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markx
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Quote: Originally posted by ecos  | I have a question.
I found some offers on the internet for crucible graphite. some of them are used and with good price.
anybody know if they can work as electrodes? |
They will definately work as inert electrodes, but when we are talking about anodes for Cl- conversion to ClO3- then the wear rate may be not too
good. And yes, there might be some unwanted additives in the crucible composition, but one can not be sure about that.
Graphite anodes inevitably crumble and wear down in this application, especially under higher current densities and temperatures. If I remember
correctly from older russian literature, then the critical point for graphite erosion in chlorate production was at 40C. Any higher than that will
cause increased wear on the anodes. But then again in amateur application this aspect may not be that important. If you can get the material cheap
then a bit of erosion will not be a problem. What may be a problem is getting the carbon residue out of the cell liquor during purification. It
requires meticulous filtering to clear up the solution and when potassium chloride is used, the filtering must be done while solution is hot. It can
be accomplished, but presents a rather uncomfortable stage in the process. And from the point of safety and stability it is not a good idea to leave
carbon residue in your final product.
Exact science is a figment of imagination.......
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ecos
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Thx all for the help.
I am planning to electroplate it with PbO2.
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ecos
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here is my carbon rod
length = 26 cm,
Diameter = 4 cm.
Weight = 630 g
it costs = $2.5
  
its time to electroplate it 
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markx
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Just make sure to avoid any contact with the lead nitrate solution.....one can receive a lifetime worth of damage in a single afternoon with this
compound. Also watch out for any airborne spray or mist that may be generated during electroplating.
Exact science is a figment of imagination.......
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Laboratory of Liptakov
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PbO2 anode
On youtube is video about prepare PbO2 anode from pure Pb (carrier substrate) only with use H2SO4, current 30 A / 5V. Very small second Copper
electrode. So simply ? Only H2SO4 30% ? I mean, that is a nonsense. (time 5:58)
https://www.youtube.com/watch?v=kylurawZEWs
...LL...
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PHILOU Zrealone
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Yes that simple!
It is what happens into a car battery when recharging.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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ecos
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I read about this procedure before.
it was stated that the coated PbO2 with this process is very bad and fall easily from the anode !
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Laboratory of Liptakov
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Thanks ecos....:-) I do not understand speaking words from video. I estimate, that in easy prepare the anode will some problem. Maybe do it some a
better process for coating from PbO2. For example rotating rod shape electrode /substrate/ and use cloth for entrainment bubble gas. And polishing of
planar surface during rotation coating PbO2. Simply help tense of cloth. ..LL..
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ecos
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I found the reference.
wiki : https://en.wikipedia.org/wiki/Lead_dioxide
| Quote: |
Electrolysis
An alternative synthesis method is electrochemical: lead dioxide forms on pure lead, in dilute sulfuric acid, when polarized anodically at electrode
potential about +1.5 V at room temperature. This procedure is used for large-scale industrial production of PbO2 anodes. Lead and copper electrodes
are immersed in sulfuric acid flowing at a rate of 5–10 L/min. The electrodeposition is carried out galvanostatically, by applying a current of
about 100 A/m2 for about 30 minutes. The drawback of the lead electrode is its softness, especially compared to the hard and brittle
PbO2 which has a Mohs hardness of 5.5.[11] This mismatch in mechanical properties results in peeling of the coating. Therefore, an alternative method
is to use harder substrates, such as titanium, niobium, tantalum or graphite and deposit PbO2 on them from lead(II) nitrate in static or flowing
sulfuric acid. The substrate is usually sand-blasted before the deposition to remove surface oxide and contamination and to increase the surface
roughness and adhesion of the coating.[12] |
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Laboratory of Liptakov
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PbO2 anode
Very important. Especially, that main problem is in different hardness between carrier and PbO2. Thanks..LL...
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ecos
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I attempt to connect my carbon rod to the shaft of a motor but i failed 
the carbon rod diameter is 4 cm and the shaft of the motor's diameter is 1 cm !
I tried to use glue or silicon to attach it, but when i run the fan motor for some time, they split !
