Sciencemadness Discussion Board

More on PbO2 electrodes

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Twospoons - 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.

Rosco Bodine - 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]

Twospoons - 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?

hashashan - 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?

Rosco Bodine - 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)
This file has been downloaded 1385 times


Eclectic - 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.

Rosco Bodine - 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 .

Cold Deposition of Doped SnO2 , the "oxidative soak method"

Rosco Bodine - 19-7-2007 at 10:10

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)
This file has been downloaded 1069 times


dann2 - 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.

Dann2

dann2 - 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]

The oxidative soak method of cold deposition of adherent SnO2 and other oxides

Rosco Bodine - 19-7-2007 at 21:32

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)
This file has been downloaded 927 times


Twospoons - 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?

Rosco Bodine - 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)
This file has been downloaded 1244 times


Rosco Bodine - 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)
This file has been downloaded 1847 times


Eclectic - 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.

12AX7 - 20-7-2007 at 13:25

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

Eclectic - 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]

Eclectic - 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+.

hashashan - 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.

Rosco Bodine - 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 .

hashashan - 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.

dann2 - 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

Rosco Bodine - 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]

dann2 - 21-7-2007 at 18:21

Hello,

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

Dann2

Rosco Bodine - 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...

Eclectic - 22-7-2007 at 04:06

How is an alkaline surface treating system going to penetrate the almost impervious TiO2 surface layer on titanium? Ti salts are stable in acid, but not in alkali.

Rosco Bodine - 22-7-2007 at 06:40

In my thoughts about this , there isn't any second fluxing or etching during the baking step of the very minimal oxide thickness on the already etched titanium required . The superficial oxide is modified while going preferentially into solid solution with an SnO2 layer . The idea which I am following is to modify the composition of the interface layer and limit its growth , by deliberately *avoiding* going through a Ti chloride byproduct intermediate which is then pyrolized .

What I am thinking is not to attempt to use the HCl evolving from decomposing Sn and Sb chlorides as
a means of fluxing away the existant TiO2 or TiO1.75 ,
which is of minimal thickness on a freshly etched Ti
substrate , but to seal and dope that interface layer before it grows in thickness which under usual exposed conditions would lead to formation of the passivating dielectric layer of dioxide . This also eliminates the further
pyrolysis of the chloride of titanium byproduct to an oxide of titanium , decreasing the loading of TiO2 into solid solution with the SnO2 layer . Using chloride precursors
for the SnO2 and Sb dopant , there is an etching of the
titanium proceeding from the HCl byproduct of decomposition of those precursors at the same time as
is occuring the formation of the doped tin oxide layer which is intended to blanket the Ti substrate from exactly
the sort of attack as the HCl is causing ....which seems to
be counterintuitive to me anyway :D It seems by the
brute corrosive force approach of the HCl being used to flux deeper and deeper into the titanium , that the result would be a growing thickness of an interface layer of Ti chlorides , later oxides , whose growing thickness is the very thing not desired to occur but to be prevented ...
this is counterproductive so why do it that way if there is any logical alternative ?

It would also seem possibly helpful to do a preliminary cold treatment of the freshly etched titanium , with chromic acid , cobaltic acid , or something else which
would apply a very superficial very thin , perhaps even not visible layer which would further retard any growth
of any TiO2 layer , and yet which would readily go into solid solution with the SnO2 layer on baking .

Eclectic - 22-7-2007 at 07:12

Well, the doped mixed metal oxides incorporating titanium should be both tightly adherent AND conductive. Also, going with your idea of having SnCl2 in the treatment as well as SnCl4, the reducing properties of SnCl2 and Ti metal may lead to the formation of a conductive titanium suboxide mixed with, or under, the doped SnO2? Titanium dissolves in concentrated HCl as TiCl3.

That may be where the black layer Dann read about could come from.

I don't think there is going to be much solid solution formation with the metal oxides at 500 C or less, unless the oxides grow already mixed from a melted flux like the chlorides.

I'll get around to running my own tests after experimenting with titanium welding and machining. I want to try an aluminum filled Ti tube welded to perforated Ti plate as substrate. The Al should wet and bond to the Ti, and a copper insert would make a very good electrical connection.

[Edited on 7-22-2007 by Eclectic]

Rosco Bodine - 22-7-2007 at 08:18

I have seen SnCl2 used as the precursor for doped SnO2 baked coatings , especially those doped with SnF2 , but the oxides are formed in a baking atmosphere which contains superheated water vapor .

And yeah about the TiCl3 , you might actually want that chloride precursor present as part of a doped valve metal oxides intermediate layer ....but in that case you would form it externally and probably be optimizing your semiconducting intermediate layer chemistry for the doping of the valve metal oxide , which would be grown even thicker by the substrate itself contributing TiCl3 as a byproduct .
But that is a somewhat different scheme ...though related , to the use of an intermediate layer that is principally doped SnO2 . That doped valve metal oxide interface scheme requires Ruthenium dopant to work properly IIRC ....and the Ti interface with a doped SnO2 layer is not as thick with Ti oxides , as the solubility afforded by Ruthenium for mixed oxides is absent .

BTW ...

Magnetite can actually be formed on a titanium substrate ,
without any deliberately formulated and applied intermediate layer ....by electroplating freshly etched titanium with iron metal in a ferrous sulfate bath ,
and then firing the iron plate titanium at 650C for a couple of hours in a mixture of steam and hydrogen .

The interface is highly conductive and the magnetite coating is a tough continuous pore free coating which will operate as an anode in an electrlolytic cell for a year .

This is a good example of the blanketing effect of an oxide layer sealing off the titanium , even as a very thin layer of a few microns . There is almost certainly some
thin layer of TiO2 between the metallic titanium and the iron metal during plating ....but it never grows thick enough to be of any significant electrical detriment .
And on baking ....there is doubtlessly some sort of mixed oxide of iron and titanium which bonds the magnetite to
the titanium metal ....it may only be a few atoms thick , but it would have to be there .

This is a good example of working with the properties
of the materials to exploit the natural tendency of the
titanium to "dope itself" using whatever is available , and/or alternately for the growth of the oxidation layer on the titanium to be kept so thin that it is not an effective barrier to the flow of current .

That is something like the idea I am following for limiting the thickness of the interface diffusion layer by blanketing the titanium with a coating of some very superficial thickness in the cold ....to stunt its growth in thickness during baking . It cannot form a barrier to current unless
it can oxidize and grow in thickness to the point that occurs . And if whatever small development of TiO2 is
occuring during baking is immediately going into solid solution in SnO2 , then passivation of the Ti is prevented .

If it all goes in reality like it would seem it should go in theory .....well great . But I can't guarantee anything on this , except it seems to me like it should work .

Actually about the pH , the presence of basic condition favors the formation of the suboxide of Ti ...rather than
non-conductive TiO2 ....which is what we want .

Eclectic - 22-7-2007 at 08:55

My thinking is that O2, Cl2, and HCl are able to migrate through the mixed oxides at 500 C, but that the metal atoms themselves are fairly static at that temperature. If the SnO2 is able to act as an O2 diffusion barrier, that facilitates the formation of conductive titanium oxides underneath, and prevents oxidation from PbO2 or other oxidants above. This is all the more likely if pre-etch or other titanium surface treatments load the Ti surface with H2.

In an acid etching bath, SnCl2 should plate out a very thin flash coating of tin on the metallic titanium surface as soon as the TiO2 dissolves... :D

[Edited on 7-22-2007 by Eclectic]

Rosco Bodine - 22-7-2007 at 09:15

Yeah , any kind of superficial non-valve metal superficial plating would probably provide substantial enough of a blanket against the formation of a TiO2 dielectric barrier ,
and possibly even an electroless flash of silver or nickel or even copper could function in that way . All it needs to do
is afford a temporary shield which will then deteriorate via oxidation and then diffuse and integrate with the heavier film of oxides during baking . I have even wondered if there is possibly some amalgamation scheme where tin
antimony alloy solder could be applied , or some fluxing of titanium after which a metal to metal solution could be applied to the titanium .....like copper being tinned with a
thin mirror film of solder ......then heated much higher to oxidize , or in the case of an amalgam to boil off the mercury . Such a strategy might also create a conductive interface from the titanium metal substrate through a layer of doped oxides derived from the metals and oxidation by the air .

Eclectic - 22-7-2007 at 09:44

The surface flash coating of metal is going to form from Sn/Sb chloride solution, as long as the initial surface coating of TiO2 is etched off and what immediately reforms is not too thick. Ti is MUCH more reactive than Sn. This would be an analog of the zincating process for aluminum, where an alkaline zinc salt solution dissolves the surface Al2O3 and plates out a thin layer of zinc, preventing the Al2O3 from reforming. For Ti and Sn, the conditions would need to be acidic, as I doubt the surface TiO2 would dissolve at all under alkaline aqueous conditions.

Maybe electricity could be used to electrostrip and then plate a thicker Sn/Sb layer.

Rosco Bodine - 22-7-2007 at 10:26

I'm not sure for certain if it does work to form an adherent metallic coating for passivating metals ,
or if there is some interfering surface reaction of hydroxide or oxide which prevents it going metal to metal .

It could work in either basic or acid conditions , or both , depending on the precursor salts , the solvent , temperature , ect.

It maybe could work with the chlorides to just dip the freshly etched titanium into an acidic HCl solution of SbCl3 or SnCl2 or SnCl4 or some blend of those , to deposit the metal(s) via the displacement / exchange as titanium reduces the chlorides . It could be like putting an iron nail in copper sulfate or silver nitrate , and getting a
plate of copper or silver from the iron entering solution ,
and reducing the salt to the metal . Then apply the mixed ammonium stannate and ammonium antimonate and bake , having no further need for an acidic side reaction from decomposition of chlorides , except for the initial treatment .

