Substances that load up with D.

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Substances that load up with D.

Postby chrismb » Wed Nov 30, 2011 1:59 pm

Doug, in another thread you have posted;

The books also mention Zr, which I've got and should be relatively easy to sputter. In the Ti case, the issue is prep of the Ti and doing it in an atmosphere really free of O and N and COx - so you'd have to ship it to me in argon or something, else it will refuse to accept any D (or that other isotope).


Some questions on this;

1) If D has problems loading into Ti if exposed to these gases first, then is that true for any piece of Ti (or is it just very thin sputtered layers)?

2) If Ti can get contamination easily by exposure to the atmosphere then a) is there a means to rid a piece of Ti after it is installed in a vaccum (viz. would a long bombardment period not undo any such exposure effects) and/or b) is there another material (you mention Zr) whose D-adsorbing behaviour is not degraded following atmospheric exposure?

3) I find it interesting that these materials are [I think?] also the same ones that have the least secondary electron/sputtering rates. Is this co-indicence?
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Re: Substances that load up with D.

Postby Doug Coulter » Wed Nov 30, 2011 3:45 pm

Those are good questions I think we're going to have to find the answers to the old fashioned way. The issue with the Ti is that O, N etc don't absorb so much as combine into very stable compounds (see how hard it is to reduce in the rare metals handbook - it's why it's so expensive). My guess would be that you could sputter or blast off the bad surface layer if you put it on a little thick to start. Just have to try it!

Most of the older stuff used Zr, which is why it's in the literature. Zr lets go of D easier, so Ti would be better if you couldn't actively cool the target. Zr also likes to combine with air...
In the U of Wis paper they did something I think stupid - they evap'd the stuff with D present, which makes TiH - which is a very crappy material (stiff and brittle) for a thick coating, no wonder they had troubles. You can load it up the right amount after deposition by heating it in D, or driving it in with the beam, though, and that leaves a ductile matrix, should work better (and that's how the big boys report doing it). For T, you'd want to use the beam method so as not to have as much of that around the place. Evidently around 4-500C Ti will eat D just fine, you let it cool in that atmosphere and it loads up fine, wastes a little D that's left over, but not bad considering.

Ti has less stopping power than Zr, being lighter, so it lets any incoming ions that miss on the first layer retain more energy for possible fusion deeper in.

Clean metals aren't that low in secondary emission compared to say, carbon, though. No matter the metal, though, the more electropostive ones are the worst for that - and Ti, stripped of it's oxide coating (it gets one like Al) is pretty positive. Low sputtering is true of Ti, at least. But it definitely sputters some. You can see it on my tank walls from running Ti grids, and it may account for my somewhat better results? :?: Obviously we have more to learn here. Right now, I'm still chasing leaks, and what turned out to be a bad valve in my forepump, sigh. Gotta tear it down and rebuild it, and they stuffed it in there real tightly.
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Re: Substances that load up with D.

Postby chrismb » Wed Nov 30, 2011 6:08 pm

Doug Coulter wrote:Ti has less stopping power than Zr, being lighter, so it lets any incoming ions that miss on the first layer retain more energy for possible fusion deeper in.


Did this mean to say that Ti, or Zr, allows more energy to be retained?

To clarify, Ti is lighter than Zr, and kinetic energy of a colliding particle is lost according to how close the projectile's mass is to the target mass. A higher mass target means less KE lost for a light projectile.
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Re: Substances that load up with D.

Postby chrismb » Wed Nov 30, 2011 6:09 pm

So, the tokamak JET folks are always complaining that their graphite walls retain T (so is a radiological hazard for them), does this mean carbon is a viable material for this purpose too?
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Re: Substances that load up with D.

Postby Doug Coulter » Thu Dec 01, 2011 10:00 am

We're not worried about the all-too-rare collision between a D nucleus and one of the metal in the target. It's those pesky electrons that slow incoming D's down very quickly as they try to penetrate to the point they find another D. More charge = more electrons = more loss per atomic layer, pushing those around. Targets are often specified in kev/something (usually mass or thickness) of stopping power due to this. The neutron spectroscopy boys like "thin" targets by this measure so all the reactants have consistent energy, producing narrow band of neutron energy to work with. Ti gives you more real H cross section available per thickness in kev than anything else reported on that doesn't easily lose all the H due to heat.

