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Jai Ganesh

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Lanthanum

Lanthanum

Gist

Lanthanum (La) is a chemical element with atomic number 57. It's a soft, silvery-white metal that belongs to the lanthanide series, also known as rare earth elements. It's known for its ability to increase the resistivity and malleability of steel and is used in various applications, including catalysts, optics, and batteries.

Lanthanum is primarily used as a catalyst in petroleum refining and in nickel-hydride rechargeable batteries. It has refractive properties and is used in optical glass, especially in cameras. It comprises 25% of pyrophoric alloy known as mischmetal which is used for flints of cigarette lighters.

Summary

Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the rare earth elements. Like most other rare earth elements, its usual oxidation state is +3, although some compounds are known with an oxidation state of +2. Lanthanum has no biological role in humans but is used by some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.

Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustaf Mosander in 1839 as an impurity in cerium nitrate – hence the name lanthanum, from the ancient Greek (lanthanein), meaning 'to lie hidden'. Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead. In minerals such as monazite and bastnäsite, lanthanum composes about a quarter of the lanthanide content. It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.

Lanthanum compounds have numerous applications including catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, and gas tungsten arc welding electrodes. Lanthanum carbonate is used as a phosphate binder to treat high levels of phosphate in the blood accompanied by kidney failure.

Details

Lanthanum (La) is a chemical element, a rare-earth metal of Group 3 of the periodic table, that is the prototype of the lanthanide series of elements.

Lanthanum is a ductile and malleable silvery white metal that is soft enough to be cut with a knife. It is the second most reactive of the rare-earth metals after europium. Lanthanum oxidizes in air at room temperature to form La2O3. It slowly reacts with water and quickly dissolves in diluted acids, except hydrofluoric acid (HF) because of formation of a protective fluoride (LaF3) layer on the surface of the metal. The metal is paramagnetic from 6 K (−267 °C, or −449 °F) to its melting point at 1,191 K (918 °C, or 1,684 °F) with a nearly temperature-independent magnetic susceptibility between 4 and 300 K (−269 and 27 °C, or −452 and 80 °F). Lanthanum becomes superconducting at atmospheric pressure below 6.0 K (−267.2 °C, or −448.9 °F) in the face-centered cubic β-phase or 5.1 K (−268.1 °C, or −450.5 °F) in the double close-packed hexagonal α-phase.

The element was discovered as the oxide (lanthana) in 1839 by Carl Gustaf Mosander, who distinguished it from cerium oxide (ceria). Its name is derived from the Greek lanthanein, meaning “to be concealed,” indicating that it is difficult to isolate. Lanthanum occurs in the rare-earth minerals monazite and bastnasite. It is as abundant as cobalt in Earth’s upper continental crust.

Two isotopes occur in nature: stable lanthanum-139 (99.9119 percent) and very long-lived radioactive lanthanum-138 (0.0888 percent). A total of 38 radioactive isotopes of lanthanum (excluding nuclear isomers) have been characterized, ranging in mass from 117 to 155 and in half-life from 23.5 milliseconds (lanthanum-117) to 1.02 × 1011 years (lanthanum-138). The isotope lanthanum-140 has been detected as a fission product in snow after nuclear test explosions.

Lanthanum is concentrated commercially by crystallization of ammonium lanthanum nitrate. Ion-exchange and solvent extraction methods are used when high purity is desired. The metal is prepared by electrolysis of fused anhydrous halides or by metallothermic reduction of its halides by alkali or alkaline-earth metals (e.g., reduction of the fluoride with calcium).

Lanthanum exists in three allotropic (structural) forms. The α-phase is double close-packed hexagonal with a = 3.7740 Å and c = 12.171 Å at room temperature. The β-phase is face-centered cubic with a = 5.303 Å at 325 °C (617 °F). The γ-phase is body-centered cubic with a = 4.26 Å at 887 °C (1,629 °F).

Highly purified lanthanum oxide is an ingredient in the manufacture of low-dispersion, high-refraction glasses for lens components. Lanthanum is often used as LaNi5-based hydrogen-storage alloys and nickel–metal hydride rechargeable batteries in hybrid automobiles. Lanthanum is added to ferrous alloys (to scavenge oxygen, sulfur, and other impurities) and to nonferrous alloys such as superalloys, magnesium alloys, and aluminum alloys. Lanthanum compounds are used as hosts for phosphors in fluorescent lighting and X-ray detectors and in petroleum cracking catalysts, one of its major uses. Misch metal (typically 50 percent cerium, 25 percent lanthanum, 18 percent neodymium, 5 percent praseodymium, and 2 percent other rare earths) is primarily used for lighter flints and alloying additions. When combined with iron and silicon, lanthanum forms cubic intermetallic compounds with a general chemical formula that exhibit the giant magnetocaloric effect. When those compounds are hydrogenated to about 1.2–1.5 hydrogen atoms per formula unit, they have magnetic ordering temperatures near room temperature and, therefore, are useful as magnetic refrigeration materials for near-room-temperature applications.

In compounds, lanthanum exhibits only one oxidation state, +3. The ionic radius is the largest of the rare-earth R3+ ions, and, as a consequence, the white oxide La2O3 is the most alkaline rare-earth oxide.

Element Properties

atomic number  :  57
atomic weight  :  138.9055
melting point  :  918 °C (1,684 °F)
boiling point  :  3,464 °C (6,267 °F)
specific gravity  :  6.146 (24 °C, or 75 °F)
oxidation state  :  +3

Additional Information:

Appearance

A soft, silvery-white metal. It rapidly tarnishes in air and burns easily when ignited.

Uses

Lanthanum metal has no commercial uses. However, its alloys have a variety of uses. A lanthanum-nickel alloy is used to store hydrogen gas for use in hydrogen-powered vehicles. Lanthanum is also found in the anode of nickel metal hydride batteries used in hybrid cars.

Lanthanum is an important component of mischmetal alloy (about 20%). The best-known use for this alloy is in ‘flints’ for cigarette lighters.

‘Rare earth’ compounds containing lanthanum are used extensively in carbon lighting applications, such as studio lighting and cinema projection. They increase the brightness and give an emission spectrum similar to sunlight.

Lanthanum(III) oxide is used in making special optical glasses, as it improves the optical properties and alkali resistance of the glass. Lanthanum salts are used in catalysts for petroleum refining.

The ion La3+ is used as a biological tracer for Ca2+, and radioactive lanthanum has been tested for use in treating cancer.

Biological role

Lanthanum has no known biological role. Both the element and its compounds are moderately toxic.

Natural abundance

Lanthanum is found in ‘rare earth’ minerals, principally monazite (25% lanthanum) and bastnaesite (38% lanthanum). Ion-exchange and solvent extraction techniques are used to isolate the ‘rare earth’ elements from the minerals. Lanthanum metal is usually obtained by reducing the anhydrous fluoride with calcium.

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