Thoughts On Anodes

No comments on my .DOC? It's simply a meshing of multiple patents re: PbO2 deposition, averaging values where needed, and trying to scale what is really a too-large industrial process, down to a home lab size. Larger plating systems have better chemical stability than smaller ones, and will probably do a better job, but just what size that might be is unknown.

Hopefully as plating starts and results come in, I'll be able to add to the document with some definitive observations.

The initial test setup will use some pretty small test anodes, and with the cathode at 2X to 3X the current density of the anode, I needed to make a pretty small Cu cathode that will also contain a 100 watt cartridge heater. The best form to present to a rotating anode is a hemispherical one, so I took the cut sheet, bent it, and soldered it (lead electrical solder) to the Cu tube that contains the cartridge heater.





For cathode "area" I am counting only the area of the Cu sheet facing the anode. In this case, it is about 30 square cm. The test anodes have an area of about 60 squared cm.

At the top is the connection for the system, and the leads for the 100 watt cartridge heater. This rig should be able to heat up a liter to 70 degrees with ease.



If the weather cooperates, I am going to mix up about a liter of plating solution and at a minimum set things up before I have to go back to work.

One thing I read that was interesting was a "thermal shock" effect... you want the anode to be at the correct temp prior to turning on the power, yet you don't want it immersed in the plating solution to heat up, so probably the best answer is a beaker of DI water at 80 degrees or so to pre-warm the anode after initial prop, but prior to plating.

[Edited on 25-12-2008 by Swede]

I've got PbO aplenty, no lead carbonate. I like all the ideas behind a slow/steady "diffusion", or periodic additions of reagents. I will attempt to produce lead carbonate from lead nitrate, since I have plenty of the latter, but none of the former.

That is a good thought, to do a bit of chemistry (experimentation) with nitric acid and various lead salts prior to plating, to get a feel for what is likely to happen. I would KILL for the lab I worked in in the AF... we had every analytical instrument known at the time. Now it's back to basics... literally, as 25 years away from chemistry has caused me to dump most of what I learned. My kids come for help with HS chem, and it takes me a while before I can help. The knowledge is there, it's just buried, VERY deeply.

The patents are explicit - lead dioxide plates exceptionally well at low acid concentrations, and the plating suffers as the concentration climbs. Perhaps something as crude as low-range pH paper and an appropriate additive to keep pH in check. I do have a pH meter but am leery of using the one good probe I have in this bath. There will probably be gross interference anyhow to the pH meter from the plating current, requiring sampling of the bath into a separate vessel.

Anyway, the initial experiments are going to be small. If a particular bath and methodology appears to work very well, then anodes sized approx. 12cm x 4cm will be plated, as these are the correct size for my actual perc cell.

Roscoe, I am now the proud possessor of 1 ea kilogram of ultrapure gamma ALOOH, water-dispersible Boehmite alumina. Research/experiments to follow!

Hmmm...samples are always good.....but I think the gamma there would be Al2O3 ...unless they sent you some of the
unfired air dried precursor material which is the hydroxy form there. There is likely something useful to be gained with whisker alumina as a "modifier oxide" reenforcing in these coatings I think especially the baked coatings and possibly even in the plated coatings. It sort of reminds me of the
fiber reenforcing that wall plasterers and stuccoers used, horsehair in the olden days and later chopped fiberglass,
it's the same idea for the nano-whiskers of alumina.

If you are running a near neutral plating bath, to keep the pH constant will probably require a pumped electrolyte .....
with some kind of a power filter containing a neutralizing lead compound, like perhaps a finely divided lead oxide.
I think ideally to accomplish a steady state plating bath,
you would need a small secondary isolated AC electrolysis cell having two Pb plates , in the electrolyte recirculation loop
for the anode plating cell, and whatever lead was consumed
by the anode plating would be replenished by AC erosion
of the "Pb ion replenishment anodes" .....now that would be perfection huh ? But a compromise arrangement could
probably be gotten that would work good enough just using
a manual incremental neutralization and a generous sized
plating bath to dampen any wide swings in the cell chemistry
between the increments. If you know what rate of reaction
your plating current is producing , then you can calculate
the rate at which you need to add neutralizing material to
maintain the chemistry of the plating bath.

