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Author: Subject: More on PbO2 electrodes
Twospoons
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[*] posted on 18-7-2007 at 16:16


This mention of the volatility of the chloride jogged my memory of a web page describing a DIY method of making conductive glass. Essentially two sheets of glass were spaced about 1 cm apart, the SnCl4 put at one end. The whole lot was heated and the vapour was gently blown between the sheets of glass, depositing SnO2 over the surface. This was descibed as a 'kitchen sink' process, so may be a better basis for experiment than trying to read between the lines of patents.

Maybe 'enclosing' the Ti when baking would assist with getting a good coat, as the SnCl4 vapour would be trapped in close proxitimty.




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[*] posted on 18-7-2007 at 21:45


I am wondering now if a mixture of SnCl2 and SnCl4 might have better usefulness than SnCl4 alone , ( for the tin oxide precursor ) . SnCl3 anybody???:D ( SnCl2 - SnCl4 )
I have also wondered about adding other materials like lead or zinc or iron as the chlorides or nitrates .


[Edited on 19-7-2007 by Rosco Bodine]
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[*] posted on 18-7-2007 at 22:20


Why?

Its interesting to look at a periodic table: there's tin, under Ge and Si. To the left are the common P-type dopants, B, Al, Ga, In. To the right are common N-type dopants N, P, As, Sb, Bi. Given the majority carrier mobility is higher in N-type semiconductors (hence higher conductivity) it would be interesting to try some of these alternates as dopants for SnO2. Maybe try some tin phosphate?




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[*] posted on 19-7-2007 at 00:06


Correct me if I'm wrong' but isnt the Sb, Sn doping meant to be just a relaying layer between the Ti and PbO2? if so then why are you trying to run a chlorate cell with no coating?
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[*] posted on 19-7-2007 at 05:53


@Twospoons

The conductivity of undoped SnO2 is poor and it was
the effect of a mixed oxide of SnO and SnO2 ....maybe a suboxide O value of ~1.5 that I was thinking about there
as a scheme for increased conductivity aside from other doping . Anyway I am pretty sure I have seen Sn(II) compounds used in coating schemes and they tend to oxidize to Sn(IV) in the baking process via oxidation from the air and/or reaction with other materials that are present .

Many of the patents show examples using one tin compound like SnCl4 - 5 H2O , but they specify a list of other tin compounds which may also be used , neglecting to give any details concerning those alternatives .

Also there is the possibility of a substituted bimetal oxide
along with the possibility that some of those mentioned
can have a doping action on the titanium oxide diffusion layer , along with the reducing action of SnCl2 which could
compete with the complete oxidation of Ti to TiO2 .

In several articles I have seen the intermediate stage of formation for the doped tin oxide layer described as forming a transient sol - gel system which then dehydrates and the dispersed colloidal particles then sinter as a solid solution ...which is the mechanism which produces a tough vitreous like coating , and the conductivity and amount of doping possible to be in solid solution is directly dependant upon the smallness of the oxide particle size and homogeneity of dispersion .

These sols can even be produced externally by separate synthesis and then applied as a coating to shortcut and make more complete what occurs in situ . By such a strategy , a conductive doped tin oxide coating can be
cold applied to even a polyethylene substrate . If anyone has need of an electrically conductive soda pop bottle for example .....then that is a can do :)

BTW , this is another reference which shows an upper limit of Sb doping in the range of ~8-10% , before Sb oxide exceeds the capacity of a solid solution in SnO2 and appears as a separate phase with conductivity going down , and confirms other references reporting the same thing for Sb doped SnO2
prepared under the most ideal conditions . And in a usual
baking scheme the upper limit is something on the order of one third that amount before the same effect occurs . I am doubtful that the diffusion from a substrate of what would be an additional material trying to find room in the tin lattice would improve those figures . The SnO2 is something like a sponge that can only hold so much in the way of dopants ,
no matter where they originate .

What I conclude from all of the stuff I have read is that when you think of what are probably useful percentages of dopants ......
think small :D

With the higher levels of Sb , perhaps a spinel formation
comes into play ?

