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Author: Subject: More on PbO2 electrodes
dann2
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[*] posted on 15-6-2007 at 04:11
Lead Layer


Hello,

There is a patent (would you believe) that uses a Lead Layer on top of Titanium. An Alpha Lead Dioxide layer is put on top of the Lead metal with Sulphuric acid (like you are doing). Then a Beta is plated on, from a Lead Nitrate bath.

There is no mention of using the anode in a Chlorate or Perchlorate application, only a Fluoride electrolyte.
I think that if the anode could be use in a (Per)Chlorate cell they would have mentioned it.
I think that the (Per)Chlorate cell is a very unfriendly environment compared to a lot of applications (including Chrome plating).

Patent here:


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

Dann2
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hashashan
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[*] posted on 15-6-2007 at 13:11


Well i seem to loose any track of the discussion about coating PbO2 on metals. What would be the best metal(just not platinum etc. ) for deposition of PbO2 over it? The metal is only temporary substrace, it will be eroded off after the coating.
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Rosco Bodine
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[*] posted on 15-6-2007 at 13:54


IRON
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[*] posted on 15-6-2007 at 15:16


Thanks for the info, Xenoid.

I hope it works, as we need a cheap and quick way to make some perchlorate; but even if it doesn't work, there are so many ideas floating around, it's useful to get the ideas that don't work out of the way, so as to narrow down the field of contenders and concentrate on something else.
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dann2
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thumbdown.gif posted on 15-6-2007 at 17:31
DON'T USE IRON


Greetings all,

Quote:
Originally posted by Rosco Bodine
IRON


Not wishing to start a long, high bandwidth, low content rant (would I do that :P).......I would not recommend Iron as a temporary substrate.
Iron is mentioned (along with Cobalt) as a contaminant in Lead Nitrate plating baths as something you do not want. If you do not control pH very well (especially at the start when Iron is exposed) then some will dissolve into plating solution and pollute.

Dann2
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Rosco Bodine
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[*] posted on 15-6-2007 at 18:16


Iron has reportedly (from numerous sources) worked for the purpose so why not try it instead of guessing that it won't work ..... just because it is simple ? Does it sound good to be true ?

I see it this way .....

If your plating electrolyte is low dissolved iron content initially , ( and it will be at a mildly acid pH , because Iron
salts will have low solubility , and likewise the corrosion of metallic iron at that low solibility for iron salts pH will not be favored ) .......
And you are using a stainless or copper or nickel or graphite cathode , there shouldn't be a problem . You see if metallic iron tried to dissolve into the lead salts solution , it would tend to deposit lead metal at the site of erosion . But that site being held at a reverse polarity and the anodizing voltage should result in PbO2 being formed there instead , sealing off the site . Obviously
the deposition of PbO2 is favored over the corrosion of the iron , so the iron is quickly buried beneath PbO2 ,
in effect being anodized by the PbO2 and thus protected from corrosion .

Beginning the plating at a neutral or just slightly acidic pH
the iron should not be attacked , especially if the degreased iron is connected to a live voltage feed outside
of the bath , so that plating begins at the very instant
it is immersed , the PbO2 should seal it immediately .

Perhaps some method could be used for primer coating the iron if that is desired .....but I would expect the initial plating of PbO2 to effectively seal the surface . If resorting to a nickel plating , then you may as well
use an aluminum substrate .

It is possible that you could make the iron cathodic for initial immersion so that metallic lead is initially plated onto the iron as a "strike" plating , and then after 30 seconds or so , reverse the voltage and establish the PbO2 simultaneously
from oxidation of that metallic lead strike with added PbO2
that is "incoming" from the electrolyte .

The surface of the iron could be converted to magnetite
if you wanted to go to the extra trouble , but I don't think that is necessary .

As for pH control ....that is going to be necessary anyway
with a bath containing lead nitrate . Only an acetate bath
for the alpha PbO2 would be capable of self-buffering to
any reasonable extent , perhaps using an added component like sodium acetate or ammonium acetate . With a mineral acid salt of lead , and lead being plated out , the pH will rapidly go highly acidic in the absence of some pH control and that variation is known to produce an inconsistent and lowered strength deposit of PbO2 .

