Re: Technique for Deuterium Drying

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UG!
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Re: Technique for Deuterium Drying

Post by UG! » Thu Dec 14, 2006 5:47 pm

i built a D2 dryer from a coil of copper tubeing and a peltier heat pump, the theory being that the large internal serface area of about 4" of 1/4" tubeing would allow a heigher temperature to be used. unfortunatly the electrolytic watter splitter i spent a lot of time and effort on was a compleat failure, so i gave up on the whole contraption and decided to dribble some D2O on Lithium in a glass tube, by injecting it in through a silicone plug. half the Deuterium would be wasted in LiOD but so little will be needed it won't matter much and the Lithium will dry the D2 very adaquatly.

Oliver

Wilfried Heil
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Re: Technique for Deuterium Drying

Post by Wilfried Heil » Thu Dec 14, 2006 6:05 pm

For drying D2 a small column of CaO should be enough.

While all of this is certainly possible, I think it will cause less hassle to buy a small bottle of dry D2 instead, like the Linde Minican with 12 l of D2. Why bother? There will be enough challenges with the rest of the system.

As an alternative, I would suggest loading D2 into a metal electrode such as a palladium/platinum wire by electrolysis. The gas could then be released into the chamber by heating the wire and reabsorbed when it cools.

Or use a palladium tube for the electrolysis ($$ at Goodfellow), which should then release dry D2 on the inside (equilibrium pressure is around 50 Torr at room temperature) and could be directly coupled to the chamber by a capillary tube. This should also allow for a rather sluggish regulation of gas pressure.

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Carl Willis
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Re: Technique for Deuterium Drying

Post by Carl Willis » Thu Dec 14, 2006 6:35 pm

How about this? Just pass the gas, still full of D2O vapor and whatever other contaminants, into a thin palladium tube that is kept at red heat by passing a current through it. The gas will diffuse through the metal easily; the contaminants will not. You could probably support flows on the order of scch's with such an arrangement. And this is highly suitable for low-tolerance, cheap construction at home.

-Carl
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JohnCuthbert
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Re: Technique for Deuterium Drying

Post by JohnCuthbert » Thu Dec 14, 2006 6:53 pm

Just a thought but, would the rate of diffusion be temeperatre dependent? If so then you have a flow controller, dryer and purifier in one there; very neat.

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Re: Technique for Deuterium Drying

Post by Wilfried Heil » Thu Dec 14, 2006 7:03 pm

And an electrolyzer, if you wish, all in the same device. It isn't exactly cheap, unless you have a source for palladium tubes.

Just the Pd tube costs more than a bottle of D2 with the regulator on it.

John Cuthbert wrote:
> Just a thought but, would the rate of diffusion be temeperatre dependent? If so then you have a flow controller, dryer and purifier in one there; very neat.

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Re: Technique for Deuterium Drying

Post by Carl Willis » Thu Dec 14, 2006 7:21 pm

The rate of diffusion is highly temperature-dependent. Indeed this would lend itself to closed-loop control fairly easily.

-Carl
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Wilfried Heil
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Re: Technique for Deuterium Drying

Post by Wilfried Heil » Thu Dec 14, 2006 7:28 pm

Carl - I see that you are designing along the same lines. A Pd- or Pt-tube should work fine as a regulated leak valve for the small amounts of D2 that are needed in a fusor, while also sealing it against the atmosphere.

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Alexi
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Re: Technique for Deuterium Drying

Post by Alexi » Fri Dec 15, 2006 1:25 am

Nickel tubing works just as good as Pd. We built several such leaks/filters using "Nickel tubing, 0.81mm (0.032in) OD, 0.51mm (0.02in) ID, 99% (metals basis)" from Alfa Aesar www.alfa.com
Our hydrogen sources needed only about 6 Amps to start leaking.

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Re: Technique for Deuterium Drying

Post by Wilfried Heil » Fri Dec 15, 2006 2:21 am

How much H2 did the nickel tubes leak and at which pressure?
What length of tubing did you use?

Thanks for the tip. Titanium tubing should also work, but nickel is easier to braze or solder.

Small nickel tubes can be had almost for free, flea market wise: they are used for the indirectly heated cathodes in most electron tubes. Inside of the tube is a tungsten wire heater for 6.3V and on it's surface is a layer of barium oxide, which can be removed.

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Alexi
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Re: Technique for Deuterium Drying

Post by Alexi » Fri Dec 15, 2006 3:22 am

We could get 1e-5 torr H2 while continuously pumping at 500L/s. We did not need any higher flow, but I think that the source could provide much higher flow. The tube was 60 cm long, coiled. "Dirty" hydrogen was at 15psi pressure.

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