| Pages:
1
2 |
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
Hello,
@12AX7 Did you use the same huge Cathode when running the Perchlorate cell or was it the home plated Pt on Ti that you are referring to?
Perhaps Persulphate should be seen as the Green Mans Cell Additive. (AKA GMCA). Dichromate is out for LD, it's also nasty, Flourides are out (IMO) for
Ti substrate anything as it seems to erode Ti (toxic too).
Don't know how Persulphate fits (or dos'nt) into pyro stuff though.
"I've been at "real" work for a couple of days."
Great! So what exactly were you mixing with the Perchlorate for the couple of days................
I would be inclined to agree that bare Ti will not work. Quite alot of the Anodes that had LD put onto bare Ti were used for electrowinning and often
where a (bare)Valve metal was coated with LD the long term electrical connection was made directly (using Silver paint) to the LD. ie. a massive
Anode.
Tin Oxide on Ti(my hobby horse). Easy enough to actually do and cheap but SnCl4 is not easy to obtain.
MMO on Ti is the business (so long as you can get it).
Perhaps a single coat of Manganese Dioxide or Cobalt Oxide on Ti would solve the Ti Oxide problem. Never seen it mentioned by any reputable source
though. These coats are easy enough to do and materials can be had easily and cheaply.
Ebonex (an Oxide of Ti) on Ti works too I believe, but Ebonex is not easy to form on Ti.
Conversion of ground up Lead Dioxide warts for inclusion into Dragons eggs can only be a good thing. 
Dann2
|
|
|
Swede
Hazard to Others
Posts: 491
Registered: 4-9-2008
Member Is Offline
Mood: No Mood
|
|
dann2, do you have any references or recommendations for coating Ti with MnO2? Both of those I have in large qty.
Another consideration when coating/plating Ti is mechanical surface prep. As rolled, the Ti is quite flat, smooth, and of course coated with its own
oxides. Roughing the surface aggressively, then immediately coating or plating would be beneficial. For flat sheet, a harsh scoring with coarse
silicon carbide paper, or even a file, will create a surface that mechanically is ideal. For a round anode, a large Ti bolt (or turning a thread on a
tube section) might work as well.
|
|
|
Swede
Hazard to Others
Posts: 491
Registered: 4-9-2008
Member Is Offline
Mood: No Mood
|
|
Preliminary investigation of the anode:
In those areas which I had popped warts free, there was erosion of the LD in a rounded, convex manner, with the strongest LD being adhered to the MMO.
The areas of LD which formed the bulk of the anode, such as the faces, appeared untouched. The flat area which was plated onto the Ti strap I could
tell was loose, and sure enough, it also popped free.
It appears that once the material's surface is breached, some erosion may be inevitable. Whether it ceases or not, I have no idea. Again, I may have
screwed myself with a very poor setup, a voltage that was too high.
The surfaces of the cathodes had a white smut which seems typical. I ran a couple of Rhodizonic acid Pb detection swabs over them, and it yielded a
faint positive, nothing startling.
Future LD plating thoughts: Sharp edges suck, don't plate well, and cannot be expected to maintain their plate. Once the electrolyte has access to a
cross-section of LD, there will likely be erosion. A good starting anode would be a round MMO-coated tube, especially if one could be found with a
test-tube shaped hemispherical bottom, but where such an anode could be found, I have no idea. Second best would be a MMO tube with a squared-off
bottom. I'd plate THICK, at least 5mm or better, and the upper portion of LD would be a cm or two above the electrolyte level. This anode would be
inserted into a pure Ti tube to act as a cathode. Gas generation would cause a perfect flow upwards through the cathode tube, and you'd have a very
even current density throughout.
The frame concept may also work. What would be nice are pictures of small, commercial LD anodes, to see what sort of shapes and geometries they
execute.
I am not discouraged. I learned a lot from this episode, and am anxious to continue experimenting. This anode will see at least one more use, if not
more, if edge erosion ceases. Pics to follow.
[Edited on 14-12-2009 by Swede]
|
|
|
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
Hello,
Xenoid made an MnO2 Anode some time back. Details here:
http://www.oxidizing.110mb.com/chlorate/mno2.html
It's pretty easy to do as you do not need a very hot oven. It would be interesting to try it in a pH controlled cell. All you need is Manganese
Nitrate (Nitric acid + Manganese Carbonate) The carbonate can be had from the ceramics store.
I do not believe the undercoating (first coat on Ti) of Cobalt Oxide in necessary or an advantage.
IMO There is nothing going to beat Ti mesh (or flat plate with lots of holes in it) as a LD substrate. The fact that the LD is wrapped around the
substrate in all and every direction is a huge +. Tubes etc will not have this advantage no matter how well they are plated.
