Aluminum cathode melt-down

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Jon Rosenstiel
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Aluminum cathode melt-down

Post by Jon Rosenstiel »

Was testing out a 6061 Al cathode in my cube fusor the other day and got carried away a little. Seems it couldn't handle the kW I threw at it. What seemed a little unusual was that the neutron count started climbing as it was melting. (Then, of course, dropped to zero when it finally fell off the hv stalk)

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Frank Sanns
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Re: Aluminum cathode melt-down

Post by Frank Sanns »

Results, no matter how confounding they seem, often lead to new discoveries. A good researcher notices things others totally miss.

Not saying there is any new physics there but it is always good to figure a at least a plausible mechanism for what you observe.

Geometry change? Symmetry change? Work function? Conductive path with vaporizing metal? An extra side aperture for ion collisions?
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Mark Rowley
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Re: Aluminum cathode melt-down

Post by Mark Rowley »

I'm leaning towards the "extra side aperture for ion collision" angle.

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Richard Hull
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Re: Aluminum cathode melt-down

Post by Richard Hull »

Interesting result. Super loading as the Cathode heats? Frank brings up a lot of ideas. Too bad we can't make a nice thick, heavy palladium cathode. It would not melt as easy.
Light metals might be the answer for a cathode.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
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Jon Rosenstiel
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Re: Aluminum cathode melt-down

Post by Jon Rosenstiel »

At the time it failed I was about 30-minutes into a electrode conditioning run, attempting to burn off the aluminum oxide layer. I've not done this before so have no idea how long it should take for the oxide to burn off, but judging from the low NPR I'd say it was most likely still intact. So maybe the increase in NPR was due to the oxide starting to burn off? Or maybe my cube just doesn't like aluminum cathodes?

The aluminum cathode was a replica of my best performing 304 SS cathode. Before the aluminum one failed it's NPR was about one-half that of the SS cathode.

At the time it melted my first thought was along the lines of "conductive path with vaporizing metal".

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Re: Aluminum cathode melt-down

Post by John Futter »

It might be the aluminium was starting to act as a getter that was purifying your fusor interior ie water vapour and stray nitrogen and oxygen from air
hot Al is extremely reactive
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Richard Hull
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Re: Aluminum cathode melt-down

Post by Richard Hull »

Aluminum that is pure and clean is extremely reactive. The thin oxide coating is really alumina! They make high temperature crucibles out of alumina! Other high temp crucibles are titania, zirconia and thoria.
Of course a thoria crucible is pretty hot to start with..... could not resist that one.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Maciek Szymanski
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Re: Aluminum cathode melt-down

Post by Maciek Szymanski »

My 2 cents:

My hypothesis is that the fusion rate should increase with the increased ionization ratio. The ionization ratio increases with increased electron emission from the cathode (more electrons - more collisions with deuterium molecules and more deuterium knocked out by electrons from the walls). And the thermionic current for aluminium (work function 4.25eV) in the 1500°C region increases by almost an order of magnitude per 100°C. So I suppose that the poor cathode was giving all the electrons it could while was melting.

image.jpg

An the second tough - why not make the graphite cathode? It will withstand temperatures close to tungsten but is inexpensive and easy machinable. It will outgass like a hell, but a short high current dry run on air to heat it prior to final pumping and admitting deuterium should solve this.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland
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Richard Hull
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Re: Aluminum cathode melt-down

Post by Richard Hull »

Good thinking! Yes the torrent of electrons off the aluminum or any internal grid bombard the shell or walls and these create "knock out" deuterons from the deuterium neutrals buried there, creating deuterons just where we want them created the huge surface area deuteron emitter, the shell!

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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