Lanthanum

Atomic Number:

57

Melting Point: 918 ºC
Atomic Symbol: La Boiling Point:  1897 ºC
Atomic Weight: 138.9055 amu Density: 6146 kg/m 3
Atomic Radius:

187.7 pm

Oxidation States: 2
Covalent Radius: 169 pm Electron Configuration: [Xe]6s25d1
van der Waals Radius:

--

State of Matter: solid 

History

(Greek lanthanein: to lie hidden) Mosander in 1839 extracted lanthana from impure cerium nitrate and recognized the new element.

Lanthanum was isolated in relatively pure form in 1923. Iron exchange and solvent extraction techniques have led to much easier isolation of the so-called "rare-earth" elements.

Properties

Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly.

The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens.

At 310ºC, lanthanum changes from a hexagonal to a face-centered cubic structure, and at 865ºC it again transforms into a body-centered cubic structure.

Sources

Lanthanum is found in rare-earth minerals such as cerite, monazite, allanite, and bastnasite. Monazite and bastnasite are principal ores in which lanthanum occurs in percentages up to 25 percent and 38 percent respectively. Misch metal, used in making lighter flints, contains about 25 percent lanthanum.

The availability of lanthanum and other rare earths has improved greatly in recent years. The metal can be produced by reducing the anhydrous fluoride with calcium .

Uses

Lanthanum is added to steel to improve its malleability, resistance to impact and ductility.  It is also added to molybdenum to decrease the hardness and sensitivity to temperature variations. Mischmetal, a pyrophoric alloy used in lighter flints, contains 25% to 45% lanthanum.

There is current interest in hydrogen sponge alloys containing lanthanum. These alloys take up to 400 times their own volume of hydrogen gas, and the process is reversible. Every time they take up the gas, heat energy is released; therefore these alloys have possibilities in an energy conservation system.

The oxide and the boride are used in electronic vacuum tubes. Hydrogen sponge alloys can contain lanthanum. These alloys are capable of storing up to 400 times their own volume of hydrogen gas in a reversible adsorption process.

Lanthanum is also used in as a petroleum cracking catalyst, in gas lantern mantles, and as a glass and lapidary polishing compound. It is used in age dating of rocks and ores as well.

Rare-earth compounds containing lanthanum are extensively used in carbon lighting applications, especially by the motion picture industry for studio lighting and projection. This application consumes about 25 percent of the rare-earth compounds produced. La2O3 improves the alkali resistance of glass, such as infrared absorbing glass, camera and telescope lenses. It is also used in making special optical glasses. Small amounts of lanthanum, as an additive, can be used to produce nodular cast iron.

Isotopes

Natural lanthanum is a mixture of two stable isotopes, 138La and 139La. Twenty three other radioactive isotopes are recognized. All of the radioactive isotopes have half-lifes that are less than 24 hours and the majority of these have half-lifes that are less than 1 minute. This element also has 3 meta states.

Hazards

Lanthanum and its compounds have a low to moderate acute toxicity rating; therefore, care should be taken in handling them. In animals, the injection of lanthanum solutions produces glycohemia, low blood pressure, degeneration of the spleen and hepatic alterations.

It is a flammable solid. As such it reacts with water and dilute acids to produce flammable, explosive hydrogen gas. Dusts in high concentrations may cause skin, eye and respiratory tract irritation.