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watson.fawkes
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| Quote: | Originally posted by Swede
On a totally different note, has anyone heard of pulsing a plating bath to produce a superior plate? This would be extremely easy to do with a
half-wave rectifier on a variable AC transformer. |
The purpose behind a pulsed power supply is to remove the
polarization zone that develops at the surface of an electrode through which desirable ions move only by diffusion. To do this, a counter-pulse
typically goes in the opposite polarity, but not of the same amplitude. Simply taking the voltage to zero accomplishes some of this, but not as well
as a negative-going pulse. Pulsed plating is often faster, particularly when tuned to electrode geometry (including size), because electric-field
induced drift is faster than diffusion, and pulsed power sources repeatedly strip off the polarization layer. The forces on an ion at the time of its
adhesion to the surface differ between the diffusion and drift regimes, which is what leads to a difference in coating quality.
Such power supplies are usually switched-mode these days, with internal microcontrollers. To get negative-going pulses, the switch array is doubled
and hooked up in the opposite sense. Clearly both arrays are never on at the same time. There are ways of hacking this up with a pair of ordinary
supplies and some MOSFET's, for the slightly more adventurous.
The waveform is generally a form of pulse-width modulation, with more than two pulses. The parameters of each pulse are its voltage and its duration.
A typical pattern I see recurring in the literature is the Forward-Reverse-Zero, a six-parameter class of waveforms.
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dann2
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Hello,
There is some good simple pH info. here:
http://www.sensorex.com/support/education/support_education....
Taking some volumes of 100% Nitric acid and making a solution of it to a liter volume gives the following pH's.
ml's Nitric.......... pH
0.0025............. 1.23
0.005............... 0.92
0.01................. 0.62 (10ml Nitric acid per liter)
0.02................. 0.32
0.03................. 0.15
0.04................. 0.02 (40ml Nitric per liter)
0.05................. -0.08 (cannot be measured with pH probe?)
The Molarity of 100% Nitric acid is 23.8
Molecular weight of Nitric acid is 63
Density of 100% Acid is 1.5 Grams per Liter
The above readings cannot be taken as absolutely accurate in a solution that also contains Lead Nitrate and other stuff but give an idea of pH range
variation. (I think) as acid increases.
Dann2
[Edited on 30-12-2008 by dann2]
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Swede
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I need to catch up a bit with what's been posted, but I wanted to say, I have worked hard on my "paper", and one of the things that really jumps out
is control of the evolved nitric as a perhaps critical and deal-breaking aspect of plating... It's the same doc, but with the new additions in blue:
http://www.5bears.com/perc/pbo2.doc
Most of the additions are at the bottom, and this is what I came up with regard to nitric acid evolution:
Nitric Acid Concentrations too high: Patent 3,463,707 explicitly states “Nitric Acid concentrations higher than 20 grams per liter make it
physically impossible to plate lead dioxide continuously” and recommends keeping it at <= 5 g/l concentration. Considering that the process
creates its own HNO3, you may as well start small, 5 g/l. The next step becomes control of the acid as it builds. If a single mole of lead dioxide
plated on an anode produces THREE moles of HNO3, let’s make some assumptions… Your plating bath is 1 liter, contains 331.2 grams of lead nitrate
(1 M Pb++ ion), and you start with 5 grams of nitric acid. Your anode receives a plating of (for demo purposes) of 59.8 grams of PbO2, or 0.25 moles
of Pb. The Pb concentration has dropped from 1M to 0.75M. With the production of 0.25 moles of PbO2, you have produced three times that amount of
nitric acid, or 0.75 moles. With a weight of 63 grams per mole, the 0.75 moles of nitric acid weighs in at 47.25 grams. The total HNO3 concentration
has gone from 5 g/l to 52.25 g/l, which is well above the maximum recommended HNO3 concentration. The plating rapidly begins to devolve into a coarse
mass that will NOT adhere well, and will allow corrosive electrolytes relatively free access to the substrate. We know what happens next. The
substrate fails, the lead dioxide flakes, and yet another hopeful anode is trash.
It is easy to think (and hopeful) that the bath can be restored to its pristine state after the plating is complete. I think the demo above has shown
that the nitric acid levels will climb during plating, and do so rapidly enough so that the plate job will be ruined. The HNO3 concentration MUST be
controlled as it is evolved. How this can be done is a subject of much debate.
