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The unique structure of cerium: Do you know how unique the crystal structure of cerium oxide is?
Cerium(IV) oxide, also known as cerium dioxide or cerium, has a special crystal structure, which makes it particularly important in many industrial applications. Its chemical formula is CeO2, which usually appears as a light yellowish white powder. It is the main commercial product and industrial intermediary of cerium and is very important for extracting the element from ores. It is worth noting that the reversible switching properties of cerium oxide make it one of the hot spots in research and application.
Cerium usually exists in the form of oxides, mixed with other rare earth elements, and the main ores are pasternite and single porphyry.
Natural production and extraction process of cerium
The extraction of cerium first requires the transfer of metal ions to the aqueous phase, and then the cerium is separated from other rare earth elements by adding oxidants and adjusting the pH value. This process takes advantage of the low solubility of cerium oxide and the fact that other rare earth elements are not easily oxidized, allowing for efficient separation of cerium oxide. The final product cerium oxide is produced during the roasting process of cerium oxalate or cerium hydroxide.
Characteristics of cerium oxide
Cerium oxide (CeO2) is one of the most widely studied cerium oxides. As the most oxidized form of cerium, its 4f electrons can be strongly mixed with the 2p electrons of oxygen, causing the electrons to appear in a delocalized state. This property has an important impact on its electronic conductivity and catalytic activity.
Cerium oxide releases oxygen at high temperatures, producing a non-stoichiometric oxide form that retains the fluoride lattice.
Structure and defect characteristics
Cerium oxide adopts a fluoride structure with space group Fm3m, containing 8-coordinated Ce4+ and 4-coordinated O2−. In high-temperature environments, cerium oxide forms an oxygen-deficient non-stoichiometric form, which allows it to exhibit significant ionic and electronic conductivity at high temperatures. Among them, ionic conductivity is particularly prominent at temperatures exceeding 500°C.
Defect Chemistry
In the stable fluoride phase, cerium oxide exhibits different defects depending on the partial pressure of oxygen and the stress state of the material. Defects of primary concern include oxygen defects and small polarons (localized electrons present on cerium cations). As the oxygen defect concentration increases, the diffusion rate of oxide anions in the crystal lattice also increases, which makes cerium perform well in solid oxide fuel cells.
Natural discovery of cerium
Cerium oxide occurs naturally in the mineral cerianite-(Ce), a relatively rare tetravalent cerium mineral. The existence of this type of mineral is related to the oxidizing property of cerium, which is easily oxidized and separated from other rare earth elements that depend on their trivalent state.
Application fields
Cerium oxide has two main areas of application. First in industry, cerium oxide is widely used in polishing, especially chemical mechanical planarization (CMP). Secondly, cerium oxide is used to decolorize glass, improving the aesthetics of the glass by converting the green color of iron-containing impurities into almost colorless iron oxide.
Catalysts and their emerging applications
Cerium oxide has attracted widespread attention in the field of heterogeneous catalysis because it can catalyze the water gas conversion reaction and oxidize carbon monoxide under the action of OXIDANT to release hydrogen. The properties of cerium oxide make it an important component in automobile catalytic converters, which can effectively control NOx and carbon monoxide emissions in exhaust gases.
Energy and fuel potential
The significant ionic and electronic conductivity of cerium oxide makes it an ideal material as a hybrid conductor, especially in solid oxide fuel cells. The cerium-cerium trioxide cycle (CeO2/Ce2O3) is used for hydrogen production, using oxygen deficiencies to form hydroxyl radicals in water.
Optics and welding technology
In the field of optics, cerium oxide is valued for its excellent polishing ability and its ability to improve the scratch resistance of optical surfaces. It is used as an additive in argon arc welding to improve the stability and service life of tungsten electrodes, which is of great significance to the technological improvement in the welding field.
Cerium oxide nanoparticles (nanoceria) have been extensively studied in recent years, and their antibacterial and antioxidant properties provide new directions for various applications.
The diversity of cerium oxide and its practical performance in various fields cannot be underestimated. In the future, we look forward to seeing the realization of more innovative applications. What new doors will the unique structure of cerium open for us?