[Edited on 19-7-2007 by Rosco Bodine]

Attachment: Antimony doped Tin Oxide colloidal nano-sols.pdf (584kB)
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[*] posted on 19-7-2007 at 07:37


Dann, the blow by blow details are good for being able to figure out what is going wrong and being able to reproduce your results when you get it right. Use patents just to point you in the right direction. Go for the type of experimental detail you find in chemistry journal articles. You seem to be getting 3-4 out of 5 critical variables in each experiment, and then changing to another random 3-4 out of 5.

My best guess:

The solution needs to be very concentrated. Evaporate over hot water or steam until it starts to crystalize, then cool and see if you can redissolve with a little HCl and either 99+% isopropanol or butanol. There will be a small amount of fine precipitate. Don't worry about trying to get EVERYTHING dissolved, just let the solution settle and decant the clear liquid, or filter with glass frit and cellite. You can try experimenting with coatings on glass until you can get an optically clear coating, then move to titanium. Steel wool is going to scrub off any coating you get, stop doing that. Forget the burnishing and black surface description you read about in ONE patent. You want a clear, maybe slightly tinted coating. SnCl4 and SnCl3 in the finished coating solution is what you want. Use only enough H2O2 to get there. I see a color change in my solution at the point that enough H2O2 is added, and if I add a little of the SnCl2 solution, the color changes back.
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[*] posted on 19-7-2007 at 08:27


Add my ditto to what Eclectic is telling you . The alcohol
is used to try to increase the dispersion via an alcoholate
derivative or simply to cause precipitation of the oxide as finer particles ...more than is it used as a plain solvent .
Dittos for the patents which use thickeners , that is to
do two things , though , to build a thicker layer per pass ,
hopefully getting a solid coating on the first coat .....but also to increase dispersion and decrease particle size for the oxides , inhibit crystallization , and facilitate an amorphous film formation .

For some of the coatings which are dipped , it isn't even a room temperature solution which is applied ...but an actual melt of the hydrated salts @~80C or more .
For this you could probably remove the hot
titanium from the hot etching bath and immediately dip
it in the molten precursor , which may not even be a clear melt ....but a milklike colloidal dispersion if the dopant is not completely soluble , but suspended . I have even seen
loading methods described where separately made SnO2
or perhaps SnO is added as a thickener to the molten salts .

Regarding adhesion , I have seen reports that would indicate that this sort of coating can be tough , and
will even withstand some *gentle* abrasion without
being removed or damaged ...but that related to ceramic and glass substrate heating elements being able to withstand a housewifes cleaning of cooking surfaces with BonAmi cleansers and the like ....not steel wool .

The same level of adhesion should be possible for titanium or other metal substrates .
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[*] posted on 19-7-2007 at 10:10
Cold Deposition of Doped SnO2 , the "oxidative soak method"


This is a *very* interesting paper , with regards to usefulness of SnCl2 as a precursor , and also with regards to a cold process first layer deposition method .

This could possibly be very applicable as a method for application of the first layer of SnO2 that is gentle to the
titanium susbtrate . It should also be applicable to a titanium substrate which has an existing surface suboxide as described in US2711496 , or perhaps has received an initial
cold surface treatment with cobaltic or chromic acid .

Also note that with regards to the doping soak times ,
the highest conductivity achieved was for the shortest soak time which resulted in the slightest level of doping in the
SnO2 layer after baking .....more evidence it doesn't take very much dopant to do the job . Every in depth reference where the varying SnO2 layer chemistry is evaluated seems to follow this same track .

Attachment: Antimony doping of tin oxide coatings prepared by the oxidative-soak coating method .pdf (325kB)
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[*] posted on 19-7-2007 at 11:44


Hello Hashashan,

Quote:
Originally posted by hashashan
Correct me if I'm wrong' but isnt the Sb, Sn doping meant to be just a relaying layer between the Ti and PbO2? if so then why are you trying to run a chlorate cell with no coating?


That is true. I am going to use the Sn/Sb Oxide coat as an inbetween coat for Ti and LD.
In order to test the coatings I am simply putting the Ti coated strip into Chloride solution to see how well it stands up. It is far too much trouble to coat each with LD just to test the Sn/Sb Oxide coat.
Perhap this test is not appropriate.
I also give a small portion at the top end (only one small place the top) a rub of steel wool to see how well the coating has stuck or hard it is. A patent (one only!) did this and they were able to obtain a glossy black appearance. Sounds like a good coat to me.