Essentially, we must give something for the HNO3 to chew on that both neutralizes the acid, and replenishes the Pb ion concentration to keep it in a
healthy range. Classic solutions include litharge (PbO) exposed in the bath, or some other lead salt like lead carbonate. Lead carbonate (more
correctly: 2PbCO3•Pb(OH)2) is an insoluble lead salt that may be ideal. It can be made easily by adding an excess of sodium carbonate or
bicarbonate to a solution of lead nitrate. When the brilliant white precipitate ceases to form, allow the lead carbonate to settle, decant the bulk
of the liquor, and collect (preferably by vacuum filtration) the white lead carbonate powder.
Almost all of the patents describe their plating baths as having strong agitation. If an excess of PbO or PbCO3 is present, as the nitric evolves, it
should, in theory, by acidifying the bath more strongly, allow these lead salts to dissolve, and serve a double service… nitric acid concentration
remains reasonable, and Pb ions are replenished. My guess for a good starting weight might be that which would replace the lead on a molecular basis.
One final answer may be in simple suspended lead sheets, or pure lead shot in the bottom of the plating bath. Nitric acid, of course, dissolves Pb
into Pb(NO3)2, and since the bulk of the bath starts with lead nitrate, to me this seems the ideal solution. The lead metal will simply sit there,
inert, until the nitric acid concentrations climb high enough, at which point the Pb will begin to dissolve. The question remains, at what nitric
acid concentration will this occur? I don’t know, but it is worth a try.
Note: NONE of the patents used what I now call a “one pot” plating process. They all use circulation. Used electrolyte is pumped from the bath,
altered with litharge or some other lead salt, and reintroduced to the active plating bath.
In summary, control of the Nitric Acid may be a critical feature of plating a strong, durable anode.
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Swede
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I am going to try a simple experiment... I have a bit of lead carbonate, and also lead sheet. I am going to prepare a 20 g/l solution of nitric acid
(assuming your plating bath is producing nitric, and you are at the maximum level for a good plate) amd then introduce Pb metal (weighed first) or
lead carbonate, also weighed, to see if there is significant dissolving and lowering of the nitric concentration.
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dann2
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From my experience of making Lead Nitrate from Lead Metal and 60% Nitric acid you will not have a hope of keeping the Nitric acid close to where you
want it. With 60% you need to heat way up. Careful of brown gas (Nitrogen Dioxide). It will goose you if you get a dose of it!!!!!!!!!!!!!
You could try connecting an AC to the Lead Metal as Rosco suggested. Will it give brown gas? Be careful with that stuff.
If you start with a molecular weight Lead Compound that when dissolved will replenish all the Lead Ion you intend to plate and that compound reacts
very easily with Nitric (Basic Lead Carbonate say) then the tank will stay more or less neutral all the time. ie. No or very little Nitric acid in
solution. That may be OK though.
Dann2
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Rosco Bodine
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@Swede
Unless you depolarize the lead metal with a current, it probably won't react until the acidity is a lot higher than what you would want to maintain.
http://www.youtube.com/watch?v=fNx6HH8qt_I&feature=relat...
[Edited on 30-12-2008 by Rosco Bodine]
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Swede
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OK, lead metal is out, lead salts are in. One patent explicitly states that litharge is the prime carrier of evil Fe which ruins a plate job.
Perhaps part of the process of preparing the crude litharge does not adequately remove iron, unless you are willing to shell out $$ for the ultrapure
variety. Sulfosalicylic acid apparently can be used to chelate or trap free iron in a bath.
Dann2, you are right, I'm burned out reading this stuff. I think the big nuggets of info for a 1-pot plating process is elimination of iron (easy)
and control of nitric (more difficult). With those two gone, with good surface prep, and control of the current, I think the acid process will work,
and you'll end up with a sturdy plate job.
I think everyone, me included, is ready to see if what I've gathered together can make an anode that works. I've been stalling a bit. The problem
is, I DO need adequate time away from work, chores, etc, one good day to get it going, but unfortunately I've got 4 days solid of real work that I've
got to get through, so the first plating will probably be in 5 or 6 days.
