Tungsten failure

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Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bigfoo39-at-telocity-dot-com>

Hi all...

another autopsy report on the SRSG electrodes that made contact with the
falling cap...

I brought the bolts to work today to replace the tungsten electrodes which
broke off during
the " catastrophy" ...  I decided to take a closer look at the electrodes
under the microscope
we use for metalurgical proceedures and found a rather interesting site.
The electrodes had
become extremely brittle ( squeezing with a pair of pliers shattered the
electrode as easily
as glass) upon examination, the electrode ( 3/16" dia.) had developed a 6
pointed star shaped
fissure about 1/2 the way from the center of the shaft. The inner portion
inside of the star
had a very fine grain structure ( same as new tungsten .. unused tig
welding type) the fissure
was a definate crack/gap break. The material outside the star shaped
fissure was very grainy,
large swirling crystal forms from each of the "points" of the star to the
outer diameter of
the rod. Examining a used piece of tungsten Tig rod revealed the same large
crystal patterns.

What I am going to conclude from this is that the major portion of the
current does travel on
the outer perhiphery of the conductor and that this can be considered a
possible failure mode
of tungsten when applied in a spark gap enviroment.

Scot D