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Xenoid
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Multilayer Metal Oxide / Titanium Anodes for Chlorate/Perchlorate
Much as I dislike starting a NEW thread on this subject, I feel the various OLD thread titles are not really descriptive enough to cover what is
presently being done by various members in this field. Some of the early ideas we had concerning oxide coatings were perhaps a little naive. It now
appears extremely unlikely that a simple single coating of oxide over titanium will make a successful anode for amateur chlorate and/or perchlorate
production.
I would like this thread to incorporate all titanium coating processes (baking, electroplating and perhaps plasma coating) which utilise oxides as
working, interface or intermediate layers. As such we will be able to bring together the ideas which are now spread over several diverse threads on
PbO2, MnO2, Co3O4, Fe3O4, SnO2/Sb etc. Many of the processes and techniques used in some of these oxide coatings are applicable to others. There is no
reason to separate plating and baking procedures as both can be used on the same anode. Unfortunately they are being spread over several threads.
I feel this thread can be a natural successor to the following threads:
Cobalt Oxide Anodes.
More on PbO2 electrodes (as applied to coating titanium)
Magnetite Anode (as applied to coating titanium)
Tin Oxide + Antimony Oxide Anode
MnO2 Anode
Thoughts on Anodes
..... and several other minor and earlier threads
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Xenoid
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Hubert Lives!
After Hubert's unfortunate accident resulting from the power failure, the electrode assembly and container were cleaned up, refilled with fresh,
saturated KCl and reborn as "Purple Haze 2". Hubert appears little changed, I am starting to think that most if not all the black/brown mess in the
cell came from the cathode. When I started up "Purple Haze 2" the electrical parameters were identical to those previously. I have now increased
Hubert's current to 3.6 amps, this corresponds to a current density of 100mA/cm^2.
Interestingly "Purple Haze 2" is neither purple or hazy, but crystal clear. It seems weird seeing a chlorate cell so clear, it has iridescent,
platelet-like crystals of KClO3 floating around like snowflakes, before settling on the 3 cm high pile on the bottom of the container.
It would appear that some of our earlier ideas on the origin of the purple MnO4- were wrong. I now think it was coming from unconverted Mn++ in the
pyrolitic coating. It may be possible to remove the pink colouration, if deemed necessary, by a quick electrolytic leaching, pretreatment in a brine
solution!
Another possibility, really too awful to seriously contemplate, is that all the MnO2 coating was stripped of Hubert during the "accident" and that he
is now running on the 4 Co3O4 interface layers, much like my earlier "4 coat anode" from the "Cobalt Oxide Anode" thread. I think this is unlikely
though as both coating schemes were put on under the same conditions, and the "4 coat anode" started to shed oxide very early on! There is no sign off
this happening with Hubert at the moment.
Hubert has now been in a chlorate cell for nearly 2 weeks and scarcely seems affected by his "ordeal". He has produced copious amounts of KClO3 (Na -
free) which I am still extracting. He has been running most of this time at 50 mA/cm^2 and for the last few days at 100 mA/cm^2
[Edited on 13-1-2008 by Xenoid]
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Xenoid
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Meet Mathilda!
In a continuance of my Teutonic naming scheme, my latest anode is called Mathilda (brave little maid). Mathilda is destined for a perchlorate cell
like her predecessor Gertrude. I have put together a 400 ml cell for this purpose, which closely matches Mathilda's length. About 10 cm of her is in
electrolyte for a surface area of about 30 cm^2. She will be run at 3 amps, which is 100 mA/cm^2, my new "benchmark" for anodes of this type. Running
at any higher current density will only cause the 400 ml cell to overheat.
Mathilda was pretreated for several hours in a saline solution at 100 mA/cm^2 to leach out any unconverted Mn++ from the coating. This produced a
purple colouration similar to Hubert's first cell.
Mathilda's coating scheme closely follows that of Hubert. Major changes were:
1) Even higher temperature, 400 oC +/- 10 oC. versus 380 oC.
2) More MnO2 coats, 15 versus 10
3) The 4th Co3O4 interface coat was alternated with the 1st MnO2 coat. I did this on a whim, I thought perhaps it would produce a more "diffuse"
boundary layer, with less stress. Who knows!