Hmmm....new years is not far away , and Valentine's Day
a bit around the corner still ...sooo , just being forward looking there at the possibilities , it is definitely time for a diva break Whew this song is beautiful, a real wedding song if there ever was one. Enjoy.

http://www.youtube.com/watch?v=Dcy2zOsmK48&NR=1 (lyrics)

http://www.youtube.com/watch?v=LbtJR6sy3KE&fmt=18 (stereo and video) Wow !

Now I wouldn't mind some samples of that, even a lifetime supply, and I'm sure that's a popular sentiment among any men who still have a pulse

Perhaps the scheme like below would do for keeping Lead Ion replenished + neurtalize. It's getting close to two tanks as it were. You already have a pump. The neutral solution will flow into plating bath proper as you pump liquid from plating bath into neutralizer.

There is plating equations on an article I attached (next post). It also states that anodes (ozone production) last longer if manufactured from a plating tank that is warm. Lots of patents state that a 'better' plating is obtained from a warmed bath. I would agree that 70C is about right.
You will soon start to suffer from 'Article/patent fatigue', so watch out.
For every mole of Lead you get three moles of Nitric acid.
If plating efficiency goes low (say Nitrites build up) this may no longer apply. I don't know.
I do not think putting a pH meter into a plating tank liquid sample will harm it. But can you really monitor acid concentration by measuring pH?
People have always said that a new fresh plating tank always give the best coat (garage operators). All sorts of things were blamed. Nitrites perhaps? One guy suggested bubbling air (O2) into tank between plating sessions. (You can use H202 of course).

Nope, for now just this stuff. They are also sending some material from Germany that is going to take some time to get here, but it is more of the same, just different crystal and pore sizes, and perhaps acid-dispersing as opposed to water dispersing.

@Dann2, where do you come up with all this stuff? I remember Tentacles had troubles with his plating bath when it became a "used" plating bath. The implication is strong... if a one-pot anode is attempted, you just might get one or two good anodes before the bath goes to hell, and the size of the bath determines how long it takes.

Lead Nitrate is selling for $10 kg, which will make about 3 liters of solution. That is a big bath for a garage lab, and should produce several good anodes before becoming exhausted.

The initial thought is "Add lead nitrate on a molecular equivalence to the weight of the plated lead dioxide" but that doesn't help when the nitric acid levels are climbing.

Traditional replenishment lead sources have been litharge (PbO) and Pb metal. Lead carbonate may be a superior replenishment material. Determine the amount of lead nitrate lost, add that amount to a beaker, convert to the insoluble carbonate with Na carbonate or even bicarbonate, decant the bulk, which will be sodium nitrate dissolved in water, and add the lead carbonate to the bath, which will be in the form of white lead:

2PbCO3·Pb(OH)2

I might be able to come up with an equation, but my gut feel is that excess nitric is neutralized, CO2 is gassed off, water forms, and lead nitrate levels are restored.

Just a thought.

There are two paths we can go down... the first is to use up a bath until it no longer plates worth a damn, the second is careful maintenance of the bath no matter how large. Some sort of circulation setup is tempting, but I think the best results would come from a medium to large bath plating modest electrodes. At the end of the plating session, the anode is weighed, and an appropriate amount of lead (in whatever form) is returned to the bath. If the bath is large to start with, changes to the chemistry of the bath DURING plating will be small, and hopefully be optimum thoughout the given plating session. The small changes that take place during plating are then "repaired" with lead carbonate or litharge after the session.

