Usage of brass in a demo fusor

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John Doe
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Usage of brass in a demo fusor

Post by John Doe » Sat Dec 29, 2018 4:51 am

I recently stopped by a Home Depot, and picked up some 1/2” hose barbs and adapters for my demo fusor. I remembered though, that brass internals in vacuum systems were not ideal. I read that brass and it’s zinc coating usually outgass easily (my demo fusor will be running @50 microns), and don’t know if I should use the barbs or not. They were pretty cheap so I’m not sure if they will do well in a vacuum. Any experiences? Recommendations?

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Richard Hull
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Re: Usage of brass in a demo fusor

Post by Richard Hull » Sat Dec 29, 2018 4:59 am

Brass should be OK on a demo fusor. I used brass ball valves on fusor I and II and ran as low as 10 microns just fine.

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John Doe
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Re: Usage of brass in a demo fusor

Post by John Doe » Sat Dec 29, 2018 5:06 am

Thanks Richard.
I also have a length of 1/2” nylon reinforced vinyl tubing, the barbs don’t fit snuggly on their own. Just making sure, I have to use clamps on these connections, right?

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Dennis P Brown
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Re: Usage of brass in a demo fusor

Post by Dennis P Brown » Sat Dec 29, 2018 11:17 am

Clamps are fine on use of a hose for your device.

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Richard Hull
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Re: Usage of brass in a demo fusor

Post by Richard Hull » Sat Dec 29, 2018 5:41 pm

The whole idea of a hose barb is that your hose is going to be a bit smaller and a force-fit is necessary to tightly slide over at least two of the barb's ridges, (hopefully more). If it is a loose fit, then yes, a clamp would be demanded.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

ian_krase
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Re: Usage of brass in a demo fusor

Post by ian_krase » Sun Dec 30, 2018 2:44 am

Brass outgasses, but unless it gets quite hot it's pretty insignificant at fusor pressures.

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Rich Feldman
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Re: Usage of brass in a demo fusor

Post by Rich Feldman » Sun Dec 30, 2018 5:44 am

Yes, what Ian said. Zinc is more volatile than most structural metals, but its vapor pressure is below 1e-6 torr (0.001 micron) up to about 175 degrees C.
vp.JPG
Chart from https://www.powerstream.com/vapor-pressure.htm, which fails to give proper credit to original source.

The following reference lists zinc and cadmium among metals to pay attention to in high vacuum systems. (Fusors need medium vacuum).
They say that if Zn and Cd plated surfaces are exposed to vacuum _and_ get very hot, you might get films of condensed metal on cooler surfaces.
https://www.mtm-inc.com/ac-20120328-vac ... lloys.html
Of course that applies to any metal, it's just a matter of whether it happens at 300 C or 1000 C or 3000 C.
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