During these decay processes, it has been found that radioactive materials are formed, including radium and radon. These substances give off radiation, including alpha and beta particles, and gamma radiation, which can be extremely harmful, and usually fatal to any human being when in direct contact with it.
In its pure form, thorium is a silvery-white metal, which is air-stable and is capable of retaining its luster for several months. Pure thorium is soft, very ductile, and can be cold-rolled, swaged, and drawn. Thorium can only be thrashed by water at a very slow pace and does not dissolve readily in most common acids, except hydrochloric acid. When contaminated with the oxide (O2), thorium slowly tarnishes in the air, becoming gray and then finally transforming into a black color. The physical properties of thorium are greatly influenced by the degree of contamination with the oxide. The purest specimens have been found to contain several tenths of a percent of the oxide in the high-purity form of thorium. Thorium has a boiling point of 4790°C and a freezing point of 1750°C. Thorium oxide (ThO2), also called thoria, has a melting point of 3300°C, which is the highest of all oxides. Only a few elements, such as tungsten, and a few compounds, such as tantalum carbide, have higher melting points. Powdered thorium metal is often pyrophoric and should be handled with extreme caution. When heated in the air, thorium metal turnings ignite and burn with a brilliantly white light. Because of these numerous characteristics, thorium has a wide variety of uses ranging from household to industrial applications. .
Some common uses of thorium are in light bulb elements, arc-light lamps, welding electrodes and heat-resistant ceramics. The principal use of thorium has been in the preparation of the Welsbach mantle, used for portable gaslights such as lanterns. These mantles, consisting of thorium oxide with about 1% cerium oxide and other ingredients, glow with a dazzling light when heated in a gas flame.