Ned Simmons wrote:
On Sun, 21 Oct 2007 00:33:17 GMT, "Harold and Susan Vordos"
wrote:

Slight variations in density are

likely due to the degree of fusion. Dunno! :-)


That's more or less the situtation with the density. Fine tungsten
powder is pressed into bars. The bars are resistance heated (imagine a
rod the size of your thumb glowing at 4800F!) to sinter the powder.
The bars shrink and get denser as the tungsten crystallizes. Swaging,
rolling, and drawing increase the density and deform the crystals,
yielding the typical fibrous structure.

Lamp filaments run hot enough that the tungsten recrystallizes, which
is why a filament is more fragile once it's burned for a while.

This is SURE true! I make filaments for our vacuum leak checker
at work. I have a couple small spools of Tungsten wire (.007")
that comes annealed. It is a certainly stiffer than copper or
even mild steel wire, but not brittle at all. After a filament
has been in the machine, even for a few minutes, it is totally
impossible to do any work on it. Even the slightest touch, or
especially fiddling with the screws that mount it will cause it
to shatter.

Jon