Thorium dioxide

Thorium dioxide, also known as thorium(IV) oxide or thoria, is a chemical compound made of thorium and oxygen. It has the chemical formula . Like every thorium compound, it is radioactive.

It can be found as the mineral thorianite. Thorianite is similar to pitchblende, but rarer.

 Properties 
Thorium dioxide is a refractory material with a melting point above . This is the highest known melting point of all oxides. Only a few elements and some specialized compounds have higher melting points.

Thorium dioxide shines with a bright blue light when heated and exposed to air. It is candoluminescent, meaning it emits more visible light than an ideal blackbody would at the same temperature. Because of this, people used to use thorium dioxide in gas mantles, especially mixed with cerium dioxide.

 Sources 

Category:Oxides
Category:Actinide compounds