Never tried it on plating, but I have tried it on electrolytic
reductions, and it works supposedly better for some reactions than smooth DC. It will make an audible power hum in the cell at high currents...so you won't need any vibrator at high currents..the cell itself becomes one
Of course that is sort of the extreme in terms of current density

Yeah it is a special technique which can be used but I'm not sure how to predict the effect, it is purely experimental.
You can use phase control to shape the delivered waveform
to an assymetrical AC with whatever pulse sequence you
want to send the cell......sort of like sending it Morse code
in power pulses , hoping it will get the "telegram" of what you want it to do. If it is not cooperating ....hey just increase
the power until something breaks

The power company really loves you for what sort of untypical and unpredictable noise loads this imposes on the grid, it really makes every transformer along the road to your house "sing for joy" over the experiments you are doing, and might elicit a visit from the grid maintenance people to see what in the hell you are doing

For a neutralizer you might want to look at basic lead hydroxide, but it is temperature sensitive and above 45C it
converts to the normal oxide. Basic carbonate would be good too possibly better for a hot electrolyte, but you really do need a pumped electrolyte so you can allow for the effervescence of the CO2 byproduct to occur in a separate neutralizing tank which is a low velocity flow rate reservoir. Really there is a need for using pumped flow on all of these processes for various physical considerations, and I think when this is all over, pumped flow electrolytes and coaxial electrode assemblies is inevitable......for plating or for perchlorate. Tanks will become reservoirs, but all the
electrolysis will occur inside the flow through electrode assembly.


[Edited on 28-12-2008 by Rosco Bodine]

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.

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!"

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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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!

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]

workplace lead mitigation

Rosco, I guess the idea is to have a brutally efficient and heavy plate job on bare Ti. Several patents claim they're doing it. I have no idea if it would work. I've got a lot of chemicals, and it may be worth a try. For now, MMO.

I'm taking a break right now from plate #1. The bath is mixed and heating. I am going complex on the first attempt, with added Nickel salts, surfactant, the whole 9 yards. But adding Bismuth hydroxide was a mistake. Being insoluble, the bath turned opaque. It was stupid to even consider Bi.

The small MMO anode (8 X 4 cm) was soaked for 1 hour in acetone. It was then etched in dilute HNO3 for a few minutes, rinsed, and is now soaking in 300 ml of distilled water plus 1 ml Triton X-100 surfactant at 80 degrees. It will then get vacuumed, and plated.

The bath looks like an opaque, turquoise-colored body wash. Toxic as hell, NaF, lead salts, nickel salts. I'm dressed like an astronaut. There's lots of pics that will hopefully turn out. I keep thinking "This is nuts" as I'm weighing out 700 grams of lead nitrate for a 2.25l bath.

If this doesn't work, attempt #2 will be "simple". I've got the litharge doses ready.

I could have purchased 5 good Pt anodes (or at least 100 pounds of perchlorate) for the $$ I've shelled out so far... but where's the fun in that?

Dann2, I understand the need for a simple process for the average garage chemist, and I'm headed in that direction, definitely. I'll be back in a few hours with a report + pics.

Time to don the astronaut gear again. Here we go, into the void...

There has been some discussion in the patent literature and the scientific literature indicating that plating onto a naked Ti substrate requires a special technique or the result is not a long life and good performing anode because of interface problems. I have an assortment of references that I am trying to organize. Basically the plating baths which are optimal for a graphite substrate are not optimal for a bare Ti substrate, even though the PbO2 is plated out beautifully, the Ti/PbO2 interface tends to be semi-passivated by the acidic electrolyte and it gets worse with aging in service, even buried beneath the PbO2 it slowly passivates, so you don't really have a permanent conductivity there and it can delaminate also.

So a bare Ti substrate is a special animal, and may need an alpha PbO2 plating alone, built to a working thickeness,
or as a primer coating then followed by the beta PbO2.

I have found a reference or two which indicates that glycine may be a useful additive in both electrodeposition schemes and pyrolysis schemes for MMO, as it reacts with
nitrate salts of the types we are interested forming soluble complexes that are easily decomposed in a controllable way for production of nano scale particles of either the oxides or the free metals depending upon the conditions, and also forms the mixed oxides of spinel, perovskite, or ferrite variety when mixed nitrate/glycine complexes are the precursor, so it should be interesting for that reason alone ....aside from it's possible value as a surfactant in plating baths