Pickling and Pretreating the iron with chromic acid has been reported for iron to be plated with PbO2 from an acidic
lead sulfamate bath .....so here's another industry reference
concerning plating of PbO2 onto IRON :D


[Edited on 15-6-2007 by Rosco Bodine]

Attachment: US2430304 PbO2 on iron group metals from suphamate bath.pdf (118kB)
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[*] posted on 15-6-2007 at 20:10
In-situ PbO2 plating again!


I plated my previously described Pb electrode for about 2 hours to get a thicker, more impervious coat, although it didn't look all that different to the first attempt.

I used some of my finest quality NaClO3 (triple recrystallised, to try and avoid any problems with chloride) to make a saturated chlorate solution.

When I placed the anode in the solution, it was immediately covered with a wispy white precipitate (with no current flowing). The ppt. washed away when the anode was agitated and didn't form again.

When the current (1-2A) was turned on, no oxygen was generated and the anode looked like it was doing its job (making perchlorate)!

After about 5 mins. I turned off the current and removed the anode for examination. The part of the PbO2 coating which had been immersed seemed to be lighter in colour. When I tried squirting it with some water from a wash bottle it started to slough off in parts, revealing a shiny Pb surface.
Meanwhile the Ti cathode which had happily been producing H2 was coated in a dark grey non-adhesive sludge (presumably Pb).

Thus endeth my attempts at in-situ PbO2 plating, unless anyone has any suggestions!

Regards, Xenoid
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[*] posted on 15-6-2007 at 20:34


If anyone wants to actually MAKE an iron substrate lead dioxide anode, you might try soaking the iron in concentrated nitric acid first to passivate it. This effectively forms a coating of magnetite (?), preventing further dissolution. Maybe preventing Fe contamination of the plating bath? Experimentation will tell...
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Rosco Bodine
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[*] posted on 16-6-2007 at 09:19
Some chromating methods of interest


Here are a couple of methods for chromating ....
which is to say modifying the surface oxide layer
of a metal substrate to form a mixed chromium oxide layer which is adherent and has improved resistance to corrosion
and differing electrical conductivity from the unmodified
natural oxide which would otherwise be present .

The first of these patents is an old method which involves
simply dipping or brushing the cleaned metal with a mixture of phosphoric acid and sodium dichromate and then baking
at a mild heat to develop and complete the reaction .
It is not known to me at this point if the electrical conductivity
of this type of chromating layer is good or not . There are variations on the process and I am still looking at these to see if I can learn more specifically concerning the electrical
conductivity . I am hopeful that the electrical property of the chromate coating is conductive , and it would seem that
such a process is applicable also to titanium and other metals . Chromium and vanadium are both dopant materials
useful for improving conductivity of oxide coatings .

Attachment: US2030601 Chromated Steel from sodium dichromate and phosphoric acid dip and bake treatment.pdf (207kB)
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Rosco Bodine
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[*] posted on 16-6-2007 at 09:30
A known conductive chromating for aluminum


This method for chromating aluminum is specifically for
improving the conductivity at the surface for the making of good electrical connections .

Whether this method is directly applicable also to other metals besides aluminum ....I am not certain , but it would seem likely . I especially thought of the case involving
the "blue titania" which was described in that earlier
lead peroxide on titanium rectifier patent ...that this
chromating method could be applied to that and the result
could be a desirable and easily made conductive modified
oxides for the "primer layer" on the titanium to be further
coated with other conductive oxides .

Attachment: US2993847 Conductive Chromating for Aluminum.pdf (79kB)
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Rosco Bodine
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[*] posted on 17-6-2007 at 02:23
This is interesting


Looking through patents concerning "conductive anodized"
I found this patent which would seem to also have more general applications ....possibly for many of the valve metals .

Very neat process , which is also related to the manufacturers art of producing colored anodized coatings
by the use of dyes which are absorbed by a porous
anodized coating .

