Cerium metal

Cerium or Cer - Ce - atomic number 58

Cerium was discovered by Jons Jacob Berzelius in 1803 and named after the then newly discovered dwarf planet Ceres. Like most of its rare earth elements - of which it is the most common - this one was first identified in the form of its oxide, the so-called cerium, and was only extracted as a pure metal decades after its first discovery.

Nevertheless, both metal salt and metallic cerium containing mixtures have been rapidly used in the industry. Cerium salts had an antiemetic effect and soon found their way into cough tinctures and antibacterial therapies.

Around the same time, Carl Auer von Welsbach, an Austrian scientist with a flair for the commercialization of his discoveries, developed two products that required the use of cerium with great success: gas sleeves and lightweight flint stones. Auer's gas envelopes were simple devices - a cotton fabric soaked in a salt mixture - from which the embers emitted when heated provided a bright, white light in the gas lamps.

Cerium found a third use in the early days of artificial lighting in charcoal arc lamps, which were particularly prized in movie studios because of their extreme brightness, so they could mimic the look of natural sunlight.

With the exception of cerium nitrate, which is still available as an antiseptic and anti-inflammatory topical treatment for burns, cerium compounds find little use in modern medicine, but the use of cerium in lighting has continued and expanded: cerium-containing lantern pods and flint from one Ceria alloys are still in production, but today CER-containing fluorescers are also indispensable for the manufacture of monitors and fluorescent lamps.

The optical properties of cerium are an important building block in the development of non-toxic alternatives to cadmium-based pigments and an important component in glassmaking where it is used for gold coloration and allows selective blocking of UV light. Cerium also provides valuable properties when added in small amounts in various alloys: it makes aluminum more corrosion resistant, magnesium more heat resistant and helps to reduce the sulfur and oxygen content in the steel. The largest use of cerium is in its use as a polish cerium (IV) oxide used on precision optical components and for polishing silicon wafers in microchips.

Cerium oxides are also useful as catalysts and are used for this purpose in automotive catalytic converters, petroleum refining and solid oxide fuel cells.

Like other elements of the rare earth, cerium is never found in its pure form in nature. It can only be obtained from rare earth minerals like Xenotime, monazite and bastnasite included, or off Ionenadsorptionstonen.

Cer occurrences

There are four isotopes in nature: stable cerium 140 (88,48 percent) and radioactive cerium 142 (11,08 percent), cerium 138 (0,25 percent) and cerium-136 (0,19 percent). Without the core isomers, a total of 38 radioactive isotopes of cerium were characterized. They are in the range between 119 and 157 with half-lives of only 1,02 seconds for Cer-151 and 5 × 1016 years for Cer-142.

Cerium is mainly extracted from cerium-containing monazite and bastnasite. It also occurs in allanite, Zerit, samarskite and the titanium mineral perovskite. It is mined in the USA, China, Russia, Australia and India.

Cerium or cerium oxide

Recovery of cerium

The metal is produced by electrolysis and metallothermal reduction of the halides with alkali or alkaline earth metals. It exists in four allotropic (structural) forms. The α-phase is face-centered cubic with a = 4,85 Å at 77 K (-196 ° C, or -321 ° F). The β-phase forms just below room temperature and is doubly densely packed hexagonal with a = 3.6810 Å and c = 11.857 Å. The γ-phase is the room-temperature form and is cubic face-centered with a = 5.1610 Å at 24 ° C (75 ° F). The δ phase is cubic-body centered with a = 4,12 Å at 757 ° C (1.395 ° F).

After a complex separation of the cerium companion, the oxide is reacted with hydrogen fluoride to Cerfluorid. It is then reduced to cerium with calcium to form calcium fluoride. The separation of remaining calcium residues and impurities takes place in an additional remelting in vacuo.

Features

The silvery white shiny metal is the second most reactive element of the lanthanoids after europium. Superficial damage to the protective yellow oxide layer ignites the metal. Above 150 ° C it burns with a violent glow to form ceria. It reacts with water to form cerium hydroxide.

Cerium occurs in compounds as a trivalent colorless or tetravalent yellow to orange cation.

Under the influence of heat, it is strongly attacked by ethanol and water. It is also heavily attacked in alkalis to form cerium hydroxides. In acids, it is dissolved into salts.
Since the chemical properties of rare earths are similar, metallic cerium is rarely used in pure form, but in the mixture in which it is obtained in the production of the rare earth minerals, the so-called mischmetal.

The periodic table with elements of strategic metals and rare earths

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Cerium, like all lanthanides, is slightly toxic. Metallic cerium can ignite from 65 ° C. As a finely divided metal, it can heat up in the air without energy and finally ignite. Among other things, the ignition readiness depends very much on the particle size and the degree of distribution. Cerial fires must not be extinguished with water as gaseous hydrogen evolves.

Cer use

Cerium compounds have a number of practical applications. The dioxide is used in the optical industry for fine polishing of glass, as a decolorizer in glassmaking, in petroleum cracking catalysts and as a three-way auto-emission catalyst, which utilizes its dual valency properties (3 + / 4 +). Cerium, together with the other rare earth elements, is part of many iron alloys to trap sulfur and oxygen and to crosslink cast iron. It is also used in non-ferrous alloys, especially for improving the high-temperature oxidation resistance of superalloys. Mischmetal (typically 50 percent cerium, 25 percent lanthanum, 18 percent neodymium, 5 percent praseodymium and 2 percent other rare earths) is mainly used for lighter flintstones and alloying additions.

In metallurgy, cerium is used as an additive for aluminum alloys and high-temperature-resistant iron-based alloys. It supports the separation of sulfur and oxygen in the melting process. The iron-mischmetal alloy Cereisen serves as the starting material for flints for use in lighters and for generating sparks on roller coasters and in movie scenes (accident scenes). Cereisen in the composition 70% cerium and 30% iron, also known as Auermetall, was registered for a patent by Karl Auer von Welsbach in 1903. A modification found worldwide distribution as a flint for lighters.

Small additions of (more or less pure) cerium compounds impart certain properties to other materials:

1. Ceria (CeO 2) is used to stabilize the alumina ceramic catalyst support for automotive exhaust catalysts.
2. Part of some special lenses, for example UV filters and windshields, and dehumidifiers in glass manufacturing
3. For coloring enamel
4. Ceria is used as a polishing agent in glass processing
5. Cerium-doped fluorescent dyes (phosphors) in picture tubes and white LEDs
6. as doping in mantles
7. Self-cleaning ovens contain a cerium-containing coating
8. Cerium (IV) sulfate as oxidizing agent in Quantitative Analysis (Cerimetry)
9. as a contrast agent at nuclear resonance
10. as a phosphor in gas discharge tubes
11. added to the regeneration of soot particle filters dissolved in the fuel
12. as part of non-precious metal-containing bonding alloys in dental technology (ceramics)
13. as an oxidant for organic syntheses with CAN (cerium ammonium nitrate), (NH4) ²Ce (NO³) 6

Cer special features

Cer differs from praseodymium and terbium from other rare earths in that it forms compounds in which its oxidation state is + 4; it is the only Rare Earth to have a + 4 oxidation state in solution. Salts of Ce4 + ion (core salts), which are powerful but stable oxidants, are used in analytical chemistry to detect oxidizable substances such as iron (iron in the oxidation zone + 2). Cerium in its + 3 oxidation state behaves like a typical Rare Earth.