Cerium dioxide (CeO2) is an oxide of the rare-earth metal Cerium (chem. Ce), which belongs to the lanthanide group. Technical grade CeO2 is generally present as micro- or nanoscale white to light yellow powder.
In applications cerium dioxide gives infrared filters their anti-reflection coatings and is found in colour television tubes. Together with cobalt it serves the production of powerful magnets. As a consequence of that cerium glows intensely as soon as it is warmed-up, it is also used for incandescent mantles, combined with other rare-earth metal oxides. This leads to a considerably improved light yield of gas lamps.
In addition, cerium dioxide is used as a polishing agent for optical glasses and is applied as a grinding medium for computer parts, camera phone lenses, or CD player lasers.
A huge market for nano-structured CeO2 is cleaning and polishing of silicon wafers, which are required by the electronical industry for ultra modern chip systems and solar cells. Due to the reaction of CeO2 with the processed material, it can be removed in a way extremely fine dosed which enables the manufacturing of ultra smooth surfaces, which pose the basic prerequisite for miniaturizing circuits. Together with aluminium oxide, cerium dioxide constitutes the material of first choice in the matter of chemical-mechanical polishing (CMP) .
Nano-structured cerium dioxide, among other things, is used as an oxygen-storing diesel additive in vehicle exhaust catalysts. It still oxidises carbon monoxide and excess hydrocarbons into CO2 when there is a temporary lack of oxygen in the exhaust mixture. During that process, CeO2 is reduced to Ce2O3 that is re-oxidized later as soon as there is enough oxygen again in the exhaust gases. Aside from its role in exhaust catalysts where it mainly supports the much more active but also more expensive platinum, there is also a direct addition to the fuel intended. The cerium dioxide particles are supposed to reduce the fuel consumption as well as the emission of soot particles of diesel engines [4,6,7].
In fuel cells with other rare-earth metal oxides coated CeO2 particles are applied to improve the oxygen ion conductivity and so to enable reduced operating temperatures.
Moreover, nano-structured CeO2 poses an ideal UV absorber and is therefore used as an additive in lacquers and coatings for wood preservatives to enhance their UV stability.
Cerium, named after the planet Ceres, can relatively often be found in nature in minerals like cerite, monazite or bastnaesite (ranked 28th in elemental abundance). In combination with oxygen it is easily converted into CeO2. Apart from CeO2 cerium forms the oxides Ce2O3 and C3O4. Normally cerium dioxide is the result of the oxidation of cerium hydroxide and cerium carbonate.