Attachment: US6228241 Electrically_conductive_porous_anodized_aluminu.pdf (87kB)
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hashashan
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[*] posted on 17-6-2007 at 02:36


Will Iron will be any good for a cell where the PH isn't maintained?
how about copper? Graphite isnt really good because as the PH drops it gets eaten away.
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Rosco Bodine
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[*] posted on 17-6-2007 at 10:00


Iron will be attacked without pH control . The lower limit
on the pH is reportedly a bit over pH 2.0 and the range
for an iron substrate is reportedly good up to pH 3.5
by one source .....and higher by other sources . Going more basic doesn't seem to bother iron , but increasing acidity does erode it .

The added problem with no pH control and a lead nitrate bath is that it doesn't really matter what substrate is used , as the resulting PbO2 quality will be poor due to
the varying composition of the electrolyte , the nature of
the deposited material will vary by the minute .

With an acetate bath or an alkaline bath you would be more likely to get by without a pH controlled electrolyte ,
but using a lead nitrate bath without any pH control is IMO an exercise in futility for anything but the very thinnest of PbO2 platings . Understand that for every
molar amount of PbO2 being deposited that *TWICE* that molar quantity of freeform nitric acid is appearing in
increasing concentration in the electrolyte , and you can see that in a couple of minutes of plating you have driven the pH nearly to the low end of the scale unless you are
continuously counteracting that acidity . It takes very little
addition of freeform nitric acid to decrease a pH from around pH 4 to below pH 2 where the iron would be attacked . You could literally watch the current meter reading climb with the increasing conductivity of the bath
due to the changing acidity .....and the changing composition would be all over the place so quickly that
with manual additions and pH checks and adjustments ,
you could *never* maintain a constant reaction condition
unless your bath was the size of a swimming pool ,
and you were pumping the electrolye past the anode
like it was sitting in a Jacuzzi .
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hashashan
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[*] posted on 17-6-2007 at 13:06


Ok im getting the point.
I just dont want to make lead carbonate (quite a mess) can i neutralize the acid with another substance(i mean non-lead) ?
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Rosco Bodine
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[*] posted on 17-6-2007 at 13:29


If you did that , then you would be looking at a continual decrease in the available Pb in the bath as lead plates out as PbO2 . You kill two birds with one stone if you just flow the electrolyte through a bed of some lead compound which will act as a neutralizer , it controls the pH at an equilibrium and it keeps the Pb content of the
electrolyte constant . This also conveys some honest rate control to your power supply settings , which sort of become meaningless if the composition of the electrolyte is constantly changing .

[Edited on 17-6-2007 by Rosco Bodine]
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[*] posted on 17-6-2007 at 16:04
DTO coated Ti


Hello,

Got around to coating a Ti strip with Doped Tin Oxide.
Had problems with getting Oxalic acid to etch the Ti. It etched the first piece OK but for some reason or other it would not etch a second piece even though I added a further 60grams Oxalic acid into the 700ml water. There was already 60grams in there.
Switched to hot sulphuric acid which seem to do OK.

The DOP was made up using info in US Pat. 3,940,323. They used SnCl4:5H2O + (NH4)2MoO4 in Example one. I used SnCl2 + Ammonium Molybdate. The SnCl2 + Ammonium Moly. give a dark green ppt. The SnCl2 had problems dissolving due to formation of hydrates (meta stannic acid??) The Ammoniom Moly. had problems dissolving too. There seems to be a portion that will not dissolve. The patent calls for from 0.1% to 15% Mo based on the moles of Tin. I used 10 grams SnCl2:2H2O + 1.47 grams (NH4)6Mo7O24:4H2O (I am guessing the water content as my chemicals are ebay with simply the names Ammonium Molybdate and Stannous Chloride written on tubs). That works out at just over 15% Mo based on the moles of Tin (Welcome to check the math...please).
To make a long story short I baked four times at about 480C. Each bake consisted of three coats of the 'stuff' that I had in the jar after mixing the SnCl2 + Ammonium Moly. I dried each coat with a heatgun. 12 coats total. The whole thing looked good. I decided to try the coated Ti in a Chlorate cell just too see how it would hold up but it was not very conductive. It needed 11 volts applied to get current to flow. Then the current started to drop as the coating was eroded and the Ti then started to passivate. This took about one minute. Bollox. (Sorry about that).

