New candidate for refractory grid metal club?

For posts specifically relating to fusor design, construction, and operation.
Post Reply
User avatar
Rich Feldman
Posts: 1470
Joined: Mon Dec 21, 2009 6:59 pm
Real name: Rich Feldman
Location: Santa Clara County, CA, USA

New candidate for refractory grid metal club?

Post by Rich Feldman »

This post was prompted by Mark Scott-Nash's melted grid story. Figured it was time to start a new thread, rather than to extend an old, long, misplaced one (Metallic - Non Metallic Grid under High Voltage - Fusor Input Power). In which RH stated an important point from analysis and experience:
4. Only the melting point of the pure metal is a key issue and the weak point in any metal grid.
Tungsten #1 choice. Molybdenum and Tantalum tied for #2, Hafnium #3 and maybe Titanium #4 as suitable for a real fusor.
What's missing?
Look at the elements with MP's above 2000 degrees C. (Titanium falls far short, almost as much as steel). I proposed carbon in the above-mentioned thread, recognizing its fabrication challenges. And stand in solidarity with Richard Hull in dismissing rhenium, osmium, iridium, and ruthenium -- all generally too expensive and hard.

Prominent in the pruned list is a useful metal called niobium, perhaps overlooked by many fusioneers. Nb has the 7th highest MP of all elements, right behind Mo. It's become popular in jewelry, so Internet searches for "niobium wire" point mostly to earrings and other body-piercing ornaments. It's easily prepared with colorful anodized finishes. I would love to see somebody try a fusor grid made from Nb.

Here is a catalog page with niobium wire in many grid-ish gauges, at around US $17 per one-ounce spool.
http://theringlord.com/cart/shopdisplay ... obium+Wire
There's also an ebay vendor called onyxmetall in Poland, with 2mm Nb wire for $30/meter and 2mm Mo wire for $8/meter.

To close, here's a little demonstration of the metal's excellent formability. I made and am now wearing the thinner ring in this picture. Cold-forged it from a 1/4" long, 3/8" diameter rod of niobium C-103. (Some large artifacts on the Moon are made of the same aerospace alloy, which contains about 10% hafnium.) No cutting tools were used; the piercing was done with a hammer, anvil, and my least favorite center punch. No annealing. That project belongs in yet another thread, along with the zirconium billet in same photo.
DSCN0234.JPG
All models are wrong; some models are useful. -- George Box
Tom McCarthy
Posts: 405
Joined: Wed May 08, 2013 3:36 pm
Real name: Tom McCarthy
Location: Ireland
Contact:

Re: New candidate for refractory grid metal club?

Post by Tom McCarthy »

Wait, 2mm wire? Should it not be around 30mm for the grid, or do you mean we should meld 15 wires together?

Sounds like a lot of work, but maybe I'm missing something...

Tom
Richard Hester
Posts: 1519
Joined: Thu Jul 05, 2001 12:07 am
Real name:

Re: New candidate for refractory grid metal club?

Post by Richard Hester »

There's also tungsten-rhenium alloy - more workable than tungsten and not far shy of its melting point (hard to find, though). I'd shy away from a carbon grid, as it might burn if you got an up-to-air accident.
alexsulyman
Posts: 9
Joined: Mon Jun 10, 2013 1:35 am
Real name: Alex Sulyman

Re: New candidate for refractory grid metal club?

Post by alexsulyman »

Tom,

I think you are confusing mils (thousandth of an inch) with mm (thousandth of a meter).

30 mm would be very thick for a grid. Take a look at your ruler.

Alex
Tom McCarthy
Posts: 405
Joined: Wed May 08, 2013 3:36 pm
Real name: Tom McCarthy
Location: Ireland
Contact:

Re: New candidate for refractory grid metal club?

Post by Tom McCarthy »

Yup, guess that's it Alex...Thought it was a bit off, and so did Dad when I told him 'wire 30mm thick' but just went along with it.

In Ireland here, so we're not as familiar with the Imperial units.

Cheers!
Tom
User avatar
Monroe Lee King Jr
Posts: 105
Joined: Thu Aug 22, 2013 11:57 pm
Real name: Monroe Lee King Jr
Location: Lampasas, Texas
Contact:

Re: New candidate for refractory grid metal club?

