identified in the literature as having good effect as a dopant for tin oxide useful as an oxygen diffusion barrier , anti-depassivation coating on Ti substrate anodes, the Bismuth also having catalytic activity in the production of perchlorate.

Niobium (formerly Columbium), a closely similar sister element of Tantalum found intermixed in their ores the same as Nickel and Cobalt, is also reported in the literature to
have a similar value as a barrier to oxygen diffusion caused
passivation of a Titanium substrate anode. What may be
if any catalytic activity in the production of perchlorate is unknown. The patent US4471006 Niobium DTO enhanced oxygen anti-passivation Anode describes how the combination of 5-valent Nb2O5 as a dopant material with
4-valent indigenous TiO2 or SnO2 also applied thereon,
results in an N-type semiconductor coating which is
anti-depassivating , allowing anodic current flow.

Probably Vanadium Pentoxide, V2O5 would behave similarly
and may even have catalytic effect via an unstable pervanadic state. This is something I have postulated earlier in some of these threads, but have done no experiments to confirm. IIRC in one of the patents posted by
JPSmith a baked coating containing vanadium doping on a hydrided Ti substrate was a successful scheme.

Niobium compounds are probably three times as expensive
as Bismuth, but this still is much less expensive than Ruthenium / Platinum series candidates for the intermediate layer or DTO coatings, and because of the excellent oxygen
diffusion barrier anti-depassivation performance reported for Niobium, this seemed worth making note . Niobium might find
usefulness in combination with other dopants or layered MMO schemes where the "labrynth effect" of differing oxygen
overvoltages for differing sequential layers is applied, testing
another one of Rosco's postulates , of course

And obviously ....that's right , now it's time for another diva break

http://www.youtube.com/watch?v=YNlpxJO1Uiw&feature=relat...

http://www.youtube.com/watch?v=koi_f3fB2h8&NR=1

Other Niobium related patents of possible interest are
US3950240 Niobium Doped Tin Oxide Anode
US4873352 Niobium DTO via Oxalate H2O2

Attachment: US4471006 Niobium DTO enhanced oxygen anti-passivation Anode.pdf (140kB)
This file has been downloaded 1224 times

another organic precursor MMO of possible interest

@Swede, Among those other reagents is there nitric acid, acetic acid, ammonium hydroxide, ammonium carbonate or bicarbonate, ammonium fluoride or bifluoride, hydrogen peroxide, citric acid, glycerine ?

BTW with regards to soluble Niobium salts, US5419824
describes a preparation of ammonium niobate which reportedly has good solubility in water.

There may be a fair amount of surplus Niobium-Titanium alloy wire available cheaply, as an associated scrap from the Cern supercollider project.....and maybe some other relatively exotic materials also. I have been anticipating getting my hands on some of this scrap at some point and contemplating possible uses for it .....like superduper anodes

[Edited on 27-1-2009 by Rosco Bodine]

@jps - A High voltage supply is something that I am currently lacking. DLC films - yet another resource to investigate!

@RB - Of the additional reagents you mention, I am LACKING ammonium hydroxide in any real strength, acetic acid, and the ammonium fluorides... the others I do have.

I'm digging through some of the boehmite literature right now - there is a lot of it. The basic problems - introduction of the catalyst into the boehmite pore structure, transition of the catalyst(s) to active oxides, and dipping/adhering the slurry to an appropriate shank. I have some niobium metal, and the possibility exists to create salts of niobium.

One limiting factor is temperature - above 400C, apparently the boehmite breaks down and the desirable microtubule structure is destroyed.

The anode obviously must conduct, and like the traditional electrodeposited lead dioxide anode, the barrier between PbO2 and Ti must not passivate. Perhaps once again, the commercial MMO substrate may be the material of choice.

Some notes on MMO/MnO2 anodes from a while back!

Whilst not wanting to return to the heady days of early '08, I've been spending the last few months experimenting with an MnO2 anode aimed at perchlorate production. Rather than try to coat etched Ti directly or via the Co2O3 interface layers, I decided to thermally coat some MMO mesh as it is so readily available now.

