How to measure the temperature of tungsten wire?

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Jeroen Vriesman
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Re: How to measure the temperature of tungsten wire?

Post by Jeroen Vriesman » Sat Jun 04, 2016 9:26 am

Thank you Roberto! (and the rest).

One question, benzene or toluene is used as the hydrocarbon for carburization, both are a bit toxic.

Is there any reason why something like butane would not work? The temperature seems high enough to break down any hydrocarbon.
Or is does the reaction require double bindings to form tungsten carbide? Would ethylene work?

And just to completely understand the process:

a) Is the carbon also reducing the ThO to Th, so the layer of tungsten carbide is not the only reason for carburization, it also provides a bigger reservoir of Th?
b) Is a short reduction cycle with H2 after the carburization useful? From some texts it seems that on top of the WC+Th layer a thin layer of W + Th is formed by reduction with H2, but Roberto's procedure doesn't include that step.

Roberto Ferrari
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Re: How to measure the temperature of tungsten wire?

Post by Roberto Ferrari » Sat Jun 04, 2016 10:55 am

Jeroen

The carbide layer will keep the Th in the filament, reducing its evaporation, no higher reservoir.

I never learned of using gaseous hydrocarbons but they may work. Is just a little more cumbersome to handle them. Try xylene, easy and low toxicity.

I never decarburized and don't see the need of. The chemistry is complex, several alternative carbides can be deposited. Horsting talk about them, related to C6H6 concentration.

See two more papers.
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Bruce Meagher
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Re: How to measure the temperature of tungsten wire?

Post by Bruce Meagher » Tue Jun 07, 2016 2:07 am

There’s lots of great info in this thread. One of the things I learned in George’s vacuum tube workshop is making temperature measurements of fine filaments using a micro optical pyrometer (like Rich and Frank mentioned). These routinely come up on eBay such as this link, and can often be had for a reasonable price. You need to correct for the absorption of the glass, and for the emissivity as described in figure 10 of the Harbaugh paper Roberto posted, to get an approximate absolute temperature.

I’ve been activating Th/W filaments in some diy triodes, but have not been able to get to a vacuum level where the Th level emission lasts but for a few moments. Also see http://www.fusor.net/board/viewtopic.ph ... ion#p66058

Below are a couple pics of my setup looking at a halogen light filament (excuse the poor picture quality through the eye piece).

I look forward to hearing about your progress.

Bruce
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IMG_7117.JPG
Optical pyrometer setup
IMG_7128.JPG
The optical pyrometer's filament is set too hot
IMG_7123.JPG
The optical pyrometer filament temp matches
Last edited by Bruce Meagher on Wed May 20, 2020 11:28 pm, edited 1 time in total.

Roberto Ferrari
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Re: How to measure the temperature of tungsten wire?

Post by Roberto Ferrari » Tue Jun 07, 2016 6:02 pm

Hi Bruce

Let us know how is your vacuum system.
Do you use some getter?

Bruce Meagher
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Re: How to measure the temperature of tungsten wire?

Post by Bruce Meagher » Wed Jun 08, 2016 6:55 pm

Roberto,

My first triode (the pickle triode) was continuously pumped with a mechanical pump (as a proof of concept). To my surprise it worked, and I even observed increase emission after activating the filament (even for just a brief time). I’m currently using a cryo trapped, turbo pump based, vacuum setup where the tube bases are epoxy to the envelope, baked, getter flashed, and then tipped off under vacuum. Th/W activation is more of a curiosity right now, and just learning practical tube building techniques is more my focus. There is a new forum http://diyvacuumtubes.com dedicated to home built vacuum tubes. Discussion about the vacuum setup might be more appropriate for that forum.

Bruce

Roberto Ferrari
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Re: How to measure the temperature of tungsten wire?

Post by Roberto Ferrari » Wed Jun 08, 2016 8:43 pm

Right!
"See" you there...

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