I've got some CP Ti tubing coming, an ideal substrate (shape-wise) if the MMO mesh causes problems. Rosco, I also got two more kilos of freebie
AlOOH, 23N4-80 Boehmite, and 25F4, each with different characteristics. Once the PbO2 thing is successful, or I surrender, I'll mess with it a bit.
I need to thank the salesman who sent the samples - he is a good guy, and understands I'm just an experimenter, not a giant corporation.
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Rosco Bodine
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That Boehmite has been mentioned in patent literature as a useful component in the coatings of anodes useful for *perchlorate* production specifically
when doped with PbO2. And it is also useful for reenforcing sintered ceramic
compositions which are formed under pressure at high temperature, and it is useful as a rigidizer for kaowool and as a reenforcing material for
refractories that are wetmixed
and then fired. So you have some useful material there good for a lot of different things.
The Boehmite could probably be converted to a conductive lattice support and carrier structure using cobalt nitrate
which should convert the surfaces of the fibers to conductive cobalt aluminate spinel which is itself a catalytically active anode material, forming a
porous rigid
cagelike lattice which could retain particles of yet more
cobalt aluminate formed from a mix with some ordinary non-fibrous colloidal alumina which should fill the open spaces in the lattice structure ,
resulting in something
of a cobalt aluminate spinel coating analogous to a "fiberglass reenforced sintered glass" if you can follow what I mean, where the structural
component supports
the non-structural form of the same material used as a filler.
The cobalt aluminate lattice could also be useful for
filling with other nano-particles of catalytically active anode materials, like magnetite or bismuth doped manganese oxide, or bismuth doped tin
oxide, palladium black, ect.
The filled or unfilled lattice of cobalt aluminate would probably also make a good substrate for electrodeposition
of other oxides. There's a whole bag of tricks you could
try using that stuff in various ways. It is also a wetting agent, a dispersant, and a thickener that is temperature and pH sensitive. You should
have fun finding ways to use it.
If I recall correctly there were a couple of patents which had identified that the absence of iron impurity from the
Pb nitrate could eliminate the necessity of using a surfactant in the plating of good deposits of PbO2.
And in the lead salts preparation thread, I recall posting
a patent which described routes to ultra pure oxides
which could be indentified by color, middle of page three
in that thread. There is also a possibility of using a mixed nitrate and acetate plating bath where the pH is somewhat regulated by the acetate
functioning as a buffer
for the nitrate, the byproduct acid then being acetic acid
which is volatile and escapes from a hot plating bath, or at any rate results in a less rapid rate for lowering of pH than if the usual nitric acid
byproduct was accumulating
by itself, having nowhere to go for neutralization.
Ammonium carbonate or bicarbonate is something useful you should have on hand for neutralization of stannic salts
if you are going to do work with the sols which can be derived from those. Methylcellulose, PVA, and possibly hydroxyethylcellulose are other
materials of possible interest, and oxalic acid for etching, perhaps ammonium fluoride, and nickel nitrate as well are a few things that
would be good to have if you are shopping and run across any of these at the technology supermarket or art store.
[Edited on 31-12-2008 by Rosco Bodine]
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Swede
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RB, a while back, you posted this in the Lead Salts thread:
"Use of sodium carbonate for neutralizing solutions of soluble Pb++ salts precipitates the *basic* carbonate
Pb3(OH)2(CO3)2 which is the old lead paint pigment called "white lead" .
Use of sodium bicarbonate is required if you want to
precipitate the *normal* carbonate of lead PbCO3 ."
I used sodium bicarb to ppt lead carbonate froma lead nitrate solution, and thought I had prepared BASIC lead carbonate, Pb3(OH)2(CO3). Not true? Do
I have plain Pb(CO3)? Can you elaborate on the mechanism and the difference? I'd have thought either sodium salt would produce the basic lead
carbonate.
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Rosco Bodine
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I think I'm correct about that, but I'll have to go back and find the references on the specifics. It probably has to do with the increased basicity
of the carbonate and the near instant reaction producing a nearly insoluble product which drops out immediately, otherwise you would think
for a slower reaction, you could simply adjust the equivalents to get whichever product you wanted, and then that product would form "later" and
gradually precipitate. So it probably relates to a local reaction
condition for things where solubility and pH at the point and instant of reaction is governing, and can't really be steered to a different outcome by
bulk stoichiometry
which may contradict and offer a different expectation as the result. There are other reactions like this where the
expected result from stoichiometry is over ruled by the
physical chemistry which is governing. This is probably another "one of those" exceptions.
http://www.youtube.com/watch?v=gmfY_ezb9j8&feature=relat...
