Re: Thoriated Tungsten Electrodes

[William Kolb <William.Kolb@faa.dot.gov>]

Jason, 

Tungsten welding rods intended for electric inert-gas welding are alloyed with 1
to 2-percent thorium oxide to improve electron emission. The addition of this
small amount of thorium increases the alternating current carrying capacity by
approximately fifty-percent for a given size electrode. This translates to
reduced welding equipment cost.  In direct current applications, electrodes are
often ground to a taper or point and the addition of thorium helps retain this
shape.  Zirconated electrodes are also available but I'm not aware of other
tungsten alloys. 
 
Although thoriated rods can produce surface radiation rates of about 0.1 mR/hr,
inhalation of radon-220 and radioactive materials volatilized during grinding,
welding and incineration of the discarded rods are the major source of exposure
for welders and people working with welders.  

bill
william.kolb@faa.dot.gov
_______________________________________________________________________________
Subject: Thoriated Tungsten Electrodes
From:    jgf7@cdc.gov at Internet
Date:    12/16/97  5:06 AM

Hello Radsurfers!

I would like to know why Thorium (Th-232) is used in
tungsten electrodes during arc welding ?

Have other elements (actinides?) been used to
replace thorium in electrodes?

A short abstract on this subject was written by
Crim et al  in the June 1993 Health Physics Journal
(Vol 64, S85).

The author lists the advantages of Th as:
easier arc starting, reduced weld contamination,  and
greater stability.

Any other information on this topic would be of interest
to me,    Thank you,

               Jason Flora
               Cinc   OH
(Comments are those of the author and not my
employers)