The glycine intermediate with an assortment of metal nitrates actually results in a sort of pyrotechnic composition
at certain balanced proportions, and the material can be ignited to produce the MMO material as the ash remaining
following ignition. Evidently the reaction is highly energetic
and at certain proportions may even partially sinter the resulting ceramic from its own heat of reaction. I have speculated before that it would be great to come up with a sort of "self-casting" all ceramic anode where the powdered precursor is poured into a form and ignited and the heat of reaction does the rest, similarly to a thermite reaction being used to make an "instant metal casting" ...and this glycine / nitrate complex is sort of headed in that direction. But I anticipate it may have more applicability in less extreme applications where its usefulness could be its easy decomposition and self-reaction to form MMO composites
in film coating schemes, it's value there being the homogenous distribution of the reacting oxides by the decomposable complex in which they are contained. This could be desirable for producing very consistent doping of interfaces and intermediate layer films where the complex could be useful as a carrier for the dopant ions.

Here is another sort of summary listing of some of the metals which are chelated / complexed by glycine and you can see that this probably incomplete list , along with those listed in the patent, includes metals of interest whose oxides are useful as components in anode coatings.

http://cat.inist.fr/?aModele=afficheN&cpsidt=3532220

http://www.youtube.com/watch?v=oXCkEEWQxgg&fmt=18

http://www.youtube.com/watch?v=KKPBtZ0Zzok&feature=relat...

[Edited on 14-1-2009 by Rosco Bodine]

Attachment: US5114702 aqueous precursor for metal oxide ceramics.pdf (207kB)
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Got to get to work fast. Anode #2 pulled... VERY HEAVY! LOOKS GOOD! It actually has that "shiny, ceramic-like" finish described in the patents. YES!!!!!!

Good stuff! RB, I like the idea of a one-shot 316SS anode. Picture this: 316 screw stock, say 3/8 X 16 pitch. You've got a nice, coarse surface to plate. Sandblast the bugger, clean it like crazy, and plate away.

You've now got a (perhaps) 8" long rod, 7/8 PbO2, 1/8 SS. Screw the stainless into a PVC plastic lid until the lead dioxide bottoms; maybe use a viton o-ring or two.

Dann2, thank you for all your encouragement and great info. IF (Big if) this anode works, I'll have learned a lot.

I made a monstrous blog entry. Rather than repeat all the info here, well, here's a link:

http://www.apcforum.net/forums/blog/swede/index.php?showentr...

Anode #1 is fugly and 90% estimate it will fail. It took up only 27 grams of lead dioxide (these are small 8 X 4 cm anodes). Anode #2 is hopeful, and plated 182 grams of lead dioxide. While anode 1 leaves behind little flakes of PbO2, anode 2 seems solid.

Still wet:


Dried... crappy Anode #1 to the left

Congrats

Good luck with the anode.
You have definitely notched up a new mile stone on the humpy, potholed, crucked, twisting, winding, never ending, idea strewn, tear soaked highway of the Lead Dioxide Anode.
The No. 2 Anode looks almost edible in the first photo! You can see the classic velvet sheen in the next photo where it has dried.

To stop nodules/warts appearing at the edges/points you could round them off as much as possible before plating. There will be no MMO on the cut ends.
Rounding off will not be too easy to do and you will rub off more of the MMO. You will end up with rounded ends that are bare Ti which may not plate the same as the MMO, or may not plate at all if you leave the MMO lying around for a long time after the rounding/cutting operation before plating (Oxide will appear on bare Ti and may stop plating). You could try bending each loose end inwards (if there are loose ends sticking out). Another possible way to stop the warts would be to put a baffle, like blobs of glue, to insulate the sharp ends/corners so that you get a abrupt end to the LD plating at the edges.
As you said yourself they are not really much of a problem anyways. Perhaps even an advantage, more surface area!

Lead Dioxide is impossible to get to plate into (inward) right angles or accross small hair-line cracks. In the picture below at B you have lots of extra LD,(where you don't really want/need it). At A (where you would like extra LD for current distribution) there is less LD than the average coat thickness, BAH!.

Hard to know about the first anode. You may be surprised how long it will work. It won't fail suddenly but will go on working untill all LD has gone off it, and will continue to 'work', (as in current will still flow into solution) but if making Perchlorate nothing useful will be happening. Then plate again hopefully of use as regular MMO. It's a win win substrate.
Try doing that with (the substrate from hell if ya ask me) Graphite.