I went back and looked at some references and still haven't fully sorted this one out. It looks in part this might be order of addition related, for
example if the soluble lead salt is added to a solution of sodium bicarbonate in excess then the normal carbonate of lead is produced, and otherwise a
mixture of normal and basic carbonate across a range to predominately the basic carbonate of lead by usual addition schemes. This is uncertain, and it
seems sodium plumbate is another possibility there. I'll try to find more on this. I am not sure either if the more usual order of addition produces
only the basic carbonate or a mixture. I think my statement
about this is conditionally true, a "to be sure" sort of specification for sodium carbonate being preferable.
What I said definitively about this earlier is probably true in a more qualified sense that using sodium bicarbonate as the neutralizer in addition to
a soluble lead salt is more likely to give a mixed product impure with the normal carbonate, dependent upon the concentration and excess of sodium
bicarbonate which is present. I think there is actually some
mixture of the basic and normal carbonates that is variable
dependant on the conditions of synthesis, which is the reality, even for the commercial products. My earlier definitive statement was probably an
exaggeration weighted towards what would be desirable for producing the product where the basic lead carbonate would be the more favored product
predominating in the mixed product which will be unavoidable in any case. I haven't actually done this precipitation both ways and then compared the
product weights against the "lead values" known to be present to
see what the variation is there.
[Edited on 2-1-2009 by Rosco Bodine]
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Swede
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Well, I'm on day 3 of 4 days of "recurrent training", 4 days of stress and long hours. I could use an illegal substance right now to try and drop my
cortisol + adrenaline level in my blood down to less than 1M but that's just not cool for commercial aviation.
The CP aluminum tube arrived and is looking good. Those following APC are aware I'm trying to use some surplus (but new) PTFE/PFA heat shrink tubing
to protect the Cu-encased cartridge heater. I've noticed even with pure water, when the Cu heats up, corrosion of the Cu skyrockets, and I'm guessing
the lifetime of heated, bare Cu in a bath will be short.
I bit the bullet and bought a PTFE-encased true immersion heater:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=37011...
I wish it was a 240V device, so it'd be 250 watts rather than 1,000. The full kilowatt will be ideal for anything more than 6 liters, but the heater
itself is physically too large to be used outside my full tank. Short of a huge resistor, any thoughts on reducing the output a bit?
My thread on sulfosalycilic acid (chelation of Fe++) went nowhere. Any thoughts on scavenging or removal of iron from a bath?
Finally, @Dann2, I found that patent that discusses nitrites, and the use of 30% peroxide to treat. Excellent patent and an elegant and simple
solution. A big veterinary syringe of 25ml capacity, or a buret positioned over the bath, would be a simple means to add the peroxide.
My initial bath will consist of lead nitate, probably 300 g/l, a dash of nitric, no more than 5ml of 68% acid per liter, and I am going to try both
nickel nitrate (10 g/l) and surfactant. The bath will be small. The initial pH should be measureable and not much worse than 1.5 to 2.0.
Anode prep will consist of degreasing with acetone, a dip in dilute nitric, followed by a vacuuming immersed in hot distilled water plus a dash of
surfactant. From there, the hot anode will IMMEDIATELY enter the plating bath with no chance to cool. Tapered current profile.
pH control will be attempted with manual additions of basic lead carbonate. If that doesn't work, then litharge. Occasional peroxide additions
cannot hurt and may help.
Several additional platings on small anodes (all MMO) will follow, with varying parameters. These then will be tested using a gang of mason-jar
perchlorate cells, run under identical conditions, to observe the performance of the anodes.
I've talked the talk, ready to walk the walk. 
Oh yes, they'll be THICK. A really beefy anode may require more than 1 liter, perhaps 2, although the generation of nitric acid and the addition of
lead salts should keep the Pb ion concentration high.
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dann2
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Hello Swede,
You might wish to see if your Lead Carbonate wets easily. It can have a very annoying tendency to float on top of the solution (even when there is
quite alot of Nitric in it) and refuse to wet. If this is a problem you could make a slurry of the stuff by putting the Carbonate into a well capped
container with a small amount of water and shaking hard.