4) The final "baking" time was extended to 1 hour. I did this to hopefully make the pyrolysis of the outer layers more complete.
In addition, I made a major blunder with the MnO2 coating solution. I forgot to 50:50 dilute my ~2.4 molar "stock solution" manganese nitrate. I
couldn't understand why I was getting MnO2 rubbing off each coat, when this had not happened with Hubert. It was not until after I had finished that I
realised my mistake! The last 5 coats were somewhat experimental:
Coats 11,12, 13 used "stock solution" diluted 50:50 with isopropyl alcohol, and various schemes of controlled heating, eg. 100/200/300/400 oC.
Coats 14 and 15 used the previous solution diluted further 50:50 with water.
Mathilda has been running at 3 amps in the perchlorate cell for 15 hours. There has been a little brownish precipitate, the coating looks OK, although
the electrolyte level line is visible. I have decided to filter the solution. and it is now perfectly clear. This will allow me to more easily monitor
ongoing corrosion. The pH of the cell was measured after 3 hours and was 11.3, it was measured again after 15 hours and found to be 11.7.
Methylene Blue test indicates perchlorate is present, but only does this after making the test solution more alkaline with NaOH. This happened with
Gertrude also, I just don't understand what is going on with this!
[Edited on 13-1-2008 by Xenoid]
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jpsmith123
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Some of the early ideas we had concerning oxide coatings were perhaps a little naive. It now appears extremely unlikely that a simple single
coating of oxide over titanium will make a successful anode for amateur chlorate and/or perchlorate production.
That may be generally true, but I would consider Beer's MMO coatings to be relatively "simple". (BTW how is your pool chlorinator cell doing?)
At this point, after having read more patents and more papers on the subject, I see TiO2 as a "unique" oxide, and instead of MMO, I tend to think of
these coatings as "doped TiO2".
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Xenoid
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| Quote: | Originally posted by jpsmith123
(BTW how is your pool chlorinator cell doing?)
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Hi, jp'
Actually, I'm a bit disappointed in it's performance.
I did a "runtime" calculation based on a 60% efficiency (yes, I know, a bit optimistic), and then let it run for about twice that length of time. I
did one concentration and extraction of NaClO3, I tried concentrating the remaining liquor, but got quite alot of NaCl precipitating during the
evaporation. Given the amounts involved, I didn't go any further, and it's now in my "recycling" tub. I'm still recrystallising the NaClO3 I did
extract as it was pretty dirty from some cathode corrosion problems. There was also a certain amount of "black material" which could only have come
from the anodes. I think I'll redesign it, but not at the moment as I have 3 cells running and it's quite a handfull. So basically they work OK, but
will they last and be value for money.
Edit: If these pool chlorinator anodes are RuO2/TiO2 MMO they will not stable in alkaline brine solutions. Remember
industrial set-ups are pH controlled (6.8 for chlorate production). The pH of my chlorinator electrode cell was 8.3 at the end of the run! pH control
is an aspect of (per)chlorate production that industry takes for granted, whilst being difficult (if not impossible) for the amateur to master. Thus
coatings which are used industrially may not necessarily be satisfactory for the amateur, where pH may rise to 12 in perchlorate cells.
[Edited on 14-1-2008 by Xenoid]
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chloric1
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See Xenoid, I told Hubert was fine. I have seen stainless make some ugly messes. Especially in the presence of dichromate antireduction catalyst. I
never told you what I did the very first time I hooked up my chlorate cell. My mind was in space somewhere and I put negative on the graphite and
positive on the stainless steel . In 5 seconds I noticed wisp of blackish material coming off the cathode and saying"Hum thats interesting". It
still was so obvious yet I did not acknowledge. When I took my digital photos and posted to my website, I looked at my setup and said" What the
hell?" I went outside immediately switched the power clips and lo and behold, chlorine started to evolve at the graphite anode. After some hours,
the solution smelled of hypochlorite. So, what does this mean? Well, when you described your situation I new that your anode was OK and your
Stainless cathode gave up the ghost. May it rest in pieces  .
It is interesting what came of the purple haze situation. I wonder if your pretreat brine can accumulate enough manganese for you to extract it as
the carbonate. Hopefully these multilayer schemes prove to be durable as it might be cumbersome and difficult to reclaim metals from failed coating.