I may try again with a lower Moly content. Also the Pat said to bake at 400, I baked at 480, I do not think it would make any difference.
Also the patent says that Ammonium Molybdate can be used (it lists lots of compounds). The formula for Ammonium Moly is (NH4)6Mo7O24:4H2O coming for a chemical supply house catalogue. The compound the Pat used in their Example 1 (with SnCl4) is (NH4)2MoO4. What compound is this? I presumed it is Ammonium Molybdate?, it is 'nearly' Ammonium Moly:-)

SnCl2 will dissolve in Methanol without any problems (no formation of hydrates) but I cannot get the Ammonium Molybdate to dissolve in any organic solvent that I have. Alas.




If I obtained Antimony Trichloride instead of the Ammonium Moly would it dissolve in Methanol? This would give a clear solution without the complications of Tin hydrates forming.
I could try HCl as Rosco suggested but I did not get around to it.
Perhaps all the Tin Hydrates (or whatever is in there) will decompose to Tin Oxide anyways when they are baked?

It may be better for me to go back to SnCl4 + SbCl3 as all or most of the patents seem to use that combination.
Lead free solder and Chlorine perhaps.

Thats enough rambling for one post.

Regards,
Dann2
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[*] posted on 17-6-2007 at 17:05


You want a heteropoly acid called stannomolybdic acid. 12 moly-oxide units in a cage around a tin atom. If it's anything like silicotungstic acid, it should be extremely soluble in acidic ethyl ether. Try boiling a mix of 1-2 parts tin compound to 12 parts molybdenum compound by mole in 1N HCl for a few hours, cool, and extract 2-3 times with ether. Combine and evaporate ether layers (they may be DENSER than water, make sure you don't discard the wrong layer!)
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Rosco Bodine
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[*] posted on 17-6-2007 at 20:23


I know titanium is expensive to experiment with
so maybe some rods and test tubes would be the best way to go for economy of many coatings test scenarios .

The simplest "combination" titanium dopant system I found using Tin compounds was a 70-30 mix of tin chloride - tin fluoride . See US5756207 , US5683567 , perhaps also US4510219 , and US2564707 .
The tin compounds convert to oxides during baking ,
with the fluoride functioning as both a flux and a dopant
for the tin oxides as well as the titanium oxide boundary layer .
The tin oxides doped with fluorine have about three times the conductivity of graphite or about the same conductivity as PbO2 . Now ....if only it is an non-polarized ohmic resistance , then you're in business:D


I apologize for recently getting completely ass backwards turned around on the polarity of the Schottky diode structure
that I had right at first , then reviewed and studied it carefully until I had it completely reversed in my mind . It must be age telling on me . Anyway I went back and deleted my "corrections" post concerning what I earlier had right in the first place when I first mentioned the Schottky architecture , the natural behavior of which is to block
anode current flow .

The whole idea of the doping of the titanium *is* to decrease the reverse breakdown voltage of that metal to semiconductive oxides rectifying junction , and make a chemically resistant barrier to any new growth of a rectifying layer - junction there .... which most definitely is in the wrong polarity for the conductivity of current by the anode .

The Ruben patent US2711496 which I attached a couple of pages back is still very relevant in terms of its detailing of the
etching of the titanium and the subsequent plating of alpha PbO2 . And it may also be relevant in its description of the
formation of a substoichiometric titanium dioxide layer which
is conductive via an electrolytic process . This layer is reportedly immeasurably thin in dimension and also reportedly porous ....so this may be an ideal material for
adsorption of dopants , or being subject to other techniques
to lower its resistance to anode current .

