I wonder if anyone could steer me in the direction of an answer to a
question I have regarding an effect I have observed in numerous lab runs. I
am growing rare-earth boride crystals in BN crucibles in a graphite element
heated vacuum furnace. The element is a vertically serpentine cylinder, and
the crucible is located as close as possible to the center point. The
resultant polycrystaline products always seem to have a hollow vortex-shaped
void running almost to the bottom, generally with some sort of a twist near
the bottom. It is somewhat like what looking down a tornado might be. The
material is electrically conductive, and does not climb to wet the surface
of the crucible like a metal would, though there is some loose deposition
presumably from vapor. Could this possibly be the result of fields from the
heating element, surface tension, or something else? I would like to
eliminate this effect, and would greatly appreciate any suggestions.
57 North Putnam St.
Danvers Ma. USA 01923
"To invent, you need a good imagination,
and a pile of junk."
--Thomas A. Edison (1847-1931)
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