Unless the metals have wide variations in there aqeuos chemistry. Still waiting on my thermocouple. I also ordered an aluminum tube 1 1/2" ID for the
baking.
[Edited on 1/13/2008 by chloric1]
Fellow molecular manipulator
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Xenoid
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| Quote: | Originally posted by chloric1
I wonder if your pretreat brine can accumulate enough manganese for you to extract it as the carbonate. Hopefully these multilayer schemes prove to
be durable as it might be cumbersome and difficult to reclaim metals from failed coating. Unless the metals have wide variations in there aqeuos
chemistry.
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You would have to be desperate to attempt this, 10 coats of MnO2 would lower the level of the Mn nitrate solution in the dipping test tube by no more
than 10 mm. The amount of Mn used is miniscule. Mn carbonate is dirt cheap at the pottery suppliers anyway! Manganese solutions are just not worth
messing around with, believe me!
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chloric1
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Yeh good point but after awhile the manganese would build up maybe after a year. I guess I like to reuse chems as long as it is reasonably easy and
not overkill. I am sure 5 grams of MnCO3 over a few months is not going to make or break you. At least it is better than dumping though.
Your Pool MMO might be a good candidate for a recoat Strip it down to bare Ti
and put your coatings on it. It would be interesting to see how different shaped substrates work with this.
Fellow molecular manipulator
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Rosco Bodine
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There was a suspicion by me expressed earlier in the other thread that the catalytic component for perchlorate in combination with MnO2 was likely
bismuth . That earlier idea
remains , and I have turned up a couple of more references
which describe a Bi and Mn mixed oxide compound which
forms in the temperature range which is operable for these
baked coatings . So it looks like a good bet , especially for
this one that forms from the mixed nitrates by thermal decomposition . It precisely fits the template of conditions
which seems to make it fit as a candidate dopant for the MnO2 to achieve the desired selectivity for perchlorate .
US5419986
Of course the chemistry involved here would have to be included in the coating scheme , but it looks like it would be an easy fit .
[Edited on 13-1-2008 by Rosco Bodine]
Attachment: US5419986 Bismuth doped MnO2.pdf (615kB)
This file has been downloaded 1017 times
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Rosco Bodine
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Here's another method for formation of the Bi and Mn mixed oxide .
US4520005
Attachment: US4520005 Bismuth substituted Manganese Birnessite.pdf (250kB)
This file has been downloaded 1086 times
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Xenoid
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@ chloric1
Yes, I only used the two best anodes of the chlorinator assembly. There are another 4 to play around with. I'm not sure of the best way to strip off
the remaining MMO coating. May have to be sandblasted. Also they are perforated plates, I'll need some sort of new baking system.
@ Rosco
I have sent an email to a metals company, here in NZ, ordering some Bi (min. quantity was 1Kg). They still haven't replied, so I'm still waiting. I
didn't particularly want 1Kg, but it has interesting magnetic properties (repelled by magnets) so I can "play around" with that aspect as well! Yes,
I'm very keen to dope the MnO2 with Bi, it definitely needs "something", but the MnO2 seems brilliant in the chlorate cell.
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chloric1
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@Rosco-Fascinating patents indeed. From my general overview, it seems this synthetic Birnssite is made at much lower temperatures than our other
coating schemes. Heck one might be compelled to use the kitchen stove when the wife is sleeping Although NOx fumes in my kitchen are NOT cool. What I am wondering is, what is the highest temperature that can be
used here for birnssite?
I tried to look but could not turn up any data on decomposition temperature etc.
@Xenoid-Yes a new baking set up would be needed. Possibly a metal box with suitable refractory and nichrome wire with an inlet for a small blower.
Would not have to be too fancy as it is used at 400°C and only needs to max out at perhaps 600°C.
Fellow molecular manipulator
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Rosco Bodine
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It may seem somewhat tangential to the attached patent ,
whose use of Ru doped TiO2 is more parallel with the Beer patents , but the function of the bismuth doping in the attached patent is really pretty
much the same in the scheme I am contemplating .