Side Note

Mrs. Jones would need some elbo grease to remove that coating if it were on glass....but we are discussing anodes :P
End of Side Note!

Some of the Sn/Sb Oxide coatings were used on their own to electrolyze brine solutions in the patents for quite a period of time too.
I noted that any of the patents that give an example where by the Sn/Sb Oxide coat was used to electrolyse brine (no overcoat), the Sn/Sb Oxide coat was put on the Titanium using anhydrous SnCl4. They refluxed it with an alcohol for some hours first to obtain a compound for adding the Sb Chloride to.

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[*] posted on 19-7-2007 at 12:13


Hello,

Quote:
Originally posted by Eclectic
Dann, the blow by blow details are good for being able to figure out what is going wrong and being able to reproduce your results when you get it right. Use patents just to point you in the right direction. Go for the type of experimental detail you find in chemistry journal articles. You seem to be getting 3-4 out of 5 critical variables in each experiment, and then changing to another random 3-4 out of 5.


Alas, I have no Journal articles on *anodes* involving DTO.
You guys are placing great faith in the DTO processes involving glass transferred to Anodes.
You may be right.
I maintain that the Anode patents using DTO are more relevant to my suituation.
I may be wrong. Variables are coming into play (for me anyways) because I cannot obtain (or have not tried too hard) SnCl4:5H20, SbCl3, Butyl Alcohol, all AR Grade. If I could walk into a lab suply house and purchase these chemicals I would. I would them come home and follow EXACTLY an example in one of the Diamond Shamrock (Ti Substrate with LD outer coat) patents. I would not follow a 'conductive coating on glass patent'.
Perhaps this is a sign of my ignorance of the whole DTO subject.
I am inclined to assume that those's patents (Diamond Shamrock) worked as successful anodes.
Since I cannot buy the chems. I have to go the way yourselves have suggested and make the Chems.
Thank you, BTW, I would be a long time figuring it out myself........IF EVER.
If the examples in the Diamond Shamrock (and Imperial Chemicals London) patents (followed exactly like a parrot!) did not work, then I would try varying the 'recipe', maybe even considering following a 'conductive coating on glass' patent.

Quote:

Snip

. Steel wool is going to scrub off any coating you get, stop doing that. Forget the burnishing and black surface description you read about in ONE patent. You want a clear, maybe slightly tinted coating.

Snip
.


All the Anode patents have reported a black coat. Why do you thing that I should get a clear coating on Ti.
I agree you do get a clear coating on glass.

Regarding the rubbing bit, I only rub a small amount at the top of the Ti just to see how adherent the coat is.
The part that I rub with steel wool is not involved in the 'test' where I then put the DTO coated Ti into a solution of Na Chloride as an anode.
As I said before my 'test' may not be very illuminating but it is quick and handy.

One last salvo on Sb %'s in DTO.
US 3,627,669 Examples 1, 2 and 3 are somewhat illuminating
with regard to making Anodes. They are not LD outer coat anodes but bare DTO Anodes, Ti substrate.
Very rough synopsis:
Example 1:: 10% Sb as I would calculate (10% Sb2O3 from Patent), ... OK after 5 days
Exmaple 2:: less than 10% Sb (1% Sb2O3), ...not so good at start, anode not tested for long.
Example 3:: more than 10% Sb (14.5% Sb2O3), ...same as Example one.

Patent here:

http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

The patent is not directly relevant to obtaining a interface coat between Ti and LD but close enough IMHO.
This in not a 'dodgy' Diamond Shamrock patent either :D
The patent gives some info. on DTO in regard to Anode making. It also gives two
book refs. for anyone interested in some reading and can get them.
Controlled-Valency Semiconductors by E. J. W. Verwey et al., Philips Research Reports No. 5, 173-187, 1950.
Chemical Physics of Semiconductors by J. P. Suchet (D. Van Nostrand Company Ltd., 1965).