Dann2
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Rosco Bodine
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You could use a diode in series with the heating element
to half wave rectify and drop the power 50%.
US3463707 describes how to precipitate the iron by shifting the pH and boiling the electrolyte.
I'm thinking use a circulated, pumped electrolyte with a couple of digital crock pots used as heated reservoirs in a series arrangement with cascading
overflows. Using maybe two and half gallons of electrolyte would tend to put the kibosh on any rapidly changing cell chemistry
during plating of one anode, and it would probably stay within parameters without adjustment, except between plating runs when you would replenish the
lead. Having a good working volume allows for low turbulence in the reservoirs where continuous neutralization or incremental neutralization may be
done
where the weight of the particles of litharge used for neutralization will prevent their being carried away in the current and clogging filters for
the recirculating electrolyte.
I still believe there is good use can be made of MMO coating of the Ti substrate, for an interface coating, and experimenting with a Pytlewski polymer
as a wetting and bonding agent for the first layer of electrodeposited PbO2,
even though this has not been described so far as I know in the literature, it may work very well as simple dip and dry preplating "activator" for
adhesion of the PbO2 via
a chemical bonding, stronger than the adhesion of a physical attachment to a "roughened surface" strategy.
Another possibility which has been mentioned with regards to MMO, but so far as I know has never been
the source of any experimenting here, is sort of the opposite of hydriding Ti as a pre-treatment for a baked
spinel coating. This would involve treating a freshly etched Ti substrate with a very brief anodization, limited to a current drop at maybe 5 volts,
for example two to three minutes, in a basic electrolyte like 50% KOH and then doping cobalt nitrate and baking, or perhaps better anodizing for a
couple of minutes in a basic electrolyte of an ammine complexed cobalt or nickel or binary mixture, followed by a single dip in the slightly
acidified nitrate(s) and baking....the idea being to create a somewhat thicker but well doped and conductive interface layer, which may be tougher
than the usual method. IIRC in some of the Beer patents there was described something similar as a strategy for increasing the thickness of the
interface layer
which consisted of doped Ti suboxide. It may be possible
to increase the thickness and integrity of that conductive interface without substantial loss in conductivity, but gaining considerable hardening of
that interface as an
ionic oxygen barrier, better sealing the substrate against
passivation. Even at the loss of a tenth or two tenths volt
(or more) for a loss in conductivity, that price might be worth paying for having a more robust interface on a substrate which would last longer in
use.
Similarly even following the established methods, Bi doped SnO2, or tertiary mixture Co and Bi doped Sno2 or Mn and Bi doped SnO2, or quaternary Co,
Mn, Bi doped SnO2 could be useful baked MMO coatings, by themselves as a baked working anode coating or as a substrate over which
is electrodeposited PbO2.
[Edited on 3-1-2009 by Rosco Bodine]
Attachment: Lead related Gmelin Vol V.pdf (1.2MB)
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Swede
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Any surface prep and subsequent coating of a bare Ti substrate that is conductive, acts as an oxygen barrier, and accepts a PbO2 electroplating, would
be a boon. Electronic losses in that layer for an amateur would not be troublesome. Industry might throw a fit because their perc now costs an
additional 2 cents per kilogram due to increased electrical costs, but for us, who cares.
As I mentioned, I got my 0.020" wall CP Ti tube, and it is prime stuff, ideal for anode research. Unless forced to, I don't think I am going to
return to flat straps for electrodes. They are just too hard to use in a real cell. The round shank is perfect for sealing (o-ring) and the working
end can be slotted and flattened to accept flat sheet, or the tube may be used as-is for anodes.
I'm looking forward to proceeding. Mentally I'm still waffling on initial bath size, and am now leaning towards the jumbo bath because of the
stability it will create. There's only one addition that can cause real probs, and that is the surfactant, which will break down. Skip the
surfactant for now. Small anode initially, and we'd be looking at 4% lead loss and not too much nitric evolution. The bath will be easy to maintain.
A 1 liter bath will be all over the place with regards to pH and lead ion concentration.
Wish me luck, it's check-ride time. <bells ringing, horns blaring, red lights all over the place> "Fire, left engine, fire, left engine. Apu
fire. Apu Fire. Loss of system A and standby hydraulics. Yaaaah! We're going down! Mayday! Mayday!"