The attached Diamond Shamrock european patent is about the same year as the US4072586 patent related to MnO2
perchlorate anodes , and describes the use of Bi doping
for the same purpose . According to the MnO2 patent , there is only needed something in the range of 0.5% to 5%
of the Bi doping in the MnO2 for achieving the desired effect
in that differing composition , ( if indeed the dopant being referenced is Bi as I suspect , and not As or Sb which are the other two choices of
dopants ) . I believe the lack of specificity on this choice was a deliberate ambiguity in the patent description , where the authors were being
cryptic
for business reasons , and Bi seems to be the most likely suspect dopant which they try not to single out and declare .
I also have a suspicion that the ~20% " SnO2 component " may be the anomalous solubility Fe doped metastannic acid hydrosol . This would also fit
within the boundaries of what is described in that US4072586 MnO2 perchlorate anode patent .
[Edited on 14-1-2008 by Rosco Bodine]
Attachment: WO-1979-000842 Diamond Shamrock Bi doped SnO2 perchlorate anode.pdf (637kB)
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tentacles
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I was making a CoO/MnO2 anode last night, got 5 coats CoO and 4 coats of MnO2 so far. I've read the previous two Bi patents (relating to batteries)
and I happen to have a piece of crystallized Bi. I'm thinking about breaking a small chunk off and making a few ml of Bi dopes MnO2 tonight. If I get
to it (and find the damned crystal) I'll let you guys know if it adheres. The Pb doping is also a possibility.
The anode I'm working on is another 15x2cm strip, baked in a tube attached to my heat gun. I don't have a thermocouple yet but the "high" setting is
supposed to be 450C. Thermocouple is on it's way, though!
[Edited on 14-1-2008 by tentacles]
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Xenoid
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@ tentacles
You haven't told us the IMPORTANT information, what's the name of your anode? ...
Yeah, good point about the Bi crystals, there is someone locally who is selling them, might be the way for me to go! With the Bi doping, you could add
say another 6 coats of MnO2, but with say an extra "drop" of Bi nitrate in each successive coat (depends on your solution concentrations off course)
this would produce a range of doping levels in the outer layers.
If you are using thin metal strip it may be advantageous to "anneal" or slowly cool after an extended baking period at the end of the coating
sequence.
I wouldn't take too much notice of what heat gun manufacturers claim as a maximum temperature ...
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tentacles
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Xenoid: Which is why I used a piece of my sheet lead to test the temperature at the end of the "plating barrel". The temp seems to hover right at the
melting point of Pb, so it seems like it should be just about perfect. I can block some airflow for a bit more heat.
I think my Bi crystal is like 34g, and we gave like $17 for it, but all you really need is a few grams to dope with.
The strip is 1mm thick, my Mn(NO3)2 was initially far too strong, and bubbled some, I brushed and wiped the majority of that coating off and thinned
out some. It seems to be adhering fairly well.
I have two more Ti strips, so I may try one with Pb doping and one with Bi doping. I've got another piece of Ti on the way (19"x2"x.063) for bigger
cathodes and some longer anodes.
Oh, and I'm calling the anode... Ugly Betty
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Rosco Bodine
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Regarding heat guns , I have surveyed the thermocouple
controlled heat guns . The Steinels seem to be top of the line , but the Milwaukee 8988-20 seems to be about the same thing for less money and is
Swiss and German made . The Makita HG1100 is another possibility . And the cheapest of the thermocouple guns which also seems to have gotten good
reviews is the Wagner HT3500 , probably the best bargain .
There's a few others , NTE , Eddy , and Master which are
mid price range .....and there are some really high end
swiss made production line guns that are several hundred dollars .
The least expensive of the true incremental adjustment
digital temperature readout heat guns is the Milwaukee
8988-20 at about a hundred and forty dollars if you really need that sort of accuracy . I think it steps in 10F increments and regulates the temp
regardless of airflow
while showing a real time sensed temp readout on an LCD display on the top of the housing .
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chloric1
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| Quote: |
The least expensive of the true incremental adjustment
digital temperature readout heat guns is the Milwaukee
8988-20 at about a hundred and forty dollars if you really need that sort of accuracy . I think it steps in 10F increments and regulates the temp
regardless of airflow
while showing a real time sensed temp readout on an LCD display on the top of the housing . |
Are you kidding me? I like my chem hobby but I am not spenfing $140 on a heat gun. I have the entry level Milwaukee $29 special. With a maximum
output of 538°C, the other end of my aluminum tube should be just right at 400-420°C.
