[time-nuts] Better quartz crystals with single isotope ?

Fri Nov 16 15:22:37 UTC 2018

This effect is real, as this Russian paper shows,
https://www.sciencedirect.com/science/article/pii/S0038109803003673 .

Natural carbon diamond conducts heat five times better than copper whereas
natural silicon conducts heat three times worse.  Isotopically
pure carbon makes 50% better thermal conductivity,
https://en.wikipedia.org/wiki/Isotopically_pure_diamond.   Also
silicon isotopes are:

silicon 28  92.2%
silicon 29   4.7%
silicon 30   3.1%
https://en.wikipedia.org/wiki/Silicon.

Mono-isotope silicon has been investigated in order to make possible the
exact determination of Avogadro's number, ~6.02x10^26
atoms/mole=protons/kilogram. It can then be grown in a precise diameter
sphere.  See
https://www.nist.gov/si-redefinition/kilogram-silicon-
spheres-and-international-avogadro-project
.  The Kibble balance just recently won out over the Avogadro project
because it is more repeatable and accurate.

BTW, quartz is silicon oxide, which is a totally different beast than pure
silicon.  Even if the quartz is mono-isotopic the oxygen would have to be
as well.  Oxygen is also present in three isotopes:

O-16 99.76%
O-17  0.04%
O-18  0.20%
https://en.wikipedia.org/wiki/Oxygen

I doubt that crystal improvements are possible with quartz made with atoms
that are mono-isotope.  Mechanical properties depend upon electron shell
attractions and the number of neutrons in the nucleus have little to do
with it.  Quartz molecules are five times heavier than carbon atoms.
Isotopic effects must also be much less. Growing pure quartz crystals is
more important that worrying about isotopes. Any impurities disrupt the
structure and cause dislocations.  This reduces Q by increasing ESR.
Quartz has an intrinsic Q of 16x10^6 divided by the frequency in
megacycles.  I don't know the source of that limitation but I doubt that it
is thermal conductivity.

Even then this would be a multi million dollar project.  What good would
slightly better thermal conductivity do if the crystal blank is all at the
same temperature to begin with? I cannot find anything on Q effects from
single isotope quartz.  Even an improvement of 50% in Q is hardly worth
raising the price of quartz by 1,000:1 to make it mono-isotope.  Money is
likely much better spent on ways to grow
quartz better and faster.

There has been a little work done on levitating crystal blanks by high
voltage RF fields so that no loss or instability is present in lead
attachments.  I have done a lot of  calculations on that subject.  I talked
to Bliley about it some 15 years ago.  Less than a Watt was sufficient to
levitate a crystal by a few microns in a 100 g vibration environment.
Something like 30 pFd of series capacitance would be present on each face
of the blank.

WB0KVV

On Sun, Apr 22, 2018 at 9:22 AM Poul-Henning Kamp <phk at phk.freebsd.dk>
wrote:
>
> Silicon comes in a number of isotopes but 95% of it is Silicon-28.
>
> When you make pure mono-crystaline silicon, you get 50-60% better
> thermal conductivity if you only use Silicon-28 atoms.
>
> Yes, you read that right:  50-60% improvement for removing the
> remaining 5% other silicon isotopes, and for this and other reasons,
> sorting silicon atoms by isotope is now a thing, which amongst other
> side effects have made the Advogardo Project possible.
>
> I can't help wonder if there may be similar interesting effects in
> quartz crystals, if they were monoisotopic ?
>
> Several relevant mechanisms can be imagined, lower internal damping,
> higher stiffness etc. etc.
>
> We know a LOT about quartz and have a very good theory for its
> behaviours, but i find no signs anybody has ever touched monoisotopic
> Quartz.
>
> The obvious experiment is not rocket-science, nor does it demand
> inordinate resources for amateurs, see for instance from 03:35:
>
>         https://archive.org/details/59554KrystallosCF
>
> But it is clearly beyond what I have time to persue.
>
> Do we know anybody in the quartz business who needs a really cool
> research project ?
>
> Poul-Henning
>
> --
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe
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