[Edited on 18-6-2007 by Rosco Bodine]
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hashashan
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[*] posted on 18-6-2007 at 01:38


Quote:
Originally posted by Rosco Bodine
If you did that , then you would be looking at a continual decrease in the available Pb in the bath as lead plates out as PbO2 . You kill two birds with one stone if you just flow the electrolyte through a bed of some lead compound which will act as a neutralizer , it controls the pH at an equilibrium and it keeps the Pb content of the
electrolyte constant . This also conveys some honest rate control to your power supply settings , which sort of become meaningless if the composition of the electrolyte is constantly changing .

[Edited on 17-6-2007 by Rosco Bodine]


and how would you recomend maintaining the PH? i dont have any PH sensors (got only the papers)
so for what i see the only method i can think of is hanging a tea bag with lead hydroxide in the tank. but wouldnt that make the solution basic?
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[*] posted on 18-6-2007 at 08:35
pH regulation


The teabag idea was simply a "better than nothing" sort of comment . It surely wouldn't make the bath go basic IMO .
It would probably be an evolution of the teabag idea to have a lower sump pump section in a deep plating tank . A submersible pump under a grate with a filter sock - bag wall to wall across inside the tank and sitting atop the grate so that the pump draws electrolyte through the neutralizer and discharges the neutralized electrolyte back into the main plating section above . This would work in the same way as a power sand filter in a large aquarium , a sort of filtered sump pump arrangement could be a "one tank solution" .
The conventional aquarium power filter arrangement may also be directly applicable .

Figuring out a completely effective way of controlling the pH is exactly the task that has been in my mind .
The recirculation pump and percolation or fluidized bed
with filtering scheme would hold a steady pH . The
pH equilibrium value would depend upon which neutralizing lead salt was chosen to be used . I have no chart or information on what are the pH values associated
with a saturated solution of lead nitrate at various temperatures in contact with various neutralizing lead salts , like lead oxide , or lead oxide hydroxide , or lead carbonate or basic lead carbonate . This method would also reach a pH operating equilibrium value at a pretty concentrated solution value , perhaps an even saturated solution value for the temperature of the neutralized electrolyte ....
so temperature control of the plating tank would have to be used in combination with filters that would prevent any crystallized lead nitrate particles in suspension . The neutralizer sections output solution would need to be warmed further slightly above the temperature of the neutralizer and the plating tank warmer still . When handling
nearly saturated solutions , the temperature gradients across the lines and tanks has to be regulated to prevent
crystallizations from plugging up filters and lines and the pump itself , so the arrangement of things has to consider
the temperature gradients which are needed to prevent clogging .

In a very real sense , the cell itself can function as its own
pH meter once you know the baseline pH , if you have a laboratory power supply operating in constant voltage mode , an increasing current reading will indicate a dropping
pH . You see when the composition of the electrolyte is being maintained constant at a constant temperature and
the plating volatge is constant .....then the plating current
should hold at a steady reading as the plating proceeds .

Anyway , the activities of my internet alias are about to be curtailed by some pressing business which must occupy me
otherwise to keep the lights on and the family fed , so I am
going to have to set this aside for awhile and get back to it .
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biggrin.gif posted on 18-6-2007 at 18:31
PbB2O4 , possible quick and easy TiO2 dopant


This is definitely a titanium dopant that should be experimented with to see what results .

In another thread ,
http://www.sciencemadness.org/talk/viewthread.php?tid=8612&a...
12AX7 and I were discussing spinels which may be semiconductors like magnetite and lead borate came up .

PbB2O4 m.p. 490-510C

Red lead Pb3O4 has a tetragonal crystalline structure .
It may be that the lead borate likewise has that tetragonal structure which would qualify it physically as a candidate material for use as a dopant in the tetragonal TiO2 boundary
layer , and the lead and boron ions both also qualify it as
a candidate dopant . Further , the lead borate has a low
melting point so this would enhance its performance in baking and possibly dissolving into the TiO2 to form a desirable fusion reaction at a relatively low temperature .
Lead borate is also a glass former ...and it may be formed from soluble precursors which may be applied to a porous substrate .