I re-examined De Nora et. al's (Diamond Shamrock) 1978 US Patent Number 4072586 which among other things mentions applying thermally decomposed coats of beta-MnO2 over thin layers of RuO2.TiO2 on Ti (aka MMO). Beta-MnO2 is apparently isomorphous (rutile structure) with RuO2 (and TiO2) and thus bonds well to the MMO surface. In particular my attention was drawn to column 5 (lines 22 - 54), which mentions the suitability of beta MnO2 for perchlorate production, especially when enhanced with up to 5% As, Sb or Bi (actual element not specified).

Indeed the thermal beta-MnO2 does indeed bond well to the MMO coating and will form a thick, hard, crusty coating. It will even bond directly to non-etched oxide coated Ti, because of the rutile structure, but will of course be non-conducting.

Because of the size, instead of dipping the anode in the coating solutions, I used painting and eventually a spray technique. For mesh material, spraying is ideal as it is easy to coat all surfaces of a complex electrode assembly. A small (30 ml) plastic perfume sprayer proved ideal.

For thermal decomposition I used the same hot air gun technique as described earlier. Because of the larger electrode size I used a larger diameter tube and mounted it on a stand, otherwise the set-up was basically the same. The sprayed on coating was dried over the turned down hot air gun, this prevents drips and runs. The electrode was then baked for 10 mins at about 380 oC. Initially 25 coats of Bi-doped MnO2 were applied.


Crusty, black MnO2 thermal coating over MMO dual anode assembly.

Stock Solutions:

Mn(NO3)2 - made from pottery grade MnCO3 (31g) and 68% nitric acid (50 ml). This should fully react, may need a little more depending on purity of MnCO3. Solution was filtered and made up to 100 ml, it contains 48.25g Mn(NO3)2 or 14.8 g Mn.

Bi(NO3)3 - crystals made by dissolving Bi metal in 68% nitric acid (see thread). 6g of moist (nitric acid) Bi(NO3)3.5H2O crystals were placed in a small beaker and covered with 20 ml 68% nitric acid, diluted to 40 ml with water and stirred until dissolved. This solution was made up to 50 ml with water in a volumetric flask and contains about .0635 g Bi / ml.

Co(NO3)2 - crystals made by double dissolution of CoSO4 and Ca(NO3)2 or reacting CoCO3 with 68% nitric acid (see thread). 10 g of moist crystals (Co(NO3)2.6H2O) were dissolved in about 25 ml of water and made up to 50 ml in a volumetric flask. This solution contains .0405 g Co / ml

Dipping / Brushing / Spraying Solutions:

These are loosely based on Pat. #4072586, but are by no means definitive. They are just what I came up with for initial tests.

Pure MnO2: 16 ml of the Mn(NO3)2 stock was transferred to a 50 ml volumetric flask, along with 5 ml of isopropyl alcohol, and made up to 50 ml with water.

Bi doped MnO2: 16 ml of Mn(NO3)2 stock was transferred to a 50 ml volumetric flask, along with 1 ml of the Bi(NO3)3 solution (.051 g Bi) and 5 ml of isopropyl alcohol and made up to 50 ml with water. This solution is roughly 50g / litre Mn with 1.3% Bi in MnO2.

Co doped MnO2: 16 ml of Mn(NO3)2 stock was transferred to a 50 ml volumetric flask, along with 3 ml of the Co(NO3)2 solution (.121 g Co) and 5 ml of isopropyl alcohol and made up to 50 ml with water. This solution is roughly 50g / litre Mn with 3.0% Co in MnO2.

Some results with the MMO/MnO2 anode.

I'll be the first to admit I have been less than scientific in testing this anode. Hopefully, because it's so simple to make, others will have a go at evaluating it's performance as well. From the earlier work with MnO2 anodes, I knew they would make both chlorate and perchlorate, I really wanted to test their practicality in this new configuration.


Electrode assembly, note 3 titanium cathodes and 5mm spacing!

All testing has been carried out in a 1 litre cell.

