Re: general question X

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

Ralph,

Remember that in arc welding, the object is to be able to easily ignite
and maintain the welding arc. Thorium (typically 2%) is added to
tungsten welding rods because it greatly increases the thermal emission
of electrons versus pure tungsten. These thermally liberated electrons
are very useful in starting and maintaining the welding arc. Thoriated
tungsten filaments in transmitting vacuum tubes use a similar effect to
improve cathode emission versus a bare tungsten filament. 

However, when used in spark gaps, this property is really not desirable.
Pure tungsten would be prefered in order to improve gap quenching
performance. Because it's recognized that thorium or thorium oxide
dust/vapor presents a very real cancer hazard when inhaled, the welding
industry is migrating to non-radioactive alternatives to thorium. 

While coilers are not subjected to the long term exposure seen by
professional welders, we should still take note of this unnecessary
danger. This is a second reason to use pure tungsten electrodes. 

Better performance and lower risk - it's a no-brainer... :^)

Best regards,

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Parpp807-at-aol-dot-com>
> 
> In a message dated 6/18/01 8:46:51 PM Central Daylight Time, tesla-at-pupman-dot-com
> writes:
> 
> << The pure kind is
>  common now so best to avoid the thorium kind IMHO. >>
> 
> Terry,
> Why are the tungsten welding rods thoriated? Is it in there as an alloy? A
> coating?
> Another entry in the stupid question contest.
> Glad the list is back up.
> 
> Cheers,
> Ralph Zekelman