Titanium RF properties (was Thorated vs Pure Tungsten)

>Someone asked (a few days ago) about using titanium as electrode
>material. While I am not sure about the RF characteristics of Ti, I do
>know that Ti can burn (very similar to Mg), so it might not be a wise
>idea to use it. Esp. if they are small in diameter and run at high
>power (multi kVA) levels. Due to this factor, the electrodes might
>not quench (if they start to burn, you canīt "quench" with anything
>but sand..... Sorry for the pun, but I couldnīt resist ;o]) very well.

Titanium is often used in pyrotechnic blends to get nice white sparks with
the added benefit of a dense white smoke (TiO2) which makes the colors show
up better.

About the RF properties of Ti: JPL has a pair of small probes with Titanium
antennas that will be dropped from orbit around Mars and embed themselves in
the dirt (no parachute, so they hit going up to 200 m/sec). The antenna
looks like a 6-8" long spike tapered from 1/2" diameter at the bottom to a
point on top. It is made from titanium because it has to take a 60,000 G
shock on landing. (lots more at http://nmp.jpl.nasa.gov/ds2/ )

We found that Titanium is a terrible RF material for VHF and UHF
frequencies. It forms an oxide layer, much like aluminum, but, much to our
dismay, the oxide is semiconductive and very lossy (Al oxide is a good
insulator). Skin effect, particularly at our frequency of about 400 MHz,
made our signal travel in this lossy layer...Arghh. The moral of this story
is: don't wind your primary out of Ti tubing, or use Ti wire for the
secondary. However, in a spark gap, it would probably work OK, since skin
effect isn't a big issue. Ti is a real pain to machine, though (don't think
you are going to use a regular hacksaw to shorten those surplus Ti bolts you
got, for instance).