Dann2

[Edited on 19-7-2007 by dann2]
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[*] posted on 19-7-2007 at 21:32
The oxidative soak method of cold deposition of adherent SnO2 and other oxides


This is a method which reportedly produces coatings
having excellent adherence to substrates and very even coatings via a cold process . The process uses a lower
valency salt of the metal oxide precursor , which is oxidized
to the higher valency and deposited as colloidal particles
of a hydrated oxide , then baked to dehydrate .

Reportedly the SnO2 film is so tough and adherent that
it cannot be scraped off with a knife :D

Since this method has been used to apply SnO2 to TiO2 ,
then it would seem very likely to work on Ti as well .

This oxidative soak method can also be used for the
cold deposition of Co3O4 and MnO2 and Mn3O4 ,
and likely also for other metal oxides .

Attachment: Preparation of SnO2 thin films by the oxidative-soak-coating method.pdf (324kB)
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[*] posted on 19-7-2007 at 21:48


Looks like it needs some fairly rigid temperature control - not hard though, and worth the effort. I guess dopants would be added in proportion to the initial SnCl2 loading? Have you any refs to other oxide depositions?



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[*] posted on 19-7-2007 at 21:59


@Twospoons

Yeah the commonplace example of this reaction in an uncontrolled system is the iron slime and stain which appears when soluble ferrous salts are oxidized to insoluble ferric salts in open water containers or even in toilet tanks .
Ever tried to remove that stain ? Basically you have to use an acid to etch it away . Otherwise it isn't coming off , even without baking .

I am not sure if the dopant can be coprecipitated or if it
must be added in alternate fashion as sequenced layers
that may fuse on baking .....I only know it can be done .

Actually I am looking for more concerning this because it is so intriguing .

Attached is the article on MnO2 .

[Edited on 20-7-2007 by Rosco Bodine]

Attachment: Preparation of thin films of MnO2 and CeO2 by (oxidative-soak-coating) method.pdf (163kB)
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[*] posted on 19-7-2007 at 23:19


Here is the oxidative soak method for cold deposition
of cobalt spinel that was linked above

@dann2

*If* there is a more convenient method of applying the DTO
layer , adaptable or directly applicable to the titanium substrate , but gotten from a parallel application .....
then it very likely would provide the advantages of
the more advanced art which applies to the DTO film
quality . Getting a better coating in fewer steps and using less corrosive and volatile precursors , would be a real advantage . It is seeing the potential problems and uncertainties which exist in some of the patent methods ,
that is the reason I have been looking at the alternatives .
Glass substrates are used in many of those alternatives
because the intended end product would likely be using a glass substrate in a sensor or in some optical application .....
but that is not necessarily limiting , as the same method for
applying the film *should* work on a variety of substrate materials . The parallel technology is focused on the film itself , more than being concerned with the substrate material ....which may be just about anything , including titanium . If this works out the way I am thinking it might ,
it could be a way simpler and *way better* method of getting the resulting DTO layer that is desired . So don't diss the "glass substrate" patents as being irrelevant , especially since it looks like what works on SiO2 sticks even better to TiO2 . Interface diffusion layer conductivity and doping seems to be the open question more than whether the
coating would stick ....as it appears that the film adhesion
for this cold soak oxidation is extremely tenacious .

Many of the patents mention the sensitivity of the titanium to unwanted oxidation during the baking , before an obscuring film of the DTO completely seals it from exposure
to oxygen . So it could be a real advantage if the preliminary
sealing of the titanium with a precursor interface already close to completion could be formed in the cold ....so that
the vulnerabilty of the titanium to oxidation during baking is
eliminated . This could greatly improve the anode durability
and performance and be much less work to accomplish .
A thicker and more conductive , tougher film of DTO obtained
in two realatively simple steps would certainly be better than an inferior film produced by more than a dozen using a more awkward and less advanced method .

And it is also very possible that what I am describing is either
already known and proved and not yet published , or it is entirely novel . It wouldn't be the first time , if we came up with something entirely new and better than what is already published , if only by combining existing methods in a logical way , to achieve what is desired . Try to keep an open mind .



