Horace Heffner wrote:
You are maybe thinking of the term "exchange reaction", e.g.:
http://en.wikipedia.org/wiki/Hydrogen-deuterium_exchange
Yes, thanks.
The H-D is a version of the more general chemical exchange reaction. I
am not sure how many elements have isotopes which can be enriched this
way. There are several including lithium, carbon, oxygen, nitrogen, and
so on. Urey developed the N(15) method.
Perhaps there is a threshold level of mass difference which must exist
as the covalent bond strength does not seem to matter much.
Here is a patent on enrichment of carbon(12) and (13) which is said to
have been widely used. Supposedly, it took the Russians years to figure
out why our graphite reactors worked so much better than theirs.
http://www.freepatentsonline.com/4406870.html
I cannot find a patent for oxygen, but it would not surprise me if there
was one. The Canadians had a number of trade secrets for H-D that they
did not patent at all!
Jones
BTW - I was planning a separate post on a few 'anecdotal' Candu trade
secrets which I have recorded from an old fried, now departed. My notes
are riddled with inconsistencies, however.
The most amazing purported secret - for enriching heavy water is so
obvious, it defies imagination that others have not realized that in the
Canadian winters, COLDNESS is not only cheap but highly effective.
Here are some known "Representative Separation Factors" for important
nuclear isotopes.
H/D C-12/13 U-235/238
Chemical Exchange 1.2-3 1.02 1.0015
Distillation 1.05-1.6 1.01 nil
Gaseous Diffusion 1.2 1.03 1.00429
Centrifuge (250 m/sec) 1.01 1.01 1.026
Centrifuge (600 m/sec) 1.233
Electrolysis 7
The total number of stages in a cascade is given by:
Ln[R[N_p]/R[N_w]]/Ln[s] - 1
where N_p and N_w are the isotope concentrations in the feed and waste,
s is the separation factor, and R[N] = N/(1 - N).
This is from Sublette's excellent site.
The one missing item from most such tables is this factoid
Comparison of an interesting but largely neglected physical property
which can be exploited in enriching heavy water:
H2O D2O
melting point 0 C 3.84 C
compare that spread with the most used separation properties:
boiling point 100 C 101.41 C
density 1.000 1.106
Geeze Loise !!! How could the yanks have missed this!
Do you see it ??
Think "cold filtered" ;-)
HDO freezes at closer to 0 than to 3.8 but accurate temperature control
is soooo easy and cheap from September to March around the Great Lakes!
...once HDO becomes a significant fraction, heavy water will naturally
become more prevalent in the mix as water molecules trade hydrogen atoms
frequently. The three have different magnetic properties to boot, which
are used in conjunction with cold and chemicals.
To produce heavy water by distillation or electrolysis requires a large
cascade and consumes vast amounts of power, so chemical methods are
preferred - even with free waste heat - but the Canadians (reportedly)
developed a "trade secret" magnetic/chemical/freezing method, extremely
cheap, which uses the higher melting point in combination with other
factors - for at least many levels of enrichment, but I'm not sure which
levels.
I suspect that the Candu actual cost for heavy water was pennies on the
dollar - over what was the "official line" and the sales price. Good for
them. It probably kept the Arabs away from heavy water manufacture for
years, and even now, the Iranians probably use the expensive method.
Jones