@Xenoid-yeh I know you cannot take the advertised temperatures as gospel but when I held my 250°C rated thermocouple at 5 cm from the gun nozzle on
low, it happily was reading over 300°C before the thermocouple sheathing turned brown and started to smoke. Hence I ordered a different K-type
thermocouple with the stainless probe rated at 700°C. Antisipating....is keeping me waiting..
Fellow molecular manipulator
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Xenoid
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Methylene Blue Testing
On page 11 of the "Cobalt Oxide Anodes" thread, I described some of the "inconsistant" problems I was having testing the "Gertrude" perchlorate cell
for perchlorate production using 1% Methylene Blue (MB) solution. A similar situation has arisen testing the "Mathilda" perchlorate cell. I have now
spent a couple of hours experimenting to try and work out what is wrong.
There is a problem with the Methylene Blue test at low perchlorate concentrations (ie. when testing a perchlorate cell in the early stages of it's
operation). At low concentrations the test is remarkably TEMPERATURE SENSITIVE. The "Mathilda" cell is operating at
35 oC. at the moment, when tested with MB the solution remains blue, indicating no perchlorate. When a similar aliquot is cooled in a fridge for a few
minutes, the same test gives a distinct violet precipitate.
To test this further, I made up a very dilute K perchlorate solution, and divided it equally between two test tubes. One was heated, and tested at 40
oC. the solution remained blue, no precipitate. The other was chilled to 15 oC. and produced an immediate violet precipitate.
To some extent, the reactions are reversible, when heated gently the violet precipitate will dissolve and the solution turns blue. Also chilling the
blue solution does seem to bring about some violet colouration. The effect does not happen with high perchlorate concentrations, where a violet
colouration occurs at very high temperatures.
Although I haven't determined the concentration and temperature limits in any formal way, suffice to say, ensure your sample
is at less than 15 oC. if testing for low levels of perchlorate.
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chloric1
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Ahha! I will note that Well, IIRC from the "perchorates" book the MB actually
forms a perchlorate salt and there might be a solubity product issue especially at 35°C or above. Or it is an abduct that is loosely bound and high
perchlorate concentration favors the bond to the point where cooling is not needed.
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Rosco Bodine
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| Quote: | Originally posted by chloric1
I have the entry level Milwaukee $29 special. |
for want of an additional $2.29 this is what you missed
http://www.acehardwareoutlet.com/(gxqv5sb5x4lwi145md1rxuu1)/...
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Xenoid
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| Quote: | Originally posted by chloric1
..... it happily was reading over 300°C before the thermocouple sheathing turned brown and started to smoke .... |
Yes, I had this problem with a new thermocouple I bought, the end was finished with a bit of heatshrink tubing! I cut it off and used a length of
plumbers teflon tape. I folded the end of the tape over itself a couple of times, then inserted it between the two wires, about 10mm back from the
junction, then wrapped it around, back over the glass fibre sleeve for about 2 - 3 cm. I have two like that now, and have not had any problems up to
400 oC.
Edit: Also, having the soft tape over the end means I can "push fit" the thermocouple into the Al tube, and it stays there, with the junction in the
airflow about 5 mm from the anode.
[Edited on 14-1-2008 by Xenoid]
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chloric1
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Probaby has the same 1 1/2 inch nozze also. I will have to control heating by more mechanical means.
That international patent you posted was pretty blatant on stating the significance of bismuth doped tin oxide coating. In fact line #9 and #13 had
the same word for word statement that the preferred undercoating is tin oxide doped with bismuth oxide. It was odd like it was jumping off my
computer screen.
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tentacles
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I called a local rock shop, and he "knew a guy" with some Bi, so 25g for $10, he's supposed to have it saturday (damn I hate waiting!). It felt so
damn shady, and all I wanted was some metal!
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chloric1
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DON'T
It seemed shady because it is DEFINATELY shady. It is nothing less than a RIP OFF. You can find bismuth on ebay for about $20 per pound. I linked
this auction:99.99% pure Bismuth 17 ounces
Fellow molecular manipulator
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