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not_important
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Using NaHCO3 to get PbCO3 is correct, adding the lead solution to an excess of the bicarbonate; Na2CO3 gives basic carbonates. This holds true for a
number of other metals, for some such as Co and Ni not only do you use bicarbonate but you saturate the solution of it with CO2 and then add the metal
solution. See Mellor for example.
Tweaking the pH and heating is a traditional way of removing iron and manganese. In older books on purification of chemicals you'd often see the use
of an excess of a carbonate being treated with an acid, meaning all the acid was consumed, then heating to boiling for awhile, possible with the
addition of H2O2, cooling, and decanting/filtering from the solids - a mix of the particular metal's carbonates/basic salts and Fe(III) and Mn(III)
/Mn(IV) hydrated oxides and such. If making the nitrate an excess of acid would be used, the solution brought to boiling for a few minutes, then
enough of the metal carbonate added to fully combine with the remaining nitric acid and be present in excess to give alkaline conditions. The excess
carbonate gives a large surface area for absorbing trace amounts of Fe and Mn, freshly precipitate carbonate (or basic carbonate) is preferred as it
tends to be more reactive. Lead presents a problem with the solubility of many of its insoluble salts in solution of the nitrate; sometimes quickly
filter the nitrate solution through a bed of the carbonate will work.
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dann2
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Hello,
The figure for Nitric acid formation was given here as 3 moles per mole Lead Dioxide deposited. It is two moles Nitric per Mole LD deposited.
It takes two moles Electrons per mole LD deposited at 100% CE. Don't know about Nitric acid formation when CE is not 100% (Nitrites interfering,
Oxygen coming off (damm all I guess) anode etc).
Overall reaction:
Pb(NO3)2 + 2H2O =====>> PbO2 + 2HNO3 + H2(gas)
Or broken down: (cut and paste from Journal)
H2O --> OHads + H+ + e-
[ii] Pb2+ + OHads --> Pb(OH)2+
[iii] Pb(OH)2+ + H2O --> PbO2 + 3H+ + e-
Yet another patent is attached. There is nothing in it you have not seen before but it gives some figures for adding Litharge per hour per amp for
keeping the plating tank happy.
35 grams Lead Monoxide per hour per 10 amps was added to the tank.
They used a six liter tank which gives an idea of tank size/deposition rate between each addition of Litharge. It is next to impossible to get a
figure for surface area they were plating.
Big tank = big soft landing strip
Dann2
[Edited on 5-1-2009 by dann2]
Attachment: US4130467.pdf (319kB)
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Swede
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That is an interesting patent. Once you get past the amazingly complex rotary drum, they begin to discuss the chemistry of the bath. The bath
constituents, per liter:
lead nitrate - 200
Nickel nitrate - 10
Cu nitrate - 10
igepal (surfactant) - 1.33
Concentrated nitric acid - 6 ml
NaF - 0.5
All of this is right in line with other patents. Interestingly, this is the ONLY patent I've seen that discusses nitric acid addition as volume vs
grams. Assumming a typical 68% azeotrope, the 6ml would translate to 4.08 grams nitric, right in line with other patents. 5.8 grams per liter of
litharge was used every hour to neutralize the acid evolved and add Pb ions.
More disturbing: "The entire bath was changed out every 8 hours." At first glance, it does not discuss treatment of the bath, but a bath at 8 hours
of use is FULL of useful lead nitrate, probably excess nitric, and if a surfactant was used, perhaps "used" surfactant.
A method of post-plating bath treatment needs to be considered part of the entire process; otherwise, the methodology will be too wasteful.
Right now there's freezing rain outside, and my lab is uninhabitable. I'm hopeful that the weather will break very soon.
My checkride went well. We lost an engine between DFW and Memphis, and landed single engine uneventfully with 200 overcast, 1/2 mile visibility...
all in an advanced "level D" simulator!
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Rosco Bodine
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Acetic acid would seem to be the first thing to look at if anything organic is going into that electrolyte to aid wetting. There is also the
possibility of using ethanol
which will itself be oxidized in the process eventually
to acetic acid, but may aid wetting during the electrodeposition. Both the ethanol and the acetic acid
have solvent properties and should decrease the surface tension of the electrolyte so that it more easily wets the substrate onto which plating is
done. It might save a lot of grief in reprocessing the electrolyte to get rid of organic residues later, to try a volatile like acetic acid first and
leave the other organic "surfactants" as a last resort.
