Aluminium for a fusion reactor

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shazalee
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Aluminium for a fusion reactor

Post by shazalee » Fri Jul 28, 2017 11:03 am

Could I use an aluminium sheet as the base of a stainless steel cf flanch pipe? I plan to put all the feed-throughs and turbo pumps through it.

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Shaza Lee

ian_krase
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Re: Aluminium for a fusion reactor

Post by ian_krase » Fri Jul 28, 2017 7:12 pm

Not sure what you mean. It will need to be a bit thicker than a "sheet" unless it is very small. Also, aluminum doesn't really go with CF fittings very well. You would need to use one of those viton cf gaskets.

However, aluminum in general isn't a bad material for vacuum chambers as long as it is done properly. It's low vapor pressure and doesn't sputter much. The downsides are that you can't braze it, it can be tricky to TIG weld vacuum tight, etc.

Niels Geerits
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Re: Aluminium for a fusion reactor

Post by Niels Geerits » Mon Jul 31, 2017 12:35 pm

I do not have a fusor yet, however the parts that I have gathered for the vacuum chamber are Aluminum because you can get tubes and sheets made at whatever size you want for very little money in my country. From my reading I have found that you wanna keep the zinc content low because zinc will release gases in a vacuum. Also aluminum is one of the most neutron transparent materials that exists. Again I do not have a fusor yet but this is what I have read.

ian_krase
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Re: Aluminium for a fusion reactor

Post by ian_krase » Mon Jul 31, 2017 12:42 pm

Zinc is problematic if it gets hot - it evaporates. Not so bad if it is kept reasonably cool.

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Rich Feldman
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Re: Aluminium for a fusion reactor

Post by Rich Feldman » Tue Aug 01, 2017 2:56 am

Yup. That volatility came up recently in another forum that I follow: http://4hv.org/e107_plugins/forum/forum ... ost_179677
I learned that most materials have a nearly linear relationship between the logarithm of vapor pressure and the inverse of absolute temperature, and made this illustrative chart:
elements_vp.JPG
One might expect that low-melting metals have high vapor pressures, and vice-versa, but there are many examples where it ain't so. At 200 °C, VP of zinc is millions of times higher than that of lead, while the VP of gallium is still almost unmeasurably low.

Paul F. Dietz, writing in 2000, http://yarchive.net/space/metals_vapor_pressures.html includes both mercury and lead among elements that have very low vapor pressures at their melting points.
low_vp_mp.JPG
Zinc is prominent in his list of elements near the opposite extreme. Copper (bottom-most in my chart) comes in above mercury by a factor of 150.

Who has a simple explanation for the chemical bonding that makes gallium and indium have low melting points and high boiling points?
Richard Feldman

ian_krase
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Re: Aluminium for a fusion reactor

Post by ian_krase » Tue Aug 01, 2017 3:05 am

You may be able to have a lot of things plated.

In any case it doesn't seem like people in the 1940s lost too much sleep over brass.

John Futter
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Re: Aluminium for a fusion reactor

Post by John Futter » Tue Aug 01, 2017 6:47 am

Ian
Brass is quite different it is a very good candidate for vacuum work and it takes hard silver solders almost as well as copper.
I have seen all brass beam lines in accellerator halls siting at 10^-8 millibar using diffusion pumps without cold traps.
Zinc on its own and all it takes is one small screw M4 10mm long bright zinc plated to bring a big vacuum system down to being useless. zinc on its own is a very big problem.
For anybody contemplating welded aluminium
It is very unlikely that a weld does not leak either at the start or the finish of the weld. that is why when used each aluminim item for high vacuum work is hewed out of billet in one piece.

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Richard Hull
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Re: Aluminium for a fusion reactor

Post by Richard Hull » Wed Aug 02, 2017 1:00 am

I once had a fellow ask me if I wasn't afraid of leaning over a pot of molten indium, tin or gallium vapors. The vapors just don't exist at normal temperatures of their early molten state.
Lead isn't even too bad, but cadium can and has killed slightly above its molten state...Time for a fume mask with appropriate rated filters, if you play with these a lot.

Zinc is famous for "fume fever" almost never kills, but you will feel bad for a while until the zinc metabolizes.

I work with all the heavy metals in melts fairly often in my low melting point alloys work. The key is never use a flame on the metal to melt it and never take a metal much beyond its melting point (liquidus) In working with most LMP alloys, the secret is to melt the indium or tin first then drop in the lead and up the temperature slowly until the lead is in solution and only then drop in the needed cadmium. It will float on the surface and slowly dissolve like an aspirin without having to take the melt up to cadmium's melting point.

More to the point of the post.........An aluminum chamber, in a working fusor, operated above 30kv, might be a far greater x-ray hazard than a stainless steel fusor.

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.

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