Definition
A naturally occurring radioactive metallic element (chemical symbol Th, atomic number 90) that, in aviation, is added in small amounts to certain materials to improve their performance at high temperatures. It is most commonly used as an alloying additive in tungsten electrodes for inert-gas welding and historically in the gas mantles and coatings of some lamps and instrument components.
Plain English
A slightly radioactive metal that is mixed in small amounts into other materials, mainly welding electrodes, to help them stand up to very high heat.
Context Anchor
Seen in aircraft maintenance, welding, shop-safety, and material-handling references.
Derivation
Named after Thor, the Norse god of thunder, by the Swedish chemist who identified it in 1828. The name was chosen to mark it as a powerful new element, and it persists in modern aviation materials science.
Why Pilots Care
Pilots themselves rarely handle thorium, but maintenance technicians do. Thoriated tungsten electrodes are slightly radioactive, so handling, grinding, and disposal follow specific safety practices in the maintenance shop.
Intuition Check
Thorium is not a special aircraft part or a type of fuel. In this context, it is a chemical element that may be present in a maintenance material.
Example Sentence 1
The technician selected a thoriated tungsten electrode to weld the engine mount because thorium helps the tip hold its shape under the heat of the arc.
Example Sentence 2
Technicians followed special procedures when machining the thorium-containing bracket.