1. The anode assembly along with 3 Ti cathodes (5 mm spacing) was placed in a 100 g/L KClO3 solution (saturated at 30oC.). The pH was reduced by the addition of 1 ml conc. HCl to about 2.8 this in an attempt to shift the Mn stability away from the wide end of the MnO4- field (high pH) and into the region of maximum stability for MnO2. The idea behind this was to try and avoid the "Purple Haze" effect which plagued earlier efforts with MnO2 anodes. Sadly this had no effect whatsoever, and the cell turned pink within 15 mins. The cell was run at a conservative 3.8 V / 3.5 A, this limited the temperature rise to 30oC. The cell was run for 48 hours (168 Ah), no perchlorate was detected during this time. A little, brown hydrated MnO2 was deposited on the cathodes and the cell bottom and sides.


First assembled 1 litre test cell, note permanganate "Purple Haze" and MnO2 scum!

Thinking that perhaps the cell voltage was a little low for perchlorate production (industry use 5 - 6 Volts) I dismantled the cell and removed the close spaced cathodes and replaced them with a single Ti mesh cathode spaced about 4 - 5 cm away. This had the immediate effect of raising the required voltage to 5.7 V at 3.5 A. After a further 17.5 hours (61.2 Ah) in this new configuration there was still no positive test for perchlorate!

Disheartened, I tried an NaClO3 cell

2. The 1 litre cell was filled with 500g / L NaClO3 solution. The single cathode with 4 -5 cm spacing was retained and the cell operated at 4.8 V / 3.5 A. Cell colour was pale pink and a test for perchlorate was negative after 3 hours. The next day after 23 hours (80.5 Ah) a positive test for perchlorate was obtained.

Heartened by this, I dismantled the cell and added another 10 coats of Bi-doped MnO2 to the anode assembly, although it still looked in good condition. The electrode was reassembled with the original 3 Ti cathodes with 5 mm spacing, and the cell was connected to a new power supply and now running at about 4.6 V / 7.8 A. The cell was run for a further 68 hours (530.4 Ah). Positive perchlorate tests were obtained directly from the warm liquor.

3. The cell was dismantled and refilled with the 100 g/L KClO3 solution from earlier. The anode assembly was coated with an additional 5 coats of Co-doped MnO2. A single Ti cathode with spacing of 5 to 10 mm was used. The cell was operated at about 5.8 V / 9.5 A for about 21 hours (199.5 Ah), no perchlorate was detected.

4. The cell was dismantled and the anode assembly had an addditional 5 coats of pure (un-doped) MnO2 added. The reassembled cell was operated at about 5.2 V / 7.6 A for 21 hours (160 Ah), no perchlorate was detected.

5. Added 5 coats of Bi doped MnO2 to anode assembly and placed in a 300g / litre NaCl cell in an attempt to progress all the way to perchlorate. The cell was operated at about 8 - 9 Amps. After about 6 days and 1188Ah the presence of perchlorate was indicated. This became stronger, and after about 12 days (2376Ah) the cell was shut down (pH=8.3). The anode still appeared to be in good condition (still plenty of coating).

6. Started a new 1 litre cell containing about 80g / L KClO3 solution, this was mainly to test if the pink colouration was generated with well-used (leached) MnO2 anodes. I used the anode assembly from the NaCl -> NaClO3 -> NaClO4 run. A pink colouration appeared in the cell within 15 minutes. I left the cell running at about 5.0V / 8.0A, after about 48 hours I got a positive test for perchlorate (384Ah).

7. I made 4 identical test strips of MMO coated with 5 coats of pure MnO2, 1.3%Bi/MnO2, 3.9%Bi/MnO2 and 3%Co/MnO2. I carried out some electrical measurements with these anodes in NaClO3 solution, but there was no obvious difference in their performance.

Summary: Poor man's lead dioxide!

Pros: Very cheap, readily available, non-toxic and easy to make. Easy and quick to apply to an existing MMO coating (5 coats in an hour). Coat seems to last quite well, and a few more can be added quickly before a run. Will make chlorate and perchlorate and will convert NaCl to NaClO4.

Cons: Contamination with pink MnO4- and brown MnO2. Not very efficient and require solutions to be highly concentrated. The low solubility of KClO3 means particularly low efficiency in this system.





[Edited on 15-3-2010 by Xenoid]