There's definitely room for experiments sorting out the details on these unknowns .

Eclectic - 22-7-2007 at 10:33

Aluminum IS a passivating metal.

Anyway, yeah, that's what I'm talking about. :D

Rosco Bodine - 22-7-2007 at 10:41

It would also be interesting to see if titanium amalgamates in a dilute HCl solution of HgCl2 ,
because if it does , then that thoroughly defeats the
passivating oxide layer and you have Ti in solution
in a film of mercury eating its way into the Ti . If such a depassivated Ti was made the cathode in a plating tank , the Hg layer could be saturated with tin or silver to solidification , and then baked to distill off the mercury and oxidize the remains to a solid solution of conductive oxides .
This might even proceed simply by sticking the part into a bed of glowing coals .....no kiln required .

[Edited on 22-7-2007 by Rosco Bodine]

Eclectic - 22-7-2007 at 10:49

But WHY would you want to do that if that's what the Sn/Sb chloride treatment does anyway once the process details are worked out? :o

K.I.S.S. Less variables, not MORE. :D

Rosco Bodine - 22-7-2007 at 10:53

The amalgam could produce a much heavier layer and might provide a one coat thickness about a hundred times thicker ....that's all I was thinking .

Eclectic - 22-7-2007 at 11:14

OK. As long as we are speculating, I wonder if SnO2 can be grown electrolytically from chlorides like PbO2 is from nitrates? Electrostrip with the polarity one way, then reverse and grow the protective conductive oxide layer. :D (I'm a bit unclear about anodes and cathodes, I haven't gotten that far yet.)

(BTW, when do I get to be an International Hazard too?)



[Edited on 7-22-2007 by Eclectic]

Rosco Bodine - 23-7-2007 at 07:39

Keeping it simple .....

The Dow patents relating to cobalt nitrate alone or in
molar combination 2:1 with a second nitrate like zinc or copper , applied directly and baked onto a freshly etched
titanium substrate , produced a conductive interface which
was equal or better than Ruthenium doped titanium .....
in terms of conductivity anyway .

So the use of chlorides and the mechanism by which they
work is not essential , if nitrate precursors can also work .
And other precursor compounds for both cobalt and tin
have been mentioned as operable , acetates , organometallic complexes ....basically any compounds which will decompose on baking to produce the oxide .

So it is evident that the oxides themselves are the essential component , and that too much emphasis should not be placed upon the composition of the oxide precursor .....for example it is wrong to presume that
a particular chloride or even a particular valence compound is somehow essential , because of some
byproduct of its decomposition having some additional
reaction with the substrate . Obviously the oxide will
somehow find a way by one route or another to form a solid solution with the titanium interface , or by formation of some bimetal oxide , or other doping mechanism .....
conductivity will be imparted to the interface with the titanium . Some precursors may perform better than others in terms of the adhesion , conductivity , thickness
and toughness of the coating . But somehow the different
schemes work .

The Dow patents extensively tested SnO2 alone as a first
interface layer on titanium , compared with Sb doped SnO2 , and no SnO2 interface at all , in conjunction with
cobalt spinels even directly applied to the titanium .....
and there was little electrical difference .

The benefit of the SnO2 layer seems to be mechanical ,
as it can form a tough and adherent continuous film with
one or two coats ....and given that the amount of doping
is a lesser issue , the more important parameter shifts to
what amount and type of doping would produce enhancement of the physical toughness and adhesion
of the SnO2 layer when it is used .

This information supports my thinking there is a high probability that an oxidative soak deposition of SnO2
alone on a titanium substrate , followed by a mixture of ammonium stannate and ammonium antimonate and baked .....would work fine .

The idea that a corrosive chloride based precursor system is required for an adherent conductive interface with titanium ....is false IMO , and holding fast to that pyrolytic
fluxing and decomposition strategy , will be an impediment to experiments that are more likely to produce a superior SnO2 coating from less corrosive precursors whose utilization is simpler .

Much of our discussion here has related to what weight should be assigned to certain parameters , what is the prioritization which should be assigned to percentage of doping , what type of oxide precursor is best , and how
applicable is the data from glass substrate experiments to titanium substrate experiments . Even though there is no direct description confirming that the oxidative soak deposition of SnO2 and/or the ammonium stannate plus ammonium antimonate PVA thickened mixture , are applicable
to titanium substrates as specific examples , I can find no reason why such schemes should not also be directly applicable to titanium .


[Edited on 23-7-2007 by Rosco Bodine]

Eclectic - 23-7-2007 at 11:42

Rosco, I've got no problem with other coating methods. I just don't think there is anything wrong with using the chlorides. Very cheap and readily available from OTC materials. I like cobalt also, but that is a different process. I'd like to explore what can be done starting with 95/5 solder, and understand what's been going wrong with Dann's experiments using tin chlorides. I suspect cooking technique, rather than bad recipes. ;) (How to make bread: Mix flour, water, and yeast, then bake. Simple, yes? But there is a bit of technique involved.)

By all means, keep up the good work posting all those great patents and articles you've been finding. :D

It might be best to avoid oxidizing anions when trying to get a conductive coating on reactive metals that form an insulating, tenacious, and chemically impervious oxide surface coating.

[Edited on 7-23-2007 by Eclectic]

What were those Dow patent numbers again?



[Edited on 7-23-2007 by Eclectic]

Rosco Bodine - 24-7-2007 at 06:14

The Dow patents were beginning on page 19 of this thread , but the discussion of cobalt actually began on page 18 . I can't go back and accumulate the list right now .

Anyway the the alternates I am suggesting are also pretty much OTC .

Regarding the use of an amalgam as a possible strategy for getting an intimate mixed oxide interface on titanium the following is what I had in mind ......( you did say to keep supplying the thinking outside the box ideas and patents ect. )

US3049437 Amalgam brazing fluxes ( don't breathe the fumes! )

If nothing else , the use of an abrasive paste made from DE
or perhaps even fine sand along with brushing of the mixture
using a stiff wire brush would seem to be a good way of applying any sort of cold chemical treatment , as this would tend to abrade any TiO2 surface film and expose the bare metal to the reactant , whether the idea is amalgamation or some other sort of surface treatment .


[Edited on 24-7-2007 by Rosco Bodine]

Attachment: US3049437 Amalgam METAL_PLATING.pdf (192kB)
This file has been downloaded 631 times


dann2 - 24-7-2007 at 10:01

Quote:
Originally posted by Eclectic
I'd like to explore what can be done starting with 95/5 solder, and understand what's been going wrong with Dann's experiments using tin chlorides. I suspect cooking technique, rather than bad recipes.



Definitely not the cooking technique.
It's the dodgy recipes, I tell you

Dann2

Eclectic - 24-7-2007 at 13:23

There is one thing that looks "dodgy" or intentionally misdirecting in some of the patents: Why would you want to etch the titanium and THEN sand or sandblast? It seems that the mechanical abrasion would remove most of the oxide, and then you would etch to remove any oxide that immediately reformed.

[Edited on 7-24-2007 by Eclectic]

dann2 - 24-7-2007 at 17:34

Quote:
Originally posted by Eclectic
There is one thing that looks "dodgy" or intentionally misdirecting in some of the patents: Why would you want to etch the titanium and THEN sand or sandblast? It seems that the mechanical abrasion would remove most of the oxide, and then you would etch to remove any oxide that immediately reformed.

[Edited on 7-24-2007 by Eclectic]


Hello,

Perhaps a small amout of Ti Oxide is acceptable or even diserable? Perhaps etching after sand blasting will remove the sharp edges and re-enterant angles that the sand blasting has developed.
Alembic (the original DTO on Ti with LD on top anode maker) drilled lots of holes in the Ti (along with sandblasting) to help the LD anchor itself.


From www.azom.com
____________________________________________
Oxide Film Growth
The oxide film formed on titanium at room temperature immediately after a clean surface is exposed to air is 12-16 Angstroms thick. After 70 days it is about 50 Angstroms. It continues to grow slowly reaching a thickness of 80-90 Angstroms in 545 days and 250 Angstroms in four years.

The film growth is accelerated under strongly oxidizing conditions, such as heating in air, anodic polarization in an electrolyte or exposure to oxidizing agents such as HNO3, CrO3 etc. The composition of this film varies from TiO2 at the surface to Ti2O3, to TiO at the metal interface. Oxidizing conditions promote the formation of TiO2 so that in such environments the film is primarily TiO2. This film is transparent in its normal thin configuration and not detectable by visual means.

A study of the corrosion resistance of titanium is basically a study of the properties of the oxide film. The oxide film on titanium is very stable and is only attacked by a few substances, most notably, hydrofluoric acid. Titanium is capable of healing this film almost instantly in any environment where a trace of moisture or oxygen is present because of its strong affinity for oxygen. Anhydrous conditions in the absence of a source of oxygen should be avoided since the protective film may not be regenerated if damaged.
__________________________________________


Dann2

Rosco Bodine - 25-7-2007 at 03:44

Quote:
Originally posted by dann2
Quote:
Originally posted by Eclectic
There is one thing that looks "dodgy" or intentionally misdirecting in some of the patents: Why would you want to etch the titanium and THEN sand or sandblast?


That is to provide "surface roughening" to increase the
chances of something sticking to the surface and staying put . Not very encouraging about the adhesion when you
see that sort of treatment described . It reminds me of someone trying to reglue a rear view mirror mount to a windshield , and getting instructions to first sand the
surface of the glass very well , then plunge immediately
the puddle of melted wax on the mount against the surface , and thereafter to never park the vehicle in direct sun :D
It would seem like they haven't quite got things worked out in terms of materials which should be agressively adherent in the existing condition .....like they haven't quite discovered
the equivalent of a cyanoacrylate "super glue" which will marry the different materials inseparably and with a substantial permanency (like years and years to forever) .