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tentacles
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That's a damn good idea, Rosco - I wonder if the acetic acid would have any stress benefits as well, as the lead acetate baths plate alpha PbO2. Even
if not, the volatile nature would lend itself well to being removed from the bath.. just wait and it'll evaporate.
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dann2
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It's used here (Sodium/Lead Acetate) to relieve stress and as a pH buffer:
Electrochimica Acta. 1971. Vol. 16, pp. 1301 to 1310.
Dann2
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Swede
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I agree with Tentacles, a wetting agent that could be easily separated by a simple heating and evaporation would be a boon. My guess would be it
would be better than NO surfactant, but not as good as the polyoxyethylenes... otherwise, I'm sure the big boys would be using the simpler wetting
agents.
But if it is a choice between fatally poisoning a large, expensive bath with a polyoxyethylene, vs acetic acid/ethanol, vs nothing, then the middle
choice is definitely the best.
I mentioned to Tentacles yesterday that our favorite lead nitrate source almost doubled in price. There is an alternate source at $130/10kg, still
decent. Finally, for smaller-scale experiments, there is a guy on eBay selling for $10/500g. I know a lot of guys dislike eBay, but I cannot imagine
the DEA/FBI/BATFE/CIA/OSS/Project Bluebook having a beef with lead salts in general... about as far from a drug precursor, at least, as you can get.
The WX still has not broken, and now I have to get to work for real.
Daydreaming the other day about all the efforts at "composite" lead dioxide anode, almost all of which have failed. My Ti tube made me think of a
thin copper tube, rammed with a lead dioxide slurry, HARD, in a hydraulic press, said slurry consisting mainly of CPVC resins in a very low ratio of
resin to PbO2.
You now immerse the Cu rod 7/8 of the way into strong ferric chloride. The Cu tube is eaten away except for a small cap at the top where you can
attach your lead wire. That might form the basis of a strong composite lead dioxide anode. The trick will be in the formulation of the CPVC resin /
PbO2, the pressures involved, and ultimately the strength of your rod when completed. From there, plate it, or perhaps you may get some modest
efficiency as is, despite the fact that the PbO2 is of the wrong form.
The only reason I mention it is because of a very simple experiment I did a while back. I made a similar slurry using chemically-resistant IPC CPVC
cement and lead dioxide, spread it like butter onto wooden sticks, and after curing, was pleasantly surprised at both the strength of the coating, and
the low resistance, which was about an ohm across 6 inches. Just a fun thought.
Edited to add: Those of us with lathes could hydraulically press the slurry into drawn, hard Cu pipe, 1/2" or 3/4". Those would normally be too
thick for ferric chloride, but the bulk (say 85 to 90%) could be turned off first, and the remainder of the Cu gently etched away with the ferric
chloride.
[Edited on 7-1-2009 by Swede]
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Swede
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Well, I was hoping to plate today... and I ran out of time. It's Saturday, I have a spouse, and that = chores. I wanted to show you guys where I was
at.
To execute the plating in a manner consistent with the tons of research I've pursued (weeks worth) requires, unfortunately, a lot of gadgets. I keep
finding myself making more and more stuff.
First, the plating rig overall:
I incorporated xenoid's ingenious vibrator motor, and discovered something quite interesting. Even without the anode immersed in the solution, there
is a powerful agitation factor as the vibrations travel through the rig, the stand, and into the solution. In this case, I am using a 2 liter plastic
tank. Check out the surface of the plain water!
The first runs are going to be 2 liters IF the plastic can withstand 70 degrees. Note that I have a "catch-pan" in case of catastrophic failure.
There are two things I ignored that I need to accomplish before I can plate. The first is cathode(s). I need more than one, because I will be
plating anodes of different sizes. With my acquisition of Ti tube, anybody see any problems using Ti as a cathode? The round tube is perfectly
shaped for a rotating setup. I have tubing in 3/4", 1/2", and 5/16", and am considering "squashing" the working end in a press to create an ovoid
shape, again to create an even flux with the rotating anode. Next, with cathodes made, I need a way to firmly attach them to the system. Spacing
will be by the simple expedient of moving the tank closer or farther as needed.