I don't have a clue about graphite - there's a ton of forms that would all act differently, I suspect. Kohl covers this pretty well for vacuum tube uses and points out some big variations in properties depending on processing. We've looked for and not found significant hydrocarbons after a run on the mass spec, FWIW - something one might worry about when bashing hot H into carbon. On the other hand, T is so hot that it wouldn't take much retention (for example, not enough to be useful to a beam-target device) to still be a big problem safety wise. Carbon can get into so many diverse forms - perhaps many in the same sample - who knows?

To the extent we notice any time-variable behavior in my fusor, it's best at the start of a run, before things heat up. Not sure if that means anything much in this context, and it's not a huge effect, maybe ~5% output.

The "Fast neutron" books from Rice indicate people have had luck with gray chromium plating, and a couple sources give real variable takes on gold. Silver as a backing (behind the D-holding substance) has mixed reviews, blistering being mentioned. My takeaway from this is those guys don't know much about laying down a good film of *anything* and are seeing all the same problems I had as a beginner at evap deposition, sputtering, electroplating. Things have to be so insanely clean to get a good job, and parameters have to be so tight, that only a surface science guy gets it - or maybe a semi or vacuum tube manufacturer. Some very refined shops hit the required levels these days with tight controls, but a scientist/academic futzing around in his lab generally wouldn't realize how hard it is.
Or to put it more bluntly, assume they knew it all and industry had nothing to teach them, but they really don't know quite a lot of practice. The thing is, due to trade secrets, industry wouldn't be telling much unless you dig pretty hard. The U of Wis paper recently put up here and fusor.net points this up. Their technique for depositing Ti was pretty ignorant and bound to lead to the terrible results they had with some of it.

Pd and Pt were used some as well, but they give back the hydrogen too easily as does Tantalum it seems. That high Z (A really is what matters) is a big issue too - how much energy does the beam lose going through the stuff on its way to the desired H isotope target is really important. That's why I was looking into the somewhat bizarre idea of using oriented silicon crystals, that look like a bunch of open pipes from one orientation, as any scattering would tend to send the D down the middle of those pipes, with low loss to the electron clouds along the way.
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Re: Substances that load up with D.

Postby Jonathan Schattke » Wed Oct 08, 2014 2:21 pm

Our neutron generator http://www.adelphitech.com/products/dd109.html here at Missouri University of Science and Technology is a Ti target with 20keV D accelerator; the target is a "v" shape, in order to spread the heat. There is a delay in reaching peak flux, because of the load-up time.
Ti has the advantage that an atom of hydrogen will fit nicely in the lattice gaps, but any similar lattice would work as well. I have heard of Palladium, Platinum, and tungsten used as target material (in the LENR community).
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Re: Substances that load up with D.

Postby Doug Coulter » Fri Oct 10, 2014 2:05 pm

One problem with modern science, or should I say, modern academics, is a short memory. You might find this stuff from the '50s interesting. The neutron generator stuff is at the end of the chapter.

This book also contains the design info for plasma triodes - something I saw "invented" again about 2 years ago on physorg, as if...they were used in car radios way back when...I could go on (and on) about people re-inventing the wheel.

I've tried various coatings for my fusor tank walls, Ti and Pd among them. The trouble with Pd is that it gives it back up too easily, and not only that, the high Z means it's very good at making more X rays when electrons hit it. Don't do that.
Ti, well, my first few attempts failed as I made it too thick. Turns out it will load up with so much D as to become TiHx, which sadly, has very different mechanical properties, and flakes off if put on too thick. As I said above, the devil is in the details here. The Ti has to be thin, and on a compatible substrate you can keep cool, as temps in the couple hundred C range make it lose all its H (or D), which in my system gives me not only gas pressure control issues, but eventually no D in the wall where I want it, since it's hard to keep the inside of the tank wall (stainless steel) that cool from the outside - the SS is a lousy thermal conductor.

Interestingly, when the Ti coating is right, and loaded, the total fusion in our machine more than doubles - it seems D (of whatever flavor and charge) is slamming into the walls quite hard - maybe charge exchange is causing that. We (and this was duped in another lab) first thought we were seeing beaming of the neutrons,but it wasn't (no math or prior work supports that at these energies, FWIW). It was simply locality of fusion where the beams hit the D in the tank walls.
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Re: Substances that load up with D.

Postby Jonathan Schattke » Sat Oct 11, 2014 12:24 pm

My theory on the fusion rate of D-D in a matrix is that the energy required to push a hyrdogen atom through the lattice gap acts as an additional force on the Deuterium in the lattice, and thus even fairly low energy deuterium impacting the surface will set up a wave of deuterium being dislocated, and at each dislocation there is a dwell time with two atoms in a lattice position with a small but real chance of fusion.
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