The cold application of a colloidal particle sized SnO2 via the oxidative soak method is the "most likely to succeed" in terms of adhesion , which I have read about anyway , which seems easily attainable . I think that the most adherent coatings are likely to be achieved from the compositions which deposit in the smallest particle size since that is closer to the "solid solution" and requires the least heating for the shortest duration to develop .

Also perhaps possible is the electrodeposition of the substoichiometric cobaltic oxide , followed by baking .

Quote:

It seems that the mechanical abrasion would remove most of the oxide, and then you would etch to remove any oxide that immediately reformed.


Removing all of the Ti oxides will be impossible so the idea is to retard the growth of its thickness and control the composition of that layer so that its properties are modified and it doesn't become an insulating or rectifying boundary layer .
Quote:

[Edited on 7-24-2007 by Eclectic]


Quote:

Hello,

Perhaps a small amout of Ti Oxide is acceptable or even diserable?


Yes . But the chemistry and thickness of that oxide must be controlled .

Quote:

Perhaps etching after sand blasting will remove the sharp edges and re-enterant angles that the sand blasting has developed.
Alembic (the original DTO on Ti with LD on top anode maker) drilled lots of holes in the Ti (along with sandblasting) to help the LD anchor itself.


That probably has more to do with reenforcing the PbO2 adhesion than the intermediate layer to the substrate .
Quote:

From www.azom.com
____________________________________________
Oxide Film Growth
The oxide film formed on titanium at room temperature immediately after a clean surface is exposed to air is 12-16 Angstroms thick. After 70 days it is about 50 Angstroms. It continues to grow slowly reaching a thickness of 80-90 Angstroms in 545 days and 250 Angstroms in four years.

The film growth is accelerated under strongly oxidizing conditions, such as heating in air, anodic polarization in an electrolyte or exposure to oxidizing agents such as HNO3, CrO3 etc. The composition of this film varies from TiO2 at the surface to Ti2O3, to TiO at the metal interface. Oxidizing conditions promote the formation of TiO2 so that in such environments the film is primarily TiO2. This film is transparent in its normal thin configuration and not detectable by visual means.

A study of the corrosion resistance of titanium is basically a study of the properties of the oxide film. The oxide film on titanium is very stable and is only attacked by a few substances, most notably, hydrofluoric acid. Titanium is capable of healing this film almost instantly in any environment where a trace of moisture or oxygen is present because of its strong affinity for oxygen. Anhydrous conditions in the absence of a source of oxygen should be avoided since the protective film may not be regenerated if damaged.
__________________________________________
Dann2


If you look at the activity series , aluminum is just slightly
above and maybe .03 volts different from titanium ....so
the reactivity is very similar . The titanium produces a
tougher oxide , but otherwise the two metals should behave similarly .

Silver could have usefulness in this scheme involving SnO2
and titanium . In the art of mirror silvering , SnO2 is used
as a catalyst for creation of microscopic nucleation sites where metallic silver is deposited . Colloidal particle sized
silver and silver oxides seem like a natural candidate as
a modifier / dopant for the Ti oxides interface layer ....
and I have seen one passing mention of silver mirroring
in one patent , which I reported earlier in this thread .

Al would be useless

dann2 - 25-7-2007 at 09:34

Hello,

Al is no substitute for Ti in any anode application. Have no doubt about it, regardless of what the theory may suggest or indicate.
Al does not even make a good cathode. See Wouter Visser's page.


Dann2

Rosco Bodine - 25-7-2007 at 10:22

What I was saying at is that Al is similar in reactivity and even more active in film forming . I know that the film is not as tough as is the film for titanium and did not say that it can substitute for titanium , simply that the metals behave similarly although the oxides are different in their properties .

dann2 - 25-7-2007 at 18:14

Hello,

A strange thing happened today. I noticed a piece of Ti that I had coated with DTO at some stage (about 9 days ago) and it looked extremely black.
Would time be a factor in getting an improved coat?
Sounds ridiculous.
I dunked it into a NaCl solution as an anode and it took about 10 minutes to passivate. I ran it at a small current density but this was the best yet and this particular anode had been tried before in a NaCl solution and had passivated (and was therefor condemmed).
I left the anode aside for about an hour, dunked in into the solution again as an anode and it seemed to have recovered, ie. it was not passivated. It did passivate after a few minutes. It seemed as if the anode (as I said) had 'recovered' from passivation.
WTF

Perhaps my 'test' for DTO is a load of Boalderdash. (rubbish if in USA :D)

Dann2

dann2 - 26-7-2007 at 12:10

Hello,

I looked at two of my DTO 'painting' solutions yesterday and both has formed large amounts of Oxides. One of them was like yogart. You could invert the bottle and nothing would come out. The DTO 'paint' was formed as shown below.
The second (lowest below) was the paint that went like yougard. The first one was like milk.

Note: What is between the lines (below) was posted before up the thread.
_________________________________________
I preformed another coating attempt using SnCl4 made from
SnCl2:2H2O + H2O2 + HCl.
This was a (high) 20% Sb content coating.

Added 4 grams SnCl2:2H2O to 2.4 grams HCl. Cooled down and also cooled down
H2O2 using salt and ice. Added one drop of Ti indicator solution.
Added a untill Ti indicator went orange. (about 3g 30% H2O2)
Added 12.3ml surgical spirit.
Added 1.28 grams SbCl3 (stock) solution in HCl (solution contains 0.41% Sb)

As soon as I started to add the SbCl3 solution I got a white PPT.
The solution went milkey white.
Went ahead and painted and baked. Three bakes, one coat per bake.
The Ti passivated after about 1.8 minutes in Chlorate cell.
I will attempt to dissolve ppt using HCl some other time and try again
with this solution.

I repeated the above paint formula only this time I added in the SbCl3 stock
solution before I converted the SnCl2 to SnCl4 (using H2O2).
Towards the end of adding in the H2O2 the milkey white ppt appeared
_______________________________________________

Dann2

chloric1 - 26-7-2007 at 16:30

Quote:
Originally posted by dann2

Perhaps my 'test' for DTO is a load of Boalderdash. (rubbish if in USA :D)

Dann2


I am American and I understand this.:D

..but seriously dann I wonder if this is like the electrode plates in automotive batteries that improve with a few charge/discharge cycles. Next time don't show mercy just run the hell out of the anodes say 200mA per cm2. Even if it passivates in 60 seconds. Maybe you need to do this 10 timesor something?!?!?!:o
Maybe your DTO has captured the titanium in a lower oxidation state and letting it set in open air corrects this. Can you take pictures of these anodes or your DTO mixtures?

Eclectic - 26-7-2007 at 17:02

You are not using enough HCl. Your solutions are not behaving at all like what I made from 95/5 solder. Also, you may have too much H2O2. Back titrate with Ti blue tinted SnCl2 solution until the color is stable at 90-95 C for at least an hour. Use 1 part 30% H2O2 with 3 parts 10-12N HCl as the oxidant.

Rosco Bodine - 26-7-2007 at 18:12

Why are you even worried about titrating with a redox indicator ? I would think just to use excess H2O2 and let the temperature decompose the excess , would be fine .

Eclectic - 27-7-2007 at 05:38

I'm not sure how long it takes for the excess to decompose, and excess H2O2 may be one of the reasons why Dann's coating solutions gelled and made a bad coating. Blue Ti indicator in SnCl2 is a no brainer when you are working with titanium anyway. You can use acidic SnCl2 as the pre-etch, and make the back titrant at the same time.

SOMETHING must account for the radically different behavior of Dann's solutions and mine. I'm just trying to pin down the differences in technique.

[Edited on 7-27-2007 by Eclectic]

another idea

Rosco Bodine - 27-7-2007 at 07:25

Getting a good interface at the titanium metal without growth of the oxide layer on the titanium is a bit tricky ,
and I have an idea how this might be done using SnCl2 ...
not as an HCl solution , because HCl attacks the Ti and/or
its oxide .....but rather to use *anhydrous* SnCl2 in an organic solvent with an abrasive , and scrub the titanium
with the mixture .

I wonder if it wouldn't be useful to just work with the completely anhydrous SnCl2 gotten from heating the
the SnCl2 first to drive off all the H2O @ 110C overnight ,
and then in a covered beaker continuing the heating to fusion ~250C . When the melt has cooled to ~200C and solidified , cover it with anhydrous glycerin , and on further cooling add some anhydrous isopropanol . Then break up
and dissolve as much as possible the SnCl2 in the combined solvent . Decant the SnCl2 solution and thicken it to a paste with diatomaceous earth or corrundum or pumice , and use it as an abrasive scrub on freshly etched , possibly hydrided titanium with a wire brush or a scotch brite pad , wearing gloves , and covering the titanium with the mixture in a shallow tray .

I believe this would get the surface plating of Sn at the interface which you have described , without an undesired growth of the oxide layer on the titanium . The vapor of the isopropanol would provide a shielding atmosphere from the oxygen and moisture of the air ....allowing the reactivity of the SnCl2 to prevail as the primary effect on the titanium .

I think the presence of HCl as solvent for the SnCl2 is going
to interfere with what you are trying to accomplish and this is possibly the way around that problem .

After the titanium is treated as above decribed , rinsed with isopropanol and dried , the next step IMO would be to apply the dip coated alkaline sol of combined stannic and antimonic acids , as their ammonium stannate and ammonium antimonate precursors , that I have mentioned before in regards to US6777477 . Then the substrate is baked .