So the big question du jour - Ti as cathode? Yea or nay? I'm leaning towards yes with the addition of a bit of copper nitrate to the bath.
I hope to plate Tuesday or Wednesday, weather permitting. I apologize for the delays! Wish me luck!
[Edited on 10-1-2009 by Swede]
[Edited on 10-1-2009 by Swede]
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dann2
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Hello,
There is an old patent kicking around using Lead Dioxide powder + glue of some sort. It was of course a superior to all other anodes anode, better
than anything............
It may be worth a bash. I have never tried it.
I cannot see anything wrong with using Ti. You will need the Cu ion as you said to stop Lead going on Cathode.
Careful of the spray that will come off from the solution around the cathode(s) where Hydrogen will be coming to the surface. Put a cover on that can
of Coke if you intend to drink it!!!!!!!!!!!!!!!!!!!!!!!!! or better to put some sort of cover on the tank. When making Chlorate (it goes on for much
much longer with far more H2 evolution I admit) the contents of the garage/shed get coated with Chlorate after some days. Bad enough Chlorate, it
rusts things, you don't want Lead Nitrate.
I don't think that the shape of the Cathode(s) is of major importance. A flat one(s) will probably do OK if you are having problems getting a curved
one(s).
Have you figured out the actual surface area of the MMO'ed Ti to be plated. The surface area will probably increase a bit as plating builds up, or
will it?
Since you are going with Nitrate bath all the way (no Tartrate bath for Alpha) do you intend to plate at a high current density at the start of the
plating process to get an Alpha coating next to the MMO? Just wondering.
Evaporation can be a problem sometimes. Keep top of anode below surface a cm or so and keep an eye on liquid level.
Good luck with the plating...................and DO hurry up.
Dann2
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Swede
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Yeah, the potential for spray exists, and that is not a happy thought. I'll rig some sort of cover for it. I'm also going to take a big plastic
garbage bag, cut it into a single piece, and create a backsplash area. I need to contain spray or migrating droplets by whatever means possible.
The reason I'd like to go Ti vs Cu is that the Cu seems to be corroding badly (these are just water tests) and of course Ti tends to be immune to
corrosion. Just a thought. Today is cathode and vacuum jar day. Tomorrow is plating day. I am going to follow a schedule that looks something like
this:
Plating Period Current A / cm2 Duration
Initial: 0.125 15%
Median: 0.050 50%
Final: 0.030 35%
The total duration is something I'll just have to figure out based upon the rate of PbO2 deposition, but at a minimum, I am going to run the higher
current until I see 100% coverage of PbO2, then a bit more; then, I'll begin to dial the current down a bit, perhaps in more increments than those
shown here. There's no hard and fast rule that says there must be three plating currents. The bulk of the patents do the majority of their plating
at 0.050 A / cm2, so that's where the bulk of mine will be, I guess.
If it works on MMO, the next step will be to sand blast and prep bare Ti and see if that is possible. The round Ti rods will be an ideal shape.
I've still got composite lead dioxide ideas I'd like to try. The IPC PVC cement I used to build the PVC cells withstood both chlorate and perchlorate
electrolytes at near boiling (remember the "banana cathodes"?), so that glue, plus perhaps powdered PVC, combined with PbO2 powder in a ratio (I am
guessing)
85% lead dioxide
10% cement
5% PVC powder
MEK to thin
Might form the basis of a composite anode. The correct beta PbO2 can be created and gathered from a lead nitrate cell, and in fact one of the patents
discusses this, with the goal being POOR adhesion of the plate - the anode is removed, agitated, and the beta PbO2 simply falls off to be washed and
processed. This may be a way to get good PbO2 for yet another process!
Paranoia time - Goggles, gloves, face shield obviously. What about clothing? I am tempted to buy some painter's Tyvek disposable coveralls to wear.
Silly idea? I'd rather not use street clothing and track lead nitrate into the house.
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watson.fawkes
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workplace lead mitigation
Brass foundry and machining operations have to deal with environmental lead in their workplace. Lead is a common alloying agent in yellow brasses.
Unfortunately, I don't have a reference for the lead safety techniques I read about years ago, but it is a place to go look for accepted industry
practices.
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