page_title: Cerium
section_title: Applications
hierarchical_section_title: Cerium / Applications
caption_attribution_description: Karl Auer von Welsbach (1858-1929)
context_page_description: Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series, and while it often shows the +3 oxidation state characteristic of the series, it also has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no biological role in humans and is not very toxic.
  Despite always occurring in combination with the other rare-earth elements in minerals such as those of the monazite and bastnäsite groups, cerium is easy to extract from its ores, as it can be distinguished among the lanthanides by its unique ability to be oxidized to the +4 state. It is the most common of the lanthanides, followed by neodymium, lanthanum, and praseodymium. It is the 26th-most abundant element, making up 66 ppm of the Earth's crust, half as much as chlorine and five times as much as lead.
context_section_description: The first use of cerium was in gas mantles, invented by the Austrian chemist Carl Auer von Welsbach. In 1885, he had previously experimented with mixtures of magnesium, lanthanum, and yttrium oxides, but these gave green-tinted light and were unsuccessful. Six years later, he discovered that pure thorium oxide produced a much better, though blue, light, and that mixing it with cerium dioxide resulted in a bright white light. Additionally, cerium dioxide also acts as a catalyst for the combustion of thorium oxide. This resulted in great commercial success for von Welsbach and his invention, and created great demand for thorium; its production resulted in a large amount of lanthanides being simultaneously extracted as by-products. Applications were soon found for them, especially in the pyrophoric alloy known as "mischmetal" composed of 50% cerium, 25% lanthanum, and the remainder being the other lanthanides, that is used widely for lighter flints. Usually, iron is also added to form an alloy known as ferrocerium, also invented by von Welsbach. Due to the chemical similarities of the lanthanides, chemical separation is not usually required for their applications, such as the mixing of mischmetal into steel to improve its strength and workability, or as catalysts for the cracking of petroleum. This property of cerium saved the life of writer Primo Levi at the Auschwitz concentration camp, when he found a supply of ferrocerium alloy and bartered it for food.
  Ceria is the most widely used compound of cerium. The main application of ceria is as a polishing compound, for example in chemical-mechanical planarization (CMP). In this application, ceria has replaced other metal oxides for the production of high-quality optical surfaces. Major automotive applications for the lower sesquioxide are as a catalytic converter for the oxidation of CO and NOₓ emissions in the exhaust gases from motor vehicles, Ceria has also been used as a substitute for its radioactive congener thoria, for example in the manufacture of electrodes used in gas tungsten arc welding, where ceria as an alloying element improves arc stability and ease of starting while decreasing burn-off. Cerium(IV) sulfate is used as an oxidising agent in quantitative analysis. Cerium(IV) in methanesulfonic acid solutions is applied in industrial scale electrosynthesis as a recyclable oxidant. Ceric ammonium nitrate is used as an oxidant in organic chemistry and in etching electronic components, and as a primary standard for quantitative analysis.
  The photostability of pigments can be enhanced by the addition of cerium. It provides pigments with light fastness and prevents clear polymers from darkening in sunlight. Television glass plates are subject to electron bombardment, which tends to darken them by creation of F-center color centers. This effect is suppressed by addition of cerium oxide. Cerium is also an essential component of phosphors used in TV screens and fluorescent lamps. Cerium sulfide forms a red pigment that stays stable up to 350 °C. The pigment is a nontoxic alternative to cadmium sulfide pigments.
  Cerium is used as alloying element in aluminum to create castable eutectic alloys, Al-Ce alloys with 6–16 wt.% Ce, to which Mg and/or Si can be further added; these alloys have excellent high temperature strength.
caption: Carl Auer von Welsbach, who discovered many applications of cerium
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