4 my 8cm Anode are not to be sneezed at, it sounds better if you describe them as a '15 amp' anode. (approx. 200mA+ per square cm). If making Perchlorate you can get quite a lot at 15 amps over a period (coming from Chlorate).

Hope it does not erode like the one I made. It had a total weigh of LD = 31 grams from 800ml tank with 360 grams Lead Nitrate dissolved in it with no addition of any Lead compounds. That's 0.129 moles LD, giving 0.129 X 2 moles Nitric = 16 grams (+ what was in the tank at the start, a few mls) Nitric acid per 800ml. Nitric conc. getting high. Perhaps thats a major disadvantage from the, shall I call it, in service erosion perspective.
Perhaps pH controll of Chlorate cell would help with regard to anode erosion. Perhaps the same for a Perchlorate cell too.


TENTACLES...............get your (goddamm) skates on


Dann2



[Edited on 17-1-2009 by dann2]

Back in the PbO2 anode thread I posted a series of references and the first two are really keepers to keep in mind, but especially the second one which details the role of the fluoride in reducing the grain size by a factor of 10 and improving the adhesion of beta PbO2 in scenarios where your initial coating of PbO2 is going to be beta PbO2.

http://www.sciencemadness.org/talk/viewthread.php?goto=lastp...

This also goes into some explanation about the use of Bi doping.

The use of dopants complicates things greatly because of the pH conditions required, even beyond the usual pH sensitivity which plays a huge role ordinarily anyway.

To achieve stable coatings of substantial thickness, pH control is essential, where the allowable swing is tenths of a pH not several pH , meaning like for example holding plus or minus a tenth around 5.5 if that is the target ....not letting the pH wander from 0.5 to 6.5 That kind of control isn't going to happen unless a pumped electrolyte having a pretty good reserve volume and some sort of "filter bed" neutralization scheme is in effect. Otherwise you will need a huge volume plating cell ....like gallons of electrolyte for plating something the size of a pencil , to keep the pH from wandering all over the place.

There is some indication in the references that if you are going to use an uncirculated one-vat kind of setup as the plating cell, you may be better off plating alpha PbO2, if it
is a fairly thick PbO2 coating which you are desiring via a one stage plating process.

An issue which can arise with the beta PbO2 coatings which are plated at too low a pH is that the coatings can look beautiful and be perfectly sealing, and yet have low activity
and low efficiency in operation. Evidently there is a "surface active" catalytic kind of property for the PbO2 coating and
if the pH isn't just right, then that desired structure to the PbO2 doesn't form and you can end up with a beautiful looking anode coating which doesn't work properly when
put into service in the perchlorate cell. There is a sort of
controlled porosity required for the PbO2 on the nanoscale
of things which makes the surface active. And it is related to the electrodeposition strain also, the more of these tiny voids
which convey the surface activity, the lower is the strain in the material, sort of like air entrained concrete, it has a lowered density there for the surface active coating which does have an open cellular structure of interlocked crystals.
Too low a pH and you get something like a solid glasslike coating very dense which loses its desired surface activity.
So there is a "happy medium" where the ceramic like hardcoating appearance and strength is there, but if you
zoom in for a closer look at electron microscope resolution,
you want to see something like you would want to see with silica gel, swiss cheese sort of structure where the volume
surface area of all the inside walls of the exposed "tunnels and caves" is perhaps 20 times the exposed surface area of the 2 dimensional outer surface, or more. That porosity is one parameter that is affected by pH, and why it is important.

I'm not trying to foretell doom or anything, so don't get me wrong, I'm just saying that you won't really know what you've got is good as an "active anode" until you test it in a perchlorate cell and see what the efficiency is for what you have made, because it can look really pretty, but not all that glitters is gold. Don't count the chickens before they hatch.
If it works fine ....then you got lucky

[Edited on 17-1-2009 by Rosco Bodine]

Satiny is good Kind of a semigloss sort of sheen as opposed to a "high gloss lacquer effect" which would probably be too compact and dense. It would last forever in service, and it would make perchlorate, but the efficiency would be way down below what it ought to be.