Anyway .....that's my theory and proposed experiment .
Call it the star trek approach ....to go where none has gone before :D

[Edited on 27-7-2007 by Rosco Bodine]

Eclectic - 27-7-2007 at 07:41

12N HCl isn't really that corrosive to titanium. Dann did an experiment for me with 25% SnCl2 in 10-12N HCl with a piece of Ti half submerged overnight. The solution turned blue indicating SOME attack on the Ti, but there was no apparent surface corrosion, only a slight change in color, which I suspect is due to a thin flash coat of tin.

Rosco, How did you get stuck on the idea that acidic chloride solutions are BAD in this application? Your insistance on using alkaline coatings seems completely counterintuitive when you look at the chemistry of titanium. Dunk a piece of Ti in HCl and see for yourself how slowly it reacts.

'Course, classical physics says bee's can't fly, but they do anyway. :D

[Edited on 7-27-2007 by Eclectic]

Rosco Bodine - 27-7-2007 at 07:52

Apparent or not , there *is* attack of the titanium oxide by HCl at even 0.8 N HCl . I was reading the data on leakage current for valve metal capacitors where the TiO2 layer was being used as a dielectric , and a SnO2 intermediate layer formed from SnCl2 and baking was applied ....and the HCl concentration had to be kept minimal like 0.4 N for HCl to prevent formation of TiCl3 which trashed the dielectric layer and made the interface semiconductive . The semiconductivity of course is our objective but it is only a narrow range of pH where that occurs productively .....
as too much HCl just becomes the primary reaction ,
eating more into the titanium metal and adding more thickness to a layer where keeping it thin and doping it not growing it in thickness is what we want to do .

If you insist on growing the layer thickness with chlorides then you need to use Ruthenium for a mixed RuO2-TiO2 conductive oxides layer .....and just use TiCl3 as a deliberate precursor in the dip coating .

Anyway I think I have posted this before ....in connection with the observation that the structure for the valve metal interface is a semiconductor called a Schottky diode ,
and referencing a patent for such a device I found the only
method I have ever seen for producing a Ti *suboxide* interface not requiring a pyrolytic process with hydrogen reducing atmosphere , but using an electrolytic anodiztion
of titanium in a basic electrolyte which was KOH , the result being a "blue titania" suboxide . Electrolysis here was being used simply to drive the natural reaction as would occur chemically , to produce the desired effect of a very thin and controlled chemistry oxide interface on titanium ...a "soft mixed oxide" which would be semiconductive and receptive of doping to enhance its conductivity as a PN junction in
the case of the patent .....but which could be subverted to our purpose of non-polarized semiconductivity using a different doping material ....like SnO2 instead of PbO2 as in the patent .....and developed into a diffusion layer by baking .
This is exactly what my premise about the usefulness of an
alkaline reaction is about . It creates a stable porous and semiconductive oxide layer on the titanium substrate *directly* , while acid etchants do not . Easier to soak dopant into a sponge than to penetrate a layer of diamond .

[Edited on 27-7-2007 by Rosco Bodine]

Attachment: US2711496 Blue Titanium Conductive Oxide Anodization.pdf (295kB)
This file has been downloaded 651 times


Eclectic - 27-7-2007 at 08:38

Can I read that capacitor reference? That's some good info.

I'm thinking that with SnCl2 in the HCl pre-etch, a flash plating of tin will cover ALL exposed titanium while the oxide is dissolved. This should limit the reformation of a TiO2 layer.

We'll never be sure what is really going on with the surface chemistry without some fancy analytical instruments, but really it just boils down to "try it and see if it works".

Oooh! US27711496 has a wealth of info. You haven't convinced me SnCl4 is BAD, but now I'm more willing to experiment with alkaline conditions.


[Edited on 7-27-2007 by Eclectic]

Rosco Bodine - 27-7-2007 at 08:49

You can't "see" what is going on in these nano scale layer chemistry reactions ....only detect it with instruments and then make an educated guess . Maybe I have the dots connected wrong from what I have read and how I interpreted it ... but then what are experiments for ?

In other words ..at least we agree on something:D

The capacitor patent US3454473 is attached

BTW .....I know what you are meaning to happen with the Sn deposition in the etching scheme ...I just don't think it will happen in the presence of the HCl , as the Ti will preferentially react with the HCl and the H2O also present , instead of reacting only with the SnCl2 .
What I was suggesting was a way of getting past that likely problem ......by having no HCl and no H2O present along with the SnCl2 .

You see then , there is only one reaction route and no competing reaction .

What I am describing does not seem to me at all to be counterintuitive . I am proposing something which steers the natural inclination of the materials ( as I understand it anyway ) to produce the layer structure and chemistry that is desired , instead of trying to force formation of a layer structure and chemistry that goes against the way I suppose the materials will react . One theory on which I am operating is that titanium doesn't just go directly to an oxide but probably first forms a transient hydroxide which then dehydrates .....and this mechanism will predominate in anything other than anhydrous reaction condition .

[Edited on 27-7-2007 by Rosco Bodine]

Attachment: US3454473 Titanium film capacitors.pdf (178kB)
This file has been downloaded 667 times


Some pictures for some light entertainment

dann2 - 28-7-2007 at 12:30

Hello,

Some picutures below:
Note:
Paint No. 2 is:
__________________
The SnCl2:2H2O was obtained as Tin Mortant (white solid).

The 'painting' solution consisted off:>>> [Solution/Paint No. 2]
5 grams SnCl2:2H20 {2.63 grams Sn (77% of Sn/Sb ratio of final paint)
1.92 grams of SbCl3 solution {0.787 grams Sb (23% of Sn/Sb ratio of final paint)
2.2 grams 35% HCl
10 ml Iso-Propyl alcohol (surgical spirit used)
__________________________
Paint No 1 is:
_________________________

Solution consists of 16.7 grams SnCl4 (SnCl4 is 45.5% Sn)
+ 4.5 grams SbCl3 (SbCl3 is 53.4% Sb)
in 38cc liquid (HCl + H202 + Water)

Ratio is 76% Tin, 24% Antimony. [This is solution/Paint No. 1]
________________________________
Theses paints have been posted before way up the thread.

@Electic
-----------------------------------------------
I painted and baked the Ti which was left to soak overnight in HCl + SnCl2.
Put on 3 coats of 'Solution No 2' then baked and took some pictures.
There was no visible difference between the part of the Ti
that was soaked and the part that was not.
Applied another 3 coats, took some pictures!, and baked.
Due to the fact that the coating seemed to soak in water from the atmosphere this ruined
the coating when it was baked. The surface of the (unbaked second coat) anode went wet and had to be
dried with the heat gun again.
It was white in colour in places and not even over surface when baked. I did not
continue with the piece of Ti as a potential anode.

---------------------------------------------------

Made up anothe paint using SnCl4 (Made from SnCl2 + H2O2) + Ammonium Moly. in 12% HCl.
[Solution No. 5]

0.2 grams Ammonium Moly.
1.5 grams SnCl2:2H20 +H202 (min. amount added)
+ HCl. Total volume of Paint made was 7.6cc

Painted and baked. Bad coating. Did not test in Chlorate cell. Did not turn black.
No crystals visable on Ti after drying.

Water based (or HCl based if you like)
are inclined to dry in puddles. Better to have Alcohol if at all possible IMHO.
I think this paint was too dilute too.

Ammonium Molybdate forms a green ppt when added to SnCl2 if there is alot of water
in the solution. When SnCl2 is dissolved in 12% HCl this does not happen.
The solution of SnCl2:2H20 + Ammonium Moly (both dissolved in HCl (12%) before mixing)
is an orange clear colour, not unlike the colour of the 'Ti Oxide indicator stuff'.

Will try again just using SnCl2:2H20 + Ammonium Moly in a min amount of HCl + Isoproply
Alcohol. ie. will not add any H202 to convert Tin(II) to Tin(IV).
Perhaps pure IsoProply alcohol will stop the green PPT. If so
I will use no water.

Camera not great BTW. One photo out of focus/bad equipment or both. The crystals in the photo can be clealy seen as (pretty) squared on the surface of Ti (this is before bake).
I think way the paint is appllied (dilution rate etc) may have aloth to do with getting a good coat. (my 2c worth).

http://s168.photobucket.com/albums/u200/anodes_2007/?action=...

http://s168.photobucket.com/albums/u200/anodes_2007/?action=...

http://s168.photobucket.com/albums/u200/anodes_2007/?action=...

http://s168.photobucket.com/albums/u200/anodes_2007/?action=...

http://s168.photobucket.com/albums/u200/anodes_2007/?action=...



Dann2

Two more attempts

dann2 - 28-7-2007 at 18:18

Hello,

I returned to solution No. 5 and attempted to evaporate some of the liquid off by heating.

Reminder if needed__________________________
[Solution No. 5]
0.2 grams Ammonium Moly.
1.5 grams SnCl2:2H20 +H202 (min. amount added, had Ti indicator added)
+ HCl. Total volume of Paint made was 7.6cc
Orange coloured paint. When baked did not turn black.
______________________________________________
(The above solution No. 5 was posted before up the thread BTW.)

The solution changed colour from Orange (Ti Oxide indicator) to light yellow.
Oxide started to PPT. I stopped heating. A very small amount (~0.4 cc from 7.3cc)
of solvent was evaporated.
Painted and baked with the solution.
As soon as I pointed the heat gun at the painted Ti, the coating turned black.
After baking, the coating was less black but blacker that the first time I had
used this paint (before I had attempted to evaporate some solvent away).
I coated again and the same thing happened. As soon as I pointed the Heat Gun
at the painted Ti the coating went black. It is a bluish black. It may be the Ti
indicator in the paint turning blue again??

