Page 1 of 1

Deuterium Amount

Posted: Thu Feb 06, 2014 4:37 pm
by Aidan Kehoe
As I'm sure everyone on this site knows, deuterium is expensive. I've considered electrolysis, I've asked my school if they could order the gas at a discount, but it seems to me as if there is no way around the price. I'm curious as to the amount of deuterium necessary in a reactor. Is there a ratio of total volume to deuterium volume? It would be very helpful if someone could tell me the approximate volume of their fusor and the amount of deuterium they used.
Thank you very much,
Aidan Kehoe

Re: Deuterium Amount

Posted: Thu Feb 06, 2014 5:09 pm
by Richard Hull
The amount of running deuterium in a fusor is tiny, but varies wildly, fusor to fusor, based on operational experience, the volume of the fusor and settings made by the operator. So there will be no answer of of great precision.

A general, broad brush estimate might be as follows: Using a 6" sphere. the total volume used over a 30 minute run might require a few cubic centimeters at STP provided a skilled operator is at hand. Thus, a 50 liter STP lecture bottle might run a fusor for 100-200 hours or more producing 2 million fusions/second over that period. Of course, no fusor is normally operated for more than 10-30 minutes in a run with 3 or 4 runs on a very active day. Few real fusors ever see more than about 1 run per month. Thus, the lecture bottle might be expected to power a fusor for about 2-3 years of normal, single amateur operation by a skilled operator.

My current 50 liter cylinder is going on its fourth year.

Richard Hull

Re: Deuterium Amount

Posted: Thu Feb 06, 2014 5:56 pm
by Aidan Kehoe
Great, thank you! How much did your cylinder cost, if you don't mind me asking?

Re: Deuterium Amount

Posted: Thu Feb 06, 2014 6:12 pm
by Scott Moroch
I will spare Richard the time of responding to your question. While I do not know where specifically Richard bought his deuterium, most people buy their deuterium from Sigma-Aldrich. They have relatively good prices for a large amount of deuterium. Here is a link with assorted prices: http://www.sigmaaldrich.com/catalog/sea ... partialmax

Re: Deuterium Amount

Posted: Fri Feb 07, 2014 10:31 am
by Richard Hull
My last cylinder was a 50 liter lecture bottle and was about $375 delivered. (Cambridge Isotopes) That included the hazmat delivery fee. That was in line with the info. that Scott supplied......

A hydrogen regulator is needed and an adapter for the regulator to the lecture bottle and that is usually adds about $150.00 extra. Figure on $500.00 for the deuterium gas system with a 50 liter cylinder. You'll note that smaller quantities are not that much cheaper. It all depends on your long term needs.

Hydrolysis of heavy water will drop the cost to under $100.00 for everything, but it is a crap shoot so far as purity of what you let in the chamber.

Bottom line, bottled gas is easier and a snap to use and setup. Hydrolysis is much cheaper, but is difficult to mechanize and correctly administer to the fusor system.

Richard Hull

Re: Deuterium Amount

Posted: Fri Feb 07, 2014 12:05 pm
by Aidan Kehoe
Great, thank you! I will keep that in mind. Does the purity effect the amount of deuterium you have to add, or just the probability that the atoms will fuse? Furthermore, you mentioned that the cost decreases when doing electrolysis, but don't you have to buy a litre of heavy water to obtain a little less than a litre of deuterium?
Thanks,
Aidan

Re: Deuterium Amount

Posted: Fri Feb 07, 2014 4:31 pm
by Rich Feldman
Re. needing a liter of heavy water.

Perhaps not in the FAQ's, but we don't expect to be teaching elementary chemistry & physics.

What is the mass of 1 liter of air at STP?
What is the mass of 1 liter of H2?
What is the mass of 1 liter of D2 gas (hint: double the previous answer).

Compare that to the mass of 1 liter of heavy water.
What fraction of the latter is deuterium?
For extra credit: what volume of heavy water is consumed by evolving 1 liter of D2?