[Edited on 20-7-2007 by Rosco Bodine]

Attachment: Preparation of Co3O4 thin films by a modified chemical-bath method.pdf (264kB)
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[*] posted on 20-7-2007 at 08:11


Dann, use something like a plastic spoon or knife to check the coating's adherency. You need to use something softer than SnO2. Steel is 5.5-6.5 on the mohs hardness scale. I'd guess SnO2 is 4 or less.
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[*] posted on 20-7-2007 at 13:25


http://www.galleries.com/minerals/oxides/cassiter/cassiter.h...



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[*] posted on 20-7-2007 at 13:48


Ok, thanks for the info. That's what I get for guessing when my main internet connection is down. ;)

I like the oxidative-soak approach. I saw this sort of translucent film deposition on my glass bowl while evaporating and oxidizing my SnCl2 solutions. (Steel wool cleaned it off the bowl). Recall from some earlier posts that Na does not have beneficial effects on film conductivity though, so HNO2, H2O2, or just air may be a better oxidant for our application.

Regarding Rosco's idea of protecting the clean Ti surface from oxidation, again I suggest experimenting with HCl/SnCl2 solution as an etchant to lay down a thin flash coating of tin on bare titanium. Maybe etch and oxidative coating can be done in a one pot process with some development?

[Edited on 7-20-2007 by Eclectic]
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[*] posted on 21-7-2007 at 06:03


I got my internet connection back, so I can use Google and not have to read and post through my cellphone. :D

The info I can find says steel wool is hardness 5.5. Titanium is 6?

Regarding titanium etching: reducing conditions seem to help. The etching seems to speed up once the acid gets a blue color from Ti 3+.
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[*] posted on 21-7-2007 at 07:28


Quote:
Originally posted by dann2
Hello Hashashan,

Quote:
Originally posted by hashashan
Correct me if I'm wrong' but isnt the Sb, Sn doping meant to be just a relaying layer between the Ti and PbO2? if so then why are you trying to run a chlorate cell with no coating?


That is true. I am going to use the Sn/Sb Oxide coat as an inbetween coat for Ti and LD.
In order to test the coatings I am simply putting the Ti coated strip into Chloride solution to see how well it stands up. It is far too much trouble to coat each with LD just to test the Sn/Sb Oxide coat.
Perhap this test is not appropriate.
I also give a small portion at the top end (only one small place the top) a rub of steel wool to see how well the coating has stuck or hard it is. A patent (one only!) did this and they were able to obtain a glossy black appearance. Sounds like a good coat to me.

Side Note

Mrs. Jones would need some elbo grease to remove that coating if it were on glass....but we are discussing anodes :P
End of Side Note!

Some of the Sn/Sb Oxide coatings were used on their own to electrolyze brine solutions in the patents for quite a period of time too.
I noted that any of the patents that give an example where by the Sn/Sb Oxide coat was used to electrolyse brine (no overcoat), the Sn/Sb Oxide coat was put on the Titanium using anhydrous SnCl4. They refluxed it with an alcohol for some hours first to obtain a compound for adding the Sb Chloride to.

Dann2


So I still don't understand all those efforts. All you need is to create a conductive Ti coating to push current to the PbO2. Even if the layer is not perfect there will be nothing to worry about, because there will form an oxide film in the non-perfect places and it won't be harmed by the electrolysis to perchlorate.

Even if there will be a crack in the PbO2 then once again the Ti under the crack will passivate.
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[*] posted on 21-7-2007 at 08:11


Quote:
Originally posted by hashashan

All you need is to create a conductive Ti coating to push current to the PbO2.


Yeah that's right , but doing that and getting a good result is not so easy from what dann2 is reporting . The bonding and sealing properties of the conductive layer must be there so it is a tough enamel-like layer ...not a flakey or dusty soft material which detaches easily . It must be something like a primer paint under the finish coatings of whatever is subsequently applied over it .

Quote:

Even if there will be a crack in the PbO2 then once again the Ti under the crack will passivate.


Right again . *But* passivation won't stop there unless the conductive layer of SnO2 or other material is a truly adherent covering which sticks like glue to the titanium and seals it completely across the surface . If not , then the electrolyte will get under it and passivation will spread across the entire surface of the titanium . If the SnO2 doesn't stick well to the titanium , it would be like having loosening plaster on a ceiling ....putting fresh paint over it would not somehow glue it there , it would simply fall off carrying the new paint with it .
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[*] posted on 21-7-2007 at 09:17


Rosco of course you are right about that. But i do recall that dann2 reported to have a good layer(i mean a layer with good adhesion).