When baked the the coating was less black than when it went into oven. It looked better than first time I use the paint (up the thread) but does not look good enough for it's intended purpose.
Did not 'test' in Chlorate cell, and probable will not.

----------------------------

New paint!!!!!!!!!

Solution No. 6

1.5 grams SnCl2:2H2O dissolved in 2cc Iso Proply Alcohol
2cc HCl (12%)added.
0.2 grams Ammonium Molybdate added to solution and the lot mixed.
Solution turned deep green/yellow with some (very little) solid at bottom.

Painted and baked.
6 coats total, 2 coats per bake, 3 bakes total.
There was no visable crystals on surface of Ti when drying with Head Gun.
The paint covered and wetted the surface well.
The baked paint was a black colour and looked good.
Electic please skip one line :D
Steel wool could remove coating.
Piece of plastic does not remove coating.
Have yet to 'test' in a Chlorate cell.
This looks the best coat yet.
US 3940323 uses Mo though it is an Ru based anode.
_____--------------------------------------____________


'Water based' paints seem not too good at covering surface of Ti. They do
not wet the surface and are inclined to form puddles when drying. The dissolved
solids are inclined to migrate to theses puddles and you get too much solid
when the puddles eventually dry. Hard to get even coating.
The HCl in last in puddles too where it may be etching holes in the Ti ( perhaps this does not matter) as I have seen lots of pits where the puddles have been.
If you use small amonts of paint to stop puddles from happening it is then hard to get the smaller amount of used paint to wet the surface successfully.

Dann2

[Edited on 29-7-2007 by dann2]

Eclectic - 28-7-2007 at 18:29

It sounds like you are trying to apply too much coating before baking. Also, the alcohol may be in the formulas to facilitate surface wetting and rapid film drying.

Damn, this research by proxy is frustrating!

What happens if you just etch, dip coat, shake, and bake?

[Edited on 7-28-2007 by Eclectic]

Rosco Bodine - 28-7-2007 at 21:26

Quote:
Originally posted by Eclectic
Damn, this research by proxy is frustrating!


It's hard to find good help anymore .

Quote:

What happens if you just etch, dip coat, shake, and bake?


"shake and bake" ......LOL



Oxidative soak should be looking pretty good about now :P

[Edited on 29-7-2007 by Rosco Bodine]

hashashan - 29-7-2007 at 11:51

Well guys got everything ready for my PbO2 coating. except for one thing, Temperature, how the hell can i keep it at constant temperature of 55 degrees? i wont put it in the house. i dont have an oven and the differences between day and night here are quite intense and can reach up to 20 degrees difference.

Any suggestions?

dann2 - 29-7-2007 at 16:48

Hello,

I have used a glass tube with a spiral of Nicrome wire in it connected to a variac. The tube was put into the plating tank and the variac adjusted to give temp. I wanted. Open loop temp. control I guess.
An aquarium heater has been used by others.
A deep fat friar or kettle, if filled with water and connected to a variac with the plating tank sitting in it would do. Not very elegant.
If you do not have a variac a high power resistor can be made from Nichrome wire with a connection to it where it give the correct current into kettle/deep fat friar/tube + Nichrome wire or whatever. Wastes a bit of power and you need to keep clear of it but will do job.

Insulate the tank + heater with fiber glass wool to shield against the effects of changing ambient temperature.

Do you actuall want a controller?
I made a very simple and crude controller out of a comparator IC + thermocouple connected to a relay, once, which swithed the heater on and off when needed. Bang Bang controll, I believe, is the term for this type of control stragegy.


Dann2

[Edited on 30-7-2007 by dann2]

dann2 - 29-7-2007 at 17:04

Hello,

Will solid SnCl4:5H20 dissolve in water without forming Oxides like SnCl2:2H20?

US Pat. No. 3940323 useses SnCl4:5H20 in water (+ Ammonium Mo.)
(Hooker Chemicals & Plastics Corporation)

Can anyone suggest a fairly common solvent (other than water) that will dissolve Ammonium Molybdate and is also miscible with water (easy eh!). There probably is none but I thought I would ask anyways.
I tried Ethanol, Methanol, Iso Proply Al., Ether.
Perhaps acidified Ether?

Dann2

Rosco Bodine - 29-7-2007 at 19:57

Maybe try DMSO (dimethyl sulfoxide) , acetone , ethylene glycol , glycerin .

You could probably avoid all the chlorides related problems
if you would simply *try* the SnCl2 to SnO2 oxidative soak method for the initial coating followed by the mixed ammonia derived sols and baking . This could put you far ahead of whatever you might try to copy from an existing patent , if it works like I suppose it may . It is also easier than what you are still trying to do now .



[Edited on 29-7-2007 by Rosco Bodine]

Eclectic - 29-7-2007 at 21:50

Dann, this is about the 3rd time you've asked these questions going down this path...:o

Are we being Punked? A good game of rile up the old codgers, eh?

Rosco Bodine - 29-7-2007 at 22:01

Hard headed tunnel vision younguns are a real pain 'eh :P

I used to be a regalar Einstein too 'fore I grew out of it :D

Eclectic - 29-7-2007 at 22:42

Rosco, I read through the Ti capacitor patent, and found some good info in there about alcohols facilitating the wetting of titanium surfaces. The idea of strongly acidic solutions chewing through the TiO2 seems to be correct too. I think I'll be happily studying the interaction of titanium surfaces and various tin chlorides for a while, not that there might not be a better way to make an anode, but because I've gotten a LOT of the stuff, really cheap, made from a $12 1lb roll of 95/5 solder, and a $10 roll of 97% Sn leadfree solder, balance Cu, which does not seem to dissolve in plain 31% muriatic acid and settles out as a gray colored powder.

I'm more into the chemistry than the final product. :D

hashashan - 30-7-2007 at 00:53

Firberglass insultaion, contorllers ... damn.
How important is tempereture vcontroll?
what will happen if the anode will be grown just at room tempererature without any insuklatoins or anything.
the temperature will vary about 27-35 degrees ?

Rosco Bodine - 30-7-2007 at 09:14

There are some patents which describe mixed alkoxides being used as the precursor for the baked oxides on titanium . And here is an abstract where this reportedly even works on aluminum as well . If the aqueous chlorides
are not giving good results ....I wouldn't keep trying to find the niche condition that gives the desired result , but look at something different which may not be as tricky. If baked chlorides are proving to be problematic , why keep beating
your head against the wall on that approach instead of trying something different which might work even better ?
I can't prove that the things I have been saying are certain ,
but from the references available my interpretations are logically justifiable .

Abstract of JP2007070673

PROBLEM TO BE SOLVED: To provide an electrode which is inexpensive, can be adapted to various systems, and has a desired shape, for instance, an electrode having a structure consisting of an aluminum substrate and an antimony-containing stannic oxide film formed right on the substrate.
SOLUTION: The structure comprises: the aluminum substrate which is obtained by preparing a coating liquid containing a tin alkoxide and an antimony alkoxide, applying the coating liquid onto the aluminum substrate, drying the applied liquid and baking it; and the antimony-containing stannic oxide film formed right on the substrate.
COPYRIGHT: (C)2007,JPO&INPIT


BTW , if you are going to pursue the chlorides route anyway ,
one of the things you might try is adding some NH4NO3 to the HCl when dissolving the solder . The aqua regia formed in situ might facilitate the solution and serve a similar function as H2O2 without added water , and the presence of ammonium salt might enhance the solubility and even provide some possible complexation . Some small amount of Zn added might also be of benefit . The byproduct NH4Cl and the ZnCl2 as well are also fluxes whose presence might be beneficial .

[Edited on 30-7-2007 by Rosco Bodine]

dann2 - 30-7-2007 at 17:01

Quote:
Originally posted by Eclectic
Dann, this is about the 3rd time you've asked these questions going down this path...:o

Are we being Punked? A good game of rile up the old codgers, eh?


?? Greetings old codgers, (thanks for the compliment :D)

Apologys about the post, I was rather tired and not thinking too straight. Is it only the 3rd time....

The latest coating (solution/paint No. 6) on Titanium passivated soon after placing coated Ti into Chlorate.
:(

Same goes for Solution/paint No. 5 that was heated in an attempt to evaporate off some solvent.

Dann2

dann2 - 30-7-2007 at 19:16

Hello,

What are Alkoxide's? Is an 'Alkoxy-Tin' compound the same?
Will I not need SnCl4 (anydrous) in order to obtain the Alkoxide. ie. back to square one.
A few of the patents doing the rounds have used the Alkoxy-Tin to obtain a coating for the
electrolysis of brine without any coating on top. They refluxed SnCl4 (anhydrous) with
n-amyl alcohol for some hours to obtain the Alkoxide. eg. US 3627669 Example 4,
US 4040939 Example 6.



Regarding one of those's question I have asked before:

From US 3,940,323 Example 1:
___________________________________________________
snip
A solution of 2.2 parts of SnCl4:5H2O and 0.2 parts of (NH4)2MoO4 in 5 parts of water is brushed on to
the cleaned titanium surface.
snip
___________________________________________________

Will Oxides of Tin not ppt when the Tin(iv) Chloride is put into the water?
Just trying to pick holes in those's patents or am I shooting myself in the foot.


snip from post by Rosco
Getting a good interface at the titanium metal without growth of the oxide layer on the titanium is a bit
tricky, and I have an idea how this might be done using SnCl2 ...
Snip

The problem of my DTO coatings is not that a Ti Oxide layer is forming between the DTO and the Ti
substrate (unless perhaps the very poor paints that did not even turn black)
but that the DTO will not stand up to Chlorate cell anodic conditions. The coating wears away as
soon as the DTO coating is exposed to Chlorate cell electrolyte with current flowing.
They will work as an anode for some minutes with a smell of Chlorine but the coating gets eaten away,
the Ti gets exposed and then the Ti Oxide layer appears.