I'm going to suggest again that you think about using large "crock pot" containers *instead* of plastic tanks.
I have about four different ones which were gotten over the years cheap as "closeout specials" and have never seen kitchen use but have strictly been used as very handy laboratory appliances. All of them have removable
liners and a couple of them are even thermostatically
controlled. They are great for evaporations, drying crystals or even dehydrating hydrated crystals, or for
use as hot water baths, or in this case they could be used
as heated reservoirs for electrolyte. The ones I use have
"corningware" removable liners that are either white pyrex glass or "corelle" and the liners are very heavy
with molded handles. Some of the more recent manufactured crock pots have digital programmable controllers and a few of those even have ported lids
through which a thermocouple probe can be inserted as a meat thermometer like into a roasting turkey to sense when a target temperature is reached. It seems like
these crock pots are very close already to what is needed and could probably be adapted if some alteration is needed to refine their control scheme.

Ultimately you *are* going to need a pumped electrolyte
when you are plating any serious "production scale" anodes, so you may as well view the "one vat" cells
as sort of "test cells" for short duration plating runs where
you are wishing to observe short term plating effects, rather than long runs for heavy and thick deposits.

The same 6-8 liters of electrolyte being pumped for recirculation through a filter bed neutralizer will be
better than having fifty gallons in a single cell. The
Gibson patents and even earlier patents show the
industrial setup and something a bit less complicated
can be improvised to accomplish the same thing.

And the same equipment can be used later for perchlorate production, where you add a "cooling tank" in the loop,
where perchlorate should drop out of the cooling solution
and accumulate as a bed of crystals, while the spent effluent is reheated and run through a salt bed filter
to replenish. Basically all of the requirements for a
home setup which works well are going to be a miniature scale model copying of the larger industrial scale factory.

Something I observed fairly early in reviewing the literature is that using a Ti substrate certainly doesn't simplify the requirements for a plating bath to less than what control would be needed for plating a massive anode, you have the same headaches either way for the plating bath requirements, plus you have the added complication of the interface at the Ti to PbO2. So using
a Ti substrate actually doesn't simply things with regards to the PbO2 bath requirements, if a thick PbO2 coating is intended to be applied .....in which case you are probably not really better off using a Ti substrate than simply going ahead with a massive PbO2 anode, because the added
technical complexity for the Ti substrate offsets its value.

So really for a Ti substrate you shouldn't set a goal of getting a "heavy thick coat of PbO2", but more like getting a millimeter or two maximum thickness of a very specific quality of coating, and even at that thickness it is still well into the area where a pumped electrolyte is probably needed if the anode is of significant size in relation to the plating cell. Additionally when the design is evolved it is near certainly going to a coaxial electrode assembly, and
when that occurs, the recirculating pump will be unavoidable. So ....you probably know where this is eventually headed is away from a one-pot batch process
towards a continuous process scheme.

[Edited on 17-1-2009 by Rosco Bodine]

electroless deposition of Tin-Bismuth solder alloy

You could have gotten them for half what you paid in mid-November when they were three for $30

If it is MMO it will have a flat black look to it.

For electrolysis you are probably going to have a cell voltage requirement in the 2.5 to 3.5 or max 4 volt range . If that is a linear supply you will want to use a variac in front of it or at least a fixed stepdown transformer like maybe a 36 or 48V 10A so that you don't have to "burn off" the other 10 volts at 30 A which you don't need . With that supply, assuming it is a straight linear without an SCR voltage adjustable input which compensates, at full output your supply will be consuming three times as much power as your cell.


[Edited on 21-1-2009 by Rosco Bodine]

Tentacles, I didn't know that was the guy you bought those from. Have you tried to make chlorate yet with them?

Edited to add: Rosco, check out the new "crock pot" thread - thanks! That thing was ridiculously easy to hack. It's very interesting, the temp controller I made was a bit of a PITA, but now that it's put together, it's a great addition to the shop. Attach anything to it that draws less than about 25 amps, and it'll control beautifully. I've bought a 2 quart crock pot, and another is 3 quarts. They are CHEAP.

