Properties and Overview of Cerium

Overview:

Cerium (Ce) is a chemical element with the atomic number 58 and the symbol Ce on the periodic table, belonging to the lanthanide series. It is one of the most abundant rare earth elements, making up about 0.0046% of the Earth's crust, which is relatively high compared to other elements in its group. Discovered in 1803 by the Swedish chemists Jöns Jakob Berzelius and Wilhelm Hisinger and independently by the German chemist Martin Heinrich Klaproth, cerium is named after the dwarf planet Ceres, which had been discovered just two years earlier. Its abundance and chemical versatility make cerium valuable in various industrial applications. Physically, cerium is a soft, ductile, and silvery-white metal that readily tarnishes when exposed to air, forming a protective oxide layer. This property is typical of many rare earth elements. Cerium has a melting point of approximately 800°C and a boiling point of 3,440°C. It exhibits a hexagonal close-packed crystal structure at room temperature but undergoes several allotropic transformations as the temperature changes. Cerium's relatively low hardness and high malleability make it easy to shape and work within various industrial processes. Its density is approximately 6.8 g/cm³, comparable to other lanthanides.
Chemically, cerium is the most reactive of the rare earth elements. Cerium forms compounds such as cerium chloride (CeCl₃) and cerium nitrate (Ce(NO₃)₃), which are typical of lanthanide chemistry and exhibit properties like strong fluorescence and the ability to form complex ions. Cerium also forms compounds such as cerium dioxide (CeO₂), also known as ceria, which is a prominent industrial catalyst and an essential material in fuel cells and other applications requiring oxidation processes.
Regarding safety, cerium is generally considered to be of low toxicity in its elemental form. However, cerium compounds, particularly cerium oxide (CeO₂), can pose health risks if inhaled as fine particulates or dust, potentially leading to respiratory issues. Additionally, like many rare earth elements, cerium can cause skin and eye irritation upon contact. Handling cerium compounds with appropriate protective equipment, including gloves, safety goggles, and respiratory protection, especially during processes that generate airborne particles, is crucial in industrial settings. Furthermore, cerium is a reactive metal, particularly in fine powder form, where it can spontaneously ignite in the air, leading to fires or explosions if not handled properly. Therefore, cerium and its compounds are typically stored in airtight containers or under inert gases to prevent unwanted reactions with air or moisture.

Production:

The production of cerium primarily involves the extraction from rare earth minerals such as monazite and bastnäsite. These minerals are typically mined and then subjected to a series of processes to separate Cerium from other rare earth elements. One standard method is the extraction of Cerium from bastnäsite, where the ore is first crushed and then treated with hot, concentrated sulfuric acid. This process converts the rare earth elements into water-soluble sulfates, which are then separated through solvent extraction or ion exchange techniques. Cerium is unique among the rare earth elements because it can be separated from other lanthanides by taking advantage of its ability to exist in both the +3 and +4 oxidation states. During production, cerium can be selectively oxidized to cerium oxide (CeO₂), which can then be separated from other rare earth elements that remain in the +3 oxidation state. The purified cerium can then be reduced to its metallic form using electrolysis or metallothermic reduction techniques.

Applications:

Cerium has a wide range of applications due to its unique physical and chemical properties. One of the most significant uses of cerium is in catalytic converters, where cerium oxide is employed to improve the catalyst's efficiency and extend its life by preventing the sintering of precious metals like platinum, palladium, and rhodium. Cerium oxide is also used in glass polishing, where its fine abrasive qualities make it ideal for smoothing and polishing glass surfaces to a high degree of clarity. This application is critical in producing precision optics, mirrors, and other high-quality glass products.
In metallurgy, cerium is used as a component in mischmetal, an alloy that typically contains about 50% cerium and is used to produce flints for lighters. Cerium's pyrophoric properties—its ability to ignite when struck—make it an essential ingredient in these flints. Cerium is also added to cast iron and steel to improve their properties, such as increasing hardness and wear resistance. In the steel industry, cerium is used to remove sulfur and oxygen impurities, which helps to enhance the strength and durability of the final product.
Another significant application of cerium is in the energy field, particularly in solid oxide fuel cells (SOFCs). Cerium oxide is used as an electrolyte material in these fuel cells due to its high oxygen ion conductivity, which is essential for the efficient operation of SOFCs. Additionally, cerium-based materials are being explored to produce advanced batteries, such as lithium-cerium batteries, which may offer improved performance over traditional lithium-ion batteries.

Summary:

Cerium is a highly reactive rare earth element with extensive industrial and technological applications. Its production involves complex extraction and purification processes, often exploiting its unique ability to exist in multiple oxidation states. Physically, cerium is a soft, malleable metal with several allotropes, while chemically, it is distinguished by its versatility and reactivity, particularly in redox reactions. Cerium's wide-ranging applications, from catalytic converters and glass polishing to advanced energy systems, highlight its importance in modern technology and industry. Despite its reactivity and the associated safety concerns, cerium's benefits in various applications make it a valuable resource.

See a comprehensive list of atomic, electrical, mechanical, physical and thermal properties for cerium below: