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Re: Thorated vs Pure Tungsten

The thorium could easily cause the sporadic firing. The alpha and beta
particles
coming off the thorium would ionize the gap, and the laws of probability
would say
that every so often, a few would shoot out in a line and ionize enough for the
existing voltage to go the rest of the way. It's the same effect that makes a
Geiger counter work--when a high-energy particle passes through, it ionizes the
gas, and in the geiger, it's set just at the breakdown voltage, so when one
goes
through, it trips the arc over.

Tesla List wrote:

> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
> At 04:08 AM 6/15/99 +0200, you wrote:
> >Hi Terry, all.
> >
> >My comments below.
> >
> >> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> >> I use 1/8 inch diameter thorated tungsten rods in my new neon
> >>protection circuit as safety gaps. However, they tend to
> >>sporadically fire at low voltages. The ends are cut pretty square
> >>instead of being rounded.  I can replace the rods with the pure
> >>tungsten ones and grind them round on the ends.  However, I
> >>was just wondering if the thorium was mostly to blame for
> >>the sporadic firing or the square ends?  This happens with nothing
> >>else connected except the neon running at full normal voltage.
> >>
> >> I really think, now, that the pure tungsten is by far the best for
> >>Tesla coil applications. The slight radioactivity of the thorated
> >>versions is unsettling and this sporadic firing thing is a pest. The
> >>tungsten rods seem to be far far better than anything else I
> >>have used and are definitely the way to go for gap electrodes,
> >>as so many have found...
> >
> >
> >The reason why thorium is used at all, is to decrease wear in their
> >normal (tig welding) usage. For a safety gap (which shouldnīt fire
> >at all ;o]), this is of no interest, so you can use the non-thorated
> >ones here anyway. For welding aluminum, magnesium (i.e: easily
> >oxidized materials) you weld with AC (to continiously rip up the
> >oxide coating). During welding minute quantities of thorium can be
> >embedded within the weld bead. For this reason you canīt use
> >thorated electrodes, when welding Al, Mg, etc. This will contaminate
> >and weaken the weld bead (it gets brittle). For welding steel, the
> >thorated ones allow a higher current (for equal wear). Interestingly
> >enough, the thorium also prevents "sticking" of the tig electrode (you
> >can start the arc with HF power = no contact of the electrode with
> >the base material or you can "strike it like a match" to start the arc).
> >This is of great importance to the weldor, because any tungsten
> >in a weld bead (due to sticking and breaking off) will absolutely RUIN
> >the weld bead. It must be completely ground off and rewelded. The
> >metal tungsten is almost impossible to melt. Even the 50,000°F of a
> >plasma cutter or plasma welder will only very, very slowly erode this
> >material. This superb resistance to wear and high temperature stability
> >is what makes it such a great RSG electrode. The newer (but non
> >thorated) replacements for the thorated electrodes are a composition
> >of different materials (no idea what exact materials they are made of,
> >except that it isnīt pure tungsten), that have similar wear and start-up
> >characteristics of the old thorated electrodes. My guess is these are
> >probably the best for RSG usage (i.e: no radioactive material, but
> >better wear characteristics than pure tungsten). If you use a side
> >pick-up arrangement on the RSG, you probably can use the pure
> >tungsten ones too, because the arcing surface is much, much
> >larger than on an end-to-end setup.
> >
> >You sporatic firing might be due to small quantaties of thorium being
> >burned in the arc. Where does the spark jump (from the middle or
> >more at the edges of the thorated electrodes)? What color is the
> >arc?
> >
> >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.
> >
> >
> >Coiler greets from germany,
> >Reinhard
> >
>
> Hi Reinhard,
>
>         The sparks are thin purple blue that occasionally shoot from the
edges.
> Today I picked up some pure tungsten and cut it but I haven't tried it yet.
>
> Apparently TIG rods come in all kinds of "flavors".  These are from NASCO
> and they offer the following types:
>
> ZIRTUNG
> 2% Thoriated Tungsten
> 2% Ceria Tungsten
> PURETUNG (pure tungsten)
> 1% Thoriated Tungsten
> TUNGSTEN-LANTHANA ONE POINT FIVE
>
> They are available in the following stock diameters:
> 0.040"
> 1/16 "
> 3/32 "
> 1/8 "
> 5/32 "
> 3/16 "
> 1/4 "
> 3/8 "
>
> They also come in the following lengths:
> 3 "
> 6 "
> 7 "
> 12 "
> 18 "
>
> The guy at the shop said he could order any of these, although, I hate to
> think what 18 inches of 3/8" would cost!  However, 3/8 inch tungsten
> electrodes would run a lot of current!!
>
> I'll see tomorrow if the pure tungsten cures the arcing.  If not, I'll try
> to round the ends. If all else fails, I have brass rods that I could solder
> 1/4 inch steel balls to ;-)
>
> Cheers,
>
>         Terry