The idea is that plain boric acid and lead nitrate or acetate
could be used as dopants applied in sequence to a titanium substrate , perhaps one having a very thin substoichiometric
TiO2 layer already prepared as in US2711496 . Or perhaps
a freshly etched sheet of titanium could simply be rubbed with a paste of boric acid and a lead salt and then fired .
There could be different ways of applying this mixture of
lead and boron values so that lead borate is the resulting
residue .

Vanadium pentoxide and lead oxide similarly are dopants for TiO2 and form a relatively low melting combination , which likewise could be formed in situ from soluble precursors .

The same applies to Chromium and Phosphorous , which could use a dichromate and phosphoric acid as commonly
available precursors .

All of these combinations of dopant ions and/or oxides for increasing the *anodic* conductivity of TiO2 are listed separately and individually in US3948751 , but *not* as specific paired combinations ruled in or out , and all have relatively low melting temperature to develop a possible melt phase solution reaction with the TiO2 which is the goal .

Of course then you may come over the top of these with the
Tin Oxides doped with Antimony or Fluoride if desired to
create the conductive and chemically resistant layer if the
preceding materials are not themselves adequate in chemical resistance .

Anyway , the ready availabilty of the precursors for the Boron - Lead combination , and the Chromium - Phosphorous combination , and their low heat developing temperatures ,
would seem to make these two combinations definitely worth looking at as TiO2 dopants . What their performance may be I have no idea because I can find no examples of these combinations having been tested . That obscurity makes these possible combinations even more interesting as complete unknowns :D

Another possible TiO2 dopant combination from easily available precursors , but not listed in the above patent , is manganese chromite , MnCr2O4 . In fact , Mn is not even listed as a dopant ion for TiO2 and it may not be , but IIRC it has been mentioned in some other patents . I am not sure about the crystalline habit of this spinel being tetragonal either . But it is conductive and it is chemically resistant ,
and some data on it is in US6054231 , which describes a fuel cell application . Anyway this is another combination possibly worth looking at with an experiment .

[Edited on 18-6-2007 by Rosco Bodine]
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[*] posted on 18-6-2007 at 20:10


Quote:
Originally posted by hashashan



and how would you recomend maintaining the PH? i dont have any PH sensors (got only the papers)
so for what i see the only method i can think of is hanging a tea bag with lead hydroxide in the tank. but wouldnt that make the solution basic?


Hello Hashashan,

If you can get Litharge, PbO, it is inclined to react less vigerously with the Nitric acid formed and therefor may not raise the pH too much.
Another way may be to make a slurry with the Lead Hydroxide and water and add small amounts every minute or so. This of course requires staying and 'baby sitting' the plating tank.

Dann2
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hashashan
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[*] posted on 19-6-2007 at 01:04


i believe that i can make some PbO by fusing Pb and NaNO3 (btw do you think that a simple gas burner will do the work?)

and just got another thought. why not to use lead as the temprorary substrate? or maybe even lead coated with the alpha layer of PbO2 (that wouldnt have to be so strictly controlled PH)
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[*] posted on 19-6-2007 at 06:51


the lead salts preparation thread is your friend

http://www.sciencemadness.org/talk/viewthread.php?tid=5490&a...

You should look at US3497382 , if an exceptionally high purity , easily made lead oxide is the goal .
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[*] posted on 20-6-2007 at 07:46


Quote:
Originally posted by Eclectic
You want a heteropoly acid called stannomolybdic acid. 12 moly-oxide units in a cage around a tin atom. If it's anything like silicotungstic acid, it should be extremely soluble in acidic ethyl ether. Try boiling a mix of 1-2 parts tin compound to 12 parts molybdenum compound by mole in 1N HCl for a few hours, cool, and extract 2-3 times with ether. Combine and evaporate ether layers (they may be DENSER than water, make sure you don't discard the wrong layer!)

Hello,

I refluxed 10 grams SnCl2 with about 70 grams Ammonium Moly in 1N HCl for about 6 hours.
There is a dark blue colour. When washed with Dietyl ether there is nothing visible dissolved in the ether. Should I evaporate the ether to dryness to see if there is anything there? ...or abandon:o

My patence with Ammonium Moly + Tin Cl2 is wearing thin.

Cheers,

Dann2
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