There is nothing wrong with good old flat Anodes. Thats what all the Chlorate makers use. Sometimes the Anodes + Cathodes are plated into pipes so
that the solution is moved past the Anode/Cathodes fairly quickly without much dwell. This is to keep the 'Electrochemical formation of Chlorate'
(current robbing) reaction to a minimum.
You should be able to get months of service out of the Anode you have.
Dann2
|
|
|
12AX7
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
Hmm, LD over MnO2 should be indestructible, without having to buy MMO mesh, eh?
Tim
|
|
|
Rosco Bodine
Banned
Posts: 6370
Registered: 29-9-2004
Member Is Offline
Mood: analytical
|
|
Quote: Originally posted by dann2  | I do not believe the undercoating (first coat on Ti) of Cobalt Oxide in necessary or an advantage.
Dann2 |
So there you have it, just disregard all the useless research about needing a conductively doped anti-passivation interface for the Ti used as an
anode substrate, as there are no problems there which may arise And all that
data about needing also some sort of anodically conductive ionic oxygen barrier, most economically achievable by using a bismuth doped tin oxide, well
that's probably all nonsense too.
I have a furnace, good instrumentation, and some materials to test out all that possibly irrelevant theory if I can ever
get the time to confirm those wild ideas. I can't really take the credit for inventing those ideas, since they were ideas derived from exhaustive
search of the available literature.
Oh well, time will tell. I'll have to get back to you with any experimental results if and when.
Has anyone chemically tested the MMO mesh to see if it is possibly an IrO2/Ta2O5 coating ?
Whatever it is, it might be good for perchlorate with an added baked coating of a few coats of Bi doped SnO2, derived from the 100% hydrolysed PVA
thickened ammonium bismuthate / ammonium stannate precursor hydrosol.
Alpha PbO2 may possibly also be workable as a working perchlorate anode coating applied directly to the MMO mesh and the Alpha PbO2 should be even
more adherent and make a finer grain and more dense coating, requiring no use of surfactants as some of the Beta PbO2 processes.
I like the idea of coaxial electrodes having a pumped flow electrolyte, like the California surfers would say ......
totally tubular
http://www.telprocompanies.com/tubular.html
Some interesting rod anodes are available also.
[Edited on 15-12-2009 by Rosco Bodine]
|
|
|
Swede
Hazard to Others
Posts: 491
Registered: 4-9-2008
Member Is Offline
Mood: No Mood
|
|
RB, I do not have your knowledge. But I have a lot of crap... Titanium, niobium, bismuth salts, boehmite, a few manganese and tin salts, and an
extremely accurate computer-controlled furnace, 100C to >1,000 C. Every Pb salt known to man (almost). Most other essential lab chemicals. Two
hands.
What do you have in mind? I'll try it. You just have to translate it into college freshman chemistry language. 
The MMO mesh I have (both varieties) are Ruthenium-based. I can verify one of the two types by contacting the manufacturer, but I am 98% sure it is
Ruthenium rather than iridium or tantalum. Their performance in a chlorate cell is unquestionable. The LD plated MMO was new MMO and not the eBay
surplus material.
Dann2, I'm not sure how to solve the edge wart problem. Most MMO sheets are cut and have a bare Ti edge. These warts were about 6mm in diameter and
appeared very solid. I thought that the barrier created, and the mechanical connection to the remainder of the LD coat, would have ensured their
strength. Apparently not.
Perhaps: During the LD plating, at the 80% complete point, pull the anode and pop the edge warts free. Re-immerse the anode and plate additionally
so as to seal the fractures with another layer of LD. Or perhaps an edge coating of some sort of sealant or polymer? I don't know.
|
|
|
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
Hello,
That's the advantage with Titanium substrate Anodes. The warts are NOT a serious problem. Simply go on using the Anode. I do not believe that the
small amount of exposed Ti at the edges of the Anode will have any bearing on the life of the Anode worth talking about. The only issues are cosmetic
and the fact that it wastes some Lead Nitrate (and generates more acid in plating tank etc). A simple baffle (plastic or welded Ti or even blobs of
hotmelt) will get rid of the problem if you so wish. If some exposed Ti was going to cause destruction of the Anode then we might as well go back to
doing Graphite substrate stuff 
Regarding the color of the LaserRed MMO. It is black. I purchased some MMO wire (Ti with Copper up the middle) used for corrosion contol approx. 10
years ago. It had a black coating on it and it was stated by the makers that it had an Iridium Oxide outside coating. It seemed to have an
undercoating of MMO (of some sort) as when the black coating wore off, gassing was still taking place on the Anode surface. I tried making Perchlorate
with the stuff. Let it run for approx. one week. No Perchlorate.