Hashashan
Most of the patents say that the coating of Lead Dioxide has a higher quality if the temperature is raised up from Room Temperature.
What sort of heater have you available? What is the plating tank made from?
Could you use a 'slow cooker' hotplate underneath the tank?
A large container of Cooking oil with a heating element in it with the plating tank sitting it?

The fiber glass insulation will be good to shield the set up from the varying ambient temperature but it
is not essential. Run the heater for the tank for a few hours to see where the temperature goes and how
stable it is. It may be good enough without the fiberglass.

Dann2

hashashan - 30-7-2007 at 23:35

I can get a heater, the heater is not a problem, i can buy a wire, use some primitive type of a stove or anything like those, oh yeah i can use a thing i once used... placing a candle under the tank :) (the candle does keep it in a good temp at night but at day it gets too hot.
The main tank is just a chemical glass (600ml) i think it is a good tank, no need for anything else.
The problem with all those heaters is that i cant sit by the electrode for 2 days and watch it getting plated, and it does get really hot here at daytime.

Rosco Bodine - 31-7-2007 at 09:35

Quote:
Originally posted by dann2
Hello,

What are Alkoxide's?

Generally an alcohol which has a metal substituted for the hydroxyl group hydrogen . Also called alcoholates , and sometimes perhaps less accurately for this arrangement "esters" . It is an organometallic compound which can be dissolved in organic solvents , may itself be a volatile liquid and can be hydrolyzed to the metal oxide by water or dilute acid , or by heating sufficiently . They are generally basic , alkaline in nature . Sodium methoxide is probably the simplest example .
Quote:

Is an 'Alkoxy-Tin' compound the same?

Yes .
Quote:

Will I not need SnCl4 (anydrous) in order to obtain the Alkoxide. ie. back to square one.

Not necessarily , other precursors , even the free metal can be used .
Quote:

A few of the patents doing the rounds have used the Alkoxy-Tin to obtain a coating for the
electrolysis of brine without any coating on top. They refluxed SnCl4 (anhydrous) with
n-amyl alcohol for some hours to obtain the Alkoxide. eg. US 3627669 Example 4,
US 4040939 Example 6.


You mean to tell me that a DTO precursor which is *alkaline* in nature can actually be used instead of a chlorides precursor , where the chloride is there to flux and etch the
titanium ???? Well imagine that :P ...must be a misprint or something , huh ???:P:P:P: Actually you will likely find the alkoxide based coatings in the earlier patents , where it was probably used first as a butoxide , later as an ethylene glycolate , or a glycerylate . The theory was probably that the molten organic material afforded some blanketing of the titanium at up to ~200C , whereupon the precipitation of SnO2 would begin , and the formation of a solid solution of TiO2 in the SnO2 would commence ....limiting the growth thickness of the TiO2 layer and modifying its chemistry . What a novel idea ! :P There might even be other better ways of going about that :D
Quote:

Regarding one of those's question I have asked before:

From US 3,940,323 Example 1:
___________________________________________________
snip
A solution of 2.2 parts of SnCl4:5H2O and 0.2 parts of (NH4)2MoO4 in 5 parts of water is brushed on to
the cleaned titanium surface.
snip
___________________________________________________

Will Oxides of Tin not ppt when the Tin(iv) Chloride is put into the water?

Let me guess ....you follow the patents description and you get a precipitate when the described mixture is prepared ?
Quote:

Just trying to pick holes in those's patents or am I shooting myself in the foot.

If there was any neglect in describing the mixture as being a "clear solution" , then you shouldn't be surprised to get whatever you have gotten .....since they left the door wide open to whatever it may be . This is a good example of the ambiguity of "patent speak" in "described examples" which may not be a precise blueprint which you can follow verbatim . Sometimes yes ....sometimes no . What might take ten pages of detailed decriptions to represent a full technical disclosure may have been pared down to three pages by the lawyers who wanted to tell only as much as
required to legally claim a technology .

Quote:

snip from post by Rosco
Getting a good interface at the titanium metal without growth of the oxide layer on the titanium is a bit
tricky, and I have an idea how this might be done using SnCl2 ...
Snip

The problem of my DTO coatings is not that a Ti Oxide layer is forming between the DTO and the Ti
substrate (unless perhaps the very poor paints that did not even turn black)
but that the DTO will not stand up to Chlorate cell anodic conditions. The coating wears away as
soon as the DTO coating is exposed to Chlorate cell electrolyte with current flowing.
They will work as an anode for some minutes with a smell of Chlorine but the coating gets eaten away,
the Ti gets exposed and then the Ti Oxide layer appears.


Your test may not have validity since the ATO is not really a working anode coating , but an intermediate layer . Still it would seem that days would be more expected than minutes for the coating to fail . I'd try baking on some
cobalt spinel over the outside . Everything you have described sounds like porosity is what you are getting rather than a sealed vitrified continuous coating of ATO . I really think that is what you will continue to get with any chlorides based precursor system applied alone in a coat and bake sequence like you are doing ...believing you are following a "recipe" which is likely a greatly abbreviated description from what was actually done . I think you are pursuing an exercise in futility where hope springs eternal for solving a puzzle for which you do not have the missing pieces , particulary in regards to any one patent . There is no
single "magic anode patent" , but you may learn the elements required from several different patents , and then
put them together to accomplish what you want to do .

I have personally done a lot of experiments which have been inspired by patented processes .....and usually find ways of improving , refining process examples where they don't tell you the whole story ... as they may leave that for them to know and for you to figure out :D

Personally I think the chlorides based precursor strategy
is useful in a limited context , not fully described and not as simple as following any single patent example as a good stand alone recipe . What I am getting at is step one may come from one patent , step two from another , step three from yet another ....and so on . That's the *only* way you will put the pieces of the puzzle together .

[Edited on 31-7-2007 by Rosco Bodine]

dann2 - 31-7-2007 at 12:44

Hello,

The puzzle has been solved. The 'solution' was posted here many moons ago. I /we are trying to do the same thing with more OTC materials. It ain't working for me I guess.

See here for working homemade Ti substrate, DTO + Lead Dioxide anode.

http://www.sciencemadness.org/talk/viewthread.php?tid=1425&a...

from a guy who actually made lots of anodes.

More discussion of anode here:
http://www.sciencemadness.org/talk/viewthread.php?tid=2465&a...

He use Butter of Tin and Butter of Antimony + water + Buthanol.






Dann2

Rosco Bodine - 31-7-2007 at 14:32

If the SnCl4 plus SbCl3 was so straightforward as to be the simple solution , then you wouldn't be having huge problems with it , would you ?

Alembic wasn't very forthcoming with the particulars concerning the intermediate layer ...was he ?

The problem of volatility has been mentioned with regards to the chlorides precursor mixture .

There is a gap in the temperature range where there is an indeterminate variable loss of the chlorides precursor mixture
due to volatility .....before the decomposition to the non-volatile oxides takes place ....at a higher temperature .
This alone is a problem I have pointed out before , which
makes the rate of heating affect the composition of the
residue of oxides , as well as how much of that residue is
even there .

Attached is a patent which uses a vapor deposition method
for metal oxide applied to a ceramic substrate to produce
resistors as an electronic component . The mixed chlorides
precursor is used , not as a liquid applied to a substrate and baked .....but as an aerosol vapor contacted with the substrate already raised to the much higher pyrolysis temperature where the vapors of the mixed chlorides on contacting the much hotter surface , then deposit the desired
oxides as a decomposition product . What makes this vapor deposition process work is precisely what presents a problem
when the mixed chlorides precursor is applied to a cool surface and then gradually heated ....most of it simply evaporates and leaves on the wind , literally gone with the wind .....get it ?

[Edited on 31-7-2007 by Rosco Bodine]

Attachment: US3632429 Sb2O3 SnO2 METAL_OXIDE_FILM_Resistors.pdf (196kB)
This file has been downloaded 766 times


Twospoons - 31-7-2007 at 18:08

@Hashashan

Here's the controller I built for a hotplate:
http://www.sciencemadness.org/talk/viewthread.php?tid=4896&page=1#pid55520

Works well, holds within a degree or so, and is very simple.

Why mixed valence oxide precursors may be useful

Rosco Bodine - 1-8-2007 at 07:04

Stable colloidal dispersions of mixed antimony and tin oxides
are known , where a colloidal dispersion of antimony oxide is *intimately* mixed by *coprecipitation* with a colloidal dispersion of tin oxide , so that doping is already accomplished at a relatively low temperature for
a dispersion that is a transparent emulsion ....a sol .

Antimony doped tin oxide nano *crystals*of X-ray diffraction
identified character showing only the tin oxide crystal structure , fully enclosing and masking the antimony within the tin oxide crystal structure are formed from such mixed colloidal dispersions , even at temperatures as low as 200C
in water dispersions heated for 6 hours in an autoclave .....
where the reaction goes entirely to completion . The nature
of the material is a solid solution of antimony entirely caged within the tin oxide crystal matrix . See US4775412 . Compare the coprecipitation of the Sn and Sb which is performed and *required* in the process with the similar process and material produced by US6777477 . These materials are probably identical as precursors .....or close enough , and the method of the later patent is simpler .

As a side note of possible interest .....
For colloidal sols of antimony oxide alone see US5008036 .
This patent also references other patent methods for
antimony ethyl glycolate .

