So it doesn't burn up? I don't know how to keep oxygen off it and how to heat it best.
The one I have is on the inside 75 mm deep and 50 mm ID. If I melt something in it, do I need to worry about stuff sticking on to the walls?12AX7 - 5-3-2006 at 09:30
Quote:
Originally posted by Quince
So it doesn't burn up? I don't know how to keep oxygen off it and how to heat it best.
I would recommend vacuum induction heating, with an atmosphere of low-pressure argon and hydrogen.
Failing that, any strongly reducing atmosphere (rich in CO or H) will at least slow it down.
Quote:
The one I have is on the inside 75 mm deep and 50 mm ID. If I melt something in it, do I need to worry about stuff sticking on to the walls?
Metals that don't wet graphite don't stick to it, but I would expect glassy ceramic materials to maybe bond to it.
TimMetalCastr - 5-3-2006 at 16:24
Alot of instructions on the internet reccomend heating it in an oven for a long time, slowly increasing the temp to drive off moisture. If you don't
do this, it may crack. That's what my friend's crucible instructions said.Quince - 5-3-2006 at 22:39
I'm curious how one would go about DIYing a suitable vacuum furnace. Has anyone here done something like this?12AX7 - 6-3-2006 at 10:48
Just get a vacuum pump, bell jar, etc. You have to have money or be very lucky, but it's nothing impossible.
TimQuince - 10-3-2006 at 01:06
Tell me Tim, what's the easiest way to do this induction heating thing?Fleaker - 12-3-2006 at 14:46
Quince: check out his project page, he details it clearly there. As far as clay-bonded graphite crucibles go, depends on what you plan to do with it.
You should of course gradually heat it up to drive off water. To keep the oxygen from reacting with it, heat the whole crucible to orange heat and
lightly dust anhydrous borax over it. The borax quickly melts forming a sticky glaze. This will protect the crucible from oxidation and facilitate
casting (the metal will not stick to it now). There are also a variety of sprays and washes designed to protect graphite crucibles; boron nitride
comes to mind.
I wouldn't even use a vacuum furnace for it, as I seem to remember graphite is prone to sublimation at higher temperatures. if anything, do what Tim
said and use a cheap vacuum pump to remove most of the atmosphere, then purge a few times with argon.
