On Sunday, December 6, 2020 11:06 PM, jim bell <jdb10987@yahoo.com> wrote:
[snip]
Zinc, similarly, is made up of isotopes. https://www.webelements.com/zinc/isotopes.html Only 4.1% of natural, stable zinc is Zn-67 and it has a nuclear 'spin'. The rest is Zn-64, Zn-66, Zn-68, and Zn-70, and none of them have nuclear 'spin'. And I notice that some early work on GaN LEDs used Zinc as a p+ dopant. It worked, I suppose, but somehow it was abandoned early on, since magnesium worked better. Why? Could that be because 10% is greater than 4.1% ? Well, THAT can be fixed!
"Doing some more research, I also notice that the radius of gallium atoms is 130 picometers. https://www.webelements.com/gallium/index.html The radius of zinc atoms is 135 picometers. https://www.webelements.com/zinc/ And the radius of magnesium atoms is 150 picometers. https://www.webelements.com/magnesium/ So I can certainly understand the difficulty they had packing a 150 picometer-radius magnesium atom into a position for suitable for a 130 picometer gallium atom. They must have used a shoe-horn to pack the magnesium into the spot! Zinc's 135 picometers looks far more easily matched!
Merry Christmas. And you're welcome!
>Jim, it would be interesting to focus on isotope separation techniques. i get the impression that lack of affordable options precludes the use of enriched elements in most manufacturing.
By far the cheapest method of separating isotopes involves the gas centrifuge. But in order to employ the gas centrifuge, it is necessary to find a compound containing the target element that is reasonably stable and volatile, and hopefully well-behaved.
Zinc can be separated by Gas Centrifuge: I think one compound is dimethyl zinc. Although, if you actually saw dimethyl zinc you wouldn't label it "well-behaved"! In air, it's not only flammable, it's also self-igniting! (This video is actually diETHYL zinc, but it behaves similarly!)
https://www.youtube.com/watch?v=99wPiMb-k0o At 2:15 Wow!
Fortunately, gas centrifuges are nicely-sealed systems. And, there is a huge excess of otherwise-unused gas centrifuge capacity in the world. Why? They built them to separate uranium isotopes, and when you've separated all the uranium you need, they don't (currently) have anything to do with them. So, when the need for separated isotopes explodes, some day, there will be no lack of gas centrifuges to make them.
The 'worst' (costliest) way to do separations is by the Calutron,
https://www.youtube.com/watch?v=HC8LUTisqPQ which can be thought of as a huge mass-spectrometer that has 'buckets' that collect the isotopes that get deflected by the magnetic fields. A few years ago, I was quoted a price of about $17,000 per gram for Hf-177 and just about the same price for Hf-179.
A few years ago, I wondered if it was possible to do Hafnium isotope separation using a gas centrifuge. I found a reference to a study in Russia where they used a Hafnium isotope (Maybe it was Hf-174?), still mixed with other Hafnium isotopes, to study its radioactive decay. They used a relatively large amount of Hafnium, maybe a kilogram, which was said to have been separated from zirconium years ago (in the Soviet Union era). The researcher who is currently using that Hafnium said that they really didn't know how or why this particular element, hafnium, was separated. This was NOT an isotopic separation, just a separation of two elements of rather large mass-difference.
But it tells me that it is possible do form a gaseous compound containing hafnium that can be centrifuged. The reason they don't do that, yet, is presumably because the demand for Hafnium isotopes is (so far) quite miniscule. I calculated that it would take about a milligram of hafnium to cover a 300 millimeter silicon wafer with 2 nanometers of a hafnium dielectric. (Assuming no wastage.) Or, $17 per wafer, which I think the industry will find economical.
>have you given this aspect consideration?
Extensively! Repeatedly! Over and over again!
I have understood, for well over 11 years, that the main limitation to isotope inventions is there it is necessary to get more than the cost of the isotopes separated in order to make an isotopic invention 'work'. Fortunately, as of now I have figured out many dozens of separate isotopic inventions that will probably provide more such benefit than the costs involved.
Jim Bell