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kilowatt
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Ok here's basically a summary of everything:
I've only done one experiment before with a 3/32" pure tungsten rod in 25% NaOH connected to a 9V battery. The diameter had notably decreased within
some seconds, and had reduced by several hundreds of an inch (maybe half the original diameter) within some minutes; I did not record exactly. The
electrolyte was at room temperature and a great excess of NaOH was used. The continuous setup I used for the platinum/tungsten alloy had a
water-cooled cell consisting of a small jar sealed inside a larger one, with holes being drilled in the larger jar for the water lines. I used a
variac connected to a step-down transformer (I re-wound a microwave oven transformer to output about 10V max at high current) and a single stud diode
as a rectifier. I used a graphite cathode and anode mount; the anode mount wore down much faster than the highly resiliant alloy. My water-cooled
cell ran at about 40-50°C but this just depends on the flow rate and the cell power, and isn't too important. For digesting the thoriated tungsten
rods I would just use the rods as both anode and cathode and use either 60Hz AC (probably at around 5V) or a timed relay to reverse the polarity every
few minutes.
I can't find much solubility data for sodium tungstate. One MSDS states 41g/100g H2O at 0°C. I would start with plenty of water to dissolve the
entire batch. I would add to that enough saturated NaOH solution to react all the tungsten with about twofold molar excess based on Na2WO4. Thorium
oxide or hydroxide should simply collect at the bottom of the cell (according to not_important, not me). After it is filtered you could check the
solution with a geiger counter to make sure there is no thorium left, but I don't have one. Heat the thoria precipitate to a high temperature to
obtain dry ThO2 and weigh to make sure it is close to the calculated amount. If there is no thorium left in solution, the tungstate can be
precipitated as ammonium paratungstate by adding ammonium chloride. Copious amounts of ammonia will be evolved at this stage as the excess NaOH is
neutralized. If there is any soluble thorium left in the solution, it could be acidified by adding hydrochloric or nitric acid (though H2SO4 could
work too, but not as ideally due to the low solubility of thorium sulfate). The acidification will precipitate WO3 hydrate, so the thorium will
remain in solution, which after filtering can be boiled down or precipitated, likely by adding NaOH. A peroxide method was also mentioned.
[Edited on 7-10-2008 by kilowatt]
The mind cannot decide the truth; it can only find the truth.
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not_important
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Thorium hydroxide is soluble in solutions of alkali carbonates, forming complex double carbonates; sorry not hard numbers on how soluble but some
double carbonates can be isolated. H2O2 will precipitate thorium from mildly acidic solutions of its salts, redissolving it takes addition of
something that destroys peroxide (like iodide or stannous compounds).
Thorium sulfate s a mess. It can crystalise with 0, 2, 4, 6, 8, or 9 H2O. The anhydrous sulfate is soluble, up to 25 weight percent at 0 C, but the
solution soon deposits the 9 or 8 hydrate; the 8 hydrate slowly changing to the 9. The 9 hydrate is stable below 43 C, the 4 hydrate between that and
100 C, the 2 hydrate above 100 C. Increasing temperature reduces solubility of the tetrahydrate but increases solubility of the other hydrates. In
grams per 100 g water, the 9 hydrate is 0,74 @ 0 and 3,0 @ 40; the 4 hydrate is 4,0 @ 40 and 1,9 @ 55 C. Interchange between the various hydrates
tends to be slow, along with the low solubility making the sulfate less than attractive for use during purification.
The simplest way of separation, in my opinion, would be as follows. Use recently boiled water for making solutions. Make up alkali hydroxide
solutions by first making a very strong solution of Na or K OH, and letting it sit without exposure to air until any suspended solids settle, the
carbonates have lower solubility in the concentrated hydroxides, then carefully pouring off the clear solution for diluting to the needed strength.
Electrolytic dissolution in alkali, or H2O2 + alkali, should leave the thorium as the very insoluble hydroxide/oxide along with small amounts of
unreacted tungsten and trace impurities. Filter and wash with dilute hydroxide and then boiled water.
Now comes an annoying part. Reports from several people indicate that the thorium may or may not be in a form easy to dissolve; apparently
differences in the manufacture of the rods or slow crystallisation from solid solution may give a difficult to dissolve oxide.
First attempt to dissolve the thorium containing precipitate in warm to hot moderately strong HCl, adding a few drops of HNO3 or H2O2. If you're
swimming with it, HNO3 will work in place of HCl. Expect a small amount of tungstic acid to remain as a solid, filter the solution and save the
solids as well as the filtrate. Precipitate the thorium with NaOH, wash with dilute NaOH, aqueous ammonia, boiled water, then alcohol, and acetone,
let dry. Weigh the solid to determine the recovery of thorium as Th(OH)4.
If the precipitate from acid treatment was large or if thorium recovery seems low, the solids from the acid treatment can be processed in several
ways. One is fusion with a bisulfate or mix of Na2SO4 and (NH4)2SO4, keeping it molten with occasional stirring for 5 or 10 minutes, then pouring
onto a stone slab or iron plate, crushing the solid, boiling with an excess of 5 to 10 percent NaOH for some minutes, filtering and treating the
solids with acid as above. Alternatively the precipitate can be treated with hot HNO3 plus a little HF or soluble fluoride, then the Th precipitated
with hydroxide.
If carbonates were an issue during the original dissolving of the rods, one approach that could be taken is the following. Estimate the amount of NaOH
remaining, add an equivalent of that of ammonium chloride or sulfate as a solution. Boil gently until no more ammonia is given off, ammonium
carbonates are not stable in hot solutions and are driven off as NH3 and CO2 along with the steam.
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blogfast25
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That was detailed, thanks. I hope kilowatt will keep us informed of any progress...