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Laboratory of Liptakov
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rod
You can drilled to carbon precise center hole, diameter 10,3 - 10,6 mm. Estimate depth 3 cm. And on small different (10,0mm steel carrier) use paper
tape. Was try I am, hold it a good. Condition is long of steel rod from motor 35 mm. Connect and disconnect is possible. Recomend the slit between
carbon and steel (for paper tape, not plast) is 0,1 - 0,3 mm. ..LL...
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ecos
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I am afraid to drill into the rod. it might get cracked
I was thinking of a solution to avoid the air bubbles that stick to the electrode while plating and affects the quality.
what if i put the electrolysis cell in a reduced pressure room ! won't that get rid of the air bubbles?
if yes, there will be no need to use a motor to rotate the rod so fast !
[Edited on 20-9-2016 by ecos]
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yobbo II
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Goog luck with the graphite subsrate. As the page, where the pictures at the top of this thread came from states, all the anodes fell apart.
The original Japanese spinning graphite article here.
http://www.sciencemadness.org/talk/files.php?pid=143479&...
and attached as well
Get some mmo and coat that.
In the extract from Wiki above I quote
"Therefore, an alternative method is to use harder substrates, such as titanium, niobium, tantalum or graphite and deposit PbO2 on them from lead(II)
nitrate in static or flowing sulfuric acid. "
If you add sulphuric acid to lead nitrate you will get an immediate ppt of lead sulphate. The line is wrong.
Yob
Attachment: Bulletin of CS Japan.pdf (748kB)
This file has been downloaded 561 times
[Edited on 20-9-2016 by yobbo II]
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ecos
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| Quote: |
If you add sulphuric acid to lead nitrate you will get an immediate ppt of lead sulphate. The line is wrong. |
I think you are right, it shall be lead nitrate and copper nitrate not sulfuric acid. This is also found in the first posts in this thread !
I will read the document you sent and provide my comments later.
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markx
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Oxidizing lead metal surface under anodic potential in sulfuric acid solution does not tend to form a durable layer of PbO2. The layer is thin and
will not work in chloride solution for long. All in all it does not seem to be a practical solution....more a visualisation of the effect. Atleast in
my experiments I could not get something that would resemble an inert anode by function.
The only somewhat working way still seems to be the electrodeposition of PbO2 from lead nitrate/copper nitrate solution. But also this method is quite
complicated to use for the practical electrodeposition of thick PbO2 layers. Properties of the plating bath have to be corrected/stabilised during
lenghty deposition process. Suitable additves or operating regimes established to avoid pitting, cavitation, dendrites and internal fracture stresses.
Not an easy task to be honest....also one can expect to contaminate the premises that the experiment is conducted on and oneself with lead nitrate
quite severely. There will spills and spray during the process that accumulate on surroundings, so there is a real danger of lead poisoning.
So perhaps if the goal is not to study the PbO2 electrodeposition process in depth, but more the electrosynthesis of perchlorates then it would make
more sense to spare up for a platinum anode. They do run expensive, but trust me, a functional lead dioxide anode shall not come for a cheap price
either.
Exact science is a figment of imagination.......
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yobbo II
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The alpha way?
The toxicity of the lead nitrate is what makes the whole process nasty. If lead nitrate (and lead in general) was harmless it would make a great fun
process.
I have seen mmo and tin oxide coated titanium coated with first a thin layer of alpha lead dioxide, then the thicker beta coat. Where the beta
falls off in places after some use of the anode (in chlorate or perk cell) the alpha layer can stay on for an amazing length of time (sometimes).
Someone once suggested that perhaps the way to go would be just coat with thin layers of alpha lead dioxide. This has been shown to work. You need a
lead plumbate bath. Lead oxide (litharge) + sodium hydroxide and plate slowly at low current density. You do not need large amounts of lead compounds.
Litharge is easy to get. The bath is still toxic of course.
Not much toxic spray from bath (not many bubbles). No ph control. Not much reduction in concentration of lead compound in bath as the actual volume of
Pb doixide being plated is small in total.
It will make chlorate /perchlorate. The beta is preferred. A reason that beta is preferred is that the voltage accross cells (chlorate or perk) is
lower that with alpha which is very advantageous in industry but irrelevant with the home maker.
Alpha paper attached.
Yob
Attachment: AlphaLD.zip (229kB)
This file has been downloaded 472 times
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ecos
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do any body know PbO2 anode provider on internet ?