For our purposes of producing an amorphous film structure
as opposed to a layer of solid solution nano crystals ...it appears that a variation on the mixed colloidal precursors could be useful , involving the mixed valency precursors which have a long chain polymeric form and dehydrate intact in that form , rather than precipitating as solid solution nano crystals . A desirable physical property of such a dispersed polymer is that it has profound effect as a wetting agent and
also has a strong electrostatic attraction to a surface to which it is applied , attaching itself as a persistent coating .
This is reported specifically for SiO2 , but the similar property
likely also applies to TiO2 . The effect is so pronounced that
even teflon is readily wetted by the inorganic polymer and the effect of wetability is persistent , for this material which
remains as a permanent surface layer adhering to the teflon .

Since the dispersion distribution of particles would be so complete already in the "doped colloid" , which would dehydrate as the polymer rather than a solid solution crystalline form .....during drying and baking , and the electrostatic property is so favorable for adhesion to a substrate , this would seem to be an ideal candidate for an initial coating .

BTW , this polymer is very possibly involved in the oxidative soak method for deposition of SnO2 . In that deposition method a +II valency Sn(OH)O? is being gradually oxidized to
a less soluble +IV SnO2 which is precipitated ....but it would seem that the mixed valency polymer would necessarily be present in that reaction system . And this may be what accounts for the reported strong adhesion of the deposited
films of SnO2 gotten by the oxidative soak method .

[Edited on 1-8-2007 by Rosco Bodine]

Attachment: US3890429 STANNIC_OXIDE_POLYMER_Film Wetting Agent.pdf (399kB)
This file has been downloaded 998 times


more specifics concerning oxidation of titanium

Rosco Bodine - 9-8-2007 at 08:46

From a couple of pages earlier in this thread ....
Quote:
Originally posted by dann2
From www.azom.com
____________________________________________
Oxide Film Growth
The oxide film formed on titanium at room temperature immediately after a clean surface is exposed to air is 12-16 Angstroms thick. After 70 days it is about 50 Angstroms. It continues to grow slowly reaching a thickness of 80-90 Angstroms in 545 days and 250 Angstroms in four years.

The film growth is accelerated under strongly oxidizing conditions, such as heating in air, anodic polarization in an electrolyte or exposure to oxidizing agents such as HNO3, CrO3 etc. The composition of this film varies from TiO2 at the surface to Ti2O3, to TiO at the metal interface. Oxidizing conditions promote the formation of TiO2 so that in such environments the film is primarily TiO2. This film is transparent in its normal thin configuration and not detectable by visual means.

A study of the corrosion resistance of titanium is basically a study of the properties of the oxide film. The oxide film on titanium is very stable and is only attacked by a few substances, most notably, hydrofluoric acid. Titanium is capable of healing this film almost instantly in any environment where a trace of moisture or oxygen is present because of its strong affinity for oxygen. Anhydrous conditions in the absence of a source of oxygen should be avoided since the protective film may not be regenerated if damaged.
__________________________________________
Dann2


To provide a more detailed look at the pH and electrical parameters which define the reactivity of titanium , these Pourbaix Diagrams are helpful . This data is useful in predicting what conditions may be helpful not only in plating schemes for titanium , but also in preparation of and coating
and doping schemes for titanium .

The first diagram is generalized and does not account for higher concentrations of dissolved hydrogen , for which titanium exhibits a very strong adsorption . The second diagram accounts for and shows the effects of the hydrogen .
These diagrams are important so I have saved them locally on the forum server .
Pourbaix diagrams for titanium below were found here
http://www.engr.sjsu.edu/WofMatE/projects/srproject/srproj5....






There are cathodic etching / hydriding schemes which are applicable to plating and also preparation for other coatings for titanium and other metals . It is possible to do this in a plating bath by first applying a low cathodic voltage to etch and hydride the metal , and then increasing the voltage to quickly deposit the metal plating so that a good metal to metal interface is produced .

Patents of possible interest concerning this technique are
US5368719 , US5456819 , US2801213 , US4153742 .

I posted this in response to electroplating of iron on titanium
in another thread , but this is also highly relevant here .

[Edited on 9-8-2007 by Rosco Bodine]

Oxalic acid related

Rosco Bodine - 17-8-2007 at 16:13

There is a patent US3650861 which directly relates to the usefulness of oxalic acid for etching titanium in a controlled way which improves the adhesion of coatings or platings as compared with other methods .

Also it reportedly is possible to use the mixed oxalates of tin and antimony as non-volatile precursors for baked ATO coatings of high quality on a titanium substrate , by a simple
dip , dry , and bake method . See US5431798 attached .
Eclectic has mentioned the possible usefulness of an initial
plating of metallic tin directly on the etched metallic titanium substrate , and this is described in the attached patent .
However ...there may be easier or better ways of obtaining
such an initial plating , as the oxalate of tin will itself plate
out tin at an appropriate pH , if the substrate is made cathodic . There are patents which relate specifically to plating of tin from tin oxalate electrolytes .....and I will have to dig them up to see if there is an example for the conditions for titanium . It may be possible to perform the titanium etching , tin strike plating , and dip coating for baking ATO , all in one pot using an oxalate / oxalic acid system :D . Anyway , for an example of the plating of tin
from an oxalate bath .....there is a brief description of this
tin plating in a rectifier patent US2368749 , see last page .

Also a variant of these mixed oxalates reportedly produces transparent optical quality coatings . No examples are given for titanium substrates in these further patents , but the chemistry is described in some detail and the conductivity
of various levels of antimony doping in the finished oxides is charted .....the ~5% figure for antimony oxide agrees nicely with most other sources which report an antimony percentage range from a minimum of 2% to a maximum of 8% , IIRC . See US4873352 and US4924017 .

Edit :
I just found a later version of the same patent attached below , apparently a parallel application , same inventors , same company , same subject material ... US5683567 .


[Edited on 17-8-2007 by Rosco Bodine]

Attachment: US5431798 Oxalate Precursors for ATO coated Ti substrate anodes.pdf (130kB)
This file has been downloaded 838 times


hashashan - 19-8-2007 at 04:56

Say guys, I think i will be able to lay my hands on a nice pice of Ta + Nb foil (surprizingly it will be easier to get then Ti ) Do you think that a protective DTO layer should be applied on this substrate also? or the Ta wont get oxidized form the PbO2 layer?

Eclectic - 19-8-2007 at 05:27

Absolutely, if you can get it to work. Ta oxide is even better at insulating than TiO2. I don't think it's going to work without some fluoride in the mix.

hashashan - 20-8-2007 at 04:19

Oh never mind, somone outbidded me on ebay. I guess ill find some Ti there.
maybe somone here care to sell some Ti?

Tin Oxalate, where/how to obtain?????

dann2 - 20-8-2007 at 17:56

Hello Folks,

Been doing some Patent digging Rosco eh?

The Pat. using the Tin Oxalate is good since it uses a new Tin compound for me/us in the examples, ie. Tin Oxalate.
The obvious question that I am going to ask is, where/how can one get Tin Oxalate?
Tin metal + Oxalic acid is my wild assed guess but quite frankly I don't have a clue.

I am looking at a piece of Ti, on the bench, that I coated with DTO about 4/5 weeks ago. The coating seems to be getting more and more shiney as the days go by. (The part of the coating at anode top end not etched away when I 'tested' it some weeks ago). I will try putting it into a Chloride solution as an anode and see what happens. This piece of DTO coated Ti has been tested before in a Chloride electrolyte and it lasted some minutes when it had sat on the bence for about 2 weeks after it was coated. (Simiarly coated Ti had only lasted about one minute when tested just after coating).
Perhaps the coating gets better when aged for a few weeks?? ...................Like Whiskey.
We shall see.

Dann2

Rosco Bodine - 20-8-2007 at 19:28

Quote:
Originally posted by dann2
Hello Folks,

Been doing some Patent digging Rosco eh?


Yeah you know me ...I occasionally look at a patent or two
trying to find anything interesting :D

Quote:

The Pat. using the Tin Oxalate is good since it uses a new Tin compound for me/us in the examples, ie. Tin Oxalate.
The obvious question that I am going to ask is, where/how can one get Tin Oxalate?
Tin metal + Oxalic acid is my wild assed guess but quite frankly I don't have a clue.


I looked briefly for a preparation but didn't find anything other than the oxalates have a low solubility in plain water .
I thought probably either direct reaction with the metal
and a hot oxalic acid solution perhaps with added hydrogen peroxide . Boiling a solution of the chlorides with oxalic acid
may also possibly do it , with the HCl byproduct boiling away .

Or perhaps make ammonium stannate and then make the oxalate from that , although the ammonium stannate itself is probably a better precursor to use directly .

I still think that mixed valency polymer of the approximate oxychlorides composition has the most promise , or an oxidative soak method for getting the first layer ....but anyway there sure are a few promising alternatives to
the mixed chlorides which are presenting complications .

I have an idea for shortcutting the process if the anode substrate could be a solid titanium rod . Get a rectangular form cast iron burner from an old radiant space heater , and
chuck the solid rod in a slow speed rotisserie drive like a
zeromax stirmotor or light duty conveyor motor , and do
the baking over an open flame with the part rotating .
You could spray coat your precursor liquids directly onto
the hot part , in several passes as a more or less continuous
process until you get the desired thickness ......instead of doing several separate manipulations . One of those Preval
sprayers like hobbyists use could do the job , or an airbrush
if you have one .

[Edited on 20-8-2007 by Rosco Bodine]

dann2 - 23-8-2007 at 17:15

Hello,

Done some Googling [tin oxalate] and came up with this

http://64.233.183.104/search?q=cache:2v4fAkdugnwJ:www.ias.ac.in/matersci/bmsdec2004/491.pdf+tin+oxalate&hl=en&ct=clnk&cd=5&gl=ie

You may need to cut and paste this link.