Aidan, I hope you will favor us with actual numerical answers, within 10% or so. Most of them can simply be looked up on the Internet, or found with help from a science teacher.
Thanks!
-Rich

Re: Deuterium Amount

Posted: Fri Feb 07, 2014 5:53 pm
by Aidan Kehoe
1. 1.29 g
2. 0.09 g
3. 0.18 g
4. 2/3
5. 1.324

Re: Deuterium Amount

Posted: Fri Feb 07, 2014 6:18 pm
by Rich Feldman
Thank you, Aidan. Results are:
1. Right
2. Right
3. Right
4a. no answer
4b. Unexpected right answer (question was ambiguous)
5. Probably very wrong (but you didn't state a unit of measurement).

Would you mind another try, starting in the middle?

4a. What's the mass in grams of 1 liter of liquid D2O?
4b. Yes, 2/3 of the atoms are deuterium. What fraction of the MASS is deuterium, if each O atom weighs as much as 8 D atoms?
4c. What's the mass of deuterium in 1 liter of liquid D2O?
5. How many liters would that be in the form of D2 gas? (Refer to answer #3).

Re: Deuterium Amount

Posted: Sun Feb 09, 2014 5:44 pm
by Aidan Kehoe
4a. 1.1056 kg
4c. 1/5
4b. 0.22112 kg
5. 6.1422 litres

Re: Deuterium Amount

Posted: Sun Feb 09, 2014 7:21 pm
by Rich Feldman
Hi Aidan. Thank you for sticking with the unsolicited lesson.
You got 4 a, b, and c right this time.
But your final answer, the associated volume of D2 gas, is still wrong by a factor of more than 100.

In real life it's numerical answers that matter.
Please give it one more try, and perhaps show your work.

Beware of mixing up units, such as grams and kilograms.

* mass of deuterium in 1 liter of liquid D2O.
* mass of deuterium in 1 liter of gaseous D2.
* ratio of the two previous answers. Do you see how that's the same as the volume ratio
between portions of the two substances containing the same mass of deuterium element?
Express the result either way: amount of D2O consumed to make 1 liter of D2 gas,
or amount of D2 gas that could be evolved from 1 liter of D2O liquid.

-Rich

Re: Deuterium Amount

Posted: Mon Feb 10, 2014 7:29 am
by charlie_mccartney
All of this is covered in high school chemistry, it is just a matter of explaining the proper way to convert these units.

Re: Deuterium Amount

Posted: Mon Feb 10, 2014 11:01 am
by Richard Hull
A mole of heavy water is only 20 grams, ~ 20cc. If fully electrolyized that would make ~44 liters of D2 gas.

The last time I checked 100 cc of heavy water was about $65.00. If fully electrolyized, that's about 220 liters of D2 gas. The cost of that much bottled D2 would be well over $1000.00.

Still, electrolyizing is a process filled with purity issues when it comes to putting the gas into the chamber, but it can definitely be made to work.

Were I to do it. I would have the D2 gas go through dryerite first and finally through a 10 foot coil of copper tubing under LN2 before admitting it.

Richard Hull

Re: Deuterium Amount

Posted: Wed Feb 12, 2014 6:01 pm
by Rich Feldman
Oops, Richard, you had two values wrong, one by a factor of two.
Here with corrections:
A mole of heavy water is only 20 grams, ~ 18cc. If fully electrolyzed that would make 1 mole = 22.4 liters of D2 gas at STP.
Perhaps your analysis was remembered from long ago, and overlooked the diatomic nature of hydrogen gases.
100 grams of heavy water (only 90 ml, that's why it's called heavy)
would yield about 110 liters of deuterium gas.

That's consistent with the volume ratio I was leading Aidan to, using looked-up densities instead of having to learn about moles.

Re: Deuterium Amount

Posted: Fri Feb 14, 2014 11:28 am
by Richard Hull
Thanks for the correction. that's the kind of normal mistake I make when playing chemistry. I forgot about the mass of the neutron in the D....and with me loving neutrons...Go figure.

I think the upshot for both of us, in this thread, is to show any would-be "roll your own D2" person that there is a heck of a lot of D2 gas at STP in 100CC of fully electrolyized heavy water.

Richard Hull