Turns out, yes, you can. :(
Molten alumina is a bit weird, I'm not sure whether it's thick and
sticky or thin and sticky. I guessed the first, the latter seemed more
in tune with what happened - but I haven't worked it out. Getting the
tube to blob and seal over was unexpectedly hard, or rather it didn't go
as expected - but by no means impossible.
To stop the tube cracking, get an insulating firebrick, grade 26 or
better (grade 23 won't do), drill a deep hole a couple mm larger than
the alumina tube, and insert the tube so only a cm or two are showing.
Surround the tube end at a distance of an inch or so with some extra
bits of firebrick to form a hearth. It helps to be able to turn/rotate
Oxy/MAAP (real MAPP, not propylene), 1/4 by 1/8 Omegatite 450 99%+
impervious alumina thermocouple protection tube, j26 firebrick.
For reference, if anyone is interested.
Now, how do you weld miniscule 0.005" 0.0125mm tungsten/rhenium
thermocouple wires together?
Anyone know of a source of tungsten tube, about 3mm OD, in 6" lengths?
They make 1" lengths for fishermen...
The traditional method is to twist the ends together and use capacitor
discharge between both cores commoned together and a piece of platinum,
tungsten, graphite, whatever is appropriate.
Voltage and capacitor size are subject to experimentation.
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