Number
143-EN
Section
General Section
Use
Sector
Manufacture of basic metals, including alloys
Manufacture of fabricated metal products, except machinery and equipment
General manufacturing, e.g. machinery, equipment, vehicles, other transport equipment
Building and construction work
Function
Conductive agent
Process
Manufacturing and processing of minerals and/or metals at substantially elevated temperature
Open processing and transfer operations at substantially elevated temperature
Handling of solid inorganic substances at ambient temperature
Product category
Welding and soldering products, flux products
Application
additive in electrodes used for welding
Abstract
Thorium dioxide is used in electric welding as additive to tungsten refractive rods. One of thorium isotopes is hazardous, because is radioactive, therefore alternatives were sought.
Substituted substances
Thorium dioxide
CAS No. 1314-20-1 EC No. 215-225-1 Index No.
Chemical group
Thorium compound; oxides
Alternative Substances
Cerium dioxide
CAS No. 1306-38-3 EC No. 215-150-4 Index No.
Chemical group
Metal oxides; lanthanides
Lanthanum oxide
CAS No. 1312-81-8 EC No. 215-200-5 Index No.
Chemical group
Lanthanum compounds; metal oxides
Reliability of information
Internet information: data are from an internet document and only a basic and partial evaluation could be performed
Reason substitution
other toxic effects
Hazard Assessment
Substance to be substituted: Thorium dioxide is not included in the EU harmonised classification. But thorium 323 isotope is radioactive and classified as carcinogen by IARC. Alternative substances: Alternatives cerium oxide and lanthanum oxide are not included in the EU harmonised classification. They are not listed in the database for substances known to be of high concern (SDSC) according to SUBSPORTplus criteria.
Description of Substitution
Thorium oxides are used as additives in electrodes for electric welding to improve rods stability and to facilitate arc starting. Because the rods may contain an isotope of thorium that is radioactive and therefore carcinogen, workers' health may be at risk. Alternatives to thorium oxide are available and in use. Cerium oxide or lanthanum oxide can replace thorium oxide as additive in rods. They are more expensive than the thorium rods, but provide good welding quality, especially for manual welding.
Case/substitution evaluation
The substitution is easy to implement but the alternative has higher costs. It helps eliminate the use of a substance that may contain a radioactive isotope. Worker exposure may occur during welding but it seems that exposure during the re-shaping the point of the rod is generating even higher exposure (see Further Information). Because of the long half time of radioactive thorium all wastes containing it present a long-term hazard for the environment.
State of implementation
In use
Date and place of implementation
France
Availability ofAlternative
Alternatives available on the market
Type of information supplier
Research
Contact
INSTITUT NATIONAL DE RECHERCHE ET DE SÉCURITÉ pour la prévention des accidents du travail et des maladies professionnelle), France, http://www.inrs.fr www.inrs.fr
Further information
Type of publication and availability
Fact sheet freely available on internt in French
Publication source: author, company, institute, year
The Fact sheet was developed by CNAMTS and INRS, France and published by INRS on its website in 2008.
Publication source
Type of publication and availability
http://www.inrs.fr/accueil/produits/mediatheque/doc/publications.html?refINRS=FAS%2020
Date, reviewed
December 11, 2020