I want to order one. Unfortunately most of the internet sources i know are gone !
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Laboratory of Liptakov
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anodes
Early coming times, when will stop sale for all perchlorate anodes. Stay only graphite rods for welding (and chlorates).
For luck, is here method heated conversion Na/K ClO3 on Na/K ClO4. Yield is about 60% on insert xClO3, but still is it better than nothing........LL
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RogueRose
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| Quote: Originally posted by Laboratory of Liptakov | Early coming times, when will stop sale for all perchlorate anodes. Stay only graphite rods for welding (and chlorates).
For luck, is here method heated conversion Na/K ClO3 on Na/K ClO4. Yield is about 60% on insert xClO3, but still is it better than nothing........LL |
Could you please make this intelligible in some way?
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Laboratory of Liptakov
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Here is method on conversion KClO3 on KClO4 https://www.youtube.com/watch?v=EC4OPnvPkLU
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Bert
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Have any tried a copper coated Carbon arc light electrode for the substrate when plating a Lead dioxide anode for perchlorates? I have a few, 3/8"
Dia. x 9" long as I recall
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markx
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| Quote: Originally posted by Bert | | Have any tried a copper coated Carbon arc light electrode for the substrate when plating a Lead dioxide anode for perchlorates? I have a few, 3/8"
Dia. x 9" long as I recall |
I see no reason why it should not work once the copper coating has been removed either chemically or electrochemically.
On another note regarding the lead dioxide anode....I've been contemplating a novel approach for generating the required bath constituents in
situ electrochemically from rather benign raw materials. The idea was to use a common cell with a solution of ammonium nitrate into which several
sets of electrodes are immersed, driven by separate power supplies (or separate h-bridge style mosfet switches at least) to first electrochemically
generate lead nitrate and copper nitrate by dissolution of sacrificial anodes made from the respective metals and then electodeposit the lead dioxide
from these previously generated bath contituents on a separate set of electrodes....
The power supplies would be driven one at a time for predetermined intervals to minimise side reactions/cross polarisation and to allow for the more
or less complete conversion of the generated bath constituents with every cycle. The cycles could be quite short in fact, perhaps on the scale of
milliseconds. A sort of multi power supply pulse plating setup if you will....
Granted the ammonium nitrate cell would have to be probably separated by a suitable membrane to avoid the alkaline cathodic compartment products from
migrating into the anodic compartment and precipitating the lead and copper nitrates before there is a chance to use them in the lead dioxide forming
reaction. Surely this approach is techically complicated and presents some serious electronical challenges, but I like the idea of not having to mess
around with coupious amounts of lead nitrate and the fact that one probably will not have to build up a serious concentration of it in the bath at any
given point in time with this approach.
I did test this concept in a very simplified form several years ago: took a solution of ammmonium nitrate and drove current through it for a short
period of time (5 seconds range) by using a lead metal anode, thus propagating lead (II) ions into the solution, then replacing the sacrificial lead
anode with a stainless steel substrate.
And the damndest thing happened: a nice shiny black layer of lead dioxide deposited on the substrate. Of course my cell did not have a membrane, so
most of the lead that got into solution quickly precipitated in contact with the cathodic products, but the concept worked for a short period of time.
In fact I also tested the thus obtained lead dioxide layer as anode in sodium chloride solution and was pleasantly surprised by the notable evolution
of free chlorine (organoleptically detected). Of course the plating was not perfect, so the stainless substrate quickly started to dissolve in the
chloride solution under anodic potential, but as a proof of concept that was quite encouraging.
I never got into more involved research regarding this concept, but perhaps the time is here...
Exact science is a figment of imagination.......
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Laboratory of Liptakov
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Maybe is time, because almost identical method I did also. However my attempt was ending as an smoke bomb with Pb steams. Melted AN + dissolved
PbNO3/2 , during cell - current run, did increased temperature. After some second was started autoreaction between all materials together. Was used
dry sand for stopped this madness. But I believe, that this is maybe way...
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Simoski
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Guys I have lead nitrate and copper nitrate and have wanted to electrodeposit Pb02 over MMO Ti mesh for a while now, what current density must I use
for the alpha and what current density for the beta? What other additives do I need? Does the pH rise during plating and I need to acidify the
electrolyte ?
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