Sorry, I can't seem to stop editing... anyone have any recommendations for inexpensive USB voltage and temperature data loggers? There are a couple on eBay - most of them are temp and humidity. I'd really like a 3 or 4 channel device that will do temp, current, and voltage. It'd be a great addition to the lab, especially being able to graph and overlay data with things like Cl- ion concentration.



[Edited on 21-1-2009 by Swede]

MMO reportedly does indeed make perchlorate and Bismuth
is the catalyst which improves even Platinum as an anode, where platinum itself becomes a substrate for a bismuth doped MMO working coating. Even a metallic Pt-Bi alloy
is superior to pure platinum for an anode. Sheesh what do I have to do here to peddle bismuth, when it seems to be the one thing that is reportedly the best for catalytic activity favoring perchlorate production. Is it something about the name "bismuth" which just turns people away
Maybe we should rename it "mojo metal" and press on

I have been looking at "conversion coating" schemes for
Titanium substrates, following up an idea I mentioned early on in this discussion along with others about the possibility
of getting titanium to react as a reducing material towards
tin or other metal salts, electrolessly plating a metal to metal
interface on the Ti substrate which could then be baked to the oxide. My idea was to mix some abrasive grit with the
precursor salt liquid to make a paste sort of like valve grinding compound, maybe with glycerine instead of water, and then to wet sand the rotating Ti substrate with the
mixture, to "flash plate" an electroless metal interface plating
simply by double decomposition, reduction reaction of the
naked Titanium with the precursor salts. This is done for
aluminum machine parts, applying a "conversion coating"
to aluminum, which is a Tin-Cobalt-Bismuth alloy, via a
simple dipping process, which "case hardens" the aluminum
with a cold process chemically applied alloy wearing layer.
The same process is probably workable on titanium, and those are precisely the three metals of interest which are
most likely to produce a desired result on aluminum or titanium.

[Edited on 21-1-2009 by Rosco Bodine]

ahh, now that setup makes sense, thanks.

cool, well i think i will start off with just chlorates using the mesh for + and -, i'll cut it into some smaller pieces.

I'll let you guys know how it ends up. Any one care for pics, or are simple cell like this of little interest?

[Edited on 21-1-2009 by y2kbugger]

Hello folks,

Used a deep fat fryer for some time as a heater for round bottomed flasks. Had it up to near 200C with 'liquid paraffin' (veternary product) with woeful smoke. 'Controll' was with a variac with internal thermostat on DFF disabled. Are Crock pots similar to slow cookers?

The co-axial arrangement that is being mentioned above is not a co-axial arrangement but a series of flat plates in parallel with just electrical connections going to both end plates of the stack. Each plate is an anode on one side and a cathode on the other side, except the end plates. It's called a bipolar cell (as opposed to monopolar where each anode and cathode has an actual current carrying wire going to it). It's OK to use MMO as both an Anode and a Cathode as it is done in the bipolar cells, expensive though.

I think we should reserve the Mixed Metal Oxide (MMO) term for anodes using Noble metal Oxides on a valve metal, (Ru and Ir with perhaps Pt, Oxides making up the vast majority) otherwise LD or Magnetite etc etc with just about any metal Oxide will be an 'MMO Anode'.

@y2kbugger
You can bend all you like. It the MMO chips off it will be no big deal as the Ti will protect protect itself with it's own Oxide, that's why it's called a Valve metal.
We love pics too!

Has anyone here actually established that the 'Ti' mesh sheets on sale (the ones about a meter long and bent at right angles all the way along) ACTUALLY HAVE an MMO on them???????????????????????? Perhaps I missed the post?
Perhaps they do not have MMO on them at all .


Sedit said this:
____________________________
I cant say that i have read through this whole threed but i do know for perclorite production that this threed started about I have read about alot of gold electrodes being used
____________________________

Where did you read that?


Where there's a will............................................................
There are relatives :-|

Dann2



.

Some microphotographs of anode 2. Under a Meiji scope, the surface looks interesting, and promising. These pics are nothing more than a Sony camera held up to the eyepiece, set on manual, with a bit of fiddling on exposure and f-stop. The coating is BLACK, but can look to be different colors in these pics.