Dann2
|
|
|
Rosco Bodine
Banned
Posts: 6370
Registered: 29-9-2004
Member Is Offline
Mood: analytical
|
|
| Quote: Originally posted by Swede | RB, I do not have your knowledge. But I have a lot of crap... Titanium, niobium, bismuth salts, boehmite, a few manganese and tin salts, and an
extremely accurate computer-controlled furnace, 100C to >1,000 C. Every Pb salt known to man (almost). Most other essential lab chemicals. Two
hands.
What do you have in mind? I'll try it. You just have to translate it into college freshman chemistry language.
|
What I had in mind was to simply proceed with a baked coating of Bi doped SnO2 directly onto the MMO and let
the MMO serve as the anodically conductive interface layer,
whereas without the MMO and working from a bare Ti substrate, you would then need the Co doped TiO2 and
Co spinel interface which is cheaper than MMO but also does the job for providing a good anodically conductive interface coating, sort of like the
first "primer coating" on the substrate, over which then follows the sealant and working coating. You are going to need some 100% hydrolyzed polyvinyl
alcohol for a thickener for the hydrosol I am suggesting should be tried as a baked coating over the MMO
You could probably bump up the amount of PVA a bit to
obtain a thicker coating per dip. If wettability for the MMO is a problem for the initial dip, then use a Pytlewski polymer
for that first dip and simply air dry and proceed.
http://www.sciencemadness.org/talk/viewthread.php?tid=9783&a...
I went to the search page and entered search for posts containing the term Bismuth posted by the user name
Rosco Bodine, unchecking the option to show only one post per thread, and five pages of links to search results were displayed. It's not that I
dreamed up the idea that bismuth is probably useful as a catalytic component in a perchlorate anode coating, but simply found it reportedly is one of
the few things that reportedly is useful. And please, if anybody checks this out, it won't need 88 coats to test, probably
a half dozen to a dozen coats would be entirely adequate.
http://www.sciencemadness.org/talk/search.php?token=&src...
I'm pretty sure there was discussion about the usefulness of ammonium carbonate also as a neutralizer for precipitation of the hydrated stannic oxide
precursor, if the
use of ammonium hydroxide alone for the titration is touchy with regards to the desired pH and process. For awhile I think tentacles was going to try
this, but gave up on it. Also there are complexing agents which can be used to get around solubility issues for Bismuth, for easier use of Bi as a
dopant in baked coating precursor solutions or as an ingredient of an electrolyte for an electroplating scheme.
[Edited on 16-12-2009 by Rosco Bodine]
|
|
|
Swede
Hazard to Others
Posts: 491
Registered: 4-9-2008
Member Is Offline
Mood: No Mood
|
|
RB, I didn't mean for you to go to all that trouble, but I do appreciate it. Thank you.
In my very first LD plating effort, I made use of a number of patents that use Bi as part of the process, and it seemed to give me a lot of grief in
creating an even, fine-grained coating. I know that has nothing to do with what you refer to, but it made me suspicious of Bi in an irrational way.
I am going to spend some significant time and look at alternate anode
methodologies. The sheer volume on this board is intimidating, and sometimes ideas tend to merge with others.
My limited understanding is that primarily Ru-based MMO is optimum for chlorate, and that Ta and Ir are used in varying proportions more for cathodic
protection, corrosion control, etc. The laserred material is black, once the brown smut is cleaned off, and I have seen it shrug off extreme
conditions without any sort of failure. Whatever the proportions of oxides, it is an excellent chlorate producer, and with even crude pH control,
CE's at ~90% have been demonstrated. I too tried making perchlorate with it, and while it suffered no damage, all I got after a lengthy period were
aqueous traces of perchlorate. If there is an efficiency, it cannot be much above 1 or 3% and not practical. Interestingly, the smells generated
were lacking the O3 whiff that I have distinctly noticed with both Pt and LD.
I know the O3 smell is not scientific or conclusive, but it is something I have consistently observed in successful perc cells. It even led me to
attempt bubbling ozone through saturated chlorate solution, and traces of perc were definitely made, but very, very slowly.
Anyway, plenty of lessons learned. I recrystallized the perc produced by the LD anode, and it required two hot filterings to clean the blackened
product. It is at 0 C right now and the crystals are lovely. But it was a PITA compared to a Pt batch.
Two prime objections to Pt... initial high cost, and Pt erosion. I know this has been discussed before, but I wonder if a flash of LD over Pt would
adhere well, protect the Pt, while simultaneously having a substrate that will not passivate and become non-conductive.
|
|
|
Swede
Hazard to Others
Posts: 491
Registered: 4-9-2008
Member Is Offline
Mood: No Mood
|
|
I carefully cleaved one of the LD warts along a line that would display the LD crystal growth from beginning to end, and put it under my microscope...
I was curious at to what the grain structure would look like. What I saw was a bit baffling.
