Hi Dan,
!!!! - I want to see the process and of course results, good luck!!!
thanks! I have a rotary pump here that goes down to 10^-2 mbar, which is
not terribly low (a diffusion pump would sure be nice), but it is OK for
a start. My current problem is leaks leaks leaks, my system gains .1
mbar per second when the pump is deactivated, I have to improve the setup.
But my "tube" is nothing special, only two parallel wires in a glass
tube, so not even a symbol, it is a simple glow lamp.
What is the process steps to fill the gas mixture in to? I'm handy
with all glassblowing but process of evacuation and filling with gases
is new for me.
Actually, you need to pull down the tube to a good vacuum (better than
0.01 mbar) and hold it there. While there, you flash the tube, i.e. heat
the cathode and anode, and basically every metal part inside the tube
with an induction heater. This is how you get rid of all the
contaminations inside the metal components.
After that you fill in the noble gas / gas mixture until the pressure
reaches your desired value or the glow discharge ignites, and then you
seal of the tube.
Another alternative is to bake out all impurities before: put the metal
parts in a quartz glass tube and then put this tube in an oven at 800
degrees Celsius or so. This heats the metal very well and leaves the
quarz glass unharmed because it has a very high deformation temperature.
The Quarz glass tube needs to be pulled close to vacuum, of course.
Of couse, when cooling down etc. the metals pick up some impurities
again, but it is not that much if you are careful.
Another idea is to include some kind of getter (Barium) inside your tube
that binds impurities (not the noble gases, of course, they are called
noble for a reason).
Jens
Sorry for noob questions.
Dan.
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