Cerium Oxide, also known as ceric oxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. Cerium Oxide is formed by the calcination of cerium oxalate or cerium hydroxide. Powdered ceria is slightly hygroscopic and will absorb a small amount of carbon dioxide from the atmosphere. Cerium also forms Cerium Oxide, Ce2O3, but CeO2 is the most stable phase at room temperature and under atmospheric conditions.
Cerium Oxide is used in ceramics, to sensitize photosensitive glass, as a catalyst and as a catalyst support, to polish glass and stones, in lapidary as an alternative to "jeweler’s rouge". It is also known as "optician's rouge". It is also used in the walls of self-cleaning ovens as a hydrocarbon catalyst during the high-temperature cleaning process. While it is transparent for visible light, it absorbs ultraviolet radiation strongly, so it is a prospective replacement of zinc oxide and titanium dioxide in sunscreens, as it has lower photocatalytic activity. However, its thermal catalytic properties have to be decreased by coating the particles with amorphous silica or boron nitride. The use of these nanoparticles, which can penetrate the body and reach internal organs, has been criticized as unsafe. Cerium oxide has found use in Infrared filters, as an oxidizing species in Catalytic converters and as a replacement for Thorium dioxide in incandescent mantles.