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Author: Subject: More on PbO2 electrodes
Eclectic
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[*] posted on 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.
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[*] posted on 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 .
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[*] posted on 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]
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[*] posted on 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 .
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[*] posted on 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]
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[*] posted on 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 .
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[*] posted on 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.
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[*] posted on 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 .
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[*] posted on 22-7-2007 at 10:33


Aluminum IS a passivating metal.

Anyway, yeah, that's what I'm talking about. :D
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[*] posted on 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]
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[*] posted on 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
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[*] posted on 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 .
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[*] posted on 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]
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[*] posted on 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]
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[*] posted on 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]
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[*] posted on 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 644 times

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[*] posted on 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

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[*] posted on 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]
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[*] posted on 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.
__________________________________________


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[*] posted on 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 .
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thumbdown.gif posted on 25-7-2007 at 09:34
Al would be useless


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.


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[*] posted on 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 .
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[*] posted on 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)

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[*] posted on 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
_______________________________________________

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[*] posted on 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?




Fellow molecular manipulator
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