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kilowatt
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Progress comes slower than usual during the school year, and my usual is slow enough. I will try this next time I'm home though.
The mind cannot decide the truth; it can only find the truth.
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jshine
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I'm curious if anyone has attempted the procedure outlined in 2006 by "not_important" to determine whether it works and, if so, how well? It's very
detailed and makes sense based on what little I know of the chemistry of thorium & tungsten, but it would be great to get experimental
verification of what works & what doesn't.
Any experiences would be appreciated.
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IPN
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In an attempt to obtain some thorium compounds from welding rods I did an experiment in dissolving tungsten in a sodium hydroxide/sodium nitrate melt
(I have loads of alkali nitrates available, but not much hydrogen peroxide and I don't like electrolytic methods). I decided to try pure tungsten
first so I don't have to worry about thorium contamination before I get the procedure perfected. So 27g (0,147mol) of relatively pure tungsten (not
welding rods) in the form of short 3mm thick rods was placed into a ceramic pot with 24g of sodium hydroxide pellets and 100g of coarse sodium
nitrate. The amounts weren't really calculated as I couldn't come up with a balanced reaction. I just took a good excess of oxidizer and half the
amount of hydroxide in moles.
Mixture was slowly melted using a gas portable stove and stirring with a steel rod. Few minutes after the reaction mixture had become completely fluid
a very vigorous reaction kicked in heating the mixture instantly into orange glow and shattering the ceramic pot while lots of steam or some other
white vapour was generated (I was expecting this to happen so I had the pot in a steel pan, containing the melt). No visible red gasses were seen (did
it outside and it was pretty windy so can't be sure). After the reaction had slowed down the melt formed a light green/white solid cake with visible
pieces of tungsten. This was carefully drowned with water and left to sit.
I haven't yet worked it up, but just thought I'd report this for now.
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cal
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EWTH-Th-2 welding rods
Quote: Originally posted by IPN  | In an attempt to obtain some thorium compounds from welding rods I did an experiment in dissolving tungsten in a sodium hydroxide/sodium nitrate melt
(I have loads of alkali nitrates available, but not much hydrogen peroxide and I don't like electrolytic methods). I decided to try pure tungsten
first so I don't have to worry about thorium contamination before I get the procedure perfected. So 27g (0,147mol) of relatively pure tungsten (not
welding rods) in the form of short 3mm thick rods was placed into a ceramic pot with 24g of sodium hydroxide pellets and 100g of coarse sodium
nitrate. The amounts weren't really calculated as I couldn't come up with a balanced reaction. I just took a good excess of oxidizer and half the
amount of hydroxide in moles.
Mixture was slowly melted using a gas portable stove and stirring with a steel rod. Few minutes after the reaction mixture had become completely fluid
a very vigorous reaction kicked in heating the mixture instantly into orange glow and shattering the ceramic pot while lots of steam or some other
white vapour was generated (I was expecting this to happen so I had the pot in a steel pan, containing the melt). No visible red gasses were seen (did
it outside and it was pretty windy so can't be sure). After the reaction had slowed down the melt formed a light green/white solid cake with visible
pieces of tungsten. This was carefully drowned with water and left to sit.
I haven't yet worked it up, but just thought I'd report this for now. |
'EWTH-Th-2 welding rods " These welding rods contain 2% thorium oxide and tungsten only. See MSDS, When the rods are treated with nitric acid the
thorium becomes a nitrate and the tungsten does not react with acids. Thorium nitrate is water sol. and tungsten is not. Then heat the Thorium nitrate
to 450-500 to convert to oxide.
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Dave Angel
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Possible thorium exposure!
I wish I had known that TIG electrodes may be 'thoriated' before I ground one into separate electrodes for my spot welder yesterday... It didn't even
cross my mind that I might be working with radioactive materials, but in looking to buy a new electrode I've just made this slightly worrying
discovery!
Did the work in an open garage, with face shield but no dust mask. This was a red-tip electrode so turns out it was indeed thoriated. Now wondering
just how much I've been exposed to and whether there's anything I should, or even, can do? I'm hoping it's one of those 'chronic exposure' hazards and
that the small amount from a few grinding operations won't be a significant health hazard....
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vmelkon
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The packaging should say 2% thoriated. The rods are also color coded (red tipped in your case) so that when they are out of the package, they can
still be IDed.
As for the danger, they are only dangerous when you grind the tip to make it sharp like a pencil. It is better to do that outside.
People have been exposed to it for a long time. That's why new rods contain lanthanum or one of the other lanthanides.
Same thing for gas mantles. They use to contain thorium nitrate and cerium nitrate. Now it is yttrium and I think cerium as well.
Good bye thorium!
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Poppy
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| Quote: Originally posted by blogfast25 |
Would anodic digestion of these rods be the best and easiest way or would fusing them with an alkali + oxidiser work too? |
Yes nice idea, would powdered TIG rods survive a trip with chlorate in a black powder like fashion?
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Dave Angel
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| Quote: Originally posted by vmelkon | The packaging should say 2% thoriated. The rods are also color coded (red tipped in your case) so that when they are out of the package, they can
still be IDed.
As for the danger, they are only dangerous when you grind the tip to make it sharp like a pencil. It is better to do that outside.
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Unfortunately the pack was not marked. I remember buying it many years ago from a big chain shop in the UK and whilst they knew it was some sort of
welding electrode, it was just a very plain piece of card with shrink wrap. They just put an abitrary price on it and I thought 'why not?' Had I seen
the word 'Thoriated' anywhere I would have picked up on it!
I ground it into three pieces with the edge of a bench grinder and ground the tips down a bit. Hopefully not too much dust came off this small
operation.
Lesson learned anyway; zirconated electrodes next time, and decontamination of garage the next job!
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