In document it describes synthesis of Tin Oxalate:
_______________________________________

2.2 Preparation of tin oxalate precursor

This precursor was prepared by dissolving equimolar quan-tities of tin chloride and oxalic acid and stirred well. The precipitate of tin oxalate obtained was filtered through sintered glass crucible and was washed with oxygen-free distilled water till free from chloride ions and oxalic acid, finally with dry acetone and was then dried under vacuum.
_______________________________________

Which Tin Chloride do you think it is?

Looks dead easy to me if it is Tin(II) Chloride (SnCl2)!


This link states that SnCl4 forms when Tin metal is added to Aqua Reiga:
http://www.neymetals.com/tin.htm

Oxidizing acid,,,, same as HCl then H2O2?????? I guess.

US 5116468 uses Sn/Sb metal + Oxalic acid to obtain DTO in electrolythic set up. May be applicable to us.

Cheers,
Dann2

[Edited on 24-8-2007 by dann2]

Rosco Bodine - 23-8-2007 at 21:25

The SnCl2 is probably what they were using and it would be the stannous oxalate precipitated . The patent however is
producing the higher oxidized stannic oxalate by anodic oxidation of the tin metal . You can get the same thing
I think , without the lengthy electrolysis .


Probably the easiest route would be to just make your clear solution of mixed chlorides with HCl + H2O2 ,
or HCl + NH4NO3 (toxic fumes!) and then neutralize with ammonia to a pH of 7 to 8 to precipitate the mixed basic hydroxides , that is the stannic and antimonic "acids" . The precipitate will probably settle out by gravity and the waste liquid can simply be decanted , and oxalic acid solution added and the mixture stirred and heated to form a solution of the mixed oxalates . IIRC you will need some small excess acidity of oxalic acid and possibly also some small amount of ammonium oxalate present for increasing the solubilities of the mixed oxalates well beyond what is their usual low solubility in plain water .

[Edited on 24-8-2007 by Rosco Bodine]

Eclectic - 24-8-2007 at 06:00

Sn(II) oxalate is poorly soluble, Sn(IV) soluble. H2S bubbled through a solution of Sn(IV) and some Sn(IV) oxalate precipitates antimony sulfide, but not tin.

(I'm still experimenting with 95/5 solder as a source of tin) ;)

[Edited on 8-24-2007 by Eclectic]

Rosco Bodine - 24-8-2007 at 07:31

IIRC there is a window concentration of diluted HNO3 ....maybe 5-35% concentration range where
the metals are dissolved by the boiling acid and the
nitrates formed are then immediately hydrolyzed with
precipitation of the oxides , or basic oxides . There is an evolution of deadly toxic oxides of nitrogen as a byproduct during the process similarly as when lead or silver or mercury are dissolved in nitric acid .

After producing the oxides , then they could be converted to other materials by further reaction to produce the desired salt ......like the oxalate .

The implications for the electrolysis are also interesting in another way .

The use of electrolysis in regards to the oxalate
could perhaps be used in an exactly opposite arrangement from that patent , to partially reduce
the higher valency materials to a system of the mixed
valency "polymer" , or sol type of liquid system as has been described for the chlorides . The chlorides could probably be treated the same way as an alternative electrolytic method of production of that mixed valency polymer , instead of stirring the solutions of the higher
valency salts with the powdered metals , or addition of the
lower valency salts , to form the polymer . A gentle , partial reduction in a divided cell where the higher valency
salts are the catholyte should accomplish the same thing
and the polymer of mixed valency materials should result ,
as an intermediate in reduction before the free metals are plated out .

[Edited on 24-8-2007 by Rosco Bodine]

not_important - 24-8-2007 at 08:32

Quote:
Originally posted by dann2
...
In document it describes synthesis of Tin Oxalate:
_______________________________________

2.2 Preparation of tin oxalate precursor

This precursor was prepared by dissolving equimolar quan-tities of tin chloride and oxalic acid and stirred well. The precipitate of tin oxalate obtained was filtered through sintered glass crucible and was washed with oxygen-free distilled water till free from chloride ions and oxalic acid, finally with dry acetone and was then dried under vacuum.
_______________________________________

Which Tin Chloride do you think it is?

It's Sn(II), note the use of oxygen-free water for washing.
Quote:

...

Oxidizing acid,,,, same as HCl then H2O2?????? I guess.


Note that H2O2 contains stablisers, which might affect the product and the end use, given that you are working towards semiconductive materials that often are sensitive to small amounts of other ions.

Eclectic - 24-8-2007 at 09:01

H2O2 stabilizers are usually in PPM and are generally either tin compounds or phosphoric acid. From my experiments with various lead free solders, I'd say dissolving 1 lb (500g) lead free solder with about 1 quart (liter) 10-12N HCl in a ceramic crock pot @ 90C for 12-24 hours is cheap and easy route to obtain fairly high purity SnCl2. The intermetallics from the alloying elements don't seem to want to dissolve unless the oxidation state is raised with H2O2 and additional HCl. Dropwize addition of 1 part 30% H2O2 to 2-3 parts 10-12N HCl (foaming hazard if acid contains Fe) with vigorous stirring to the COLD (much heat produced) SnCl2 solution will convert it to SnCl4. Excess H2O2 produces a white precipitate.

Concentrated SnCl4 solution WILL dissolve tin and tin intermetallics.

hashashan - 26-9-2007 at 05:54

Sorry for reviving a dying thread,
Anyone knows any way to make an alpha lead dioxide coating? I don't want to electrolyze lead in H2SO4 because i need this alpha layer to be plated directly on silver. Also i would prefer not to use lead tartarate because i just don't have tartaric acid and for some reason it is quite expensive.

Antwain - 26-9-2007 at 09:11

Have you tried looking in the supermarket for tartaric acid? In Australia, we can get food grade tartaric acid for ~$2/100g and I can't see why it wouldn't be available everywhere. Its usually near the baking supplies or herbs and spices. If your only shortage is tartaric acid then this may help.

hashashan - 26-9-2007 at 09:26

Never seen it here.

dann2 - 26-9-2007 at 10:17

Quote:
Originally posted by hashashan
Sorry for reviving a dying thread,
Anyone knows any way to make an alpha lead dioxide coating? I don't want to electrolyze lead in H2SO4 because i need this alpha layer to be plated directly on silver. Also i would prefer not to use lead tartarate because i just don't have tartaric acid and for some reason it is quite expensive.


Hello,

It would be a pity to let the thread die!
This may help.
http://www.geocities.com/CapeCanaveral/Campus/5361/chlorate/...

Dann2

chloric1 - 27-9-2007 at 01:47

Suppliers of wine making materials carry tartaric acid. If you are adventurous, and I am still considering this, by cream of tartar and neutralize with the appropiate amount of sodium or potassium carbonate. Then when everything is in a clear solution add a soluble calcium salt to precipitate calcium tartarate. When this is thoroughly washed and dried, prepar a dilute (10%) sulfuric acid solution with the exact stochiometric amount of sulfuric acid and heating with constant stirring for about 2 hours. I would heat to boiling or just under. The resulting calcium sulfate should consist of large enough crystals to be easily filtered. Concenrate said filtrate until crystals start to form then chill. Tartaric acid is VERY soluble in water so I do not know how hard this is. Also, adding alcohol to the concentrated solution may help.

hashashan - 1-10-2007 at 00:01

Hi, did some alpha lead plating, weired thing... i only got a thin brown plating, couldnt get the thick black deposition. Anyone tried to plate alpha?

dann2 - 1-10-2007 at 16:42

Quote:
Originally posted by hashashan
Hi, did some alpha lead plating, weired thing... i only got a thin brown plating, couldnt get the thick black deposition. Anyone tried to plate alpha?



Hello Hashashan,

Never plated Alpha myself. I used to communicate with a guy who did lots of plating from a Lead Acetate bath, (made from vinegar and Lead metal). It plated OK but anodes were falling apart. The substate was ceramic.

You cannot plate Alpha onto Graphite for some reason or other.

What is your substrate and bath type.

Dann2

quest - 2-10-2007 at 15:52

I've been searching and found patent 4,064,035, and got an idea of making PbO2 with no substrate.

I thought of using iron as base
Quote:

Examples of substances which satisfy these requirements and which are inexpensive include graphite, titanium, iron and stainless steel.


Quote:

Where the electrode is desired to be manufactured in a sheet-like form containing no substrate, it can be obtained by first electrodepositing on one surface of the substrate an .alpha.-PbO.sub.2 layer and then electrodepositing thereon a .beta.-PbO.sub.2 layer by following the procedure described above, subsequently repeating this cycles of operation to have additional .alpha.-PbO.sub.2 layers and .beta.-PbO.sub.2 layers electrodeposited alternately until the combined thickness of layer reaches a required value (about 10 mm), and thereafter separating the substrate mechanically by use of a cutter or, if the substrate happens to be made of iron, chemically dissolving out the substrate from the substrate by use of an acid


I made all the bathes for alpha and beta PbO2 plating and a iron anode\cathode.

And then I found this link:

Quote:

Ions that are bad news in a plating tank, according to the literature, are:
Chloride, Cobalt, selenium, arsenic and iron. The only ion that is likely to effect you is iron. If you are using 'crocodile' clamps made of steel to make connections to an anode that is being plated, you must be careful that no corrosion (it is very likely to form on the damp clamp) falls or gets into tank. Better not to use Iron at all. Not too sure about SS but it has been in a plating tank and had no corrosion or ill effects reported. Keep Gouging rods out of the tank as them may contain Iron particles.



long post for small punch line:
So it is OK to use iron in a PbO2 electrolysis bath?

[Edited on by quest]

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