Zooming in revealed a crystalline structure that looked like velvet, for lack of a better term:



And as I mentioned earlier, I decided a vigorous stirrer would be best for a plating bath. The motor is 24VDC, gobs of torque, yet turns over at 3 VDC, and can be varied infinitely in speed and power:




I used a lot of loctite both for the vibration mechanism, and this stirrer, to keep everything secure. The vibrator motor can easily back a nut off if care is not taken.

All I need to do now is come up with a compact paddle setup that will gently stir, yet not toss toxic electrolyte everywhere.

LONG LIVE THE POOR MAN'S MMO

Coming from a direction where you only have Graphite for making Chlorate then the Sodium salt is the way to go as it is difficult to get the Carbon powder (black shit) out of the less soluble K salts. All that changes with squeeky clean MMO.

The one shot all the way to Perchlorate may be a bit of a pipe dream. Industry got 64% CE (using pH control). Accounts in the Journals I have read give 50% (using pH control). We will get half that (and less in my experience) using no pH control with wear on LD anode. Perhaps with pH control it will be much better. More CE guraranteed and hopefully less erosion of LD.

Going off on a bit of a tangent, I am about to set up a pH controlled cell using <FONT> <UNDERLINE>POOR MAN'S MMO</FONT>. Control of pH will consist of simply adding 12% HCl at 1.2ml per hour into the cell. 4.5 amps, thats 30 something mA per square cm on anode.
Simple glass jar cell, computer PSU, perspex lid
Will be using four small cathodes with the backs of the flat cathodes covered with plastic. This keeps current density high on cathodes and will reduce hypochlorite reduction. Cathode are Ti so there should be no reduction of Chlorate. (as stated elsewhere in some thread somewhere).
I will be using no additives like Chromate, F etc, ie. a green cell!!
Hopefully there will be little Graphite (POOR MAN'S MMO) erosion. It has been reported as low as 4kg per ton Na Chlorate (4 grams per kilo ). That would give MMO a run for its money eh.


Forgot to ask:
Swede, can you see any pin holes in the LD when looking at it under the microscope? I was surprised to see many on the anode I made. They were not visable to the naked eye.

Dann2


[Edited on 24-1-2009 by dann2]

@Dann2: I like your setup! Healthy slab of graphite plus high current density Ti cathodes. That is one thing I was unaware of when I was constructing my cells, the need to keep cathode density high, thus I made giant Ti cathodes that were a waste of material. It still worked, but the efficiency was probably reduced as a result. It looks like 2 of the cathodes are Ti wires. An alternate setup would be about 8 of those wires in a pattern around the anode. Or how about "U" shaped Ti wire cathodes? Install from the bottom, with each "U" of course requiring two holes in the perspex. Where all the "U"'s intersect at the very bottom, below the anode, wrap a few turns of Ti wire to secure. Tie them all electrically together on the dry side, and there's your all-wire cathode cage. Such a cage would work well for LD plating, too.

"Green cell" I like that too! I've never added anything to my cells yet, either, and have no problem sacrificing efficiency for safety. Chromium and NaF... yuck.

I understand the need for sodium when using graphite, but am I to understand you are attempting potassium here?

HCl: With "T-Cell Jr" (18 to 20 liters) I had the dosing timer set up to turn on 6 times per day for one minute, and each cycle of the dosing pump delivered 12-15 ml, so somewhere around 100 ml per day of 15% acid worked. I could probably have added more, the pH was more often than not around 7.5 rather than 6.8, but I was very pleased at the stability. Once it was "forced" down to near neutral, there was no tendency to rapidly climb; periodic acid dosing as a concept works, and I believe it is a good alternative to full pH control with an immersed probe, with its associated probe poisoning problems.

No pinholes on the LD! Between rotation + vibration + maybe surfactant, I believe it created an environment in which bubbles simply couldn't stick. I'm hopeful strong stirring will also help create a quality plate.

RB, For Bismuth salts, I have maybe 1 lb each of Subnitrate and Hydroxide.