Another possible idea:
Did anyone tried to use Ti as a non conductive substrate? i mean to make the DTO only on top of the Ti (where it is not in contact with the electrolyte) and then coat the Ti with PbO2. (Is it possible to coat Ti without the any doped layer? or it will passivate too fast)
and then the current will be applied to the Ti, through the DTO(even if it has a poor layer) to the PbO2. The cracks in the PbO2 wont matter' because in the electrolyte there will be no DTO on the Ti and it will passivate immediately wherever there are cracks.
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[*] posted on 21-7-2007 at 09:44


Quote:
Originally posted by hashashan
Rosco of course you are right about that. But i do recall that dann2 reported to have a good layer(i mean a layer with good adhesion).

Another possible idea:
Did anyone tried to use Ti as a non conductive substrate? i mean to make the DTO only on top of the Ti (where it is not in contact with the electrolyte) and then coat the Ti with PbO2. (Is it possible to coat Ti without the any doped layer? or it will passivate too fast)
and then the current will be applied to the Ti, through the DTO(even if it has a poor layer) to the PbO2. The cracks in the PbO2 wont matter' because in the electrolyte there will be no DTO on the Ti and it will passivate immediately wherever there are cracks.


Hello,

Some of the layers I got were not 'too bad'. I don't know how to judge them. They were not clear and shiny by anymeans.
They were black (the better ones) but somewhat powdery. Perhaps they are good enough to use as in intermetiate layer for the Ti and LD. I don't really know.
You can doposit LD onto bare Ti once you start your bath with not too much acid. Connect the + of your supply to anode before you put it into plating tank so that plating will start IMMEDIEATLY. Then use anode as if it were a massive anode.

Tantalum can be coated easily from a LD bath. The oxide coat does not seem to form as quick (or something in that line) An anode has been made this way (discussed somewhere in this (short :D) thrread. They then went on to use the anode as if it were a massive andoe. They ignored the substrate and connected 'Chlorate current' to LD.

Dann2
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[*] posted on 21-7-2007 at 11:20


The black color with the antimony doping might be a bimetal oxide or oxychloride of titanium and antimony ,
and that might be forming an unidentified diffusion layer
beneath the ATO . Increasing antimony doping in SnO2
reportedly produces a deepening blue color , so it may
be actually a blue color that has become so dense it appears black .

Last night I saw one of the patents related to the use of Ruthenium as a dopant on titanium oxide , mention that
10% was the observed saturation limit for Sb doping of SnO2 , ( applied as the chlorides to a titanium substrate ) and so the amount being used for test electrodes was held to 8% maximum to avoid the formation of a separate phase . I would expect that some of the SbCl3 evaporates , and some of it possibly is captured as dopant for the growing thickness of TiO2 which probably reduces the actual level of Sb doping for the SnO2 .
The method of baking therefore probably has some bearing on what amount of SbCl3 is optimum . If the
coating mixture is sprayed onto an already hot substrate ,
maybe 2-3% is maximum because the loss is smaller
when it flash decomposes and sticks where it lands .
But in the case where it is dip coated , and then slowly
dried and baked ....it takes more SbCl3 due to losses
or side reactions .

This is another reason I like the ammonium stannate and ammonium antimonate mixture , it stays put and then the
coating composition doping level stays close to what theory would predict . If that mixture could be used for
thickness , atop a primer coat applied using the oxidative soak method .....a superior coating might be possible using non-volatile and non-corrosive precursors which behave in a predictable way that eliminates the variables
from rate of heating , and growth of the TiO2 interface layer .

[Edited on 21-7-2007 by Rosco Bodine]
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dann2
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[*] posted on 21-7-2007 at 18:21


Hello,

Where or how can one get the Ammonium Stannate and Amm. Antimony compounds.

Dann2
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[*] posted on 21-7-2007 at 19:05


On page 4 of the other thread
http://www.sciencemadness.org/talk/viewthread.php?tid=8592&a...

link to attachment US6777477
http://www.sciencemadness.org/talk/viewthread.php?action=att...
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