Post by Monroe Lee King Jr »

Tungsten thorium doped TIG welding electrodes are easy to get anyone try those? I'm thinking about trying that in our first fusor. Also I think induction welding of the grid elements should be better and actually easier! I'll have to do a bit more research as we approach making the grid. Not to change the topic but why not aluminum for the chamber? I can cast aluminum and machine a sphere on my lathe pretty easy.

Monroe

I suppose a industrious amateur could refine Rhenium from it's alloys with aqua regina. Rhenium would suffer catastrophic failure should you loose vacuum at 600 C as well. Rhenium would have to be worked (welded) in an inert atmosphere as well. There are a few things one could find enough Rhenium in to refine if it where important enough. It does work harden and would need to be annealed during working as well.

Edit: You can and I suggest use just plan ol tungsten electrode rather than the thorium doped ones. Forget I mentioned those :)
Edit 2: Hafnium may absorb your neutrons if your using Niobium with 10% Hafnium and ionic Hafnium is not good either! Hafinium is pyrophobic and ignites on contact with air. Hafnium dust is bad for you.
Today's the Day! We go into Space!
User avatar
Monroe Lee King Jr
Posts: 105
Joined: Thu Aug 22, 2013 11:57 pm
Real name: Monroe Lee King Jr
Location: Lampasas, Texas
Contact:

Re: New candidate for refractory grid metal club?

Post by Monroe Lee King Jr »

Tantalum would be my second choice and it is also easy to obtain as a wire.

Monroe

A Boron doped diamond filament might be interesting? :)
Today's the Day! We go into Space!
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: New candidate for refractory grid metal club?

Post by Richard Hull »

I used pure niobium for my very first fusion grid in 1999 and have also used Tantalum. Both worked great. Now, I use Tungsten only. All three metals become brittle and very hard rapidly due to hydrogen embrittlement. Such imbrittlement is as common as the seasickness in metallurgical circles and are generally to be avoided for structural reasons. We have no such restriction in the fusor at all. As a matter of fact it is a great result as the grid retains its shape forever with no springiness remaining. Just what the doctor ordered.

I settled on Tungsten as the wire is one of the highest m.p. metals, embrittles rapidly and nicely and is relatively cheap in wire form. As with all things, it has drawbacks; the worst being the coating (evaporation) on glass view windows and insulators is not easily removed with acid or alkali without damaging the glass or porcelin glaze and must be abraided from the surface of viewports and insulators using a very fine grit alundum finishing polish or Barnesite, if you can get it. I have a 1lb can stockpiled from my amateur astronomy days. It is no longer produced, is slighly radioactive and contains about 5 rare earth oxides. It polishes faster than any known compond. Cerium oxide is a great second choice and readily found. It is usually mildly radioactive due to tramp thoria.

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
AFW
Posts: 157
Joined: Sun Dec 10, 2006 5:51 pm
Real name:

Re: New candidate for refractory grid metal club?

Post by AFW »

Re carbon grids: the early carbon lamp filaments were made by heating Rayon in an inert gas stream - probably nitrogen, tho' argon would be better. A rayon grid could be pre- formed with the "wires" welded by a drop of acetone. I think carbon also tends to evaporate above red - heat, in a vacuum.
Tony Webb
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: New candidate for refractory grid metal club?

Post by Richard Hull »

Carbon grids sound nice but metals are a bit more strong and I might posit that a large D2 absorbant grid metal might be an interesting choice. Once the grids embrittle through use in a fusor, they are proof against unraveling or springing open. Who will make and use in a fusor to actually do fusion with a carbon grid? Time will tell.

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
Roy Anderson
Posts: 2
Joined: Sat Dec 14, 2013 7:23 pm
Real name: Roy Anderson

Re: New candidate for refractory grid metal club?

Post by Roy Anderson »

I would think graphene could come into play somehow here
User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 7:05 am
Real name:

Re: New candidate for refractory grid metal club?

Post by Chris Bradley »

Wouldn't a carbon grid already be layers of graphene?

How would you use 'graphene' to make a macroscopic 3 dimensional shape? Wouldn't you just end up with 'carbon'?
Post Reply

Return to “Fusor Construction & Operation (& FAQs)”