During the plating, the current was gradually diminished (in steps) from start to end. Normally, a lower current would encourage a finer grain. What
I saw was exactly the opposite. The LD grains at the base of the anode, closest to the MMO, were the finest and most compacted. As you progress in
the direction of the plating, the grains get progressively larger, and coarser. The effect was not obscure, it was very obvious and consistent
through several pieces.
I tried to photograph, but it really did not work well... I need a real camera for microscopy, not the POS I currently have. Anyway, does anyone have
any thoughts on this? Was my supposition of low current = finer grain structure incorrect?
Another possibility is the chemistry of the plating bath drove the phenomenon. As the LD plates, the nitric acid concentration climbs, and is kept in
check with litharge or similar. The possibility exists that the grain size grew despite the current reduction, rather than as a result
of current reduction.
|
|
|
watson.fawkes
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
Temperature also affects the grain size.
Higher temperatures favor larger grains, because of what's essentially a kind of annealing process. When plating metals, the annealing effect is
attenuated, since their crystals anneal at significantly higher temperatures than the plating bath. It's possible (but I don't know) that the
effective annealing temperature of LD is rather lower. Did you measure the temperature of the plating bath over time?
|
|
|
Swede
Hazard to Others
Posts: 491
Registered: 4-9-2008
Member Is Offline
Mood: No Mood
|
|
The plating bath was within 2 degrees C the entire time.
The grain size was more of an oddity than a concern. Both fine and "coarse" grains were not that far apart, size-wise, and they were not large enough
to worry me in terms of strength. It's simply that I was expecting the opposite, coarse to fine over time with reduced current.
|
|
|
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
I don't think larger CD gives coarser grain (and vice versa) with LD deposition?
The CD will not be constant over the Anode surface. Sharp corners/smaller radius of curvature give larger CD. Hollows (inside corners) give lower CD.
As the warts grow, they have larger radius of curvature giving less CD as they grow. Perhaps this explaines what happened.
(Finer grains the greater the CD?)
The ability of particular solution to plate inside corners and outside corners evenly is referred to as the 'throwing power' of the bath. Infinite
throwing power will give a plating that is even over the whole surface regardless of sharp outside corners or deep inside corners. I believe it is
closly related to conductivity of the solution. Nitric acid concentration going up increases conductivity and increases throwing power of these baths.
At a lower Nitric acid conc. the plating will be more inclined to form warts etc (higher CD at outside corners) than if conc. is higher. How much I
don't really know. Together with increasing radius of curvature of warts and acid conc. increasing (both giving less CD at a wart surface) the
grains will get coarser. (Assuming less CD gives coarser grains).
There are two papers enclosed (they were posted elsewhere on the board at some time or other). They show some pictures of LD. May help to explain what
you saw.
There are a large quantity of articles written on LD plating with no general consenses on what causes what.
As an added note high current density is sometimes used at the start of deposition so that a large amount of nucleation sites are formed giving
better adhesion (allegedly with Tin Oxide), Alpha LD also forms with the initial high CD. Lower CD gives fewer initial growing sites on substrate. The
sites (many or few) will merge into each other as plating progresses.
My two cents worth.
Dann2
[Edited on 18-12-2009 by dann2]
Attachment: The_fabrication_of_lead_dioxide_layers_on_a_titanium_substrate_.pdf (1.7MB)
This file has been downloaded 576 times
|
|
|
dann2
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
h
Attachment: dopants and conditions of LD.pdf (634kB)
This file has been downloaded 876 times
|
|
|
Swede
Hazard to Others
Posts: 491
Registered: 4-9-2008
Member Is Offline
Mood: No Mood
|
|
^^ that is an excellent paper for anyone into plating LD. My LD crystals under the microscope looked closest to figure 1B, which had adhesion rated
as "very good" by the researchers. Further, it took place in baths at 60 degrees C, high Pb++ concentrations, and lower current densities. Perhaps
the standard "start w/high current and transition to low" is incorrect, and the plating should be done from the start at a lower CD.
| Quote: |
Indeed, with a bath containing 0.5 M Lead Nitrate + 1 M HNO3, a temperature of 60 C and a current density of 5 mA cm−2, it was readily possible
to deposit 10 µm thick layers of PbO2 onto the gold disks and the layers required aggressive abrasion to remove them.
|
The addition of Ni as a dopant produced a grain structure between 1B and 1C, which would (visually at least) produce a stronger structure with finer
grains, yet still having a good surface area.
Unfortunately the target reagent was DMSO and a few other organics rather than chlorates. It would further appear that sulfates in the electrolyte
can cause problems, and that prolonged open-circuit soaking is not healthy for LD.
Interesting read.
|
|
|
| Pages:
1
2 |
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
